What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Hinge Placement of Electric Rudder Trim

Russell Hilton

I'm New Here
I'm getting ready to start the empennage kit and I am going to add the electric rudder trim that many have done with the section cut from the rudder. Like this one done by Brian Steeves. I've studied all the posts and many pictures taken of other builds and there seems to be no consensus as to the hinge placement side or the side that the servo control rod is placed.

It seems to me that if you normally use right rudder, thus requiring the trim tab to swing to the left (pilot side) of the plane, that the most logical placement would be to put the hinge on the right (co-pilot) side which would minimize the gap on the pilot side as the tab moves leftward. Likewise, placing the servo control arm on the opposite side of the hinge would slow the travel and create more leverage for the servo to operate.

Is there a consensus to this, am I thinking about it correctly or am I missing something?
 
Hey Russell,

Great questions! I was thinking along the same lines when I was entertaining the thought of having the electric trim.

Then I decided to leave the rudder integrity alone and perhaps place an internal system.

I am watching to see where this question leads.

Andy
 
By the way, still contemplating adding this feature.

by the looks of the wait time on the fuselage I'll probably have plenty of time to mess around with such things.
 
Andy,

I've done quite a bit of research and thinking about it. Sometimes phones will flip pictures so it can be hard to really tell if it's the left side or right side that people are using. Either way, I guess I'll figure it out at some point.

Russ
 
I'll have to look at mine. The trim motor and linkage is on the left side of the rudder/VS when viewed from the rear. I'll check where the hinge is today. From the pic it looks like the builder centered it.

-Marc
 

Attachments

  • 20201220_080913.jpg
    20201220_080913.jpg
    227 KB · Views: 351
Last edited:
I just attached a extruded aluminum hinge to the trailing edge of my rudder with a SS L bracket riveted to the trim half of the hinge. Maybe about 8” long IIRC. The servo was mounted inside the rudder on an access panel and the push rod had a custom fairing. Very simple and I used it quite a bit to avoid using rudder pedal pressure to keep the ball centered.
 
I just attached a extruded aluminum hinge to the trailing edge of my rudder with a SS L bracket riveted to the trim half of the hinge. Maybe about 8” long IIRC. The servo was mounted inside the rudder on an access panel and the push rod had a custom fairing. Very simple and I used it quite a bit to avoid using rudder pedal pressure to keep the ball centered.

Would you be able to post a photo, or a link to a photo of your trim tab?
 
I spent some time today at the Pima Air Museum looking at trim tabs because of this post.. I saw some where they extended the trim tab skin and curved it so even when it's deflected towards the hinge, there isn't a gap. Kind of like the flaps on RVs. The hinge is on the bottom, yet the skin has a curve to it, so there isn't a gap when they are deployed.
 
Rudder Trim

Here is what I did for electric rudder trim.

I cut in an access panel as close to the forward rudder hinge line as possible. I wanted to keep the weight of the servo as close to the hinge line as possible. I mounted the servo directly to the access panel.
The trim tab itself is 6 1/2" X 2 1/2". That is as large as I could make it staying between two ribs. I decided to stay away from cutting any ribs as I want minimal change to the structure. I added a u chanel to close out the rudder opening and the tab out of 0.030 aluminum and hinged on one edge.

In flight I use the rudder trim more than the roll trim to center the ball. It is very effective with only a bump or two to center things up. It also looks good on the finished plane.













 
Thanks for all the answers, pictures, and comments. I think I'm going to put the hinge on the right and servo arm on the left as I originally described. It seems most logical to me. If I learn something different in doing it, I'll post again.

Russ
 
Aerosport trim

I can’t help wondering if the full effects of cutting the trailing edge of the rudder and then adding extra weight to the rudder have been calculated for flutter.
Changing both the strength and weight of the rudder could have unknown risks.

Personally I opted for the aerosport trimmer, as it is a simple, easy to install solution, that will have no aerodynamic effect.
 
What's the ideal trim tab size?

A large trim tab would be heavier, but wouldn't move much for the desired effect for less overall drag.

A small trim tab would be lighter, but would have to move more (more drag) and might even get flow separation (even more drag) if moved too far.


Then what location? top, middle, bottom. One advantage of top would be the possible location of trim servo in the rudder horn................
 
How are you attaching the wedge?

-Marc

I used a 10" piece of the trailing edge wedge material (rudder, elev, etc). Filled in the pre-drilled holes and painted. I secured it to the rudder with RTV/silicone. It is so small it isn't really noticed when looking at it. same adhesion method on the 6 and hasn't fallen off in 700 hours.

Larry
 
Here's another pic of my trim tab. This is looking from the right side of the rudder.

Rudder trim.jpg

This is looking from the left:

Rudder tab.jpg

-Marc
 
Last edited:
Pheonix

After this thread was brought back to life, I re read it. Seems everyone is hanging a huge bellcrank/ pushrod out in the breeze. Curious if the trim tab can be controlled internally without anything sticking out in the breeze; like the sailplane guys do?
 
After this thread was brought back to life, I re read it. Seems everyone is hanging a huge bellcrank/ pushrod out in the breeze. Curious if the trim tab can be controlled internally without anything sticking out in the breeze; like the sailplane guys do?

Yes. I know that Mike S. (here on the forum) built one into his RV-10 rudder.
 
Spring Bias Rudder Trim

Here's an example of a spring bias type driven by a Ray Allen servo that I used on my -10. This approach avoids adding weight to a control surface with the associated unknown impact on flutter characteristics.

i-VJfDhfn-M.jpg
i-XTkBwVw-L.jpg
 
Last edited:
@Paddy, this seems like a really great approach. I've seen a very similar application that is basically the same thing but mounted above the rudder pedal control tubes instead.

Do you know if this would work in conjunction with the Garmin yaw damper?

As I understand it, rudder trim removes any out of balance condition first and then the yaw servo smooths out any wag in the ride caused by turbulence. My preliminary understanding is the Garmin system is smart enough to use both the trim and yaw servos in combination to achieve this.
 
Back
Top