View Full Version : Up and down in the turn

02-20-2013, 07:29 PM
At the risk of beating a dead horse, here's my situation.

With the TruTrak auto pilot in control, turning the autopilot knob for a 90 degree heading change produces a nice steady turn with no loss in altitude for the whole 90 degrees.

But when controlling the autopilot via the 4500 heading bug, the turn starts off ok for the first 30 degrees but then becomes a roller coaster ride, constantly trying to hold attitude by overshooting and undershooting while progressively getting worse. Once on course it settles down.

So the only thing I can think of to adjust is the ATL Gain on the EFIS. Yet no setting from 1 -12 seem to make a difference.

Any suggestions?

02-21-2013, 02:59 AM
call lucas at trutrak. you may need a software upgrade. you can try adjusting static lag.i'm still waiting for good weather to test mine after having software upgrade.

02-21-2013, 08:04 AM
Actually, based on your previous suggestion I sent my autopilot in for an upgrade and got it back last week. I was hoping that that might make a difference but unfortunately, not so.

So I'm thinking that it's not a trutrak issue since it performs flawlessly on its own. Somehow, either my setting on the 4500 are wrong or I have a bigger problem. I'm using the setting suggested on the manual but can't seem to tell where I need to adjust them.

I may call Lucas anyway..

02-21-2013, 11:24 AM
use page 38 on the 4500 manual for settings. maybe it is a connection issue with the 4500 but I'd talk to lucas.

Rob Hickman
02-21-2013, 12:16 PM
I suspect that you have the bank angle set to MED or LOW in the AP? When the EFIS is turning the plane it is trying to do a standard rate turn and I suspect it is steeper than your test with only the AP? When I fly with people that are having the problem you are describing it is almost always being caused by the pitch servo slipping from poor pitch trim.

What is the bank angle with AP 90deg turn?

What is the bank angle with EFIS 90deg turn?

1. Is your Pitch Torque set to 12 in the AP?

2. Are you positive that the plane is in trim? Try giving it some up trim and see what happens. Can you feel the servo slip when it is doing it?

Autotrim usually solves this problem.

3. What happens if the static lag is at 3?

4. Is your GPSS gain set to 16?

5. You can monitor what the EFIS is commanding the AP to do from the CHECK MENU. The EFIS only sends the AP ROLL Angle and Vertical Speed.

The EFIS ALT gain is the only setting in the EFIS that has any input on the vertical AP control.

If you have the EFIS ALT gain set to 1 you have almost eliminated any command input from the EFIS and all the control input is from the AP.

Is your Micro Activity set to 2?

Make sure you have Half Step N

02-21-2013, 12:46 PM
Thanks Alan.

I'm presuming you mean page 39 which goes into what each setting does.(version 7.4 of the manual) Appendix J, page 114, has all the suggested settings for my Sportsman and that's where I checked to see where I'm different. I changed them all to the suggested numbers but still have the issue.

Some more flying and tinkering may be in order...

02-21-2013, 12:49 PM
Thanks Rob. Now I've got somewhere to start when diagnosing the problem. I'll look at it all on my next flight.

02-22-2013, 08:58 AM

Yes I have the bank angle set to MED. The bank angles are the same for each. The VERT (pitch) torque is set to 12 in the autopilot. The static lag is already 3. Gpss gain is 16. Micro activity is set to 2.

There is no slipping in the pitch servo. You mention auto trim and I assume its always on as I don't see any settings for this.

Can you please elaborate on how I can see what the EFIS is commanding from the CHECK MENUE?

Rob Hickman
02-22-2013, 10:59 AM
1. Have you tried it in AP mode with the Bank Angle set to HIGH?

2. What bank angle are you seeing in AP mode for a 90 deg turn?

3. What bank angle are you seeing in EFIS mode for a 90 deg turn?

4. Check for lost motion. On the ground turn on the AP and then see how far you can lift up and down on the trailing edge of the elevator.

5. Auto Trim
Auto trim is a separate module that looks at the pitch servo trim output and then adjusts the trim tab in the plane. A lot of the people I have flown with did not recognize a pitch servo slip and thought they had the plane in trim.

6. Bank Angle
The bank angle setting in the autopilot is only used when the autopilot is in AP mode.

7. If you press the CHECK button on the EFIS you should see AP ROLL and AP VSPD on the bottom of the check list page.

02-25-2013, 09:16 AM

Thanks again for you helpful insight.

I have posted a video of the panel during the turn so you can see the numbers. (it's slightly out of focus for some reason) I've tried changing a lot of the settings so unfortunately I can't give you the exact numbers on the EFIS and A/P at the time of the video but I believe they were pretty close to the recommended numbers. But now, for some reason even the A/P can't hold altitude :(


I haven't check for lost motion yet and forgot to try high bank angle.

Rob Hickman
02-25-2013, 01:14 PM
It looks like it is acting the same in EFIS mode and AP mode?

Have you tried lowering the AP Vertical Activity?