My plane wants to go left.

[Conrad]

I don't know what else to say. It wants to turn left on the ground. It wants to roll left in the air. With my hands off the controls it is going to go left, and with alarming speed. I'd estimate that in 8 seconds it will roll 30 degrees left in the air and maybe pull 10 degrees left on the ground. Prior to its most recent annual, this was not happening. What the heck could be going on? What other tests could I do?

[Conrad]

Note for the pedantic types: it does need to be moving for this to happen.

[carusoam]

Unless this is political humor...

Think in the most simple of ways...

I can simulate what you are describing by using the rudder trim.  I can literally steer the plane using the electric drive attached to the rudder.

What it probably isn't...

If you were to have low air pressure in the left tire, it's rolling resistance would be greater than the other side. It would steer left, but only on the ground...

 

What to look for...

Who touched what in the rudder controls...

there is a bungee that I would want to get a good look at.  A spring that has a tendency to pull the rudder one way or the other.  There should be some kind of centering device with two springs? (One of them is missing or broken?  

Does your rudder try to center itself?  Hard to tell on the ground without a fair amount of slop in the rudder controls.  Use your hands, push the rudder, sense if a spring pushes it back..?

 

This is purely hypothetical PP ideas based on old and aging M20C memories.  I am not now, or was I ever a mechanic...  

Best regards,

-a-

[Conrad]

My mind definitely goes to bungees and the rudder system. A little rudder pressure in the air keeps the roll tendency away. The ailerons are completely unloaded on the ground so they can't be feeding into the problem when the plane is rolling. There is very little slop between the nosewheel and the rudder itself, as steps were taken to minimize that both in the last annual and during this one. The system definitely does "center" itself, by which I mean that the left turning tendency is highly consistent and does not match an extreme of control inputs.

Here is the most relevant entry in the annual for this year:
Discrepancy: tee worn on steering horn needs shimmed.
Corrective action: Installed one shim on steering horn. OPS CK normal.

I also know that the gear preloads were changed.

[carusoam]

Definitely get a look at the shim on the steering horn...

Consider speaking with Lasar regarding replacement of the horn.

Talk to your mechanic to see if he can even out the shimming...?

And read up on something called the eight second ride.

All things related to steering horn wear.

There are some right ways, and some less right ways of handling this situation.

 A worn steering horn can be an awful experience on the ground.

Best regards,

-a-

[Conrad]

When the nose gear is retracted what do the pedals do to it? Is it still pivoting around inside the front wheel well? I've read the 8 second ride article and have never noticed anywhere near that kind of play in my rudder controls. LASAR removed and reinstalled the steering horn during last year's annual to fix play in the linkage, but they certified that it was good for service. (and afterwards the plane tracked fabulously straight, on the ground and in the air) The plane really hasn't flown a lot since then, so i suspect that there is not a significant amount more wear than there was at that time. The picture on LASAR's site is the best I can find of the part that has seen tweaks in both the last annuals. http://www.lasar.com/mod-details.asp?id=30

[cliffy]

Did this turning problem suddenly appear or has it been there since you bought the airplane?

[Conrad]

Quite sudden, after recent annual.

I have found several pictures of the nose gear assemblage and now understand the mechanical arms and pivots I think. It definitely is free to pivot a bit inside the front wheel well once retracted.

[Conrad]

Sorry no, I missed a joint. It doesn't pivot around with rudder inputs once retracted.

[cliffy]

Do you have a PC system installed? If so you might have a broken vacuum line to one aileron  actuator

 

[PTK]

11 hours ago, Conrad said:

I don't know what else to say. It wants to turn left on the ground. It wants to roll left in the air. With my hands off the controls it is going to go left, and with alarming speed. I'd estimate that in 8 seconds it will roll 30 degrees left in the air and maybe pull 10 degrees left on the ground. Prior to its most recent annual, this was not happening. What the heck could be going on? What other tests could I do?

Have you checked her... umm... political affiliation! Double verify where she stands and don't underestimate this influence. Some women have a tendency to behave in an illogical manner and very erratically this close to the elections! Something with that extra X chromosome! Especially with a woman on the ticket!  Remember zone of ambiguity? Well this is similar behavior! I've seen it and it's a frenzy!

[kris_adams]

8 hours ago, carusoam said:

Unless this is political humor...

I know it's bad but that's exactly what I was thinking.  Mine wants to just go straight...

[Conrad]

3 hours ago, PTK said:

Some women have a tendency to behave in an illogical manner and very erratically this close to the elections! Something with that extra X chromosome! Especially with a woman on the ticket!

Wow, I have 0 desire to turn the discussion from maintenance to politics but that's a pretty shitty comment there PTK.

