GFC 500 Yaw Damper Use

[donkaye]

I posted this on Beechtalk, but for those not following BT, I think this would be useful here, too.

I ran a GFC 500 YD test today. I have rudder trim, but kept it centered for takeoff. Given the HP of my airplane, there is a lot of P-factor and torque associated with a takeoff.

I took off and held right rudder. At 800 feet, I turned on the YD and released the right rudder pressure I had been applying. The ball would not center.

I turned off the YD, applied full right rudder trim, and turned the YD back on. The ball remained centered.

I leveled off, increased speed, then turned the YD off. Upon release of the YD, the plane significantly "kicked" left indicating the YD servo had been working pretty hard.

I centered the ball with rudder trim and engaged the YD. It remained centered.

Conclusions:

As mentioned in previous posts and by Garmin, the YD is not a rudder trim. Its purpose is to dampen yaw in turbulence, and based on its inputs, better coordinate turns.

If you have rudder trim, use it as appropriate to center the ball, THEN engage the YD. So, for example, in the climb engage it after the rudder has been trimmed. Turn it off when leveling off, trim for cruise flight, THEN turn it back on. Results will be as expected; yaw damping in turbulence and coordination in turns.

Some additional comments: The GFC 500 is really good, but I've found that if turbulence is moderate, I can fly turbulence much better than it can. Having said that, the YD stays on, as it really dampens yaw in turbulence better than I can.

If you're upgrading to the GFC 500, complete the package with the addition of the YD. You will be glad you did.

 

[PT20J]

What’s the yaw servo torque set to?

When you hand fly in turbulence, are you using the FD or raw data?

Skip

[Ragsf15e]

On the GFC700 in the Meridian I fly, it is set up the same way - electric rudder trim, yd servo.  There is an yellow caution that pops up on the pfd telling you to adjust the rudder trim if the servo is having to hold too much rudder.  I’m surprised you don’t get an announcement on your G500, G3x or g5 for the gfc500.

[donkaye]

2 hours ago, PT20J said:

What’s the yaw servo torque set to?

When you hand fly in turbulence, are you using the FD or raw data?

Skip

Per the GFC 500 setup you are supposed to set it for 100%.  You are not allowed  to deviate from any required setting on the G5.  

Regarding hand flying in turbulence: first I try to pick a time to fly to minimize it.  If that is not possible and I get unexpected turbulence in the air, I go higher.  If that doesn't work and the AP is "overworking" the yoke, I disconnect the AP and hand fly.  I can damp the turbulence much better than the AP by going with the flow.  I use my eyes and not an FD or any raw data, if I understand the question properly.  The exception is that the YD can anticipate better than I can so I leave it on, as it is independent of the autopilot when the AP is off.

[PT20J]

1 hour ago, donkaye said:

Per the GFC 500 setup you are supposed to set it for 100%.  You are not allowed  to deviate from any required setting on the G5.  

Regarding hand flying in turbulence: first I try to pick a time to fly to minimize it.  If that is not possible and I get unexpected turbulence in the air, I go higher.  If that doesn't work and the AP is "overworking" the yoke, I disconnect the AP and hand fly.  I can damp the turbulence much better than the AP by going with the flow.  I use my eyes and not an FD or any raw data, if I understand the question properly.  The exception is that the YD can anticipate better than I can so I leave it on, as it is independent of the autopilot when the AP is off.

Thanks, Don. I haven't flown mine in any significant turbulence yet (and I agree with you about avoiding it whenever possible) but the action you describe is what I would expect from any rate-based autopilot. The reason I asked about the FD vs raw data is that the GFC 500 architecture is such that the FD software is in the PFD and the autopilot software is in the servos. So I was interested to know if the "issue" (if you can even call that) is a function of the FD or the AP. If you could fly the FD smoother than the AP does then it would be the AP software. I would suspect it to be the FD, though.

Skip

[PilotX]

I have found that if the YD works too long and too hard, due to not re-trimming the tail in various phases of flight, it will eventually disconnect the AP. Thus when I turn on the AP in climb (I pull back to 2400/34” in cruise climb) I re-trim, same in cruise. 

[PT20J]

Kind of makes you wonder how much stress is on the servo during a long climb on aircraft without rudder trim. 

[donkaye]

5 hours ago, PT20J said:

Kind of makes you wonder how much stress is on the servo during a long climb on aircraft without rudder trim. 

It's probably best not to find out and just keep the YD off in that case until you are in level flight.

[rbp]

this is interesting because when i flew the PC-12, the the yaw damper went on at 200’ and never got turned off.  I wonder why that system is different? maybe its rudder trim is integrated with YD?