Landracing Forum
Tech Information => Technical Discussion => Topic started by: Ratliff on June 11, 2008, 07:49:29 PM
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The attached discussion illustrates how in a sideslip condition on an aircraft a vertical stabilizer aids roll stability as well as directional stability. A car skidding sideways is equivalent to an aircraft in sideslip.
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Other than takeoff and landing, roll stablization is an annoyance, that should be able to handle with stick and rudder.
Nobody wants their landspeed machune to roll, granted, but DOES ANY OF THIS APPLY DIECTLY TO El Mirage, Maxton, Texas Mile, Bonniville, etc.? or even Interstate 15.
Who inquired about this to warrant your posting this stuff?
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have you been sideways at 250??
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Other than takeoff and landing, roll stablization is an annoyance, that should be able to handle with stick and rudder.
Nobody wants their landspeed machune to roll, granted, but DOES ANY OF THIS APPLY DIECTLY TO El Mirage, Maxton, Texas Mile, Bonniville, etc.? or even Interstate 15.
Who inquired about this to warrant your posting this stuff?
Bluebird, Mark II.
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Other than takeoff and landing, roll stablization is an annoyance, that should be able to handle with stick and rudder.
Nobody wants their landspeed machune to roll, granted, but DOES ANY OF THIS APPLY DIECTLY TO El Mirage, Maxton, Texas Mile, Bonniville, etc.? or even Interstate 15.
Who inquired about this to warrant your posting this stuff?
Spirit of America, 1962.
The year Breedlove didn't set the record.
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have you been sideways at 250??
Donald Campbell got sideways at 250 mph.
Bluebird, Mark 1.
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Ask Ed or Richard of the Danny Boy streamliner. They are believers in the Vert. Stabilizer
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Spirit of America, 1962.
The year Breedlove didn't set the record.
no tail on that one... :-o
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Nobody wants their landspeed machune to roll, granted, but DOES ANY OF THIS APPLY DIECTLY TO El Mirage, Maxton, Texas Mile, Bonniville, etc.? or even Interstate 15.
Salt racers aren't putting them on their cars just to get chicks.
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Its all about having the center of pressure behind the center of gravity. If you don't have it that way you are probably going to have some handling problems. Easy fix is a big tail fin, make it right and it will only add a very small drag penalty but a big stability addition.
Rex
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Most have a fin, don't think its value was disputed before or after the post discussing rolling moment. On an LSR car, if you have a rolling moment you are already in trouble and the fin won't help. The fin will help correct a yaw problem, I don't think any ever disputed that. Most aircraft have ailerons and rudder to correct the problem, haven't see either on an LSR car.
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Most have a fin, don't think its value was disputed before or after the post discussing rolling moment. On an LSR car, if you have a rolling moment you are already in trouble and the fin won't help. The fin will help correct a yaw problem, I don't think any ever disputed that. Most aircraft have ailerons and rudder to correct the problem, haven't see either on an LSR car.
Among other factors, including airspeed, the vertical stabilizer has to be of sufficient height so that the side force it generates is far enough above the center of gravity to have the leverage for effective anti-roll. The stubby little tailfins many teams run don't have the height. However, the dynamics are explained in the graphic I included with my original post.
The Danny Boy streamliner and lakester look like they have fins with the height to generate effective anti-roll.
http://www.dannyboystreamliner.com/services1.htm
http://www.dannyboystreamliner.com/streamliner.htm
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Its all about having the center of pressure behind the center of gravity. If you don't have it that way you are probably going to have some handling problems. Easy fix is a big tail fin, make it right and it will only add a very small drag penalty but a big stability addition.
Rex
Correct. Until the fin has some angle of attack on it, the drag penalty is very minimal.
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Check out the vertical stab (and the canard wings) on the J-34 jet car Ab Jenkins was proposing in 1950.
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Nobody wants their landspeed machune to roll, granted, but DOES ANY OF THIS APPLY DIECTLY TO El Mirage, Maxton, Texas Mile, Bonniville, etc.? or even Interstate 15.
