Sunday, February 15, 2015

Propeller moment of inertia

In my quest for investigating the press fit hub, the propeller moment of inertia was a needed parameter. The only practical way of finding the inertia is by doing an experiment with the propeller as torsional pendulum. This is explained by EAA here, and by Hepperle here.

I don't have a Rotax diagram, so I did it as described by Hepperle. My dimensions were:
m = 2.5 kg (measured with a bathroom scale, not very accurate), 2e = 6 inch, a = 126 cm. I measured 5 full periods, and they were 38 s on average (did it 4 times). The period time, T, became 7.6 s. The propeller moment of inertia is:

Ip = m*g*T²*e²/(4*pi*a) = 0.165 kgm²

The bathroom scale could be rather inaccurate for this low weight, but good enough for the purpose.

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