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Old 11-10-2021, 11:15 AM
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BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 6,844

Originally Posted by claycookiemonster View Post
Building a taildragger 8. Trying to make sure everyone is on board with the engine room before I make serious plans. Either the James or Showplane cowls require a prop extension, though they don't specify how long of an extension. I believe they need 2.5"

Yes, I understand the stresses in this. I do not want to underestimate them.

Just trying to understand the cautious reply from Whirlwind, which was not actually a, "It's forbidden!" Aerosport power is fine with this. So, their bearings must be up to it.
Check your sources - - James recommended 2.25"

If you understand the stresses, what do bearings have to do with it?

Aerobatic cranks have the same bearings, just a thicker flange.

You had better assume that your aerobatic limit is 4 G's, maybe 5. Quantify the stresses.

Krea, I asked Hartzell long ago about that hub for aero and they said 4 G. i.e. it was the same as standard with a saber 2.5"extension. That was 6-7 yrs ago and may have changed.

Through private conversations, Hartzell and calculations, I was convinced my M1B, Hartzell composite and 2.5" Saber was good for the a "mild aerobatic" range. Any rapid axis change at high RPM is forbidden. Today I would use the extended hub. This is not an endorsement . . YMMV

Just keep in mind that Earl Findlay endorsed an RV9A for for 230 MPH airspeed (30 mph higher than Vans limit -lesson: be careful trusting your life to critical information provided without corroboration)

Last edited by BillL : 11-10-2021 at 05:06 PM.
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