On Mon, 13 Mar 2006 15:55:21 +0000, Chris Wells
wrote:


I've seen a lot of discussion on this topic in radio-controlled plane
groups, and I've been working out winglet design on the r/c planes I've
built for years. I've also seen the results of tests done by
laboratories. (on the internet somewhere, hunt & I'm sure you'll find
them) I think it's pretty well established that upwards is better,
though a small projection on the bottom seems to be a good thing.
The way the tip transitions into the winglet is probably just as
important as the shape of the winglet itself. I've had several flying
wings that flew well without winglets or any vertical surfaces at all,
by shaping the tips. The stock wings, with squared-off tips, don't fly
well at all without the winglets.
Of course, if someone can provide evidence of an advantage for
downward-pointing tips (other than non-aeronautical reasons such as LG
convenience, such as on the Quickie) I'd like to see it.

Well, the XB-70 Valkyrie is the only example I can come up with at
the moment. Although the wing tips in this case were more for
increase lift, reduced drag and increased speed at sub-sonic and
supersonic speeds.

See: http://www.labiker.org/xb70.html#compression

Ron