Re: Re: F1D motor tube stiffness?

From: William D. gowen <wdgowen_at_gmail.com>
Date: Mon, 17 Feb 2014 10:00:57 -0500

I agree that a compression wrap would be a better idea.

On 2/17/2014 4:30 AM, Tapio Linkosalo wrote:
>
>
> 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 - 07:01:02 CET