Landracing Forum
Tech Information => Technical Discussion => Topic started by: Blue on July 17, 2010, 01:54:56 PM
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I hope this provokes a lively discussion, this is a subject that I believe everyone in LSR can understand and benefit from with the end result of faster records and safer vehicles.
First, I mean no disrespect to Costella or any builder or contender in LSR. My concern and comments on the previous thread come from my knowledge of vehicle mechanical-aerodynamic stability and control. My concern is that speeds have now exceeded the area of mechanical stability and entered the area where aerodynamic stability dominates and the knowledge base of LSR is not yet wide or deep enough for safety.
I spoke to a senior SCTA board member last year about the need for the higher speed vehicles to prove their stability with analysis before going too fast, and we had a good discussion about the costs and where the break point could be for that analysis. I am still searching for a reasonable CFD cost solution for everyone and have not found it yet. However, my experience in S&C (stability and control) concerns me about some of the designs I see vs. the speeds people are seeking.
Most LSR designers use the idea of a "Cp" as a plot of the lateral area of their vehicles and presume that if the CG is forward of the 50% point of this plot, then the vehicle is stable in yaw. This is simply not true.
First, most symetrical aerodynamic surfaces rotate around the "quarter chord point" or only 25% of the length. This is called the "yaw neutral point". Very few LSR vehicles have their CG forward of this. Even so, at relatively low airspeeds (below 200 mph) the dynamic pressure is low enough that mechanical stability can override the aerodynamics. Above 300 mph, the opposite is true and any vehicle that is not solely stable aerodynamically will not be recoverable if it loses traction. Downforce can increase the mechanical advantage, but it is a bad trade since downforce usually leads to pitch instability.
Tails or other large vertical surfaces mounted far aft are used in some designs and can radically improve the overall vehicle's yaw neutral point. However, blunt tails (like chute tubes) can reduce their effect. Some of the vehicles currently seeking 400 mph are nearly neutral in stability due to their aft CG and high degree of aft separation. There are solutions and a few in the 400 mph club have done a very good job of addressing this issue. Some haven't, and that scares me.
At least a first-order, algebra-based stability calculation should be required of any motorcycle going over 200 and any car going over 300. As speeds increase, the mechanical stability is going down exponentially with speed (dependent on surface condition, traction, and tire dynamics) and up linearly with downforce. Countering this, aerodynamic instability increases with the square of speed. At some speed the two lines cross and things can go bad very quickly. Since most motorcycles do not have downforce, this equation leads to the need for positive yaw stability at the starting line. Worse, downforce-based stability is at the mercy of driver skill; and I like to be kinder to my drivers.
The REAL danger is that this "negative stability" speed may have already been achieved without external upset and then the vehicle makes another similar run and encounters an upset due to surface or wind conditions and suffers an uncontrolled departure; i.e. SPIN. Think about all of those guys who have gone fast in roadsters or stock body cars and then spun at less speed. Their driving skill may have saved them in the past, this does not mean it will forever. At any combination of speed, surface, and wind condition it is the LSR vehicle's job to go straight, not to demand an ever-increasing level of dynamic driver input.
In aviation, we call the ability to handle instability the "velvet glove": a VERY complimentary term for the pilot. And a not-so-complimentary one for the engineer who made it necessary. As an engineer I don't like being the butt of jokes, so I make the things that I design stable and controllable. My pilots appreciate this and bitch about other engineers instead.
All of this relates to yaw stability and spins. Pitch and roll stability is another subject entirely and much more complex.
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Eric:
Do you have any recommended sources of information that we could use to broaden our knowledge in this and the other related fields without each and every one of us becoming aerodynamic engineers.
Pete
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Blue... If the cg of the 222 car was at 25% it would spin out for sure and would be undriveable before that.
JL222
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I think you hit a key note Eric with the word “discussion”. I hope comments are not taken negatively and argumentative but are received as “educational”.
I read your comment about Jack’s new 8080 yesterday but didn’t understand your assumptions. I have not seen the inside of the new car but assume it follows earlier designs. Jack’s cars have two large billets of aluminum for front wheels. I’m not sure of the weight but they are located at the end of a very long moment. If you look at driver location, and his center-of-mass, it is probably quite forward of the windshield. I’m guessing that the 750 cc engine is aluminum and quite light. You said “all that weight in back”, I am assuming you meant a rearward CG; is that really true? Looking at the car sideways it is fairly easy to see the CP. It is not as easy to see the CG but my guess it is deceptively forward of the middle of the car due to the mass of the front wheels. I’m only giving another perspective here for your review because of the following questions.
If there is less flat area in front of the CG than flat area behind the CG; isn’t that pitch stable?
I’m trying to establish the 50% and 25% “quarter chord point” distance. Do you subtract the CP distance from the wheelbase and then move the CG 25% forward of that? Sorry about the confusion . . . could you use some numbers as an example? TIA :-)
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I am looking forward to this discussion and learning something. With the help of some very knowledgeable people we are looking at the correlation of different tire shapes and air and the effects it has on our car. Once I have some good data other than hearsay to post I will share it on this thread. Blue, thanks for starting the topic. Tony
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blue
You might not ever figure out why my designs are succsesful. Although you seem to know how to make them better! Thanks for the interest! I will be watching for some hot tips!Jack
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Fascinating topic to read - I enjoy the friendly "tug-of-war".
The June 2010 issue of Racecar Engineering has a 4 page article by Simon McBeath about CFD. It talks about free 'open source' vs. vendor supplied software.
At our High School, where I teach manufacturing and home of the first All Girls Shell Eco-marathon team, we use Cosmos within Solidworks for our very basic CFD, and have a low speed wind tunnel which allows 1:10 scale models.
Michael
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Tony,
I may be able to save you some time and expense. Tires are round.
DW
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Dan, you shouldn’t do that in the morning, I dropped my tea all over myself. Tony
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I always hear the "Big Brains" speak of aerodynamic designs based upon text book theories. I see very few "experts" build or drive their own designs ( I am sure there will be many postings with the photos of experts cars and all their success, such as Burkland). I know there may be cross over in theory between airplane design and streamliner design, but have yet to see it demonstrated or explained without it being negated or minimized, or completely ignored. I think it is a big leap to say that an apple is just like an orange. Poor me who has so little faith, and cannot believe without touching, seeing and reading the record books.
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blue
You might not ever figure out why my designs are succsesful. Although you seem to know how to make them better! Thanks for the interest! I will be watching for some hot tips!Jack
LOL! Jack, I'll take a stab at it: lots of power in a small vehicle with good mechanical stability from a long wheelbase. Simple rules work best, and you do a good job of paying attention to that. I really like your small displacement stuff.
JL- yes, a CG at 25% is impractical and would lead to a mechanically unstable vehicle: one that might spin long before it got up to a speed at which the aero stability could take over.
Keep it coming everybody, and be critical too. This is about safety and a broader understanding for everyone.
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Blue,
I am not an aerodynamic expert, but I have built experimental airplanes and lots of motorcycles. I was interested in your comment that motorcycles have "no downforce". I have to disagree. If you look at most bikes with factory bodywork and windsheilds, you can see that there is a lot more surface area providing downforce than upforce. Because the frontal area of bikes is such that the bottom half is much more dirty and upright with relation to the relative wind than the top side, there is ample downforce.
Maybe the A2 wind tunnel member here can vouch for that (or not).
I agree that bikes need to pay attention to aero stability, but so far it has not been a problem, even with with speeds up to 270 mph.
Don
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DW, in all seriousness, the amount of camber, how the tire was shaped all has effects on the car. In a streamliner the wheel-well and the tire play a major role in the effects of the air underneath the car. The tires are just air pumps and what ever you do up front effects what happens down stream. Blue, In a streamliner going over 300 what is the correlation of the volume of air in the wheel tub versus the tire and the shape of the wheel tub? I would think there is some optimal percentage.
We have been working with both the Good Year engineers and Nate on the tire issue and their shape. One thing they both wanted us to do was build our wheels with taller beads to keep the tires on at high speed. As the tires get up to speed the crown starts to grow and tend to pull the tires of the bead. I had no idea, but this one of the reasons they want high pressure in LSR tires. Tony
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Blue,
............
I agree that bikes need to pay attention to aero stability, but so far it has not been a problem, even with with speeds up to 270 mph.
Don
We took care for aero stability....that's the reason why there was no problem with a speed over 270 mph :roll: :cheers:
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uh don....everything is relative....
...ie stability.....
..Joe :)
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uh don....everything is relative....
...ie stability.....
..Joe :)
Joe....
I call it no problem.....when you stayed on the bike....... :wink:
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Interesting topic, I will be watching.
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Front wheel drive naturally improves stability . Too bad it's not more popular .
John Burk
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motorcycles rear wheel drive front wheel steer only willie buchta
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Most LSR designers use the idea of a "Cp" as a plot of the lateral area of their vehicles and presume that if the CG is forward of the 50% point of this plot, then the vehicle is stable in yaw. This is simply not true.
First, most symetrical aerodynamic surfaces rotate around the "quarter chord point" or only 25% of the length. This is called the "yaw neutral point". Very few LSR vehicles have their CG forward of this.
Help me out here. . . I haven't had my tea today like Tony. Just where are these two points? Assume a 100" wheelbase. The CP is at 75" from the front spindle(s). Now if the CG is 50% forward of that point it resides at (75" x .50 = 37.5"). So the CG is at 37" from the front of the car? But you say that is yaw unstable? Why? Is it too far forward?
Now where is this quarter-chord point? You say it is 25% from the CP. Same exampe, if the CP is at 75" the yaw neutral point is (75 x .25 = 19') in front of the CP. On a 100" car that yaw neutral point is at 56" which is a rearward bias! So where do you want the CG to be on a 100" car? 56" is too close to yaw neutral but 38" is unstable? All the sedans I know have the CG in the forward 50% of wheel base in the 45-48% range. What am I missing?
Edit: Since I see Willie is here I made "spindle" both singular and plural in the interest of diversity. :-D :-D
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Front wheel drive naturally improves stability . Too bad it's not more popular .John Burk
John, 4 wheel drive was run by Gary McArthur No.327 in a roadster for a few years. Then SCTA outlawed 4-wheel drive in roadsters about 3 or 4 years ago.
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Speaking from the perspective of roadsters and other bluff wide track cars....
With a spool in the rear end and the tires rolling, the car is stable!
For a car to spin tires must slide.
If the rear tires break loose due to spinning or tire bounce the car is at the mercy of aero stability, long wheel base (high polar moment of inertia) and driver ability.
At speed a minor side ways movement of the rear end results in rapid opposite sideways movement of the front end. If the driver is not quick enough the front end pulls the car around.
It takes huge aero stability to counter the lateral force of the front tires or traction imbalance of the rear tires. Stability in a bluff body, wide track car will probably never come from aero....keep the tires rolling with, a spool, weight and good suspension. Avoid running if the salt is rougher than your suspension can handle or if there are wet spots.
The above applies to streamliners and lakesters as they are typically longer wheel base giving the driver more time and typically narrower to minimize thrust imbalances. Front wheel drive is inherently more stable because spinning or hopping front tires will not pull the front end around.
Long Live Hot Rods.
Akk
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AKK
You posted "one" good example of a straight line vehicles dilemma. Please now add and remove castor using your example! Make a simple model with adjustable caster. Then decide what geometry is needed to maintain stability in a straight line vehicle. Jack
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AKK
You posted "one" good example of a straight line vehicles dilemma. Please now add and remove castor using your example! Make a simple model with adjustable caster. Then decide what geometry is needed to maintain stability in a straight line vehicle. Jack
Caster ?? If you ask 10 folks 1/2 will say more is better and 1/2 will say as little as possible.
I have a 53 Stude.. we can go as low s 4 degrees caster and as high as 13 degrees. I have it set in the middle at 9 degrees for initial testing.
My 1933 Vicky at 150 MPH wandered all over at 3 degrees, we went to 8 degrees and it drives so straight and easy now ? But that is a straight axle front end,,, the Stude is tubular A arm Mustang II set up with adj coilovers...
Charles
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Joe
That is an undisputable accurate statment. This is why designs change ether by science, and or hard work!
New designs should be asked to make enough runs to show stability. Judging a design be by its resemblence to older designs or areo interpretation, is the way to constrict inovation and choke progress!
The very thing that LSR stands for!
Roadgraders, conbines, tractors, ect, are not cars. Neither are streamliners! Streamliners go fast in a straight line, and are continuing to develop, change and improve, in order to achieve that goal!
2wheel flatbottom streamliners were stable and got a lot of records without tipping over for 7years like the traditional round bottom designs do.(Except Budfab)!Yet they were called motorcycles and forced to change to a known unstable tip rule! Why?
Please, lets not constrict 4 wheel liners in that same way!
Thanks Jack
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John Burk
You have just stated "The freedom of choice!" A term, that should help define LSR!
Jack
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I'm a little unsure of motive here so maybe you can help me out here Blue.... Why in the he11 would you have a talk with a Senior SCTA official and drop a bug in his ear to require aero stability testing on our vehicles?.... what in the he11 are you thinking? Do you have some ego problem that you feel the need to feel important to SCTA officials and others.... I for one would appreciate it if you would shut your mouth, especially to officials.... You seem to be a sharp guy why don't you spend your time actually building a race vehicle..... I know you are a aero guy but please don't suggest we all install propellers....
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Amen
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motorcycles rear wheel drive front wheel steer only willie buchta
what if you rode it backwards? We all know the front of the bike has the forks right?
JonAmo
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ive tried that ---but not on the salt------- maybe this year willie buchta
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On a front wheel drive streamliner do I want an open diff or a spool?
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"I'm a little unsure of motive here so maybe you can help me out here Blue.... Why in the he11 would you have a talk with a Senior SCTA official and drop a bug in his ear to require aero stability testing on our vehicles?.... what in the he11 are you thinking? Do you have some ego problem that you feel the need to feel important to SCTA officials and others.... I for one would appreciate it if you would shut your mouth, especially to officials.... You seem to be a sharp guy why don't you spend your time actually building a race vehicle..... I know you are a aero guy but please don't suggest we all install propellers...."
I'm sure some people said the same thing when they had to add roll cages .
John
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Blue...you talk of your pilots and drivers, who are they and what planes-motorcycles-or cars have you designed?
JL222
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what if you rode it backwards? We all know the front of the bike has the forks right?
JonAmo
Cool, a two wheel forklift. I love it. :cheers:
Tom G.
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Double post :-)
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I'm sure some people said the same thing when they had to add roll cages .
John
Yep, I could hear them from years ago saying, don't tell me what I need. I know what I am doing, it will just cost me more money, and is not needed. Sometimes it is hard to save people from themselves.
Tom G.
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I hope this provokes a lively discussion, this is a subject that I believe everyone in LSR can understand and benefit from with the end result of faster records and safer vehicles.
First, I mean no disrespect to Costella or any builder or contender in LSR. My concern and comments on the previous thread come from my knowledge of vehicle mechanical-aerodynamic stability and control. My concern is that speeds have now exceeded the area of mechanical stability and entered the area where aerodynamic stability dominates and the knowledge base of LSR is not yet wide or deep enough for safety.
I spoke to a senior SCTA board member last year about the need for the higher speed vehicles to prove their stability with analysis before going too fast, and we had a good discussion about the costs and where the break point could be for that analysis. I am still searching for a reasonable CFD cost solution for everyone and have not found it yet. However, my experience in S&C (stability and control) concerns me about some of the designs I see vs. the speeds people are seeking.
Most LSR designers use the idea of a "Cp" as a plot of the lateral area of their vehicles and presume that if the CG is forward of the 50% point of this plot, then the vehicle is stable in yaw. This is simply not true.
First, most symetrical aerodynamic surfaces rotate around the "quarter chord point" or only 25% of the length. This is called the "yaw neutral point". Very few LSR vehicles have their CG forward of this. Even so, at relatively low airspeeds (below 200 mph) the dynamic pressure is low enough that mechanical stability can override the aerodynamics. Above 300 mph, the opposite is true and any vehicle that is not solely stable aerodynamically will not be recoverable if it loses traction. Downforce can increase the mechanical advantage, but it is a bad trade since downforce usually leads to pitch instability.
Tails or other large vertical surfaces mounted far aft are used in some designs and can radically improve the overall vehicle's yaw neutral point. However, blunt tails (like chute tubes) can reduce their effect. Some of the vehicles currently seeking 400 mph are nearly neutral in stability due to their aft CG and high degree of aft separation. There are solutions and a few in the 400 mph club have done a very good job of addressing this issue. Some haven't, and that scares me.
At least a first-order, algebra-based stability calculation should be required of any motorcycle going over 200 and any car going over 300. As speeds increase, the mechanical stability is going down exponentially with speed (dependent on surface condition, traction, and tire dynamics) and up linearly with downforce. Countering this, aerodynamic instability increases with the square of speed. At some speed the two lines cross and things can go bad very quickly. Since most motorcycles do not have downforce, this equation leads to the need for positive yaw stability at the starting line. Worse, downforce-based stability is at the mercy of driver skill; and I like to be kinder to my drivers.
The REAL danger is that this "negative stability" speed may have already been achieved without external upset and then the vehicle makes another similar run and encounters an upset due to surface or wind conditions and suffers an uncontrolled departure; i.e. SPIN. Think about all of those guys who have gone fast in roadsters or stock body cars and then spun at less speed. Their driving skill may have saved them in the past, this does not mean it will forever. At any combination of speed, surface, and wind condition it is the LSR vehicle's job to go straight, not to demand an ever-increasing level of dynamic driver input.
In aviation, we call the ability to handle instability the "velvet glove": a VERY complimentary term for the pilot. And a not-so-complimentary one for the engineer who made it necessary. As an engineer I don't like being the butt of jokes, so I make the things that I design stable and controllable. My pilots appreciate this and bitch about other engineers instead.
All of this relates to yaw stability and spins. Pitch and roll stability is another subject entirely and much more complex.
For the record :evil:
JL222
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I'm sure some people said the same thing when they had to add roll cages .
John
Yep, I could hear them from years ago saying, don't tell me what I need. I know what I am doing, it will just cost me more money, and is not needed. Sometimes it is hard to save people from themselves.
Tom G.
Tom...if SCTA listens to Blue you better plan on putting a real small engine in that beautiful roadster of yours.
JL222
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Sometimes it is hard to save people from themselves.
Why is it assumed that this is anyone else's business?
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Wow, spend a few days in the shop and look at the response! I'll try to get back to all of the questions and criticisms tonight. For a few quick notes:
I think I started out with a compliment to Jack.
Aero stability is related to the bodywork, not the wheelbase.
I've seen plenty of blunt cars that were aero stable, at least in yaw.
I never cross-talk between teams. That's why they talk to me.
If it ain't cheap and easy to do, I wouldn't recommend it.
Most important:
NO PROPS!!!!!
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Looking forward to it, Eric. Please check post #19.
Speaking of bluff bodies, I think NASA Tech Briefs published a white paper 3 or 4 years ago. The research was primarily focused on big semi truck body shapes and/or trailers, IIRC. The results were not intuitive in that a blunt shape was more efficient than a semi-aerodynamic shape in some unique cases.
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Sometimes it is hard to save people from themselves.
Why is it assumed that this is anyone else's business?
You ''save the people from themselves bunch'' would surely ban hare and hound desert racing.
JL222
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Sometimes it is hard to save people from themselves.
Why is it assumed that this is anyone else's business?
IMO,
Not anyone's business if no other person is affected directly.
It is someone's business if other people are affected directly.
Tom G.
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Blue,
I am not an aerodynamic expert, but I have built experimental airplanes and lots of motorcycles. I was interested in your comment that motorcycles have "no downforce". I have to disagree. If you look at most bikes with factory bodywork and windsheilds, you can see that there is a lot more surface area providing downforce than upforce. Because the frontal area of bikes is such that the bottom half is much more dirty and upright with relation to the relative wind than the top side, there is ample downforce.
Maybe the A2 wind tunnel member here can vouch for that (or not).
From what I have seen it is not a matter of lift or downforce but the major imbalance between front to rear that seems to be typical of most motorcycles. I typically have seen lots of front lift associated with negative rear lift (or rear downforce). I’m curious if you could post a side shot of what you think is adding downforce to your bike? If it is more or less the same "type of shape" as below it is similar to an airfoil shape and this is not a characteristic of creating downforce. (Cambered top with flat bottom)
(http://pictures.topspeed.com/IMG/crop/200902/new-article_800x0w.jpg)
(http://www.labsun.de/img/RootRibComparison-2.jpg)
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A2 thanks for posting that great pic. I never thought of it that way but the rider could be the top shape or surface of the airfoil and actually be adding lift. However, from what I can see, the smoke is detached, or turbulent, from back of the rider. This would be typical of a wing stalling and a wing in stall does not add lift. So regarding your post have your wind tunnel scales actually shown lift is being produced? Or are you saying the bike's CG is in the turbulent area and that is the negative lift (downforce). Not trying to be argumentative . . . just trying interpet the results of the pic.
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A2 after returning from my first Bonneville trip in 08 to watch the GP bikes at our Phillip island track i was very much noticing aero,
on a wet track with the sunlight in the right angle the air around the bikes was quite easy to see , and most noticable was the way the rear tail acted like an air dam on the sides of a car , air displaced by the rider /bike seemed to be pulling from over the top more than the sides, and gave a 45 deg angle of contained mist from the tail down around the rear tire , sort of confirming the wear seen at the rear of a belly fairing on the salt caused by rear downforce ?? or was it likely more engine torque ??
