Jim
That is interesting. It should have been obvious from the wingtip vortices
that there was a fair amount of pressure activity going on at the wingtip (says
a pilot, with plenty of hindsight :-))
I seem to remember that some wings have little strakes on the upper surface to
reduce spanwise flow; also that some aircraft with wingtip missile rails, like
the F5 and F16, can lose a bit of drag by the same effect as a winglet.
But then the F16 and F18 have vortices off the wing root rather than tip. I
always thought that that might be an interesting indicator of a more efficient
wing. When flying the Tornado and Jaguar often thought that the wingtip
vortices were cool, but I could have done without that extra drag, particularly
when "fighting".
Chris
On 10 Jan 2012, at 21:49, Jim Nichols wrote:
> He was also interested in boundary layer control, and modified a Super Cub
> with a perforated wing surface, to pump off the boundary layer. He was
> demonstrating this airplane to a British scientist when something went wrong
> at low altitude, and Gus was killed. This was many years ago, and I can't
> recall the fate of his companion.
>
> The tip winglet is something that should have been realized early on. With
> low pressure on the upper wing surface, and higher pressure beneath, it is
> not too hard to realize that these pressures will try to equalize at the
> tip, causing a tip vortex to form. The winglet minimizes the strength of
> the vortex, hence reducing drag. This was done for years by experimenters
> using tip plates to increase effective aspect ratio and reduce vorticity,
> but the winglet is a much more elegant solution.
--
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