Landracing Forum
Tech Information => Technical Discussion => Topic started by: StraightSix on February 11, 2005, 09:43:00 PM
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GM lakester (http://www.supercars.net/cars/2003@$GM@$Belly%20Tank%20Lakester%20Conceptx.html) <-- pop-up warning on that one
same thing, different site (http://www.topgear.com/content/features/stories/bellytank_lakester/02/)
Is this the same car that holds the G/BGL record of 179.381mph?
I'm curious about those urethane tires - how well did they work? How would one go about getting tires like that?
Also generally about lakesters - what is the average drag coefficient of a well designed lakester?
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I believe it ran conventional Bonneville type tires.
Max all of your credit cards and sell two of your children.
Next answer I'll bow to the experts.
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GM used normal LSR tires, as far as normal is. The show tires are just that, show tires. The math geeks can argue the cd question.
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Also generally about lakesters - what is the average drag coefficient of a well designed lakester?
I'll comment on this, but only from the point that the following is my view only and I don't have any "hard" numbers to back it up.
:) . On the first page of my site with the link below I have the names of 3 different books on aerodynamics you might want to look at.
c ya, Sum
Lakester Construction In
Progress (http://purplesagetradingpost.com/sumner/bvillecar/bvillecarindexpage.html)
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Straight and 1FAT - Here's a couple of things I've picked up .
Streamlined 3D shapes are called bodies - Thats the key word to find information about the drag of things like lakesters and streamliners .
Information about the drag of streamlined bodies close to the ground is scarce.
Bodies with the lowest drag are rounded in front and pointy in back but needn't be fattest tward the front like a wing .
Wind tunnels without moving floors give artificaly low drag - You can't believe all the Cd numbers you see .
On Yahoo look up "Interactive airfoil analysis" (1st item)- It only shows side pressure but you can learn from playing with it .
Also on Yahoo look up "Aerodynamics of road vehicles" (2nd item), a book review with good info .
Don't finalize your design till you've done a lot of talking , reading and thinking .
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How often do you think Lola, Williams, G Force et al look up the tough aero questions in "Aerodynamics of road vehicles" or do a yahoo search??
Dave
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The fastest lakesters are the least efficent and mostly look at each other.
Right behind them are the smaller classes with a lot more aero.
In the case of streamliners, one of the smallest is one of the fastst.
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There are several reasons why F1 cars don't have low drag bodies.
The wings and exposed wide tires make low drag impossible.
The front of the car needs to be a certain shape to direct air to the underbody for down force and to the brakes and radiators.
There is so much turbulance behind the rear wing and tires there's no way to avoid drag there.
Passing normaly happens during braking or cornering where drag isn't important.
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Tires on lakesters are probably your largest drag factor. I believe you might find that large tires (24 inches +) spinning in moving air have a drag of 1.16, small tires about 1.21.
I always remember something I heard a long time ago at Bonneville. "It doesn't matter how streamlined it is, it still has more drag than if it isn't there."
Build the smallest frontal area you can and still fit engine and driver.
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I think that I agree with most of what 1FATGMC has said, build the basic body as small and slippery as possible, run small and narrow tires and streamline every thing between the body and the wheels. I also am working on a small displacement lakester, probably an "I" class car, but I have a street rod to finish first so am probably several years away. I am not sure that I agree with Stainless1 that the Cd for Bonneville style tires is as high as 1.2, where did you get that info from? I am planning to run top fuel fronts, about 22 in. OD and make non rotating wheel covers both on the inside and outside. I am planning to make my shape a NACA 6600 series semetrical aerofoil shape in plan view, low Cd, long area of attached flow good pressure gradient. I am also thinking about running a flat bottom, like Costallas cars and very low to the ground, less than one inch, but I don't find alot of info regarding how this affects the Cd. Anyone got some input on this?? I have seen alot on running aero shaps close to the ground, which generally shows that to little ground clearance increases drag, but nothing on flat planes.
I remember reading where some F1 engineer said that the modern F1 chassis is just a "bracket" to carry all of the aero stuff! When you see that these teams are running their wind tunnels 24/7 it just makes you wish you had a couple of hours in one!
A comment about the GM lakester also, they actually built two. GM built the first one with the billet wheels with the rubber bands around them and it was just for show. So Cal Speedshop built the "race" model and it ran some big Dunlop 18s in the rear and 16s in the front. I personally think they were (are) to big but So Cal has got the GM money not me!
Note to 1FATGMC, thanks for running the picture of Seth's lakester, I have looked at that car a million times and never remember that it ran so much caster! Something to remember. It really does hurt to think about it though, what a great car!
Rex
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Open wheels have tremendous drag. May not be as high as 1.2, but maybe it is? Total Cd on a Lakester is probably around/about .45.
JB
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Rex
I don't know what top fuel tires you are planning to run or what they are running now.
When Ron Benham first built the lakester that he sold to Corky Stockham, he ran the skinny top fuel tires because they were rated to 320 mph. He blew one on a pass. No problem, he had another one. Blew another one. Called Goodyear to see what was going on with their 320 mph rated tires.
Goodyears response was, they ARE good to 320 mph, for 5 SECONDS, not 5 miles.
Not trying to advise you on anything, but you might check with the manufacturer to make sure they are OK.
Ron
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If a top fuel tire can handle the speed but not the flexing at bonneville isn't it an air pressure problem .