And had a bad experiance here at Lake Gairdiner in 04 when i lowered the front too much and was rubbing the front fairing on the front guard between 216 and 175 mph when not on power (trying to decellerate without crashing ... big tankslapper)
i put it down to frontal downforce as soon as the torque trying to lift the front was removed.. ???
Are my assessments anywhere near the ball park from your experiances ?
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Just from reading the first page of this thread, i'm curious if a longer swingarm would work. The rider could slide his/her weight backwards to get traction for building speed and slide then forward at high speed somewhat changing the center of gravity as aerodynamic advantage overtakes mechanical advantage, essentialy using your body as a dynamic ballast. Of course, you would need just enough streamliner to break most of the wind around your body to be able to pull forward at 200mph+, and lots of chin-ups. Think it might work?
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On a front wheel drive streamliner do I want an open diff or a spool?
My instinct would say diff just so you can correct if you need to. An air-locker might not me a bad idea, your steering isn't affected in the pits and staging area, you lock for your run, and if there's any trouble you can unlock and try to recover. A detent could be put on the steering shaft automatically unlocking if the wheel is in any other position except straight ahead, so it's not something to forget in a panic situation.
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A2, in your photo, the rider and bikes only relationship to an airfoil is the top is very cambered. As you can see, the airflow is scattered and turbulent over the top. That is a stalled airfoil as Saltfever stated. Stalled means no lift. There is no smoke on the bottom, but I am betting the airflow is also detached and turbulent there.
In the photo, the smoke is deflected UP, meaning there is downward pressure. You have seen front lift as a a result of rear lift? That does not make sense from a mechanical point of view. I would like to see the data on that. What would account for rear lift?
Lastly, do you have wind tunnel data to show amounts of positive or negative lift on motorcycles?
Thanks
Don
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A2,
Just to clarify one aspect of what seems to be an impending discussion, if and when you cite windtunnel “lift” numbers for a vehicle, are those direct load cell readings or has the weight transfer due to drag already been backed out of them? What is standard windtunnel practice?
One would suspect that, particularly for rather “standard” motorcycles, actual aero lift/downforce might be of secondary magnitude.
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You have seen front lift as a a result of rear lift? That does not make sense from a mechanical point of view. I would like to see the data on that. Don
Don, I agree it would be extremely useful if we could see the data from the scales.
A2 said "front lift associated with negative rear lift (or rear downforce)" What he meant was as you push down on the rear the front will come up. I believe this could be correct under two conditions. We all know a body rotates about its CG. In acceleration (as in drag racing) you know the effect . . front comes up and rear goes down. But we are discussing aero forces (the bike is stationary in the wind tunnel with no acceleration to react on the CG). The possible effect here is the CP becomes the dominant force not acceleration. If the CP is rearward of the CG, as it should be, the bike "might" rotate about the CG and the rear will go down and the front will come up. But to what degree is this effect? That is why the scale data would answer a lot of questions.
You raised another issue to consider. Picture a bike on a front and a rear scale. If you lift the back upward what will happen to the front scale? You have removed some weight. You have made the bike lighter. The front scale will show less weight in a ratio to the bikes weight distribution about the CG.
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I have got it!!!?!
After deep thoughts about safety, fairness, close racing, advertising revenue, spectator excitement .... you know... the NASCAR mentality.
Assuming I have support from you guys, I propose the following:
1. Each competitor will be issued a class standard parachute.
2. The parachute must be deployed at the 1 mile mark and pulled the entire length of course.
3. Upon qualifying and backups the competitor must submit a timing ticket with verification of proper chute deployment and submit the chute for verification.
Advertising for the event sponsors will be available on each parachute. Parachutes will be sized differently by class. (we want to make sure that Streemliners are faster than Lakesters and so on down the line.
Just think how safe the competition would be!
LOL Akk
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IF you have a motor cycle in a wind tunnel and have scales under each wheel and IF the motor cycle's configuration does not develop any aero lift, positive or negative, then the readings of the scales when summed have to equal the weight of the motor cycle. When the air velocity is increased and the pressure differential between the front and the back of the motor cycle becomes a large force can be summed into a "center of pressure" on the front of the motor cylce that represents the total combined pressure applied at a single point against the front of the motor cycle. The position of this force will be above ground level and if you sum moments about the contact patch of the rear wheel, which will be the front scale reading multiplied by the wheel base and subtract the moment of the frontal aero force times it's distance above the level of the scales this summation must equal zero. This calculation will give us the amount of the front aero force or if you know the amount of the aero force (drag) you can calculate the amount of weight that will be moved from the front tire to the rear tire but in all cases (again with an aero configuration that does not generate any type of aero lift positive or negative) the sum of the scale readings will equal the weight of the motorcycle.
Rex
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I have got it!!!?!
After deep thoughts about safety, fairness, close racing, advertising revenue, spectator excitement .... you know... the NASCAR mentality.
Assuming I have support from you guys, I propose the following:
1. Each competitor will be issued a class standard parachute.
2. The parachute must be deployed at the 1 mile mark and pulled the entire length of course.
3. Upon qualifying and backups the competitor must submit a timing ticket with verification of proper chute deployment and submit the chute for verification.
Advertising for the event sponsors will be available on each parachute. Parachutes will be sized differently by class. (we want to make sure that Streemliners are faster than Lakesters and so on down the line.
Just think how safe the competition would be!
LOL Akk
:-D :cheers:
JL222
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Well -- speaking of motorcycles in the wind tunnel -- Dave Salazar and I have decided that we'll put both of the SSS fast bikes in the tunnel sometime soon -- but probably only after the '10 season is done. By then he'll (hopefully) have all of his instrumentation in place and we'll be riding in glory from all of the records we got this year.
And so, when we do go to the tunnel, I'll see if it's okay to release lots of the data we gather. That way ALL can see what happens, what gains, what losses, and all of that stuff. I'll write a full report on it -- and it'll be available for all to read.
Later --
Jon a/k/a SSS
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. . . Dave Salazar and I . . . . I'll see if it's okay to release lots of the data we gather. That way ALL can see what happens, what gains, what losses, and all of that stuff. I'll Jon a/k/a SSS
OK, by whom? Do you mean ok by Dave or A2? You and Dave bought and paid for the data. A2 is very careful with proprietary data as they should be, but you are the owner of the data and should be able to do what you want with it.
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Yes - I know that, but maybe our crew chief should get a vote, too, before I give away the store, so to speak.
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. . . Dave Salazar and I . . . . I'll see if it's okay to release lots of the data we gather. That way ALL can see what happens, what gains, what losses, and all of that stuff. I'll Jon a/k/a SSS
OK, by whom? You and Dave bought and paid for the data. A2 is very careful with proprietary data as they should be, but you are the owner of the data and should be able to do what you want with it.
Slim is being respectful by saying that because he knows that A2 is careful with proprietary data and since this will be his first visit to the wind tunnel he doesn't know the normal protocol. I'm Dave Salazar (General Manager @ A2) and I would be running the tunnel/test for Jon. That will be his data and he can post it if he would like. And I’m sure that there might be some speed that he finds that he doesn't want anyone to know about, so he might not post all of his findings. It’s totally up to him. Since it is his money, you guys should thank him for #1 going through the process of testing and #2 sharing some data with you guys about what he finds. Most people wouldn’t take the time to do that.
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Hi Dave. Sorry about my disconnect and thanks for introducing yourself. You bring up a good point that I have always found difficult to resolve. You have customers that are paying, not only for your facility, but for your expertise. Before you built A2 you had a lifetime of experience. However, undoubtedly you have gained more knowledge from former customers and their experiments. As a professional you have to protect that intellectual property gleaned from others. However, as a customer I am paying for as much of your grey matter as possible. :wink: I would want all your knowledge focused on my problems at hand. I would think finding the right balance is quite difficult.
Your postings to this forum are always interesting. I respect your protection of customer’s IP. You have done a good job. Thanks.
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Wow, there has been a lot written since I left work yesterday and I’m too busy to get to all of them specific to A2. Don't get my analogy wrong, I didn’t say the rider is an air foil, but does resemble the same shape (cambered top). The round smooth sexy curves you see and that are pleasing to the eye are not surfaces that typical of creating downforce. Those rounded shapes tend to create lift (in most cases). You are correct when saying that air is separating off the riders back, but that doesn’t automatically mean that there should be downforce (this is not an airplane). There is also a pitching moment and if the front of the bike has lift then there could be a transfer to the rear making it negative along with the separation off the riders back. The top shape is not the only component creating lift, front fender shape, air trapped between the front fender and lower fairing creates pressure differences...ect.. many variables to consider and not as simple as looking at a picture. To give you an idea here are some # of a motorcycle simular to the one in the picture
Lbs @ 190 mph (standard NACA day: sea level)
Drag = 283 lbs
Front = +134 lbs (lift)
Rear = -112 lbs (downforce)
Rex answered most of the questions but, before each run there is a wind off zero of the balance which takes the weight of the object (car or motorcycle) in addition to the balance and zeros them out. Then as the tunnel is turned on and once the air is up to speed and stable the balance is just measuring the aero effect of the object very precisely. Imagine standing on a scale and someone zeros it and then hands you a 20 lbs weight, the scale would then read 20 lbs with you standing on it. A wind tunnel balance measures in 6-components to give a drag, front lift, rear lift, front side force, rear side force, pitching moment, rolling moment, and yawing moment to give a better picture of what is happening to the entire system (vehicle). There are many interactions that happen and there might be a change in the front that could affect the rear and vise versa.
Example: NASCAR Cup series recently went from a rear wing back to the traditional spoiler. This gave the teams more downforce, but where? Most would assume that the change was to the rear so the rear was the only component that gained downforce (This is incorrect). By adding a rear spoiler the center of pressure was moved forward and there was a significant improvement on front down force from the wing allowing the cars drive better in the corners because the balance (front to rear) was improved by increasing the front percent (aero). I realize LS racers don’t turn but it is still important to have balance and not an unstable condition where the front is lifting (due to aero) and the rear is pushing down (due to aero). As some of you know, cars can have enough lift that they will become airborne.
Here are some more pictures that help illustrate
(http://image.hotrod.com/f/9354572/113_0510_aero_07_z+aerodynamic_tips_tricks+downforce_diagram.jpg)
(http://www.gmecca.com/byorc/images/liftdownforce.gif)
(http://www.auto123.com/ArtImages/111487/nascar-aero-inline.jpg)
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Hi Dave. Sorry about my disconnect and thanks for introducing yourself. You bring up a good point that I have always found difficult to resolve. You have customers that are paying, not only for your facility, but for your expertise. Before you built A2 you had a lifetime of experience. However, undoubtedly you have gained more knowledge from former customers and their experiments. As a professional you have to protect that intellectual property gleaned from others. However, as a customer I am paying for as much of your grey matter as possible. I would want all your knowledge focused on my problems at hand. I would think finding the right balance is quite difficult.
Your postings to this forum are always interesting. I respect your protection of customer’s IP. You have done a good job. Thanks
It’s no problem at all. At A2, we do try give our customers the best experience possible in the wind tunnel and get them to start thinking about aerodynamics, and the higher the speeds the more important it will become (landspeed racing). I don’t want someone to walk in and hand me a car to develop nor do I just want to spout off a bunch of speed secrets to them. I want to step by step get them involved in the process so they can understand what wind tunnel testing is all about and why teams use them so at the end of the day they know what changes worked, didn’t work, (& why) and to know that their car/motorcycle will perform better then the last time they took it out. Yes, I have seen a lot throughout the years in both our wind tunnels and there is a fine line I walk every test to not give out information another team learned but give each customer the same attention to detail and tip toe around the “grey matter” as you put it. I’m used to being around the NASCAR crowd (whether anyone likes it or not) and some might give up their first born before they give out any data about their Daytona cars. That is just how I was raised (to speak) in the wind tunnel business over the years. So, while some of you think it could make life a whole lot easier for me to just openly talk about testing and numbers, I can’t. I have said this many times and I’m sure this wont be the last, but I am on here to try and help people understand about a process that there is not a lot of information about. And as Salt said, paying customers get the facility, and although I don’t claim to be an expert I am a racer down inside and love to help people go fast. I need everyone to remember that I am NOT getting paid by anyone to post on this form so as “nonpaying” customers you guys are getting more then most.
:cheers:
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Well -- speaking of motorcycles in the wind tunnel -- Dave Salazar and I have decided that we'll put both of the SSS fast bikes in the tunnel sometime soon -- but probably only after the '10 season is done. By then he'll (hopefully) have all of his instrumentation in place and we'll be riding in glory from all of the records we got this year.
And so, when we do go to the tunnel, I'll see if it's okay to release lots of the data we gather. That way ALL can see what happens, what gains, what losses, and all of that stuff. I'll write a full report on it -- and it'll be available for all to read.
Later --
Jon a/k/a SSS
It's a shame that Amo didn't sell the website to a roadster guy! :mrgreen:
Mike
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Thanks Jon & Dave, I look forward to the write up. Once I'm out of power and chassis tweaking, a day in the wind tunnel is on my list. -Dean
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Mike, maybe if a roadster guy had started the website way back when. . .
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A2
in your pix of the airfoil overlaying the blue car.... if only the trailing air actually did converge down like the airfoil...you should know that it never happens.... see the trailing from your NASCAR CFD pix... that's more realistic.... why is it that aerodynamicist always want to compare ground plane vehicles to airplane crap
Kent
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http://www.kasravi.com/cmu/tec452/Aerodynamics/WindTunnel.htm. . . . with an index covering other issues. Course syllabus from a Michigan university. I tagged it a couple of years ago while looking for information on skin friction for nanotech surface coatings. Good overview. We hope to use a college's (restricted size) wind tunnel for skin friction tests on small flat planes. However, a full scale model in the wind tunnel appears to be the best format for evaluating separation comparisons between different membranes vs commercial paints surrounding the streamlined surface of an aero shape. If the budget allows, full scale shapes in a wind tunnel allows evaluation of reduction in the slowing forces of the surface frictional component.
A tip of the hat to JackD for steering me toward the Human Powered Vehicle realm for low drag shapes, back before he went into self-imposed exile. And another tip of it to Blue for reinforcing the importance of a testing factor available in a wind tunnel and not in Computational Fluid Dynamics computer programs.
And, if La Fortuna allows, 2011 may be when the friction reducing membrane gets tested for corrosion resistance on that practical factor test facility in Utah. This has been in the shoulda-coulda-wanta category so long, I might have to hang a prop on it.
http://www.kasravi.com/cmu/tec452/Aerodynamics/VehicleAero.htm
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(http://A2
in your pix of the airfoil overlaying the blue car.... if only the trailing air actually did converge down like the airfoil...you should know that it never happens.... see the trailing from your NASCAR CFD pix... that's more realistic.... why is it that aerodynamicist always want to compare ground plane vehicles to airplane crap
Kent)
Kent, as I said in the previous post. DON'T take it that I am calling those shapes air foils. A production car without a rear spoiler (unlike in NASCAR) will produce lift. Most of it is off the top of the roof because the air is moving faster over those surfaces and creating a low pressure... In a similar way an air foil will do the same. IF THAT IS "CRAP" then please tell me what other (my racecar is better than your racecar) shape I can easily explain lift to people on the tread? I’m not into airplanes and am not calling anything on here an airplane!! A bluff body object such as a car is NOT an air foil or airplane and I am just using a simple illustration to show that. Please don’t take so literal. There is only so much I can find on the internet as far as pictures go and I am also trying to run a wind tunnel and only get a minute or two to pop on. I agree that I could go into more detail or even publish a CFD drawing of exactly what I am talking about, but I simply do not have the time.
PS: there are some cars that dont make a big wake.
(http://img4.sportauto-online.de/Pagani-Zonda-F-08-r498x333-C-734e6041-219874.jpg)
video of same car you can see on youtube:
http://www.youtube.com/watch?v=2CYUuBiW_lY (http://www.youtube.com/watch?v=2CYUuBiW_lY)
.
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A2/ Dave,
I for one certainly appreciate your posts and help on these forums. I know you do so freely and with a passion for informing all of us. If a few hardcore know it all types get a but sassy to you on here please do not take it personally... the majority of us understand and appreciate your time and information.
Jon/SSS.... I live less than 2 hours from the A2 Tunnel,,, when you set the date please let me know,,, I will be there with bells on to help you in any way possible and my shops are open to you if you need help, tools or just storage.
Charles
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Charles, did you get the emails from me today?
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A2/ Dave,
If a few hardcore know it all types get a but sassy to you on here please do not take it personally...
Missing an extra "t", Charles. :-D :-D
Ok ok, I know what you really meant but I just couldn't pass up the Freudian slip! :wink:
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A2/ Dave,
If a few hardcore know it all types get a but sassy to you on here please do not take it personally...
Missing an extra "t", Charles. :-D :-D
Ok ok, I know what you really meant but I just couldn't pass up the Freudian slip! :wink:
was it a slip ??? LOL
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Charles, did you get the emails from me today?
Yes Jon I did get the file but it was an .ai (adobe illustrator) file and I can not open it,,,
I sent you two emails asking if you could send it again in another format like a pdf file or even a jpeg,,,, pdf is better.
I am going to print tomorrow (as soon as I can open and download your file)
Thanks
CV
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Blue...you talk of your pilots and drivers, who are they and what planes-motorcycles-or cars have you designed?
JL222
#2
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dave
im not saying you posts are crap im just saying compairing flying aero to ground vehicles is....
kent
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I tried to take this topic seriously in reply #21...and no response, I then tried to take it funny in reply #51 and got one cheer. I now try to take it seriously again.
Aerodynamic stability to airplane people is about an airplane oscillating or fluttering up/down or side/side ....or even worse being totally uncontrollable. The common sense understanding is that the center of gravity (the balance point of the airplane..a point about which the vehicle may be lifted without rotating or flopping around) should be in front of the center of pressure (the point about which all drag forces may be thought to be applied). I know this to be a gross over simplification. The center of pressure in an airplane is easier to locate than in a car. the center of pressure in a car is affected by ground interference, ground clearance, angle of attack, cross winds...... The center of gravity can move about as fluids slosh in the tanks.
Airplanes, when they are being airplanes, with aerodynamic stability... you know ...flying , do not have front wheels on the ground. If the back end of a flying stable air plane is shifted to the side, the rudder (major contributor to moving the center of pressure back) levers the airplane straight again ...working against the center of gravity which acts as a pivot point and a momentum induced force, pulling the airplane forward.
An "aerodynamically stable" airplane with only the front tire on the ground (this is very hard to do in a tricycle gear airplane as they are designed to land on the rear tires first for reasons soon to be revealed) becomes unstable. The front tire takes control and changes the center of gravity momentum force to a destabilizing force. A tail movement to the right steers the airplane left, the front tire becomes the pivot point, pulls the airplane to the left and the center of gravity pulls the airplane right. If the tail feathers are powerfull enough to overcome the tire force to the left the airplane may recover ...this is usually accomplished with active rudder control.
When the front tires are rolling on a car, aerodynamic stability as in airplanes doesn't, mean much!!!!
On our car we bias the brakes full forward so that the front tires can skid with the rear tires rolling. When the car gets out of control the driver hits the clutch and slams the brakes on. The front tires skid and loose all lateral forces, the back tires roll and the car straightens right up.
Aerodynamic stability of car should be concerned with keeping the tires rolling at all times!
Think about it!
DW what do you think about "Land Speed Chute Pulling"?
Akk
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re Nebulous reply 22
In my mind caster's primary function is to provide a natural tendancy for the front tires to stay aligned with the centerline of the car with no steering input.. ie. hands off the car goes straight. If the wheel is turned and released the front wheels will again realign to the car centerline. Caster is for hands off driving...
This is symplistic because scrub radius, weight distribution, rear axle alignment, turn banking, cross winds, tire circumfrence, ring gear carrier type, etc......get involved.
However, with the drivers hands on the steering wheel, a car with heim joints and otherwise non rubber elements involved will generally stay on the drivers heading. This assumes that there is no bump steer or roll steer in the steering linkage and front suspension.
With hands on, cross winds are a problem because the center of gravity is not coincident length wise to the center of pressure. Cross winds at speed will cause yaw. This yaw is worse in a car that has roll steer because the lateral area as well as the center of gravity is typically not vertically aligned with the car roll center. I see many cars with roll steer!
Our car is set up with 10 degrees of caster, zero scrub radius, no bump steer and no roll steer. The steering is very light because of the zero scrub radius...it tracks straight hands off the wheel but we always keep our hands on!
Akk
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Interetsing reading akk, thanks. Sorry if I missed it, but what class of a car do you run? Can you post a picture? Thanks, Dean
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Akk,
I did make a comment re: parachutes in this thread. I'm sorry I don't understand your question.
DW
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Speaking from the perspective of roadsters and other bluff wide track cars....
With a spool in the rear end and the tires rolling, the car is stable!
For a car to spin tires must slide.
If the rear tires break loose due to spinning or tire bounce the car is at the mercy of aero stability, long wheel base (high polar moment of inertia) and driver ability.
