Quote:
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