Autopilot behaviour after departure

[AirSerbia]

Hello there guys!

Thanks for the great product you've created :-) 

I have an issue that is probably related to lack of my skill - so I need a bit of help on your side. Every time after departure when I engage YD, followed by AP aircraft starts to nosedive until it starts picking up speed again and climbing via IAS or VS.

I thought it might "chase" IAS that is preselected but the same happens with VS selection.

Anything I am doing wrong? Maybe the issue is the trim? Also I fail to find trim performance table, should there be any :-( Thanks a lot for your time.

[Coop]

With IAS mode, it should never descend even when trying to catch a selected airspeed, if the altitude preselector is above your current altitude (and vice-versa on descents). If it is that dramatic, then perhaps something maybe with trimming and your flight controls? 

 

VS is much simpler, much less logic going on, it is just targeting the selected VS. If its dramatically oscillating around that or diving before capture a positive VS then it sounds like your plane was not in trim before engaging AP. 

[AirSerbia]

2 hours ago, Coop said:

With IAS mode, it should never descend even when trying to catch a selected airspeed, if the altitude preselector is above your current altitude (and vice-versa on descents). If it is that dramatic, then perhaps something maybe with trimming and your flight controls? 

ALT was always set to airport initial climb, so above the airport elevation.

Speaking about trim, where can I find proper trim for departure? Meaning, is there any trim setting needed to be set per the TOW or something as such?

2 hours ago, Coop said:

VS is much simpler, much less logic going on, it is just targeting the selected VS. If its dramatically oscillating around that or diving before capture a positive VS then it sounds like your plane was not in trim before engaging AP. 

I think the trim might be the case to be honest. Just have no idea how to properly set it up - resp. to which specific value, or it just have to be within the white area next to the trim wheel?

[Coop]

Yeah, the white area is the takeoff trim range. But, that doesn’t mean you should engage the AP with the trim there, if you are holding control pressure on the yoke, don’t expect the AP to take over seamlessly. The plane should be trimmed throughout the hand-flying phase of takeoff and initial climb, then with the plane in-trim, you can engage the AP when appropriate.