At speed a minor side ways movement of the rear end results in rapid opposite sideways movement of the front end. If the driver is not quick enough the front end pulls the car around.
It takes huge aero stability to counter the lateral force of the front tires or traction imbalance of the rear tires. Stability in a bluff body, wide track car will probably never come from aero....keep the tires rolling with, a spool, weight and good suspension. Avoid running if the salt is rougher than your suspension can handle or if there are wet spots.
The above applies to streamliners and lakesters as they are typically longer wheel base giving the driver more time and typically narrower to minimize thrust imbalances. Front wheel drive is inherently more stable because spinning or hopping front tires will not pull the front end around.
Long Live Hot Rods.
Akk
AKK...I agree with ''if the driver isn't quick enough'' and makes me wonder about most Lsr racers recommending ''slow steering'' especially on short wheelbase cars.
JL222
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The front tire takes control and changes the center of gravity momentum force to a destabilizing force. . . . If the tail feathers are powerfull enough to overcome the tire force to the left the airplane may recover ...this is usually accomplished with active rudder control.
Interesting post AAk and thanks. I am wondering if the tire force is the dominant force? I agree it starts the course deviation but the CG is now accelerating about a point. Me thinks the rudder authority has to overcome the CG acceleration which is proably the dominant force, no?
The front tires skid and loose all lateral forces, the back tires roll and the car straightens right up. Aerodynamic stability of car should be concerned with keeping the tires rolling at all times!
But in another post you indicated when the rear goes sideways the front is pulled around by the wind. I agree. However, if the front is to regain any steering control to cancel out this "pulling around effect" why would you want to skid the front tires and lose all traction. Don't you want them "rolling"? Also, when the front wheels are turned down-track, their slip angle goes to zero (maybe not zero but you know what I mean) and greatly increases their ability to arrest the "pull-around" affect. Your thoughts?
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Speaking from the perspective of roadsters and other bluff wide track cars....
With a spool in the rear end and the tires rolling, the car is stable!
For a car to spin tires must slide.
If the rear tires break loose due to spinning or tire bounce the car is at the mercy of aero stability, long wheel base (high polar moment of inertia) and driver ability.
At speed a minor side ways movement of the rear end results in rapid opposite sideways movement of the front end. If the driver is not quick enough the front end pulls the car around.
It takes huge aero stability to counter the lateral force of the front tires or traction imbalance of the rear tires. Stability in a bluff body, wide track car will probably never come from aero....keep the tires rolling with, a spool, weight and good suspension. Avoid running if the salt is rougher than your suspension can handle or if there are wet spots.
The above applies to streamliners and lakesters as they are typically longer wheel base giving the driver more time and typically narrower to minimize thrust imbalances. Front wheel drive is inherently more stable because spinning or hopping front tires will not pull the front end around.
Long Live Hot Rods.
Akk
AKK...I agree with ''if the driver isn't quick enough'' and makes me wonder about most Lsr racers recommending ''slow steering'' especially on short wheelbase cars.
JL222
I would bet that what happens is that as the car first starts to drift, the Amped up on adrenaline driver could over correct the opposite direction too much sending the car into a spin! :-D
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You mean he would stop the spin in one direction and spin in the other? I think thats the thinking, but I wonder if that happens. I have seen it happen with street drivers that didn't have a clue driving an out of control car, but thats on pavement with more traction.
Look how far sprint cars have to turn there tires to keep from spinning out, their flopping all over the place and they definitely have fast steering.
JL222
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"Sorry if I missed it, but what class of a car do you run?" AKK's primary car is the "Contrivance" '23T roadster #920 which currently holds the records in A through E (that's right, all of 'em) Gas Rear Engine Modified Roadster. You know, the one that isn't low to the ground like all the others... vic PS: See you on the Salt, Akk!
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Thanks Krusty....#920 is a GMR...gas modified roadster.
The front tires, when rolling, have great authority for making the car go left or right. When the front tires are skidding they have no directional control of the car left or right. When you lock up the front tires and let the rear tires roll, the rear tires have directional control and will trail the skidding front tires.
Ok....find a smooth assfault parking lot...on a rainy day...no shopping carts, kids or other pedestrians about.....get going say 40 miles per hour straight.... shift to neutral.....hold the steering wheel straight....slam on the emergency brake....the car will spin every time and if you are going fast enough ...stop going backwards!
If you are brave try it the otherway ....backing up....the car will simply stop going backwards without a spin!
Trust me...I have done it...for fun when I was much younger. We use to set our go-Karts up with rear bias on the brakes so that we could brake hard going in to turn and set up a drift in the turn. NASCAR, I am told set, up with forward bias to assure stopping straight?
If I had brakes on only one end, I would put them on the front for Bonneville!!!!!!
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DW
I was referring to my reply #51 above....a proposal for the land speed equivalent of NASCAR restrictor plates....or high speed tractor pulling...
Akk
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Re....Fast steering
If some of you guys are specialists on control with feed back loops you might want to correct or add to the following...The last time I performed any calculations on this subject was 40 years ago.
In my opinion a driver, on smooth salt in a car with no vibration and no head buffeting from high speed air, can detect 1 degree of heading error (yaw). In other conditions the number is much higher.
Depending on the wheel base this heading error acting as a steering angle defines a turning radius. The shorter the car the tighter the radius.The faster you go, the faster the car turns or rotates about the center of the turning radius. So, the rougher the driving environment, the shorter the car, the faster you go, the quicker the driver needs to react to input a steering correction. The longer the driver waits the greater the needed input. Some drivers are better than others!
Now...the driver is the actuator, his eyes are the feed back. The actuator has a response time and a response speed(how fast he can steer and how quick the steering is). Put some numbers into some complex equations and graphs can be produced that predict optimum steering quickness for a given speed, driver, wheelbase....All harry stuff!
Generally though... a late response, lost motion, dead band (minimum perceived heading error), too quick of a response ....lead to over steering and can result in oscillating back and forth and total loss of control.
A long wheel base, slow steering, good suspension, head rest padding and a windshield are all pluses when going fast. Not to mention a good driver with good vision and quick responses.
Akk
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Re....the front is pulled around
To clarify...the tire rolling with weight and the coefficient of friction on the salt is what pulls the front end around at spin initiation. After the spin starts and the tire starts sliding aerodynamic forces get involved with the kinetic friction. Spin initiation is the rear kicking out and creating a steering angle.
Akk
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Neil,
I got it now. I do not like that idea. I would have to redo all the records. No wait, I could start with a fresh sheet of paper.
DW
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"Sorry if I missed it, but what class of a car do you run?" AKK's primary car is the "Contrivance" '23T roadster #920 which currently holds the records in A through E (that's right, all of 'em) Gas Rear Engine Modified Roadster. You know, the one that isn't low to the ground like all the others... vic PS: See you on the Salt, Akk!
The Contrivance 23 T roadster is a unblown front engine car, not a rear engine as you stated.
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Re....Fast steering
If some of you guys are specialists on control with feed back loops you might want to correct or add to the following...The last time I performed any calculations on this subject was 40 years ago.
In my opinion a driver, on smooth salt in a car with no vibration and no head buffeting from high speed air, can detect 1 degree of heading error (yaw). In other conditions the number is much higher.
Depending on the wheel base this heading error acting as a steering angle defines a turning radius. The shorter the car the tighter the radius.The faster you go, the faster the car turns or rotates about the center of the turning radius. So, the rougher the driving environment, the shorter the car, the faster you go, the quicker the driver needs to react to input a steering correction. The longer the driver waits the greater the needed input. Some drivers are better than others!
Now...the driver is the actuator, his eyes are the feed back. The actuator has a response time and a response speed(how fast he can steer and how quick the steering is). Put some numbers into some complex equations and graphs can be produced that predict optimum steering quickness for a given speed, driver, wheelbase....All harry stuff!
Generally though... a late response, lost motion, dead band (minimum perceived heading error), too quick of a response ....lead to over steering and can result in oscillating back and forth and total loss of control.
A long wheel base, slow steering, good suspension, head rest padding and a windshield are all pluses when going fast. Not to mention a good driver with good vision and quick responses.
Akk
AKK... I agree with most of what you say but in addition to the eyes I would add BUTT :-D
I have said for years I would rather have just front brakes than just rear brakes I've told the story before about my cousins
rear brake only stude and solid suspension, he was giving it a test squirt at El Mirage [not on track] and put the brakes on ''sh...t no brakes'' well they were working but the tires were just slideing.
Anyone try to go down a real steep hill on a motorcycle using rear brakes only? Same result as above.
JL222
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Re....the front is pulled around
To clarify...the tire rolling with weight and the coefficient of friction on the salt is what pulls the front end around at spin initiation. After the spin starts and the tire starts sliding aerodynamic forces get involved with the kinetic friction. Spin initiation is the rear kicking out and creating a steering angle.
I have always greatly enjoyed talking with you. . Usually on your favorite piece of real estate. . IMPOUND! :-D I think you have identified an incredibly important subject. I'm trying to understand what some may consider finer points. But to keep needling away at this will only invite negative feedback from others which breaks down any further education. I’ll buy you a cup of coffee at the Red Flame so we can share some additional thoughts. After all, The Red Flame is not too far from where you are usually parked!
Something I’m struggling with is; once the spin is initiated and the CG is now accelerating around the steering angle, how do you react the CG momentum? With rolling rear tires (i.e. some traction) and zero-friction-sliding front tires (via full braking) I can understand the effect you mention. But if the front tires are turned into the direction of travel and rolling you might cancel out some of the CG momentum. Not sure though . . . maybe it’s the CG’s arm from the pivot point . . . the location of the CP . . . other? Thanks for introducing a thought-provoking perspective.
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:|is turn into the spin the right answer?
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The car is traveling down a course. It starts revolving (spin). You turn counter to the spin direction or in the direction of the track. Same thing . . . just two ways of describing the same effect.
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When I question slow steering I'm not recomending fast steering just normal steering ratio like were used to and I believe that one has to turn the wheel faster and further on the salt and dirt when a spin starts to happen, more so on short wheelbase cars.
JL222
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Biggest thing to learn about controlling a slide is not to over react in the steering, and this is usually caused by being too slow to react at the start, your effectively chasing your tail
quick ratio steering can help , but the salt is not a good place to learn,
I raced dirt track cars for 10 yrs and i think it took me a good part of the first 2 to learn to steer properly and now another 10 yrs on would take me a while to fine tune those skills again
most salt racers will never have a chance to develop those skills in the limited track time available and hopefully very limited sideways travel
Much better to develop a vehicle that never needs these inputs
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:-D I find these posts intertaining after spending 40 years of my life driving 72 miles, one way to work, nine months of winter, 3 months of below zero, and every morning glare ice or snow packed roads. Several times I had to play dukes of hazard through the sage brush to get back up on the road that was down hill both ways. 235 miles north of the Salt Flats.
Steve
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Biggest thing to learn about controlling a slide is not to over react in the steering, and this is usually caused by being too slow to react at the start, your effectively chasing your tail
quick ratio steering can help , but the salt is not a good place to learn,
I raced dirt track cars for 10 yrs and i think it took me a good part of the first 2 to learn to steer properly and now another 10 yrs on would take me a while to fine tune those skills again
most salt racers will never have a chance to develop those skills in the limited track time available and hopefully very limited sideways travel
Much better to develop a vehicle that never needs these inputs
Eagerly awaiting tips on being able to give full throttle at low speeds on 2500hp and 106'' wheelbase car.
Not getting sideways after blowing the tires away in the marbles at EL Mirage would be good to know also.
JL222
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Well the wheel base is the same but your hp is about 5 x my old Chrysler so i couldn't be sure until i drove it :-D
the short wheelbase was probably why i liked the quick ratio steering so much
I'll drop by and introduce myself properly at the Sept Elmo :cheers:
Back to the aero stuff , tired of blundering my way through the air on hp , trying to add some finesse
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Well the wheel base is the same but your hp is about 5 x my old Chrysler so i couldn't be sure until i drove it :-D
the short wheelbase was probably why i liked the quick ratio steering so much
I'll drop by and introduce myself properly at the Sept Elmo :cheers:
Back to the aero stuff , tired of blundering my way through the air on hp , trying to add some finesse
We probably won't be at elmo untill nov, see you then.
JL222 :cheers:
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Short wheel base, long wheel base, Bonneville, Daytona, sprint car, stock car, streamliner, front wheel drive or rear wheel drive. It makes no difference. You keep the front wheels pointed in the direction you want to go!
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Short wheel base, long wheel base, Bonneville, Daytona, sprint car, stock car, streamliner, front wheel drive or rear wheel drive. It makes no difference. You keep the front wheels pointed in the direction you want to go!
Doug....next time you watch a sprint car race notice how far the tires turn from the direction they want to go!
JL222
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Wheel base does make a difference. I had an AMC gremlin and on glare ice you had to really be on top of it. The problem is not just the short wheel base but the position of the driver. If you are sitting half way back in a 20' long car and it yaw's a degree or two the sideways motion of the driver is a lot more than the same yaw in a very short wheel base car. That means it takes more yaw in a short wheel base car for the driver to notice the lateral movement, so he is late in applying steering correction compared to the longer wheel base.
One solution for Bonneville, might be to use a progressive ratio steering box like was used on the 1973 Jeep Cherokee. It was designed so the steering ratio was relatively lazy at center point so the driver could cruise comfortably without constantly twitching the steering wheel but as you got off center point, the ratio quickened so when parking or making an emergency evasive maneuver the faster ratio at higher steering angles helped you catch up to the car.
It was a very nice setup in my opinion, and made driving in really slick conditions very easy.
A minor twitch of the steering wheel near center point did not send you all over the road but if you had to make a quick steering correction the faster ratio off center made it easy to catch up to the car even in conditions that were so slick you could not stand up when you got out of the car.
This steering box might be the sort of steering box as above but it is hard to tell from the advertisement.
http://www.agrperformance.com/catalog/products.php?cat=101
Super Box - SB2 Series
This box is nearly identical in design, brute force and performance to the Super Box 1, but is designed for the vehicle used as a daily driver. The SB2 has firmer valving and 16/13:1 variable ratio gearing for better handling and drivability at highway speeds.
http://www.google.com/patents?hl=en&lr=&vid=USPAT3753378&id=bTEwAAAAEBAJ&oi=fnd&dq=progressive+ratio+steering&printsec=abstract#v=onepage&q=progressive%20ratio%20steering&f=false
Larry
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Wheel base does make a difference. Edit . . . If you are sitting half way back in a 20' long car and it yaw's a degree or two the sideways motion of the driver is a lot more than the same yaw in a very short wheel base car. That means it takes more yaw in a short wheel base car for the driver to notice the lateral movement, so he is late in applying steering correction compared to the longer wheel base.
Nice post Larry and good point-out regarding variable ratio.
Lets trig this out so we can see the relevance. These examples are extreme only to make the point clear and numbers are rounded up or down for simplicity not precision. Take a 200" wheel base and a 102" wheel base vehicle. Put the driver right on top of the rear axel so line-of-sight is the entire wheel base. For a one degree deviation the driver will move sideways 3.5” for the 200” wheelbase and 1.80” for the 102” wheel base. There is so much going on at speed you can’t differentiate those small changes. It is pretty clear that neither driver is going to detect 1 degree of spin. Change to 10 degrees of spin and you get 35” and 18”. Some time between 1 and 10 degrees the driver will wake up and discover the situation.
Before everyone gets in a dither let me make another point. You have to differentiate “course deviation” from spin! There is so much going at speed that sensory overload dulls your ability to sharply discriminate what might be important changes in car attitude even though you think you are focusing on the important stuff. When you hit a crosswind gust the whole car can simply deviate from the course line. Yes, all four wheels can depart evenly. Unconsciously, you correct for “drift” and you do that all the way down the course. With drift, the car is still longitudinally straight but it can move from inches to YARDS from its true path! You don’t see the drift as much as feel it. Within that first few inches of course deviation you don’t know if it is drift or the start of a spin. (when only the two rear wheels depart). If you reacted correctly it will become drift but if you were wrong it’s a spin. There is no black line this year and Floating Mountain doesn’t move at all when looking at it through the windshield until you have moved quite a few degrees. I can’t say it is 5-10 degrees because it depends on the driver and the car set-up.
Whether long or short wheel base, your initial visual detection point will be about the same (which varies by driver). Both wheelbase lengths have a critical point were it is to late for a save. The Long wheel base just gives you a few more milliseconds before you get to that point.
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jl 222. look at a still picture of a sprintcar and you will see the front tires are pointed down the race track where he wants to go. I have watched thousands of laps at the sprint car races from the infield.
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Good points guys...
I was famous at least in my own mind for racing go karts in the rain....?...to set up for a turn I would initiate a slide by quickly making a turn of the wheel into the turn and then countersteer with the drift....I'll bet the dirt cars do the same.
I am guilty of this too...how many of you guys have put less than experienced drivers in a car....The rookie driver makes a pass at low power, never turns the wheel to get a feel of the car or the salt, the rookie does this through the licencing process and then they are expected to drop the hammer for a red hat!!!!!!
Akk
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OK, I want to stir this up a little....lets talk about cross winds!!!???!!!
In my mind aero stability (as in airplanes) is good if all tires are sliding....but, I feel aero stability (you know center of gravity in front of the center of pressure) makes a car more sensitive to cross winds!
Think about it... if you had a huge vertical tail fin on a 20 foot boom off the back of the car....The car would be a weather vane...it would turn in to the wind no matter what the driver wanted.
Akk
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Akk,
Move the fletching on an arrow to the front and try to shoot it. Make sure that nobody is around.
Rex
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my guess is the feathers will always stay to the rear of the arrow because of one reason DRAG willie buchta
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Come up here, into the great white north, and spend a few winters driving in the snow and on icy roads - for months at a time. It'll help you get the hang of drifting, countersteering, and using the throttle to get around turns. It's also handy to know how to slide around when trying to grab that great parking spot on the other side of a crowded street.
There's a big difference between handling a vehicle on the slippery roads and on the race course - but there are some skills that are useful in both situations.
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Eagerly awaiting tips on being able to give full throttle at low speeds on 2500hp and 106'' wheelbase car.
JL222
:-D You already know the answer to that. :-o 8-) :evil:
Tom G.
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Eagerly awaiting tips on being able to give full throttle at low speeds on 2500hp and 106'' wheelbase car.
JL222
:-D You already know the answer to that. :-o 8-) :evil:
Tom G.
I know the results ,no 200 mph club :roll: :-D
JL222
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Eagerly awaiting tips on being able to give full throttle at low speeds on 2500hp and 106'' wheelbase car.
JL222
:-D You already know the answer to that. :-o 8-) :evil:
Tom G.
I know the results ,no 200 mph club :roll: :-D
JL222
Go slow....and you go fast......... :-D
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Think about it... if you had a huge vertical tail fin on a 20 foot boom off the back of the car....The car would be a weather vane...it would turn in to the wind no matter what the driver wanted.
Akk
You are right but that is a good thing within reason. A station wagon is inherently aero stable in that situation (ignoring issues like roll steer), when hit by a gust of cross wind the rear of the wagon has more side pressure than the front does and the car will yaw slightly into the wind. This means that it self corrects and the driver does not need to make any steering input to stay in their lane. In a car that has very square front fenders like the 1970's Ford Comet. They are a night mare to drive in gusty cross wind as the car yaws away from the wind when hit by a side gust which magnifies the course deviation from the intended path. In our chinook wind storms my Wagon is perfectly happy in a cross wind of 50 mph with gusts to 70 while traveling at 75 mph at right angles to the wind. I feel a slight wiggle when the car is hit by a gust but otherwise have no clue the wind is bad.
On several occasions I have been driving to work and noticed cars ahead of me weaving a bit and braking to slow down for no apparent reason only to realize that there is a strong cross wind I had not even noticed until I passed some trees and could see them bent back from the winds.
This is a good example of why your center of aero pressure is not a fixed and static thing, it can change dramatically if the effective wind is not coming head on to the car.
In the case of a car with a lot of rear sail area like a station wagon a wind at 15 degrees off axis moves the center of pressure toward the rear of the car (an inherently stable situation). A car with a bluff front and square sides (like a roadster) the exact opposite happens the center of pressure moves forward as the wind begins to take an "angle off the bow".
Cross winds can also dramatically change down force. In the 1980's vintage Corvettes a cross wind giving an effective wind vector about 15 degrees off axis would blow the high pressure air that normally collects on the upper part of the hood in front of the wind shield off the down wind side of the windshield effectively dumping all that down force and dramatically increasing front lift. Then as the down force disappeared the front of the car unloaded and lifted increasing the front drag and inducing a yaw away from the wind.
Sometimes the automotive engineers intentionally add roll steer to a cars suspension to help cancel out some of this cross wind motion.
If the car has balanced air drag front to rear when in a quartering wind, it simply moves sideways when hit by a cross wind gust, but maintains its heading (runs over timing lights perhaps), If it has a slight rear ward bias (sail area from a tail fin etc. or a station wagon like body style) it will help the driver stay on course by aerodynamically yawing into the quartering wind. If the side wind drag is biased forward, like a roadster, with square vertical side panels on the engine compartment, and the very high drag or the radiator, the car wants to turn away from the gust. As it does the effective frontal area exposed to the air flow increases (a car has more frontal area viewed at 45 degrees than at 90 degrees and much more than when the wind is approaching head on) aero drag builds much faster on the front of the car than on the rear, as the air is trying to flow over the car body on a diagonal, so it wants to turn around.
