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Folding Mast Location of Split Point

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  • Folding Mast Location of Split Point

    Greetings all, but this might be a question for Chuck Beaty.

    Perhaps this has been covered elsewhere but I do not recall reading anything about it. Is there an optimal ratio of mast segment lengths above and below the split point of a folding mast? I ask because, imagining a vibrating guitar string, there is a null point. Of course being split, there are now 2 masses, so I would think there's a point of least stress at the attachment.

    Thank you,
    Brian

  • #2
    Asking the question the way you do, Brian, I suppose you have something like higher harmonics in mind. I think this case is not relevant, because the rotor will always force the first harmonic and therefor the highest stress will be at the end of the mast opposite to the rotor, as in the sketch below. If rrpm is close to the first mast harmonic, you have one hell of a problem.
    Click image for larger version  Name:	bending_stress.jpg Views:	1 Size:	72.1 KB ID:	1119336

    Cheers,

    Juergen

    ..Il semble que la perfection soit atteinte..
    ....non quand il n'y a plus rien à ajouter,...
    ...mais quand il n'y a plus rien à retrancher...
    - Antoine de Saint-Exupéry -

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    • #3
      Thanks for the info, Kolibri.

      Yes, I believe "harmonic" was the term I should have used. The original question was to understand where along the mast the optimal location would be for the split point for least stress on the mast. From your diagram it seems the higher the better, although too high and it defeats the purpose of a folding mast. I wasn't sure if manufacturers had a formula for this or not. Maybe it just isn't an issue, but I wanted to ask before making assumptions.

      Brian

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      • #4
        Cut the mast later ! How is the progress ?
        Happy Flying, Chris S.

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        • #5
          Hi Chris. Progress is happening. Doing the surface finishing on the tubes... not cosmetic finishing, but rather some fine sanding to remove a mil or two to eliminate any scratches that come from material handling from the extruder to the supplier. I picked the clearest tubes they (Metal Supermarkets) had in stock but just sliding tubes against each other when they stock them can cause scratches. I want the mast surfaces to be as free of any stress lines as possible. Slow going but I'm happy with the results so far.

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          • #6
            Good man ! Did you get one of those drilling jigs ?
            Happy Flying, Chris S.

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            • #7
              I might, but currently I'm using CNC equipment at my workplace that does cutting and drilling of extruded shapes. The plan is to import the CAD models into the CNC software. So far so good on the initial tests.

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              • #8
                Well that will be OK ! Let's go ! Spring is here.
                Happy Flying, Chris S.

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