Quote:
Originally Posted by fjasper
So the VGs will tend to (through energizing the boundary layer) help the airflow remain attached. If attached airflow will allow a reduction in drag, greater than the increase in drag of the VGs themselves, there will be a net decrease in drag. However, it is not at all clear that the reduction in form/pressure drag is likely to be greater than the increase in parasitic drag.
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That's essentially what a VG does - whatever it's being put on :
bending the airflow and keeping airflow attached, where it would otherwise separate.
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.
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.