Rudder Trim - Does it physically move the center of the rudder?

[Ronson2k9]

I'm looking at the Cessna A185F Parts Catalog and I have question.

Does the rudder trim physically move the pedals to a new center? As it looks like the linkage does? Or does it just adjust the (modify) the rudder position on the tail? That is rudder moves but pedals remain in there parallel neutral position. There is no tab on the Skywagon rudder.

As a further note: There is the Stabilizer trim which moves the stabilizer not the elevator. Interesting the trim moves the flight surface not the control surface (unlike the rudder).

Hope someone can help.

It would be cool to model the repositioning rudder pedals although I have no idea currently how to do that??

Cheers
Ron

[Mike.Powell]

If the C-185 rudder trim is similar to that in the C-206 and C-210, the rudder pedals always move with the rudder position. The trim adjusts the trim force a bungee puts on the rudder torque bar the pedals rotate. The trim system in the C-172 is totally different, but the 172 pedals also always move with the rudder position. (The C-172 rudder trim is a flat piece of sheet metal fastened in the trailing edge of the rudder. It's bent by hand on the ground to set the trim.)

[Ronson2k9]

Thanks Mike. Always a ton of info here.

If I had a centering spring on the rudder pedals and then was able to move that with the trim. A bell crank attached to the centering springs that moved the pedals perhaps. A couple of pulleys and a geared crank should do it.

- If the force required to move the pedals (with my feet) doesn't overcome the resistance on the trim.

I'm thinking though that the trim is used to maintain yaw during cruise (so your feet don't have to do that). Also if the trim is connected to the AP it also has an electrical (motorized connection) to the trim wheel (supplemental in nature). As the AP is a hands off flight control device. With that in mind the AP'd version of the trim could be a driver for the trim.

- Trim wheel moves and that movement signals the AP/Trim motor to a new rudder center or
- The AP signals a new trim location and that moves the trim wheel/rudder center/rudder pedals/rudder.

I had forgot about the AP in my earlier post..

Any further help would be great..
Ron

[Mike.Powell]

Thought I had lost the link, but here it is: http://www.micro-tools.com/pdf/Cessna/ There are Cessna service manuals listed there which might be of help.

[wledzian]

From the C185 parts catalog in Mike's link, see figure 99A rudder trim installation.
Component 8 is the bungee assembly (centering device). The rudder trim wheel moves the anchor point of the centering device, physically relocating the "center" position of the rudder pedals.

Whether by moving the centering spring or adding an aerodynamic trim tab, the rudder pedals are typically locked to the rudder; as the rudder moves, so do the pedals.

[ANDYSMITH]

Hi...most planes, even the 737 have no autopilot on the rudder. Ailerons and elevator only.

Andy

[Ronson2k9]

I have the parts catalog for the C185 ('74-'85) and this image from that.
http://i416.photobucket.com/albums/pp244/Ronson2k3/C185RudderTrim.png

As you say part 8 shows the bungee assembly.

From the looks of it that is attached to the tunnel (center console) and a crank on the trim wheel moves the bell crank which in turn moves the rudder.

I'm going to try and make something similar although it is the center of the rudder (neutral). So I have to use springs or a lot of gearing to move them. A second bell crank attached to the rudder trim should do the job that crank will be attached to both centers (I want duel controls).

My biggest problem is how to keep the trim in place while I move the rudder with my feet? A lock would be non prototype. Some kind of strong crank.

1 - Has to overcome the force of the springs and that of pushing the pedals?
2 - Has to be relatively easy to crank.

I was thinking of using a cable but it almost seems like a bicycle chain/parts could work too. Any thoughts?

According to Carenado's C185 it's one complete revolution from neutral to full trim. I don't know what amount of deflection that is yet or would it be full (rudder completely over)?

I appreciate the help guys.. A design is slowly gelling.. :)
Ron

Looks like AP is indeed connected to the rudder/aileron. That takes AP out of tunnel and adds it the MIP (yoke). So I'm both :) and :( anyway one bridge at time.. hehe