Could you rewrite the current default autopilot so that it works as a real unit?
I’m not talking about tweaking the current one because it can’t follow properly the desired modes in its current state. I’m talking about a new autopilot that would provide the most basic feature of any autopilot.
The most obvious thing would be to have this new AP use the elevator to control airplane pitch and not the trim. The second thing would be for this autopilot to actually trim the aircraft while engaged, as it is a requirement for any autopilot in real life to have the aircraft trimmed correctly when disengaged.
I’m pretty sure that starting from scratch, while looking like a step backward for the team would only help in the future making the autopilot work as it should, which is not the case right now.
Hopefully, this will be backed by the community and listened to by the developers.
As far as i know the autopilot uses trim to control the pitch for the various modes not so in FS2020. The trim wheel never moves when the autopilot adjusts the pitch angle and we can’t trim while the AP is on, hence the sudden change in pitch after autopilot deactivation because it remembers the old trim setting, that’s why the planes act strangely if not dangerously after AP deactivation. Plane especially affected is the TBM.
Real aircraft don’t tend to use trim for the autopilot either - that was a ‘workaround’ for earlier versions of the sim. If MSFS has done away with this and is using the control surfaces to fly the AP, great BUT if you cannot trim when the AP is on then that is an issue as roughly trimming the aircraft to maintain its current situation should always be done before disconnecting the AP under normal circumstances. Precisely to avoid the situation you describe!
I think the King Air has a manual trim wheel and an electric auto trim for AP. You set the manual trim for take off then don’t need to touch it again until AP is disconnected.
Can I ask what aircraft you are talking about that does not use the trim as part of the autopilot? The DA40 uses, pitch, roll and pitch trim servo motors. The pitch trim servo is connected to the trim wheel.
I would assume other aircraft do also. I don’t believe you are required to trim the aircraft before disconnecting the AP. The OP is correct that the trim should move and should be automatically set to relieve any pressure on the control surfaces so the aircraft does not nose up or down with AP disconnect.
I think we are both guilty of the same presumptions - you appear to be looking at modern autopilots (at a guess, the DA40?) and I’ll quite happily say I have no experience of more modern APs - do they use trim as a primary control? The ones I do know date back a bit further, primary control is generally by manual control as in the Mk9 fitted to the Shackleton
and, whilst trim may ‘keep up’ with what is going on (on the VC10 it’s described as ‘auto-trim’ and has a larger section in the manual than the primary control, mainly because of the amount that can go wrong with it! :
It is definitely a secondary part of the system and needs to be monitored throughout (again, a large proportion of the text) and checked before disengagement.
In my initial post in this thread, the main point I was trying to make was that previous versions of the sim used trim as the sole autopilot control. This is incorrect for all aircraft that I am aware of but I haven’t flown for a few years now so if you can correct me on this, great - always learning!
No matter how good your AP, I’d suggest even a system with trim backup needs to be checked before disengagement as a matter of ‘best practise’.
In every GA aircraft I’ve flown, including Cessna twins, C208s & King Airs, the trim WAS controlled when the autopilot was engaged. This is how they operate. Also, the electric trim switches and the manual trim wheel do the exact same thing. When the switches are used, the trim wheel move in response.
It HAS to work this way in every aircraft, or the aircraft would be out of trim when the autopilot is disconnected. This could be very dangerous.
No worries - I just think that the ‘old’ sim style of using trim as the sole control causes problems in developing. Was hoping for something a little more involved and thought from the initial post that this may have been the case.
I have seen, but not flown, “modern” (well, more modern than the Shackleton! : ) ) autopilot installations that have a pitch servo but no pitch trim servo. For example, in the KAP140 used in the steam gauge C172 in the sim the pitch trim servo is optional. Without it you get arrows on the autopilot panel indicating how the autopilot is asking you to trim. The S-TEC 30 works the same way (A2A implemented that system in their Comanche). Luckily for us the MSFS implementation of the KAP140 has the pitch trim servo option so we do not have to worry about that.
