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How did the propellers attach on a Lazair attach if the shafts had a woodruff key instead of opposite thread?

I understand the early Lazair prop shafts had a woodruff key. How were the props attached?

Don't you need opposite thread?

I assume you couldn't just use a cotter pin and a washer, as the props would try to shear off the cotter pins.

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I believe that while the original engine shafts had a slot for a woodruff key, no key was actually used in attaching the props to the crankshaft. Instead, a nominal arrangement of multiple (6, I believe) bolts attached the props to the crankshaft for mutual transmisal of both engine torque and prop thrust. Presumably the bolts were secured with safety wire, but I have no data on this.

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It's not good practice to use a woodruff key to transmit thrust forces on a rotating shaft. Ideally you'd use a woodruff key to transmit the engine torque to the propeller, and use a separate clamp nut or series of bolts running through the crankshaft hub and the prop hub to prevent the propeller thrust from pulling the prop off the end of the engine crankshaft.

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  • $\begingroup$ So... how did they attach the prop hub( if there was one)? I'm thinking only 1 bolt at the end of a threaded hollow shaft... I think the standard practice is to thread a prob hub onto a threaded shaft with opposite thread, and then use bolts to attached the prop blades. $\endgroup$
    – Fred
    Sep 17, 2019 at 12:32

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