Jack_K

OK. My new airplane flies beautifully after one of the club instructors flew it and trimmed it out. Now I'd like to be able to adjust the control surfaces and remove all the trim from the TX so it (TX) is neutral.

It seems I have to somehow measure and save the control surface deflections, zero out the TX trims, and then reset the control surfaces to the "trimmed" positions.

How do I do that?

Jack

jetmech05

Why do you want to do that? If your trimmed and it flies great your good. It doesn't hurt anything to leave trim in.
Besides if something changes and you need to retrim then you have to do the process all over again

RBACONS

My Feedback: (3)

Turn your transmitter and receiver on and then carefully measure and record the deflection on each control surface with a ruler. This can be relative to some other part of the plane or relative to the surface of your workbench. Then, one by one, zero out the trim on a channel and adjust the linkage for that channel (lengthen or shorten as needed) until you get the same measurement as you did before you zero'd out the trim. You can also use the sub trim function if needed but adjusting the linkage is generally better. When you've done all the channels, your surfaces should be in the same position as the instructor had them but your trims are now centered.

This is somewhat of an over-simplification. If you're servo arms weren't perpendicular to the linkage, you may want to adjust those as part of the process. Likewise, if you're sub trims weren't zero, you may want to zero them as part of the process. And finally, the need for trim usually indicates something else is wrong with the plane. For the elevator, the need for trim may be because your plane is nose heavy or tail heavy or the engine up/down thrust is off. For the ailerons, the lateral balance may be off or you may have a twisted/warped wing panel. Likewise for the rudder, your right thrust may be way off. If you can, its best to fix the root cause to eliminate the requirement for trim. Trim setting are usually set for straight/level flight. If you have non-zero trim settings, it can adversely affect the flight characteristics of the plane any time you're not flying straight and level.

HighPlains

My Feedback: (1)

But is it really in trim?

To answer your question we need to know more about the airplane model and radio. Then what is your expectation and level of experience. While a basic trainer might be trimmed out enough for basic flight, a more advanced model may take 50 flights to really trim out. There are so many things that matter so some degree that most never get to or are aware of. Today's powerful computer based transmitters and gyro stabilized receivers can mask a lot of deficiencies, but it is still best if you learn the basics.

HighPlains

My Feedback: (1)

While I was typing, RBACONS posted a good starting point and methods to get started. The answer to what he is talking about involves flying and adjustments.

Balance is your starting point.
Then you need to establish what prop you are always going to use, as it affects much of the later trimming process.
Then we start with the thrust, with right thrust and up or down thrust. From this point on it starts to get complicated, but often we can stop here until your flying skills improve with a good third or forth model. And frankly, many if not most never get past this point. They are perpetual beginners.

Jack_K

It's an Ugly Stik clone. No idea who made it since I bought it off Craigslist. It has a 58" span, weighs 5.3 pounds, and has an old (1960's) SuperTigre V60 engine. Yeah, I know that's over kill, but the engine came with the plane for a total of $70. I had to make numerous repairs and replace a lot of the Monokote, but it looks and flies great now. Flies on 1/3 to 1/2 throttle and goes straight up forever at full throttle.

The instructor who flew and trimmed it has won 1st place in several Expert class SPA (pattern) contests. He's the best pilot in our club.

HighPlains

My Feedback: (1)

Sounds like you are off to a good start. Ask him to work with you to get to the next level of flying and trimming skills. Usually takes a couple of years after you solo to get there, and he will like the competition. When he starts letting you fly his airplanes you are close.

da Rock

It's actually a good thing to do, but not required at all.

Each surface does need an adjustment somewhere. I assemble my planes with pushrods that are threaded at one end at least. The threaded end has a clevis screwed on to be in the middle of those threads. They have equal room to shorten or lengthen. Do one at a time and you won't need to record anything.

I do mine by sight, having done the building (all the servo arm to pushrod connections are right angles as are the pushrod to horns) and original flight trimming, as you will do in the future. Trimming is often an ongoing thing so I don't care if this job misses by a couple of clicks, and eyeballing it often gets it perfect and seldom misses by more than a couple.

Look at where the surface is. Now adjust the TX trim to center. (count the clicks if you wish). Now unhook the clevis from the horn and screw the clevis in or out to shorten or lengthen the pushrod enough to move the surface back where it was when you "just looked at it." Leave the TX and plane turned on while you're doing the job.

Now do the other surfaces. There are a number of reasons to take the trim out of the TX. For one, having the servo arm at 90degrees to the pushrod and the same angle of the rod to the horn insures the flying surface gets moved equally both ways. (That is, unless you set those angles up on the ailerons or elevator so there would be more down than up movement. Some planes benefit from differential ailerons and differential elevator. But that's a topic for later, when you've got more experience.)

Modern radios have excellent capabilities to do a lot of trim functions. None of them keep the 90degree angles when doing so. Remember the mention of differential? You get it whether you want it, when you leave trimming in the radio and don't take it out by adjusting the pushrod lengths. Of course, if you didn't start with all the pushrods squared, before your maiden flight, this job won't correct any differential whether it is leftover or just created. But then, that's not the only reason for taking the trim out of the radio.

da Rock

Starting with the "angles squared" is the basis for getting the most accuracy and throw out of your servos. And of course for insuring you get no differential. It's why servo arms have those teeth so they can be centered (squared up to the pushrods).

cessnaflyer54

My Feedback: (68)

Your over thinking it for an Ugly Stick!

