Quote:
Originally Posted by kach22i
The trailing wake in all examples given starts at the top of the rear window.
From that point we have several options;
1. Roof spoiler, creates vortex which eventually manages to pull the flow downward in a more controlled manner.
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That sounds like a "vortex generator", which may induce more drag than it reduces. My understanding of the roof spoiler is to provide a sharper cutoff to the airflow to reduce some of the drag caused by air partially detaching along the steeper back slope. By detaching the air completely you still have the full drag of the entire frontal area.
Quote:
Originally Posted by kach22i
2. Plane above the window (should tilt down 10 degrees but is shown flat) which extends the length of the car. A longer car should move through the air better, but with some additional surface drag. This is similar to the aero-mods many people are doing in this forum.
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Otherwise known as a Kamm back, and
if long enough makes a huge difference.
Quote:
Originally Posted by kach22i
3. A flat plane, marketed as a wing, secured tight to the body below the rear window, and completely out of any known air flow pattern. The pattern we do know about is turbulent and full of drag.
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Ernie Rogers did a flat spoiler at the window base on his New Beetle and demonstrated a Cd reduced from 0.39 to 0.30, similar if not slightly better than the VW Golf.