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Jan21-13, 12:27 AM
Sci Advisor
HW Helper
P: 9,922
Torque on a hub as a result from a flexible arm

That's relatively easy, then.
Consider an element ds of an arm. At time t it will be (in polar relative to hub centre) at some position (r=r(t), θ=θ(t)). The tangential acceleration is ##r\ddot{\theta}+2\dot{r}\dot{\theta}##. See
If the element has mass dm (=ρds if uniform density) then the reactive torque is ##-(r\ddot{\theta}+2\dot{r}\dot{\theta})