Freewing T-45 Goshawk 90mm EDF Jet PNP

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Folding prop failure

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  • Folding prop failure

    While flying the Volantex Phoenix 2400 with a 4S 3600mah Admiral battery, I had a prop failure at 200 feet.

    I had about 1/2 power applied when I heard a dull pop, and then saw the canopy separate from the aircraft and come tumbling back to earth.

    I quickly shut down the motor and did a gliding spiral to a landing in the grass next to the runway. When I walked up to the plane I saw that not only had a blade separated from the hub, but the resulting vibration tore the firewall from the plane and the motor was hanging by the wires.

    Ordered a new prop from banggood, which took forever, and proceeded to tackle the rebuild. Using ca glue, a new beefed up firewall, and some epoxy reinforced with fiberglass mat on the interior, the test flight was successful.

    Guess it was poor manufacturing that caused the failure. The prop separated right at the attachment screw.

    Anyway, it's flying again, and my only regret is not ordering 2 props.

  • #2
    It could have been poor manufacturing but it could also have been an unbalanced prop. Do you weigh each blade and make sure they both weigh the same? Do you balance the prop holder and spinner? That assembly has been known to be in need of balancing. A couple of us have had the same thing happen to your Radians many years ago. Prop broke, motor and motor mount came out of the nose, hanging by the 3 motor wires. Have weighed all folding props ever since. You would surprised how many of them came out of the box where one blade weighed differently from the other. Also, the occasional prop holder/spinner needed a bit of hot glue on the inside to balance.

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    • #3
      Before the maiden flight, I ran the motor before flight, on the bench and there didn't appear to be any vibration.

      I'll pull this new prop and weigh the blades to see how well they balance out. Due to the way the hub mounts to the motor shaft, with a collapsible collet and nut, I'm not sure how to balance that.

      Thanks

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      • #4
        Originally posted by TurboNut View Post
        Before the maiden flight, I ran the motor before flight, on the bench and there didn't appear to be any vibration.

        I'll pull this new prop and weigh the blades to see how well they balance out. Due to the way the hub mounts to the motor shaft, with a collapsible collet and nut, I'm not sure how to balance that.

        Thanks
        Your Volantex uses a prop assembly that is very typical of that sort of sailplane. In fact, it is the most common type and can be found on the more popular Radians. The Volantex swings a 10" prop on a 1050kv motor, 3s battery. That translates into about 13,000rpm max speed. A few grams either side will vibrate even if you can't feel it.
        Remove the nose cone (2 screws), undo the prop nut and take off the whole assembly. Remove the blades and weigh each. You can use a small piece of black electrical tape on the back side of the lighter blade if needed. Put those aside. Now you can use a prop balancer and balance just the back plate with prop holders. Re-install the prop retainer pins for the balance. If you can, now balance just the nose cone. Don't worry about the prop adaptor and nut. They're small diameter and don't contribute much to any imbalance. Note how the nose cone goes on (mark reference with Sharpie) relative to the back plate. Re-assemble with reference marks and put it all back on the plane.
        I've seen several Radians where the owner simply "ran up the motor" on the ground and didn't detect anything odd. Keep in mind that even a few grams difference from one blade to the other is enough to create a vibration that will cause material fatigue. You also generally run the motor on a sailplane for upwards of a minute or more to get up to altitude and some people even use the motor the whole flight. This is much more stress than just "running up the motor" on the ground. Also, keep Loctite away from everything in that area. Don't use it for the prop nut. The Loctite will fling itself out and touch the plastic parts. Loctite causes plastics to fracture. Use a little Foam glue on the prop adaptor threads if you want some security.

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        • #5
          I bought the Du-bro prop balancer and found out that, not only was my new hub out of balance, so was the prop.

          After a few minutes I was able to get it all balanced.

          Thanks again for the guidance, I'm sure it will help in the long run.

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          • #6

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