Electric Rudder Trim Questions

[N634JT]

I have made the decision to add eletric rudder trim mounted in the rudder. I would appreciate any input on the following questions:

1. I have noticed that some builders place the trim tab near the bottom of the rudder, and some place it directly behind the middle hinge. Any special rationale for one location versus another?

2. Would you consider building the trim system before completing the rudder, or do you feel that it is better to do this after the rudder has been riveted. As I try to think this through, I am not sure how the riveting/prosealing of the trailing edge could be effectively accomplished with R-1006 (extruded trailing edge piece) being in three pieces, or, in some way that I don't realize, may actually be easier/better?

3. Should I consider doing things in two steps. Layout and fabrication for the trim servo mount as a "pre-riveting" step, then cutting the trim tab "post riveting?

4. Observations from "scrounging" through various builder photos. It appears that above and below the the trim tab cutout that the rudder has been "boxed in", and that forward of the trim tab, the hinge "boxes in" that side . I cannot tell exactly what was done here. It it done with the foam blocks and/or glass?

5. How is the inside of the tab itself "framed out" ?

Thanks in advance!
N634JT
Michael J. Tippin
EAA 175

 

[Mike S]

I used the lower mounting area due to there being more room in the interior of the rudder.

The rear of the rudder cutout is filled with a bit of scrap alum, bent into a simple "C" shape. One half of the hinge is sandwiched in at the same time as the "C" is riveted in place.

The tab itself is done in a similar manner, there are a couple of pieces of phenolic board cut into ribs that are prosealed in place top and bottom.

The closeout for the front of the tab also sandwiches the other half of the hinge in place. I have a curved piece that closes the gap as the tab is moved, borrowed the idea from a photo that Tom Brink from GAHCO has posted of how he did his aileron trim.

Tom's design was pretty much the guiding inspiration for how I did mine.

http://www.gen-aircraft-hardware.com/toms/Plane_proj.asp Scroll down a bit more than halfway.

Here is a photo, borrowed from his build site.

 

[flion]

I agree with Mike, the bottom has more room for a servo. In addition, it is easier to route the wires. I cut my tab from the finished rudder because I wanted the trailing edge to match - a bent TE did not feel right to me next to the riveted rudder TE. I have some foam (same as used in the elevator trim tabs) to close off the tab and cutout and also use as the tab spar and close off the cutout trailing edge (except where the pushrod comes through. I'm using a 3/4" throw servo so I can use a shorter control arm, which is riveted to the hinge and extends through the tab so it barely protrudes from the other side.

Cutting the servo access panel could have been done before the rudder was riveted but I'm using Clik-Bond studs to mount the servo and that was easier to position inside the access with the rudder assembled (not necessarily riveted). Cutting out the tab opening was definitely easier with the rudder riveted.

If I had the tooling, I would toss the tab I am kludging out of the cutout and instead hollow-mold one. In fact, if the geometry had matched, I had an R/C sailplane rudder I was tempted to use. A hollow-molded tab would be lighter and, with an integral (possibly carbon-fiber) spar and control arm, stronger. But I think the one I am fabricating from the cutout will work just fine.

 

[Ron B.]

Make sure you use extruded piano hinge, MS20001P material stock rather than the more common rolled piano hinge, MS20257P as strength is essential.
Ron

 

[GAHco]

Hinge

I used NAS40 hinge it is still extruded but not quite as thick.

Best wishes!