Polypropylene (code 5 plastic) hinges for rotor blades. How thick should these be? 40 thou seems too stiff for a rotor of 4 feet diameter or less, is 25 thou OK? Unless the blade can freely flap the aircraft will surely tip over. Seems to me the thinnest sheet polypropylene possible is required, but of course it must have adequate strength to do the job.
Colin Duthie

I recently finished and flew successfully a 30" span 1/2A powered DC flapping head gyro (see Gyrator thread) and it uses .032" sheet polypropylene as the hinge material. It works GREAT, contrary to all my fears. I'm pretty sure that .040" would be fine, if not too thin. See what floridagyro has to say; he's da man in my book! Especially on large rotors.

The thickness of the hinge material is not real critical other than it has to be strong enough not to break. I have build hubs that didn't have any flex and also hubs that allowed the blades to droop below the gyro while setting on the ground. My blades are also heavy, approx. 110g each which will have a very high G force that really limits the coning angle even with a very flexible hub.

Phil