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Propeller Breaking Mid-Flight?

#1
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?

Note: the image below is before I switched out the motor to use an Emax Mt2213-935kv with a 10x45 propeller
 

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Hai-Lee

Old and Bold RC PILOT
Mentor
#2
I have thrown a few props in flight and normally they are the cheap plastic props and simply put they cannot handle the power and kV of the motors I was using. When I bought some of the more expensive types of props, (GRP or CF), the breakages ceased,

Just my experience!

Have fun!
 

FDS

Well-known member
#3
I don’t like the waisted root design of those props, an APC style one in the same spec will be better. Look how little material there is round the prop shaft of the motor.
 

quorneng

Well-known member
#4
With that motor a 10 x 4.5 prop is recommended for a quad. It is intended to generate high thrust as low air speed.
In a plane at speed I wonder is the prop blade is actually 'fluttering' hence the repeated failures. A 9x6 might be a better choice.
 
#5
Thanks for the replies. I have been using really basic ABS plastic props and had not thought about the low pitch of that 10" prop. I'll try out both a higher quality 10x4.5 and a basic 9x6 to see how those both do.
 

Bricks

Well-known member
#7
Dumb question are you using the plastic insert, that fits the shaft size of the motor? I see you are using a ruber band to hold the prop on is it tight enough to keep the prop from fluttering?
 
#9
Dumb question are you using the plastic insert, that fits the shaft size of the motor? I see you are using a ruber band to hold the prop on is it tight enough to keep the prop from fluttering?
That picture with the rubber-band "prop saver" is from before I switched to the new motor. The Emax motor I'm using now has a threaded prop shaft with two straight edges that catch in the hub of the prop. Thanks for the response!
 

Bricks

Well-known member
#11
That picture with the rubber-band "prop saver" is from before I switched to the new motor. The Emax motor I'm using now has a threaded prop shaft with two straight edges that catch in the hub of the prop. Thanks for the response!

Are you using the platic inserts that center the prop on the shaft?
 
#13
Interestingly before new props arrived I tried another one of the cheapo ABS plastic propellers and it worked fine. I have now flown with it more than a dozen times and over an hour of flight time. I'll still replace it with a nicer prop the next time this one breaks, but for now it seems to be working fine.