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+1 vote
asked by (17 points)
No matter which aircraft I fly or where I fly from, at random times the trim will go to full-back setting causing a sudden nose-up attitude. This makes it impossible to fly straight and level or achieve any kind of flight.

Any idea's?
commented by (10 points)
I had three more instances of the problem today.  All three on autopilot and all three without anything bound to the pitch trim up or down.

I've bound the "takeoff" elevator trim to a joystick button, so I'm able to quickly correct it now.  But the quick correction time has taught me that it was not just a single "max pitch up" event.  It's actually about 3-5 seconds of max pitch up.  I can set the elevator trim back to "Takeoff" three or four times, and it just keeps rolling to max pitch up.

Still not sure of the root cause, but i'm going to give it some thought this week.
commented by (570 points)
Can you try with a different joystick? It can be a faulty pot spiking its output. There's an option that let you see graphically command axis and the joysticks command axis. Something like "Show command deflection". I'm at work, so I'm not sure how it's called and where.
commented by (10 points)
Will do - good idea.  I've been using the data output to monitor icing (I think that's fair because it's not modeled visually right!?!).  I'll turn that on, but probably won't have any chance to test it until the weekend.

Edit: But again - I didn't have any joystick button or axis bound to elevator trim.  And I seriously got like 8 hours of flying in over the weekend and it only happened about three times.  So hardware is feeling unlikely.
commented by (10 points)
edited by
I've got a saved flight right in the middle of the symptom happening right now.

Oddly, this time, every time I press the button bound to "takeoff pitch trim", it resets to takeoff trim, but not permanently.   It resets to takeoff for only for as long as I hold down the button.  Then it shoots right back to max pitch up.  It just may be the aircraft.

With data output on, I have ~.9200 on the elevator trim, but I think that's just the trim setting not an input on the trim.  It changes to .2000 when I press the "takeoff trim" button.  It's ruined the flight, of course, because I can only adjust the trim when I'm not pressing the "takeoff trim" button, and I can only let go of the button for a couple of seconds before overstressing the airframe.

I'd like to use this saved flight as some sort of diagnostic, but I think it's actually AFTER the symptom took place.  It just feels like it's still happening because of the unusual behaviour of the "takeoff trim" button.

I should point out that this is about the fourth flight and the fourth hour that I've flown today and the first time it happened.  I had grown complacent.


edit:  The Pitch, Roll and Heading "Control deflections" all remain relatively flat by the way.  It's just the trim, not the pitch input.
commented by (59 points)
I'm having the same issue with all Jet aircraft.

Can't attach the Log file though.

2 Answers

0 votes
answered by (24 points)
Same problem with me. You are not alone !

But I have no solution !
0 votes
answered by (17 points)
This happens regardless of the autopilot being activated or not.
commented by (570 points)
If it happen all the time I would activate DATA OUTPUTs 8, 9, 13, 14, 17 viewable in cockpit and see from where this input comes from.
commented by (17 points)
This shows the elevator trim going to full deflection at random, even when no other inputs are made.