Model Forum / Radio Controlled / Air Models / June 2007

If the model was suddenly looping, I would suspect not enough rubber bands.
Tucking under is a problem with some forms of flying wings. I remember one
in particular that had the engine amidship that was notorious for tucking
under - can't remember the name, but I remember the model. <G>

If the model is a low wing, with the wing being held on with rubber bands...

My first "multi" digital proportional rig was a Micro Avionics XL-IC four
channel set. It was on 27.195 MHz. Every time I flew my Senior Falcon over
the power lines at the old Seabrook field in NJ, the radio would give me
full down elevator. It never crashed my model, but it came very, very close
a few times. Yes, I'm sure it was the radio causing the problem. It only
happened when I flew over the power lines in that particular spot. Weird.

Ed Cregger

If the incidence? of the horizontal stabilizer is wrong, and the stabilizer
has a "flying" airfoil, it may be going in and out of the flying mode.
(I think flutter is more likely, or some sort of problem with the elevator
control servo or linkage. If you have plenty of travel, consider reducing
it.

There was a real airplane, made by Cessna in the 1970's that had a problem
with the horizontal stabilizer, and as I remember, might do strange things
similar to what you are describing, although usually at low speed and a high
attack angle.

Well, I'd take out(free flight style) and do some test glides, engine
off, controls in your normal cruise mode trim position, and ideally
somewhere with tall grass.
    Put it in flight trim and hand launch it nose-level, at flying speed
into a glide.
    It should glide down to a gentle landing.
    If it doesn't dive but goes into a quick, short period stall, you've
got the cg too far forward, and you're balancing that out with excessive
nose up trim.
    If it begins to nose over, and assuming your CG is close to correct,
you need more nose-up trim and/or move the CG back.
    To figure out which, throw it a bit nose-down, at a little above its
trim flying speed, ideally it should bouyantly glide to a slight nose-up
position, and to a gentle stall.  If it dives even harder for the
ground, you definitely need more incidence. If the model seems to do a
little better, and you can see the trim at the higher speed is trying to
hold the nose up, try moving your CG back a little.  I'm betting it will
dive.
   
    Those Bees seem like big sport free flight models, and I wouldn't be
surprised if they even had cambered airfoiled tail surfaces.
    That's my basic glide test trim technique
    Uncle Pauly