HighPlains

My Feedback: (1)

Years ago when I flew at a Rochester NY club, a fellow club member was struggling with a Ugly Stik. His landings were atrocious, and so he asked me to tell him why my landings were so much better. Well it might have something to do with the many tens of thousands of touch and go landings I had done, or the model he watched me fly had over 150 hours of flight time. Never the less, I flew his plane and quickly determined that it needed down thrust. A couple washers later he was amazed that he could make reasonable landings. I noticed that shortly after he started doing touch and go landings on a regular flight instead of avoiding a landing until the very end of each flight.

Jack_K

Yeah, probably for the Stik, but I also want to do it for my U-Can-Do SF.

rgburrill

On my old Hitec Prism 7X once you had everything trimmed correctly all you had to do was start up the transmitter with certain buttons pushed and the internal zeros were all set to the trimmed values. You then set all trim switches back to neutral. A good radio should do that.

A. J. Clark

You could count the clicks on the trim as you move it back to zero. Then pin or mark the position of the control surface. After this remove the control linkage. Now move the trim in the opposite direction the same number of clicks.

Edit-Adjust the linkage here before hooking backup to the control surface

Hook the linkage back up without moving the control surface from its starting position. Move the trim back to zero and your ready to go fly.

da Rock

I don't think this will work as written. The problem comes from the underlined part of instruction 5.

If you pin the surface as mentioned in step 2, it should insure it won't move from that position. And you won't be able to move it from that position. But instruction 4 moves the clevis away from the horn. And hooking it back up without moving the control surface will be impossible as you must move the horn on the surface to where the clevis now is.

da Rock

If you leave out step (2) and the part in step (5) about moving the surface, it should work. Pinning makes step 5 impossible as written, and marking is unnecessary as you get perfect accuracy using the number of clicks in step 4 that you counted in step 1.

However, those modelers who don't assemble their linkages with right angles (90degrees) at the servo arm and horn are going to double the problems that come from their casual/sloppy assembly. Which is often what you get too when you have your radio zero out the numbers which doesn't fix the problem. Granted, the problem usually isn't very significant, but squaring a servo arm only takes a minute, and adjusting a pushrod length about the same.

A couple of weeks back a plane I was going to maiden wouldn't turn one way on taxi. The Chinese who'd slapped it together hadn't squared the rudder pushrod. A week back the motor in a real nice H9 spitfire wouldn't go flat out. Turned out the throttle linkage wasn't squared and full stick gave full closed and maybe 3/4 open. Explained how to fix it and went off to fly. Was called back and the guys said it wasn't possible to fix. Turned out the pushrod now was running into the bulkhead behind the servo. It was a favorite of the previous owner "who flew it a lot". Wonder if he posts here?

600Bob

I start with my elevator trim centered and the elevator surface centered. I then fly and find I need 5 clicks of up elev. trim.

I then give the TX 5 clicks of down trim. I unhook the linkage and adjust it so the elev. is re-centered, I then set the TX trim back to center, 5 clicks up, this will run the elev. up 5 clicks

A. J. Clark

OK. I forgot to write in between step 4&5 is where the linkage would be adjusted to get the trim lever back to zero.

rgburrill

Seems like a lot of work. Why not just pin the control surface, disconnect the pushrod, zero the transmitter and then adjust and reconnect the pushrod.

da Rock

Mainly because pinning the surface takes something to pin it with or something to tape it with and pins leave holes and tape..... whatever...

Why not just eyeball? Don't have to remember to bring them and they don't leave marks?

da Rock

OK, so wouldn't you want to then not do step 6. Having two steps that "correct the trim to zero" doesn't really work.

da Rock

Good method, but a question:

"give it 5 clicks of down trim" or "set it to 5 clicks of down trim" ?

When maidening somebody else's plane, "centering the surface" right off isn't usually in the cards. And not necessary if it's my plane. If it is your plane, while you're doing this at home while assembling the sucker, take a minute and start with the servo arm squared up to the pushrod, THEN do whatever it takes to "start with the surface centered". (adjusting the pushrod length usually)

With somebody else's plane at the field, after I've cranked in the TX trims to get the surfaces right, looking at what's on the TX trims is worth knowing. It tells you how square the servo arms are to their pushrods. Too much trim and we open up the plane and "Installing Pushrods 101" begins. If they're too impatient for that, then I ask around to see if anyone else would like to do the maiden. Why act like a hardaxx, if nobody else wants it, I go fly it. And on landing, look at where all the trims are now. Often one or two has lessened the TX settings. They've often got the servo arm off one way and the pushrod length off the other way. If they're both off the same way, that showed up as too much trim.

I always ask if they're done any of the magic tricks the TXs today can do to "save you time zeroing trims". If they have, I usually ask to see inside the model because you got no clue where the servo arms are relative to their pushrods.

BTW, if right off any surfaces go the wrong way, I ask 'em to take the plane over to the shelter and open it up. Fiddling with trim settings to center the surfaces isn't the best next step.

A. J. Clark

You would still need step 6. Unless you did it as rgburrill suggested which would eliminate one step.

600Bob

Well yes I meant that was 5 clicks of actual down trim. If it needed 5 clicks up trim to fly right and i gave it 5 clicks back down I would be back to center where I started.

And yes this is for my own planes that I have set up. If I were doing it for someone else it would depend on how right or wrong their own initial setup is

da Rock

Your method is the simplest so far and I wanted the beginners who come here to benefit from it. If they were the kind who follow each step to the letter, they might have thought they were doing it wrong. I knew what you meant 'cause I've done it that way a bunch of times.

And it works great for others planes.