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Turning off Autopilot causes Cessna 172P to dive down

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Turning off Autopilot causes Cessna 172P to dive down

Postby kemosabe » Mon Jun 21, 2021 7:15 pm

HI all,

I am flying FG 2020.3.9 using iMac Retina 5K 2017 with 24 GB RAM and Intel quad-core I5.

I have no problem with Cessna 172P controls in normal flight. On recent flights, I have been trying out (ROL or HDG modes). However, when I turn off AP (deactivate), the plane dives down and spins out of control. I am able to regain stable flight only with difficulty.

Am I doing something wrong?

Thanks
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby benih » Mon Jun 21, 2021 8:38 pm

Are you pulling the yoke, causing the AP to trim the plane down to counter?
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby kemosabe » Tue Jun 22, 2021 4:53 am

I don't think so. I will try again and see if that is the problem. Thank you.
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby wkitty42 » Tue Jun 22, 2021 1:01 pm

i was going to suggest to turn on the default HUD but IIRC it has been disabled for reality because the IRL craft doesn't have one... if the HUD can/could be turned on, you could see at a glance where the control surfaces and trims are set... i/someone would have to dig into the craft's code to find the properties that could be monitored in the property tree that would also tell these states...
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby TheEagle » Sun Feb 20, 2022 10:49 pm

(If you still have this problem) Try pressing the key 5 before disengaging the AP - this will center the yoke.
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby benih » Mon Feb 21, 2022 7:26 am

If input controls are left alone and the AP did trim the plane into stable flight, there should be no changes in attitude when releasing the AP.

If you are flying with a joystick/yoke (instead of mouse or keyboard) it could be that it is not calibrated good enough. This will cause permanent „pulling“ or „pushing“ on the virtual yoke, causing the ap to try to counter with trim. That will manifest badly once releasing the AP.
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby Octal450 » Tue Feb 22, 2022 6:25 pm

Stop stop stop
Beware all that only applies to old badly modelled APs that drive the TRIM directly - that is bad and never used IRL.

No longer problem since the reworked the KAP140. The control loop now uses elevator like it should and then trims. So you can no longer make invalid states like these.

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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby benih » Wed Feb 23, 2022 10:21 am

Octal450 wrote in Tue Feb 22, 2022 6:25 pm:No longer problem since the reworked the KAP140.

Confirm Josh, just tested.
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby Doorknob747 » Fri Feb 25, 2022 8:48 am

wkitty42 wrote in Tue Jun 22, 2021 1:01 pm:i was going to suggest to turn on the default HUD but IIRC it has been disabled for reality because the IRL craft doesn't have one... if the HUD can/could be turned on, you could see at a glance where the control surfaces and trims are set... i/someone would have to dig into the craft's code to find the properties that could be monitored in the property tree that would also tell these states...


Boeing 787 and C-17 Globemaster do actually come with a HUD in real life from what I seen from pics of the aircraft ..... somewhat.
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby Doorknob747 » Fri Feb 25, 2022 8:51 am

kemosabe wrote in Mon Jun 21, 2021 7:15 pm:HI all,

I am flying FG 2020.3.9 using iMac Retina 5K 2017 with 24 GB RAM and Intel quad-core I5.

I have no problem with Cessna 172P controls in normal flight. On recent flights, I have been trying out (ROL or HDG modes). However, when I turn off AP (deactivate), the plane dives down and spins out of control. I am able to regain stable flight only with difficulty.

Am I doing something wrong?

Thanks


If the solutions of the others don't work, it could be ( I never used the Cessna 172P, so I do not know if random failures is available for it, but am making an educated guess) that vertical trim stabilizer failure may have been set to on.
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby benih » Fri Feb 25, 2022 5:58 pm

Afaik you have to turn that feature on manually.

I can’t reproduce the problem here.
It would be very interesting if you could provide exact steps you do (settings in launcher, airport, weather, flight parameters), or even better a replay file.

Edit: FG 2020.3.9 I’m not sure there is the revised ap included yet. When you turn on the avionics and battery, does the AP beep and spin up a preflight test procedure? (Displaying „PFT“ and some numbers, finally all led segments and then it’sshirtly waiting for baro input)
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Re: Turning off Autopilot causes Cessna 172P to dive down

Postby WoodSTokk » Tue Mar 01, 2022 7:19 pm

AFAIK the new KAP 140 is only in next (aka 2020.4).
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