Just completed my first 30% model. I have a 3W-70 engine. 2000 mAh on the radio, 1600 mAh on the ignition.

I ran the engine several times without the wings attached and it ran fine. Just today I completely assembled the model and ran it to test the control surfaces. For no apparant reason, the engine runs erractically, it revs up and down with no control input and the control surfaces also jump around with no control input.

It appears to be an interference issue but I am stumped as to how I can isolate it.

I was hoping to maiden the model later this week but I can't even think about it until I solve this problem.

Any suggestions would be most appreciated.

Do you have a killswitch? Is your spark plug wire shielded properly(metal mesh)? Is everything ignition related isolated from everything rx related? If you have pull pull cables are they touching metal on metal? Is your spark plug cap on tightly? I have dealt with this before...I feel your pain.

Perhaps run it again without the wings???

Add servos one at a time to the system and see if any particular servo precipitates the jitterisms....

Sounds like a good idea. You may have a bad extension or servo in the wings.

Originally Posted by Mithrandir

Perhaps run it again without the wings???

Add servos one at a time to the system and see if any particular servo precipitates the jitterisms....

You are a master wordsmith...hah that cracked me up

The spark plug did fall off after one start. Could something that simple cause this?

Thanks.

Originally Posted by myfivezees

The spark plug did fall off after one start. Could something that simple cause this?

Thanks.

The plug cap not being pushed onto the plug far enough is probably the #1 reason for ignition interference with modern shielded ignitions. Most of these caps push on quite hard the first time or two. In most cases, the hex part of the plug will be completely covered when the cap is firmly in place.

I wouldnt run the engine without wings. The wings absorb a lot of the vibration...I have seen rudders and stabs come off a plane during idle with out the wings attached..

ARe you 72mhz or 2.4? How are you powering the ignition? You cannot power it with the same batteries that power the receiver if you are running 72mhz, and it is still frowned upon by some even with 2.4.
What brand and part # are the plugs? They need to be a resistor-type plug - NGK CM-6 plugs are what is used exclusively on 3W engines so that is what they should be - at least that is the case with today's 3W's.

CM-6 plugs are not resistor plugs! Most shielded ignitions used on CM-6 plugs have the resistor built into the cap.

Thanks all for your suggestions. It turns out a loose plug cap was indeed the problem.

I secured it and everything checked out perfectly. A very good lesson learned.

Now if I can just keep my knees from knocking on the maiden flight...................................

Voit makes some good kneepads.....that way you won't hear the knocking at least