Rudder trim tab

[chickenhawk47]

Has anyone installed a rudder trim tab? As I accelerate above 100 mph, my 4 place drifts to the right about 1 degree per second. Very annoying! I want to design a proper trim tab and properly install it. I haven't found any past posts about it.

[Chris In Milwaukee]

I don't plan on a tab, but I do plan on a rudder trim similar to that used in the Archer and Cutlass I've flown, which is essentially a spring tension adjustment on the rudder pedals to keep the nose pointed and the ball centered.

[alaskabearhawk]

For starters:

What Mark and Budd said. Here's what I did, which needed to be done before fabric.

http://www.mykitlog.com/users/display_log.php?user=jonesronc&project=191&category=1913&log=19766&row=14

The trim's effect is airspeed dependent, also. The faster you go, the more left rudder, the slower, the more right. I set my trim to about 120 KIAS, which is about 55% power, kind of the average speed I cruise at.

Kelley Babin has installed a rudder trim in his, which as I recall is this one, or one somewhat similar:

http://www.stevesaircraft.com/ruddertrimstc.php

Ron QB64.


My plane needed a touch of right rudder at cruise so I took a 3/8" dowel about 5" long, cut in half lengthwise, and painted it the same color as the rudder. I taped it to the left side of the rudder at the trailing edge with a strip of 3M clear packing tape. Not noticable and works great. It usually doesn't take much.

Regards,

Ted

Another solution to rudder trim is to install a heavy or shorter spring on the rudder pedal as needed.

Eric Newton

Hi Paul

I put three 6-32 nut plates on a .032 tab welded to the perimeter tube and rib.
Once adjusted for hands off flight in cruise, I have never adjusted since.
Also put a trim tab on each aileron , mounted to the underside and attached to the trailing edge with 6-32 nut plates, between the two control hinge ribs.
Same thing once adjusted,( one slightly up and one slightly more down) I have never adjusted since.
All trim tabs are 2024 x .032
It was worth it !

Gavin

[Mark Moyle]

I'm adding an Aerotrim servo to my rudder. The tab will be built just like the elevator trim tabs... Adding rudder trim for the following reasons.
1. I'm installing a 300 hp engine.... Cessna 185's with virtually the same engine has an adjustable rudder trim.
2. Fly lean of peak at 55%.... On wheels...need less trim if operating at continuous maximum rated power.
3. On floats at gross may need to run 285 hp continuous...
4. Then there is everything in between...would like to trim for all occasions.
5. Maule M4-7 has an adjustable rudder trim.
6.... It's always windy

On a side note...I've ordered the B model elevator and horizontal stabilizer from Mark G... Will install Pat Fagans version of elevator trim...Will not be using the flat ones I've built...my hinges aren't quite right...
Still waiting on the second set of Dakota Cub spars for my Pacer...the first set disappeared somewhere between Dakota Cubs shop and Anchorage..

The Pacer waiting in her wings. She sits unloved on the new concrete floor in the Hanger.

Mark M.


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[whee]

I would probly install Steve's Aircraft PA20 rudder trim system if I wanted rudder trim. Mark Moyle I know you installed it on your Pacer; why not use it on the BH?

[Mark Moyle]

I would probly install Steve's Aircraft PA20 rudder trim system if I wanted rudder trim. Mark Moyle I know you installed it on your Pacer; why not use it on the BH?

I've installed a Cessna parking brake where the Steve's Aircraft rudder trim would be located. The other issue is where my rudder cables are located...they run down the middle of the aircraft under the floor.


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[jaredyates]

I've been thinking, could something like a Ray Allen trim servo be used to adjust spring tension on one side?

[Mark Moyle]

I bet you could..... Look at Steve's rudder trim drawing. Using two sheaves assemblies to clear the firewall tubing...the top two sheaves.....Put the top two sheaves where the bottom two are....rotate them 90 degrees. Mount the servo low on the firewall between the sheaves using a bellcrank to increase the Ray Allen servo travel and a spring on each rudder cable.


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[jaredyates]

Has anyone figured out the amount of travel or forces involved in a spring bias system?

[Zzz]

Ray Allen now makes a mini servo that's only 3/4" thick. A guy who has yet to cover could fit one inside his rudder to drive a small rudder trim tab.

Similar to this: http://www.n127tl.com/?p=422

[Rollie]

I had never thought of the very simple solution of putting a stronger spring on one of the rudder pedals to even things out in cruise. I think I really like that idea. I had considered adding a fixed/bendable trim tab but when I mentioned it to an IA friend, he was concerned about changing the aerodynamics from what has been proven and opening up the risk of flutter. Probably not much risk of that, especially if some have already done it, but I really like the idea of something even simpler that is inside instead of on a control surface. Seems to me it will be very easy to experiment with a few different springs on the pedals, of course this only compares to the fixed trim tab, it won't be inflight adjustable like some of the complex systems being discussed. Although its been awhile since I've flown a plane with rudder trim, from what I remember of my Aztec, I'm pretty sure once I had it set for my normal cruise setting I rarely touched it again. It was handy for reducing the workload during single engine training, and I think that's the only time we ever used it.

[Battson]

Ray Allen now makes a mini servo that's only 3/4" thick. A guy who has yet to cover could fit one inside his rudder to drive a small rudder trim tab.

Similar to this: http://www.n127tl.com/?p=422

A small electric servo is an elegant solution - probably the best solution in my opinion. It might need to live inside the vertical stabiliser unless you want a small blister in the fabric, that rudder is pretty darn skinny. The fabric would beat against the hard parts inside and soon wear a hole.

I think it would be worth having electric rudder trim, but it's never going to mean you can take your feet off the pedals completely (unless your in perfectly clear air, or if your return springs are very strong).

I simply retrofitted a trim tab after test flying. We just screwed in straight onto the 4130N tube at the aft side of the rudder. By injecting a small amount of linseed oil into the tube, you can prevent / slow corrosion while still drilling directly into the tube.

[Zzz]

A small electric servo is an elegant solution - probably the best solution in my opinion. It might need to live inside the vertical stabiliser unless you want a small blister in the fabric, that rudder is pretty darn skinny. The fabric would beat against the hard parts inside and soon wear a hole.

I think it would be worth having electric rudder trim, but it's never going to mean you can take your feet off the pedals completely (unless your in perfectly clear air, or if your return springs are very strong).

I simply retrofitted a trim tab after test flying. We just screwed in straight onto the 4130N tube at the aft side of the rudder. By injecting a small amount of linseed oil into the tube, you can prevent / slow corrosion while still drilling directly into the tube.

It's a tough call. A fixed tab that's optimized for cruise flight is dead simple and won't malfunction. Really the only time having to hold sustained rudder input is annoying is during straightline cruise when you'd kinda like to relax and think about fuel and clouds, so while the servo idea might be neat, I think a fixed tab is the way to go. Or a short return spring.

[Bcone1381]

....once I had it set for my normal cruise setting I rarely touched it again. It was handy for reducing the workload during single engine training, and I think that's the only time we ever used it.

I have experienced what Rollie said. Once rudder trim is set, its never used it again. Rather, proper application of the rudder consistent with the phase of flight is all that most of us do. In cruise, I want the ball centered with my feet off the rudders. This "Set it once, and forget it." practice would call for one adjustable rudder cable, or an adjustable spring mechanism.

Something like this elevator trim design used on a Schliecher K-6 glider.


+1 486705DSCN0102.JPG

[whee]

Here is a rough idea I've been thinking about. Depicted is the left side rudder pedal arm. Tighten the wing nut for left rudder, loosen for right rudder. Right side arm has typical rudder spring.