Spoiler (Car) Question

General Questions
#1

I was watching a show on dsicovery channel this week about suped up cars. It showcased 3 different cars. One was a Super Corvette, a Super Porchse and a Super Ferrari. I don’t know anything about cars so I Cant remember the models. Sorry. I do know that the Vette was one that an aftermarket company suped up. I would know the name if I heard it.

Anyway, when they were talking about hte Ferrari they said that the 3 inch spoiler on the back would create enough down force on the back of the car to keep it stuck to the track UPSIDE DOWN at a mere 220mph!!

Is this really possible? I find that very hard to believe.

#2

It is certainly not outside the realms of possibility. Certainly I know that I have heard discussions of the downforce created by the wings on Formula One cars and I’m pretty sure that figures of a tonne or more have been mentioned, and they have a top speed of around 200mph. The Ferrari probably would not weigh much more than that.

#3

Think of the upforce created by an airplane’s wings. The car’s spoiler is essentially a wing turned upside down. I believe the effect increases geometrically with airspeed, so I could see there being a very significant force developed at 200+ MPH. I also believe that Ferrari’s are typically built to be fairly light. The same spoiler may not keep the (heavier?) Corvette in place upside down.

#4

Yes, a high-downforce race car, such as a Formula 1 or Indy car, can produce several tons of downforce at speed, so it is literally possible for one of these cars to stick to an inverted track.

However, road cars are a different beast entirely. For practical reasons, they simply can’t be built to fully utilize the ground effect. The best most street-legal road going cars can do is minimize lift. I’m not familiar with this particular model of Ferrari, but I seriously doubt their claims.

Doing some quick back-of-envelope calculations, a three-inch, five-foot wide wing on a car, assuming standard sea-level conditions and a very generous C[sub]L[/sub] of 3 (if it’s not some huge multi-element rig, it’s almost certainly much less than that), would produce 464 lbs. of downforce at 220 mph. I don’t know what the body is doing, but it can’t be producing much more than a couple hundred pounds of downforce itself, and most likely is actually generating a little bit of lift.

Therefore, I would guess that the car has no more than 600 or 700 pounds of downforce total. Since the curb weight is probably around 3,000 lbs., it would not be able to stick to an inverted track. I wouldn’t believe any claims that a street car could generate that kind of downforce without seeing some wind tunnel data.

#5

BTW, the Corvette was probably modified by either Hennessey or Callaway. Do any of those names sound familiar?

#6

Yep. It was a Callaway.

You seem to know alot about this subject so let me ask you, what advantage do you get by having a spoiler that is 3 high off the trunk as opposed to having the spoiler an inch off the trunk? I am assuming that the both spoilers have the same surface area and slope etc…

#7

Are we talking wings or spoilers? The purpose of a spoiler is to “spoi” the airflow and make it more turbulent. Since cars don’t have long, tapered rear ends, a low-pressure zone develops behind the car and pulls it backwards. A spoiler minimized this effect by making the air more turbulent. It’s the same purpose as the dimples on golf balls. Spoilers are attached directly to, or close to the body.

Wings are for creating downforce. Here, you want the wing sitting in a high wind-speed region, so they are mounted higher up above the body.

#8

scr4, from the wording of the question, I take it to mean wings.

Like so many things in racing, wing height a trade-off for the designer where the best answer depends on his priorities. Do you want give up something in one area in order to gain somewhere else?

The advantage of mounting a wing up high is that it is working in clean air, where it will be able to generate maximum downforce (and drag) with minimum interaction with the bodywork. A good rule of thumb is to mount the wing at least 3 chord lengths (chord length being the length of the wing from the leading edge to the trailing edge) above the bodywork, though in practice this could be higher or lower depending on how carefully/poorly managed the airflow around the rear of the car is.

Mounting a wing low, close to the bodywork, will cause interactions with the airflow around the body and generally reduce the downforce and drag produced by the wing. However, the wing can be designed to interact favourably with the bodywork. For example, the lower element of an F1 car’s rear wing is used to reduce the pressure under the vehicle, in order to generate more downforce. Another example is the use of a low rear wing by some Le Mans prototype sports cars to reduce overall bodywork drag (because at Le Mans, low drag is a premium and high downforce is relatively unimportant).

On a production street car, where you mount the wing is really unimportant because you simply aren’t going fast enough to make effective use of one (though a few do use them to reduce drag or tweak overall balance). The same wing making 464 lbs. of downforce at 220 mph would produce just 40 lbs. at 65 mph. 95% of the wings on production vehicles are mostly a fashion statement.

#9

IN line with what Jet Jaguar said, my understaning was that F1 cars actually created a vacuum in addition to the downforce. But also, yeah, spoilers on production cars are for looks, not function.