Bob Kuykendall wrote:
Hoo-yeah! I love the smell of snake oil in the morning!

Bob K.

Nothing new here. A Sport Aviation article, in the late 80s if I
recall, breathlessly told the story of a C-150 with identical wing tips,
back during days when Jack Cox's articles were uniformly uncritical puff
pieces (not sure if this particular article was written by Cox, it was
just that SA never reported real criticism of homebuilts back then). I
remember it had a fancy stars and stripes paint job. This C-150 had
those venetian blind thingys on the tips plus VGs and fences and was
supposedly capable of impossibly low stall speeds, which to the extent
that stall was reduced would have been a function of the VGs mainly.
The tip 'blinds" just looked ridiculous and speed limiting.

The problem with fancy wingtips is this: If they do anything to extract
benefit from tip vortices, they only do so when the wing is working
hard, at max L/D. So such a device MAY improve rate of climb or sink
rate. It won't have all that much effect on stall speed. At higher
speeds with low AOA they are just drag makers. Who is willing to give
up 15kts of cruise just to get an extra hundred FPM of climb? Thus such
things never appear in the real world in any great quantity.

Note that the only wingtip devices that actually do anything useful are
winglets, which generate some thrust from tip circulation that is more
than their drag, and this only when the wing is at max LD. As a result,
they are only used on two types of a/c in general; gliders and high
altitude cruisers like airliners and bizjets. Both do their thing at
close to max LD, the glider for obvious reasons and the airliner because
at 36000 ft it is operating at cruise effectively in the same indicated
speed regime and AOA as the glider at max LD. In both cases the
winglets are only there because their benefit is available at the
aircraft's intended cruising speed range.

Same applies to any other wing tip device that proposes to use tip
vortice energy.

JohnK