Sylmar Hang Gliding Association

http://www.northwing.com/freedom-hang-glider.htm

If you go to that link and click
"Streamline Crossbar Fairings"

you can see a photo of it. I heard about this design concept but have never actually seen it. I wonder if it makes much difference in the glide ratio.

dhmartens wrote:...........I heard about this design concept but have never actually seen it. I wonder if it makes much difference in the glide ratio.........

My guess is that it either makes little difference or actually makes the performance worse. The fairing in that photo is not only a poor streamline section but is angled so steeply against the true airflow out toward the leading edge that it may induce severe airflow separation that's worse than a bare tube. The fairing needs to have a twist that keeps it parallel with the under-surface at every point from keel to LE junction. If I ever have the time and energy I will make one that does this. At 25 mph a bare crossbar produces roughly 3# of drag. That's roughly equal to one point of glide angle. A properly designed fairing can reduce that drag to under 1/2#. That's significant.

I wonder if the fairing is attached to the crossbar or if it can rotate freely so to alter its pitch by it self to find the least drag. Worst case it might start spinning around the crossbar though. It might be used as a flap in its down position, but a flap in the middle of a wing?? That might be usable in a super restricted LZ. I wonder why they don't make a faired carbon crossbar, other than the additional $4,000 to the price of the glider. Also does it add any lift to the glider like a biplane.

Take this with a large grain of salt. It's not my area of expertise.

I had a conversation with a hang glider pilot / sailplane pilot / Aerospace Engineer about just this topic. He has extensive experience in this area (and owns a Falcon). He claims it would be hard to make it worse than a round section. Almost the worst of the simple shapes. Especially at speed.

On the other hand, he also said that the under-camber was even worse than the exposed x-bar. At least on a Falcon. Essentially, above some speed (low-30's? High 20's? I can no longer remember.) separation occurs on the undersurface, and from then on drag rises dramatically. Even a small improvement in extending double surface should make a big difference. Maybe that's the real improvement going from the Falcon to the Freedom?