[aerohead]

Originally Posted by Gerrelt

I think at the time they developed the beetle, the 1930-tees, aerodynamics was an upcoming science. And they didn't know what we now know today.
Add to this that the beetle was developed for a TOP speed of 100 km/h, aerodynamics at high speeds as we drive today wasn't interesting.
Yes, the VW beetle was one of the first cars that attempted a aerodynamic body. But if Dr. Porsche would develop the VW beetle today, with the knowledge we have now, I think he would have reconsidered the placement of the vents.



Those cars have a "sharp" edge at the end of the roof, so seperation is easier.
Look at figure 21.23 on page 143 of the book I posted earlier ( This one ).
That edge is a trick to get the airflow to seperate at the end of the roof.

The VW beetle roof is round, making it easier for the airflow to stay attached.



Ah, I think we're talking about two different things. Those vortices are one aspect of aerodynamics, what I am talking about is what Genta calls "streamlines in the symmetry plane".
Both contribute in aerodynamic drag.

I still think the wool tuft tells a valid story and the flow is attached. If the flow wasn't attached there, the wool tufts would be going all places, and not nicely in straight lines to the bottom.
The rear of the VW beetle is not steep enough to get the flow detached, creating lift and drag. It's the same effect what caused the Audi TT to be retrofitted with a spoiler on the rear.
The effect can be seen in this picture:

Up to 30 degrees the flow stays attached, steeper then that, the flow is detached.

Maybe we should agree to disagree.

Disagreement is healthy and I always learn.
I do have a smoke-flow wind tunnel image of a Beetle in Volkswagen's wind tunnel.The smoke is departing the body exactly where Mair predicts it would.It's at the backlights upper weatherstrip.
If you will put the AUDI TT,with its rear spoiler deployed under the Template,you will see the path that smoke follows from the point of separation back to re-attachment on top of the spoiler.The TT roofline is also too steep for attached flow.
When smoke is introduced only at the vehicle centerline it can appear that the flow is good when it is not.
With respect to the 30-degree fastback,flow will be attached along the centerline only,with attached longitudinal vortices on both sides.You can correct this by pushing the rear angle up to the Template as Hucho did with the Golf/Rabbit in the wind tunnel,scoring the lowest drag.
With respect to the tufts,their orientation is influenced by vortices which can only be revealed with smoke.Their
false-signal can lull us into mis-interpreting what is actually happening in the 3-D flow field around the vehicle.