Rudder Wheel Trim

[schurch379]

When I move the rudder trim wheel all the way to the right the rudder moves only to neutral--straight away, and in the air I can barely get to fully coordinated flight. No problem moving it left, of course. It's been this way since I've owned it, but I am pretty sure this is not the proper setting.

 

I need to adjust the trim wheel so that the rudder is neutral when the trim wheel shows neutral; i.e., the wheel is fully right now when the rudder is physically neutral.

 

But, I don't have a maintenance manual that shows how to do this.

 

If anyone can point the way, I'd appreciate it.

 

Aloha.

[Tom Baker]

It sounds like your rudder cable is off the pulley on the trim mechanism. It is hard to see, but it is down in the tunnel behind where the center tray access between the seats is.

[Roger Lee]

The trim indicators are just screwed on to the cable. Just loosen the trim indicator and move it over ot where you want it. You made need to grab the bottom part of the indicator with some pliers while you turn the top part. 

DO NOT just turn the indicator and not hold the bottom part. If you were to turn just the top part and did it far enough you may break the string cable it is mounted to.

[cdarza]

I believe Flight Design USA has the maintenance manual which shows how to make adjustments.   Question: When you mention that the indicator is fully to the right, does that also mean you cannot turn the wheel any further?   If you can turn the wheel further, then i would agree with Roger in adjusting the indicator position only.  However, if the wheel can turn no more (and indicating full right - with rudder in neutral position) - you need to make a adjustment to the cables as per maintenance manual instructions. 

[Runtoeat]

If the trim wheel can turn further, follow Roger's advice although it appears by your comments that you have the wheel turned "full stop".  It the wheel can not turn further, I would follow Tom Baker's recommendation that you first look to see if the trim cable has slipped off the pulley.  You may need to use a mirror to see back down the tunnel where the trim pulley is located to determine if the cable is off the pulley.  If the cable is properly located on the pulley and the wheel is at "full stop", follow cdarza's advice to get a maintenance manual and follow directions it gives for rigging the trim.

[Tom Baker]

I have found 2 airplanes this year that had the rudder cable off the trim pulley on one side. This can happen anytime that you have the nose wheel steering removed, and the rudder cables slack.

[Runtoeat]

Tom, is there something one might do prior to removing the front steering system which will insure the cables stay in place on the pulleys?  If I remember correctly what I saw last time I looked at this, one can reach down the tunnel and put the cables back in place on the pulley if they have come off?

[cdarza]

I have reached down and put the cable back in place without needing to do anything else

[cdarza]

Since the day i took delivery of my aircraft, i have had a strong yaw to the left  (at level flight, cruising speed)  I almost have to turn the rudder trim wheel to full right to get  the 'ball centered'   Note: without this trim my AP would not cope with the out of trim flight.  

So with this setting, the right  rudder pedal is VERY stiff to press.  Almost feels like i could not input much more right rudder.    I havent felt comfortable with this so i center the wheel and fly with constant right rudder pressure.  (this gets very tiresome)  

Could i set the 'neutral'  rudder with a already slightly right rudder angle.?  

[Tom Baker]

Tom, is there something one might do prior to removing the front steering system which will insure the cables stay in place on the pulleys?  If I remember correctly what I saw last time I looked at this, one can reach down the tunnel and put the cables back in place on the pulley if they have come off?

I can't reach back there with my fat arms, but I have been able to do it with a long stick. I don't think just disconnecting the steering rods is what does it. I think it is doing other things while it is disconnected.

[Tom Baker]

Since the day i took delivery of my aircraft, i have had a strong yaw to the left  (at level flight, cruising speed)  I almost have to turn the rudder trim wheel to full right to get  the 'ball centered'   Note: without this trim my AP would not cope with the out of trim flight.  

So with this setting, the right  rudder pedal is VERY stiff to press.  Almost feels like i could not input much more right rudder.    I havent felt comfortable with this so i center the wheel and fly with constant right rudder pressure.  (this gets very tiresome)  

Could i set the 'neutral'  rudder with a already slightly right rudder angle.?

 

Does the airplane taxi straight with your feet off the pedals? You might need to check your rudder rigging.

[Runtoeat]

cdarza and Tom, thanks. 

[cdarza]

Tom,

 

Yes the front wheel is straight and yes the aircraft tracks a straight line during taxi.     WIth the front wheel in center /straight position the rudder deflection is also neutral (not deflecting to either left or right).   With the rudder trim wheel way to the right, ofcourse the deflection of the rudder is quite prominent.

 

Oh, i will add that this yaw to the left is quite strong at cruising speed of say 100+kts (indicated)  When down to 85-90kts the aircraft doesnt require much right rudder or rudder trim

[Runtoeat]

cdarza, a few questions which might rough out what is causing your pull to the left.  Have you checked to see what amount of force is required to pull your rudder to the right and also what force is needed to pull it left?  Are these equal and at the pound-pull required?  Is the travel equal right and left from the centered position?  Does the amount of travel in both directions from center meet the distance the manual calls for?  You indicate the front wheel is straight.  Is the wheel pant also straight?  How about the engine position?  Is this positioned parallel to the centerline of the fuselage?  The specs might even show the position to be slightly pointing to the right to offset P- factor.

