F1D motor tube stiffness?

From: Tapio Linkosalo <tapio.linkosalo_at_iki.fi>
Date: Mon, 3 Feb 2014 08:35:16 +0200

I went to test fly my new F1D on Saturday night; aiming for Slanic this one
has a fixed pitch prop. The flights were otherwise OK, except that on
launch the wing tended to warp, resulting in right wing tucking, this
increased the warp until the model rolled to right and inverted and started
diving down.

I managed to resolve this by launching with more nose-up -attitude; looks
like with fixed prop the initial speed was too much when launched flat (as
I used to do with VP), got off with up to 22 g*cm launch torque. Did not go
to full 30g*cm, as I was climbing already too fast to the low (7 meter)
ceiling, have to try higher launch torque on taller sites. Unfortunately,
the problem seems to be more related to speed than torque: while trying to
steer the model away from the ceiling, I once managed to pitch it down, and
as a result from the dive the wing twisted and tucked again.

The wing supports are OK (2* 4thou boron) and wing spars stiff (boron on
them too), so now it seems to me that the motor tube is twisting too much.
The tube is 13 thou #4.5 balsa, and has 4 pcs 4thou boron on it. I wonder
if a spiral boron between the wing supports would help (glued on in
compression I suppose), or if I just should go to 14 or 15 thou wood?




-Tapio-
Received on Sun Feb 02 2014 - 22:35:17 CET