If you look at a roadster at an angle of 15 - 20 degrees as the wind sees it at the beginning of a spin, you can see that the front of the car is much dirtier aerodynamically than the smooth trunk region. That means that as the car yaws away from the wind the center of pressure jumps forward a substantial amount, and your CG is suddenly behind the center of pressure, when while running in dead calm it might be slightly behind it.
This is a bad thing :)
Larry
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Willie
You seem to know, that you are smart enough,to know that you don't know everything! And
Thats good!
Keep making good stuff !
Jack
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The good thing at Bonneville is there are no guard rails etc along the course. This gives the driver a little flex room to let the vehicle drift and slowly bring it back with out over correcting. But the drivers still need to be heads up and use common sense.
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jack i will if they will quit changing the rules on me ---its about time i paid my mom a visit willie buchta
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Larry ...good points
To me stability in a car is about drive-ability...a car that lets the driver make the decisions...a car that does not suprise the driver...a car that is a careful balance of tradeoffs.
Shure... aero is a big part of stability at the speeds we run...but the car set up is the bottom line.
I hope the guys new to landspeed racing think about it. I hope the old guys keep sharing experience for safety sake!
In that regard...I am building a streamliner...would someone with experience talk about the yaw damping of the in line front wheels of some streamliners versus 4 wheel drive. If you could only have one would you pick yaw damping of tires on the ground or a tail fin? And no I don't mean tail feathers first...a balanced car without eather feature.
Akk
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jl222
I like neutral steering for straight line control. 0 caster,0 camber 0 scrub 0 suspension. The driver must be in control. More important on a wide track vehicle. Thats what I do..
jack
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Wow Jack, zero caster. That is very interesting. I'm going to have to think about that.
Doug in big ditch even more confused than normal.
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Doug, I have been told by a circle tracker that he uses caster for "weight jacking" in the corners on certain tracks
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akk
Could you build a couple of models one with inline and one with side by side tires,then blow air at each?
jack
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I have to agree with Jack on the 0 caster. Most drivers use a lot of caster to help make the car go straight. This will make the car track straighter with less driver input but can cause a big problem when the car starts to spin. Just imagine making a run at Bonneville and the car starts to spin to the right. Naturally you are going to counter steer to the right to get the car straight again. What happens is when you counter steer to the right or the left depending the direction of the spin, a car with a lot of caster will cause the cross weight to jack weight to the opposite side at the rear. Now you lose traction on the right side and cause the car to want to spin even more. The more input you put into the spin the more the car will want to spin. This is not as big a problem for longer and more narrow cars like liners but I can see it being a big problem for short wheel base cars with a wider track, like roadsters. Just my opinion, but I think running as little caster as possible and slow the steering. The driver steering input is what keeps the car going in the direction needed, not more caster.
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Good to see you back on the board Jerry. Hope you start another project.
Pete
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Jack,
Is the reason that you go with 0 caster related to the solid aluminum wheels? My thinking is that caster gives camber gain when turned and your front wheels probably don't like camber.
Rex
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Hmmmm . . . . good point Rex. And when they turn do they "knife edge" into the track with caster?
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it is the design of the steering ----0 caster (rake ) 0 trail 0 camber--going straight or turning it remains the same 0 willie buchta
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The 222 camaro has front wishbones and spindles with 22 deg caster made by Stock Car Products for high speed tracks
like Taladega and Daytona, when Pro Chassis was building the car they had a 16 deg unit on and I had them change it
to the 22 deg as some of the bville cars had far more at the time. I know a lot of caster can cause the rear chassis to move up when the steering is turned because I have seen it happen on a bare roadster chassis and I was surprised that stock cars used that much, this was in 1989. Still weight jacking from caster must not be a problem for them or they would not use that much.
Anyhow their the pros racing for big bucks with a lot of learning miles. This is what I was told, I have no knowledge of actual caster settings used today
We get a confident ride at over 300 mph with no need of wheel correction, accelerating and decelerating with or with the chutes. [ look at videos in build diaries under getting ready for Bonneville]
I also have no eyeball vibrations because we are suspended, unlike some streamliners that see the cones as being 3 ft. high.
We also have toe in on front tires as we have front brakes and don't want them going into toe out when applied, which is an unstable condition.
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let me make something clear here---i know about jacks steering because im building a vehicle with similar steering---the bike i run now has 54 degrees of rake (caster) i did that for a couple of reasons mainly to slow down the steering--i do not recommend 0 or 54 degrees when i first started building drag cars i found a good front alignment shop and went with what they recommended 10 degrees and never had a problem with any car i ever built---there is a lot of things that come into play on each vehicle--do the research ---if you cant figure it out ask someone with a vehicle like yours --------willie buchta
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For a while I thought this thread was dead...we were in the dyno room...speed week cometh but there is still time to learn something...
The jacking effect of caster is caused by scrub radius and wide tires...if the king pin points to the center of the tire contact patch going straight ..minimum jacking...I think!??!
Akk
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If the king pin points to the centre of the tire contact patch going straight the car has no caster.
Pete
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if the kingpin hits the ground in the center of the tire you have 0 scrub--that has nothing to do with caster--caster is the rake of the front axle looking from the side of the car---Akk is very close--the raising of the car (jacking effect) is caused by caster --the more caster the greater the effect--the problem with to much caster (rake) is the jacking effect only effects the wheel on the inside of the turn--if the inside front wheel raises the chassis in a turn then the opposite rear wheel will see the extra weight applied ----some caster is usually required its what makes the front wheels want to go straight---on a car its called caster on a bike its called rake ---i have built race cars and street rods all of my life and have built almost every kind of front and rear suspension and steering there is ---the one im working on now has 0 rake (caster) 0 camber 0 trail---i must admit i did get some help from jack---mine is not the same as his --hopefully i will have it done for speedweek 2011---thats what i like about lsr there is room to do your own thing so far if it changes i will do something else--when i get a chance i will do some suspension stuff on willies builds willie buchta
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Willie:
If there is caster in the axle the extension line from the kingpin will hit the ground ahead of the center of the tire patch.
Pete
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Isn't most of this discussion regarding caster etc pretty much a moot point related to a land racing car. Johns (JL22) likes caster because it makes it stable going straight, Jack's cars run 0,0,0 because of the type of front tire/wheel and the zero suspension that he runs and it goes straight which is really all they are looking for. Sprint cars and go karts run lots of caster and scrub radius because both of these types of vehicles are ran in a very "loose" condition and the extra caster and or scrub radius will transfer weight to the opposite corner which will both help forward drive and also lessen the chance of spinning out. Sprint cars and land racing cars run in very different enviroments and both require different approaches to suspension parameters based upon the way they are designed and their designers thinking of what will work best for their car.
Rex
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pete the more caster the farther that point moves forward ---and the more the steering will raise the car-- and the more it will try to steer straight willie buchta
pete sorry i missed your point in an earlier post --you are right king pin angle center of contact patch (viewed from side) = no caster
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Rex
Read Jerry O's Reply Over and over and over!
Those are my feelings exactly!
Although, this is only one of the things that improve straight line controllability!
jack
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Rex
A P.S. to my last post
Rock climbers need a lot of caster for weight jacking. Think how much steering imput it takes to change lanes at 60mph. Think what just a little weight jack at 200mph could do to a rectangle wheel layout that "some vehicles" have!
Jack
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When I was running '39 Chevy hubs with my 21" Goodyears I had almost 3.5" positive scrub radius with 15 deg caster---turn the wheels and I got a lot of weight jacking. Above 160 the Rat started to hunt and wander his way down the race course if the Course was hard you could keep him gathered up fairly good if it was tractionaly challenged so was I! :-P
I change wheels & hubs and got scrub radius down to 3/8" positive very little weight jacking and now the Rat goes pretty straight now. I will have 5 deg max when I relocate the axle.
The big tail feathers kept me from going completely around---The Rat has a flat bottom and 3.5" rake on a 209" wheel base with my smallest 25" rear tires
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One of the things that we are not talking about which I think in the case of Jack's cars could be very important are the gyroscopic forces developed by the wheels. A 20 inch diameter wheel at 200 mph is turning at almost 3400 rpm, it takes a pretty large amount of force to try to make that wheel deviate from its path, especially if the rate of deviation is fast. This force is what keeps bicycles and motorcycles from falling over at speed and the way Jack's cars are designed with very narrow tracks I would think that this force would also be a great contributor to keeping his cars vertical (bottom side down) and going straight.
Just another thought to ponder.
Rex
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Rex, as an aside to your comment about the gyroscopic forces of a fast-spinning wheel -- I've often tried steering the bike at speeds of 200, and it's bloody near impossible to move the handlebars. Steering, when needed, is done more with hanging an elbow out in the breeze on the side toward which I want to go. If I did manage to turn the bars -- I'm always afraid that they'll be too hard to turn back and I'll fold the front wheel under and do a high-side catapult.
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If the steering and frame geometry is correct, the front wheel will return to straight ahead when you decrease your input. That is if you are not already way out of shape or something else is providing input.
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With a rectangular foot print weight jacking requires scrub .
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John
I agree with the scrub comment. Jack
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Back to gyroscopic wheel force, that is why gran prix motorcycle riders throw their knees out to steer. The wheels spinning that fast want to remain plumb and the rider must create drag and counterbalance to navigate through the turns.
Also, way back to a question i asked earlier this post, could a rider change his riding position during a run to act like a dynamic ballast? I used to drag race my old Maxim X, a naturally aspirated 700cc bike that ran very well. In one race, because of the low number of bikes that showed up at the track that weekend, i went up against a N2O breathing 1300CC 'Busa. I had an excellent light, my opponent did not. Being so overmatched, i was a little too hard on the throttle out of the hole and had my bike travelling up on it's rear wheel until i found 4th gear. Because my opponent had a poor light and wasn't ahead of me, i thought i might have a shot and rather than ease out of the throttle, i stood up on the footpegs and leaned out over the front fender desperate to keep the lead. Would it be possible to do something similar if the rear wheel was to have trouble hooking up or the bike started to develop a high speed wobble?
-Chad-
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Back to gyroscopic wheel force, that is why gran prix motorcycle riders throw their knees out to steer. The wheels spinning that fast want to remain plumb and the rider must create drag and counterbalance to navigate through the turns.
Also, way back to a question i asked earlier this post, could a rider change his riding position during a run to act like a dynamic ballast? I used to drag race my old Maxim X, a naturally aspirated 700cc bike that ran very well. In one race, because of the low number of bikes that showed up at the track that weekend, i went up against a N2O breathing 1300CC 'Busa. I had an excellent light, my opponent did not. Being so overmatched, i was a little too hard on the throttle out of the hole and had my bike travelling up on it's rear wheel until i found 4th gear. Because my opponent had a poor light and wasn't ahead of me, i thought i might have a shot and rather than ease out of the throttle, i stood up on the footpegs and leaned out over the front fender desperate to keep the lead. Would it be possible to do something similar if the rear wheel was to have trouble hooking up or the bike started to develop a high speed wobble?
-Chad-
Did you win?
And I think you'll find the answer is yes but maybe to a lesser degree.
You sure do have a bunch of questions. My advice is "kiss". 8-)
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Back to gyroscopic wheel force, that is why gran prix motorcycle riders throw their knees out to steer. The wheels spinning that fast want to remain plumb and the rider must create drag and counterbalance to navigate through the turns.
Also, way back to a question i asked earlier this post, could a rider change his riding position during a run to act like a dynamic ballast? I used to drag race my old Maxim X, a naturally aspirated 700cc bike that ran very well. In one race, because of the low number of bikes that showed up at the track that weekend, i went up against a N2O breathing 1300CC 'Busa. I had an excellent light, my opponent did not. Being so overmatched, i was a little too hard on the throttle out of the hole and had my bike travelling up on it's rear wheel until i found 4th gear. Because my opponent had a poor light and wasn't ahead of me, i thought i might have a shot and rather than ease out of the throttle, i stood up on the footpegs and leaned out over the front fender desperate to keep the lead. Would it be possible to do something similar if the rear wheel was to have trouble hooking up or the bike started to develop a high speed wobble?
-Chad-
As far as the high speed wobble ....just jump off but don't let your leathers or boot get stuck on the footpeg [ like Ron Cook] :-o
and make sure you have your aerodynamic leathers and helmet on so you will not tumble but just slide head first through the timing lights with no loss in speed.
JL222
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Hopefully, a steering damper and CVT will keep me straight and hooked up, i'd rather not bail off a mostly hand made bike.
I didn't win against the 'Busa, but he didn't pass me until about 60 feet from the finish. I do ask a lot of questions here, but looking dumb on a forum is much better than the look i'll have if i show up to my first speed week and don't get to run.
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Using every piece of information available is far from dumb.
For the body position, weight bias thing , may be usable on an open bike but my APS and many others in APS/MPS are fairly fixed in position due to the bodywork and seat design ,
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Hopefully, a steering damper and CVT will keep me straight and hooked up, i'd rather not bail off a mostly hand made bike.
I didn't win against the 'Busa, but he didn't pass me until about 60 feet from the finish. I do ask a lot of questions here, but looking dumb on a forum is much better than the look i'll have if i show up to my first speed week and don't get to run.
I'm surprised the bike guys have not advised you to Not stand up on footpegs and lean forward at high speed. On U-tube there's
a video of a top fuel harley rider getting blown off his bike when his glove caught the air.
JL222
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cuz he might not be riding a top fuel harley...
Joe :)
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JL222
Do you know the name of that video? I figured there would come a point where that wouldn't work considering 1/8th mile speeds are much slower than LSR speeds, i was just wondering if i could slide forwards up to the fairing to help fight some of the high speed handling problems.
-Chad-
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JL222
Do you know the name of that video? I figured there would come a point where that wouldn't work considering 1/8th mile speeds are much slower than LSR speeds, i was just wondering if i could slide forwards up to the fairing to help fight some of the high speed handling problems.
-Chad-
No, but I'll try to find out and don't take my comment about jumping off to seriously :cheers:
JL222
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JL222
Do you know the name of that video? I figured there would come a point where that wouldn't work considering 1/8th mile speeds are much slower than LSR speeds, i was just wondering if i could slide forwards up to the fairing to help fight some of the high speed handling problems.
-Chad-
Chad... google....[Death of a top fuel harley] also videos of Ron Cooks get offs at Muroc and El Mirage and Korry Hogans crashes.
JL222
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It's a shame really, I got to page 5 before posting and felt I had reached the pint of "go no further". The start of the topic got my interest immediately. I was looking forward to reading about aerodynamics and the experiences that many of you who have "been there", "done that" and "worn the shirt", had to say on this topic. A chance to participate in a master-class! Unfortunately, this topic has strayed away from the initial intention to develop into the usual forum discussion where one gets offended and has a go and others follow suit. The Author of the topic did not set out to offend anyone but to simply gather opinion and fact of experience for which everyone would benefit. So why be offended? :? Pitty
Paul
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Re....the front is pulled around
To clarify...the tire rolling with weight and the coefficient of friction on the salt is what pulls the front end around at spin initiation. After the spin starts and the tire starts sliding aerodynamic forces get involved with the kinetic friction. Spin initiation is the rear kicking out and creating a steering angle.
I have always greatly enjoyed talking with you. . Usually on your favorite piece of real estate. . IMPOUND! :-D I think you have identified an incredibly important subject. I'm trying to understand what some may consider finer points. But to keep needling away at this will only invite negative feedback from others which breaks down any further education. I’ll buy you a cup of coffee at the Red Flame so we can share some additional thoughts. After all, The Red Flame is not too far from where you are usually parked!
Something I’m struggling with is; once the spin is initiated and the CG is now accelerating around the steering angle, how do you react the CG momentum? With rolling rear tires (i.e. some traction) and zero-friction-sliding front tires (via full braking) I can understand the effect you mention. But if the front tires are turned into the direction of travel and rolling you might cancel out some of the CG momentum. Not sure though . . . maybe it’s the CG’s arm from the pivot point . . . the location of the CP . . . other? Thanks for introducing a thought-provoking perspective.
Wanted to leave the topic but had to read on :roll: I think I understand the theory behind locking the front wheels>. the CG is,at the point of spin moving faster than the front of the vehicle. Once the front wheels start to skid, they begin to increase in speed thus the correction is possible. I think? :roll: :roll:
Paul
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I have been following another team that has not posted they have a roadster that will, no "wants" to spin one way in the wind tunnel and not the other---they are thinking that they are dealing with some issues as to how the chute pack influnces the "aero"
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It's a shame really, I got to page 5 before posting and felt I had reached the pint of "go no further". The start of the topic got my interest immediately. I was looking forward to reading about aerodynamics and the experiences that many of you who have "been there", "done that" and "worn the shirt", had to say on this topic. A chance to participate in a master-class! Unfortunately, this topic has strayed away from the initial intention to develop into the usual forum discussion where one gets offended and has a go and others follow suit. The Author of the topic did not set out to offend anyone but to simply gather opinion and fact of experience for which everyone would benefit. So why be offended? :? Pitty
Paul
Paul... are you talking about Blue's post? After more than 60 years,you don't think that having to prove aero stability for motorcycles over 200 mph and cars over 300 mph might offend someone, when an unstreamlined motorcycle has gone over 270 and a car [ Lindsleys and Liggitt] 333 avg this with a top speed over 340+. No roadster is going to prove aero stable over 300. This would outlaw all cars over 300 most bikes all roadsters and most lakesters and some streamliners and you don't think we should be offended?
JL222
P.S. Do you think he was gathering opinion and facts talking to our senior official?
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Wanted to leave the topic but had to read on :roll: I think I understand the theory behind locking the front wheels>. the CG is,at the point of spin moving faster than the front of the vehicle. Once the front wheels start to skid, they begin to increase in speed thus the correction is possible. I think? :roll: :roll:
Paul
Good point, and makes sense, Paul. Same effect with a swinging pendulum. If you move the pivot point in the direction of travel you cancel out the momentum or swing and stop the pendulum.
I am kind of disappointed in Blue's participation here. I was assuming he is a PhD Aerodynamicist from his postings and his statements of aircraft design prowess. He started the subject and I anticipated he would kind of act like a moderator and jump in from time to time to clarify, or add some good science or engineering, to the issues. He has mentioned a few platitudes like quarter chord or yaw neutral point, or the Center of Pressure instability. However, when sincere questions result about these statements they are completely ignored. I have had no response to my posts #3 and #19. He has also made assumptions about a CG location on a vehicle (and continues to stick to that assumption) without knowing any of the individual masses or their moment. He has calculated the CG in his mind, completely ignorant of the facts. I want to learn from everybody. But to be valuable the learning process must filter out B+S. He has made me think about some very important points (that I am appreciative for) but is lacking on follow-through. I am off to Bonneville now so will be silent the next 10 days. Hope to see you there Mr. Blue . . .
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It's a shame really, I got to page 5 before posting and felt I had reached the pint of "go no further". The start of the topic got my interest immediately. I was looking forward to reading about aerodynamics and the experiences that many of you who have "been there", "done that" and "worn the shirt", had to say on this topic. A chance to participate in a master-class! Unfortunately, this topic has strayed away from the initial intention to develop into the usual forum discussion where one gets offended and has a go and others follow suit. The Author of the topic did not set out to offend anyone but to simply gather opinion and fact of experience for which everyone would benefit. So why be offended? :? Pitty
Paul
Paul... are you talking about Blue's post? After more than 60 years,you don't think that having to prove aero stability for motorcycles over 200 mph and cars over 300 mph might offend someone, when an unstreamlined motorcycle has gone over 270 and a car [ Lindsleys and Liggitt] 333 avg this with a top speed over 340+. No roadster is going to prove aero stable over 300. This would outlaw all cars over 300 most bikes all roadsters and most lakesters and some streamliners and you don't think we should be offended?
JL222
P.S. Do you think he was gathering opinion and facts talking to our senior official?
HI JL222,
I can appreciate your opinion but, as I read it, Blue was, bringing a valuable topic up for discussion. I would not be offended if a young apprentice told me how to form sheet steel to make a vehicle panel, I would look at what he was trying to tell me then see if I could benefit from his information. If I thought I could not, I would offer my opinion to him.
:-)
Regardless of our experience there is always new technology and innovative ideas on the horizon, and with the aerodynamic brain power within this thread alone, together, we could maybe, find an answer or two to solve those niggling issues that prevent us from achieving our ultimate goal. It's easy to feel offended and I appreciate that but would it be possible to respond with facts that answer the questions put forward for discussion. :roll:
If it wasn't for people like Blue, then the forums probably would not exist because everyone would be reluctant to offer an opinion for fear of being scalded due to unintentionally insulting anyone. :wink:
Cheers and good health :cheers:
Paul
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As far as proving aero stability and facts.
Which aerodynamist are you to believe, as porkpie says ask 10 aerodynamist and get 10 different answers.
As far as Blues theories, unstreamlined bikes at 270 and passenger car at over 340 proves him wrong by real racers :-)
What do you think of a rapid lane change at 600 mph as suggested by an aerodynamist?
The same person suggested I try it at high speed in the 222 car to test aero stability. I replied, suggesting that showed his basic missunderstanding of traction on salt of rear wheel drive vehicles.