Salt racers aren't putting them on their cars just to get chicks.
So any truth to the tale about the lakester (wing tank) that always spun out to the left (or maybe it was right - but consistently the same direction) when at speed?
I guess it was a wing tank where they (Airforce) had slight angle to the fin so it would spin away from the plane when ejected . . . hard to see unless you knew to look for it.
Can anyone verify?
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From aero tests I've done with a 1:16 scale model of my streamliner I believe it's not possible to get the AC behind the CG of a rear drive car . With my model w/o a tail fin the AC was at about 30% , with a 2.5 sq ft tail fin it was at about 33% and a 4.5 sq ft fin moved the AC back to about 35% . In my opinion a tail fin on a conventional car increases the margin between ideal and trouble .
John
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The attached discussion illustrates how in a sideslip condition on an aircraft a vertical stabilizer aids roll stability as well as directional stability.
the hows and whys there are reasonably easy to understand , however.....
A car skidding sideways is equivalent to an aircraft in sideslip.
at zero traction yes , however unless the tyres are off the surface there IS a difference( many) between a car and a plane going sideways....it's trying to tipover..
On an LSR car, if you have a rolling moment you are already in trouble and the fin won't help.
....looking at it logically , once you're going sideways it's all over, the fin is out of a job , it's effect may be useful before that...as long as there aren't unstable cross winds..............
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If you have a rolling moment, you are not side slipping, that is a yaw, you are rolling. Once you are rolling you have wheels losing contact on the high side and digging in on the low side due to CG shifting from the normal relationship to the about to be on your roof. Depending on the aero of your car, ground effects, and about a million other factors coming into play faster than you think about them the car will continue to roll, the fin may delay it long enough for the laundry to catch it, or not... you are on the roof and probably tumbling or... You could just get lucky.
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In other words, yaw, OK, roll, NADA!
Well stated Stainless!
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If you have a rolling moment, you are not side slipping, that is a yaw, you are rolling. Once you are rolling you have wheels losing contact on the high side and digging in on the low side due to CG shifting from the normal relationship to the about to be on your roof. Depending on the aero of your car, ground effects, and about a million other factors coming into play faster than you think about them the car will continue to roll, the fin may delay it long enough for the laundry to catch it, or not... you are on the roof and probably tumbling or... You could just get lucky.
Sideslipping is simply skidding sideways while going forward.
Whether it's a car or airplane, a vehicle skidding sideways will try to roll.
Since their side force acts below the center of gravity, the wheels on a car skidding sideways are like those small ventral fins on the F-104, increasing the destabilizing rolling moment.
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From aero tests I've done with a 1:16 scale model of my streamliner I believe it's not possible to get the AC behind the CG of a rear drive car . With my model w/o a tail fin the AC was at about 30% , with a 2.5 sq ft tail fin it was at about 33% and a 4.5 sq ft fin moved the AC back to about 35% . In my opinion a tail fin on a conventional car increases the margin between ideal and trouble .
John
With a long slender vehicle, a vertical stabilizer typically produces at the most "one caliber" stability. That's a one diameter (one body width) separation between the c.g. and the c.p.
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The attached discussion illustrates how in a sideslip condition on an aircraft a vertical stabilizer aids roll stability as well as directional stability.
the hows and whys there are reasonably easy to understand , however.....
A car skidding sideways is equivalent to an aircraft in sideslip.
at zero traction yes , however unless the tyres are off the surface there IS a difference( many) between a car and a plane going sideways....it's trying to tipover..
On an LSR car, if you have a rolling moment you are already in trouble and the fin won't help.
....looking at it logically , once you're going sideways it's all over, the fin is out of a job , it's effect may be useful before that...as long as there aren't unstable cross winds..............
A vertical stabilizer doesn't start generatiing a side force until it's got an angle of attack on it. As long as the vehicle is going straight, there is no angle of attack on the vertical stabilizer.
