Just put a new G-20 in a KMP p-47. Radio works fine on all controls. Start up engine and just the rudder servo goes crazy, All other controls are fine. The egnition box is 5" away from the reciever. Tried another servo and it was the same thing. Just wondering what could be the problem

Need a little bit more info about the set up of the rudder and the servo. Is it pull pull cable or is the servo in the tail with a short push rod?

Have you tried moving the transmitter away from the plane?

I had a similar problem and it turned out to be a loose pin in the reciever that when engine is started the vibration caused the servo to react. I had purchased the radio new but I must have hurt the pin when installing the reciever plug. I also had one do the same thing with a bad extention.

chuck

You state that your receiver is 5" away from the ignition module.You need to have at leat 12" between any radio
equipment and the ignition module.Also you will need to do a thorough range check to make sure there is no interference.
What radio system are you using? I am using a Futaba 9CAP 72 mhz in my GP Extra 300 with a DL-50 gas engine without
any interference problems.I set up my plane systems by using this as a refernce to go by from Futaba.I range checked my plane
with this method and have not had any problems.

Hope this will help.
http://www.futabarc.com/faq/faq-q331.html

Since it is only on the rudder servo and only when the engine is running, it is almost certainly a connection problem in the rudder circuitry. It could be at the receiver where the connector plugs into the receiver or anywhere between the receiver and the electonics within the servo. First, plut the rudder servo into one of the known good channels and see if it continues to act up with the engine running. If not, you have a problem in the receiver itself. If it still acts up, you have a connector problem in the harness to the servo or within the servo itself. Change out servos, if the problem still exists it is in the harness, if not you have a bad servo.

A flying buddy instslled chokes on his servo leads solved the problem. Don't know where to get them.