As far as responding with facts go back and look at all the post with unanswered questions to Blue.
Its as though he started this thread so he can sit back and say [I told you so]
Paul who is your aerodynamist?
JL222
JL222
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I believe the racers, the record holders,the people who love this venue should keep on racing. Blue has caused nothing but controversy and dissension, with his hypotheses. Let him argue and speculate with the other 9 aerodynamicist, who think they know it all.
old...
He might even be a guv'mint spy.
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Is this "Blue" i.e., Eric Ahlstrom?
(Edit . . . ) link has been deleted, with my apologies, based on post #162.
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Isn't that interesting.
No credentials at all in aero engineering.
BSME is something I respect, and knowledge of fluids is very likely, but not enough to tell SCTA that flat bottom car/bike liners are so unstable they should be eliminated.
I think I'll stick with my "real" Aerodynamics Engineer who has a lifetime of study of the aerodynamics of cars.
OH, isn't Howard Nafzingers old car, now Charles Nearburg "Spirit of Rhet" a flat bottom car?
Sorry I just can't resist.
Everyone be safe on the salt. I'm prayin for good weather, salt, and racers luck for you all.
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That is not the same Eric.
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As far as proving aero stability and facts.
Which aerodynamist are you to believe, as porkpie says ask 10 aerodynamist and get 10 different answers.
As far as Blues theories, unstreamlined bikes at 270 and passenger car at over 340 proves him wrong by real racers :-)
What do you think of a rapid lane change at 600 mph as suggested by an aerodynamist?
The same person suggested I try it at high speed in the 222 car to test aero stability. I replied, suggesting that showed his basic missunderstanding of traction on salt of rear wheel drive vehicles.
As far as responding with facts go back and look at all the post with unanswered questions to Blue.
Its as though he started this thread so he can sit back and say [I told you so]
Paul who is your aerodynamist?
JL222
JL222
My opinion is irrelevant, what is relevant though is that you feel he is talking through the top of his head and that opinion is fine and the right of anyone else on the forum. All I was suggesting is, rather than gathering a lynch mob cause "were gonna have a hanging", Offer some genuine facts as to why he is wrong then people can use those fact to assist them with their projects.
Once the arguing starts, the topic goes to pot and the discussion results in a waste of server space and may as well be deleted. I have no intention of standing up and telling anyone on these forums that they are doing it wrong, I'm here cause I want to learn about aerodynamics and vehicle stability, I am here because I want to design and build a vehicle that will travel across the face of the earth at over 1000 mph and the back again, with one sole purpose in my mind and that is, at the end of it, the driver can climb out un aided and say "We did it"!
As for my aerodynamist, I am not going to divulge and information re: any of the personnel involved in The Bullet Project at the moment. I designed the car and CFD testing will commence in due course. I can say that our aerodynamist was the chief CFD engineer for a major Formula One team and has recently left Formula One just last year.
We are 10 years + behind all the other teams out there in this challenge. Only one of them has acknowledged the fact we are going for 1000 mph (thank you Waldo) the rest are pretending we don't exist. My site has links to all the other players websites I get none in return. Thats why I'm playing my cards close to my chest. All up to date info will be on our website.
Cheers
Paul
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My opinion is irrelevant, what is relevant though is that you feel he is talking through the top of his head and that opinion is fine and the right of anyone else on the forum. All I was suggesting is, rather than gathering a lynch mob cause "were gonna have a hanging", Offer some genuine facts as to why he is wrong then people can use those fact to assist them with their projects.
Once the arguing starts, the topic goes to pot and the discussion results in a waste of server space and may as well be deleted. I have no intention of standing up and telling anyone on these forums that they are doing it wrong, I'm here cause I want to learn about aerodynamics and vehicle stability, I am here because I want to design and build a vehicle that will travel across the face of the earth at over 1000 mph and the back again, with one sole purpose in my mind and that is, at the end of it, the driver can climb out un aided and say "We did it"!
Hear Hear,
I read a lot on this site and post very little. I have to concur that the linch mod mantality it pointless and detracts from forward momentum. If 1212 and JL222 don't like the discussion, it is very simple to skip over the string when "showing unread posts since my last visit", or start your own string named "Why aero vs. vehicle stability is a crock of sh&#" or "aero vs. stability linch mod string". Let the rest of us discuss the matter in a forum that moves the conversation forward. And this shooting the messanger because you don't like the message is real junior high crap. BLUE is just trying to get some ideas flowing around in people's heads. If you do not agree with position, state your opinion about the discussion. If you want to tear down the person making the arguement, get out your tape measure, lay yours out on the table, and show us what you got.
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well said :cheers:
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The thread went sideways when Blue said that he was talking to a SCTA official about providing aerodynamic proof of stability over a certain speed for certain vehicles. So you want people to ignore this kind of statement?
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I think B'ville is correct,,, the thread went negative after that statement.
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well said :cheers:
Thanks for the reach around sparky. I guess this means that you will be needing those leathers I offered? :-D
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well said :cheers:
Thanks for the reach around sparky. I guess this means that you will be needing those leathers I offered? :-D
Don't get carried awar here, you'll have to start a new topic on the subject. :-D
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I think B'ville is correct,,, the thread went negative after that statement.
I agree with what you are saying, but people could pass over the statement or voice that you disagree is one thing. To loose all sense of decorum and start chest beating is uncalled for. We could have 5 pages of "your a jerk", "no, you are", "no, you are" and that would be about the same.
It always amazes me how a person's chest can grow at a far greater rate than their intellect when they have a tiny little computer screen to hide behind.
Or to put it in the words of my brother...."the main thing, is to keep the main thing the main thing;" and I think a discussion of aero vs. stability is the main thing.
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Read Blues first sentence on the post. He wanted it to go in this direction. If he was interested in keeping the thread on tract he could post more often. No chest puffing that I could see. I don't know who is hiding, I and many others will be at speed week, where we will be running and proving our theories. :cheers:
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Go FAST and Be Safe B'ville,,, we are all pullling for you to set yet another record.
Keep us posted and take a bunch of pics (in car too)
Charles
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Slings and arrows, aim here. Just got back into town, leaving tonight for Bonneville so everyone can beat me up in person. Sorry if the absence was construed as a lack of participation.
Actually, the 675 mph lane change was attempted by Craig Breedlove and resulted in an upset. I was the schmuck who had to figure out why it happened and fix it. Whether we want to do a rapid lane change or not we sometimes have to. As far as can cars and bikes go very fast without being aero stable? Sure, the question was really: how fast?
Some of the people here are the best in the world at this sport and viewed my comments here as somehow questioning their already proven competence. Sorry, no. I'm one of those engineers who actually believes that when theory doesn't match reality we need to fix the theory. I was actually looking for information and got a lot of it and I thank every single angry racer who told me to stuff it. You all increased my understanding of multiple steering geometries in multiple sports in just a few posts.
After speed week (I'll have the white shirt on with my logo) and after everyone has all of the salt washed off, we can come back and post more. I look forward to learning a lot.
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Most LSR designers use the idea of a "Cp" as a plot of the lateral area of their vehicles and presume that if the CG is forward of the 50% point of this plot, then the vehicle is stable in yaw. This is simply not true.
First, most symetrical aerodynamic surfaces rotate around the "quarter chord point" or only 25% of the length. This is called the "yaw neutral point". Very few LSR vehicles have their CG forward of this.
Help me out here. . . I haven't had my tea today like Tony. Just where are these two points? Assume a 100" wheelbase. The CP is at 75" from the front spindle(s). Now if the CG is 50% forward of that point it resides at (75" x .50 = 37.5"). So the CG is at 37" from the front of the car? But you say that is yaw unstable? Why? Is it too far forward?
Now where is this quarter-chord point? You say it is 25% from the CP. Same exampe, if the CP is at 75" the yaw neutral point is (75 x .25 = 19') in front of the CP. On a 100" car that yaw neutral point is at 56" which is a rearward bias! So where do you want the CG to be on a 100" car? 56" is too close to yaw neutral but 38" is unstable? All the sedans I know have the CG in the forward 50% of wheel base in the 45-48% range. What am I missing?
Edit: Since I see Willie is here I made "spindle" both singular and plural in the interest of diversity. :-D :-D
OK, sorry to not address this specifically. I really messed up by starting this thread on the front end of month of long hours and multiple road trips.
First, we need to uncouple the aero from the wheelbase. Lots of cars have lots of bodywork well aft of the rear axle, so tails can be far from the CG while the CG is close to the rear axle for traction.
The fundamental of the 1/4 chord point relates to any streamlined aerodynamic object of smooth contour, i.e. an airfoil without separation. Cars, bikes, and especially streamliners are very complicated aerodynamic objects. To actually get the yaw neutral point, we have to look at aft vertical tails, forward vertical surfaces, round edges vs. square (round in front and sharp in back moves the CP aft), where the separation is, etc. and how all of this changes with yaw angle. Look me up on the salt. As far as whether my knowledge is opinion or BS, I'll bring a few reference books and a box of yarn tufts and tape. Between the books and some yarn in the breeze anyone can figure this stuff out.
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I hope this provokes a lively discussion, this is a subject that I believe everyone in LSR can understand and benefit from with the end result of faster records and safer vehicles.
First, I mean no disrespect to Costella or any builder or contender in LSR. My concern and comments on the previous thread come from my knowledge of vehicle mechanical-aerodynamic stability and control. My concern is that speeds have now exceeded the area of mechanical stability and entered the area where aerodynamic stability dominates and the knowledge base of LSR is not yet wide or deep enough for safety.
I spoke to a senior SCTA board member last year about the need for the higher speed vehicles to prove their stability with analysis before going too fast, and we had a good discussion about the costs and where the break point could be for that analysis. I am still searching for a reasonable CFD cost solution for everyone and have not found it yet. However, my experience in S&C (stability and control) concerns me about some of the designs I see vs. the speeds people are seeking.
Most LSR designers use the idea of a "Cp" as a plot of the lateral area of their vehicles and presume that if the CG is forward of the 50% point of this plot, then the vehicle is stable in yaw. This is simply not true.
First, most symetrical aerodynamic surfaces rotate around the "quarter chord point" or only 25% of the length. This is called the "yaw neutral point". Very few LSR vehicles have their CG forward of this. Even so, at relatively low airspeeds (below 200 mph) the dynamic pressure is low enough that mechanical stability can override the aerodynamics. Above 300 mph, the opposite is true and any vehicle that is not solely stable aerodynamically will not be recoverable if it loses traction. Downforce can increase the mechanical advantage, but it is a bad trade since downforce usually leads to pitch instability.
Tails or other large vertical surfaces mounted far aft are used in some designs and can radically improve the overall vehicle's yaw neutral point. However, blunt tails (like chute tubes) can reduce their effect. Some of the vehicles currently seeking 400 mph are nearly neutral in stability due to their aft CG and high degree of aft separation. There are solutions and a few in the 400 mph club have done a very good job of addressing this issue. Some haven't, and that scares me.
At least a first-order, algebra-based stability calculation should be required of any motorcycle going over 200 and any car going over 300. As speeds increase, the mechanical stability is going down exponentially with speed (dependent on surface condition, traction, and tire dynamics) and up linearly with downforce. Countering this, aerodynamic instability increases with the square of speed. At some speed the two lines cross and things can go bad very quickly. Since most motorcycles do not have downforce, this equation leads to the need for positive yaw stability at the starting line. Worse, downforce-based stability is at the mercy of driver skill; and I like to be kinder to my drivers.
The REAL danger is that this "negative stability" speed may have already been achieved without external upset and then the vehicle makes another similar run and encounters an upset due to surface or wind conditions and suffers an uncontrolled departure; i.e. SPIN. Think about all of those guys who have gone fast in roadsters or stock body cars and then spun at less speed. Their driving skill may have saved them in the past, this does not mean it will forever. At any combination of speed, surface, and wind condition it is the LSR vehicle's job to go straight, not to demand an ever-increasing level of dynamic driver input.
In aviation, we call the ability to handle instability the "velvet glove": a VERY complimentary term for the pilot. And a not-so-complimentary one for the engineer who made it necessary. As an engineer I don't like being the butt of jokes, so I make the things that I design stable and controllable. My pilots appreciate this and bitch about other engineers instead.
All of this relates to yaw stability and spins. Pitch and roll stability is another subject entirely and much more complex.
Here is my take on CFD for what it is worth:
Swift Engineering has just finished a detailed CFD study of the ACK Attack to try to determine why the bike becomes unstable at speed with the rear doors attached. This was done on their brand new Cray Supercomputer and CFD software which was installed in July. http://www.swiftengineering.com/
The bike originally was designed with the rear of the body cut off and open with an open area of about 8” X 24”. After setting the record in 06 and running as fast as 349 mph the bike handled very well and showed no signs of instability.
In 07 after adding doors to the rear we crashed at the Bub event when the bike became unstable and began to oscillate side to side at about 300 mph. In 07 we blamed the crash on track conditions.
In 08 at the Shootout we spent the first three days trying to figure out why the bike began to experience a side to side phugoid oscillation at about 330 mph which increased in frequency as the vehicle accelerated. After many tweaks on the bike I finally told Rocky to open the doors when the oscillation began. When he did the bike became absolutely stable. We set the record with the doors off in 08.
We commissioned Swift to do the study and try to determine why the bike became unstable with the doors on. The first phase of the study looked at the bike at 350 mph and 6500 ft density altitude at 0, 2, 4 and 8 degree of yaw. The study showed that the bike was unstable at these speeds and tended to wind cock away from a cross wind. They said the rider could correct for this up to a point at which the bike would be uncontrollable.
The second phase studied the bike with the tail off my friend Ken Mort who helped with the design and has many years experience with the 130 ft wind tunnel at NASA Ames bet me a beer that they would find it is unstable with the doors off and that is exactly what they found. There was a slight increase in stability but nothing that would correlate with what the empirical data told us.
The other interesting thing they ask was what was keeping us from going faster with the doors off. They calculated we needed 180 HP with the doors off and 163 HP with the doors on to go 350 mph. The reality is we used all of at lease 800 HP with the doors off to go 360 and the bike was just not going to go any more than a few miles per faster. While these calculations might hold true for a moving body in free air they don’t work for ground vehicles.
The folks at Swift are very smart with practical knowledge and I appreciate the work they did on this project. While the CFD is well developed and understood for the Champ and Indy cars which they work with at 200 MPH and aircraft at higher speeds as my friend Ken Mort says there is really no good understanding of the dynamics of ground vehicles running at half the speed of sound especially a motorcycle. We did receive a lot of interesting data from the study such as boundary layer thickness, pressure gradients, drag in different configurations and other data but the basic question about the change in vehicle stability with the door on was not resolved.
I would not trust CFD data to reliably predict the stability of a ground vehicle at 300 MPH + and knowing the cost of CFD; to require such studies at this point I belive would be counter productive and detrimental to the sport.
One last comment as the bike has been displayed at a number of venues including the SEMA shows and a number of people who claim aerodynamic knowledgeable and expertise have come by looked at the vehicle and they know exactly what’s wrong with it and explain how I have designed it wrong. I always answer “how fast has the motorcycle you designed gone”?
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Here is my take on CFD for what it is worth:
It's worth quite a bit IM<HO.
I make my living in aero mods specifically focusing on areas where CFD is weak and inaccurate. As CFD scientists like to believe, CFD can solve everything and anything. This is true IF and only if the vehicle in question has no separation or stagnation. We struggle every day to make aircraft unbelievably simple and totally streamlined. Complex vehicles like LSR can NEVER be fully streamlined. In these areas, wind tunnel analysis breaks down due to lack of accurate road-to-vehicle interaction and CFD breaks down because separation is an integral part of LSR aero, not an afterthought to be squashed like a bug.
The chute tube cover on Ack replaced disorganized separation with unstable vortexes on both sides. Much like the experience we have all had driving down the freeway behind a tractor-trailer, a semi-stable vortex builds on one side of the vehicle and grows until it sheds and imparts a yaw moment. Then the other side grows one and the cycle repeats. This phenomena is easily understood by anyone following a truck, yet CFD and wind tunnels have a very hard time duplicating it accurately let alone predicting it.
Correct design of aft doors can cure both problems of drag and stability, but it's not so simple to contour the doors and tail correctly to prevent both separation and shedding vortexes.
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I think that "Blue" has made a very interesting observation of the reasons for the instability problems with the Ack Attack after the addition of the chute covers and also I think that his statements regarding CFD and LSR vehicles are something that we all can agee with to some point, remembering that the JCB streamliner was totally designed using CFD and it was certainly successful. Eric "Blue" is a big believer in tuft testing, I would ask Ack if you have ever done tuft testing with the Ack Attack before the tail modification or after or both??
Rex
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Prime example of this topic. Did anyone at speedweeks find out any info that led to this crash from the driver/team?
Link to story: http://www.sltrib.com/sltrib/home/50114112-76/car-speed-kirk-salt.html.csp (http://www.sltrib.com/sltrib/home/50114112-76/car-speed-kirk-salt.html.csp)
(http://i263.photobucket.com/albums/ii147/SeldomSeenSlim/Speedweek%202010/IMG_1750.jpg)
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I drove the long course after the drivers meeting and I could feel a lot of bumping inside of truck from bumps in track, in other words it was not as smooth as in other years. Not big bumbs very small just not graded completely
out. I thought at the time that cars might have a hard time hooking up, especialy unsprung cars. Dave Mcdonald said their Firebird wanted to dance around more than usual and I heard they spun later in the week. It will be interesting to see how many spins and crashes this meet had compared to past meets.
JL222
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There reportably lots of spins real close to the 4 on the long course at almost the same spot
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As far as proving aero stability and facts.
Which aerodynamist are you to believe, as porkpie says ask 10 aerodynamist and get 10 different answers.
As far as Blues theories, unstreamlined bikes at 270 and passenger car at over 340 proves him wrong by real racers :-)
What do you think of a rapid lane change at 600 mph as suggested by an aerodynamist?
The same person suggested I try it at high speed in the 222 car to test aero stability. I replied, suggesting that showed his basic missunderstanding of traction on salt of rear wheel drive vehicles.
As far as responding with facts go back and look at all the post with unanswered questions to Blue.
Its as though he started this thread so he can sit back and say [I told you so]
Paul who is your aerodynamist?
JL222
JL222
My opinion is irrelevant, what is relevant though is that you feel he is talking through the top of his head and that opinion is fine and the right of anyone else on the forum. All I was suggesting is, rather than gathering a lynch mob cause "were gonna have a hanging", Offer some genuine facts as to why he is wrong then people can use those fact to assist them with their projects.
Once the arguing starts, the topic goes to pot and the discussion results in a waste of server space and may as well be deleted. I have no intention of standing up and telling anyone on these forums that they are doing it wrong, I'm here cause I want to learn about aerodynamics and vehicle stability, I am here because I want to design and build a vehicle that will travel across the face of the earth at over 1000 mph and the back again, with one sole purpose in my mind and that is, at the end of it, the driver can climb out un aided and say "We did it"!
As for my aerodynamist, I am not going to divulge and information re: any of the personnel involved in The Bullet Project at the moment. I designed the car and CFD testing will commence in due course. I can say that our aerodynamist was the chief CFD engineer for a major Formula One team and has recently left Formula One just last year.
We are 10 years + behind all the other teams out there in this challenge. Only one of them has acknowledged the fact we are going for 1000 mph (thank you Waldo) the rest are pretending we don't exist. My site has links to all the other players websites I get none in return. Thats why I'm playing my cards close to my chest. All up to date info will be on our website.
Cheers
Paul
Paul...I'm not saying he's wrong, I'm saying if you have to prove aero stability on cars,roadsters,lakesters and motorcycles,
it will outlaw most vehicles [ get it]?
Do you honestly think a roadster will prove aero stability, if not who is going to be hanged?
JL222
P.S. You want facts so other people can use them, yet you wont even name your aerodynamist.
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A2WindTunnel,
You have a PM.
Tom G.
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a hint :?
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Sparky, I think Seth is going to run 340 NA before he puts a hair dryer on it for the big #s. Are you a gambling man??? Of course you are. You stay every year in Wendover.
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lol :cheers:
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Paul...I'm not saying he's wrong, I'm saying if you have to prove aero stability on cars,roadsters,lakesters and motorcycles,
it will outlaw most vehicles [ get it]?
Do you honestly think a roadster will prove aero stability, if not who is going to be hanged?
JL222
P.S. You want facts so other people can use them, yet you wont even name your aerodynamist.
Hi Jl222, I really do feel that if someone builds a vehicle to reach a speed whereby the speed has not yet been achieved, and then attempts that speed without proving the stability of the vehicle first then that said person should not be allowed to run his vehicle. If you have concerns about a roadster being able to prove aero stability, then don't build a roadster! I will not run any vehicle unless it is proven to be capable of reaching its intended speed safely. I don't want to risk that precious gift called life, nor do I want that on my conscience nor do I want any spectators of the sport to witness injury or worse just because I think I know and understand enough about aerodynamics that I don't need to test.
Safety should be paramount! First and foremost and if we have the will do do something then, usually we will find a way to do it.
Just my opinion on this subject and it should not concern anyone else nor offend anyone else because I do not intend to sport with anyones feelings. :cheers: Good health
Paul
PS I know a man who is building a WLSR car who claimed that he didn't need CFD and that's why I am not working with him!
