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Aileron Trim

Old 05-10-2004, 08:34 PM
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mtomas
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Default Aileron Trim

Hi,

Is it normal to need 11 or 12 clicks of left aileron for straight and level? This doesn't seem right to me.

With the ailerons in the neutral position (trim at 0 and ailerons flush with wing), the right wing drops relatively sharply while in the air. 11 or 12 clicks of left aileron are needed to attain level flight. Once trimmed for level flight, left turns done with the ailerons look rather strange. It almost looks like a rudder turn does. The plane does not want to come around. As the turn progresses, more left aileron is needed (i.e. i am having to use constant and increasing pressure on the left aileron). Sometimes, I will get to full left aileron and the plane looks like it just won't make it through. Airspeed also seems to drop significantly while trying to make left turns. I am not attempting to do particularly sharp turns, just normal gentle turns.

So far I have checked the following things:
[ul][*] balance is dead on in the recommended range[*] plane balances perfectly lengthwise (i.e. nose to tail)[*] fuselage is straight and not warped[*] wings and ailerons are straight and not warped, dihedral lift on each side is equal[*] elevator assembly is straight and not warped[*] stabilizer assembly is straight and not warped[*] elevator assembly and stabilizer assembly are square at 90 degrees[*] when viewing the plane from the front and rear, everything lines up good
[/ul]

Does anyone have any ideas on what I am missing? While I am able to keep good control of the plane, it just doesn't feel right when making left turns.

Also, right turns are completely normal and the plane is a Nexstar.

Thanks!
Old 05-10-2004, 08:52 PM
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Default RE: Aileron Trim

There's definitely a problem of some sort... What I can't guess because you do seem to have covered them all!

GENTLY twist the wings and see if one flexes more easilly than the other. Might be an internal problem. Don't apply a lot of pressure... just enough to see a SMALL ripple appear in the covering is PLENTY. If its an internal structural problem... contact Hobbico.
Old 05-10-2004, 09:18 PM
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mtomas
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Default RE: Aileron Trim

Could a misaligned nose wheel or incorrect incorrect engine thrust angles make the plane react this way?
Old 05-10-2004, 09:28 PM
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vinnie
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Default RE: Aileron Trim

With the ailerons at neutral, try trimming for level flight using rudder trim only. Then try some turns and see if the response is more normal. If it is, take a closer look at the vertical stab/rudder alignment with the fuselage. Check for wing warpage as well.
Old 05-10-2004, 09:39 PM
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Default RE: Aileron Trim

The nosewheel has essentially no effect on how the model behaves in the air. (on th ground it has a large effect)

The engine thrust line being incorrect can have the effect you are refferencing.

Also... having the RUDDER offset can cause you to "cross-correct" with ailerons... (this can get dangerous... cross-correcting is inviting a stall-spin on final approach.)
Old 05-10-2004, 10:20 PM
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Cjsworks
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Default RE: Aileron Trim

I noticed you only refered to your balance from front to back. What about from side to side? Is your plane heavy on the right side? I had one like that and had to move the battery and reciever to the left side of the plane and still add some weight. Flew much better after that.
Old 05-10-2004, 10:24 PM
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mtomas
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Default RE: Aileron Trim

That's actually what I meant, sorry for not being clear. The plane balances from front to back (within the specified range) and from side to side.
Old 05-11-2004, 02:06 AM
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Default RE: Aileron Trim

If the CG is right, and the balance is right, try flying with the rudder more. You never mentioned using the rudder in your turns. Try to trim the rudder for straight and level as mentioned by vinnie and set your aileron trim back as close to center as possible by adjusting the clevises on the pushrods. Are you using the SWOOPS, and spoiler thingy?
You know...not to start anything here, but I have seen a few people having trim problems with the Nexstar. Dunno!
Old 05-11-2004, 02:17 AM
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Default RE: Aileron Trim

If using the nextar's autopilot, and gain is too high, you can have a lot of trouble turning. (but that would be both directions...) However... with the extreme trim setting...that may be the amount of trim needed to overcome the autopilot when cross-correcting for a MINOR rudder trim problem.

