Aerodynamics of a bug

[oasis]

Nice touch with exhaust exit.

[cpgn0805]

In Perú we use for 110 Mph this 2

bumper and in front the windshield (trasnparent)

http://groups.msn.com/vwclubdelperu/starosamayo2005.msnw?action=ShowPhoto&PhotoID=4517

http://groups.msn.com/vwclubdelperu/starosamayo2005.msnw?action=ShowPhoto&PhotoID=4521

http://groups.msn.com/vwclubdelperu/starosamayo2005.msnw?action=ShowPhoto&PhotoID=4522

http://groups.msn.com/vwclubdelperu/starosamayo2005.msnw?action=ShowPhoto&PhotoID=4525

http://groups.msn.com/vwclubdelperu/starosamayo2005.msnw?action=ShowPhoto&PhotoID=4531

CARLOS PALOMINO

This thread has been dead for a while, but I thought I'd post this picture of airflow over a bug that I found.

[DORIGTT]

Find one of those for a Ghia and we're talkin!

[volkdent]

Wanted to raise this one from the dead:

Here's my thoughts on aero on a bug:

Green: downforce

Red: lift/resistance

Yellow lift/resistance zones



Thinking about slotting out this area of my fender:



How well do either of these work?:





Jason

[Wally]

The fender slotting is generally a good idea I think.
The Remmele bug also has extensive holes in the rear apron and rear fenders for letting out hot exhaust radiant heat as well as decreasing rear lift imo.

I suppose any rear roof device works, if only to distort the laminar flow there so lift is reduced.

Look at these race bugs for reference of things you can do. Racing brings out the best developments in people don't you agree?

[Humble]

Generally the reason you put vents in the fenders is to let the high pressure air out of the wheel well. Bug and non-bug alike all have this problem where high pressure high builds in the fender wells (because of the wheel openings, tire/air interaction, brake/radiator ducting) causing drag. Louvers on top for the fenders or holes in the back relieve the air pressure and if done right can even add down force or reduce drag.

I'm going to make similar cuts in the backs of my front fenders though possibly higher up. On the rears I haven't decided if or where I'll cut but I've considered hacking 4" off the bottom of the rear fenders so they didn't catch air. One of my sources of inspiration is the 997 turbo, with the larger rear fender vents and I thought about something like that as well

I've been looking for one of those lip spoilers for the top of my car but I'm not sure who has them in stock. I'd like to put one one the race bug and decrease the angle of attack on the wing.

[evilC]

Originally Posted by volkdent

Wanted to raise this one from the dead:

Here's my thoughts on aero on a bug:

Green: downforce

Red: lift/resistance

Yellow lift/resistance zones



Thinking about slotting out this area of my fender:



How well do either of these work?:





Jason

Jason,

I think you will find that the area at the base of the screen will be a high pressure area (that is where most manufacturers put the cabin air intake) and there will be a high pressure area at the very front of the car with a low pressure area immediately behind it that usually equates to the front quarter of the nose. As regards the flow over the rear window, I did see some years ago a flow path photo that implied that the air hugged the body shape pretty closely. If so, that would not create a low pressure area as you suggest it would be closer to neutral although I am inclined to believe that this is actually a mildly high pressure zone given the shape of the venting immediately under the rear window. This area is where VW expect the engine to take its cooling air from and supply cool air to the carb. If it were low pressure then the fan and the carb would be fighting for breath. This logic is further enhanced by the use of engine cover wings and the siting of intercoolers.

The roof lip spoilers are there under normal circumstances to create a break in the laminar flow to induce a negative (i.e. below atmospheric) pressure bubble at the rear that in a beetle ought to cause lift and poor cooling unless say, air was ducted from below the floor pan to vent into the engine compartment and then into the low pressure air zone.

Whilst I have not seen many aerodynamic assessments/records for the bug I have for the 911 particularly the racing 935s etc, which in many respects is a squashed bug ( forgive the pun) and much of what I have said holds very true. there was some interesting work done on the 911 with regards to the effect of the wings that were hugely extended beyond the main body that was not too dissimilar to the beetle. The aerodynamic findings was that drag was significantly reduced if the tops of the wings were extended rearwards as much as possible - connecting the front and rear wings showed the least drag. The wheel arch areas were indeed high pressure and rear venting was benefcial not least in brake cooling.

Clive

[Humble]

Jason, if you order one, double it for sure and I'll grab it off you. Thanks!