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If you didn't want to rub anyone the wrong way--then why did you spout off :?
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Paul...I'm not building a roadster but plenty of people have and gone fast. If people like you and Blue were around
in the beginning of LSR there would be none today and highboy roadsters would never have reached speeds of
291 mph + :-o
JL222
P.S. I personally know of a highly successfull lakester that used a high dollar CFD computer program to design his body that had to redesign the body [ added tail ] this year as it was having a bit of handling problems. So don't put to much trust in those programs, just something for you to think about on the way to 1000 mph :-D
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Actually, the 675 mph lane change was attempted by Craig Breedlove and resulted in an upset. I was the schmuck who had to figure out why it happened and fix it.
Very strange......there was nothing to fixed...due to this that Craig had fixed it for the 1997.......only what he forgot was to align the bent frame after the 2 mile U - Turn in 1996....
Decal Dave done this than in 1998......the car was 12 inch out of the alignment after the accident......but strong enough to protect Craig......
....and the lane change......did someone forgot which cause this lane change...... :|
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JL222
P.S. I personally know of a highly successfull lakester that used a high dollar CFD computer program to design his body that had to redesign the body [ added tail ] this year as it was having a bit of handling problems. So don't put to much trust in those programs, just something for you to think about on the way to 1000 mph :-D
7717 AA FL 323.473 Tanis Hammond New Record, not to shabby. :-D Is this the Lakester you talk of JL222? I heard rumor that this was done on gas, anyone know?
Tom G.
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JL222
P.S. I personally know of a highly successfull lakester that used a high dollar CFD computer program to design his body that had to redesign the body [ added tail ] this year as it was having a bit of handling problems. So don't put to much trust in those programs, just something for you to think about on the way to 1000 mph :-D
7717 AA FL 323.473 Tanis Hammond New Record, not to shabby. :-D Is this the Lakester you talk of JL222? I heard rumor that this was done on gas, anyone know?
Tom G.
Gasoline & a bit of the bottle Tom. :-)
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Sparky...glad to meet you.
Our bluff wide track roadster...AA/GMR car #920 set the record at 284 MPH...we went out and re qualified at 287 with a 13 MPH head wind...sure wish it was calm ..or better yet a tail wind....Ro Yale said the car handled fine...the wind blew him around a bit but he could drive it back to the middle just fine!
Akk
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I heard rumor that this was done on gas, anyone know?
Tom G.
Gasoline & a bit of the bottle Tom. :-)
Thanks Mike.
Tom G.
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I will put my experience in for motorcycles specifically. I crashed at Speedweek. When I made my modifications the lower part of my fairing was not symmetrical. The right rear went from horizontal with a nice smooth 90 to vertical, tucked in tight to the frame and swingarm. The left side went from horizontal to a 45dg, 3 or 4 inches out from the frame. this section is about 14 inches long. Sound like a nice wing? Yup, at 180mph it started leaning the bike over. On the first run the bike had virtually no clearance. It rubbed holes in the bottom of the fairing. We raised the bike up about an inch. The next run I went down at about 210. I guess raising the bike up allowed enough air to get under it to eventuall unload the rear tire. Me and the bike are a little beat up but nothing broken. We live to race another day. The moral of the story is keep it symetrical. :roll:
Fred
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Sparky...glad to meet you.
Our bluff wide track roadster...AA/GMR car #920 set the record at 284 MPH...we went out and re qualified at 287 with a 13 MPH head wind...sure wish it was calm ..or better yet a tail wind....Ro Yale said the car handled fine...the wind blew him around a bit but he could drive it back to the middle just fine!
Akk
Unblown and on parts wash :-o great accomplishment :cheers:
JL222
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Akk, :-o what constitute the meeting :? Slow witted senior minds with CRS ned to know-- lol
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The question about Stringfellow and Kirks crash with the Cavelier: I spoke to Jim Kirk and he told me his run was going well but he got a little loose and the car started coming around. He said that once it started getting sideways he know it would spin (we all pretty well know what that feeling is like). As soon as it got backwards, the air got under the car and up it went. My son Cam got it all on a sequence of photo's and donated them to Stringfellow and Kirk.
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Doesn't the car have a wing or flat plate on the back?
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I have a friend here in Houston with a beautiful Studie...it has a front air dam, low sides and a spoiler on the back.... he took it to a wind tunnel and found significant down force going forward....and that backward it would fly at 200.
Akk
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I have a friend here in Houston with a beautiful Studie...it has a front air dam, low sides and a spoiler on the back.... he took it to a wind tunnel and found significant down force going forward....and that backward it would fly at 200.
Akk
I would agree, backwards is not good on that configuration, I have the same setup, frontwards is stable, like on rails (at least on pavement and concrete).
tunnel test show roof flaps can help, a tunnel with yaw capabilities is REAL expensive to use. You can load the car in the tunnel backwards as well.. we are working on other ways to spoil lift should the car go backwards. (those rear deck spoilers and spill plates work great straight, we are looking into options back there as well (folding, venting etc..)
Charles
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It could be worth a trip to Art Chrisman's shop in Santa Ana, CA. His son, Mike, is doing what should be a 300 mph car that incorporates both flaps and a spoiler that opens inward should the car go backwards. TWO
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I have a friend here in Houston with a beautiful Studie...it has a front air dam, low sides and a spoiler on the back.... he took it to a wind tunnel and found significant down force going forward....and that backward it would fly at 200.Akk
Precisely my point! :wink:
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tunnel test show roof flaps can help, a tunnel with yaw capabilities is REAL expensive to use. You can load the car in the tunnel backwards as well.. we are working on other ways to spoil lift should the car go backwards. (those rear deck spoilers and spill plates work great straight, we are looking into options back there as well (folding, venting etc..) Charles
Charles I agree the roof flaps spoil lift caused by the shape of the roof but they are there to primarily reduce roof lift. There "may" be some turbulence spillover from the roof flaps to the wing and this may or may not help reduce wing lift for a couple of reasons. (1) If the car is going directly backwards the "wash" from the roof flaps "may" be across the wing and help a little. But to make it to the 180 position the car had to yaw through those 180 degrees. At some point the relative wind (from the flaps) was not flowing over the wing. So at some point, before you are completely lined up going backwards, the wing will already have produced substantial lift, most likely flying the car and also rendering the roof flaps useless in your new flight attitude.
(2) Most people think the airfoil shape of the wing (which produces lift) is the only issue. The wing produces down force when you are going the right direction and produces the equivalent lift when going the wrong way. Only half right :wink: Wind by itself has force. Think of a barn door (certainly not an airfoil). Wind applies pressure/sq.ft. per velocity. What that means is; hold any flat plate area (or spill plate if you will) into a head wind and you will get a force. When the cars is going backward that area under the wing and the new blunt front end become a high pressure area. The high pressure, working on the area of the wing, is enough to raise the attitude of the car. Now many bad things start to happen. The wing can simply be “flat-plate area” and lift due to dynamic air hitting it. Lift increases the angle of incidence and the lift becomes even more aggressive. And, of course, air is now building under the car leading to more bad things.
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Having been to the A2 tunnel with a Stude this year, I can confirm that at 180* to the original direction, the lift developed is HUGE! You have to determine how much yaw the vehicle can accept before you are going around; the "big" Aerodyn tunnel can yaw a car up to 3* and identify a "trend". If you can get (and afford) time at Lockheed in Marietta, you can yaw the car on their turntable and identify the "point of no return". Then you can develop a sequence to deploy anti-lift strategies (flaps, etc) and their activation. vic
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It will be interesting how Chrisman constructs the spoiler, a piano type hinge with non locking supports?
JL222
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Vic, the Big Tunnel next door to the smaller A2 tunnel is if I remember double or triple the cost per hour.. well above my ability to afford.... I do agree with you about finding out "the point of no return" but it would be costly to find that out (but less costly than an backwards car going airborn at 200 mph).
I would think rather than spending research dollars to find that point, when in reality when a car gets to that point, the driver is not going to be able to react quick enough to employ any defensive counter measures to correct.
If my thinking above is close to correct, my plan would be to put the car in the small A2 tunnel and see what we can do to keep the car from flying in the backwards position.
My thoughts are a pivoting rear spoiler that folds up or has a few flaps that release when backwards or when Yaw exceeds X degrees? also maybe a rear valance plate the has no front wards aer advantage, but deploys at X yaw, thereby acting like a front air dam but on the rear ?
Just my thoughts and I did not stay in a Holiday Inn Express last night, and am not even qualified to properly spell Aerodynamic !!!
Charles
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Anybody notice that WAY too many posters on this topic are like the guy that went to the knife fight with a RUBBER KNIFE?
A2 and Blue - keep posting, WE @ LANDSPEED NEED YOU - (and keep TUFTING, everyone!)
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It will be interesting how Chrisman constructs the spoiler, a piano type hinge with non locking supports?
JL222
I already designed that, have just not tested it yet,,, may go to tunnel late Sept before Maxton or shortly after, depends on time and money.
Charles
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all cool,
Charles
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Kid --
I think you misread him. He's telling us that we ought to listen to those that know, not just guess, about these things.
Some of these problems don't show their ugly faces until upper speeds are reached.
Stan
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Stan, you may be correct.
Charles
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I met Eric (blue) at speedweek By recognizing his aircraft logo on his shirt. I will say that I believe he is the real deal. If a person wants to build a high speed car and is unsure if a certain design would be safe he would certainly be one to run your ideas by.
You can sometimes always never tell what you least expect the most. George
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We were waiting for him to stop by our pits.....never happened. :roll:
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We were waiting for him to stop by our pits.....never happened. :roll:
Emailed me he stopped by but we wern't there, said the car was well done but got busy helping 3 others in our class :roll:
JL222
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.... I do agree with you about finding out "the point of no return" but it would be costly to find that out (but less costly than an backwards car going airborne at 200 mph).
I would think rather than spending research dollars to find that point, when in reality when a car gets to that point, the driver is not going to be able to react quick enough to employ any defensive counter measures to correct. ...
This is the problem, and it is clearly better to keep the car going straight than to spend a lot of time on blow-out panels and figuring out whether the car will lift between the time it gets sideways and the time it's going backwards. Nascar spent tens of millions solving this problem for one car (COT). In LSR we don't have that kind of budget.
Sorry for the people I didn't see on the weekend, I did walk the whole pits twice and introduced myself to anyone who wanted to take a stab at me if they were there. I missed at least a dozen people I'd really like to spend some time with. I met a lot of great people I'd missed in my last two trips, I look forward to meeting more next year.
This whole thread seems to have evolved into a discussion of steering control vs. yaw stability vs. how we keep cars from flying. Several highly experienced sedan and roadster record holders have firmly stated that control trumps aero (at least up to the point of their current setups). More than one have asked me if there is anything to make things more aero stable (meaning yaw-stable). With a firm grasp on the rule book, here's a couple of suggestions:
1. Tuft the car. OK, I'm flailing the deceased equine here. I don't want anyone to take my word for anything, I want people to go down to the craft store, buy some rug yarn (3" long) and tape it to the spoiler, sides and roof and trunk of the car and then tell me what they see. It's not pretty, and everyone who does will have a better understanding of how their B-to-C pillar and roof-to-trunk flow interacts with their "flat" spoilers and "flat" spill plates. Relative to the flow off of the car, these things are anything but flat.
2. Test. It only takes 20 to 40 mph for most of the separation and reversed flow effects to show up on the yarn. It will be the same at 300. Find some parking lot without law enforcement and spin some doughnuts. Video and photograph the tufts at the yaw angle of the doughnut; it's cheaper and faster than a wind tunnel with yaw capacity. Put cheap tires on. I would ask anyone who believes the flow going off the back of the car is fine to post pictures of their tuft tests. I didn't see a single good aft closure during all of speed week. If anyone disagrees, post some photos of the aft deck and bumper areas with tufts. Even if you KNOW it's bad, do the test anyway: the data will help you make a better setup within the rules. I have told the best test pilots in the industry where the reversed flow is and they believe me; it doesn't matter. They act on it when they see the yarn go backwards.
3. I saw lots of cars of all classes that allow wings with rules-limited "spill plates". In the aero world, we call these things "end plates". For a wing, their function is to make the wing more effective by minimizing tip vortexes. For yaw, they should simply be as big, high, and as far aft as possible. To this I would add that most car bodies would benefit from wider, not narrower, end plates. If this creates too much spoiler downforce, de-camber the spoiler. Keep the end plates at the maximum size and width that the rules allow.
4. Remember to add the yaw stability that comes from diffuser fences. About half of the cars I saw used diffusers, some well, some not-so-well. Verticals down there are tails too. A few lakesters and roadsters were quite impressive in this area IM<HO.
Now we get into the tricky stuff. 3 teams have told me that they know they are unstable and, with varying levels of interest vs. derision, have asked me how to make it better. Here goes: Make the spill plates bigger, align them with local flow areas induced by the rest of the car (what works on a '53 Stude is different from what works on an '86 Camero), do everything you can under the car, and set the parachutes to eject up into clean air, not back into dirty air, so they can deploy before you are all the way around in a spin. If anyone wants help, call me. If anyone thinks I'm an idiot, fine, tuft the car during some doughnuts and post photos; we all learn from tests.
The time to find out about stability is BEFORE the spin.
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Thanks for some really constructive information Eric. :cheers: :cheers: :cheers:
Pete
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Eric, thank you very much, I actually understood what you said....
I think my side plates are to narrow (mounted to open with the trunk). I have a design from Hooley's 974 Stude and his are as far to the outside as can be, I may have to make entire new spoiler and side plates for Bonneville.
What I have works so far on pavement/concrete .
Here is a rear view (the chute deploys and acts well, so it must be in good air ??) I do have a video of that if you want to see and advise ? The side plates could be relocated to the outside about 3" and mounted to the body.. or maybe I could leave this as is and just "add" a second set of side plates to the outside of these (making these more like jumbo diffusers??)
(http://i888.photobucket.com/albums/ac81/venablerodsandracing/DSC01026.jpg)
Charles
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Eric,
Very sorry that I missed you at Bonneville! the car I was working on proved to be more work than we expected. I also missed you at the Salt Talks and that was my fault, got talking to Linchy and Gary from Oz and lost concentration.
Thanks also for all of your aero words of wisdom in this thread and also our correspondence. Still planning to build a lakester with many of your thoughts incorporated into the design.
Rex
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Eric...the problem with good aft closer [ on a coupe or sedan ] is lift
On the spoilers SCTA allows due to the lower pressure under the spoiler and behind the car the air rushes up
at high speed causing a turbulent wake. But the downforce is better than the streamlining.
I tried to find out from those [ that should know] what kind of pressure differance there might be,but no luck
On the 222 Camaro there is 530 sq inchs of area if there was 1 lb of difference there would be 530 lbs of downforce.
JL222
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Here's a video of our wake.
http://www.youtube.com/watch?v=55XA0vrNNj0
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Gentlemen,
I spent enough time with Eric to know that he is the real deal. The cool thing about Eric is that he won't just let me take his word for anything. He makes me investigate it to come to my own conclusion. He has helped tremendously with our liner design.
I highly recommend his services!
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OK, I set aside a little time and want to hit the four separate topics of the last 10 posts.
1. Spill plates. I'm working for a Stude team right now, so I can't talk about what they have already paid me to come up with for performance. What I saw long before speed week on a safety side is true for all cars using spill plates: Bigger is better, taller is better, and best of all is when they are aligned with the car sides so that they turn the entire side-of-quarter-panel-plus-spill-plate into one big vertical tail. This does widen the spoiler and that leads to more separation drag, and this leads to...
2. Aft closure issues: John, my comment was meant for streamliners and lakesters. I know that sedans and roadsters are rules restricted in this area and I'm sorry if this sounded overly critical of sedans. John is right that separation is inevitable in these classes, and that tapering off the upper deck to fill in the back would lift the car. If someone is in a class that allows diffusers- DO IT. Seth Hammond did a nice job of covering his chute tubes, it would be even better if the closure was integrated into the whole design like Bub-7. If we're in sedans and roadsters, there are techniques that are within the rules. I wish I had answered this before speed week because now I can't talk about some of this. What I can say is that a lot of the spoilers I saw were "over-cambered" leading to more drag than needed. You guys all have a good feel for the traction you've got, it would be good to get some weight-on-wheels data to do better tuning of the spoiler angle. Then you can actually put marks on the end plates and make a concious decision every run on how much force you want vs. the extra drag. This year, the salt got awfully soft between the 3.5 and 5 mile. Under firmer conditions it would be practical to flatten out a little and gain some speed. This means we need course reports, like seeing the size of the roostertail behind Speed Demon triple at the 4 mile marker. That was some soft salt. Back to the closure, that leads to:
3. Bvllercr's video: A little tough to do detailed aero from the dust, here goes. First, there is an unstable shedding vortex off of the front tire. This is responsible for the perfectly spaced dust clouds going down the side of the car. This is an important thing to minimize because it disturbs the flow on the side of the quarter panel and since the left and right vortexes will seldom be synchronized, it induces a yaw instability. Next, the aft separation is pulling the dust from the wake forward into the lower spoiler/ bumper area. The vortexes from the rear tires are messing with this too. Look at some of the new high mpg hybrids for ideas on how to organize the rear tire vortex; it's one of the tricks to getting 60 mpg and it works for LSR too without creating lift. The air in the separated area is literally going forward, not back, and this leads to...
4. Chute position: I see a lot of chutes that eject straight back into dirty air and this is not good. The chute is ejected into air that is recirculating and this delays the chute opening. In some cases, the bag drags on the ground before it opens. A lot of teams have theirs mounted at an up angle, and this is better, but the angle often is below the angle of the spoiler, so the chute is still buried in dirty air. Either arrangement will work fine when we're straight, let's worry more about how it works when "oh-shoot-we're-spinning-I-pulled-the-handle-and-why-hasn't-the-darned-thing-opened-yet???" A Honda red hat holder narrated his spin video for me and said that chute opening seems fast during a clean run and awfully slow when spinning. Mount it vertically. Yes, I said shoot the chute straight up. As soon as the drogue clears the aft lip it's in clean air and it will deploy in a fraction of the time that it takes in dirty air. Use a d-bag too, if you're spinning a d-bag will help prevent the chute from fouling on the car. Bob Stroud and I talked about this at length and the more vertical the better.
One funny note from speed week, I was the guest of a mod roadster team (one of the more challenging classes to do aero work in) and was asked how effective the long nose is. I replied that the car would be much faster running backwards: i.e. round in front and pointy behind. I said this might be a fun thing to do and one of the legends of the salt, Marlo Treit, replied: "You're about 50 years too late." Apparently someone did this way back in the day at Elmo and after two years of whipping everyone else the SCTA made a rule that the bodywork must be run in the stock direction.
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You don't even need to drive the car to get basic data if you live in an area that has steady straight line winds and can find an open parking lot or scenic overlook.
These tuft tests were done on a scenic over look west of Denver during a chinook wind event with steady winds of 70-80 mph with gusts to 110.
(Yes it was a tough day to be outside -- the storm blew down 150' of board fence at my house while I was doing this breaking the fence posts off at the ground).
At the time I was trying to achieve a local drag strip record for the WRX with the stock turbo and OEM 2.0 liter engine (I eventually got it with my nearest competitor in this unofficial competition being 2 mph slower in his trap speed).
These photos were to determine best air dam width and to understand the cars aerodynamics.
Photo #1 was to figure out frontal area and see what the "air sees"
Photo#2
Then I went out to the scenic over look when the weather cooperated and tufted the car.
Photo #3
Side view, note the strong vortex that forms on the side of the passenger compartment where local flow is nearly vertical on the drivers side window due to the sheet of air that dumps off the side of the windshield then rolls up into a tube behind the side view mirror.
Photo #4
After thinking about the results of this test I went out and did a more complete tuft test in low winds (about 20-30 mph) to better understand the flow on the side and rear of the car.
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Then I borrowed a page from the glider folks and did some oil tests. To do these you put spots of used engine oil on the car body, and drive it at about 60-70 mph for a mile or so, then pull over and quickly take a picture of what the oil does as the air flow in the boundary layer blows the oil across the body surface.
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More oil tests
The first photo attached here shows the flow separation and then re-attachment on the hood scoop then the formation of a rotor behind the airscoop as the flow again separates.
The second shows the flow separation line on the rear pillar as the air tries to curve over onto the low pressure area behind the rear window.
As an extension of Blue's comments on end plate locations. On the WRX body that separation line on the rear quarter defined by the oil would be an excellent place to mount a side plate (end plate) for a spoiler.
Larry
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3. Bvllercr's video: A little tough to do detailed aero from the dust, here goes. First, there is an unstable shedding vortex off of the front tire. This is responsible for the perfectly spaced dust clouds going down the side of the car. This is an important thing to minimize because it disturbs the flow on the side of the quarter panel and since the left and right vortexes will seldom be synchronized, it induces a yaw instability.
I wouldn't jump to conclusions about that front tire. The motor is putting out 1,000+HP (per side). Look at the exhaust zoomies! You have tremendous pulses of gas disturbing the flow along the side.
