My WM T-34 seems to fly fine, except that I can`t get a straight, round loop out of it. The loop upline starts straight but as it climbs it seems yaw to the left. By the time it pulls through the top it`s on a downline of about 45 degrees. Plane flies straight and level OK ( trims seem OK ). Could it be the rudder trim? What`s the best way to check rudder trim anyway? Any ideas appreciated. Otherwise, I love the plane.

tideflyer,

another thing it could be is the lateral balance might be off, or as you stated rudder trim could be off center. keeps us posted.





bassman

TideFlyer, your plane might need some right-thrust.

This is accomplished by using a washer behind the left engine mount screws so the engine points SLIGHTLY to the right, or at least "less to the left"... and I repeat: SLIGHTLY

try this just to make sure while on the ground as if you are doing a loop watch your control surfaces closely make sure you're not getting some wierd interfernce causing the rudder to move slightly at full throw or you dont have a mix added in by mistake. also check your thumbs to make sure you dont have some slop in the right stick of your transmitter
let us know good luck

People underestimate the difficulty of doing a "common everyday inside loop" precisely! There are many factors involved and the inside loop will allow these factors to show their influence. There was a great article written in the May 2005 issue of Model Airplane News magazine discussing trimming and I suggest seeing if you can get a copy somehow, or maybe the article can be accessed on their website. The article is so good, however, repeating what it said here is more time then I'm willing to take.

ain't that the truth!


check for thrust angle....

and the left stick needs be used to fly a good loop

I have had a couple of airplanes that would not loop straight but flew well otherwise. Turned out that the vertical stab was at a very small angle. The vertical stab can be checked for straightness by tying a string to the prop at 12 o’clock and holding it tight on the right side and then the left side of the stab. It the stab is off you can observe a small difference.

The rudder is more effective at slow speeds and at the top of the loop. Engine yaw also seems to be more pronounced at slower speeds and probably should be fixed first. Never did figure out how to fix the vertical stab without major surgery so I just flew it.

Bill

All good advice here.

One other thing to check is, are the elevator halves moving symmetrically? I seem to recall that this airplane has separate elevator halves driven by a split (Y) pushrod. If the pushrod is not adjusted properly, it could be moving one half of the elevator more than the other.

However, that will cause a roll; and what you describe sounds like a thrust problem. Serious aerobatic pilots deal with this by either altering the engine thrust line, or mixing the yaw out. The latter requires a rather sophisticated programming capability; otherwise, the mix will interfere with "normal" flying.

Anyway, check your elevator travel; you never know.