I posted in another forum (the general 172 forum) about having trouble getting the AP to work (my ignorance, nothing to do with A2A), but I was in some kind of AP mode (holding altitude and heading) when I went to external view, and gave aileron input, just to see what it would do. No effect on the flight behavior, but the ailerons did move their full range?
I hope I am being clear: in VC, no change in flight attitude (being in AP mode), and in external, no change in attitude, but ailerons showed full deflection?
Then I pulled full up elevator, and the 172 shot up like it was a jet, almost. Still in whatever AP mode I was in at the time.
Odd behavior, external view, when AP is on?
- Pistonpilot
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Re: Odd behavior, external view, when AP is on?
I had a curious set of hands pull my yoke for me during an autopilot-engaged moment and also saw this behavior, as well as significant porpoising (to the point where I thought something broke!) afterwards. I performed a divert to a nearby air field with repair facilities, assuming the worst, and found the aircraft to be in good health. Phew.Li'lJugs wrote:Then I pulled full up elevator, and the 172 shot up like it was a jet, almost. Still in whatever AP mode I was in at the time.
From what I can gather, the AP modeled in A2A's 172R controls pitch purely with the trim tab, so, if you yank the yoke while a pitch mode is engaged, you'll establish a new attitude from which the AP tries to recover via tweaking just the trim tab (in whatever the mechanical/electrical equivalent of a panicked frenzy is). From what I've seen of real-world GA aircraft auto pilots that use electric pitch trim, they tend to alter pitch trim at a very slow rate, thus the porpoising resulting in a phugoid oscillation, which kind of looks like an 'out of control' aircraft. I've not read the manual for the AP unit modeled, but this scenario fits my understanding of how this AP works.
I've never flown a real 172 with an AP, so, this is all conjecture from me!
Hope this helps!
-Ian C
DWC Alumni. Commercial Instrument Single/Multi-Engine Land. [Former] Police, Fire, & 9-1-1 Dispatcher. [Former] MAINEiac Crew Chief.
- some1 - A2A
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Re: Odd behavior, external view, when AP is on?
Yes, some limitations of the current system. We have plans to revisit it in the future (it won't change how the autopilot is operated by pilot, but some internals in the autopilot engine).
Michael Krawczyk
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