how do you know if its your rudder or aileron trim that needs adjusting?? foolin around with the trims in the air at a good altitude and noticed it doesnt matter which trim to use to level the wings. is there a trim you should start with? does leveling the wings with rudder trim make the plane handle better? its one of those questions ive been wanting to ask but kept forgetting! [:@]

Well, I'll try to keep this simple, but It's difficult to tell which needs trim since I can't see what it's doing and since there is so much roll coupling on trainers. If I could look at the airplane I'd be able to tell you in a second. I'll give it my best shot.

I'm not sure if you know this, but...
Imagine sticking a skewer through the back of the fuselage and having it come out the nose. The ailerons control this axis of rotation (banking).
Imagine sticking a skewer through the top center of the fuselage and having it come out the center of the bottom. The rudder controls this axis of rotation (yaw).

Usually when the rudder is out of trim the wings stay fairly level, but the nose does not point in the direction the model is flying. The wings may eventually bank, but first the airplane will look like it's flying sideways at an angle.

When the ailerons are out of trim the wings just bank and the nose points in the direction the airplane is traveling.

When you take your hands off the controls does the model roll to one direction or another (banking)? If you don't have an instructor (which I would definitely recommend) my advice would be to set the rudder and ailerons to center on the ground, and if the airplane starts banking in the air, use the aileron trim. If the airplane is pointing where it's headed no rudder trim is necessary, unless you are flying in a crosswind. In that case all bets are off and the plane may yaw simply because of the wind.

My apologies in advance...I'm no artist.. [:-]

You explained it very well Nathan.

According to your findings, I do believe you must be using a high-wing trainer for your experiments. Different aircraft can provide some strange reactions to rudder, especially at a cruise or higher speed. Some machines will actually yaw in the direction of applied rudder, then roll in the opposite direction. The old Dave Platt designed original Contender, by the original Top Flight, was notorious for this. Sterling also produced a large .60 job that was the same, and I designed a sport model along the same lines that also had the characteristic. You are doing the right thing by trying things.

Highwing trainer usually roll well with rudder. (After all, that's how 3 channel works.) I have my students slow fly just near a stall using rudder to maintain level wings and also make turns. They get a better understanding of just how important rudder is. Larger models can be flown to better approaches if you can coordinate rudder with the ailerons, and during the round-out phase use ONLY rudder, rather than aileron unless cross-wind demands cross control touchdowns.

When you are just boreing some holes in the sky, try to control your roll/bank with the rudder and observe the reaction. That will tell you how to use the rudder for any trim needed there and not be doing it backwards. BTDT. [X(]

Make a mid-bank slightly climbing turn, where you can fairly well see the model in plan-form. If the nose appears to be pointing in a direction other than the turn circumference, apply rudder and observe the reaction. You can then notice if the turn is "uncoordinated" and that too will tell you if you need rudder trim, which may then require some other aileron trim. However don't get confused with drift-angle in a wind condition.

Some low-wing models will simply YAW when you apply rudder. Those are the easy ones. Good luck.

I believe RC Ken has posted something, (perhaps a link??) as to the steps to follow when making adjustments to control surfaces like that. These are procedures that are followed step by step to adjust out any yaw and roll tendencies caused by mechanical adjustments not being optimal for that particular aircraft.

Simply centering the surfaces is not the answer because of other factors that will cause the airplane to fly with some roll or yaw tendencies even though the surfaces are centered. This will require some trim adjustment followed by mechanical adjustments to remove the trim adjustments you just made.. but I don't exactly recall what the procedure is. Perhaps RC Ken can post the link, if in fact he is the one that originally posted it, and since he is the "all-knowing guru" here he can probably point you in the right direction.

DS.

Correct, centering everything will not necessarily make the plane fly straight, but it's a good starting point to make sure we are all on the same page. I recently took up someones old cub they were using for training. They had just fixed it and everything was centered. It needed full left aileron trim to fly straight!

It's also a good idea to center the trims on the TX and mechanically readjust the surfaces to where they were. This way you can take full advantage of your trims if you ever need them again. (I knew I missed something)

I hope RC Ken has that link, I have yet to find an effective flowchart geared toward the beginning pilot. I have a flow chart for this, but it's geared toward advanced aerobatic pilots and requires the pilot to put the airplane in situations uncomfortable to the beginner.