I was an RC aircraft beginner 12 years ago, when I decided to give up, because I didn't have proper consent from a loving wife. I no longer have the loving wife so i retrieved my Sturdy Birdy II from the basement, bought some new batteries and fuel, and hand launched it in a cow pasture. Made a couple of turns and cut the throttle, because I couldn't get it trimmed. Made a hard landing and broke the prop, but no other damage.I

My question: How do you know whether it needs rudder trim or aileron trim when it's in the air? I don't remember, and don't know if I ever knew.
Thanks

Hankster-

I would start out with your rudder trim pretty neutral (pointing straight back) and assume you probably need to work with aileron trim at first. You are much more likely to have noticeable issues with aileron trim. For aileron trim, when you are flying, if the plane keeps wanting to bank one direction, add opposite aileron trim. In other words, if it banks to the left, move the trim lever to the right.

Once you have the trim set so that it flies level, then work on the rudder. I usually check rudder trim by flying the plane directly away from me. I then pull back on the elevator to go straight up. If it does not track straight, then I adjust the rudder accordingly. After adjusting the rudder, you will probably have to go back and adjust the aileron a little bit to counter the effects of the rudder adjustment.

Now that you know where the control surfaces should be, adjust the clevises on the pushrods, so that the control surfaces are in the proper position when the trim levers are centered.

Have fun!

I don't know if there's a right way and a wrong way really.

Without sitting in the cockpit looking at a slip ball you wont really know exactly what you need, so it's a trial and error process.

Here's what I do though...

I trim with aileron until it stops trying to commit suicide.

Next I fly it straight over myself and just relax for a moment and observe what it does. If it's crabbing it could be the wind, so I'll turn round and fly back over myself again in the opposite direction. If it still crabs the same way then it needs rudder trim. As you add rudder trim you'll need to reduce the aileron trim you added initially.

I just repeat this process over a few minutes until it appears to track straight and flies hands off.

I hope this helps.

Have you considered seeking out a club? An instructor can help with this sort of thing - it's much easier to understand seeing it rather than reading it....

OK proper trim: calm day at no more than 1/2 throttle...this is to start...elevator trim so the airplane does not climb or descend, thumbs off...I start with aileron trim,not drifting off course and wings level, thumbs off...if ok rudder trim is good enough

Very good advise from the members .
You did check your CG and lateral balance`s right ?

Start by making sure it's in balance - laterally and longitudinally.
Then make sure your control surfaces are properly aligned.
Are your wings and stabilizers set right? Same incidences, dihedral, angles, etc?

I'd suggest starting out by joining a club and getting some one-on-one help.

Tennessee is a big place. Care to narrow down your location a bit? Welcome back.

Have you check the wing or the tail section to see if it's slighty warp?

if the tail is a liitle bit off, you can install paino wires to correct it.

check the wing saddle or when you mount the wing that the wing sits
properly.
set the model in front of you around 5-10 feet and close one eye ball.
Or you can do measurements.


Hopfully your wing is not warp.
there's trick to correcting a warp wing. if your wing is warp you make
wanna reserch on that.

A model won't be perfectly trim anyways. Depending on how much power
you give it, the model nose up or dowm slightly.

Your CG will change anyways do to fuel consumption.
i adjust my trim accordingly during flight.

After giving up your loving wife I'm surprised that you had a basement to go to.

chopper man

Looking at the plane in still air or doing a loop as above is probably the best way to trim.

However, here's a quick-and-dirty trimming check I use for this sort of thing. It doesn't actually do it "Right", but it does work to make sure that the over-all yaw and roll issues are balanced out. And it works when there's a wind, even a variable one or where the wind isn't blowing the same direction at altitude as it is on the ground.

(while writing this up, I realized that this might actually require more piloting ability than most beginners have, since it requires you to be able to hold a stable turn in both directions long enough to see waht is going on. But what the heck, here is is anyway)

Get the plane trimmed to straight and level by eyeball as best you can, you need to be able to have hands-off level flight.

Now, roll in to a bank, at least 45degrees, steaper is better, but don't over-do it. Hold enough elevator to do a constant level turn. You want to fly a constant circle, several laps around. In an ideal world, you should just be holding elevator, and nothing else. Watch the plane, you're looking for a tendancy to go "up" or roll out of the turn, or a tendancy to tuck the nose down or roll upside down. Watch the yaw angle of the fuse, in a co-ordinated turn, it should be level.

Now repeat the test turning the opposite direction, with the same level of bank.

If everything is right on, the fuse will be at the same angle when turning in either direction. If things are off, the fuse will look more "nose high" when turning one direction than the other. If you don't use rudder to enter the turn (and the test works best if you don't (planes with so much adverse yaw that they can't roll in to a turn with out rudder are left as an exercise for the student)), then you'll have a bit of a slipping turn going on, so you're looking to see the same slightly nose-high angle in both directions.

It could be too much or not enough right-thrust, or it could be the rudder and aileron trims being off and causing the plane to be slipping in level flight, and the slip becomes a lot more obvious in the turn.

Assuming you've already checked the balance, and you don't have a larger aileron hinge gap on one side than the other, then you can use rudder trim to make adustments until the plane tracks smoothly through the turn.

If the plane tracks smoothly through the turns in both directions, or rolls either out of the turn or tucks under in both turns, then it means that the forces are equal when turning in both directions, and that's pretty good for most flying.

I use this technique a lot on student's trainers when I'm just trying to get things "right enough" to do some flying, and on many of my own planes when I'm trying to see if the rudder trim is right, espeically my combat planes that don't have rudders. This test will really show if the vertical tale is twisted or if the thrust-line is really off, and I use this test to determine if, and how much, I need to twist in some "rudder trim".