Roof spoiler effectiveness

[Wally]

I really like the deck-lid idea , but not so much the roof lip

[effvee]

Walter hi, well concerning the roof spoiler, I hope it works. If not, I'm down alot of labor and body work. Hay concerning the front spoiler, the one you modded from I beleive a Rabbit. How well did it work? I sure wish someone were to make a front spoiler some-watt less in width (ground clearence). I know the roof spoiler won't fly off though

[SilverBullet]

Anyone doing a flat plate under the car?

[effvee]

Hello, well the pan is pretty flat already. When I was in private pilot school, I was taught the concept of dirty air. Dirty air, consists of the dantance of the plane to the ground. While a plane is landing, half the width of its wing span, that ditance above ground; the air acts as a float or cushion. The VW pan being that close to the ground, will suffer the same effect. I think the best way is deflection (air dam, front spoiler) don't let it under the car as much as possible.

[Wally]

Originally Posted by effvee

Hey, concerning the front spoiler, the one you modded from I beleive a Rabbit. How well did it work?

It did look cool, but only worked a little compared to the Kamai front air dam.
Like you predicted, that really does work extremely well, even at lower speeds!

[beetle1303]

Effvee, great craftmanship. Im not trying to put you of, i like what u r trying to achieve. Im just giving you a different angle, playing a bit of devil's advocate...

considering the decklid, i have some hesitations... I think the effect will be comparable to just normally opening the decklid a bit (not stand offs), which is a real no, cos the hot air leaving the engine is getting trapped by the high speed air passing over the decklid thats gets turbulent, and because of the low pressure created by opening the decklid it gets drawn into the engine compartment. i wrote the above only after looking at the pics, and using basic thoughts. the other thought is that the air will just run along the inside of the decklid and escape through the lower louvres. If this happens it will be possible to "steal" some of the air going into the fan (stock) because of reversed louvre amount and positioning.

s for the metal lip, i belive it is a great idea, but i suspect that it will cause too much drag, and stress on your mechanicals to reach and sustain high speeds.

rule of thumb for cars aerodynamics/mechanicals relation.

A. Up to 80 km/h the engine's work is spent to overcome rolling resistance and friction. any speeds above that, the engine is working against the aerodynamic resistance caused by the vehicle's shape.

B. Aerodynamics start working at around 80 km/h depending on vehicle's shape and size (justifies point A) but only air flowing above the vehicle. A speeds over 120 km/h downforce starts to be generated. so the underside will play some role.

Effvee, according to the dirty air concept, this would happen if a beetle was lifted roughly at half of the average of front and rear track. but because every one going on the road is lower than that, it is more important to aid the venturi effect created between the road surface and the car's belly.

Also, very important air is not flowing around, above the car. the car pushes through the air, similarly the air passing under the car is considered static that then get disrupted by the vehicle, pressing it against the road (front splitter) and theen allowing the air to smouthly transist back to a more stable state through a flat bottm, preferably along with a diffuser at the back.

Sorry for the long post. god this gave me a headache...

Chris

[beetle1303]

forgot to add something...

huge front air dams with increase the stagnation area (it is considered mostly as a point) size. thats y i believe that instead of stopping the air getting under then car, it is more efficient to use it, directing it to places that will have more positive effect such as cooling

Chris

[effvee]

Hi Chris, hay I don't have any experience in this, just trying to get a safe car in the end. So I'll post in the end on how the results came out. I love this talk, due to it gives us all avenues of possibilities. Now back to the dirty air concept, I really believe deflecting as much air from under the car while considering the pan area and lite weight of the VW; need real consideration. The venturi effect, is really an issue for temperature and air speed causing a vacuum effect, but does not effect the under pan (in my opnion). Now I don't know: confused: but dips, bumps and the like will cause the care to need to get ride of the extra air of the rebound. My car (work in progress) has the rear window slits/and interior louvers altered. that means I removed the louvers behind the rear window slits. So as air in the area of the rear window rolls, it should cause a lift, but having the slits/interior louvers removed and reverse louvers applied; will still suck, but on what? I think the 28 blade fan will do fine for itself (normal type 1 fan). Also weather it sucks or blows, the engine tin, can be altered (for my application) to further aid in the lifting rear end issue. I have also alter my behind the seat area to accept my muffler there, so the tin can be drilled with lighting holes to aid in keeping the air moving along.

[oasis]

Before Kamei spoiler:


Two angles with Kamei spoiler:





When my 1302 was without the Kamei spoiler, I had a stock engine. I rarely went up to 70 MPH. It was an insecure feeling once I got to 65-70 MPH.

I did 110 MPH once since the Type IV upgrade with the front spoiler. Driving was much, much more secure. While driving over 90 is unusual for me on a daily basis, driving at 70 is not so unusual. The spoiler makes a big difference -- even around 18-wheelers.

The extra air for cooling is a noble idea but thus far I don't need it with a DTM cooling system.

I have no experience with a roof spoiler. I was considering one from Carbon Joe before he stopped production.