Weird autopilot behavior

[KMKaine]

Doing some flights in the SAAB after picking it up this friday. I was climbing out of NZQN this evening, AP engaged. Then suddenly an AP warning sound and red AP text in the EFIS was blinking. No annunciators lighting up, so I have no idea why this is happening, and how to fix it? I think it might be triggered by a stall, but I could not recover from this weird behaviour.

After a short while I had some different behaviour as you can see in vid 2. I tried to push the plane down, didn't respond, and then all of a sudden it seemed to snap out of its weird behaviour, or at least a part of it...

Can somebody explain to me what I'm doing wrong, or how to recover this behaviour?

Thanks in advance and thanks for your time.

Log.txt

[KMKaine]

I tried another flight, it happened again... I climb for 16000 feet. Then when level, I set the throttles and condition to 75% and 1330 rpm... Slowly but steadily my airspeed falls back to below 120 knots... Then the AP warning goes off, without it ever shutting up again. Also AP logic seems to be malfunctioning once this situation triggers? Any help greatly appreciated. Cheers!

[xterminator24]

You ran out of airspeed and stalled. 

The reason based on the gauges (in video 2) appears to be that you have no torque. That indicates you over-stressed the engines earlier in the flight. Once that happens, you aren’t going to recover. Make sure you stay within operating (green range) on all gauges at all times. Not doing so will lead to failures. 

[KMKaine]

I do seem to be losing torque indeed. However I did not overstress the enige as far as I know. I took off with the settings in the screen below. All in the green, except prop oil, seems to be against orange, but I have no idea how to lower that.

Also the hydraulics seem to loose pressure slowly. when I set it back to OVRD it ups the pressure again... I feel like I'm missing something, but I'm following one of the checklists made by another user on here, which seems to be quite complete...

[KMKaine]

It seems that if you ever make the mistake of activating the AP on the ground, it results in an un-silenceble AP alarm. I made the error of clicking the white button on the left of the throttle quadrant (looking for the T/O inhibit), and there it was, unable to quit it again...

[mmerelles]

24 minutes ago, KMKaine said:

It seems that if you ever make the mistake of activating the AP on the ground, it results in an un-silenceble AP alarm. I made the error of clicking the white button on the left of the throttle quadrant (looking for the T/O inhibit), and there it was, unable to quit it again...

 

This aircraft as most regional & jetliners requires a double push for A/P disconnect, one push to disconnect and an aural warning will kick in just in case you did it by accident, a second push will clear the alarm.

 

Map any button or key of your liking to 'LES/CMD/CW/button/AP_disconnect'

 

Edited March 25, 2018 by mmerelles
misspelling

[mmerelles]

As per all of your other issues, did you dissengage the CTOT switches after takeoff?

[KMKaine]

Thanks for all your feedback, I'll try it tomorrow and report back. Cheers!

[Goran_M]

There is a tutorial included in the documentation.  Try that and see how you go.

[KMKaine]

H Guys,

I did some flights yesterday with good results ;-). 

One of the things I did is to use the AP_Disconnect suggestion and bind it to a key. To disable the AP and the annoying warning, one has to press this twice. It is then fully disconnected. 

Another one was activating the AP with the button in the center console. This resulted in the AP becoming green. I did this before with a button on my yoke (Toggle Servos), but this doesn't turn on the AP fully. The plane seems to follow the AP, however the AP text in the EFIS remains white. Perhaps this is only cosmetically... The Toggle Servos can't properly disconnect the AP so it seems, I guess that is why there is an additional dataref AP_Disconnect.

As for power on takeoff, I set the CTOT to 100% or a bit above and used that. I then when climbing out disconnect the CTOT and the TRQ drops back to around 50 - 60. In the manual it says to keep it here but TRQ drops very slowly when climbing, is this normal?

A couple of observations; The prop-oil temp seems quite high (almost in the yellow) when using the listed prop rpm. Is this normal? I tend to lower the prop rpm for now... Also the trq on climb results in high engine temps... when using 70 - 87 trq. I tend to use the lower and safer values now.

And one last question... I got a config warning when taking off, even tho I followed the checklist... Is there something sneaky I missed ;-)

Cheers, and great plane and product.

