Aerodynamics of a bug

[beetle1303]

back home...
well, the best for me, even for a daily is to get a flat bottom for the pan. this would extend forward under the head (1303 talking) and expand toward the sides of the car, leaving exposed the wheel wells and the control arm mounts on the head. at the back it should stop at the torsion bar housing, leaving the rear exposed.

the even more extreme solution would be to conseal the tranny as well (bottom) and sides, trying to form two wells for the rear wheels. In order to cool the tranny, i would use naca ducts starting at the torsion housing and blowing through two eclipses at the sides of the tranny box towards the axle mounts.although there will be a need for a means of cooling the bottom and getting access to the drain plug and fill plug of the tranny.

That's where differencies start, depending on rear tire size, offset and engine/exhaust configuration, the size of the rear wheel wells will have to vary for the rest of items to fit.

best would be to fabricate a diffuser at the back, keeping the tire and part of the suspension to the outside of each side of the car, tranny in the middle, but narrowing both diffuser paths (extending away from the centreline) for the engine/exhaust combo to fit.

Depending on the angle of the diffuser the fender/rear apron/fender combo will have to be chopped in order to for a bit of a proper profile for the 2 diffuser paths.

This only some idea, based on physics, NOT calculations. it also provides a means of "hiding" all enhancements from others, and not increasing drag the biggest aero prob of the bug imo is the rear, where we got an engine aft of a huge well ( where the tranny sits) and two wings that perform in a "parachute way" for the car

In the end it comes to the owner to decide which way and how far to go...

Chris

[volkdent]

Just wanted to add this link for searches:

Bug Aerodynamics

Jason

[Gerrelt]

Thanx Jason for posting the link here!

I made my own Roof Spoiler that's attached to the rear window rubber:






See this article on how I made it: Creating a Roof Spoiler.

[volkdent]

That turned out great, that was my first choice as it is very subtle. I decided to go with the roof spoiler however because I fear that by that far back on a bug the lift is already quite considerable, the roof spoiler breaks up the laminar flow about 8 inches more toward the front.

How did you come up with the angle of the lip?

Jason

[Gerrelt]

Thanks, Jason,

A guy who was into gliding (airplanes without engine), told me that everything above 12 degrees becomes an obstruction, while 12 degrees and lower is a deflector.

I don't know if it also applies to cars, but it turned out to be a nice angle.

Regarding roofspoiler placement:
I think a small roofspoiler further up front equals a bigger spoiler further back.
But it also depends on the speed you drive, the faster you go, the bigger the spoiler must be.
But I am no aerodynamics engineer...

Greetings,
Gerrelt.

[Oldskool1303]

Nice rear spoiler Gerrelt.
I also had the same idea as Gerrelt, but never finished it. It was slightly bigger with the same mounting concept.

[Gerrelt]

Thanx Oldskool1303!

Yours would have been great too. It's got a more race-track look, more extreme.

[volkdent]

Originally Posted by Oldskool1303

Nice rear spoiler Gerrelt.
I also had the same idea as Gerrelt, but never finished it. It was slightly bigger with the same mounting concept.

I really like this, it would probably work pretty well, especially for how unobtrusively mounted it is. It makes a lot of sense to me not to bolt through unless you have to.

Jason

[Steve C]

Originally Posted by beetle1303

prob of the bug imo is the rear, where we got an engine aft of a huge well ( where the tranny sits) and two wings that perform in a "parachute way" for the carChris

Hi

I was driving my sons 1303 on a freeway today and I was thinking of this subject, is that weird?

Anyway I wondered what the affect would be on the "Parachute" area when you run a non air cooled motor, Subaru etc which has no sealing around the engine to body area, the otherwise trapped air would be able to escape through vents in the engine lid or the under rear window vents.

Steve

[Humble]

I think everyone's seen my aero by now, hard to miss...



Large vents in the front fenders seem to help a bit but I won't know for sure until I take it to a race track. The rear wing is almost necessary above 120, and can be felt as low as 50-60mph. I've also trimmed up the rear fenders to help them air out a bit as well. Currently I'm working on front aero which is not present and the bug understeers as a result. With the airdam and splitter in place the balance should be a lot better and I'll be able to dial in the rear wing properly.

For street use something above the rear window is best. A small strip like carbon joe did but a little bit taller, 2.5"-3" from drip rail to drip rail, would be ideal. Vents in the top of the front fenders might work for the street but I don't think they will be as effective, however they won't ruin the paint on your rear fenders.

[Jadewombat]

Originally Posted by Humble

I think everyone's seen my aero by now, hard to miss...



Large vents in the front fenders seem to help a bit but I won't know for sure until I take it to a race track. The rear wing is almost necessary above 120, and can be felt as low as 50-60mph. I've also trimmed up the rear fenders to help them air out a bit as well.

How did you decide to put the vents there, vs. like along the rear near the bottom of the fender, or the middle or ? Just wondering if you did some pressure readings in the fender beforehand or if this is a known trapped area of air along the inside near where the fender bolts to the body.

I ordered a punch and flare tool to do some holes on the fenders on my bug (autocross car).