I just got my new 1.20 Yak 54 in the air for the first time last Friday and was checking it out today for loose bolts, etc., when I found that both elevator servo arms have "play" in them. I thought it might have been the arms loose on the servo shaft, but new arms have just as much movement (about 1/64" or so at the rod connection). This suggests it is in the gear train of the servos. The servos are Hitec 5645MG's. The same type servos on the ailerons don't seem to have the "play". During the one flight I heard a buzz that might have been flutter, but couldn't pinpoint it and it wasn't where I could identify the flight regime when it was happening. Has anyone else experienced this on this airplane? I have the gaps sealed as per the model's instructions.

First question, if it is flutter, what can be done to eliminate it? I was thinking of some counter-weight in the outer elevators where they extend forward of the hinge line, but the CG is marginal already and I don't want to make that a problem. Second, have I already ruined these expensive servos? How do I check them? Is the gear train replaceable (by me)? Comments and suggestions welcome!

How many flights are on those servos?

Yes you can replace the gears yourself, do one at a time and look at how they are assembled. You will also want some proper gear grease designed for servos. I believe the gear sets are around $17.99. If you send them into Hitec they will also do it for you.

Just the one flight. I hope that I'm not jumping the gun on this, thinking that it is damage due to flutter or some other flight-related issue. If it is, I need to correct the problem first. No point in repairing/replacing the gears if it is going to happen again as soon as I put the airplane in the air again. Is the small amount of play at this point actually something to get this worked up over?

How fast were you going when this happened? I haven't seen anyone else report flutter on this plane; however, excessive speed might cause it. If you were not going excessively fast, maybe the buzz was a loose piece of leading edge covering??? I understand flutter to be caused by insufficient hinge points, that's why I'd be surprised if that was the problem (absent extreme speed)

I'm really still hoping that it is not, in fact, flutter after all. The hinges are all still tight. There is no loose covering that I have been able to find. But I do have the play in the servos that concerns me and I want to find out the cause if possible. Any other possibilities that you can think of?

I had a QQ 1.20 yak a few years ago with Hitec 5625 servos. I had initially set it up so I could get 3D throws. I found the plane wandered and hunted in pitch and roll so badly that it was not enjoyable to fly. When I reduced the length of the servo arms, the slop in the servos wasn't amplified as much and the plane was much better.
That doesn't really help you other than to tell you that you're not the only one who considers the 56xx series servos to be too sloppy.
Dan

If it is elevator flutter the buzzing should stop if you lower the air speed. One way to stop flutter is to have a small amount of force (positive or negative) on the elevators. This can be done by changing the CG. Change the CG just a small amount to see if it stops the buzzing. Flutter is a very destructive event. It can rip an airframe apart in seconds. When I worked for Boeing, they had a film of a flutter test model for the wind tunnel (a 707 I think). When the flutter started the wings oscilliated like a sine wave in geometry and in about 3 seconds the model disappeared down the wing tunnel. On an RC model it probably would just rip the elevators off or pull the control horn loose. Not good either way.
Ralph White, Neoga, IL

what servo arms are you using?

Well on one flight and new servos I doubt it's a problem in the servos. To be realistic you have to expect a little play in servos.

What engine / prop do you have on this plane?

If a little play in the servos is normal, I may be all right. It is just a very small amount, but more than I can detect in the aileron servos of the same type. The servo arms are the single leg plastic ones that come with the serevos. I was going to use the metal arms (also came with the servos), but they are significantly shorter than the plastic ones. I'm running an O.S. 1.20 AX with Bisson muffler like shown in the assembly instructions. Prop is an APC 17x6. This seems to be a noisy combination and "could" be the source of the odd noise that I thought might be flutter. The only flutter I have ever heard for real sounded more like a loud "rasberry" (the pilot saved the airplane, but it was coming apart at the hinges).

BTW, thanks everyone for the comments.

That would be an accurate description of the sound. Almost like you took a piece of paper, held it between your fingers and blew on the leading edge. It vibrates, same basic sound.. just not as much air going over the surface.

You have more than good enough servos for the size of plane. You can try ordering some aluminum arms that will be a little tighter and using ball links at the end that screws into the servo arm as well.

If you hear flutter, throttle back right away and land to inspect the plane. In most cases you have time to throttle back and save the plane, its when people keep flying at full throttle to verify the noise when it gets bad. You can also do some high speed passes with someone watching your surfaces for movement.

I would wonder if really there is just a small piece of covering loose somewhere that you haven't found. With good linkage, sealing the gaps, and minimal play it's hard to get flutter unless you are flying at full throttle on an over powered plane.