jlatorre wrote: ↑
Thu Jan 24, 2019 12:20 pm
mario wrote: ↑
Thu Jan 24, 2019 1:00 am
It was basically a Rogallo wing that had the crossbar extending out to the tips to create truncated tips
That rang a bell for me. Back in the 70s, Chandelle came out with the "Competition" glider, and one of its design features was a crossbar that attached toward the aft end of the leading edges. I think the idea was to reduce deflection at the rear of the spar. At any rate, the glider quickly earned a reputation for "adverse flight characteristics" and was at least part of the company's ultimate demise. Maybe there's somebody on the board who can give more details than this.
I remember the Chandelle Comp glider. What follows is all to the best of my memory, and the teachings of pilots I trusted . . . The leading edges were 18,' and the crossbars attached at 15' from the nose. Those skinny leading edges would flex upward in slow flight, creating a Cylindrical sail. (In theory, the glider would "fit" in flight on two large parallel cylinders, that had some overlap between the cylinders.) The Cylindrical variant of the Rogallo wing did
fly better, but did not handle very well. It did also fly slower than a Standard Rogallo. That much is the good news.
The bad news was that if the Chandelle Comp glider ever stalled or went weightless, the leading edges became straight again. The glider then became a fully stalled Standard Rogallo, and the nose dropped into a dive. Now there was little or no lift (so, no Cylindrical, and no airfoil shape to the sail), but only drag. With the drag on the sail, the leading edges then bowed inward
at the nose, not upward, which caused the wingtips to pivot outward. That pivot action pulled the trailing edge down flatter, creating a "down elevator" all across the wingspan. That "down elevator" caused the glider to dive steeper, faster, and steeper, until stopped by the ground. Weight shift by the pilot would have no effect on the dive. Luff lines (which were almost completely unknown, and not in common use then) might have caused the glider to recover from the dive. A modern HG parachute (which did not exist then, either) would have saved the day, if the glider was high enough to use one. We seldom flew high enough to use a parachute, in those days.
It was not long after that time when the Pitch-Testing truck was developed, and now all HGs are REQUIRED to pass the truck testing.
NONE of these problems would apply to Frank's new Puffin design, because the Puffin will have large and strong leading edge tubes, fixed ribs (so the airfoil can NOT collapse in a stall), and (ANTI-) luff lines, so the trailing edge can NOT get pulled downward even if the frame flexed at all.
We did pay a high price for the aerodynamics lessons 'way back when, but we have