Vertical stabilizers also improve roll stability

[John Burk]

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

[Dr Goggles]

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..............

[Stainless1]

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. 

[interested bystander]

 In other words, yaw, OK, roll, NADA!

Well stated Stainless!

[Ratliff]

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.

[Ratliff]

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.

[Ratliff]

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.

[Kansas Bad Man]

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

[Ratliff]

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

[aircap]

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".

[Ratliff]

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.