3 Axis Autopilot and Trim

[Everwild]

Working on the empennage and researching approach to trim options. Any insight would be very much appreciated!

I'm leaning toward Garmin 3 axis autopilot with yaw dampening. My understanding is you use aileron, pitch and rudder trim to remove any unbalanced control forces.

Once balanced, the autopilot servos take over and do the work of flying the plane and take the wag out of the tail if you opt for yaw dampening. Please correct me if I'm wrong but as I understand it, autopilot servos are NOT designed to adjust for an out of trim condition and the system will squawk at you.

Which leads me to my main question. Can the Garmin autopilot control all three axis of trim AND three axis of autopilot? If that's the case I would assume I would need three electric trim motors and all three autopilot servos?

When I looked up some specs on the GSA28 interface it shows two inputs for controlling trim. Not three. https://support.garmin.com/en-US/?fa...Zw3qmcMthIHNw9

Can the Garmin system in fact control all three axis of trim? Or does the pilot control the rudder trim manually? Options being the pilot meat servo on the pedals, a spring yaw system, or electric trim system option.)

Thanks in advance if there are any Garmin experts out there who can provide some insight into the best way to set up a three axis system.

[rocketman1988]

I have the garmin g3x T system in my -10. I installed the yaw damper and aping bias rudder trim. The system easily auto trims the pitch and roll. I modified the spring bias to be controlled with a linear actuator, however, it is not wired for auto trim. I am fairly certain that had I wired it, it would auto trim the rudder as well.

That said, I find that I really do not use the rudder trim that much. I found a setting that is in the ballpark, and that is where it stays. The yaw damper works exceptionally well at stopping the tail wag. Not sure if the gfc500, though…

[togaflyer]

I have the yaw dampener installed and it’s works good. You get spoiled with the Garmin 3 axis system installed. I also installed The Aerosport rudder bias trim. It does two things. One, when the AP is off (so is the yaw dampener) you can set the bias trim. Once you find the sweat spot with the bias trim you rarely need to mess with it after that. The other thing is your rudder doesn’t get whipped from the wind or prop wash. There is no need for a separate electric rudder trim. The yaw dampener hold the bubble center when activated. The Aerosport trim takes care of the rest when the AP is off and can save your rudder from damage.

[g3xpert]

Originally Posted by Everwild

Working on the empennage and researching approach to trim options. Any insight would be very much appreciated!

I'm leaning toward the Garmin GFC500 3 axis autopilot with yaw dampening. My understanding is you use aileron, pitch and rudder trim to remove any unbalanced control forces.

Once balanced, the autopilot servos take over and do the work of flying the plane and take the wag out of the tail if you opt for yaw dampening. Please correct me if I'm wrong but as I understand it, autopilot servos are NOT designed to adjust for an out of trim condition and the system will squawk at you.

Which leads me to my main question. Can the Garmin autopilot control all three axis of trim AND three axis of autopilot? If that's the case I would assume I would need three electric trim motors and all three autopilot servos?

When I looked up some specs on the GSA28 interface it shows two inputs for controlling trim. Not three. https://support.garmin.com/en-US/?fa...Zw3qmcMthIHNw9

Can the Garmin system in fact control all three axis of trim? Or does the pilot control the rudder trim manually? Options being the pilot meat servo on the pedals, a spring yaw system, or electric trim system option.)

Thanks in advance if there are any Garmin experts out there who can provide some insight into the best way to set up a three axis system.

You are able to drive autotrim through a GSA 28 yaw damper just fine. Page 27-10 of the G3X Touch Installation Manual provides an example of how the GSA 28 would be wired to the yaw trim motor.

You are correct in that the GSA 28 yaw damper servo should not be relied upon to correct for an out of trim condition. The yaw damper dampens the yaw axis movements and makes the ride more comfortable, especially for those in the back seat in turbulent air, and while the yaw damper assists the yaw trim in keeping the ball centered, the yaw trim should do the heavy lifting.

You will need to ensure that the trim motor falls within the spec's of the GSA 28 trim output, namely drawing 1A or less. A trim motor that draws more than 1A will ultimately damage the GSA 28.

Please feel free to reach out to us with any other questions that may come up. You can reach us directly at G3Xpert@Garmin.com, or 1-866-854-8433.

Thanks,

Justin

[Nukeflyboy]

The GSA28 servos can handle trim in all 3 axes. However the 10 doesn’t really need rudder trim and certainly not a yaw damper. Roll trim is worth doing and elevator trim a must.

I recently upgraded from the TruTrak GX Pilot to the GMC507 with the Garmin GSA28 servos. Very happy with it, super on coupled approaches.

[rocketman1988]

“Certainly not a yaw damper”…it may not be NEEDED but is certainly a nice option, especially for the back seat passengers…

[Auburntsts]

My personal opinion is a yaw damper is not needed. Others will argue the point but after 420 hrs I don’t see the need. Some have a Dutch roll but my 10 doesn’t exhibit it. Rudder trim, on the other hand is something to seriously consider. It’s not a must have but I can fly feet on the floor in cruise with the Aerosport spring bias system so I’m a big fan. Before I had to rest a foot on the right pedal— that gets old on a long X-country but it isn’t a show stopper. YMMV….

[dmattmul]

Although not much time in the 10 have about 200 hours in the 14 and they fly very similar. I have a yaw damper and that's pretty much it on the rudder. For the 7 minutes during the take-off to level flight phase I use right rudder (Really not much after I leave the runway) and it provides some exercise (which I need for my right leg) and after that zip for hours at a time. Even high bank angles don't need much rudder. (I'm a sailplane pilot so maybe I got use to using the rudder) Building a 10 and would not think of spending a minute adding anything more. The trim mods I've seen on the 10 and 14 rudder seem excessive for the time it's needed. In the end we are experimental builders and it's everyone's right to build what they want.

[lr172]

Originally Posted by dmattmul

Although not much time in the 10 have about 200 hours in the 14 and they fly very similar. I have a yaw damper and that's pretty much it on the rudder. For the 7 minutes during the take-off to level flight phase I use right rudder (Really not much after I leave the runway) and it provides some exercise (which I need for my right leg) and after that zip for hours at a time. Even high bank angles don't need much rudder. (I'm a sailplane pilot so maybe I got use to using the rudder) Building a 10 and would not think of spending a minute adding anything more. The trim mods I've seen on the 10 and 14 rudder seem excessive for the time it's needed. In the end we are experimental builders and it's everyone's right to build what they want.

Same here. Simple wedge on the rudder and no damper. The 10 requires very little rudder when climbing at 130 Kts and have never noticed any tail wagging even in turbulence. Possible it's there, but have never felt it.

Larry

[rocketman1988]

How often do you ride in the back?...