Lorm From United States of America, joined Jun 2004, 409 posts, RR: 1 Posted (10 years 7 months 1 week 5 days 2 hours ago) and read 4777 times:
You've probably seen this photo that was added to the database recently. Quite an interesting wing. Don't think I've ever seen a wing like it, only other thing I could think of that looks vaguely similar, would be the bi-plane setup.
QantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 24
Reply 2, posted (10 years 7 months 1 week 4 days 20 hours ago) and read 4579 times:
I actually thought up that wing design myself, oblivious to the fact that it had already been tried, and asked about it on here a little while ago. The theory behind that sort of layout has to do with wingtip vortices and the reduction/weakening of them.
Wingtip vortices are generated at the tips of wings, and are big swirling airmasses which rotate up from the lower surface of the wing (higher pressure) to the upper surface of the wing (lower pressure) - as I'm sure you know already. You probably also know that these vortices increase drag ('induced drag') by basically deflecting the departing airstream down and thus 'tipping' the lift vector backwards; any backwards component of force on an aircraft is a drag.
So, how could the above design help? By eliminating wingtips altogether. If there are no wingtips, there's not much of a place for the aforementioned vortices to form. In theory that does sound pretty good, however in truth you're almost back to where you started. While there's no distinct tip, you still have the situation of higher pressure on the bottom-most surface and lower pressure on the top-most one (simply spread over two wing sections) - what's going to stop a much larger-scale vortex swirling up and around from the very bottom to the very top? Unfortunately, vortices would still exist.
It's probably the case, though, that what vortices do still exist are reasonably weaker. This is simply because the pressure differential remains the same - the vortices have the same "strength" - as with a normal configuration, but the distance they need to travel around the wing is greater. In that case, they should be "diffused" and weaker. So, that sort of layout could very well reduce induced drag to some degree in the end.
The question then lies in the magnitude of the drag reduction compared to added weight and other detracting factors...