Ben,

Thanks for bringing some authoritative information to the discussion.

One thing I find surprising from Hoerner is the conclusion that the wing tip can be more important than planform for performance. What makes this less surprising is that this analysis seems to be limited to the case of low aspect ratio, which is actually a primary characteristic of planform. So Hoerner's statement seems to be that, once you have decided you need a low aspect ratio, the tip shape can become more important. To the extent that the tip shape can increase the vortex span, this is not too surprising, since a small increase in vortex span would be a bigger improvement for a short span wing than for a long span wing. It's not clear from the context, but I am curious which flight regimes are being considered in his conclusion. Since induced drag goes up in proportion to the square of CL, but goes down proportionally with AR, it would seem that even a low AR wing would be concerned with induced drag mainly at high CL. High CL conditions are things like takeoff, landing, and pylon-like turns. We don't much care about a little induced drag for landing, but it would be nice to reduce it for takeoff, if power is limited. For 'sport flying', induced drag is not a concern.

From Hoerner's first paragraph above, I see that my preferred round tip is indeed the worst choice for induced drag, which surprises me a little. For a wing of typical AR, I still tend to think that it would outperform a square tip in terms of overall drag. It would seem that a sharp tip might be best of both worlds. This is pretty much what a Hoerner tip is. No coincidence, I suppose. I did do some more looking around on the web, and I can't find any source that shows test results regarding wing tip shapes, apart from winglets. If Hoerner's book, which is a little expensive for me, has results from wind tunnel tests, I'd be interested to see a summary.

Thanks,

banktoturn