Extra-large rear wing

[MadMatt]

There was a slalom race this weekend in Switzerland, and that car was present :



What do you think about the rear wing ? Isn't it enough to put more angle on the planes of the rear wing rather than making it larger (and less stable/stiff) ?

I am wondering what are the advantages of such configuration !

[tomislavp4]

The higher the aspect ratio of a wing the more efficient it is at generating lift. The wing on the picture provides the same lift as a narrower wing with higher angle of attack but with less drag.

[Lycoming]

a wide wing has a higher aspect ratio, generally speaking. This leads to weaker wingtip vortices and lower drag. Most racing cars run relatively narrow wings, but this is for practical reasons, or because of the rulebook. If it were practical to do so, all race cars going fast enough or well budgeted enough to have aero would be running wings like this

http://upload.wikimedia.org/wikipedia/c ... /Dg800.jpg

because in terms of efficiency with respect to drag, you don't get much better than that, long span, short chord, single element. competition sailplanes like that can achieve travel forward 50 meters for every 1 meter of altitude they lose. the lift to drag ratio is much higher than that of any wing used in motor racing. In actual usage, the best you can typically get is the wings that you see on the back of LMP1 cars, which this is very similar to.

You could achieve the same level of downforce with a smaller span by adding more elements or jacking up the wing angle up to the point of stalling, but it would not be as aerodynamically efficient. Its not uncommon to have a turbulent boundary layer in motor racing wings because it will delay flow separation and let you run more angle and get more downforce, but it will come at the expense of drag.

[Reca]

The above explanations are correct in the principle, for a given amount of lift needed the longer the span the higher the efficiency, and that's nice and good for an airplane which in cruise needs only enough lift to compensate the weight and that's it, but for a race car it's really not correct to do the reasoning in term of fixed lift.

In particular that's a slalom car we are talking about, what kind of speeds is that supposed to reach in its competitions?
Probably not a range where drag is really a concern, so the only real need is to generate max downforce you can get.
In that sense you maximize the chord, the angle, the span, as much as rules allow, and optimize the airfoil design, all in order to get as much downforce you can from the wing, caring little about drag.

That car seems to be an ex-Lola F3000, the model used between 99 and 2001 going by the "bulge" on chassis (I forgot the exact name, but it probably had a 99 in it...), and the original rear wing was completely different from that that they took/made a totally different one most likely simply signifies that rules of that specific competition required so because original wouldn't have been legal; rules presumably define a box inside which the wing has to fit, and that wing just exploits at max the allowed box with the only aim to maximize downforce within rules' boundaries.

[MadMatt]

Thanks for the answers ! I don't know all details about slalom competitions in Switzerland because I'm not following the competition closely anymore, but if it hasn't changed, you can do the modifications you want on the car. There are classes depending on your car :

Groupe SuperS : super series cars (only Swiss drivers)
Groupe IS : special cars «InterSwiss»
Groupe N/ISN : production cars
Groupe A/ISA touring cars
Groupe R : touring rallycars
Groupe B* : GT cars
Groupe GT : GT cars
Groupe C : sportscars
Groupe D/E : single seater and free formula cars

And you are classified depending on the capacity of your engine. The speed of the single seater cars depends on the track of course, but they don't reach more than 180kph I would say. Hillclimb is different and usually the competitors use the same car for hillclimb races too, so I will keep an eye if he's using the same type of car/wing at hillclimb events.

I would say that at this speed the drag is a concern and especially on such short distance courses where every tenth makes the difference. The car is a Lola B 99/50 driven by Eric Berguerand, that was at the "Slalom de Bière" this year.