Ever notice that a lot of the newer commercial aircraft today have winglets?? They increase performance by reducing the wingtip vortices, a major component of drag produced by any wing.? I imagine that the increase in performance on a hang glider is next to nothing due to the slower speeds, but next to nothing is better than nothing when it comes to competition.? The quote about the US not benefiting may be due to the narrower nose angle versus the high-per gliders, which makes next to nothing closer to nothing.
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Winglets
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Danny Brotto
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Winglets...
Adding drag behind the center of pressure might server to dampen yaw oscillations which is what I think HG winglets actually accomplish. However increasing drag means lower L/D.
I sat in a winglet theory/design seminar at an SSA convention presented by Dr. Mark Maughmer, Penn State prof., aerodynamics, and winglet designer; a very interesting presentation. What I gathered from the presentations was that at high Reynolds numbers, winglets work well; think Boeing 747-400's. At lower Reynolds numbers, (think sailplane) they add about 1% to the performance up to some high speed where the added drag degrades performance. Hang gliders have lower even lower Reynolds numbers than sailplanes and Maughmer claims (side conversation I had with him) that on hang gliders, winglets are ineffective at improving performance.
Increasing span generally yields better performance improvements than vertical winglets. In practical terms, increasing span on a 747 would not allow it to fit in the standard sized piers (along side of another parked jet.) Sailplanes are flow in classes based on their wingspan; typically 15 meter (although there are other classes.) Increasing span would invalidate their competing is a particular class so winglets are a way to get that slight improvement and stay in class.
Winglets generally work by redirecting the tip vortex more inboard thereby reducing drag and increasing thrust. Again at relatively low Reynolds numbers like sailplanes, redirection of tip vortices put allow the ailerons to be more effective imparting better handling at low speeds (more air over the ailerons) and improving low speed performance (which is what one feels when flying a sailplane fitted w/ winglets.) Hang gliders don't have control surfaces and they have low Reynolds numbers. According to theory, winglets do not improve HG performance... but maybe they dampen yaw due to the increased drag behind the CP?. And on some gliders, they do look cool!
More information here:
http://www.mandhsoaring.com/articles/ostiv97.pdf
Let's go flying!
Danny Brotto
I sat in a winglet theory/design seminar at an SSA convention presented by Dr. Mark Maughmer, Penn State prof., aerodynamics, and winglet designer; a very interesting presentation. What I gathered from the presentations was that at high Reynolds numbers, winglets work well; think Boeing 747-400's. At lower Reynolds numbers, (think sailplane) they add about 1% to the performance up to some high speed where the added drag degrades performance. Hang gliders have lower even lower Reynolds numbers than sailplanes and Maughmer claims (side conversation I had with him) that on hang gliders, winglets are ineffective at improving performance.
Increasing span generally yields better performance improvements than vertical winglets. In practical terms, increasing span on a 747 would not allow it to fit in the standard sized piers (along side of another parked jet.) Sailplanes are flow in classes based on their wingspan; typically 15 meter (although there are other classes.) Increasing span would invalidate their competing is a particular class so winglets are a way to get that slight improvement and stay in class.
Winglets generally work by redirecting the tip vortex more inboard thereby reducing drag and increasing thrust. Again at relatively low Reynolds numbers like sailplanes, redirection of tip vortices put allow the ailerons to be more effective imparting better handling at low speeds (more air over the ailerons) and improving low speed performance (which is what one feels when flying a sailplane fitted w/ winglets.) Hang gliders don't have control surfaces and they have low Reynolds numbers. According to theory, winglets do not improve HG performance... but maybe they dampen yaw due to the increased drag behind the CP?. And on some gliders, they do look cool!
More information here:
http://www.mandhsoaring.com/articles/ostiv97.pdf
Let's go flying!
Danny Brotto