Re: It does seem pretty small to have much impact ...

Anyone ever look into what the wing on our cars do.

How much down force does it create? Does it apply force to only the rear of the car or the whole car?

Just curious. It does seem pretty small to have much impact??

For the 986 Boxster, my vote is that it reduces lift at the rear only.

I'm sure you'll get lots of technical and "technical" explantions.

Basically, the air flowing over the spoiler, when it's deployed, pushes down on the back of the car, helping to keep it more stable at high speeds.

As far as size is concerned, it's amazing how much air hitting roughly 105 square inches will affect the car. Just try holding a 3.5 X 30 inch board out the window at 30 mph. (I would NOT recommend trying it at 75 mph, which is the speed at which the spoiler rises, unless you've got one too many arms.)

Just remember those huge wings kids put on their Rice Rockets is mainly for the "LOOK AT ME" factor. They probably slow the car down at highway speeds more than they help to stabilize them.

Although its design might create some downforce, its main function is to break up the smooth, but less dense airflow that would otherwise pass over the rearmost part of the tail section. This smooth (I don't know anywhere near enough to safely use the term laminar) flow's lower density exerts less force on the surface of the car. This is ok on the car's sides, and maybe bottom, but on a top surface this can allow the car to be "sucked up." (The underside is actually being pushed up.) There are myriad factors affecting the pressure on the car's exterior as a whole, but the spoiler helps counteract the lift occurring at the rear. Although there is still lift at speed, the net lift is reduced.

A wing, on the other hand, can be configured to create more or less downforce, with attendant more or less weight and tire force on the road surface. To a certain point, the car effectively weighs more at speed than it does when stationary.

I believe (but stand to be corrected) that the negative aspect of any of these anti-lift or downforce increasing devices is to cause more aerodynamic drag, making the vehicle less efficient.

Oh boy, now I'm thinking of aerodynamic center of pressure in relation to center of mass! (One reason why arrows have fletching and some rockets have fins.)



Edited 1 time(s). Last edit at 10/14/2011 05:16PM by Laz. (view changes)

This same issue is around airplane wings. Some call the things that pop up during landing as air brakes. They are not. They are spoilers and they spoil lift. Notice when the airliner touches down... as soon as the wheels touch, the spoilers pop up thus killing lift and transitioning the airliner from flying to rolling.

Wiki on spoilers

This brings back memories of the "adding downforce vs. reduce lift" discussions that were so popular on PPBB.

... if you take it to the track with the spoiler disabled (fuse removed) you will certainly see how big an IMPACT there is!

The name says it all. It spoils the air flow over the car that would otherwise create lift.
Porsche claims that it spoils over 100 lbs. of lift.
The spoiler does not produce downforce. Only wings with airfoils can do that. (sorry Guenter).

I have actually tested it at Sebring.
Running by myself at the back straight with the spoiler disabled, I could actually feel the rear end start to "float" - felt like hydroplaning - after it goes to 100+ mph.
On the faster Boxsters, such as the race-prepped ones (not Spec Boxsters - faster) there is actually the need to install a GT3 wing on the back to create 250+ lbs of downforce to keep the car planted at speed.

I had completely forgotten about this debate.
I think I'll write an a Tech Article about it.

Happy Porscheing,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Quote
Pedro (Weston, FL)

The name says it all. It spoils the air flow over the car that would otherwise create lift.
Porsche claims that it spoils over 100 lbs. of lift.
The spoiler does not produce downforce. Only wings with airfoils can do that. (sorry Guenter).

I think I'll write an a Tech Article about it.

Happy Porscheing,
Pedro

Pedro, you just explained it more scientifically than I could. By spoiling the lift that would otherwise be created, the net effect is that the rear of the car is kept planted more firmly on the road.

I agree, it would be a great Tech Article.

Wasn't the original Audi TT sans a spoiler and experienced exactly what Pedro mentioned? I recall reading about a few crashes, perhaps in mule testing, or over exaggerated, so I don't want to perpetuate urban legends.

... had a recall in 1999.
There had been a couple of crashes in Germany (and reportedly also Stateside) and Audi recalled the model.
They made some suspension mods and also added a rear spoiler during the recall, but then became standard in all of the TTs.
Contrary to a wing that requires area to create lift (the bigger the wing surface, the bigger the lift), the spoiler only has to create enough turbulence to spoil the air flow and destroy the lift.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Thanks for refreshing my memory, Pedro!

its not hard to figure out what must be happening. force can only occur down - and it at the back.

All aero is a f(x) of speed.

QED

Grant