How to properly trim an airplane? - RCCanada - Canada Radio Controlled Hobby Forum
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Old 02-06-2010, 11:38 AM   #1
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Smile How to properly trim an airplane?

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I recently read a post where someone had maidened a new plane, and had to add a 3 clicks of right aileron, and one click of left rudder. (I'm not sure if the numbers are correct) I found it odd that the pilot had to add opposite rudder trim vs the aileron trim. This made me think about my maiden journey with my Parkzone Corsair. Before the flight, I made sure that all of the control surfaces appeared to be "visually" neutral. Immediately after lifting off, she banked HARD right, and I needed a fair bit of up elevator on the stick. After two close calls in the first 50' of flight (come on, you've all had this happen!) I decided that lots of altitude was required in a hurry, and then I would figure out the trim. It only needed 4 clicks of up elevator, but needed 11 clicks of left aileron. It was flying like an arrow now, so I didn't bother with any rudder trim, after all, it looked perfect sitting on the ground. However, since then, I have wondered if I should take some of the aileron trim out, and add some left rudder instead. The amount of visual trim on the ailerons now, is such that on the left wing, the trailing edge of the aileron is approximatly 1/8" above the trailing edge of the wing! To me, this seems to be way too much, but I physically adjusted the linkages so that at neutral trim on the control, the plane is physcally trimmed for straight and level flight.

So the question is, how does a relatively new pilot know if he needs rudder trim, or aileron trim. The elevator trim is pretty easy I think, but I might be missing something there as well. Seems to me that if it flies level, the elevator is good.

I am waiting to maiden a Mini Funtana X, and would really like the first 50+ feet of flight to be uneventful. Maybe I should take off and go straight up for a few hundred feet and then see what happens! (Just kidding!)
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Old 02-06-2010, 12:19 PM   #2
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Re: How to properly trim an airplane?

Trimming a aircraft for Yaw (Rudder):

- Make sure the aircraft is laterally balanced
- Control surfaces are sealed
- ensure there isn't a excessive amount of right thrust in the engine or not enough. 2 - 3 degrees of right thrust is all you need.
- Fly the aircraft away from you and directly into the wind making sure the wings are dead level, gently pull into a vertical climb. If the aircraft veers immediately to the right or left put in opposite rudder. If it gradually veers left or right it probably doesn't need any rudder trim, but keep trying until you get consistent results.

11 clicks of aileron trim is guess is you have a warp wing.
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Old 02-06-2010, 03:43 PM   #3
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Re: How to properly trim an airplane?

Thanks for the reply. That makes sense to me. Yes, I think that my wing must have a warp, and the really crazy thing about it is that I had a radio malfunction, DX5E Tx and AR500 Rx, and completely planted the plane. The wing pretty much broke in two, except for a plastic structural support that is down the length of the wing that held the two halves together. After gluing the wing back together, I figured that I would have another wild episode with the trim, but to my suprise, it flew exactly like it had before the radio failure. I think that I am going to buy a new wing for it this spring, to have a spare, but also to see if it requires the same amounts of trim.

Thanks again.
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Old 02-13-2010, 07:16 PM   #4
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Re: How to properly trim an airplane?

Well, if the airplane is well balanced, depending on the fuselage and wing type, trimming can be done mostly visually. But, if your wing is bent, you will clearly have problems, and have to correct with trim. Don't worry about it too much, this is done all the time with aging real aircraft.
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Old 02-17-2010, 03:11 PM   #5
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Re: How to properly trim an airplane?

I would say that with that much aileron difference you definitely have a bit of wing warp.

In some instances, a slight amount of wing warp can be corrected simply (unless its a fully sheeted wing) by gently twisting the wing in the opposite direction of the warp and apply heat with your heat gun to re shrink the covering in the new position. I have successfully done this on up to 40 size aircraft and eliminated the warp.

As for perfectly balancing an airplane. (Eg: High Wing), I install a 1" sq by 1/4" thick hardwood block of wood on top, in the middle of the wing right on the C of G. and screw in a small eye screw. With the plane fully assembled and ready to fly (no fuel) I hang the plane from eye screw. Now you can easily see if the plane is out of balance in any direction.

To balance from front to back, move the battery pack(s) and/or receiver around to get the plane balanced, and only if absolutely necessary, add a small amount of weight to get it to balance from there.

To balance from wing tip to tip, add small amounts of weight on the high wing tip or as close to the tip as possible until the plane is balanced that way.

Once the plane is done this way, it will be absolutely perfectly balanced in all directions. Remove the eye screw and go fly!

Note: Same procedure for low wing only the wooden block goes on the bottom center of the wing at the C of G and the plane is hung upside down to balance!
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Last edited by Gary Maker; 02-17-2010 at 03:32 PM.
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