ALL of this Post may be 100% Wrong .. Looks like the issue MAY be with the AP MODS – (not directly with Asobo – sorry Asobo)
Many are reporting, that since Update #5, the turning On & OFF the AP, makes the Plane “LURCH” in pitch.
Please, someone, tell me I am wrong (and why)
I now very little about the precise mechanical operation of a C172 Auto Pilot, but this seems just WRONG !!!
Test:
C172 (classic), level flight @ say 5000ft, full power, clean config.
So, Plane has been trimmed manually with the trim wheel for level flight, and there is some non zero trim setting.
Now, turn on AP
Before #5, AP would move the trim wheel, to maintain trim.
I think this is what Asobo realized was the BUG in the AP for the GA Planes.
In most GA Planes, the AP does NOT move the trim wheel, instead it acts on a control rod to move the elevator.
What Asobo have now done (I believe) is to correctly NOT have the AP control the trim tab, but instead have the elevator controlled correctly by the AP, with a Push rod.
Fine .. That’s GOOD .. but the mistake they “seem to have made” is ZAPPING the trim wheel to ZERO when the AP is turned on. !!!
You can see the trim wheel JUMP to a zero trim position, as well as if Monitoring the TRIM value by SimConnect, see it reset to zero
So Instantly there is a change in the trim wheel, and the plane lurches !!! as the AP re-trims the plane with the elevator.
Later, when is stable level flight, the AP is turned off.
But the Trim Wheel has been set to ZERO, so once again the plane Lurches, and the pilot has to manually re-trim the plane, back to where it was before the AP took over.
Not sure what what should be happening to the Push Rod, but the Trim Wheel is now Zero, and that was NOT the value for the plane to be Trimmed before the AP was turned on.
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Not got it all figured out in my mind – I am still getting over the shock of how a C172 Autopilot can Instantaneously, move the trim wheel to Zero Trim !!!
Please think about this, and express your thoughts (in a Civil manner please !! )
Absolutely not a real world pilot but got more years than I care for on and off with flight sims. In the more recent years that my memory recalls, autopilot flies by trim from my experience. So when disengaged, you don’t have this lurching. Whether or not that matches reality, I can’t say.
If you are trimmed for climb, say @ 5000 fpm, and that is stable state, if you turn on the AP, is it meant to
(a) capture that 500 fpm and use that as it’s VS (what I always though it should do )
(b) Init to Zero for its VS
(c) Init to whatever the last VS was set to when the AP was active
Currently, with #5, and without the Mod installed, the AP TRIM seems to now FREEZE at whatever it was set to when the AP was turned on.
It no longer sets the TRIM to Zero, as it seems to do when your current Version Mod is running.
Note If it does (a), then there should be no LURCH when the AP is turned on .
There may be a Limit on what it sets itself too, like if you were in a deep dive, at 3000 fpm, I would not expect it to Init to -3000 !!! – but in that case, what should it init to ?
It’s amazing that when all this stuff works correctly, you just take it all for Granted, but when it messes it, you realize just how complicated it is !!
It does “lurch” when you engage the “ALT Hold” mode, and then hunt for three or four cycles before settling in on the altitude selected. At least on this flight, it climbs at 500 fpm as it should.
I had a CTD event over Salinas. So… I’m flying the same plan again just to see if it happens again.
I should get something from MS/Asobo for this. Even a “badge” on the forum would be okay.
Yes, Night time flying is the best… smooth air, no sun glare, you can see other planes for miles, and I still get a big kick when I turn on all the Runway Lighting at KMTN, when I am 20 miles out, and see the whole sky light up, and know I am heading the right way to the airport.
That is something that MSFS is not simulating yet …
I think it is too “aggressive.” And, I am very careful about capturing the flight path and avoiding any sudden course/altitude corrections.
If you have attained your chosen altitude my training has always been to overshoot just tad (say 50-100 feet) and then engage the autopilot. It should settle in at the selected altitude.
OK, I have answered my own question about the VS setting when AP is pressed.
From The KAP140 RL manual (not a Sim version)
AUTOPILOT ENGAGE/DISENGAGE (AP) BUTTON - When pushed, engages autopilot if all logic conditions are met. The autopilot will engage in the basic roll (ROL)mode which functions as a wing leveler and in the vertical speed (VS)hold mode.
The commanded vertical speed will be displayed in the upper right corner of autopilot dis-play area.
The captured VS will be the vertical speed present at the moment of AP button press.
I think it did that correctly for me. I’ll pay more attention next time, but I really try to “fly by the book” and climb at Vy. The book value for the C172 is 74 KIAS, and tonight I was pretty much at that that airspeed when I engaged AP.
My VR was 500-600 fpm. That’s about my experience in a C172 with 1500+ hours on the engine. They are forgiving aircraft, but not a hot rod by any means.
AUTOPILOT ENGAGE/DISENGAGE (AP) BUTTON - When pushed, engages autopilot if all logic conditions are met. The autopilot will engage in the basic roll (ROL)mode which functions as a wing leveler and in the vertical speed (VS)hold mode.
The commanded vertical speed will be displayed in the upper right corner of autopilot dis-play area.
The captured VS will be the vertical speed present at the moment of AP button press.