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NO, it's a load problem. Have talked to Goodyear. Drag tires are not intended to run for five miles especially at the pressures that work for us (60 to 100 psi). Centrifugal force pulling on the tire for five miles is often more than the tire will handle. Not to mention the weight of many Bonneville cars far excededs the weight of a tube frame Drag car.
JB
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One more thing to remember, a tire going 300mph at the contact patch is going 600 mph at the top. Remember this fact when you put a tire not designed for speed on your car.............
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Don't believe it? Look at a picture of a Top Fuel tire at speed. The back of the tire is flat and perpendicular to the ground...........
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The 600 mph you mention is surface air speed, nothing more. The top of the tire in relation to the air tends to cool it and reduce the failure rate. The power thru the contact pateh generates the heat and contributes to ahe failure.
All tires at speed have a stending wave shape that is more exagerated in a low preassure top fuel rear.
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Jack, I am not arguing with you, but the cylical speed up the back side, and slowing down the front side has got to stress a tire more the faster it goes. I bring this up only because you and I both know that a lot of people are running unrated (for the record in their class) tires out there, and I sometimes wonder if they even think about the stresses on a tire.
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Maybe I'm just to dumb to see it, but I would think the only speed working on a tire would be rotational speed. Granted the faster it runs the more often any point hits the ground and is flexed but I don't believe the accelaration from the ground to over the top affects the tire.
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At a steady speed, the tire does not change speed except as it encounters surface speed in relation to the air. The portion of the air around the tire at any place tends to remove the heat generated by a combination of HP transmission, surface temp,and flex.
Remove the airflow around a tire and you have reduced it's ability to shed heat.
The centrifical force changes with the rotational speed and the distance to the centerline.
HI speed shots of Top Fuel tires are the best study to see the forces that act on all tires.
<small>[ February 16, 2005, 11:39 PM: Message edited by: JackD ]</small>
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Anyone who thinks centrifugal force doesn't enter the picture, should talk to Gene Burkland, who in testing LSR tires for M/T has sent many tire shards into orbit. Look up and you may see a few just now coming down. My concern is that we don't know with any amount of accuracy at what point a given tire comes appart. At least the Goodyear LSR (not to be confused with Goodyear Front Runners) and the M/T LSR tires are load tested at speed.
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Was looking at the picture of the Hammond lakester shown earlier in this topic and got wondering if the big scoop could have contributed to the lift that may have doomed the car . I went to interactive airfoil analysis (first item on yahoo under that title) and tried to simulate the shape . It showed a big spike in negative pressure in that area . If only the air inlet had been in the center of the nose the lakester might still be setting records .
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You gotta be kidding.. Yahoo solves this.. Next they will have the solution about Micheal Jackson and all his little friends.. LOL.. have you ever been to the place we are talking about or doing a Google search for it? Things are way more complicated than I think you might imagine.. Math is good I use it every day to solve many problems but I doubt that Yahoo has the definative answer..... Or even has the question at best...
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Dave
If you prefer google , interactive airfoil analysis is the first item there also . I used this interactive site because it lets you experiment with non-standard shapes .
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How would it simulate the air going into the scoop? The engine is consuming the frontal area if the soop is sized correctly.
Dave
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Dave
At 300 mph unless the scoop was supplying 75 or 100 cubic feet per second to somthing there would have been a lot of spill over . The engine would have used less than half that volume .
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Ever notice how small the air inlet is on the Nish streamliner? I think John may have a valid point. I spent 33 years in the HVAC field, and over the years discovered that more is not allways better when it comes to moving air. One mistake people tend to make with scoops is to have them end at the back of the inlet to the manifold. A plenum needs to have a buffer rearward from the inlet or a turbulance will occur right over the inlet and create a "back pressure" of sorts, which sort of defeats the whole "ram air " principle.
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One mistake people tend to make with scoops is to have them end at the back of the inlet to the manifold. A plenum needs to have a buffer rearward from the inlet or a turbulance will occur right over the inlet and create a "back pressure" of sorts, which sort of defeats the whole "ram air " principle.
Bob could you elaborate on all of that a little. I'm a little slow and don't quite know what you are saying, but I'm interested.
Thanks,
Sum
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Sum, air does't like to make tight turns. If you radius your scoop into say a carburator or injector like a current NHRA injected nitro dragster, the air has a chance to make the turn. If, however, you run a scoop that doesn/t allow for a radius to the injector, the air has a tendency to "swirll" or tumble, when it hits the back. If you are stuck with this type of plenum or scoop you can alleviate this problem by running the plenum past the rear of the carb or injector by a foot if possible. This lets the air swirl behind the opening into the manifold rather than spining over the top. This is a lot easier to explain with a blackboard and chalk, so I hope you can kind of picture it. The bottom line is you need a cushion at the rear of the scoop to negate the swirll and create the possitive pressure into the intake. In a common ductwork design using a rectangular plenum, a engineer will never draw a perpendicular takeoff in the last two feet for this very reason, and even though a internal combustion engine has the advantage of pulling air from the scoop, You still are dealing with air. This would not be nearly as important on a blown engine, but for those of us normally aspirated cars, I think this would be valid. My thoughts only.
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Thanks Bob, I have a better picture now and that all makes sense.
Have a good weekend,
Sum