Autopilot keeps climbing

[PrivateSimPilot]

I have an issue that crops up maybe roughly half the time, where I set a target altitude in the autopilot, climb out in NAV mode with altitude armed and VS mode, and find the vertical speed less than I set, and gets lower as I go higher as if I was in some IAS mode. When it gets to the target altitude, it sort of levels off but keeps climbing at maybe 100-200fpm.

In this example I set the target altitude to 8500', and it has way blown past that and keeps climbing, even though in this case I set VS mode to -600fpm. I thought maybe trim was maxed out for some reason, but at this time the trim was less then 1 back from neutral.

On other legs, AP works exactly as I expect, no problem.

Edited May 3, 2020 by PrivateSimPilot

[Coop]

Looking at the picture attached, the altitude is armed to -600 ft, so that could cause issues (assuming you aren't flying below sea level). Odd about it continuously climbing, perhaps your CG could be out of limits and you are running out of trim authority?

[PrivateSimPilot]

The -600 is the VS value that I screen captured for that second or two it’s visible. The armed altitude was 8500’. I thought about trim too, but the white bar is just slightly back (<1) of neutral.

[Coop]

11 minutes ago, PrivateSimPilot said:

The -600 is the VS value that I screen captured for that second or two it’s visible. The armed altitude was 8500’. I thought about trim too, but the white bar is just slightly back (<1) of neutral.

Hm, gotcha. I will mess around and try to replicate the issue, that is an odd one.

[PrivateSimPilot]

Thanks! Including my log.txt in case it's useful. The flight is still happening (I'm going to Far, Far, Away). Throttle does affect it; when I reduced throttle I found it consistently descending. I have the throttle now set so that it's as close to 0 VS as I can get it.

I have Experimental Flight Model set right now, but the same thing happend with that turned off.

Log.txt

[0zz]

It seems like electric trim dataref is turned off. AP can't control the trim. That happens if you disconnect AP by "servos_yawd_trim_off_any", or "servos_fdir_yawd_trim_off" commands. It is restored when you restart the sim, so you might not noticed it before. I am assuming this time you started next leg without restarting the sim, thus your electric trims stayed off when you activated the autopilot.

Check your keyboard or controller bindings and change it to "servos_fdir_yawd_off". When you disconnect AP this way in the future electric trim wont shut down.

To fix it for your recent flight, there is no electric trim activating command that you can bind unfortunately. But, if you have dataref editor installed you can set the "electric_trim_on" value to 1

Or you as an alternative, if you have FlyWithLua installed you can type the line below in a new text file and save it inside Xplane11/Resources/plugins/FlyWithLua/Scripts with .lua extension.

set("sim/cockpit2/autopilot/electric_trim_on", 1)

And click Reload all Lua script files command under plugins, flywithlua from xplane drop down menu. That should set it right.

Hope this helps

[PrivateSimPilot]

I did a couple test flights earlier today in which AP worked fine, but to make sure the conditions were the same, I restarted the sim between them. And indeed, my AP disconnect on my yoke was set to servos_fdir_yawd_trim_off. On that flight I reported on to start this thread, I did start that leg without restarting the sim. I think your theory applies very well. I also noticed after the flight was over the white bar on the trim indicator was in the exact same position it was when I started and during the flight, which seemed suspicious.

I'm about to set off again (that was an FSEconomy flight, and I was so puzzled that I restarted the sim after the flight without finishing the FSEconomy flight , so I have to do it again anyway). I'll try a few flights and post my results with AP disconnect bound to servos_fdir_yawd_off.

This is a bug in the Islander? I've used this same binding for the past couple years and never saw that before.

Awesome -- thank you very much!

[0zz]

No problem   Glad it worked

It can happen with any addon, and I discovered it in a secondary FSE leg similar to your situation.

Some addons like TBM900 and KA350 has dedicated switches that turn electric trim on and off, which are part of their checklists. Even if you turn it off with AP disengage, you'll activate it back on following the checklist before next leg. Keep in mind though, if you bind it to a non momentary switch on a controller, it will seem as if it is on  which was the problem in my case.

Some aircraft like BN-2, dont have that switch and it is suppose to be on as soon as you power up the aircraft or avionics. Disconnecting the AP shouldn't turn it off.

I guess, it can be coded that way. But simply using a disengage command without trim_off works.

Edited May 3, 2020 by 0zz