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I don't know if this is relevant to the thread, as you're talking about four wheel vehicles and airplanes I assume, but it seems to me they're two different animals. Why is it that when in an airplane in a diving spin, pilots are quite often unable to stop the spin using all of the principles suggested by people in this thread, and one guy in particular. Are you saying a fin is a cure all to keep high speed vehicles on all four, with the shiny side up?
I can only go with people "who have been there and done that". A few years back when talking to Don Vesco, we discussed stablizer fins. I asked, "Should I or shouldn't I put a stablizer fin on the motorcycle streamliner I'm planning to build?" He said, "Not necessary. IT'S NOT AN AIRPLANE. If the bike is built right, it'll go straight. The only thing a fin on a motorcycle does is increase sail area, which ain't good for cross winds, and the only thing it'll do is increase drag and slow you down."
Then I asked, "Why so has the Turbinator got a fin on it?" He answered, "Mostly for looks, it makes it look faster in a picture".
He went on to say, "If you still feel you need a
stablizer fin on the bike, hang a couple of fins on either side of the tail, but make them so they don't increase sail area. Nothing sticking up or below."
The Easy Rider had a little four inch fin on it. I asked Dave Campos about it. Dave said, "It was Joe Teresi who wanted the fin, and changed Bob George's original design. Teresi liked it better. That fin was put on there just for looks." I did the same in 2005, on the Vincent streamliner, just for looks.
Max
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I don't know if this is relevant to the thread, as you're talking about four wheel vehicles and airplanes I assume, but it seems to me they're two different animals. Why is it that when in an airplane in a diving spin, pilots are quite often unable to stop the spin using all of the principles suggested by people in this thread, and one guy in particular. Are you saying a fin is a cure all to keep high speed vehicles on all four, with the shiny side up?
I can only go with people "who have been there and done that". A few years back when talking to Don Vesco, we discussed stablizer fins. I asked, "Should I or shouldn't I put a stablizer fin on the motorcycle streamliner I'm planning to build?" He said, "Not necessary. IT'S NOT AN AIRPLANE. If the bike is built right, it'll go straight. The only thing a fin on a motorcycle does is increase sail area, which ain't good for cross winds, and the only thing it'll do is increase drag and slow you down."
Then I asked, "Why so has the Turbinator got a fin on it?" He answered, "Mostly for looks, it makes it look faster in a picture".
He went on to say, "If you still feel you need a
stablizer fin on the bike, hang a couple of fins on either side of the tail, but make them so they don't increase sail area. Nothing sticking up or below."
The Easy Rider had a little four inch fin on it. I asked Dave Campos about it. Dave said, "It was Joe Teresi who wanted the fin, and changed Bob George's original design. Teresi liked it better. That fin was put on there just for looks." I did the same in 2005, on the Vincent streamliner, just for looks.
Max
Bike liners are different animals from car liners and have not done well with high tail fins due to the increased influence of crosswinds. Stormy Mangham's original concept of using a long flattened tail instead of a vertical stabilizer seems to have withstood the test of time.
http://www.landracing.com/forum/index.php/topic,4035.0.html
http://www.landracing.com/forum/index.php/topic,3996.0.html
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Then I asked, "Why so has the Turbinator got a fin on it?" He answered, "Mostly for looks, it makes it look faster in a picture".
Oh, this reminds me of an old Penske Champ Car story.....
In the middle of a season back around 1990, a small fin suddenly appeared on the engine covers of Team Penske cars. Everyone wondered what speed trick Roger had discovered. More fins sprouted overnight on engine covers, rules changes were being discussed, etc.
Someone finally asked, "why the new fin?" Without batting an eye Roger replied - "signed a new sponsor, needed room for his decal".
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http://www.the-rocketman.com/RPV/dragsters/JOHN-PAXSON-ARMOR-ALL-CAR.jpg
Above is a link to a photo of the Armor All rocket dragster. After initial runs without a vertical stabilizer, producing some very scary handling, the car was fitted with the tail fin you see in the photo.