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Teeter bolt sheer strength

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  • #16
    Christine Toev's pitch pivot bolt on her Aurora is the only one of the 4 "Jesus" bolts I know to have failed. I know of at least 2 crashes because the rotor pivot bolt came loose due to a too large washer contacting the rotor bearing housing. I believe Christines breakage was because of the powerful Metro launch prerotator and a defective pully putting huge loads on the bolt, eventually breaking it. .
    "Nothing screams poor workmanship like wrinkles in the duct tape!"
    All opinions are my own, I've been wrong before and I'll be wrong again. Feel free to correct me if I am.
    PRA# 40294

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    • #17
      The strength we've been discussing is shear ("sheer" refers to women's stockings, a different topic entirely). For a part to be loaded in shear, the load and the (opposing) reaction to the load must be right next to each other -- just as the two blades of a pair of scissors (or shears) come together, with no space between them.

      The problem with the Butterfly Metro-launch system on Chris's gyro (and others with the same design) is that there's a tendency for the loads NOT to be pure shear. The load and the reaction to it are separated by a measurable distance. This puts the pivot bolt in bending, instead of shear. It's much, much weaker in bending than in shear. We don't want ANY of the three 3/8" horizontal Jesus bolts (two pivots plus teeter) to end up loaded in bending to any significant extent.

      IIR, the Butterfly head can be adjusted to avoid this unhealthy situation. I don't have one handy to be more specific, though.

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