Suddenly Out Of Trim

[M Towsley]

Here is something that I have not encountered before. My plane, that I have had for almost six years, has been a hands-off, well-trimmed airplane the entire time I have owned it. The last two times I have flown it with just me I have noted it wants to go into a very slight left bank. With a passenger I do not notice it. (And no, I have not gained weight).

Nothing was changed to the aircraft and the wing tanks are empty. Has anyone else encountered this sudden out-of-trim condition to a normally straight flying plane? Thanks!

[PA1195]

Re: Suddenly Out Of Trim

I have had tailwheel assemblies (springs, chains, fork) not center or follow the rudder position. Sometimes it's stiction in the fork rotation, sometimes it's been a loose connection between the rudder and tailwheel that leaves the wheel offset from the rudder deflection.

Look at the ailerons and T&B ball while flying. When are the ailerons trailing the same relative to the wing...straight and level or in the slight turn? What's the control wheel position when the ailerons are uniformly deflected (on the ground and again in flight)? Is the ball normally centered in flight, or does it take a slight turn to center it? Does it roll with a change in trim?

Airframes and fabric can change shape over time affecting rigging. Depends on the underlying material, fabric covering, and climate. Look the airframe over for any warpage. Wood isn't an inflexible medium. Engine mount rubbers compress. Doors loosen. Elevators go out of alignment. Aileron cabling and linkage changes allowing deflection. Stuff happens.

Gary

[3Dreaming]

Re: Suddenly Out Of Trim

Here is something that I have not encountered before. My plane, that I have had for almost six years, has been a hands-off, well-trimmed airplane the entire time I have owned it. The last two times I have flown it with just me I have noted it wants to go into a very slight left bank. With a passenger I do not notice it. (And no, I have not gained weight).

Nothing was changed to the aircraft and the wing tanks are empty. Has anyone else encountered this sudden out-of-trim condition to a normally straight flying plane? Thanks!

Marty, to the best of my recollection, the trim can only be right for one condition. Either it is in trim solo or with a passenger, but not both. There are some guys here with Thorp T-18's, and sometimes in smooth air they will fly around simply by leaning their body different directions inside the airplane.

As Gary mentioned sometimes just a little friction in the control system can throw things off a little.

[Ragwing nut]

Re: Suddenly Out Of Trim

make sure your cable is not slipping. It is a common problem

[M Towsley]

Re: Suddenly Out Of Trim

Thanks, Tom. I don't know if I was just lucky but both of my BC-12's would fly hands off with single or both occupants. I know it doesn't make sense but they did. I noticed this incident the first time as it started to lift the right wing on takeoff in calm air. I have ball bearing pulleys and they are smooth in operation. That is what is throwing me off as to why it is only doing it to the left and never did it before. I will do some further in-depth investigation.

Mike, my elevator trim is fine, it is the left bank issue that is confusing me as it has never done that before.

Thanks, Gary!

[PA1195]

Re: Suddenly Out Of Trim

Mine did the "it started to lift the right wing on takeoff in calm air" (mine was left wing but whatever). It started after maintenance this Spring. All the thoughts I posted above I went through until I adjusted the left wing's wash in May (washed it out; lengthened the rear screw 1 turn). It quit doing that. I'd stall the plane on wheels and skis and noted no particular wing drop before the adjustment, just the left lift first on T/O deal. VG's tend to mask bad stall behavior.

Rest of story. This Spring my mechanic replaced the control pulleys...ball bearing...and adjusted the following: Left control chain to sprocket was off 1 tooth; tightened control sprockets; adjusted aileron turnbuckles to the new pulleys and then to aileron wing bellcranks; lubed and tightened the aileron bellcrank ball-end stud connectors and adjusted pushrod ends to the connectors.

I think what happened was after the lift struts were replaced last year and the wing wash initially adjusted it flew in rig ok with no asymmetric lift on T/O, but with loose aileron cables and bellcrank fittings that allowed one or both ailerons to float up under wind load in flight...there was some free play up and down on both when pushed before control resistance felt. When the control system was upgraded and adjusted the wing wash was probably off and the left wing had more lift. Fixed it now.

