aircat

Hey to all, when I do loops my plane does cork screw looking thing. The plane is similar to an ugly stick but has a clark-y air foil. At first I thought the wing or tail was warped or flexing but I don’t see any sign of problem , other than that it flies very well .
Any suggestions would be appreciated.
Thanks
Aircat

Geistware

My Feedback: (16)

Reduce the elevator throws.

MHawker

My Feedback: (16)

Is it "snapping" out of the loop? Have you tried doing a bigger loop? In other words, don't yank on the stick. Only pull it part way.

If that helps, you can either train your fingers or do what Geist says, so that you prevent it from happening.

Mike

aircat

Thanks for the responses, yes it does tend to snap out of a loop with a lot of elevator throw, however even when the throw is reduced, or the CG shifted forward it still cork screws. Even adding rudder does not seem to help, it's almost like one wing is producing more lift than the other, but they are not warped and it requires no aileron trim to fly straight and level.
Thanks
Aircat

AKMac

My Feedback: (1)

This doesn't sound like the problem, but it won't hurt to give it a try.

Pick the plane up by the point of the spinner, and the tip of the tail, and see if it drops a wing. If it does, add a little bit of lead to the oposite wing tip. The correct term for this procedure is called lateral balancing.

Rodney

This could also be because of slight miss trimmed ailerons and rudder. Try retrimming the rudder in the direction to correct the corkscrew then readjust the aileron trim to get level flight in straight out flight. It is easy to get these two trims adjusted to give level flight yet be out enough to give you the problems you are having. It could also be because there is a slight wing warp and the trims needed to correct for that cause the corkscrewing loops. Just hope it is not the later as that is much harder to correct.

ScottyC

My Feedback: (5)

Make sure both halves of the elevator have the same throw. And that both halves are in-line with one in other?

Geistware

My Feedback: (16)

Aircat,
You are going the wrong way. Shift the CG aft and reduce throws. Also make sure that your elevator halves are equal in movement.

ilikeplanes

Geistware is right. If your CG is correct (way aft of where most people put it) your handling will improve in all areas except stall stability.

BTW, I have problems with cork-screw loops too. I have tried everything in the book. To get a very high level of flying precision, your airplane needs to be built at professional level accuracy. My airplanes are perfectly straight to the naked eye, but to precision instrument and measuring tools, I bet they look terrible. Just ask any F3A guy how much time the spend trimming a model. I bet it's more than most of us fly in a year (no joke). Oh yea, you will always have to compensate for wind. Even a small wind can cause a noticeable difference.


Good luck.

aircat

I increased the area of the vertical stab a bunch; it was kind of small; and it seemed to help considerably. I will keep you up dated.

Thanks
Aircat

BernieG

waow, I see you get a lot of answers, but.....Not the obvious one !

Assuming that everything else is correct, plane straight, center of gravity ok (Should have nothing to do with the cork screw thing..), ailerons properly set to neutral, there is 2 things to check:

(1)-Be absolutly CERTAIN that your elevator 2 halfes are aligned, and move with the exact same throw.

(2)- At the top of the loop, when you don't have much speed, you get the maximum K-factor, that is the torque of the engine apply a strong yaw effect, which only the PILOT can correct.....So, check the pilot... ;-)

Bernard

evader_handler

Either your wings arent shaped rith or you rudder servo is malfunctionning

noname-RCU

Hi!

I had a similar problem with an Ultra Stick 40. I *did* go through all the instrument & level checking routines and everything seemed close to perfect. I EVEN added weight to the lighter wing so that the plane would balance (laterally) when held up by the prop.

Later, while reducing weight like mad I removed all the wings cap-strips and made holes all over. Much to my surprise, the wood used in one half was completely different from the one used in the other half. After all the "excess wood" was gone, my plane tracked perfectly through loops & similar maneuvers (both wings weighted almost the same by now).

I also thought the problem was a miss-aligned aileron, twisted stab, engine torque, etc .. you name it ... but in the end, none of those theories stood up with reality.

My conclusion was that static balance was the same (because of the added lead in one wing) but dynamic balance was way off (the wing half's CG's where completely off) ..

NOTE: I am not suggesting you do the same as I did, but it might give you some clue on what's wrong

lynngordon

I'm surprised that no one has yet suggested off setting the engine thrust to correct the problem. If the aircarft cg is balanced correctly, the wings balance level, and the control surfaces are equal and not warped, then try putting in a degree or so of engine thrust opposite to the direction of the corkscrew.

Lynn