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4. Chute position: I see a lot of chutes that eject straight back into dirty air and this is not good. The chute is ejected into air that is recirculating and this delays the chute opening. In some cases, the bag drags on the ground before it opens. A lot of teams have theirs mounted at an up angle, and this is better, but the angle often is below the angle of the spoiler, so the chute is still buried in dirty air. Either arrangement will work fine when we're straight, let's worry more about how it works when "oh-shoot-we're-spinning-I-pulled-the-handle-and-why-hasn't-the-darned-thing-opened-yet???" A Honda red hat holder narrated his spin video for me and said that chute opening seems fast during a clean run and awfully slow when spinning. Mount it vertically. Yes, I said shoot the chute straight up. As soon as the drogue clears the aft lip it's in clean air and it will deploy in a fraction of the time that it takes in dirty air. Use a d-bag too, if you're spinning a d-bag will help prevent the chute from fouling on the car. Bob Stroud and I talked about this at length and the more vertical the better.
A very important observation and I don’t wish to minimize or discredit any of the quote. However, chute position is CRITICAL! Be very, very, very, careful about how you approach your chute attachment point. The chute must be pulling through the CG. If the initial yank is above or below the CG the load will unweight (or lift) the appropriate end of the car. That will lead to very bad things. Also, consider what happens in a partial spin as Blue mentions. If you are yawing 45 to 90 degrees and the chute deploys with a yank not in-line with the CG what do you think will happen? What might have resulted in a flat spin might throw you into a pencil roll! I understand Blue is discussing orientation and not attachment point. My point is to approach this carefully! How will Blue’s proposed orientation affect initial opening? Where will the chute be (what altitude) will it be upon initial yank? How will that pull on the CG? This is a very serious subject.
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This means we need course reports, like seeing the size of the roostertail behind Speed Demon triple at the 4 mile marker. That was some soft salt.
apparently you've never seen Burkeland, Vesco turbinator run, or the salt spray sucked up by a 400 or even a 300mph vehicle before
Kent
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Blue:
Ref: Your reply #215: “It only takes 20 to 40 mph for most of the separation and reversed flow effects to show up on the yarn.”
While the flow regime indicated by tufting at 20 mph and 300+ mph may be similar for highly streamlined bodies, one has to wonder about the degree to which this holds for more irregular or production-based vehicles.
It is not hard for the semi-layman to suspect that for these shapes there may be several different regimes due to successive flow separations as velocity increases. That is, tufting results at 20 mph (which might almost be considered potential flow) may not be representative of flow at considerably higher velocities. Indeed, this might even cause one to look askance at low speed wind tunnel results. Is there any validity to this viewpoint?
It would undoubtedly be illuminating for many LSR devotees if you could be prevailed upon to elaborate a bit on this admittedly complex question.
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I.O.
Darn, just when I was starting to understand, there ya go using them big fancy words again !! LOL :cheers: :cheers:
"Illuminating" "askance" "devotees" "prevailed upon"
Charles
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3. Bvllercr's video: A little tough to do detailed aero from the dust, here goes. First, there is an unstable shedding vortex off of the front tire. This is responsible for the perfectly spaced dust clouds going down the side of the car. This is an important thing to minimize because it disturbs the flow on the side of the quarter panel and since the left and right vortexes will seldom be synchronized, it induces a yaw instability.
I wouldn't jump to conclusions about that front tire. The motor is putting out 1,000+HP (per side). Look at the exhaust zoomies! You have tremendous pulses of gas disturbing the flow along the side.
Actually, I took that into account when I made that statement. If we look at the intermittent draw of dust from the underside of the car to the side of the door sill it looks like this is independent and well aft of the exhaust pulses. Also the spacing between the dust plumes does not vary, if they were caused by the exhaust we would see exhaust timing in the spacing. That's a big leap of faith until we look at video and pictures of other cars without zoomies and see the same effect. It can also be seen on Thrust SSC, and that was going a lot faster without zoomies. It's something I've observed for years, this video just gave a good example. The back of the tires are highly separated areas on any car, it is simply a question of how the separation manifests itself.
Completely separate from this thread is whether the exhaust can be arranged to help or hurt the local flow. Yes to both.
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4. Chute position: I see a lot of chutes that eject straight back into dirty air and this is not good. The chute is ejected into air that is recirculating and this delays the chute opening. In some cases, the bag drags on the ground before it opens. A lot of teams have theirs mounted at an up angle, and this is better, but the angle often is below the angle of the spoiler, so the chute is still buried in dirty air. Either arrangement will work fine when we're straight, let's worry more about how it works when "oh-shoot-we're-spinning-I-pulled-the-handle-and-why-hasn't-the-darned-thing-opened-yet???" A Honda red hat holder narrated his spin video for me and said that chute opening seems fast during a clean run and awfully slow when spinning. Mount it vertically. Yes, I said shoot the chute straight up. As soon as the drogue clears the aft lip it's in clean air and it will deploy in a fraction of the time that it takes in dirty air. Use a d-bag too, if you're spinning a d-bag will help prevent the chute from fouling on the car. Bob Stroud and I talked about this at length and the more vertical the better.
A very important observation and I don’t wish to minimize or discredit any of the quote. However, chute position is CRITICAL! Be very, very, very, careful about how you approach your chute attachment point. The chute must be pulling through the CG. If the initial yank is above or below the CG the load will unweight (or lift) the appropriate end of the car. That will lead to very bad things. Also, consider what happens in a partial spin as Blue mentions. If you are yawing 45 to 90 degrees and the chute deploys with a yank not in-line with the CG what do you think will happen? What might have resulted in a flat spin might throw you into a pencil roll! I understand Blue is discussing orientation and not attachment point. My point is to approach this carefully! How will Blue’s proposed orientation affect initial opening? Where will the chute be (what altitude) will it be upon initial yank? How will that pull on the CG? This is a very serious subject.
There is almost no connection between ejection angle and pull point when a d-bag is used. As a rule of thumb, the chute will fly 1/2 to 1/4 of its inflated diameter above the salt. We need to draw a line between the center of the chute at this altitude and the CG of the car and make sure that the pull point is on this line. If it is higher, we risk a wheelie, if lower the car can lift in back and stuff the air dam.
Once the pull point is set, the chute ejection geometry should be solely based on getting the chute into clean air as soon as it leaves the pack. Shoot it straight up; The pull point, inflated diameter, and riser length determine the load on the car, not the angle of ejection.
Even if the chute is significantly above the pull point at extension, the D-bag will drag into trail as the chute pulls out long before inflation ("long" being fractions of a second). If a d-bag is not used, the chute will never get above the pull line since the local air flow against the drogue will determine inflation. Although this may sound extreme, think about it: If we shoot a drogue into the air stream at 20 to 50 mph (spring vs. pnuematic chute ejection) and the air is going by at 200 to 300 mph (50 to 400 times the dynamic pressure), which way is the drogue going to go? The way the air wants it to go and nowhere else.
The point is to get it into that high velocity air and out of the dirty, slow, reversed air at the back of the car. Once it gets there, then it will pull though the pull point; which as saltfever points out should be straight through the CG, not higher, not lower.
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This means we need course reports, like seeing the size of the roostertail behind Speed Demon triple at the 4 mile marker. That was some soft salt.
apparently you've never seen Burkeland, Vesco turbinator run, or the salt spray sucked up by a 400 or even a 300mph vehicle before
Kent
Actually I have many times. Apparently you've never driven or groomed a course and actually walked on the salt at the 4 to 6 mile areas where the underground stream cuts the course at a 60 degree angle. It's quite an experience in May driving through standing water at the end of the road, standing on salt at the 3 mile as hard as a rock, then watching your feet sink at the 6 mile. The salt is always different at every quarter mile, every week, of every season and everyone's understanding of the salt would benefit from participating in grooming a course. Which I did, under the guidance of the best; for which I am very grateful.
While not an "old salt", I've spent much of my life on playas and salt beds. Over the years I've been lucky enough to learn from people who have more words for their condition than eskimos do for snow. The salt from the 3.7 mile to 4 was soft this year and from 4.2 to 5 it was REALLY soft. SCTA worked late and re-groomed these sections during speed week and we should all be grateful for that. Any observant person looking at several previous high speed runs can watch the spray vs. position and normalize this data vs. how hard the drivers were staying in the throttle and report from this how soft or hard the salt is at each mile.
It's rocket science, not rocket art. And I met plenty of rocket scientists at Bonneville.
LSR runs at Bonneville because it's flat and available. In an ideal world where Bill Gates is a land speed racer, we would have 10 miles of pavement. Not a variable, plastic, frangible surface that deposits on everything and corrodes metal.
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Blue:
Ref: Your reply #215: “It only takes 20 to 40 mph for most of the separation and reversed flow effects to show up on the yarn.”
While the flow regime indicated by tufting at 20 mph and 300+ mph may be similar for highly streamlined bodies, one has to wonder about the degree to which this holds for more irregular or production-based vehicles.
It is not hard for the semi-layman to suspect that for these shapes there may be several different regimes due to successive flow separations as velocity increases. That is, tufting results at 20 mph (which might almost be considered potential flow) may not be representative of flow at considerably higher velocities. Indeed, this might even cause one to look askance at low speed wind tunnel results. Is there any validity to this viewpoint?
It would undoubtedly be illuminating for many LSR devotees if you could be prevailed upon to elaborate a bit on this admittedly complex question.
"potential flow"? Are we talking about the difference between inviscid and viscous solutions for widely varying Rn or the differences in development of separation phenomena into unsteady, partially stable, and/or stable recirculation at low vs. high Rn? <VBEG>
OK, all kidding aside IO brings up a good point: the character of separation differs with Reynolds number, i.e. speed. The point of the previous post was two fold: #1, the existence of separation and the majority of the areas of reversed flow seen at very low speeds will translate well to high speeds. If they didn't, sub-scale wind tunnels would be useless. #2 TEST! There is absolutely nothing I can tell anyone about their car that is better than the data they can get for themselves.
To a point, separation on not-so-streamlined-production-based-vehicles will actually get better, not worse, with speed. This is due to the thicker boundary layers associated with higher Rn, and the difference is mostly irrelevant for the shapes common in LSR. At lower speeds, we may see organized or semi-stable recirculation where higher speeds will see disorganized flow; the point is that we will see the separation even at low speeds. So once we are going fast enough to straighten out the tufts we're going fast enough for reasonable data. When people have gotten that far and actually tested, then we can revisit how recirculation and separation vary with speed. One step at a time.
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More oil tests
The first photo attached here shows the flow separation and then re-attachment on the hood scoop then the formation of a rotor behind the airscoop as the flow again separates.
The second shows the flow separation line on the rear pillar as the air tries to curve over onto the low pressure area behind the rear window.
As an extension of Blue's comments on end plate locations. On the WRX body that separation line on the rear quarter defined by the oil would be an excellent place to mount a side plate (end plate) for a spoiler.
Larry
Outstanding data and an excellent observation. Kent and John, don't listen to me, do what Larry is doing.
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There is absolutely no connection between ejection angle and pull point.
That is not the point I am concerned about.
As a rule of thumb, the chute will fly 1/2 to 1/4 of its inflated diameter above the salt. We need to draw a line between the center of the chute at this altitude and the CG of the car and make sure that the pull point is on this line. If it is higher, we risk a wheelie, if lower the car can lift in back and stuff the air dam.
I agree. I am not concerned about the pull point of a fully opened, functioning chute. The pull point through the CG is fairly well understood by most everybody. Also, if you extend the CG centerline straight back you will see it is invariably in dirty air. Which, as you mentioned above, is where most of the chute will generally be flying.
Once the pull point is set, the chute ejection geometry should be solely based on getting the chute into clean air as soon as it leaves the pack. Shoot it straight up; The pull point, inflated diameter, and riser length determine the load on the car, not the angle of ejection.
Are you sure? That is my concern. I have seen no data on this but would be very interested in learning about it. I understand what you are saying. I agree that clean air is most desirable for predictable, successful, chute performance. But I am concerned about the altitude of the chute on initial opening shock. Not the flight altitude of an inflated chute. As I interpret your thesis you would shoot the chute (no pun intended) above the roof of the car (or higher) into clean air. That is fine but it will hang there until impact? What altitude will it be at impact? Sure it will settle down to the flight height you mention after deployment. But that is not the issue. LSR chutes hit with 4-6Gs and that initial impulse will be way above the CG at an extremely critical time. Any hit like that will upset the car. And if you are in a spin it will roll the car! What you are proposing sounds nice but where is the testing data? Who has done this? Using my layman math it doesn’t compute. 240MPH is 352ft/sec. That means it takes less than 1 second to get full deployment. My car is 5.5 ft high. If I loft the chute 6-8ft high (a couple of feet above the car into clean air), where will it be in relation to my CG when it hits? Assuming a ballistic trajectory of about 1 second, it is not going to be even close to my CG. If my math is wrong correct me . . . I am not embarrassed, I want to understand and be safe.
(Edit) Blue, my apologies because I see you were editing post No. 232 when I was composing this reply to that post. Your edit adroitly anticipated some of my concerns. However, please consider. The clean air above the car is stationary and laminar. We are launching a 240mph package into it. The chute package is moving, not the air! It will undoubtedly have some flight characteristics that could “hang” it in the air. At any rate I doubt it will loose altitude at 32/sec/sec. and yet it must get to my CG height in less than 1 second for deployment. Who is going to be your test pilot. :wink:
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OK, I understand how this would seem like bad math, the fact is that it is a mass vs. moments and this went through my head so fast I didn't even consider it. Let's look at the two cases with extreme ejection (pneumatic): D-bag and no D-bag.
D-bag: When we shoot straight up, the d-bag is going 40 to 50 mph and hits 200 to 300 mph air as soon as it clears the spoiler lip. The air now takes over and the d-bag goes in trail at about 40 G's of acceleration in the flow axis (5 lb chute vs. ~200 psf dynamic pressure vs. ~1 ft2 of drag area for the bag). This 40 G's totally dominates the bag's velocity of ejection. The bag and car separate to the limit of the line with the line pulling the bag in line with the pull point and the CG. The chute deploys and hopefully the car hasn't gone too far around by this point.
No D-bag: When we shoot straight up, the drogue hits clean air and the same thing happens except the chute will inflate as soon as about half of it's length clears the spoiler. It's at this point that we see the need for a d-bag. Without one, the chute inflates and basically stops in mid air while the car continues (5 lb chute vs. 200 psf dynamic pressure vs. 40 ft2 of drag area for the chute equals 800 G and the chute stops right where it inflates!). The car moves forward from the point of chute opening until the riser is tight and then the car accelerates the chute. If the car has any angle in the CG-pull point-chute line, the car will rotate.
Read that carefully.
In both cases, the chute pretty much opens at the nominal height: centered just above the spoiler lip. The point of shooting it up was to contrast this with shooting aft where the air is more than disturbed, Bvlllercr's video shows the flow to actually be reversed and sucking back into the bumper. Lots of cars have this issue and dragging the bag and the chute on the ground is the result. Shooting up at speed does not mean that it will shoot as far up as it will at a standstill.
As a matter of who has done this, drag boats now eject their chutes up and outboard at extreme angles so that at least one of the two is trailing when they flip-spin. The yank straightens them out and prevents, not causes a roll. We need to learn from other motorsports, just be careful what we learn and how it applies to what we are doing.
The air behind even the worst streamlined car gets less and less disturbed the farther back we go. Behind one to 3 car lengths, it's disturbed, but not reversed like it is at the bumper. Clearly, if we run a short riser and open the chute in really bad air right behind the car the chute will squid up, down and sideways and yank us all over the place like a funny car. If we run too long of a riser we risk going around a ways in the spin before the chute inflates and pulls us straight. Ejecting the chute straight up gets it to inflate at its nominal flying height in the shortest possible time without a mortar or rockets, which are used on fighters for ejection seats and spin recovery chutes.
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Great stuff guys thanks :cheers:
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No trouble dragging chute on ground before opening on the 222 camaro, we use a funny car type chute [ short lines] it opens instantly when applied. In 08 Bvillercr got real sideways and Glen annouced '' we have a spin''
but Troy hit both chutes and did some steering and it never went clear around. Chutes are angled up 33 deg.
We once had a guy look us up at El Mirage because he was inpressed with how fast and well our chutes opened
JL222
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I take pictures on the long course near the 2.5 mile and sometimes I get lucky and catch chutes just as they are clearing the pack.
These pictures might be useful for discussion sake.
(and yes the chute deploy on the 6050 car was taken as your hood blew off!)
Larry
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Great pics, Larry. It sure demonstrates Blue's point of view about dirty air. Many thanx. :cheers:
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The air couldn't be dirtier than behind a funny car and they work quick and well, proven many times over LSR racing and at higher speeds than most with a shorter stopping distance.
JL222
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I guess the relevant question is then, what is the difference between a typical chute and one intended for use on a funny car?
Larger drogue, longer line on the drogue, stronger spring, different method of packing or release???
Larry
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Yes Blue i have stepped on the salt at the 7mile.... actually most recently a couple weeks ago when i was getting out of my race car.... can you say that?
about them chute pix... before you guyz get yer panties all in a knot, just remember 1 thing ole Blue isnt sharp enough to figger out... that chute is travelin as fast as that car is! ever toss a beer can out of a movin car? The only thing you need to worry about is if the chute gets out or not!.... period!
We dont have a net and kitty litter box closin in fast....
kent
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Kent :?, the air its going through isnt moving at the vech speed
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In 2004 I began using a deployment bag in the lakester. I use a kicker spring to send the bag out and a
pilot chute to continue the pull until the riser line reaches full extension. At that time, the bag strips off
and the chute is allowed to stretch its lines then opens. My riser line is 3 times the length of the lakester.
I get no chute flying around, no yank, and the chute floats about 2 feet off the salt at 230 MPH.
On the Eagle, I use a 150 ft multistand plasma riser line, rated to 52,000 lbs. My chute will exert 47,000 lb
at 750 MPH. I also sew a cotton sleeve over the length of the line to prevent chaffing or burning from being
dragged on the ground when slowing down or during the initial opening of the chute. My kevlar parachute is
pressure packed into a deployment bag. The reason for pressure packing is to minimize the loss of energy when
the chute bag is fired out with an air charge. I also use a pilot chute to keep the bag oriented during flight.
The bag has assister pockets sewn on the outside to grab air which helps with it stripping off the chute when
the riser line reaches full extension. The parachute lines don't open instantaniously because I tie cotton
line around the lines at intervals to make it stretch the lines all the way out before the chute can begin
to open. Our films have shown that getting the chute way out into clean air makes it open quite smoothly
and it floats about 3 ft off the dirt. Our chutes are made of kevlar panels, lines and thread. So far, they
have worked as designed.
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The only thing you need to worry about is if the chute gets out or not!.... period!
We dont have a net and kitty litter box closin in fast....
kent
Don't you believe in the value of quick deployment to straighten a car starting to get sideways?
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"Yes Blue i have stepped on the salt at the 7mile.... actually most recently a couple weeks ago when i was getting out of my race car.... can you say that?
about them chute pix... before you guyz get yer panties all in a knot, just remember 1 thing ole Blue isnt sharp enough to figger out... that chute is travelin as fast as that car is! ever toss a beer can out of a movin car? The only thing you need to worry about is if the chute gets out or not!.... period!
We dont have a net and kitty litter box closin in fast...."
kent
A good deed never goes unpunished .
John Burk
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If my car gets sideways, no record anyway. Just clutch it, steer into the direction you want to go. If that doesn't work, let go and look at the floor, otherwise you could get dizzy. If you're using the chute to keep your car straight, you have bigger problems.
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If my car gets sideways, no record anyway. Just clutch it, steer into the direction you want to go. If that doesn't work, let go and look at the floor, otherwise you could get dizzy. If you're using the chute to keep your car straight, you have bigger problems.
Are you saying don't pull the chute to keep from spinning, just let it spin?
JL222
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The only thing you need to worry about is if the chute gets out or not!.... period!
We dont have a net and kitty litter box closin in fast....
kent
Don't you believe in the value of quick deployment to straighten a car starting to get sideways?
Thats why I like the funny car type pilot chute and short lines [like lakester in bottom pic as to long pilot chute lines on camaro and black roadster.
I wouldn't consider F104's advice for 1/10th of a sec.
JL222
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Don't you believe in the value of quick deployment to straighten a car starting to get sideways?
[/quote]
quick deployment doesn't mean squat... up in the air, out the back its still out! now if yer concerned about it hitting quicker, that's all about riser length, bags, tape, rubber bands, etc not about popping the pack into air stream... Short risers and big chutes are great for stopping on a short shut down (1/4 drag strips and paved miles) but can upset a LSR car on a loose course... if your worried about catching a spin, put a small "oh shoot chute" on it
kent
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Don't you believe in the value of quick deployment to straighten a car starting to get sideways?
quick deployment doesn't mean squat... up in the air, out the back its still out! now if yer concerned about it hitting quicker, that's all about riser length, bags, tape, rubber bands, etc not about popping the pack into air stream... Short risers and big chutes are great for stopping on a short shut down (1/4 drag strips and paved miles) but can upset a LSR car on a loose course... if your worried about catching a spin, put a small "oh shoot chute" on it
kent
[/quote]
Take a look at the pics and the long pilot chutes lines, the long lines are just delaying the opening. Why? If I don't want the chute open at shut off [Bville] I wait a while then open but if in trouble I want it open instanly.
