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Originally Posted by euromodder
Looking at what gliders use - zig-zag tape and turbulator tape - all VGs I've seen here are way too big, too tall, and as a result, too draggy despite there being too few of them.
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Apples & oranges.
Gliders can use low profile VG's and tapes because they are carefully designed to maintain laminar flow much further back along the vehicle/wings, so the boundary layer thickness is likely very small where they're applied.
On the other hand, flow is turbulent much earlier on typical automobiles., so at the locations where VG's have been placed by OEM's, the boundary layer thickness is in the neighbourhood of tens of millimeters thick (~30 mm at the rear roof area, according to Mitsu, if I recall).
A VG needs to extend through a significant portion of the boundary layer to work, thus their size. Mitsu tested several heights (15-25 mm) for the EVO application.
http://www.mitsubishi-motors.com/cor...004/16E_03.pdf
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Though he didn't see a reduction in fuel consumption, when MetroMPG tested a few of the big AirTab VGs, they did smooth the airflow over the rear window.
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The key point is: the difference they made to fuel consumption was undetectable in A-B-A testing.
The deflector on this Gremlin would also "smooth" the airflow over the rear window. And it would increase net drag.
