I have now completed 2 IFR flights in the 172SP and have some questions on the AP.  In the beginning of both flights I couldn't get the AP to engage properly. Both times I had the Heading Bug already aligned and selected HDG - the aircraft began a sharp turn away from the designated course.

I turned the AP off and tried again:

• Activated AP
• Set ALT to planned altitude
• Set climb rate
• Realigned Heading Bug
• Selected HDG again

The aircraft was now stable and stayed on the indicated heading - as I approached the FP course, I activated NAV and she followed fairly well. I ran an RNAV approach, then an ILS - both went well.

Does the AP (as it currently stands) fail a lot initially, or is it just important to engage ALT/VS before HDG or NAV?

I have seen the Garmin units act weirdly in the roll axis if engaged into ALT mode with the ALT set to 0000.  It only happened ~twice and I wasn't able to reproduce.  Since the general aviation aircraft avionics all tie into the same AP code in the core of the sim, it's possible there is some bug there.

Typically I set all of the modes, both horizontal and vertical I want before engaging the AP.

Edited December 1, 20205 yr by marsman2020

In my limited AP experience I usually preset vertical and lateral navigation and then engage AP

Understood - I've tried to do that but there are some limitations. This basic AP appears to be simply On or Off.  It doesn't appear to be a model that you can turn on, make settings, then engage? It appears to be engaged, period, if it is on, it's active - if it's off, you can't change settings?

Maybe this is something that will be corrected in the future.  Another thing I will test is to activate it and set the current altitude so that it holds it.  Then , I'll see if I can set a HDG and activate horizontal nav without loss of control.

It could be that this unit (as currently coded) simply requires a stable vertical setting first (assigned climb, descent, hold) before engaging a horizontal mode.

I bind a button on my stick to engage and disengage AP

2 minutes ago, sd_flyer said:

I bind a button on my stick to engage and disengage AP

Sounds good, but is that for this unit or a more advanced system?

The core AP key binding commands are the same for all the GA aircraft with an autopilot. (And possibly for the airliners as well, but I haven't tried those to comment).

I'll play with this a bit tonight and see what happens, it's been a bit since I tried either of the steam gauge aircraft.

Edited December 2, 20205 yr by marsman2020

I leave AP master off until airborne and established in a rate of climb and on a heading vector.  I preselect both altitude and initial heading, which is usually runway heading.  I stay totally away from the AP master switch until first established on both.  

BTW. That is realistic per current piloting.  You are 100% the PIC until established, and 99% thereafter.

Edited December 2, 20205 yr by fppilot

45 minutes ago, fppilot said:

I leave AP master off until airborne and established in a rate of climb and on a heading vector.  I preselect both altitude and initial heading, which is usually runway heading.  I stay totally away from the AP master switch until first established on both.  

BTW. That is realistic per current piloting.  You are 100% the PIC until established, and 99% thereafter.

This is exactly my procedure and it has been for years, both in the real world and while simming. But, when I engage, the stability is gone.

Then, I'll reset, try again and she's smooth as silk for the rest of the flight...

I tried engaging the AP on the steam panel C172, no problems here.  However intermittent AP problems are not unusual in the sim.

A couple things to try:

• Deflect all control surfaces completely through their range of motion before takeoff.  I've had some strange behaviors if I don't do this.
• Check in the options menu to make sure you have the flight model set to 'Modern'

Thanks - actually I've always been set to Modern and I've also deflected all of the control surfaces before flying (usually before engine start, but sometimes after run-up).  I saw a comment from Rob Young on this.

Ironically, after doing that this morning, the aircraft attempted to jump into the air at about 30KT - I had to hold her on the ground.  Then when I began to rotate, she went nose-high.  To make matters worse, my trim didn't function at all (at least on my stick).  I almost gave up and started over.  However, the aircraft stabilized when I engaged the AP so I continued.

Later in the flight, when I disengaged the AP she hand-flew normally again (though still with no trim).  The adventure continues...

7 hours ago, RandallR said:

Later in the flight, when I disengaged the AP she hand-flew normally again (though still with no trim).  The adventure continues...

Given the unpredictable nature of the MSFS autopilot, I'd be hesitant to assign a gender to it, for fear of insulting half of the world's population. It's too bad there isn't a specific pronoun that can be used to describe the actions of infants.😉

It's a Cessna 172....hand fly the darn thing 😉

Seriously though, the only consistency that I have found is to basically use altitude hold once I've attained my desired altitude by hand. Heading mode works, Nav mode works sometimes. Someday they will get all the bugs worked out but for now use of the AP is "at your own risk".

22 minutes ago, snglecoil said:

It's a Cessna 172....hand fly the darn thing 😉

Seriously though, the only consistency that I have found is to basically use altitude hold once I've attained my desired altitude by hand. Heading mode works, Nav mode works sometimes. Someday they will get all the bugs worked out but for now use of the AP is "at your own risk".

Yes, it's not that any of us need to have AP all of the time, but it does make IFR that much safer - being able to check charts, change freqs, etc., preset approaches - reducing the workload in those conditions. I wish I had had some kind of basic hold, wing leveler, etc. when I flew IFR in the 70's.

The only single-engine aircraft our FBO had with an AP in those days was a beautiful Cherokee 6.  I'll never forget the day I engaged it, set a new heading and watched the aircraft respond - it was magic. 🙂

I started this thread originally, not to complain about not having AP always available, but to be certain I was activating/using it appropriately. And, if I was, to turn in a bug report. If they're going to put it in the aircraft, I expect it to be serviceable.

11 minutes ago, RandallR said:

Yes, it's not that any of us need to have AP all of the time, but it does make IFR that much safer - being able to check charts, change freqs, etc., preset approaches - reducing the workload in those conditions. I wish I had had some kind of basic hold, wing leveler, etc. when I flew IFR in the 70's.

The only single-engine aircraft our FBO had with an AP in those days was a beautiful Cherokee 6.  I'll never forget the day I engaged it, set a new heading and watched the aircraft respond - it was magic. 🙂

I started this thread originally, not to complain about not having AP always available, but to be certain I was activating/using it appropriately. And, if I was, to turn in a bug report. If they're going to put it in the aircraft, I expect it to be serviceable.

I've been instrument rated since 2003 and flew instruments on autopilot only twice IRL 🙂 When I used to own 182 it had aftermarket autopilot installed, but it was not certified for IFR. I used it rarely and only for wing level heading hold 🙂