Hi all,

I have a Seagull PC9 with an inverted 55AX running up front. I am not sure what is going on so may need to go back to basics to try and find out. It flies well straight and level but when you go into a loop it screws to the left.

I have gone vertically up and it will fall to the left it is like it has left rudder on. So I trim it back to make it fly straight when going vertical and then it looks like it is crabbing in the sky when straight and level like it has right rudder (which it does now).

I have checked the balance both ways CG is good touch nose heavy if anythng. Wings don't dip when balanced between prop and tail..

Point in the right direction for me and where to start??

thanks

Prboz[sm=drowning.gif]

How do the elevator halves look. Are they in line with each other at center? How about at full deflection?

Hi ChuckW,

Yes I have stared at this thing from the front, back and side and nothing jumps out as to what it may be.

Regards

Thrust(engine) angle???

Years ago I had a Goldberg Sky Tiger that did the same thing. I ending up finding that with the wind load while flying on the elevator, it would flex & the right half would not go as high as the left side where the horn was attached. I increased the connector between the two halfs & the problem went away. Bill

There are lots of things that can cause this. The first is the plane not being built straight. Double check that the elevators are not only even at center but even at full throw as Chuck said.

How much roll trim is required for level flight? If you need a lot then the wing is probably twisted and the aileron trim will change as the speed changes. Check the wing for twist with an incidence meter at the root and at the tips.

Check rudder trim too. Kick it one way a few clicks and try a loop, then try the other way.

If everything is straight, the most likely culprit is lateral balance. Static balancing isn't enough, you need to check the balance in flight, it's much more accurate. Trim for upright flight until you can do long passes without correcting for roll. Then try long passes inverted without touching anything but elevator. Pay close attention to which way the plane rolls. If it rolls left then the right wing is heavy, if it rolls right, the left wing is heavy. Add some stick on lead to the light wing tip and test again. Any weight imbalance is magnified by the G forces in the loop and the heavy wing will be pushed to the outside of the loop causing the plane to screw out of the loop.

Seal your control gaps too.

Dave

Your problem is likely engine thrust angle.

Follow this trimming process:

http://www.seniorpattern.com/pdf/Kir...im_article.pdf

Like has been already said....If the airplane is built straight and elevator halves are even......then I'd check the lateral balance....then thrust angle

Too much elevator movement. Reduce it until the roll goes away.

Ed S

I had that same problem on a Texan.

TW

Just a thought,


Check all your hinges. Late last Fall I noticed my
Stik was slightly pitching to the right in loops, cuban 8's
and so on. I found a broken CA hinge on the outer part of the
right tip of the wing.


Bob

Assuming elevator halves are equal at rest and at full throw .........................

Falls to the left on verticle? Or does it pull to the left. It sounds to me like you're just experiencing the torque from the 55AX. Try flying a fast straight line and then pull verticle with the engine at idle. I will bet you that it won't pull left.

On my planes (generally overpowered) I always have to lean on the right rudder on uplines and any time I use full throttle. If you want to use your radio to mix it out program a few degrees of right rudder with full throttle. I prefer to just fly the rudder.

Adding r-thrust to the motor can help to some degree.

If follow the trim charts (in order), you will be impressed at how much better you can get your plane to fly.

Sounds to me like the plane has too much right thrust built in. That's been the case on many of my planes. Follow trim chart, but will probably result in reduction of right thrust; you can mix rudder to throttle to compensate for different speeds.

At one point all of my planes did this, sometimes they still do. I fly with finger and thumb and tend to pull in a little aileron when I'm pulling back elevator. Once I figured this out my planes started flying a lot better, most the time.

To much elevator throw. It's trying to snap roll.

Any test during this weekend, Prboz?

Mike and Ed are right......If laterail balance is correct too much elevator throw can cause you to roll out

Chuck pointed out the most obvious caise her..............add to this, is the stab square to the centerline of the fuse, and is the rudder exactly straight?

for elevator throw to induce a roll as you describe, you'd have to be pulling one tight loop to induce a sanp with elevator throw.

Hi!
As has been said earlier by Ed...as soon as well built plane snaps to the right or left, in either a loop or in a sharp turn...it's either too much elevator trow or...a too heavy model...or a combination of the two! Most of the time it is a too heavy model!

.
.
EVERYONE has that problem with their Texans...

Thanks Everybody for your help. will have to try some of this next time I'm out at the field, not this weekend I'm afraid other things to do.

Regards

Prboz