downforce/airfoil sections.

Martin Harms · Post by **Martin Harms** » Thu Sep 04, 2003 8:42 am

But the most influencial is the angle of attack. A difference of 1/2 - 1 degree
will change the lift/downforce considerably. Angle of attack can quadruple the
lift/downforce, make it stall, go negative etc. (stick your hand out of the
sidewindow when going fast and swivel your arm, you will know what I mean.)
With the airfoil at the rear of the car you can imagine the possible changes in
angle of attack through suspension travel on a roadcar. F1 cars have maximum
suspension travel of round about 10 mm. MX5 = 150mm?? Also F1 cars have wings
on both ends, front and rear. If one of them comes undone the car becomes unstable/undrivable at speed.
At speeds of less than 120 km/h even the wings on an F1 car become ineffective.
(with much larger area - estimated 4-5 times area of roadcar wing)
The rear wing airfoil on roadcars is carefully designed to be neutral in
lift/downforce with small changes in angle of attack. They'd be outright
dangerous otherwise. I don't even want to go into the issue of drag...
It does not make the car CORNER faster - it just sells faster.

My 4 cents worth.
Martin

Eric & Ann West wrote:

[...]

Simon Lord · Post by **Simon Lord** » Thu Sep 04, 2003 10:12 am

I don't pretend to understand the aerodynamic formulae, but the marketing
makes sense.

If I may be allowed a reminiscence on spoilers here, back in the 1980's I
was fortunate enough to be a co-driver in a Metro 6R4 rally car - a Group B
supercar based loosely upon the Mini Metro of the time but with 4WD, a
300+bhp 3 litre turbocharged engine and the most enormous great wings front
and rear.

We had borrowed it from the works to use as '0' car on the International
Scottish Rally and it came with its own works crew, which was nice. They
advised us extremely firmly that if the front spoiler should happen to get
knocked off, it should not be driven over a mere 50mph (80kph) as the rear
wind generated so much downforce that even at that speed the front wheels
would lift off the ground and we would have no steering. I guess when you
have that much power, drag ceases to be a concern.

I have to say that being driven rapidly in that car was the nearest thing I
have ever experienced to actually being INSIDE a video game. The trees,
gravel, spectators etc were all very two-dimensional - wonderful experience.

Simon
97 SR Ltd

Graeme Naisbitt · Post by **Graeme Naisbitt** » Thu Sep 04, 2003 10:29 am

but returning to the point (just a little), which creates more drag? A
tasteful factory boot spoiler or a luggage rack (especially one that is
fully laden) =O)

Eric West · Post by **Eric West** » Thu Sep 04, 2003 10:33 am

You're not wrong Martin, my response was to give as simple an answer as
possible, I mean, one could go into whether the boot lid provides a "slot"
effect or "biplane interference" and speculate whether the down turned ends
provide an end plate or winglet effect, but the probable truth is that they
are far more effective aesthetically than aerodynamically.

Eric

Eric West · Post by **Eric West** » Thu Sep 04, 2003 10:58 am

No contest! The rack every time, but lets face it, an MX 5 is not really a
symphony of aerodynamics at any time, we drive them cos we love them and
argue about them to exercise our brains!