Double-check that the rudder is straight in line with the vertical fin... Its one thing that you have not mentioned. (don't correct the nosewheel causing a turn on the ground with the rudder trim, make sure the rudder itself is aligned correctly for flying.... then adjust the nosewheel at the servo connection.)
Old 05-11-2004, 09:26 AM
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Campy
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Default RE: Aileron Trim

Another thing you can check is the main wing to the fuselage alignment. It should be 90 degrees to the fuselage when looking down and have equal angles when looking from the front or rear of the plane. DO NOT HAVE THE PLANE SITTING ON THE WHEELS when doing this, have the fuselage blocked up so the fuselage is 90 degrees to the ground - I would also recheck the horizontal and vertical stabs alignment. If the wing is off center, line it up and put some reference marks on the front and rear of the wing. If the main wing is off center it can cause this (one side of the wing has more lift than the other). The reason for blocking the fuselage is the landing gear/wheels may have a slight difference in height.

Have you checked the "differential" in the ailerons ? They need to have the same amount on each side. If the differential if different or they don't have any differential that can cause the problem. If there is no differential, you should put some differential in the ailerons, it will make your turns easier. Differential is where the ailerons go up more than they go down. You would put the push rods off center on the servo to do this and it is easiest to do if you use a wheel instead of a servo arm.
Old 05-11-2004, 12:25 PM
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CrashBurn69
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Default RE: Aileron Trim

Also put a little pressure on your aileron while using the servo a little. It might be slipping and thats where it stops with the wind pushing over the wing.
Old 05-11-2004, 12:30 PM
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Montague
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Default RE: Aileron Trim

If you haven't already, turn off the autopilot thingie.

Beyond that, sounds like a rudder trim problem. On many trainers, it's hard to tell if it's the rudder or aileron causing a plane to turn. I'd center the ailerons, then see if you can stop the turning with either just the rudder or with both rudder or ailerons.

Also, double check the aileron linkages. I once took off with one aileron in the wrong hole on the control arm. The plane flew very funny, mostly rolled one way much faster than the other.
Old 05-11-2004, 06:57 PM
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Ragtop
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Default RE: Aileron Trim

Try a straight ahead stall, the higher the nose angle the better. If the airplane falls left (for instance), the left wing most likely has a higher angle of attack. You can gently twist the tip l.e. down and heat monocote with a gun to fix.
Next, point the aircraft straight up in flight and reduce power to idle. If the nose falls CONSISTENTLY left (or right) the rudder is misaligned.
To find if the thrust angle is correct, measure prop tips to fuse tail with the prop horizontal. You can also see thrust alignment problems if an application of power turns the plane after being trimmed.
Old 05-12-2004, 03:21 AM
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jcflysrc
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Default RE: Aileron Trim

Man, this is all very good advice, and I think the answer to your problem is in here somewhere. One other thing you might look at...does both wings have equal amounts of washout? I had a WM Super Stunts 40 that had that problem, and it was a handfull until it was corrected. Just a thought, hope it helps.
Old 05-12-2004, 04:08 AM
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MikeEast
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Default RE: Aileron Trim

I will say that the answer to your problem is yes, you'll need a lot of left aileron or rudder trim to get the plane to liftoff and fly straight and level. I have worked with several guys flying nexstars and they ALL drop the right wing on takeoff. We had to add a ton of left ailerons to everyone for straight and level flight and they still fly to the right on liftoff. We were just discussing this exact problem and comparing 2 of them at the field the other day. I dont know what the problem is but its definitely there. With all of the dihedral in the wings, rudder behaves a lot like ailerons. Try trimming it out with Rudder and leave the ailerons level and see if that helps any. Once you get the settings corrected with trim, mark it and readjust the throws to that position so that you can get the trims back to center so you have trim again.
Old 05-12-2004, 06:06 PM
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mtomas
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Default RE: Aileron Trim

