Aerodynamics of a bug

[beetle1303]

Hi everyone, im back and about to leave again.. (I'll just be honest, i like it on the countryside with a new engine in my bug...)

Did a tiny bit of research thought...
most importantly

the air cooling the brakes is the air flowing under the car.

This is true for every vehicle that has enough ground clearance ( us for example). the opposite is true for purposely built track cars (i.e lmp class, gt2/3, and road going versions such as the radical sr3 etc)
Imagine top view of the car and the front at the top. the air goes under the front valance/splitter, under the front section (along the front wheel wells) and then it gets sucked outwards each side, due to the vortices created by the rotating wheel. Going super low requires another means of providing the brake disks of cooling air ( naca ducts on the bottom of the front splitter/ air intakes on the front surface of the car). In plain words the wheel works as a "fan" and sucks air out through its self (weird wheel covers on 934/5 P cars etc)

Jadewombat: if I understand your testing correctly there is a possibility that the positive value that you get is due to the flow reduction caused by the louvres on the front valance. Sounds weird doesn't it?? The louvres actually by letting air flow through them act like a "see through" fabric...its there supposedly covering up something but actually you can see through...
but what you see is a differentiated image of the original. If you had the normal front valance maybe you could still gain negative values (due to high turbulence) in the same area...

Now as for the rear diffuser discussion, aartjan thank you very much for the pics, on the new cup car we get a very nice idea for a diffuser.
IMO that would be, fabricate a symmetrical 4-1 exhaust system that fits and has EQUAL primary tube lengths.
Chop the rear part of the rear fenders and enclose the exhaust manifold within the diffuser.ie place two vertical pieces (one each side) somewhere between the rear upper shock mount and the inside fender wheel well (where the Z bar attaches on swing axle beetles).

I strongly believe that much is to be achieved by splitting most of the air around the engine (still providing airflow to the sump) and then expanding the air flow in a sideway's manner since the engine sits in the middle


Sooooooooooorrrryyyyyy for the long post.
I hope it makes sense

Chris

[beetle1303]

have a look at this

http://www.youtube.com/watch?v=uMEYe...BDD1ACE&lf=BFp

Chris

[Jadewombat]

Originally Posted by beetle1303

Did a tiny bit of research thought...
most importantly

the air cooling the brakes is the air flowing under the car.

This is true for every vehicle that has enough ground clearance ( us for example). the opposite is true for purposely built track cars (i.e lmp class, gt2/3, and road going versions such as the radical sr3 etc)
Imagine top view of the car and the front at the top. the air goes under the front valance/splitter, under the front section (along the front wheel wells) and then it gets sucked outwards each side, due to the vortices created by the rotating wheel. Going super low requires another means of providing the brake disks of cooling air ( naca ducts on the bottom of the front splitter/ air intakes on the front surface of the car). In plain words the wheel works as a "fan" and sucks air out through its self (weird wheel covers on 934/5 P cars etc)

Jadewombat: if I understand your testing correctly there is a possibility that the positive value that you get is due to the flow reduction caused by the louvres on the front valance. Sounds weird doesn't it?? The louvres actually by letting air flow through them act like a "see through" fabric...its there supposedly covering up something but actually you can see through...
but what you see is a differentiated image of the original. If you had the normal front valance maybe you could still gain negative values (due to high turbulence) in the same area...

Chris

Well, did some more testing. I put my off-road and snow tires on the car as I'm having the five spokes updated with semi-slicks for this weekend. Anyhoo, I decided to test with the louvers completely blocked off and see what happened. Mind you, this was different than with the 215/55 16 sticky street tires I had before and the rallycross tires put the car higher off the ground. Even so:

-Louvers blocked off pulled -1" of vacuum under the car just behind the front sway bar
-Open louvers was not even registering under the car " " " (I'm guessing this was because I'm higher off the ground than before when I tested)

So, what next I thought to improve the front area?? High positive pressure in that are behind the louvers or no pressure and send all the air down and below the car. My first thought is sending that air below the car will cause lift, but it may be smoothing out airflow though reducing drag? I've decided to split the difference and installed some screen material just behind the louvers to let some of the air pass through.



In case you're wondering why I don't just install an air dam, my driveway is way too steep. Will retest once I get the front end aligned. I also drilled the inner edge of the fenders, trying to shave as much weight as I can and hopefully vent more of that trapped air out from under the fenders.

[ace_bug]

Thats what i'm doing in the back of my front fenders.


Uploaded with ImageShack.us

[Jadewombat]

I tested it once more:

-Screen material behind louvers yields 3/8" of negative vacuum under the car

Took it out to the autocross today, did pretty well. It was my first time on semi-slicks which made the car feel quite different. Just trying to forge ahead and do any more low-cost aero. tricks to go faster then look at modifying the engine and trans.




One thing I also noticed looking at the front of my Audi RS4 (mine's black, I borrowed this picture below), there's these short deflectors almost like mudflaps on the front to counter the drag of the front tires. Gives me an idea...

[Gerrelt]

Yes, those are called "wheel deflectors" or "wheel spats". I am planning to make a pair too.

These things can be found more and more on modern cars. Not only at the front wheels, but also at the rear.
I want to make a set for the rear wheels.
It can't be hard to make, it's just a piece of flat plastic/fibreglass that sits just in front of the wheels.
I only wonder how to determine the correct size and position in relation to the wheel..

[al_kaholik]

Gerrelt - surely on the front the Kamei does the job of this?

[Gerrelt]

Yes, you are right. That's why I want to create a set for the rear..

[al_kaholik]

Just checking that I wasn't missing something!

[Jadewombat]

Is it worth it going to flat taillights?

http://www.ebay.com/itm/Flat-Tail-Li...ht_1425wt_1185

[al_kaholik]

Possibly if you want it to look hideous... They ain't for me regardless of what they do!

[Jadewombat]

I guess I asked the wrong question, I don't care about the style, etc. but along the lines of:



Does the taper of the taillights rolling off the back of the fender make an area of dead air? Would smoothing this out to follow the contour of the rear fenders be better for flow/drag or would it not matter? Plus it looks like the flat ones are a little bit lighter than the stock ones.

[Gerrelt]

I think it doesn't matter anything. The rear lights are probably allready in a turbulent or low pressure area.

I don't like the look of the new beetle style rear lights.

I've grown quite fond of the elefants feet rear taillights. They have a really nice functional look.
I only wished they were a bit better build.

[Wally]

Originally Posted by Gerrelt

I've grown quite fond of the elefants feet rear taillights. They have a really nice functional look.
I only wished they were a bit better build.

+1 'Scheisskwalität'...
I have one taillight reflector housing that has two seperate departments and is a cast/mold alu-like material and very nice quality. Never could find another one though...

[Gerrelt]

Originally Posted by Wally

+1 'Scheisskwalität'...
I have one taillight reflector housing that has two seperate departments and is a cast/mold alu-like material and very nice quality. Never could find another one though...

Ah, thanx for posting that. I never new there was a "metal" version of these lights.

I think they are from the late model VW thing (181).

Do they look like this?: Link to samba add

The Thing got them in metal for sturdiness for going off-road, is my theory..

I want a set!