Re: Re: F1D motor tube stiffness?

From: Tapio Linkosalo <tapio.linkosalo_at_iki.fi>
Date: Mon, 17 Feb 2014 11:30:22 +0200

Yesterday I had a chance to trim my models in a bit larger hall, so quarter
motor flight with full launch torque did not hit the ceiling too fast. Now
it seems to me that indeed motor tube twist is the issue: while holding the
model with fully wound motor, the tube twists and wing supports are clearly
misaligned. Looks like the wing supports are strong enough that the flight
loads _add_ to the twist, and also on the one occasion that model dived in
from hitting the ceiling was caused by the flight loads twisting the tube.

I have been 0.013" for a while now. Looks like I have so far gotten away
with using VP: even though the tube twists, with VP the speed does not
build up over critical limit. WIth fixed pitch it a combination of torque
and flight loads, that pushes the setup too far.

I might have time to try thicker walled tubes, but I was thinking if
torsional reinforcement would work. Mike was suggesting kevlar wrapping,
however I have tried polypropylen for similar case (had problems with F1M
tails warping, as the tailboom between support was too soft), but that
wrapping did not stiffen the tube enough. Therefore I'm still thinking
about adding a 3 thou boron, in a spiral (one or two rounds) between the
wing supports, and in compression (so it would be easy to see if the boron
buckles). Has anyone tried that; any suggestions if 1 turn is enough or if
2 turn would be better (2 turns would weight more, but give more stiffness)?




-Tapio-
Received on Mon Feb 17 2014 - 01:30:23 CET