Patrick, it's aerodynamics basic stuff. It is a lift vector which I have broken down into its components in the vertical and horizontal directions. Your statement above shows you have a few misconceptions about aerodynamics.
I am responding to you in case some lurker shows up and thinks that your somehow right, and I'm probably wrong.
Your “Stalled Wing” is not a fair comparison, and, your statement that it has very high drag is not quite correct. The wing, in fact, has its highest drag just before it stalls, that's what is keeping the airplane aloft. When the flow detaches from the wing in its stalled state, the low pressure area drops dramatically, the lift goes away, The Dynamically Created Low Pressure Area No Longer Exists. Think long and hard about that, if you don't understand wing theory, read up on it, cause it directly pertains to the situation at hand with this Beetle.
Of course the wing is a high drag shape when it is being shoved through the air bottom first, just like plywood, or anything large and flat.
The real stretch for you to understand is that the low pressure created behind a moving vehicle CAN NOT BE ELIMINATED! It is a 2 sided coin we're dealt here, the high pressure created in the front of your car has a corresponding low pressure behind it. There is no getting around it. We can only try to minimize it as much as possible by striving to shape our cars as close to the aerodynamic ideal as possible.
The flat area behind a car is not always a turbulent, drag producing thing. You have that all confused. If the air detaches cleanly, that's the best we can hope for, short of building full boat tails on all our cars.
What is happening on the VW Beetle back side is that flow IS remaining attached all the way down its backside. This is because the shape is totally smooth with no breaks in the curve from the bottom of the front windshield all the way to the bottom of the trunk. The website where the flow diagrams in Post 1 were retrieved from show the “Raw data” in the form of tuft tested VW’s, the air flow is doing what's depicted in that diagram. Now once the air goes past the top of the rear window, it is headed down really fast, this is creating a substantial amount of dynamic low pressure, that is what I depicted in my drawing. Since the area of low pressure is at an angle going down the back, the force being felt on the car is perpendicular to it. That is why I broke it down into it's vertical and horizontal components to make it easier to understand.
It is not always good to maintain attached airflow once our cars rear curve gets beyond the ideal arrow shape, you are better off letting it detach and creating what is essentially a dead air space behind our cars. Just cause it's detached and still above the back of the car does not make it turbulent. I have a pickup truck with big ol side rearview mirrors on it, when I put my hand close to the mirror in the air bubble formed behind there, my hand is not buffeting about wildly from the turbulent air, same thing on the back of a car, the air just puffs about a bit, no huge drag creation.
Do you think this car is creating a huge amount of drag behind it??
The problem with detached airflow is when it happens in an uncontrolled fashion over a large area of the back of a car, this creates all sorts of shredding, turbulence, and vortex's which create the drag. This is in fact happening at the trunk area on the Beetle which is probably another reason for the drag.
And lastly. Here is a VW Factory Option for the turbo Beetle.
Hmmmmmm.