Piper Autocontrol III (Century II) autopilot+GPSS questions

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greghughes

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I have a 75 Piper Warrior with a Autocontrol III autopilot (roll axis) that works quite well. I recently installed an Icarus SAM GPS roll-steering computer (along with a bunch of other cool stuff). But the autopilot and all related systems are the same as camer with the plane. The Icarus SAM is a great device, lots of cool capabilities when integrated with the GPS and audio panel (and potentially with other systems in the plane)

My problem: I am trying to configure the Icarus SAM roll steering computer to work with the autopilot, but am trying to determine what settings to use. The Autocontrol is an attitude-based autopilot, but does anyone know with certainty if it is an AC or DC autopilot? I need to tell the Icarus system which it is. The service manual for the autopilot discusses AC conversion and amplifiers, and conversion back to DC -- so I am a bit lost (especially since I don't fully understand how the signaling works and where).

If anyone's done a similar setup and can share settings and configuration, I'd sure appreciate it. Thanks!
 
greghughes said:
I have a 75 Piper Warrior with a Autocontrol III autopilot (roll axis) that works quite well. I recently installed an Icarus SAM GPS roll-steering computer (along with a bunch of other cool stuff). But the autopilot and all related systems are the same as camer with the plane. The Icarus SAM is a great device, lots of cool capabilities when integrated with the GPS and audio panel (and potentially with other systems in the plane)

My problem: I am trying to configure the Icarus SAM roll steering computer to work with the autopilot, but am trying to determine what settings to use. The Autocontrol is an attitude-based autopilot, but does anyone know with certainty if it is an AC or DC autopilot? I need to tell the Icarus system which it is. The service manual for the autopilot discusses AC conversion and amplifiers, and conversion back to DC -- so I am a bit lost (especially since I don't fully understand how the signaling works and where).

If anyone's done a similar setup and can share settings and configuration, I'd sure appreciate it. Thanks!
Click to expand...
I have a Century III (roll and pitch) autopilot with an Icarus SAM driven by a GNS480. As I suspect you know the C-III uses the same circuitry as the C-II minus the pitch axis. The autopilot's heading signal is AC but if you have a KCS-55 HSI the SAM heading interface could be DC via a KA-52 adapter. What is your heading source?
 
My heading source is a standard electric DG with a manually-set heading bug. Not sure of the model. But definitey not a HSI. I believe the Icarus SAM is asking for the autopilot heading signal type.

Also, if it helps for confirming, the SAM is set to Attitude/DC AP mode right now, and when I calibrate the heading bug the voltage values I see in the Icarus display basically don't change on the various heading calibration settings (which range from 60 degrees to -60 degrees off the lubber line).

Thanks!
 
Last edited:
greghughes said:
My heading source is a standard electric DG with a manually-set heading bug. Not sure of the model. But definitey not a HSI. I believe the Icarus SAM is asking for the autopilot heading signal type.

Also, if it helps for confirming, the SAM is set to Attitude/DC AP mode right now, and when I calibrate the heading bug the voltage values I see in the Icarus display basically don't change on the various heading calibration settings (which range from 60 degrees to -60 degrees off the lubber line).

Thanks!
Click to expand...
Chances are your DG is a 52D54 or equivalent and that does use an AC heading signal. Your SAM should definitely be wired and configured for AC heading.
 
Also FWIW, the standard max bank angle of a C-II or C-III is 22° although this is adjustable over a small range and I have my C-III set to allow about 25° because this works better with the GPSS at the speeds I fly (120KIAS approach and 180 KTAS cruise). You are correct that the autopilot mode should be attitude in the SAM setup.
 
gismo said:
Also FWIW, the standard max bank angle of a C-II or C-III is 22° although this is adjustable over a small range and I have my C-III set to allow about 25° because this works better with the GPSS at the speeds I fly (120KIAS approach and 180 KTAS cruise). You are correct that the autopilot mode should be attitude in the SAM setup.
Click to expand...

Thanks for that info. The service manual said 20° max in heading mode, 30° max in the mode where you roll with the knob, so makes sense. I'll see what the result is when it's good to fly here again. Pretty nasty out in Portland, OR right now!
 
greghughes said:
Thanks for that info. The service manual said 20° max in heading mode, 30° max in the mode where you roll with the knob, so makes sense. I'll see what the result is when it's good to fly here again. Pretty nasty out in Portland, OR right now!
Click to expand...
There's a diagnostic mode in the SAM that allows you to set the commanded bank angle going to the autotpilot. You can use this in flight to determine the max bank angle the autopilot will allow in either direction. This can also be done on the ground if you have a Century-III attitude gyro simulator (part of Century's test set).
 
