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Bent props

Discussion in 'Pro/Adv Discussion' started by Bob Hyslop, Mar 30, 2016.

  1. Bob Hyslop

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    Hi Guys,
    Found a stress crack a couple of weeks ago on my P3a after only 4 flights.

    Whilst waiting for new shell to arrive I checked the props I had on during the flight and found a couple of them were slightly bent (one of which was 5mm over length of prop, tip to tip).

    Could this have contributed to the crack forming due to excess vibration through the motor mount?

    These are the plastic props from dji.

    Would carbon fibre props be better in this respect?

    Thanks for any insight on this
     
  2. tcope

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    Why were they bent? Did they hit something? If not, in what way were they bent? I've see a lot of props and never seen two that did not match up.

    If there is a defect from the factory there is nothing to say a CF prop won't be defective from the factory. CF perform no differently from plastic props (other then they will tend to shatter on impact). You can search for threads on CF props.... the same question about performance is asked about once a week.
     
  3. eaglegoaltender

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    Depends where the crack is - if it is close to or at the area where the motor is mounted?

    It is very possible the motor would see more vibration and have it dissipate into the Phantom frame causing some thermal expansion and then a crack.

    It is possible the motor would experience higher temp due to a higher work load created via bent prop, hence vibration.

    The heat (if higher than usual) would be present at the shell area around the motor and that combined with vibration would create cracks from thermal expansion, contraction and vibration.
     
  4. Bob Hyslop

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    The props haven't hit anything, I've also stored them in a plastic tub so no pressure on them.

    I fitted the props to the motors and measured between top of shell and bottom corner of prop (not spot on I know but enough to show any variance). Turned prop on motor and measured other end.
    Swapped to other opposite motor and did the same.
    Had same values each time.

    I have 4 full sets of props and all but 4 measured with 1mm if not the same.

    The worst one could have been fitted to the motor where the crack has formed from one of the motor mount screws.

    This particular set was bought separately from the qc so I'm wondering if the had been stored with something on top of them to have bent them.

    Do the cf props have as much flex compared to the plastic ones?

    Cheers for the help
     
  5. Dounin Front

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    I would discard or return the prop that is bent, but just as or even more important is the balance of the prop. I have found all my P3 OEM props are very close to perfect, including the CF props. I was able to improve on each a little though and even tossed one that took too much weight required at the hub.
    Extra vibration from an out of balance prop certainly won't help the crack situation any either. If you see any cracks developing near the motors, get the Strong Arm reinforcement plates to keep things secure.
    As for CF props - they look nice, but they are stiffer (not necessarily a good thing). They weigh essentially the same, actually a bit more than the EOM props.
    The main thing is don't crash and don't tip it over. If you do, inspect things carefully and discard any suspect props - they're cheap. And get a DuBro balancer.
    IMO, for what it's worth.
     
    eaglegoaltender likes this.
  6. Bob Hyslop

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    Thanks for that.

    I've got a balancer and reinforcement plates on order already.

    What's the best way to balance the props?

    I've read about sanding down or adding tape to prop, is there preferred way or just personal choice?

    Cheers
     
  7. Dounin Front

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    Everyone has their favorite way of adding or removing weight. I use electrical tape - it takes only a tiny bit and you can adjust where to put it. Also those little adhesive dots you can get in the stationery dept work well. They won't fly off. Just put them on the underside of the blade.
    Watch a few YouTube videos on prop balancing for advice. And don't forget to check the hub balance too.
     
    eaglegoaltender likes this.