Re: F1D longitudinal stability

From: Tapio Linkosalo <tapio.linkosalo_at_helsinki.fi>
Date: Fri, 7 Dec 2007 09:59:59 +0200 (EET)

Ok, F1D Finnish champs flown. I ended up last/third, quite as expected. I
was no match to mr's Nore and Englund, with my overweight model. Did
manage some decent flights though.

We flew in a 24 meter / 75 foot football hall, in perfect conditions, even
though the the wind was howling outside. Nore did twice 19+, Englund 16+
and 15, my best was 12 1/2 minutes. Used 200mm (8in) motors, wound to max
(broke a few), than backed-off 20 to 30% of the torque. This climbed the
model to the ceiling, but the motor seemed to be slightly too thin, as it
did not maintain altitude in the cruise, but started to descent already at
5 mins. Anyway, my new fuselage made of balsa from mr. Benns (UK) handled
the motor torque with ease, so I'm happy that this issue is solved. My
first, hand-sanded fuz collapsed under the motor load, but now I felt
comfortable with handling the motor and fuselage.

I did use a 50mm wire spacer to bring the motor forward and adjust the CG.
Without the spacer the CG was 15mm behind the trailing edge, while the
spacer brough it to the TE. This setup seemed to be slightly towards the
critical end, with the model showing occasional slight symptoms of
tailstall (accelerated descent but in proper flight attitude, so no
tailslide), but for most of the flight the trim seemed stable and safe. I
guess I'll build for 100% CG in the future, but possibly use a spacer to
bring CG further forward in rough conditions. I also wonder whether moving
to tailplane tip rudders instead of one central fin would inrease he
efficiency of the tailplane, thus reducing the condition of tailplane
stall...

One thing that I noticed from this sortie is that I do not really like
flying fixed pitch prop. I have been flying my F1M with VP since my visit
to Canada in 2004 (did not have it sorted out for USIC or West Baden,
though), and it seems to me that a VP absorbs the small variations in
motor lenght/width/torque pattern quite nicely. Now I was again in the
situation, that I would have needed to try different motors to get the
cruise right, while I think that simply adjusting the spring pretension
would have been so much simpler procedure. So in additions to slimming 0.6
grams out of the model, I need to further slim it to accomodate the VP!
Ugh.

The current overall weight is 1.77 grams, with 0.32 for the prop, 0.40
wing, 0.25 tailplane, 0.26 boom with rudder and 0.47 for motor tube, wing
pylons and stub boom. I only have boron in the tube, boom and pylons. From
practise it seems that my wing, tail, and most of all the prop are
excessively rigid, so I must try with lighter wood, and possibly add boron
if needed. The tube and boom are quite as they should be, but the stub
boom could lose considerable amount of weight. Let's see, how it turns
out.




-Tapio-
Received on Fri Dec 07 2007 - 00:00:04 CET