I was in a heated discussion with a friend about aileron
trim. His plane yaws to the left when he pulls it into a loop. He insists
that he can drag (drop) his right aileron slightly which will add drag
to the right wing, thereby correcting the problem. I argued that since the
ailerons are a balanced control surface that it isn't possible to trim one
aileron differently than the other ( what you do to one, you must
duplicate on the other or the plane will roll). Am I off base in my
thinking. I believe the plane will roll left when this trim is added. The
resulting trim added to level the wings during flight will leave both
ailerons slightly lower - No? Perhaps someone can explain this better than I can.
Am I nuts? Is he right to hate me for making this argument? Help.

Tom

You are correct, Starcannon, in my humble opinion. Offsetting one aileron will normally required offsetting the other aileron by the same amount, so you accomplish nothing by this move. The model probably needs a little right thrust, or a combination of right thrust and right rudder trim, assuming that it has been carefully balanced laterally - and few models are.

I have noticed that many R/C flyers are not terribly good at rudder trim. I like to trim the rudder by getting the model into what seems like pretty good trim while flying level, then pulling it vertical from about half full airspeed, adding full throttle, and watching what happens as it slows down. Rudder trim will usually have to be added to get the ideal - a straight and true vertical climb with no aileron or rudder input. If the model tends to yaw to the left as it slows in the vertical climb, you need some right thrust too. Sometimes you even need a little left thrust - one of my pattern models needed a little left thrust to offset the drag of the external tuned pipe on the right side of the fuselage. After trimming the rudder for the truest vertical climb you can get, you will, of course, have to go the level flight and re-trim the ailerons.

There are a few things that could cause this. Rudder trim. Aileron differential (when the hinge line is not in the exact center of the control or mating surface). Thrust offset. Differential in elevator throws. Or a combination.

The worst offender for this "loop yaw"--is typically unbalanced load on horizontal stabilizer.
Thye cause may be warped stab/unequal throw of elevators/funky servo on one side - shifting pushrod under load - on and on -
Easy to prove this one -- just retrim the elevator on the opposite side - If it yaws left - raise the right side.
We once spent time trying to perfect the trim to hands off on all maneuvers - (the eternal search for the Holy Grail--for Pattern junkies.)
anymore, we quickly sort it all out - then add what is required as we fly -
Years back - an old friend was flying a new plane and I asked him "how do you trim it?"
He said - I don't -I just fly it.
He flew all modes and full size helicoper etc.
Most of us can't do that - so learning where trim drag originates is the best bet - In planes as in bikes - most directional change is a result of trim drag at the rear.

Tom,
I was unable to determine if you are nuts from this brief post. However your friend has no reason to hate you for the argument. I agree with you that changing one aileron won't fix his problem.

You didn't mention the skill level of this "friend" of yours. It took me quite a while before I learned to make a loop that came out in the right direction. I was convinced my Four Star couldn't loop properly until I finally figure it out. A little extra speed and getting the wings perfectly level before starting was my solution.

BTW, I'm one of the guys that doesn't trim planes. I just move the sticks to make it go. I've always felt that with all the corrections needed for wind gusts and such, it doesn't need to be perfect. Of course you pattern guys don't need to worry about me winning any contests.

Tom