Disengaging AP after Altitude Hold causing a DIVE!

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wazooda
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Disengaging AP after Altitude Hold causing a DIVE!

Post by wazooda »

So.... I'm learning the KAP 140 for use in the real world 172's I fly.

I am, however, having an issue in the sim that I don't have in real life: after disengaging the AP from an Altitude Hold mode, the fly often goes into a nose down dive.

It seems to be caused by the AP setting the trim to extreme positions to maintain the steady altitude. When I turn off the AP, the trim is WAY nose low so the dive immediately take place.

Am I missing something here to avoid this issue?

Thanks!

PAul

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Nick - A2A
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by Nick - A2A »

Hi Paul,

Please can you give us a little more info on your sim setup. For instance, the type of control hardware you use, any add-on software which my be relevant (e.g. FSUIPC or weather engines) and indeed the host sim you're using.

A couple of things to check for starters: have you applied the latest Accu-Sim update (assuming this isn't P3Dv4) and have you made sure there are no defects with the trim system or elevator in the maintenance hangar (shift 7)?

Thanks,
Nick

wazooda
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by wazooda »

Nick M wrote:Hi Paul,

Please can you give us a little more info on your sim setup. For instance, the type of control hardware you use, any add-on software which my be relevant (e.g. FSUIPC or weather engines) and indeed the host sim you're using.

A couple of things to check for starters: have you applied the latest Accu-Sim update (assuming this isn't P3Dv4) and have you made sure there are no defects with the trim system or elevator in the maintenance hangar (shift 7)?

Thanks,
Nick
Thanks for the reply Nick.

I'm running P3D v3.4 + the latest C172 and FSUIPC.

However, of course how these things go, I'm trying to recreate the problem and have not been able to do so. Thus, maybe I just had some weird input combination (I *was* messing with VS settings and ALT holding while learning) that caused this statistically outlying problem.

If I run into it again, I'll resurrect the thread. :)

Thanks!

Paul

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Nick - A2A
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by Nick - A2A »

Yes, sounds like an odd one Paul, unless somehow you've got hardware and/or software which is forcing an aft yoke input when the autopilot is engaged, causing it to respond with nose down trim. By default yoke inputs should be ignored until the autopilot is disconnected, but perhaps there's something in FSUIPC for example which can circumvent this.

Let us know if you manage to reproduce the issue though.

Thanks,
Nick

wazooda
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by wazooda »

Nick M wrote:Yes, sounds like an odd one Paul, unless somehow you've got hardware and/or software which is forcing an aft yoke input when the autopilot is engaged, causing it to respond with nose down trim. By default yoke inputs should be ignored until the autopilot is disconnected, but perhaps there's something in FSUIPC for example which can circumvent this.

Let us know if you manage to reproduce the issue though.

Thanks,
Nick
Now that you mention it, I *do* have a Brunner force-feedback yoke. Maybe that is a variable I need to explore more closely.

-Paul

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Nick - A2A
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by Nick - A2A »

wazooda wrote:Now that you mention it, I *do* have a Brunner force-feedback yoke.
Well - aren't you the lucky one! :P Yeah, could be related but afraid I have zero experience of FFB hardware, let alone how it would interact with the A2A software and their custom autopilot simulation.

Does the Brunner yoke provide a sensible physical response to different elevator trim conditions in the A2A 172 when hand flying?

Thanks,
Nick

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Oracle427
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by Oracle427 »

Oh interesting, I always wondered how the Brunner yoke performed.

I suspect that there are issues with the yoke not being "connected" when the AP is engaged in the A2A sim. In the real aircraft the yoke remains connected and it is possible to override the AP though that can lead to the behavior described here. I don't know what sort of sim outputs the yoke is receiving and how it is producing force feedback with respect to the outputs.

What is interesting is your statement that the trim wheel is running away. That suggests that the sim is possibly reacting to the yoke and trimming against it? I didn't think that was possible with the way the A2A sim was implemented.

I have RL experience with this during my training under my CFIs watchful eye. He silently allowed me "help" the KAP140 autopilot by keeping my hand on the yoke. Little by little the AP trimmed against my helpful input and ran the trim wheel nose up a fair amount before it abruptly disconnected with a few beeps and an warning message. The next thing I knew, I had to push against a very heavy yoke in an out of trim airplane and had to quickly manually re-trim to get things back in order. The KAP140 was offline and had to have the circuit breaker cycled to get the unit to reset and run its suite of self tests before it would function. Good learning and the reason why I really liked that CFI.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

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Nick - A2A
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by Nick - A2A »

Yeah, a decent force-feedback yoke would be right at the top of my 'fantasy wishlist' in terms of flight-sim hardware. I guess there might be a few issues with compatibility with the A2A line though, especially given the custom autopilot code they created. Throw FSUIPC into the mix too, and no doubt all sort of weird behaviour is possible! :P

Sounds like an interesting flight though Oracle: y'know you never did answer the little question I asked about it two years ago! :mrgreen:

Cheers,
Nick

wazooda
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by wazooda »

Nick M wrote:
wazooda wrote:Now that you mention it, I *do* have a Brunner force-feedback yoke.
Well - aren't you the lucky one! :P Yeah, could be related but afraid I have zero experience of FFB hardware, let alone how it would interact with the A2A software and their custom autopilot simulation.

Does the Brunner yoke provide a sensible physical response to different elevator trim conditions in the A2A 172 when hand flying?

Thanks,
Nick

Hehehe. Yes. LOVE the yoke. Also have their pedals as well. Hooked them up on a CKAS 6DOF motion platform. Pretty much my "Dream Machine".

Trimming still generally sucks. To Brunner's credit, their software is VERY robust and you can do some great things with it. However, since trim was designed in P3D for non-FFB yokes, it always assumes the yoke is centered. Thus, there is no real connection between the two.

I do have the option to use software trim (i.e. my trim switch on the yoke will physically move the trim wheel in the cockpit) or hardware trimming (no connection between the sim and the switch but it is a more natural feel as it removes control pressures from the yoke as I hold it in a level-flight position). I'm still experimenting to isolate how to reliably throw off the pitch/AP system so much so that I get the diving issue on disconnect. I have found that it also happens to me, although not as dramatically, flying X-Plane 11 and AirFoilLabs C172... so it seems to be FFB related.

I tried to get Brunner and A2A hooked up so Brunner could code directly into the sim, but Brunner was not willing to send a free yoke to A2A and A2A didn't want to pay for one. Personally, I think Brunner, like many niche hardware manufacturers should, in fact, send out free or steeply discounted hardware to devs if the devs agree to program for it.

Just seems like smart biz-dev to me. :wink:

-Paul

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Nick - A2A
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Re: Disengaging AP after Altitude Hold causing a DIVE!

Post by Nick - A2A »

wazooda wrote:Trimming still generally sucks. To Brunner's credit, their software is VERY robust and you can do some great things with it. However, since trim was designed in P3D for non-FFB yokes, it always assumes the yoke is centered. Thus, there is no real connection between the two.
Yes, I wondered if that might be the case. As you say, the fundamental compromises in the FSX/P3D trim simulation are going to take some overcoming, and I'm not sure if third-party software like FS Force can make much difference here. I seem to recall watching a video by another force-feedback yoke developer (Iris Dynamics) which seemed pretty impressive in terms of the trim behaviour, but since these products are a bit more expensive than I can justify, I didn't pay much attention. :P

Cheers,
Nick

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