Thanks again.

[JGregory]

50 minutes ago, KMKaine said:

One of the things I did is to use the AP_Disconnect suggestion and bind it to a key. To disable the AP and the annoying warning, one has to press this twice. It is then fully disconnected. 

Just to be clear, the first push of the key WILL disconnect the autopilot, the second push will disable the aural warning.

 

50 minutes ago, KMKaine said:

Another one was activating the AP with the button in the center console. This resulted in the AP becoming green. I did this before with a button on my yoke (Toggle Servos), but this doesn't turn on the AP fully. The plane seems to follow the AP, however the AP text in the EFIS remains white. Perhaps this is only cosmetically... The Toggle Servos can't properly disconnect the AP so it seems, I guess that is why there is an additional dataref AP_Disconnect.

The slide switch on the center pedestal for activating the autopilot must be held in position for a couple of seconds or it will not turn the autopilot on.  If the AP annunciator on the display is white, the autopilot is NOT on.  

 

50 minutes ago, KMKaine said:

As for power on takeoff, I set the CTOT to 100% or a bit above and used that. I then when climbing out disconnect the CTOT and the TRQ drops back to around 50 - 60. In the manual it says to keep it here but TRQ drops very slowly when climbing, is this normal?

A couple of observations; The prop-oil temp seems quite high (almost in the yellow) when using the listed prop rpm. Is this normal? I tend to lower the prop rpm for now... Also the trq on climb results in high engine temps... when using 70 - 87 trq. I tend to use the lower and safer values now.

You should adjust your power levers and condition levers accordingly to get the performance required after disconnecting CTOT.

Austin made significant changes to the engine model in v11.  The Saab uses very complex, custom coded, engine logic.  With  1.5 we have made SOME adjustments to accommodate Austin's changes, but in order to take complete advantage of what Austin did and make the engines behave more accurately we would have needed to re-write our entire engine code.   We wanted to get v1.5 out within a reasonable time frame so the complete re-write of the engine will be done for v2.0. 

 

50 minutes ago, KMKaine said:

And one last question... I got a config warning when taking off, even tho I followed the checklist... Is there something sneaky I missed ;-)

Not sure what you may have done but I cannot recreate this.

Edited March 27, 2018 by JGregory

[Tassierob]

14 hours ago, KMKaine said:

 

And one last question... I got a config warning when taking off, even tho I followed the checklist... Is there something sneaky I missed ;-)

Cheers, and great plane and product.

Thanks again.

If you move the condition levers past their “Max” position to their very fwd position you will get an warning as you accelerate. 

That would be my guess. 

[daemotron]

On 27.3.2018 at 1:45 PM, KMKaine said:

As for power on takeoff, I set the CTOT to 100% or a bit above and used that. I then when climbing out disconnect the CTOT and the TRQ drops back to around 50 - 60. In the manual it says to keep it here but TRQ drops very slowly when climbing, is this normal?

Yes, absolutely. Torque indicated is actually a force measured at the propeller shaft, and it's mainly driven by the resistance the propeller experiences when its blades are moving through the surrounding air. With constant barometric pressure, this resistance is a function of the speed of the blades (which could be expressed in RPM) and their pitch angle. So while on ground, the same combination of pitch and power setting will always result in the same torque.

Now let's take off and start climbing - you keep power and pitch commanded the same way all the time, but what changes is the barometric pressure of the surrounding air: it gets "thinner", creating less drag on the propeller blades and thus resulting in a lower indicated torque (and also in a lower propulsion power of the engine, as the mass of the airflow becomes smaller). To counter this effect, you actually can adjust your power settings during climb (in some aircrafts you actually have to do this, but stay within the engine's operating limits!).

This is btw. also the reason why it's so important to disengage the CTOT system after take off: CTOT (constant torque on take-off) is a system that will adjust the commanded power to keep the preselected torque. If you keep it engaged during climb, it will command more and more power to compensate for the altitude-driven torque drop, until the engine catches fire or fails otherwise.

[KMKaine]

Thanks guys for taking the time to explain this stuff! Really interesting and now I understand how it works. Thanks again.