john smith wrote:
I remember 20 or so years ago I asked some engineers from the Columbus
Ohio North American plant about vortex generators.
Their reply was that vortex generators are used to fix a problem with
the original design found after the aircraft entered service.


VGs were traditionally used as a band aid to correct the effects of flow
separation, especially in supersonic flight, and usually just ahead of
control surfaces.

The use of VGs as a STOL device is more recent development when some
bright light discovered that they increased stalling AOA with almost no
increase in cruise drag. They have become a sort or poor man's LE
slat, giving 1/3 to 1/2 the AOA increase a slat gives, or about .3 to .5
increase in Clmax.

Garrison also had a great article once about how winglets work. It's
the only time I've seen them explained properly, in that they harness
energy in the wing tip circulation to create thrust that is surplus to
the winglet's drag when operating at high L/D, as airliners do when
cruising at 35000 ft. The simply create a lift vector that is angled
inboard and forward like the sail of a boat. Which is why they are
sometimes called "tip sails".

John