air trap
 

I was wondering I've heard that a large amount of lift comes from some air being traped behind under the fenders. Is this true?

See I've seen guys that have louvered the back sides of fender to try and help, some drag guys have ever gone as far as drilling holes in the back of the fenders.

So I was thinking has anyone thought about making a vent back there? Some thing that wouldn't only free up that traped air but possible use vanes to direct air upwards creating a small amount of down force?

Some thing in which you would cut a patterned out hole and rivet in a assembly of fiberglass (carbon fiber) vents and aluminum vanes?


thanks
rip

I have done some hobbywork on my verry rusty dump fenders

http://www.keversite.nl/fotoalbum/fo...2004234146.jpg

On my bug i will use fiberglass fenders... and I'm now verry doubting if I will make some openings in the fender or not.. (the future will tell)

p.s. the openings will not look like this above.. If I do it I make the vains on the inside of the fender, so nothing sticks out the fenders.

Greetings Wiebrand

As far as I have experienced: VERY TRUE!!

I have a turbocharged 1303 (standard fenders) and have recently done a run with the revlimiter on 6500 RPM (was 5700 RPM) which enabled a (theoratical) top speed of 240 km/h.
I originally upped the revlimiter to check if the 'impossible' setup with single springs and custom camshaft would be able to turn 6500 rpm without valve float.
Since I had no problems with valve float, I decided to see if it would still pull above 200 km/h and floored it in 5th gear. I was surprised how easily the engine revved up to the redline (the gearshift light came on) and I lifted.....

Then the **** hit the fan: I had the feeling of driving on ice, and had little to no control over the car (needed both lanes to keep it on the road)..... :eek:
Luckily the car stabilized at about 200 km/h and I carefully applied the brakes.
To be honest, I was scared ****less and I thank God that I survived this incedent.
IMO stock fenders create quite alot of lift and I think that caused the scary ride......
I don't know if louvering the fenders would help, but if you're planing on 200+ km/h (or less in a lightned bug), I'd sure as hell try it!

Grt. Robin

I think the problem you observed above 200km/h was due to the shape of the topside of the car. The way the air goes off the roof causes lift at the rear.
I'm sure you have seen the wings drag racers use, adding a small one completely eliminates the problems above 210km/h.