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Using only 4 out of 6 propeller mounting bolts

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kubark42

Well-Known Member
Joined
Oct 19, 2020
Messages
90
I am constructing a folding prop hub for an electric motor which has 6 mounting holes, spaced evenly at 60 degrees.
Screen Shot 2021-03-01 at 3.35.24 PM.png

I notice some motors only use 4 holes, spaced evenly at 90 degrees. And in fact, for this motor, it is only held onto its mount by 4 bolts. So it seems there's good evidence 4 bolts are sufficient.

Looking at the holes at 6- and 12-o'clock, they don't seem to do a whole lot. Just from appearances, it seems that each blades' torque, centrifugal, and thrust forces are all contained by the two bolts at that blade's root, and that these two do very little.

It's an electric motor, so the torque pulses are almost non-existent. The hub is a CF-infused nylon core wrapped in carbon fiber tow. Safety factors will be around 4-5x.

For the construction of this hub, it would be much easier if I simply omitted the holes at the 6 and 12-o'clock positions. In particular, it lets me pull tow straight across the sides, without having to worry about matching any curvature.
Screen Shot 2021-03-01 at 3.47.10 PM.png


Does this look reasonable or are there considerations I'm not taking into account?
 
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