by Rick Masters » Wed Apr 15, 2015 1:10 pm
Yeah, but it's sad that Eddie Paul thinks I'm putting him down. We need to be able to discuss technology without getting twisted up in personality issues. In such a debate, one assertion on technology needs to be met with another on technology. My comments on the Whitney Port-a-Wing were not a criticism of Eddie Paul - unlike his criticism of me. I have a lot of respect for all the early designers. My view throughout my flying career was that the designer's responsibility ended at the point where your feet left the ground. After that, it was all on you. We were all test pilots. Anyone who didn't understand that was a fool. And you were expected, even obligated, to report everything you learned or suspected to anyone who was interested. This continual feedback drove the evolution of the sport.
My inherent dislike of the Port-a-Wing is not based on any experience with the wing. I have never seen one. I do remember an awful lot of pilots reminiscing and panning the wing when I was learning to fly hang gliders in the late 1970s. But in those years we were focused on learning to thermal and make the great leap to cross-country and serious inland turbulence. A robust airframe and a performance sail with no divergent tendencies was the Holy Grail. The idea of cable leading edges in rough air was not something to be contemplated. Cables serve a purpose only in tension. Tubing provides rigidity, compression and tension, all at the same time. If I'm going over the falls, the hang glider I'm flying is going to have rigid leading edges.
But maybe Eddie has a point that he became a whipping boy for all of the inadequate hang gliders of that era. I do not have data on the Whitney Port-a-Wing so all is conjecture. A friend of mine who flew at Playa del Ray in the old days saw Eddie flying the Whitney Port-a-Wing on several occasions. He noted that Eddie would get more altitude than anyone else. And he and his friends were jealous that Eddie could stuff the wing in a back pack, hike back to his car and toss it in the back seat. Maybe the Port-a-Wing, like a paraglider, was suitable for the laminar air of the beach. The problem for Eddie's wing and paragliders, too, is that some pilots get bored with that beach stuff and want to go inland for a little rock-and-roll. That's where most soaring parachutists die, inland, when their sails lose their aerodynamic shape.
Still, a basic tenet of stress analysis is that if you change one element under load in a closed system, the stress is going to transfer somewhere else. And when you make a design more complex, you introduce additional points of potential failure and unknowns and, as has often proved the kicker, unknown unknowns. If you wish to make a cable leading edge hang glider robust enough to survive turbulence, you will need to at least strengthen the crossbar and possibly add more cable bracing. But what tension would be needed to prevent the leading edge from bowing down during inversion or dive recovery? The added stress transfers to the keel and cross bar. The analysis quickly gets more complex than a simple conventional airframe and the unknowns, I suspect, demand an empirical test, anyway. The end result may be a complex, cable rich hang glider that weighs as much as a conventional design - so what's the point? The engineering maxim KISS (Keep It Simple, Stupid) comes in play at this point and, bingo, we arrive in a present without cable leading edge hang gliders.
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