Well, the Icarus now makes the AP do things, just not the *right* things hah. Something is still wrong.

I reset the Icarus SAM to factory defaults just because I had been in there so many times making changes. Then I set it up for my 14V airplane, AC attitude based autopilot, etc.

Before I did the reset, I flew the plane with the AP type changed to Attitude/AC. In heading mode it flies straight to the bug on the DG, perfectly. But when I switched to GPSS, the plane flew a max bank autopilot right turn, entered what seems to be a standard rate turn and then orbits in that same bank forever.

After the reset, and re-establishing the key settings above, it does the same thing only to the left.

Needless to say, frustrating.

Clearly something is set incorrectly. The SAM system is getting the ARINC data just fine and I can display it on the SAM screen, so I know it's there. Not sure where to go next: Gain, phase, offsets, etc? I'll call the manufacturer if I can get ahold of them but appreciate any thoughts

Also - when I calibrate the heading bug, the voltage value recorded for each offset of the bug from the lubber line is exactly the same. Seems to me it should be varying in voltage with each offset. Since the bug works when it's in Heading mode and I think the signal is passed through the Icarus in that mode, I am more than a little confused.
 
greghughes said:
Well, the Icarus now makes the AP do things, just not the *right* things hah. Something is still wrong.

I reset the Icarus SAM to factory defaults just because I had been in there so many times making changes. Then I set it up for my 14V airplane, AC attitude based autopilot, etc.

Before I did the reset, I flew the plane with the AP type changed to Attitude/AC. In heading mode it flies straight to the bug on the DG, perfectly. But when I switched to GPSS, the plane flew a max bank autopilot right turn, entered what seems to be a standard rate turn and then orbits in that same bank forever.

After the reset, and re-establishing the key settings above, it does the same thing only to the left.

Needless to say, frustrating.

Clearly something is set incorrectly. The SAM system is getting the ARINC data just fine and I can display it on the SAM screen, so I know it's there. Not sure where to go next: Gain, phase, offsets, etc? I'll call the manufacturer if I can get ahold of them but appreciate any thoughts

Also - when I calibrate the heading bug, the voltage value recorded for each offset of the bug from the lubber line is exactly the same. Seems to me it should be varying in voltage with each offset. Since the bug works when it's in Heading mode and I think the signal is passed through the Icarus in that mode, I am more than a little confused.
Click to expand...

Did you ever find the resolution to this? I have the same auto pilot and recently did the SAM install and it doing the exact same thing. First it was doing right hand turns when the GPSS was Activated now it's turning left. So confused!! Any help would be greatly appreciated as support for this unit is nonexistent.

Thanks
 
Is the DG bug fighting the GPSS module?
 
Not sure, all I'm getting now is a left turn when the AP is activated in heading mode or GPSS. After initial instal the avionics shop had set it up attitude AC, when you engaged the GPSS the rolled right to the max bank and stayed there. In heading mode the ap functioned as normal.

Advice from the avionics show was to change to attitude AC and invert the phase. Did that but now all I get are left turns. I have a century iiii with an NSD 360 HSI. The Sam is getting all the correct data from the GPS but something is not right
 
Have you shop tighten and reseat all the pins or replace the AP connector all together. They loosen over time. No doubt he was back in there moving stuff around. May require a new connects tour to tighten up.

I had the same issue on my Archer; uncommanded rolls. Metastasized after they were in it working on the panel. 10 minutes later, it was good to go. It's a pretty well known issue on the Century connectors.
 
I finally have my SAM GPSS functioning correctly! my only issue now is it overshoots by 5-7 degrees. The gain is at the default level of 1.000x. Which way should I go with the gain to correct overshoot? up or down?

These setting worked for me:
Attitude AC
DG Signal calibration done with engine running, AP on and radio coupler in heading mode
Bug Max = 22 degrees
Max Bnk = 25 degrees
RS phase = 330 degrees

I have yet to do the bank angle flight test procedure which I think may solve the overshoot problem. Can anyone who has done this calibration in flight provide some pointers? I assume you have to power the unit down in flight with the Avionics master switch to enter into the calibration screen.
 
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