JL222
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Ask a dozen people and you will get a dozen different answers, with no two vehicles alike and mountings different plus other conditions it's hard to agree with anyone. From my seat I have seen many conditions with chutes and when something is unusual I always try to let the crew know as well as Lee and Steve.
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Maybe I am reading the posts wrong, but it seems some are saying the larger canopy chutes with shorter lines (Drag style chutes) deploy instantly or much faster and hit harder, and those others say the smaller canopy, longer lines (LSR Chutes deploy much slower and hit softer) ?? I am not convinced there is that much difference in time from deployment to "full canopy bloom" now I truly believe the drag chute is not "instant bloom" and that the LSR is not "slow to bloom"
For your viewing pleasure I have attached a video that will allow you to look and listen as well as replay and stop the clock. If you do frame by frame or normal speed and watch the video clock or use a stop watch you will notice that from the time you see the chute deploy, to the time the lines jerk taunt with full bloom it is less than 1 second. What we do not see is how long from the time I pulled the handle to deployment, or how long it took me to pull the release from the time my brain said now ( I know, it was FAST,, I am previous quick draw and competition shooter, so hand speed is awesome fast, I can draw a six shooter from hands over head position, shoot you in the chest 5 times and re holster in less than 3 seconds. 2.2 seconds If I don't re holster) but who is counting ? LOL
back to the chute watch the video and look at the pictures and comment, maybe 1 second is slow for a LSR chute with 60+ foot lines. but then again drag chutes are not as instant as you might think either...
CLICK the PICTURE to Launch Video
(http://i888.photobucket.com/albums/ac81/venablerodsandracing/th_MVI_2284.jpg) (http://s888.photobucket.com/albums/ac81/venablerodsandracing/?action=view¤t=MVI_2284.mp4)
Still Shots
(http://i888.photobucket.com/albums/ac81/venablerodsandracing/StudeChute1.jpg)
(http://i888.photobucket.com/albums/ac81/venablerodsandracing/StudeChute2.jpg)
(http://i888.photobucket.com/albums/ac81/venablerodsandracing/StudeChute3.jpg)
Charles
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I know I'm relatively new in the LSR arena but in 21 years at the salt, I can't remember a chute preventing
a spin. Usually the chute winds up under the car and all wadded up with 10 lbs of salt to carry to the push
truck. If whats-his-name won't consider my methodology for 1/10th of a second, well, to bad. It isn't advice,
just the way I do it and it has worked for me in many many chute deployments. Before I went with the bag
and longer lines, the big chute on a shorter line used to cause the lakester to wiggle from side to side and
poke my toes out of my shoes. Now I don't have that problem and the chute deploys every time and
causes no handling problems. No advice, just the way I like to do it..........Ed
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In my 22 years on the salt and at El Mirage I usually don't have many problems with the car handling absolutely great. With the added power in the last couple years and the deteriation of the track at El Mirage I have gotten very sideways. At Bonneville two years ago I got a little aggressive with the accelaration and while in 2nd maybe 3rd I came up on the power and it took me to the right and I didn't peddle it soon enough. When I do get loose I always clutch the motor and a couple times had to pull the chute. If I didn't pull the chute I surely would have spun. :cheers:
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This is what happens if you pull the chute a bit too late.
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I know I'm relatively new in the LSR arena but in 21 years at the salt, I can't remember a chute preventing
a spin. Usually the chute winds up under the car and all wadded up with 10 lbs of salt to carry to the push
truck. If whats-his-name won't consider my methodology for 1/10th of a second, well, to bad. It isn't advice,
just the way I do it and it has worked for me in many many chute deployments. Before I went with the bag
and longer lines, the big chute on a shorter line used to cause the lakester to wiggle from side to side and
poke my toes out of my shoes. Now I don't have that problem and the chute deploys every time and
causes no handling problems. No advice, just the way I like to do it..........Ed
Thundersalt [Celia driving] this year got real side ways [ Glen reported a spin] but she did a heck of a job driving and got the chute out quickly and didn't spin same as Bvillercr above there's two. Fred Danenfelzer uses the same chute as we do on his 385 mph lakester.
Chutes need to be sized for different cars , weight and speed I just wonder about long lines from the pilot chute.
JL222
Actually at Bville chutes are not really needed for the majority of entrants except for getting off the course fast and
emergencys.
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Jl222,
Not sure if you watched my video ? On Thundersalts car is he using a LSR chute like mine or the shorter lined Drag type?
From the almost spin to saving it, looks like the chute was a major factor to keeping the car from going around,, that was most likely because of good driving, followed by quick decision to pull chute, followed by good reaction time in getting chute pulled, followed by chute deploying in good air quick enough, followed by quick canopy blossom.
I would say I listed it in the actual order of importance, as the by the time you do all of those things in the correct order, the .8 to . 9 second LSR chute blossom to the .5 or.6 drag chute blossom is not as big a deal as one might think, a fast blossom if you don't do everything else quick and correct is not going to help,, just tear up a chute.
That's my thoughts.
Charles
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Charles...you call that fast? ...Bville could run 40yds in 4.6 sec as a running back in highschool :-D
Just kidding, those skills could come in handy at times in Fresno :-P
All this discussion about chute opening time and lenghts got me off my butt to measure the chute, easy as we have not packed it after washing
Pilot chute line...5 ft
lines from car to main chute 22 ft and 8 lines
Size of chute 12 ft
The opening speed might not be instant but its got to be faster than 60 ft lines.
JL222
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JL222,
I 100% agree with you that the 22 foot lines are not instant, but would be faster than 60 ft lines.
I do know how long it takes the 60 ft lines to open, does anyone have a clear enough video so we can see shorter lines deploy?
I aslo think that yes 22 foot lines would have to open faster, but one more consideration is the shorter lines ar attached to a larger canopy, and maybe, just maybe the time gained by shorter lines does not fully translate to faster full blossom since there is more material to open ? not sure, until a "see" and time the short line chutes in a LSR setting we are all just "thinking"
As for long line LSR chutes,, at least I am glad the photographer at Loring got a decent video for my reference.
Charles
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The chutes don't know were their deployed just watch the drag races.
JL222
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The chutes don't know were their deployed just watch the drag races.
JL222
Agree, however.... The go fast drag cars over 200mph are not (or I have not seen them ) using chutes with spring loaded pilot chutes, maybe the sportsman class cars still do, but any cars over 200 that I have seen recently are using launchers ?? I could be wrong,, I will record some runs and play back and report my stop watch and frame by frame findings.
Thanks
Charles
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222 holy crap... you throw out a 12 footer at nearly 300!!! that son of a gun must give you a he77 of a yank...
kent
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222 holy crap... you throw out a 12 footer at nearly 300!!! that son of a gun must give you a he77 of a yank...
kent
KENT... I let it slow down for the mandatory pull,but hit both chutes at 275 by accident once, it stopped like he77
but being strapped in tight it didn't hurt.
Another time the cyl head torched into the water jacket at 265 and blew off the water hose and cracked the water tank, instant fog on windshield ,pulled both chutes and stood on brakes [front and back brakes] course stewart said
''man you sure stopped fast'' I couldn't see were I was going.
JL222
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Here are 3 photos I took at the drags trying to see what the air was doing
(http://[[IMG]http://i246.photobucket.com/albums/gg102/bonesracing/080628-WSIDWindTunel021.jpg)
/img]less than 100' out. note the verticle string directly behind the rider (the air must be bent)
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(http://)(http://i246.photobucket.com/albums/gg102/bonesracing/080628-WSIDWindTunel021.jpg)
1st photo
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(http://)(http://i246.photobucket.com/albums/gg102/bonesracing/080628-WSIDWindTunel032.jpg)
about 330' The harley rider was pissed--- jap bike ang girl rider
(http://)(http://i246.photobucket.com/albums/gg102/bonesracing/IMG_7634.jpg)
to end - 135 mph string goes a bit wonky.
Bones
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I have found the discussion about chutes very interesting. As a new team with a first time car and driver, we have been relying on the experience and advice of others who have "been there, done that".
Using some of that advice during our build, we went with Stroud chutes with long tethers, the chutes came with deployment bags, but at our tech inspection, we were told to remove them. Which we did. I find it intersting (and confusing) that so many posts have recommended their use.
Being a new car, with so many unconventional items on the car, we were a bit intimidated with the tech process, so I didn't ask the relevent questions when told to remove the bags. So, I would appreciate any comments as to why the gentlemen in tech would insist we not use them.
Our chutes are mounted with about a 15 degree angle, as recommended by the manufacturer, are there any cars that have run on the salt with chutes mounted straight up? I suppose the proof is in the pudding, so I would like to hear about results they may have had with this orientation.
Kevin Marsh
RSL racing, car 7007
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Kevin,
Mounting angle and location "can" be differant depending on type of car.
Stroud had me send him pictures, weight and expected speed of my car when he built my chute. he also told me where he would want my chute mounted etc..
As you can see by my video in an early post a page or two back, I do use the D bag that came with the chute and as you can see it came out quick and perfect ?
Who am I to argue with the actual designer of the chute system ? as to the tech guy who said don't use the "D" bag... I have no idea why he said that.. but I would do what ever the chute mfg says to do.
just my 2 cents.
Charles
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I agree will Charles, in tech they usually ask to deploy the chute to make sure it pops open. What kind of car are you running and how fast do you plan on going? Do you remember who the tech inspectors was? :?
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I have found the discussion about chutes very interesting. As a new team with a first time car and driver, we have been relying on the experience and advice of others who have "been there, done that".
Using some of that advice during our build, we went with Stroud chutes with long tethers, the chutes came with deployment bags, but at our tech inspection, we were told to remove them. Which we did. I find it intersting (and confusing) that so many posts have recommended their use.
Being a new car, with so many unconventional items on the car, we were a bit intimidated with the tech process, so I didn't ask the relevent questions when told to remove the bags. So, I would appreciate any comments as to why the gentlemen in tech would insist we not use them.
Our chutes are mounted with about a 15 degree angle, as recommended by the manufacturer, are there any cars that have run on the salt with chutes mounted straight up? I suppose the proof is in the pudding, so I would like to hear about results they may have had with this orientation.
Kevin Marsh
RSL racing, car 7007
Just a thought... Would the inspectors say that because they don't want the bags to end up on the track if it were to tear away?
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Jl222,
Not sure if you watched my video ? On Thundersalts car is he using a LSR chute like mine or the shorter lined Drag type?
From the almost spin to saving it, looks like the chute was a major factor to keeping the car from going around,, that was most likely because of good driving, followed by quick decision to pull chute, followed by good reaction time in getting chute pulled, followed by chute deploying in good air quick enough, followed by quick canopy blossom.
I would say I listed it in the actual order of importance, as the by the time you do all of those things in the correct order, the .8 to . 9 second LSR chute blossom to the .5 or.6 drag chute blossom is not as big a deal as one might think, a fast blossom if you don't do everything else quick and correct is not going to help,, just tear up a chute.
That's my thoughts.
Charles
Bville has a video of Thundersalts [save of a spin] on his Utube videos. Looks like they have a short...big drag race style chute. The car is starting to spin for a while before the chute blossoms, the short lines and quick opening time[and Celia's great driving] saving car from spinning.
It would be interesting to here the manufactures reason for long lines. My understanding is less shock to car and driver but long lines take more time to react to stop a spin.
Watching the drags at Indy this weekend all pro classes used a spring loaded pilot chute and prostock used a spring assist behide the main chute in addition, all chutes opened extreamely fast.
Watching the video of our 222 car on my shut off early 271 mph 21/4 run I slow for a while before pulling chute but still about 250 mph and if you watch helmet it hardly moves from chute deployment.
JL222
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Different cars, different parameters.
Like a Street Roadster. We use a Stroud chute, tailored to our car. First time use, the pilot came out and sat on the bumper all the way to the return road. Second time, it came out but wouldn't pull out the d-bag. Bob Stroud sent longer tethers for the pilot and a bigger pilot. Seems the roadster had a lot of dead air behind it. Works like a charm now (when and if we use it. Going only 200 plus in a Street Roadster, when you unapply the throttle, it slows down instantly. In fact, the first two times described, we thought it had deployed as the car stopped so fast).
Wouldn't want to use it to stop a spin and wrap it around the exposed front suspention and the roll cage, too.
Stan Back
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I was trying to use slow mo replay and and figure out haw fast the chutes deployed at Indy... yes the short lines and large canopy seem to deploy faster, but from what I can tell.. I timed prostock cars as I had a few good shots where I could see the deployment and the blossom and it was right at .6 to . 7 seconds... where my lsr chute is right at .8 seconds... Now they are going about 195 vs me 175 in the tests,,, I would only assume if I was going 20 mph faster my chute would react a bit faster too ??
either way we are only talking .1 to .2 seconds... so my point is using a chute to prevent or spoil the spin has more components to it than just the speed of the chute deployment (based on line length and canopy size)
It has many factors
1. Drivers Mental State/Awareness vs skill,experience and or luck.. (can they save the car / correct/ drive out of it, or do they abort the run ?
How long does this thought take ?????
2. Once they decide to abort and pull/push the chute release , how long from that thought until they react and the hand pulls/pushes the chute release or button ?
3, Now once they pull the chute, the chute pack mounting location and mounted angle come in to play as well with air in the deployment zone.
4. Next is line length and canopy size to full blossom.
Charles
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http://www.youtube.com/watch?v=KrJIiumxgqY
I'll just put Troy's Video of Celia here for easy viewing. It is a Simpson 12' crossform with 16' lines. Bret Kepner let us see his video through the viewfinder right after it happend and she got almost 180 degrees backwards (twice) with the chute never loosing bloom. When I spun in 07, we had a Simpson 10' with 12' lines and only got 90 degrees. Both spins were at +/- 200 mph. I do believe that a chute can save you from a 360 degree spin if you get on the lever fast enough.http://www.landracing.com/gallery/displayimage.php?pid=7548&fullsize=1
Now about aero, start and stop Troy's video when he is zoomed in and notice where the salt rooster starts.It doesn't start from the tires.
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Charles all your points make for a quick opening chute especially for a slow reacting driver.
I think your off on your times especially the top fuelers at 300 mph thats 488 ft a second, at 320 mph thats 1/2 the track length and the chutes are out close to finish line and a lot don't pull the chute early.
How fast can you start and stop a stopwatch? Its a lot easier watching a video with the seconds counting.
JL222
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jl222,
Please, show me where I referenced 320mph top fuel cars. I specifically said pro stock cars at approx 195mph.....
also the main point is not the time to deployment in my examples, it is the "difference in time" between them,
more importantly it is about all the other factors that come before the deployment...
Charles
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don't forgtet the weight involved in LSR :cheers:
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I am not an active inspector---but when I was inspecting and a competitor took issue with something I didn't think was right, or I saw something that I had a question about ---I always got a second opinion--usually the chief inspector. That is what he is there for and the reason we have a "Chief Inspector".
I would recomend ALWAYS asking for the chief inspector to make a ruling---we have new inspectors at every meet and occasionally and old hand with a grouchy attitude. :oops:
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I don't want to be a party pooper but I think you guys are getting off the point (of this thread) with all this parachute stuff. As far as the topic of the thread goes, deploying the parachute as a spin starts is like closing the barn after the horses are out. Let's build em aero stable and work with the SCTA with rules to make it easy for us to do just such.
None the less, it's great stuff. LOL.
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I don't want to be a party pooper but I think you guys are getting off the point (of this thread) with all this parachute stuff. As far as the topic of the thread goes, deploying the parachute as a spin starts is like closing the barn after the horses are out. Let's build em aero stable and work with the SCTA with rules to make it easy for us to do just such.
None the less, it's great stuff. LOL.
yea just let it spin and barrell roll with slow deployment
jl222
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jl222,
Please, show me where I referenced 320mph top fuel cars. I specifically said pro stock cars at approx 195mph.....
also the main point is not the time to deployment in my examples, it is the "difference in time" between them,
more importantly it is about all the other factors that come before the deployment...
Charles
You point makes mine :cheers:
jl222
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agree
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Rob, I understand your point---but I have had 3 chute issues in 2 casually related to how the air is coming of the car
1 kited vertically and I was actually running on the frt wheels only for a short time--was not the RAT was solved by changing to longer tether and a ribbon chute on that car.
2 the chute would flop around behind the car if I had the pilot chute deploy straight back
3 I started cocking the pilot in the tube and I was having the pilot shoot out sideways to stop the drifting in the vacuum behind the car and it momentarily kited sideways a gave me one hell of a scare. with the narrow axle and changing tubes I have not had that problem again.
I will be going to a spring pilot chute only launcher and shooting it up and out on the new car.
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http://www.youtube.com/watch?v=KrJIiumxgqY
I'll just put Troy's Video of Celia here for easy viewing. It is a Simpson 12' crossform with 16' lines. Bret Kepner let us see his video through the viewfinder right after it happend and she got almost 180 degrees backwards (twice) with the chute never loosing bloom. When I spun in 07, we had a Simpson 10' with 12' lines and only got 90 degrees. Both spins were at +/- 200 mph. I do believe that a chute can save you from a 360 degree spin if you get on the lever fast enough.http://www.landracing.com/gallery/displayimage.php?pid=7548&fullsize=1
Now about aero, start and stop Troy's video when he is zoomed in and notice where the salt rooster starts.It doesn't start from the tires.
Yea Brian... looks like the low pressure behind the car is vacuuming up the salt and the difference in real life traveling through
still air compared to a wind tunnel were the air is moving.
JL222
JL222
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Like I said earlier, in my lakester, I built one pilot chute spring in the base of the parachute tube,
I also use a deployment bag with the chute pressure packed ( if it is soft packed, you loose allot
of the launching power when the soft pack compresses ) and I use a pilot chute to keep the bag
moving when the bag exits the tube. I also attach the D bag via a tether so I don't have to go
out hunting for it and hold up the meet. The pilot chute spring inside the tube is hard mounted
so it stays inside and doesn't pop out. It may not work for some of you, but it works for me!
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t. Let's build em aero stable and work with the SCTA with rules to make it easy for us to do just such.
None the less, it's great stuff. LOL.
No... i think you and blue should keep your nose out of creating rules especialy when it comes to aero.... this sport has relied in aero innovation for 60 years and we don't need internet experts like Blue causing rule problems.... You just go ahead and build that car Blue has designed for ya and well see just how stable his theory is....
Kent
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Kent,
All Blue is doing is trying to prevent anymore casualties. Things have changed a lot in 60 years. In the last 10 years, it has become possible for a simple guy like me to build 1600hp from junkyard and swap meet stuff. That could get me in trouble real quick without some good guidelines to keep me on the straight and narrow so to speak. Lets face it, we have had a couple of fatalities and near fatalities from cars leaving the salt and crashing down hard. None of my friends have died yet and I surely won't mind a few simple rules to keep it that way.
As far as all this parachute info goes, I think it is absolutely fabulous stuff, it should have it's own thread as I believe it to be off topic.
I do believe I will take your advise though and build that car that Blue designed for me. If it is not stable, feel free to laugh hardily. LOL.
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Rob, once you get up off the canvas, stagger to your corner and have them throw the towel in. You're up against a heavy weight and Kent could inflict serious injury. Your early in you BV career and you don't want to get disfigured. If you keep on this sight defending your self will cost you valuable built time and you'll never "getter done".
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Racergeo, not sure what your post has to do with. :roll: I'm new to landracing, but even I know enough to not call Kent fat, it's just not nice.
:cheers:
Dan
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ya know.... that's what is nice about our sport, if you want to create something kooky, build it, and run it then cool go right ahead and do it.... kinda like Rob and his build... hey if he wants to follow the advise of some internet expert then good for him and i hope he doesn't get hurt.... but we don't need some internet kook jamming the rules committee with ideas that could stifle creativity and innovation just like Rob wants to build Blues kooky ideas... there's plenty of us who look at his design and say "been there and didn't work" but hopefully they will only waist 3 or 4 years finding out.... but he's lucky we don't have book loads of stupid restrictive rules like Blue is trying to jam us up with.... Blue if you wanna finally build something find a sucker to do it or build it yourself but keep your nose out of everyone else's business
Kent
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Kent,
Who has built a car like ours. If it has already been tried and failed, I'd like to know about it.
BTW, I meant no disrespect. Honest.
Respectfully
Rob
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It's all over folks. Kent Balboa has struck the final blow and it was decisive, to the point and packing enough power to send the light weight "rumblin Rob Frey" back to the woods of western Pennsylvania where he will quietly and quickly finish his build and meet Kent and all other challengers on the white salt dyno. There he and Blue will prove they deserve another shot at the champ. Or not
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Kent,
All Blue is doing is trying to prevent anymore casualties. Things have changed a lot in 60 years. In the last 10 years, it has become possible for a simple guy like me to build 1600hp from junkyard and swap meet stuff. That could get me in trouble real quick without some good guidelines to keep me on the straight and narrow so to speak. Lets face it, we have had a couple of fatalities and near fatalities from cars leaving the salt and crashing down hard. None of my friends have died yet and I surely won't mind a few simple rules to keep it that way.
As far as all this parachute info goes, I think it is absolutely fabulous stuff, it should have it's own thread as I believe it to be off topic.
I do believe I will take your advise though and build that car that Blue designed for me. If it is not stable, feel free to laugh hardily. LOL.
Here Here :-D :-D