Brian: Re your Post #22:
What keeps our blades from folding up in response to their own lift is not the rigidity of the (Bensen-style) hub bar, but rather the outward pull of centrifugal force. Cent. force* pulls out at right angles to the rotor's rotational axis, while lift pulls up; the combination of the two settles the blade into a coning angle of a few degrees only. It doesn't matter if the blade is free to rise as much as it wants; unless RPM is lost catastrophically, it won't rise more than a few degrees because cent. force won't let it. There have been rotors with centered, but independent, flap hinges designed as you described. Chuck Beaty built one that looked like a giant door hinge, and some old helicopters had blade-root yokes somewhat like the one you're picturing.
If the flap hinge is not at 90 deg. to the blade's spanwise axis, then the hinge is said to have a "Delta three" offset. The A&S 18A uses some of that. It provides the 18A with an automatic reduction in collective pitch as the blades use up their stored rotational energy and slow down after a jump. They drop from helicopter pitch to gyro pitch.
Jim Mayfield is describing a different way of achieving the same effect as a Delta three offset, while still employing a rigid teeter bar and hinge: in either case, pitch-cone coupling is the result.
Fara, yes, I am concerned about low-G situations. And, yes, trikes and teetering-rotor helos and PPCs have issues with low G, too. (BTW, trikes may have been so named to distinguish them from the original foot-launched powered hang gliders. Just a guess.) I don't know of any trikes or PPC's that have achieved STC, though. I don't know if one could pass.
But the situation with gyros and zero G (= zero disk AOA) is, in any event, unique. Our RRPM is variable (but not instantly), and is related to disk AOA. As you point out, loss of RRPM is a one-way street beyond a certain point. Most, if not all, gyro low-G crashes have clearly resulted from airframe instability (HTL, engine torque and/or low center of drag), which is preventable by design, but low RRPM is certainly another route to disaster.
My point is not that Bensen-style gyros are clearly and unavoidably uber-dangerous. Still, in discussing gyro safety, we shouldn't ignore the fact that these issues have not been explored systematically to see just where the safe edge IS, or how much better some other setup might be. This lack of knowledge is itself a risk factor: a "known unknown." Compare a C-172. It's pretty unlikely that any unexplored coffin corners are left in one of those.
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* No, it's not really a force; it's an inertial effect, but the difference doesn't matter here.