[Roger Lee]

Before making any adjustments make sure the rudder has the right amount of spring force side to side or the trim wheel will be ineffective. The side to side spring loading is spelled out in the maint. manual. If this isn't right then all else is just spinning your wheels and may make it worse. I have ad to adjust maybe 6 in my time.

[FlyingMonkey]

Oh, i will add that this yaw to the left is quite strong at cruising speed of say 100+kts (indicated)  When down to 85-90kts the aircraft doesnt require much right rudder or rudder trim

 

This seems odd, and potentially a little dangerous.  If you are cruising at 100+ knots and you have a strong need for left rudder, what happens if at that speed you pull the throttle quickly to idle?  It seems like you'd need (for a time at least) even *more* left rudder, and potential could run out of rudder authority.  

 

You should definitely check the spring forces, and fix the rigging if necessary as Roger suggested.

[FredG]

I fly a 2006 CTsw with tundra gear.  My airplane had increasing need for right rudder trim with increasing airspeed.  At cruise speed I would run out of rudder trim authority.  Below about 85 kts, the plane would trim just fine.  Definitely airspeed related.  

 

The plane was rigged correctly.  Cable tensions were correct.  Increasing the strength of the rudder centering spring helped a little, but didn't fix the problem.  

 

I removed the wheel pant from the nose gear and flew the plane.  The problem was completely gone.  I then replaced the nose gear wheel pant with the wheel pant from a CTls.  Never needed much rudder trim again.  Problem still gone.  

 

FD USA endorsed this approach.  It seems that the tundra nose gear wheel pant has about as much surface area in front of the steering stem as it has behind the stem.  Essentially, aerodynamic forces on the wheel pant were pushing the rudder control system out of trim.

 

Just another consideration.      

[cdarza]

Roger, when you measure the spring force, i am not sure exactly how this goes.  I tried as you mentioned but the initial force to move the rudder is like 5lbs.  (this is for a movement of only about 2 inch left side to right 2 inch right side)   After the initial 2 inch movement, then the tension gets much harder going all the way up to 20- 25lbs.    But as the tension increases,  the rudder moves a little more.  

Anyways, could you explain a   little bit more detail on checking the tension (not the adjustment - just how to check tension)    Is the rudder not supposed to move at all with 25lbs force??

[cdarza]

Re front wheel pant - this has been a suspect to the left yaw..  Perhaps i will try flying without the front wheel pant and observe.   But get this for troubleshooting.....   Flew today and the first 30 mins of flight the plane tracked pretty straight (didnt have much left yaw)    Later in the flight about 45 mins in,  left yaw was apparent again --   ???

 

Anyways, have bigger problems for the moment as second flight of the day,  on take off, rotate, 100ft and engine vibration, drop in rpm.   Thats for another forum page.   Initial findings though,  a small drop of water in each carb and a little bit of 'dirt'.    I have to find where this is coming from as this has happened to me multiple times already = argh.  No fun flying without confidence on engine. 

[Ed Cesnalis]

I bet it is the wheel pant and I bet it  can flex or deform or shift into a big drag maker or at  times not.

[Roger Lee]

Many of us have the 4.00-6 front wheel and wheel pant and aren't having any issues. My CTSW trimmed up and flew hands off just fine. The problem I see in many is the wrong trim inputs from the trim wheels and cross controlling.

 

When you do a rudder tension test the pedals must be in a locked in an unmovable position. I have made a bar that has cut out that I just place over the pedals that keep them from moving. I use a digital spring scale for my pull test. If the rudder tension is between 23-25 lbs of force left and right when you reach about 8.5-9 inches then this isn't your problem and you need to adjust the overall rudder trim. These procedures are spelled out in the maint. manual.

 

When the rudder tension is too lose the rudder can move left or right depending on wind and cause your problems.

[cdarza]

Thank you Roger -i guess my tension is ok then.   I will give it another try with the pedals locked also.   The Description of 23-25lbs force when reaching deflection of 8.5-9 inches is very helpful information as i haven't found that in the MM  (i might be referring to a old MM - 2005)  It clearly instructs how to increase or decrease tension but not how to test tension.  

Just on 'feel' basis.  I always thought rudder tension was fine, as even the smallest of input would have a reaction.  (not even the slightest indication of play)  But, proper checking is always better.  

[cdarza]

cdarza, a few questions which might rough out what is causing your pull to the left.  Have you checked to see what amount of force is required to pull your rudder to the right and also what force is needed to pull it left?  Are these equal and at the pound-pull required?  Is the travel equal right and left from the centered position?  Does the amount of travel in both directions from center meet the distance the manual calls for?  You indicate the front wheel is straight.  Is the wheel pant also straight?  How about the engine position?  Is this positioned parallel to the centerline of the fuselage?  The specs might even show the position to be slightly pointing to the right to offset P- factor.

I will look into all this - thank you.