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rsa rsa is offline
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Wing Aerodynamics

I saw this the other day in a post and wanted to get comments on the effect of this modification. I have not seen this configuration before. It also has a gurney lip across the back. It seems that it would force more air above and below the wing. Does the air flow underneath help reduce drag while the lip adds more downforce? Thanks.

77 911s
Old 10-17-2005, 12:57 PM
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Bill Verburg's Avatar
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Never seen that before, I believe that the purpose of the end plates is to control turbulence at the ends, it looks to be shaped to speed up air flow under the ends of the tail which will create a lower pressure area thus increasing down force or at the very least decreasing lift(probably the former)

Any time you reduce turbulence you are automatically reducing drag.
Bill Verburg
'76 Carrera 3.6RS(nee C3/hotrod), '95 993RS/CS(clone)
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Old 10-17-2005, 07:43 PM
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I agree with RSA and Bill. The angle of the end plates make it look like they are trying to direct the airflow around the sides of the car and onto the sides of the wing. The wing will make downforce if it has airflow over the top and bottom. What makes all the lift on the car in the first place is the rounded top. To get rid of this lift, a spoiler is put at the back, or on the engine lid, and this causes the airflow going over the roof to separate earlier, and not follow the contour of the rear window. This creates turbulence, and drag, but also reduces the lift. It also creates a high pressure area at the back window and engine cover. Thats why the flush mounted engine cover air inlet can suck in air.

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Old 10-17-2005, 08:23 PM
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Wing tip vortices. Higher pressure air spills from the top outside edges of the wing seeking the lower pressure found at the underside of the wing.
With airplanes, especially the big heavy 747's this becomes a mini horizontal tornado powerful enough to roll a smaller aircraft over if it gets into it. That's why aircraft are separated by a mile or two on landing. Gives the turbulence a chance to move and die down.
The spillover of the higher pressure air on top of the Porsche wing is blocked by the end plates and directed onto the Gurney flap increasing down force with a slight increase in drag.
However the angle of the end plates to the forward motion would introduce some drag and turbulence of its own.
I would like to see the end plates parallel with the direction of travel.
I'm not a Aerodynamicist, but I play one on my computer.
'76 911S 2.7, webers, solex cams, JE pistons, '74 exhaust, 23 & 28 torsion bars, 930 calipers & rotors, Hoosiers on 8's & 9's.
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Old 10-17-2005, 10:30 PM
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On an airplane or bird wing, air tends to flow longitudianally along the wing. At the tip that air smacks into the airflow that is normal to the wing. Plates are often put on airplane wings to stop that flow. The longitudianl flow has several bad effects, including turbulence at the ends as well as wing tip vortices. I suspect that this is an idea in part like the multiple small plates on aircraft wings. Birds have a more advanced way of dealing with the whole problem.

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Old 10-17-2005, 10:36 PM
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