Rudder rigging/trim in a K model

[hubcap]

I noticed some time ago that when in cruise Myrtle requires just a tiny bit of right rudder to put the ball in the center and she picks up 1 to 2 knots of speed when the right rudder is added.

It seems as if this is should be able to be addressed in the rigging. When on the ground and the nose wheel is centered, there is a little rudder deflection, which I believe is normal.

Should I worry about changing the rigging to improve/correct this issue?

[802flyer]

I notice the same thing flying my F model, so am also curious to see the replies.


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[PT20J]

The ball should be centered in cruise without rudder input. You should check your service manual, but for my J the rudder is supposed to be rigged one deg right. You have to this with the plane on jacks and a bar clamped across the rudder pedals.

Here’s a good article on rigging.

Shoptalk - rigging.pdf

 

[Ragsf15e]

3 hours ago, PT20J said:

The ball should be centered in cruise without rudder input. You should check your service manual, but for my J the rudder is supposed to be rigged one deg right. You have to this with the plane on jacks and a bar clamped across the rudder pedals.

Here’s a good article on rigging.

Shoptalk - rigging.pdf 79.55 kB · 5 downloads

 

I think there will still be some very minor variations based on cruise IAS?  For example 115kias at 12,500’ might require a little right rudder while 150kias at 4,500’might require slightly left rudder even though they are about the same cruise TAS.  Since we have no trim, the rigging aims for the middle of “cruise”, but that might vary, no?

[PT20J]

14 hours ago, Ragsf15e said:

I think there will still be some very minor variations based on cruise IAS?  For example 115kias at 12,500’ might require a little right rudder while 150kias at 4,500’might require slightly left rudder even though they are about the same cruise TAS.  Since we have no trim, the rigging aims for the middle of “cruise”, but that might vary, no?

True enough. All the aerodynamic forces are a function of dynamic pressure.

And a K will be probably have more variability than my J since it operates over a wider range of IAS vs TAS because it can fly higher. Still, if the ball is out of center in the cruise condition, it would seem worth checking the rigging. 

[Ragsf15e]

1 hour ago, PT20J said:

True enough. All the aerodynamic forces are a function of dynamic pressure.

And a K will be probably have more variability than my J since it operates over a wider range of IAS vs TAS because it can fly higher. Still, if the ball is out of center in the cruise condition, it would seem worth checking the rigging. 

Or, (tongue in cheek), if you need right rudder in cruise, try a lower cruise altitude with higher IAS!  Another solution (obviously after the rigging)… the gfc500 yaw dampner will correct for small variations in yaw at cruise.  Maybe Skip just thinks his plane is rigged perfectly !

Edited December 7, 2023 by Ragsf15e

[Z W]

Rigging can be complicated.  What shows up as rudder slightly out of center while holding a course can be a misaligned gear door, an aileron issue, or a rudder issue.  

Our plane was like that when we got it, and would also always want to drop the right wing if you released the yoke in straight and level flight.  An experienced Mooney shop went through it with proper rigging boards and got it flying straight.  Big improvement in stability, especially on approach.  I believe they started with the gear doors, then set the ailerons, then the rudder.  Just starting at the back and changing the rudder can just mask other problems and put you further out of straight and level.  I would be hesitant to let an A&P who hasn't done it start messing with the rigging.

Also - what is strapped to your yoke?  Flying with a big heavy iPad bolted on there and levered out 3" into your lap can throw the rigging off too, if it's not centered.

[hubcap]

I am not sure the issue is significant enough to justify going to a lot of trouble for a tiny tweak to the rigging at this time. 

[Jrags]

I am going to try and use a ram mount yoke clamp with my ipad mini as rudder trim.  My M20G "pulls" to the left so I'm going to mount the ipad at about 2:00 O'Clock to see if that helps.  If its not enough, I am going to try a little weight .   I saw a bolt on wing leveler that mounts to the yoke with an automated left/right sliding weight.  I thought that was ingenious so I'm going to start with just rudder trim.