Shark fins and flying

[Grand_Fromage]

I was never convinced that the ugly FIA shark fin would prevent prototypes flying when they go sideways. The sideways flip of of Marc Gene at the Porsche Curves in 2008 was supposedly one of the reasons why this regulation was brought in, but looking back at that footage and that of Davidson last week, the fin seems to do nothing to help. In fact, I would dare to suggest that it could even make matters worse.

A simple look at the physics of a sideways sliding prototype would tell you that the force of air on the fin will tend to lift the side of the car facing the airflow and make a flip more likely. I thought this the first time I saw a finned proto, but I supposed that brighter and better informed minds than mine had ascertained that this was the way to go. Events seem to have proved them wrong...

[Lazy B'stard]

They are citing the fact that it went airborne was due to it losing its near side rear wheel on impact. The air got into the arch and lifted it up.

I would have thought that the big honking holes above the wheels in the bodywork would have allowed the air pressure to escape in that case.

I too have never been convinced by the fin. I know the theory, and how it is supposed to work but it can only work if the air around the car when it yaws is clean. The air is never clean on a race track if there is another car anywhere near it.

The NASCAR solution of moveable gurney flaps that pop up seams to be much more effective in dirty air. It's proven to work so why did they not adopt it for use on sportscars?

[Grand_Fromage]

I can see that a vertical fin behind the centre of mass will help with yaw stability but that is only when correcting a yaw of a few degrees.

If the car is forcefully launched into a 90 degree sideways slide by impact or mechanical failure, that ceases to be of any consequence. What DOES enter the equation however is that great big sail above the centre of mass that will give a turning force that tends to lift the 'leading edge' side of the car.

They are citing the fact that it went airborne was due to it losing its near side rear wheel on impact. The air got into the arch and lifted it up.

I would have thought that the big honking holes above the wheels in the bodywork would have allowed the air pressure to escape in that case.

I too have never been convinced by the fin. I know the theory, and how it is supposed to work but it can only work if the air around the car when it yaws is clean. The air is never clean on a race track if there is another car anywhere near it.

The NASCAR solution of moveable gurney flaps that pop up seams to be much more effective in dirty air. It's proven to work so why did they not adopt it for use on sportscars?

[mgmark]

There was some earlier discussion about fins here - http://www.clubarnage.com/forum/index.php?topic=10831.0

Last year, McNish's Audi skipped pretty much straight and level across the gravel but, looking at the videos of both incidents, that one wasn't subjected to the same "assistance" that Davidson received this year with the wrecking of the back end of the bodywork/wing while being moved pretty quickly into being 90 degrees out to the direction of motion?     

Mark