Roof spoiler effectiveness

[effvee]

One day I'll have mine running. I hope it helps, my cay to hold the road.

I'm told the Remmele one does a good job, however I don't like the ideal of have something glued to my car, which add safety.

[beetle1303]

I feel the need to make smthng straight for the ease of everybody understanding:

Imagine, a wing mounted somewhere and air flowing through it. IF the wing's plate is flat (not the profile) ie is straight, like the ones in the pics in this post, the air leaving the trailing edge will flow straight, evenlt across the wing's width.

Vortices will be generated between the side plates and the wing's plate, and around the corners of the side plates. IE rule of thumb, vortices need edges, protrutions to be generated.

Eatoniashoprat,
you got it the other way round, lift is generated, by attached flow, or low pressure cavities...

Now, a lip may reduce local lift, and disrupt the attached air flow ( to the car's body), but how effective it will be depends on the angle of the lip, and its height,

effvee, am i silly asking or it is facing the front of your car???

Chris

[effvee]

Hi, its facing forward. I have seen many of us (including myself) trying to get it right. When I installed that lip (which is 1" or 25.4mm) height) my attempt is to force the air passing over the roof (heightest point on the roof) to not so much to cause drag, but rather push on the lip. I'm hoping for the force to aid in a down force, yes it will deflect upward, but push on the lip. I don't know what the out come will be, however I'm this works in con-junton with a front air dam. I did not like the ideal of have something glued on at 120mph weather it worked, worked good or just caused drag, go flying off and hit something. If I ever get that car running, I will post what it feels like at 120 going to Vegas.

Not only that, I heard somewhere that as air pass over the deck lid area at high speeds, there is lift of the rear deck lid, something like how a shirt lift up on the back of a motocycle rider. So I reversed louvered my deck lid to catch air and release it into the engine compartment and below the license plate.

[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