Lonestar GP - 11 June 2009 05:24 PM

Which of the two makes less wake behind the car? I would assume tunnels, but wasn't sure.

The wake from a racing wing is very different than the wake from a "true ground effects tunnel" (one that starts forward of the drivers hips).
the wing- has a wake from not only the wing/endplate assembly that create vortices at the rearward corners, it also has a gurney lip that will cause a wake that swirls towards the ground across the entire back of the wing.
Tunnels- have wakes that expand upward get caught in the wings wake and forced downward and create large side voritces which are influenced by the body and tire turbulence.
The wake behind a ground effects/winged car is much larger in size than just a winged car, and can be much easier to draft than just a winged flat bottom car.
In the years that F1 had full ground effects were the years that most recorded passes existed. To be fair this was also before carbon brake rotors and pads were commonplace as well.
The common mistake in belief is that ground effect tunnels themselves produce downforce. Someone mentioned 60% of downforce from tunnels. Actually in real world use, a tunnel on a car without any wings and just the tunnels WILL NOT produce the same 60% downforce number that is being claimed.
Tunnels reduce underbody air pressures, and ALLOW a wing to have greater downforce ability. It is a wing that produces greater amounts of downforce when a tunnel is present, not the other way around. This true even with sliders sealing the sides of the tunnel to the ground...

TURN8 - 06 December 2009 03:55 AM

Just a note, Mario said that the biggest problem they had with the functioning of the Lotus 78/79 was center of pressure travel in the tunnels. The lowest pressure area would move rearward in the tunnels the faster the car went, raising the nose and makeing it very unstable at high speed.

I could have told them this would happen if they had asked. If the picture in this link is correct, then one would expect an increase in pressure on the front side and a decrease in pressure on the rear side. Both of these effects would increase as the square of the speed.

http://www.symscape.com/blog/secrets_of_diffusers



First, ground effect for an airplane is entirely different than ground effect for a race car. For an airplane, ground effect begins at one half wing span elevation due to disruption of the wing tip vortex and increases as the wing gets closer to the ground. There is some debate about whether the wing creates a cushion with the ground or simply benefits from improved efficiency due to disruption of the tip vortex, but to the extent there is a cushion, it can only lift and that is not good for a race car.

An inverted aircraft wing held close to the ground is not a good configuration for downforce. The leading edge will create an increase in pressure due to this cushion effect of trapping the air. If you look at the leading edge of the inverted wing in the picture above, it is clear that there is a decreasing clearance with the ground and this area is trapping air against the ground and creating pressure which causes lift. It seems completely understandable to me that the car would experience increased lift on the front and increasing down force on the rear as it speeds up. From the picture, it seems that the point of minimum clearance is under the roll bar. This would be the point of maximum velocity. Pressure would build in front of this point and pressure would decrease from this point rearward.