Hi Fellows,

A friend of mine bought a Giant YAK 54 powered by a G62, I did the test flight on the bird and after 5 minutes of flying time the trothle and rudder started make some glitches, it was scary but manage to get it safe back to the ground. We check the connections on the trothle and rudder servo and everything looks ok. After disconnecting a home made engine kill swicht we flew the plane again and same results, it glichtes again.

Any suggestions or advise where to look are Welcome,

Daniel

So many threads on here with the same problem, do a search for throttle or rudder glitches, however, most seem to be because of either metal too metal contact or low battery power, others have been put down to regulator problems, the list goes on, even doggy servo's have an effect, process of elimination normally sorts it out.

Mike

If it passed a range check and then flew fine for 5 minutes, it sounds like you probably have a battery problem. It seems like it starts to fail after the initial surface charge is used up. Test the battery with a good quality, LOADED, esv

*scratches head*

What you are describing is RF interferance... if your battery gets low or is not holding a charge properly your servos are going to get weak. RF interference does not go up because your batteries aren't performing? /*scratches head*

You don't mention doing a proper range check... are you doing one with and without the engine running? You should be able to get close to or better to 90% of the range with the engine running that you got with it off.

Things to check


#1 Metal on metal contact anywhere on the plane - ie linkages etc
#2 Is your spark plug cap on tight and all the way?
#3 Are you using a resitor plug and do you have another one you can try.. bad plug can cause this
#4 Go back and look at all of your linkages again - especially throttle.. make sure plastic connections at both ends.

Dosen't sound like RF interference to me, RF would be there from the beginning of the flight, not just start to show up five minutes into a flight.

Servos don't normally start twitching from low battery issues and not 2 different channels.

It could be RF at a certain throttle setting. I will give you an example.. few years back I had a 3W 50 that would get random glitches and I spent hours trying to find it.. replaced switches, batteries, servos.. tried everything. I could fly 3 flights and thing it would be gone and then it would randomly show up.

In the end I had metal on metal in my throttle linkage right around 1/4 throttle. Since I wasnt there very often it was hard to duplicate.


I am not saying for sure it's RF... but I cant say I have read or heard of batteries causing glitches of this nature in servos. I mean you hear about JR servos when a pack is at full charge twitching.. but thats all that comes to mind off the top of my head.

Which Yak is it?
We had an RCLeague one which was assembled in accordance with the manufacturers instructions - it was our first gasser and was in the same size range as yours. It would twitch at low throttle - below 1/4 throttle. It was caused by the metal pull wires for the rudder - they crossed and rested on each other and the vibration at low throttle was just the right amount to give us a twitch. We Changed to Kevlar pull pulls and never looked back. That particular plane also had the throttle and choke servo mounting points in such a location that the linkages would either touch or the throttle linkage would rub on the fuel tank at half throttle - depending on how they were routed - I noticed that during the build and converted it to a manual choke.

Have an experienced helicopter guy take a look at it. Unless things have change over the years, they were always chasing clitches on those. Maybe they'll find something you overlooked.