<<I sometimes get a quite noticeable vibration on the ground with a gusting tailwind or in flight in turbulence which I attribute to the composite prop blades flexing.>>
Naaa. Come on now, why not fundamentals? Assume a wind from any quarter during runup. The result is a cyclical variation in AOA for each blade as the prop rotates, a well known issue and the reason we are taught to face directly into the wind for runups. I think the frequency of the cycle is (RPM x #blades)/60 = hz, but I reserve the right to think about it some more <g>
Anyway (and similar to the previous prop tip-fuselage example), the prop would resonate if it had a natural frequency matched by the frequency of AOA variation. It is a victim of the variation, not the cause. If not matched, it would not itself resonate but would pass the cyclical variation in load onward to the powertrain. If a powertrain natural frequency is matched, the shaft system resonates. And so on.
Naaa. Come on now, why not fundamentals? Assume a wind from any quarter during runup. The result is a cyclical variation in AOA for each blade as the prop rotates, a well known issue and the reason we are taught to face directly into the wind for runups. I think the frequency of the cycle is (RPM x #blades)/60 = hz, but I reserve the right to think about it some more <g>
Anyway (and similar to the previous prop tip-fuselage example), the prop would resonate if it had a natural frequency matched by the frequency of AOA variation. It is a victim of the variation, not the cause. If not matched, it would not itself resonate but would pass the cyclical variation in load onward to the powertrain. If a powertrain natural frequency is matched, the shaft system resonates. And so on.