[Conrad]

7 hours ago, cliffy said:

Do you have a PC system installed? If so you might have a broken vacuum line to one aileron  actuator

 

I thought about that. Seems like that would cause rolling if the PC system was on, but the PC system still corrects for the problem just fine.

Also the aileron rigging wasn't touched, and wouldn't account for the ground behavior.

[Marauder]

I don't know what else to say. It wants to turn left on the ground. It wants to roll left in the air. With my hands off the controls it is going to go left, and with alarming speed. I'd estimate that in 8 seconds it will roll 30 degrees left in the air and maybe pull 10 degrees left on the ground. Prior to its most recent annual, this was not happening. What the heck could be going on? What other tests could I do?

Couple of thoughts. Your left turning tendency on the ground could be nothing more than a brake hanging. Try moving the plane by hand and see if it is difficult to move.

For the left turning tendency in the air, if during the annual they changed any of the Heim joints on the aileron, you could be experiencing a rigging issue. They probably eye balled the alignment instead of putting a travel board on it.


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[Conrad]

I did have brake service, but it was all on the right side. The right brake pads were worn beyond limits and the right master cylinder had a leak. If any of that work caused rubbing the plane would pull right. The aileron rigging wasn't touched, and Lake Aero definitely has travel boards and uses them when appropriate. I know they would be happy to find and fix the problem they made, if only I was able to fly it there myself. As is I'd rather figure the problem out and have a local mechanic fix it.

[takair]

if you disconnect the PC and level the wings with the ailerons, is the ball centered?  Perhaps the rudder tab got bent.  It does not take much.  Also, check the aileron trailing edges for damage. With the ailerons centered at the weights, are the flaps lined up with the ailerons.  It's a good quick and dirty rig check.  The bungee is a little harder to check as it is best to have the plane on jacks.  That said, you can do another rough check by towing the aircraft straight forward and checking that the ailerons are level and the rudder is aligned with the stinger or slightly right.  

[bradp]

Re the ground turning tendency only - my mechanic noted that my wheel bearing were overtorqued at last annual.  He repacked and torqued to spec.  It was notable how much easier the plane rolled after that adjustment.  He mentioned the only thing that over tightening wheel bearing does is guarantee you'll need new wheel bearings in a few years.   

Rolling ok on the ground?  No scraping noises from brakes or bearing?

the only reason I bring this up is wheel bearings are part of the annual. 

[1964-M20E]

Put the plane on jacks and with the travel boards go thorough the full rudder rigging procedure in the manual and verify the aileron rigging during the process.

If it wants to turn left on the ground and in the air it should be in the rudder/nose wheel rigging.  There are certain alignments for the nose wheel and rudder during the rigging process.

 

 

 

[DAVIDWH]

Sure you have a different prob than me, but I fought an out of rig nose wheel for about a year in a Bellanca Viking.

Main issue was runway centerline aversion during takeoff and landing. Right or left, didn't matter, it would just dive with a lot of drama and could be depended upon

with great regularity.

It was my understanding that tensions in the rigging had to be adjusted with concurrent high speed taxi runs then repeated again, then again then again.

My A&P never got it close. Finally, my wife said why don't you just buy another airplane?

And so I did, the M-20R is so longitudinally stable it could probably be landed with both feet flat on the floor.

With difficult to solve, long standing probs like this, sometimes you just need to listen to your spouse.

Best,

[Conrad]

Thank you all for the amazing variety of suggestions, including just buying a longer airplane. It turned out to be a new linkage that was installed between the rudder pedal assembly and the steering horn. The linkage has heim joints at both ends and is threaded in the middle -- thus is of adjustable length. It turns out that the length of this bolt is effectively part of the ground and flight rigging.

The adjustment was incorrect leading to the airplane acting, in all phases of flight, as if there was a little left rudder pressure applied (exactly what I had experienced).

Flight dynamics are affected because of the way that the rudder is disengaged from the nose gear assembly in flight. There is a sleeve joint between the steering horn assembly and the nose gear truss that is out of plane with the rotation of the steering horn when the gear is extended and in plane with it when the gear is retracted. The connection between the steering horn and rudder pedals, however, is above the sleeve in the system of linkages, and thus an incorrect length of the double ended heim linkage can still exert pressure on the rudder controls even when the gear is retracted. With the ailerons bungied to the rudder, in a plane otherwise rigged correctly, the result is a coordinated roll in flight.

[Joe Zuffoletto]

I see Reno or NASCAR in your future....

[Conrad]

58 minutes ago, Joe Zuffoletto said:

I see Reno or NASCAR in your future....

Thanks but I have my hands more than full keeping a 50 year old Mooney in peak condition.

[Joe Zuffoletto]

Kudos to you. I meant no offense. Just made a lame joke. 

[carusoam]

Great follow-up, Conrad!

MS is a powerful resource.

Best regards,

-a-