Propeller Breaking Mid-Flight?

[namns35]

Hi All 👋
I've been getting back into RC flight after years away from the hobby. It's been especially fun to do it with my oldest son who is learning to fly with a buddy box system. Recently we built a Piper Pawnee PA 36 from Tony 65x55's plans from the old rcgroups forum. It flies great with the Emax motor from Flite Test's power pack C. In the last 2 weeks though, I've had 3 propellers split in half during flight. I'll be several minutes into a flight when suddenly I lose power and bring it in dead-stick only to find that my prop nut is still in-place and no propeller to be seen. Today it happened during a low-pass so I was able to find half the propeller and confirm that it is breaking at the hub.

Has anyone else seen this happen? Am I putting it on the motor too tight? Too loose? Any suggestions?

 

[Merv]

You could be over tightening the prop. You could have a bad batch of props. Are you balancing them? Is the prop hole too small, are you pressing them on?

 

[skymaster]

what is the size of the propeller.

 

[FDS]

I don’t like the slim hub on the Slow Fly type props, APC or Master Airscrew are better in my experience. As noted over tightening might be the cause but they are still breaking because there’s not enough material in the root.

 

[Tench745]

I have heard tales of some props being flexible enough that after enough throttle adjustments, or fluttering, or something, they fatigue and break at the hub. Never seen it happen before though.

 

[KSP_CPA]

This could be beyond the scope of this discussion, but looking at the APC max RPM chart on their website (RPM Limits) it seems that a regular thin electric 6 inch prop would have a theoretical limit of 25k RPM. While I am sure that is a minimum standard and could be much higher, it would seem that a large 2200kv rated motor would only be able to run at 11.36volts or a 3S battery or risk a prop blowing apart.

I am currently running a 2212 2200kv motor on a 3S with a 6-5.5 APC thin electric prop on an FT Arrow. I’d like to run up to a 4S on the same engine. Could I risk a prop flying apart mid-flight or will the load on the motor slow it down that significantly?

The most recent FT video had the FT2207 at 2400KV running 6S and the prop did not look like a high speed or carbon fiber specialty prop.