Trimming Question

[Greg L Bahrman]

I have a Profile Cardinal with an LA46 and it flies nice. Except for this one problem. It is rock solid in level flight but when I go inverted it hunts, not severely but enough to be irritating.....Any suggestions ??

[Steve Helmick]

I've had the same problem with mine. Last contest, I moved the LO's forward, and it got light on the lines. That told me that the LO's were previously pretty close for the current CG, so I moved the CG forward with a 1 oz spinner noseweight (while I was there, I might as well 'speriment).  I figured the line tension would be better, and it was. The control response was still fine, and corner was still there. What changed most was the inverted was much more locked in.  Steve

[Greg L Bahrman]

Well I'll give it a try. Flying upright I can look away and no problem, but inverted the plane goes wacky and I have to fight it every step of the way to try and keep it level and if there's a little breeze it gets worse. I cannot put in two level laps inverted. Discourging

[Joe Yau]

Well I'll give it a try. Flying upright I can look away and no problem, but inverted the plane goes wacky and I have to fight it every step of the way to try and keep it level and if there's a little breeze it gets worse. I cannot put in two level laps inverted. Discourging

It could also be the flap/elevator alignment..   you could try to extend the push-rod 1/2 turn out on the ball link or just a hair up on the elevator vs the flaps (maybe more if needed), and see if that helps.  

[Greg L Bahrman]

OK Joe, now I'm more confused than ever. Presently I have the elevator down 1 1/2 turns when the flaps are level. I thought this was correct Talk to me !!!

[EddyR]

Excessive offset on the motor will sometimes also couse the problem.

[Ted Fancher]

OK Joe, now I'm more confused than ever. Presently I have the elevator down 1 1/2 turns when the flaps are level. I thought this was correct Talk to me !!!

Hi Greg,

This is why they call it "trimming".  The bottom line is that no two airplanes are exactly alike in that they will probably have different degrees of small misalignments built in any of a infinite number of ways.  The only correct approach to deal with an airplane is "not" to compare it to another one but to be responsive to what it tells you is wrong with it.  This sort of dichotomy between stability upright versus inverted is almost certainly the result of angular misalignment of the wing and tail.  That misalignment could come from something as fundamental as gluing the wing and/or stab in inaccurately or as difficult to determine as having the stagnation point of the wing or tail either high or low by virtue of not shaping the leading edge correctly.

In any case, the important thing from the flier's perspective is to react appropriately to the unwanted result of "whatever" the state of trim is and, then, to adjust the trim to eliminate the problem.

To wit, an excessive amount of the very popular "positive stab incidence" (which is the same thing as a drooped elevator relative to neutral flaps) will be very stabilizing when upright but could well produce the instability you're getting while inverted.

To aid your evaluation, I'd pay very close attention to the airplane's response to inside and outside maneuvers and if it seems to turn more aggressively and be harder to stop where you want it on outside turns I would be dialing in a little more up elevator every flight until I noted a change.  If you don't use a vertical handle in level flight I would also encourage you to do the "response" check with the handle adjusted to be vertical in level upright flight.  If you're totally uncomfortable flying that way find a good flier who does use the vertical neutral position and ask him to do the evaluations for you.  The biased handle position that comes with a "relaxed" neutral position will effect the airplane response and could well disguise the symptoms you're looking for.

Ted

[Greg L Bahrman]

Thanks everyone,
With your input I have a few things to try now. I will take some of the down elevator out. I can also remove some of the out thrust. I kind of don't want to add nose weight if I can help it but push comes to shove I will do it. I already fly with a Francher Hard Point Handle and it's setup to be vertical in level flight. The inside loops and the outside loops are equal and with equal response so I don't see an issue there. I assembled it with an incident meter but I will go back and check it all again........I know, one thing at a time......Sigh........Thanks

[W.D. Roland]

Check airplane for down thrust.

[Greg L Bahrman]

<Check airplane for down thrust.>

For too much or not enough ??

[steven yampolsky]

I have a Profile Cardinal with an LA46 and it flies nice. Except for this one problem. It is rock solid in level flight but when I go inverted it hunts, not severely but enough to be irritating.....Any suggestions ??

I'll list something dumb but often forgotten: a lot of people hold the handle sideways when flying inverted. Constant change of model to handle adjustment causes hunting. I am yet to see a pilot who's model did not hunt with that style of handle holding.

[Greg L Bahrman]

I'll list something dumb but often forgotten: a lot of people hold the handle sideways when flying inverted. Constant change of model to handle adjustment causes hunting. I am yet to see a pilot who's model did not hunt with that style of handle holding.

I'm one of the few that fly with a Fancher hard point handle in the vertical position, both upright and inverted......Not a dumb question.