Adjustable rudder trim mod

[Zzz]

I was in visiting my friends at Steve's Aircraft in southern Oregon today, and Brian showed me their rudder trim STC kit. It is a cable actuated system that uses some pulleys to route the cable up under the panel where a wheel and riding detent let you adjust the rudder pressure, left or right. I thought it was pretty slick, this just days after another Bearhawker told me about how builders are adding a piece of steel inside the rudder trailing edge to attach a ground-adjustable tab to, like old 170s and 172s have.

Ha! While looking for a photo of the system, the first one that came up in a Google search was Kelley Babin's 4-place BH:

http://www.mykitlog.com/users/display_log.php?user=kbabin&project=148&category=0&log=46114&row=3

Anyone installed/used this?

[Mark Moyle]

I just installed Brian's rudder trim in my Pacer. You'll need to add a 3/4" square tube like Kelly has. The instructions with the paper work have you drill a 3/8" diameter hole through the square tube for the adjustment wheel. It needs to be straight and .375" no bigger. Mine drilled bigger. Made a bushing from 4130 bar stock and welded in. Nice and sturdy.... It needs to be installed after the rudder system has been rigged. Otherwise you'll need to install turn buckles to adjust the trim cable......which I may do...
Mark M.


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[Zzz]

I just installed Brian's rudder trim in my Pacer. You'll need to add a 3/4" square tube like Kelly has. The instructions with the paper work have you drill a 3/8" diameter hole through the square tube for the adjustment wheel. It needs to be straight and .375" no bigger. Mine drilled bigger. Made a bushing from 4130 bar stock and welded in. Nice and sturdy.... It needs to be installed after the rudder system has been rigged. Otherwise you'll need to install turn buckles to adjust the trim cable......which I may do...
Mark M.


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Yeah, I like that it's minimally invasive to the core rudder system. You could easily rip it out if it gave you problems.

For those running 540's in their Bearhawks though, have you been okay with a simple sheet metal trim tab on the rudder? Is something like this needed? I hate riding the right rudder pedal in cruise.

[Mark Moyle]

Rudder trim....in my neck of the woods is a must have. My last flight from Anchorage to Platinum was great until we exited Lake Clark for a fuel stop in Illiamna. Hit a thirty five knot cross wind. Topped off the tanks and departed for Dillingham. Crabbing into the wind for what seemed like forever....my right foot really hurt. Bout thirty minutes out of Dillimham my wife took over on the rudder.


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[Mark Goldberg]

There are a lot of Bearhawks flying with no complaints about lack of rudder trim (that I am aware of). I certainly have not needed it in my BH. Mark

[Mark Moyle]

There are a lot of Bearhawks flying with no complaints about lack of rudder trim (that I am aware of). I certainly have not needed it in my BH. Mark

The two Bearhawks I'm familiar with, Dan Schillings and Dave Roberts...no rudder trim. Neither need it. I'm probably the odd guy here because of where I live. Mild winds during the summer. Nasty winds during the winter...that never seem to be blowing in the direction you'd want to go.


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[marcusofcotton]

Rudder trim....in my neck of the woods is a must have. My last flight from Anchorage to Platinum was great until we exited Lake Clark for a fuel stop in Illiamna. Hit a thirty five knot cross wind. Topped off the tanks and departed for Dillingham. Crabbing into the wind for what seemed like forever....my right foot really hurt. Bout thirty minutes out of Dillimham my wife took over on the rudder.

Isn't it more efficient to just adjust your directional vector in cruise instead of long term slip? Never heard of the continuous slip approach before so haven't given it much thought.

[alaskabearhawk]

I don't get the inflight rudder comment either Mark. I always compensate for any wind at altitude with adjusting the heading to get the desired ground track.The old TC, TH, MH thing.

[Mark Moyle]

Now I'm confused....not hard to do I guess. My instructor told me to keep the bubble centered...steer with the rudder. If My heading is north, the wind blowing me west....point the nose east enough to maintain the ground track.


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[alaskabearhawk]

Yep, that's 100% correct. But, the ball being centered has nothing to do with the ground track. If you have to keep pressure on the rudder to keep the ball centered, then there is a trim or rigging problem, not due to winds aloft.

[Mark Moyle]

Yep, that's 100% correct. But, the ball being centered has nothing to do with the ground track. If you have to keep pressure on the rudder to keep the ball centered, then there is a trim or rigging problem, not due to winds aloft.

She flew straight hands off, feet on the floor on calm days.


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[Zzz]

You should not be flying cross-controlled in cruise any more than is necessary to correct for left-turning tendency induced by power. It's fine for takeoffs, approaches, forward slips, etc, but in cruise you simply adjust your heading appropriately for the wind correction angle. The only right rudder being held should be to compensate for the left-turning tendencies of P-factor, torque, gyro, etc. This should be reduced at lower angles of attack and lower power settings.

[Mark Moyle]

Maybe it's the type of aircraft? And at 125 max hp not much torque. When I was learning how to fly it the nose would wonder when the wings were not level. My instructor had to break me of using the ailerons to keep the wings level first. After about 30 hours I finally had the rudder input down. Hardly used the ailerons straight and level..even then minimal input to the ailerons. Perhaps that's why pacers and Tripacer pilots like the rudder trim system.


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[alaskabearhawk]

Not to disparage your instructor, but that sounds really weird. You need all three controls to maintain straight and level flight, not just the rudder. Any airplane will "wander" if the wings aren't level. That's what it's supposed to do, all that lift vector stuff.. I'm really suspect of that breaking the aileron habit thing. If you use just rudder to keep the wings level, something else is cross-controlled. I certainly could be a Pacer thing, but something just doesn't sound right. Can you maintain directional control and make turns with just the rudder? Sure, but then dihedral comes into play for stability in the turn, etc, etc. Getting waaay of topic here... https://www.gleim.com/aviation/learn-to-fly/?page=4

FWIW, I've been in some winds aloft situations where it's blowing like crazy but it's smooth. I've had as much as a 30 degree crab to maintain my ground track, but the airplane doesn't care and doesn't know...it flies the same.

[Mark Moyle]

I posted the question to the short wing site..... It's inherent to Tripacer/Pacer. The rudder trim makes long cross country flight pleasurable. I don't have allot of time in Cessna's...my instructor reminded me of that... Over and over. In the pacer you need to stay on top of directional control with the rudder. If the nose wanders off course a little the wings follow. My habit was to correct with the ailerons with quite a bit of input. Once my feet got into the habit of correcting nose drift, aileron input became infrequent or reduced to small inputs. The issue is due to the short length of the fuselage. The Bearhawk is considerably longer.


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