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Rudder Trim Adjustment


rcwagner

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Before you start making any adjustments to the trim tab I would put the plane on jacks and make sure your gear is rigged properly. If one side is hanging down a little lower than the other the asymmetric drag could be your problem. Even that turns out to be fine I think I would let a knowledgeable Mooney mechanic check the overall rigging of the plane.


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Hey... don’t forget to check the panel mounting hardware...

First check if the instrument is mounted level with the level ground...

usually the older Mooneys have the rubber panel mounts that get loose and break down...

There are many things that can cause the instrument to list... start at the ground and work your way to the panel...

The ball is a pretty sensitive device...

Chances are, the panel holes are nicely drilled in the right places...

Leveling the plane is An interesting experience...

With electric rudder trim... you can actually see the various expected inputs of right rudder needed during the climb, centered in cruise, and slight left rudder input to balance things in the descent...

Using the rudder to lift a heavy wing often provides details to a great conversation... are you always flying solo? Does the ball center as fuel is burned from one tank?   See where this comes from?

If it is a small amount... you might balance it temporarily in flight... if it changes during flight with the fuel burn... you are looking for a rudder trim adjuster... a few Mooneys have these... some are electric...

Something to consider prior to changing rudder trim...

Best regards,

-a-

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yes to all the above.. in addition.. run a straight edge up the rudder.  I had the same issue when I purchased mine.  The POH describes how to "bend" the trailing edge of the rudder to center ball for flight.  It is possible the previous owner was a little ham fisted and over adjusted.  Or had it perfectly balanced for the settings they flew at.. ie faster or slower.  It will make a diff.

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Just a thought, if you run AHRS from Stratus on Foreflight and measure the difference in deflection of ball if any.  If ball is centered in Foreflight, then couldn't we eliminate the rigging as cause?

Seems may be an easy test to eliminate or confirm rigging issue. If you don't have the synthetic vision subscription I am sure someone at your field would loan you an Ipad for a day.  I would. 

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2 hours ago, KB4 said:

Just a thought, if you run AHRS from Stratus on Foreflight and measure the difference in deflection of ball if any.  If ball is centered in Foreflight, then couldn't we eliminate the rigging as cause?

Seems may be an easy test to eliminate or confirm rigging issue. If you don't have the synthetic vision subscription I am sure someone at your field would loan you an Ipad for a day.  I would. 

AHRS uses a gravity sensor to determine which way is down. The ball in the instrument panel is centered when the plane is level. The indications are not equivalent. It can tell if the plane is slipping by measuring lateral accelerations normal to gravity. It cannot tell if the plane is in a continuous forward slip.

You can put your Stratus on the edge of the glare shield so it is sitting at a 45 deg angle to level and after a few minuets it will show that you are straight and level. Its gravity sensor is equivalent to the erector mechanism in the old iron AIs.  

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  • 4 weeks later...

I wanted to chime in... My rocket was flying a bit sideways in cruise... About 1/3rd ball out to the left.  I had been resting my left foot on the pedal during cruise to correct.  Got tired of this so before the last flight I tweaked the trailing edge of the rudder  gently with my fingers.  It didnt take much and now she flies strait as an arrow!

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What’s with the bending of airframe parts lately..?

@Austintatious sound familiar?

I think Austin was looking at tail trim and elevator trim earlier...

 

There are always adjustments available to be used in accordance with maintenance manuals and procedures...

It helps to have a friend that is a mechanic... for writing in the logs...

Keep in mind that these trim adjustments will work at a set speed and set WnB... they may not work throughout the whole range... so keep good notes as you and your mechanic sneak up on the level of adjustment that suits the way you fly... speed, and WnB...

bending airframe parts is hard to add to, and more difficult to remove... repeatability becomes terrible...

PP thoughts only, not a mechanic...

Best regards,

-a-

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6 hours ago, rcwagner said:

Thanks.  That looks a lot better than bending the trailing edge of the rudder.  I will definitely try it after I verify the ball being level with the airframe.

Adjusting the rudder rod end will do nothing for making the plane fly straight. With the rudder pedals even and parallel the nose wheel should be straight and the rudder offset to the right by one degree as measured with the Mooney rigging board.

First verify that the ball is centered when the plane is level laterally, off center can be caused by weak or broken panel mounts or improperly install turn coordinator.  When this is correct fly the plane again.  

Mooney says to bend the trailing edge of the rudder to correct trim.  They say to use a 3” duckbill vice grip plier.  I prefer to clamp 2 1X2 boards to the trailing edge and gently bend the entire edge a very small amount as opposed to the vice grip method.

Clarence 

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As I posted in a different control rigging thread, there are loads of Mooneys around that fly crooked because their owners, in the greatest CB traditions, insist that they know better than the engineers, the Service Manual, and the MSCs how to make their airplanes fly "right".  

José's suggestion above is a perfect example and one of the stupidest, misguided ideas out there.  All it will do is change the rudder pedal position.  On landing the airplane will dart to one side or the other because the rudder and nose wheel steering will no longer be matched.  If the rudder linkage is adjusted far enough, it will add pressure to the aileron interconnect springs which will make the airplane fly crooked.  Awesome!

Luckily, this provides job security for MSCs when the next owner buys the airplane.

 
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