Lancair Live!

Hi All,

On several recent flights in my IV-P I've noticed my GMC 305 autopilot is a bit aggressive on the roll axis. It will turn the plane 40+ degrees of roll, overbank past the desired heading and hunt its way back. Worse, it will quickly lose 500' of altitude during these aggressive turns without manual intervention. This behavior is most noticeable in the low flight levels, especially at FL230.

Curious if anyone would share their AP settings they have found to work best for a IV-P.

Here are my servo settings as seen from my G3X:
Roll Servo Max Torque: 50%
Roll Servo Gain: 1.5
Roll Servo Direction: Normal
Roll Servo Clutch Monitor: Enabled

Pitch Servo Max Torque: 75%
Pitch Servo Gain: 2.5
Pitch Servo Direction: Normal
Pitch Servo Clutch Minotor: Enabled
Min Airspeed Limit: 110 knots
Max Airspeed Limit: 245 knots
Vertical Speed Gain: 1.5
Vertical Accel Gain: 1.0
Airspeed Gain: 1.0

I am going to ask what seems like a stupid question but this also happened to me.

Is your GMC 305 mounted in a panel that is perpendicular to the path of flight? I had an autopilot control panel that was mounted in one of my side instrument panels that was counted in words by about 30°. Most instrument panels are completely flat across the front across the span of the cockpit. Mine is not. The last 4 inches on the left and right side are canted inward by about 30°. My original auto pilot control panel was mounted in the left angled panel. Because, it was not mounted in the main instrument panel, the accelerometers that are inside of the autopilot control panel thought the airplane was doing something different than what the airplane was actually doing. Everything was fine and straight and level Flight until the airplane was turning.


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George, how’d you figure that out? Must have been quite the puzzle.


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I think when I called tech-support, we were discussing if my panel was completely perpendicular to the line of Flight and then when I asked why they said that they were accelerometers inside the control head. And then that’s when I mention that I had angled side panels.


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Yes the control head is mounted flat on the instrument panel. See attached photo.

Ok that’s good. Did you complete the ground setup and test.

Also does the system do these weird movements when you use the heading bug. Also how about when it does NAV only to a VOR? I am in knowing if it’s just acting weird with GPS steering commands.


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