Tail wag after belt change

[gstoneberg]

I've been struggling with my p500 tail lately, after it had flown wonderfully all summer. It suddenly occurred to me all this trouble started after I put a new belt on the bird. The previous belt broke in flight, it wasn't very high, the quick auto was successful so it had no damage other than the belt. After putting the new belt on it had a fast wag. I kept lowering gain until the fast wag stopped, but now the tail doesn't hold well in fast tail first flight. It's not too bad if it's calm, but if there's wind it'll either fast wag, then when I lower the gain it'll blow out. There's got to be something mechanically wrong.

[ticedoff8]

Check all the usual suspects:

Pitch slider should be silky smooth as it travels from side to side. Keep it lubed and clean

Check the TR blade grips.
See if one grip requires more force to rotate it than the other.
Check the thrust bearings to see if they are dry (need lube) or have broken.
Check to see if the radial bearings are a little crunchy

Check the dog-bones (connect from the pitch slide to the grips).
They should be nice and smooth and easy to move.
Sometimes, a little Loctite will wick into the hinge point and that makes them stiff.

Check the control rod and the pitch control arm - they should be silky smooth and no binding

And, of course, check the servo.
Check the servo's mounting too - that could be a little loose.

Check the FBL gyro's mounting tape. It could be deteriorating and the gyro is starting to vibrate a little.
If the wire bundle to the FBL gyro is shaking with the airframe, this will move the gyro and start a feedback loop that will look like a bad tail rotor

[TitaniumFreak]

tail rotating in wrong direction ?

[DoubleCH]

If you're pretty sure nothing else has been changed except for the belt then check the proper belt tension and no lose tail boom mount or support struts.

In addition, to check tail pitch mechanism smoothness you need to disconnect tail servo movement to feel any notchiness. You may also need to run up to flying HS without blades or tail servo connection to feel smoothness/friction by moving the pushrod manually. The reason is that when the tail rotor is running at speed, the tail grips will be pulled apart. If the grips don't have identical distance from the hub center the geometry of the dog bones will be off generating a force pushing the brass sleeve inside the slider against the tail shaft. This force won't be detected when the tail rotor is not up to speed.

[gstoneberg]

Thanks guys, that gives me lots of things to try!