Having spent some time with this aircraft, I am still battling an autopilot bug.

Has anyone else run into this?

When first engaging the autopilot, I get a runaway trim situation. The elevator trim starts running up at a rapid pace. After disengaging the autopilot and returning the trim to neutral, and engaging the autopilot a second time, I get a slower trim runaway situation. After doing this twice, I can engage the autopilot without the trim running away. After this, the autopilot seems to operate fine. So, for now, either I can engage/disengage the autopilot twice on the ground as part of the pre-flight checklist, or I can fight this in the air... Is there a better way?  😉

I have posted this behavior on the Justflight Forum, but have not yet received a reply.

Update:  I have now found that if I manually set Elevator Trim to zero before takeoff, I can avoid this behavior.  And the Rob Young flight model has a higher "elevator trim neutral" value which made it worse..

So resetting the line in the flight model cfg file to

elevator_trim_neutral = 3 ; 11

pretty much fixes it.

Edited April 21, 20233 yr by Bert Pieke

Are we talking about the Black Square analog version?

Are you trimmed before engaging the AP?  I

1 hour ago, ryanbatc said:

Are you trimmed before engaging the AP?  I

Good question.  Has now been almost 40 years, but recall the Bonanza (A36) was prone to porpoising if not fully trimmed out before engaging AP Alt hold. That in the late 1970s and early 1980s.  And certainly not unique in that respect.  That said, It has been about a year since I last flew the RY mod MSFS Bonanza and I do not recall any pronounced effect upon engaging. I logged about 200 hours over perhaps 150 flights specifically with the RY mod.  The Hjet captivated me since.

 

4 minutes ago, fppilot said:

That said, It has been about a year since I last flew the RY mod MSFS Bonanza and I do not recall any pronounced effect upon engaging.

The G36 autopilot resets the elevator trim when engaging.. the A36 autopilot appears not to..

So the Rob Young flight model cfg file needs a one line fix

elevator_trim_neutral = 3 ; 11

3 hours ago, Orlaam said:

Are we talking about the Black Square analog version?

Yes

3 hours ago, ryanbatc said:

Are you trimmed before engaging the AP? 

Yes

Edited April 21, 20233 yr by Bert Pieke

Same experience.  Thanks for the fix!

Bruce

9 hours ago, Bert Pieke said:

elevator_trim_neutral = 3 ; 11

Are you using a modified model in the BSQ?  

My cfg has 3 for the value.

9 hours ago, Bert Pieke said:

The G36 autopilot resets the elevator trim when engaging.. the A36 autopilot appears not to..

So the Rob Young flight model cfg file needs a one line fix

elevator_trim_neutral = 3 ; 11

Hi Bert,

Do you mean that my modded G36 needs this tweak or that the A36 by Just Flight needs it when using my flight model with it? As far as I remember the Turbo Bonanza was not ballooning when switching on the A/P from any attitude. But there is another general tweak that might help any aircraft that tends to suddenly alter pitch on engagement, and that is in the AUTOPILOT section of the systems.cfg file:

max_pitch_acceleration =  0.1

This should slow down abrupt pitch changes, but of course this also means when selecting an altitude and engaging climb mode, the nose will take a little longer to rise, so you may have to play with the value, anywhere between 0.1 and 1.0

1 hour ago, richbonneau said:

Are you using a modified model in the BSQ?  

My cfg has 3 for the value.

Great question.  I am getting quite confused here.  G36 (understand = MSFS); but then A36; Justflight; Black Square; Robert Young Turbo Mod...  

Rob, we are using your G36TN flight model to drive the Blacksquare A36TC. (With a little tweaking.) As you appreciate, we truly appreciate your work on building flight dynamic models.

Tip of my cap to you. And very best wishes personally.

3 hours ago, robert young said:

Hi Bert,

Do you mean that my modded G36 needs this tweak or that the A36 by Just Flight needs it when using my flight model with it? As far as I remember the Turbo Bonanza was not ballooning when switching on the A/P from any attitude. But there is another general tweak that might help any aircraft that tends to suddenly alter pitch on engagement, and that is in the AUTOPILOT section of the systems.cfg file:

max_pitch_acceleration =  0.1

This should slow down abrupt pitch changes, but of course this also means when selecting an altitude and engaging climb mode, the nose will take a little longer to rise, so you may have to play with the value, anywhere between 0.1 and 1.0

Only the A36 with your flight model.. the G36 is fine.

3 hours ago, richbonneau said:

Are you using a modified model in the BSQ?  

My cfg has 3 for the value.

Affirmative.   3 is fine.