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Old Mar 04, 2013, 04:36 PM
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United Kingdom, England, Birmingham
Joined Aug 2010
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prop falls off, mind confused!

hi all, been a while, hope you can help with a quick query.

sapac extra 330L. bent a prop shaft slightly so replaced with the spare. i fitted the prop in the exact same way but it has fallen off twice mid flight!! original prop did not have this issue. what am i doing wrong?

prop shaft has a nut. then a washer. then prop. then another nut which fits perfectly into a nut recess in the prop. front nut that fits into the prop tightens clockwise (if looking at plane head on). prop when powered turns anticlockwise.

it would make sense to me if the prop turned the same direction as tightening the nut but apparently not. if i reverse polarity of motor then thrust is wrong direction.

if it makes sense i landed once when i could hear the prop was working loose and as it was stationary on the ground i could see the prop was being spun by the wind anticlockwise and therefore working the front nut loose.

as the nut recesses into the prop, i cant only tighten it until it grips and the shaft spins. no real way to make it extra tight. does that make sense?

i cant work out if im being stupid or am missing something obvious.
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Old Mar 04, 2013, 06:28 PM
29 rods from you in western WI
Karl Bē's Avatar
Joined Jan 2003
4,885 Posts
Does your ESC have a brake function? This will actively stop the prop when you throttle down to nothing. The prop's momentum may be unscrewing it if the brake stops it suddenly. Depending on your ESC, you might be able to program it for a softer brake setting.

To tighten this type of prop, you'll have to turn the lower nut counterclockwise, or hold it while using the prop to tighten the outer nut clockwise. The other alternative is to add a washer to the front of the prop to keep the nut from burying itself in the molded recess.
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Old Mar 04, 2013, 06:51 PM
Space Coast USA
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Space Coast
Joined Oct 2000
21,169 Posts
The nut recess is on the rear side of the prop so the washer would need to be between the rear nut and the prop. Do you have the rear nut all the way down and tight against the unthreaded portion? You can try using locktite on the rear nut to "freeze" it in place which should keep the prop from loosening as long as the nut recess is not rounded out.

Is the rear nut loose to turn clockwise after a prop mishap?
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Old Mar 04, 2013, 06:54 PM
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United Kingdom, England, Birmingham
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Quote:
Originally Posted by hoppy View Post
The nut recess is on the rear side of the prop so the washer would need to be between the rear nut and the prop. Do you have the rear nut all the way down and tight against the unthreaded portion? You can try using locktite on the rear nut to "freeze" it in place which should keep the prop from loosening as long as the nut recess is not rounded out.

Is the rear nut loose to turn clockwise after a prop mishap?

yes rear nut is down as far as poss and does not move. the washer is between it and the prop.
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Old Mar 04, 2013, 06:56 PM
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Quote:
Originally Posted by Karl Bē View Post
Does your ESC have a brake function? This will actively stop the prop when you throttle down to nothing. The prop's momentum may be unscrewing it if the brake stops it suddenly. Depending on your ESC, you might be able to program it for a softer brake setting.

To tighten this type of prop, you'll have to turn the lower nut counterclockwise, or hold it while using the prop to tighten the outer nut clockwise. The other alternative is to add a washer to the front of the prop to keep the nut from burying itself in the molded recess.
aaaaah yes, this makes sense. the brake is holding the shaft locked allowing wind/momentum to unwind the nut.

i have a spare esc i could program (the current one is a no brand so wouldnt know where to start), but is another alternative to simply keep some throttle on at all times during flight? that makes sense in my head.
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Old Mar 04, 2013, 07:08 PM
29 rods from you in western WI
Karl Bē's Avatar
Joined Jan 2003
4,885 Posts
Okay, this sounds like a GWS prop & prop shaft system, though the only GWS planes I've had with them I replaced with aftermarket brushless motors with different prop mounts. I might have the hardware backwards from what Hoppy says. Or maybe you're using the prop installed backwards in a pusher application?

Good luck with the ESC programming. That reminds me, I have to program a brake into a new Turnigy Plush that defaults to no brake. I'm not used to a windmilling prop.
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Old Mar 04, 2013, 09:35 PM
Space Coast USA
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Space Coast
Joined Oct 2000
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Do you also have a washer in the front?
If not, I'd remove the washer in the back and use it in the front. The nut in the hex prop recess should keep the prop from turning when you tighten down and the washer in front will let the nut turn without turning the prop (it says here).
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Old Mar 04, 2013, 10:11 PM
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Des Moines IA
Joined Dec 2005
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Locktite is your friend at least it works for me.
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