>These look different than anything I've ever seen on any r/c sailplane - >or for that matter, anything else that has wings! What's with that >sharp edge of the front? And what's the deal with that flat surface? >The flat part is on the top of one airfoil and it's on the bottom >of the other - not that there's anything wrong with that! The sharp LE acts as a turbulator. At min sink trim, the flow ideally stagnates just under the LE, and curls around the sharp edge as it goes up and over the top. At high speed in the launch, the flow ideally stagnates right on the sharp edge which "turns off" the turbulating action. The geometry has to be just right for both flight conditions to work well. The approach taken by most serious IHLG fliers is systematic trial and error via prolific building. These airfoils are extremely difficult to design the "modern" way via computation, since the turbulating action is impossible to predict reliably, and it depends on lot on the construction details. Note that their Reynolds numbers are much lower than on RCHLG's, so don't get any funny ideas! :-) The flat facet on the bottom surface serves no purpose other than provide some "LE upsweep" which we know is essential for low drag at launch. I think he'd be a bit better off if the facet was rounded off and blended smoothly with the flat bottom surface. Ron Wittman's record-holding IHLG "Supersweep" had such a rounded upsweep. FWIW, he got 90 seconds with a conventional throw. 22 in span, 67 in^2 area, about 24g (1.8 oz/ft^2). - Mark Drela RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