I mentioned the tailwheel deflection because it can act as a small rudder if offset in flight, or not allow the air rudder to properly center if deflected.

Gary

[astjp2]

Re: Suddenly Out Of Trim

I try to rig the ailerons down on both sides about 1/4" so the lift will pull them gently up, then adjust the aft struts 1/2 turn at a time until the airplane flies level. I also don't have return springs on the rudder pedals, I just rest my feet on them and they stay tight. I can fly my airplane hands off for 30 minutes with only rudder inputs and leaning forward and back if its rigged right and power is set right.

[PA1195]

Re: Suddenly Out Of Trim

Good point on the deflection Tim. I've found on several Cubs that they like the deflection you note as it stiffens the controls when they align with the trailing edge especially in slow flight in cold air when the cables go slack.

Gary

[Ragwing nut]

Re: Suddenly Out Of Trim

Sorry should have read closer. Do you have a tab on rudder? Did someone possibly bump it. Or have you checked your tailwheel rudder springs to make sure one side is not bound up?

[Scott]

Re: Suddenly Out Of Trim

I had two thoughts in addition to what's been suggested,

any chance you picked up a critter? bird or mouse nest in the aileron or wing/aileron bay? or perhaps water trapped out there somewhere. doesn't take much weight at the tip to upset things.

Second is the rudder springs on the pedals, check to see if one of them has deformed in some way such that you have more pressure on one side than the other. A little corrosion inside the spring could allow the spring to deform causing the sudden change in trim.

[M Towsley]

Re: Suddenly Out Of Trim

All great ideas, guys. I will check the next time I am out at the hangar. 107 heat index right now, should cool off this weekend.

No water, Scott. I was wondering about something in the tip but the plane, during takeoff, wants to lift that wing immediately. I will check, though.

[woodmw]

Re: Suddenly Out Of Trim

Marty...

Did you ever discover the cause of this problem? Come up with a solution or just have to live with it?

[Hank Jarrett]

Re: Suddenly Out Of Trim

I have seen this happen on several planes. The WORST case involved a very light bump of the wing tip on a hangar. It did not even scrape the tip fabric or break the tip light, but it DID use that long wing moment to cause a split in the wood of the aft spar! In flight the wood was opening up slightly and changing the angle of attack of one wing causing a pretty hard turn. The pilot brought the plane back in VERY GENTLY and started looking just like you have been. When twisting the wing from the tip he could hear a slight popping sound and the wing on one side would twist under load more than the other side. Lord knows what might have happened if he had pulled some G's and the aft spar attach had failed. The splits ran from the bolts holding the fittings to the root end and were very hard to see since when the wing was rebuilt a piece of thin ply had been put over the end grain of the spar.

One other case was caused by a pretty big Mud Doubber nest in the tip, but it was a constant wing heavy case.

Another cause has already been discussed about the tail wheel being deflected, but I think that one was found when the plane was pretty squirrely when the tail tire contacted and popped back to straight. The tail wheel deflected is one I have heard several times.

Hank

Let us all know what you find so we an add it to the corporate knowledge list!

[M Towsley]

Re: Suddenly Out Of Trim

I found nothing with the airplane. The adjusters are both painted in position and I have not been able to break them free yet to adjust wash.

This airplane, strange as it sounds, was a hands-free flyer in calm air with either me or me and my wife on board. I have noticed it is not lifting the wing as much as it was before, but it will deviate from strait and level. Definitely a who-done-it at this point.

[Hank Jarrett]

Re: Suddenly Out Of Trim

Can't imagine Tina moving the CG much. How does it behave with a 200# sack of lard like one of us? If it is lateral weight (I am doubting it) giving a ride to a "Big Boy" would show more pronounced turn.
It wouldn't take a very big Mud Dobber nest at the tip to have MUCH more impact than someone the weight of Tina. With the strong yaw roll coupling in a Taylorcraft I am still betting it is something putting in yaw at the tail over a heavy wing. Have you actually put a scale under each main and compared the ratio to your last W&B? Anyone been able to formation with you and look over the tail for a deflected tail wheel or rudder?

Hank

You don't by any chance have one wheel pant do you? ;-)