ORIGINAL: turnnburn

I have an L-39 arf that just will not stay in trim ( roll axis). If trimmed for any certain power setting to fly wings level it will be out of trim if flown slower or faster. For instance, I flew today and had it trimmed straight with half or 2/3 power. I then went to flull power and the airplane started a slow but noticable roll ( I forget which way). Conversely if trimmed for high speed full power and then slowed to 1/2 power or so it will be out of trim in the opposite direction. Its not a lot but it is cetainly noticeable and makes it had to fly smooth and precise and requires constant retriiming .

The truth of the matter is even when trimmed for straight and level with constant speed and power the airplane seems to wander and not stay ''rock solid'' level and in trim. This is less noticeable and less annnoying than the trim changes with speed and power changes but it still makes for a less than ideal situation.

Anybody have ideas why this is happening and what can be done about it ?

I have a couple of suspicions. First of all the airplane requires quite a bit of ail deflection from nuetral to be more or less in trim in roll axis, so something is obvilusly warrped or crooked some where. I wonder if the faster the airplane flies the greater the effect of the warp ??

Secondly the large nose gear door is not quite able to close 100% as it sits right now. The forward end hangs open about 3/32 to 1/8 '' at the corner opposite the hinged side. I have tried in the past to fix this but so far I havnt been successful. I think I have figured out a way to fix it now. My theory is that the faster I fly the more air it catches underneath that slightly open front corner and causes it to possibly open a bit more. Im not sure why this would or could cause a roll trim isssue however.

What do you think guys ? I forgot to mention that I have already installed better more precise digital servos on ailerons and this was little or no help.