Rudder Trim Tab?

[jax88]

I probably just missed it, but I didn't find any reference to rudder trim tabs for my '75 M20F.  Straight and level usually includes a constant pull to the left, and I was hoping there was a way to adjust the rudder to eliminate/dampen the pull.  Any suggestions?

[flhelo]

If  you have the PC wing leveler installed, you may have a bad servo or the control valve under the dash.  Mine was doing the same thing but I found that silly square control valve was clogged. Cleaned it out. Works fine now. Also, if PC equiped, your turn coordinator knob might need to play withit in flight to level the wings.

[kerry]

re rig your plane

[tablor]

I'm with kerry.  Get the rigging checked out.  I see you're in San Antonio, so you've got Lonestar there or come out to Kerrville and meet Ronnie at Dugosh.  He's got the appropriate rigging boards and the experience to get it done at a min labor cost.  Maybe you can land a tour of the factory while you're out here!

[Piloto]

Quote: jax88

I probably just missed it, but I didn't find any reference to rudder trim tabs for my '75 M20F.  Straight and level usually includes a constant pull to the left, and I was hoping there was a way to adjust the rudder to eliminate/dampen the pull.  Any suggestions?

[Stefanovm]

Quote: Piloto

 Disconnect the PC leveler by taping the yoke push button. Trim the plane to level flight and check the T&B ball to be centered. If the ball is centered but the plane still rolls to the left hands off you need to rig the roll axis. With hands off check aileron position to be the same on both wings and that the yoke is in neutral position. A rolling tendency to the left can be corrected by adjusting the left flap outboard set screw (on the most outboard flap hinge). Adjust the set screw to lower the flap (no more than two turns). You will need to do a couple of flights to find the right adjustment. If the there is a roll tendency with flaps extended you will need to adjust the inboard flaps actuating links.

José

 

[tablor]

Careful using the flap as an adjustment.  It's definitely the easy way out, but if the plane is rigged correctly it shouldn't yaw or roll.  With the flap out of alignment you're going to increase the drag.  Per the spec the flaps only get a range of +/-1 at TO & Ldg and +/-2 in the retracted position.  You wouldn't be able to measure this without the correct rigging boards ('Travel boards').  When I had the rigging on mine checked out it was only a couple of hrs labor, well worth it in my opinion.  Flies hands off now and I know that it's right.

[Mcstealth]

Quote: Stefanovm

I did this and wow what a diffrence.The airplane flys much better.

I was concerned as my left aileron was several degrees down in flight and the right was up. Now they are matched and pretty much neutral in straight and level flight, a little down on both sides. The boards would be great as the maximum on ground deflection is 2 degrees by the book. It "looks" as if it is more, so at annual time I will tackle that much more complicated, and hard to reach, turn buckle adjustment.

The outboard adjustment was a bit of trial, fly, and correct. The inboard adjustment took a minute or two, BUT an hour to get to it and put back the screws. I was glad I got it right with the first adjusment.

[Stefanovm]

The adjustments were only a few turns for the outboard flap adjustment a maybe a turn for the inboard. I will be doing a more accurate job at the annual. However, it is much better with the little that I did. I do not see how the rigging of the ailerons can affect the roll. With my C152 there was a wing incidence setting that was much harder than the Mooney flap adjustment. Both the Cessna and the Mooney procedures are listed in maintenance manuals. I had an IA mess with my aileron turnbuckles in the C152 which NEVER helped the roll. It was just as bad as my Mooney’s when I bought it. When I finally read the manual and took the C152 to another IA, it was fixed in two adjustments of the wing trailing edge by the book. This seems very similar to a flap adjustment, the adjuster is still mid adjust area, and it is now flying faster.

[Stefanovm]

By the way, mine also flys hands off now very well. This is flaps up or down. I leave my PC off except when I want to turn my attention to things other than wings level and can fly pretty much hands off. Mine has an on/off button conversion versus the temporary wheel mounted method.

My untrained, but critical eye just mistrusts the aileron 2 degree maximum down that looks like more than 2 degrees down at static conditions. I may very well be wrong. This would definitely affect the speed and other things, but so would the up several degrees on one side and down on the other side for the ailerons in level flight, which has been corrected using an IAW MM procedure. My current IA agrees.