Hi All,

Thanks for all of the suggestions! Here is some follow-up:
[ul][*] Autopilot, wing droops and speed brakes - I am not using the AFS, wing droops or speed brakes[*] wing alignment to fuselage, alignment of rudder with vertical fin - I blocked the plan up as recommended and checked the wing alignment - its right at 90 degrees to the fuselage. I also rechecked the horizontal stab alignment while the fuselage was blocked up and I found that the right side of the horizontal stab was actually drooping a little less than a 1/4" lower than the left side. Previously, I had checked this when the plane was on its wheels and did not notice the difference. The offset was caused by an un-level cut in the fuselage for the horizontal stab slot. Anyways, with some light sanding and some minor shimming I have evened out the stab. I also rechecked the vertical stab/rudder alignment and it appeared to be a perfect 90 degree angle to the horizontal stab. I'm not sure if such a small difference would have caused the right wing to drop so sharply?[*] I rechecked the balance of the plane from left to right. This time I had a helper with me which makes things easier. The right wing would hang ever so slightly lower than the left. I added about 3/8 oz of lead to the left wing tip and it evened out perfectly. I'm not sure if such a slight imperfection would have a large impact on the right wing dropping so sharply?[*] aileron differential and linkages - Both the left and right ailerons have the recommended throws and differential setup of 1/2" up and 3/8" down.[*] servo slipping - I have verified that the servos are not slipping.
[/ul]

Do you all think it's possible that the combination of the slightly uneven horizontal stab and the slight weight imbalance could cause the right wing to drop so sharply? The imperfections seem quite minor to me, but maybe?

As soon as I can get out to the field (maybe tomorrow) - I'll test her out with all of the trims reset. If the wing continues to drop, I'll then try trimming with the rudder only and see what happens. I'll keep ya posted on my results.

Again, Thanks soo much for all of the help!
Old 05-13-2004, 11:45 AM
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Montague
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Default RE: Aileron Trim

Do you all think it's possible that the combination of the slightly uneven horizontal stab and the slight weight imbalance could cause the right wing to drop so sharply? The imperfections seem quite minor to me, but maybe?
Maybe, but I don't think so. (how's that for a non-answer).

Did you check the wing for warps, espeically a warped aileron? It's real easy for the ailerons on some of these trainers to get a bit of a warp to them since they are just a solid chunk of balsa with heat-shink covering on them. If you heat the covering unevenly, you can twist the TE of the aileron a little, resulting in some roll tendancy.

Also, turn the radio on, and ceneter the ailerons. Now grab the aileron tip on one side and gently push up and down. Ideally, the aileron won't flex. In the real world, it will flex some. Compare the two sides, does one flex a lot more than the other? If so, it can cause some trim oddities (though, usually it just results in rolling faster one way than the other)
Old 05-13-2004, 12:37 PM
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Default RE: Aileron Trim

The horizontal stab and lateral balance (side to side) are/were definitely contributing to the problem. It may be the whole problem or may not.

Try centering the ailerons and trimming it out with the rudder. Also, as was mentioned by Montague, check the ailerons for flex and warping as well as the fixed and moveable part of the horizontal stab. If any of those are flexing that will also cause the problem.

Flexing is fairly easy to determine in the air. Do a loop at a relatively slow speed (just fast enough to get through the loop), then do a loop at HIGH SPEED (wide open). If the plane does some "unusual" gyrations and/or does not track straight, especially when doing a HIGH SPEED loop, you most likely have something flexing (most likely the vertical or horizontal stab). Make sure you are AT LEAST "3 mistakes" high, especially before doing a high speed loop. I would suggest A MINIMUM of 150' up AND be ready to chop the power and correct the plane, IN THAT ORDER, if "unusual" gyrations occur.
Old 05-13-2004, 12:45 PM
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Default RE: Aileron Trim

Of couse... if you pull too hard in the high speed loop... you can do a high speed stall and snap-roll out of the loop (usually near the top of the loop) even if the airplane is straight... Some experience with seeing which is in-flight warp vs the high speed stall may be required for the test. (test works.. just need to know the catch to it.)
Old 07-09-2004, 09:09 PM
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Default RE: Aileron Trim

I had to pull off the servo arm and rotate it one notch ,then my trims are very close to the middle.
Old 07-09-2004, 09:41 PM
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Default RE: Aileron Trim

whats with people resurecting old topics tonight?
Old 07-10-2004, 07:05 AM
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Default RE: Aileron Trim

Now that it has been resurrected, was the problem ever found?

mtomas?

Dennis-

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