Gurney Flap Study
12-16-2014, 04:27 PM
#181
Rennlist Member
sorry to revive this thread but i need to ask a question. . lets say that a rule change allows you to raise the height of your rear wing that is on a 911. prior to this thread i would have taken advantage of this ,raising the wing haven thought that raising it was a good thing since now the wing is in "cleaner" air making more downforce for a given degree of AOA. Or to put it differently i would be able to raise the maximal possible downforce
But is this true? mark points out that the wing at its porsche factory height is kind of taking advantage of the 12 degrees of roof line air flow that allows you to set the angle of incidence lower but achieve a better AOA. i am not saying this exactly right but you get the point . is raising the wing one of those things that sound intuitively right but in fact not advantageous . are you better off just leveling it a bit where it is now and just add a gurney flap?
thanks
But is this true? mark points out that the wing at its porsche factory height is kind of taking advantage of the 12 degrees of roof line air flow that allows you to set the angle of incidence lower but achieve a better AOA. i am not saying this exactly right but you get the point . is raising the wing one of those things that sound intuitively right but in fact not advantageous . are you better off just leveling it a bit where it is now and just add a gurney flap?
thanks
Complicated.
http://www.fem.unicamp.br/~phoenics/...304.092016.pdf
Figure 6 on Page 38.
For a sedan-style car, downforce is maximized when the gap between the wing and the body is about 0.8x the chord. That's really low! Put the wing higher and the downforce drops - a lot.
What I don't know is whether this is due to some weird interaction with the bodywork, or whether it's simply because the air is traveling downwards at a steeper angle close to the body, so lowering the wing effectively increases its AoA.
http://www.fem.unicamp.br/~phoenics/...304.092016.pdf
Figure 6 on Page 38.
For a sedan-style car, downforce is maximized when the gap between the wing and the body is about 0.8x the chord. That's really low! Put the wing higher and the downforce drops - a lot.
What I don't know is whether this is due to some weird interaction with the bodywork, or whether it's simply because the air is traveling downwards at a steeper angle close to the body, so lowering the wing effectively increases its AoA.
as far as the race car with underbody air flow designs, that's an entirely different set of circumstances.... effecting the flows from the rear of the car will dramatically effect downforce. we don't have cars that look like that, so its not really applicable to us.
I think its a little bit of both. if a cord of the wing is 13" , that's still a height of 11" or so. I agree, still pretty low. But I think the effects of wing height would be a related to air flow characteristics of the car. the net of this, is that you probably want the wing high enough to in the sweet spot of the flow deflection, without seeing much turbulence.
Aero has progressed a Loooooong way in 20 years when that was published. Not saying he's therefore incorrect, but I'd be willing to bet that there is more recent evidence to suggest that you don't have to place a wing so close to the rear of the car as pictured. That gives very little room for the underside of the wing to work properly and that is just as important if not moreso than the top.
