LEVEL command on Autopilot system

[Fabriz]

Goodmorning everyone.
I searched in the forum to see if someone has already formulated an instance on the skyview autopilot LEVEL command.
I live in Italy and the case I submitted did not only happen to me but also to another friend pilot.
Each time I press the LEVEL command, the plane seems to want to go into Hyperspace.
After 400 feet steep climb (despite setting VS to +110 ft per minute) it starts to level.
The aircraft's reaction is definitely brutish and unpleasant.
I believe in faith to my friend who says that after 400 ft begins to level up but I have, to date, always preferred to disable the AP in advance.
Has anyone experienced this situation?
Is anyone able to suggest what may be the cause?

 

[Raymo]

Have you tried re-calibrating the servos?

 

[Fabriz]

Have you tried re-calibrating the servos?

Thanks RayInGA for the suggestion.
It might be a way to reset some function that causes this behavior.
However, the autopilot today is pretty well regulated and manages correctly "trk & alt" and "hsi & alt", even in moderate disturbed air.
It changes the ALT to the value I impose and with the VS set by default (I hold it to the minimum +110 / -100) or with the one imposed by the knob from time to time
I will re-calibrate the servos, as you suggest, though, now that I remember, it was already done by the friend that has the same problem, but nothing has changed.

 

[Raymo]

The other thing to check is the shear pin in the servos.

Was it ever working correctly?

 

[Dynon]

Can you take a video of this behavior and send it to us at support at dynonavionics dot com?

 

[Fabriz]

Can you take a video of this behavior and send it to us at support at dynonavionics dot com?

I update the situation.
I calibrated the compass again - I do not know if it could be useful, but certainly does not cause any other problems - and verified the calibration parameters of the servos that, as I said, behave very well in their normal use in TRK and HSI mode.
Yesterday, pressing the LEVEL button continues to tilt suddenly, then level after 500 feet up, but it is not a definite and constant value.
Thank you for your interest and probably, towards the end of this week, I will have the opportunity to fly again and make a movie documenting the behavior. I would also like to do a low-speed test at a security level to see if pull up can also be dangerous, lowering speed beyond limits.

 

[led]

Hi Fabriz,

We look forward to seeing the video, but until then there here are some things to look for.

First of all, for any AP issue, verify that the servos are not indicating "SLIP".  If they are, that problem must be fixed before doing anything else.  Usually all you need to do is increase the torque.

It's important to understand what the LEVEL command is for: It quickly stabilizes an airplane that is out of control.  (If you just want to level off, use TRK+ALT or HSI+ALT to hold the current altitude.)

LEVEL gets the airplane right side up, *right now*.  This means that it simultaneously rolls the wings level and gets the attitude slightly nose up, after which it holds zero vertical speed.

While it does this it will obey the G-limiter and the airspeed restrictions you set, in that order.  It should have no difficultly staying above the minimum airspeed.

If the airplane is travelling at high speed, with the nose below the horizon (or the AHRS is mounted so that the nose is below the horizon at your test speed) this can result in a climb until the nose is above the horizon.

Also, if the airplane is above the maximum autopilot speed, pressing LEVEL will pull up until you are below that speed before trying to level off.

Things to look for:

• Pitch attitude before you press 'level'
• Airspeed before you press level, is it above the AP max speed?
• Pitch servo indicating SLIP at any time
  

I hope that's useful, and we look forward to your video.

--
Lawrence Doan
Aeronautical/Autopilot Engineer

 

[Fabriz]

Things to look for:

• Pitch attitude before you press 'level'
• Airspeed before you press level, is it above the AP max speed?
• Pitch servo indicating SLIP at any time
  

I hope that's useful, and we look forward to your video.

--
Lawrence Doan
Aeronautical/Autopilot Engineer

Thanks, Lawrence Doan. I sent a movie by mail at the addres you told me.
In the mail a reply to the things I have to look for as well as having attached the movie. In summary:

• I see from the movie that at the moment of activation the horizon is not perfectly leveled in the roll axis, but I did to observe the leveling effect on the roll. The variometer indicates a drop of 50 ft per minute right at the moment of activation, but the pitch axis is perfectly calibrated and neutral ;
• I still have to check it out, to be sure of my answer, but by memory and logic, I should have set it to a higher value, since the VNE is 260 kmh. I am sure that in other previous tests I performed at speeds below 200 kmh, but never at low speed.
  I want to reserve this last test to a greater degree of security in order to prevent the sudden climb of the plane from bringing me into stall in unusual trim.
  As you can see in the movee, the climb by the autopilot is quite steep, up to a 1600 ftm rate, even though G acceleration is not remarkable.
• The servos are not indicating "SLIP", neither before, nor during activation. The torque is set 100% in pitch and roll.

 

[led]

Hi Fabriz,

It doesn't look like your video made it here, can you re-send it?

I forgot to mention that if the Autopilot is above max speed it will say "ASPD HIGH" on the screen and in an audio annunciation.

--
Lawrence Doan
Aeronautical/Autopilot Engineer

 

[Fabriz]

I do not get those alarms and, I checked, the max speed is high ... I'll resend the mail with the movie
Thanks

 

[Fabriz]

Hi Lawrence
I sent the movie via email to the support ...

 

[Fabriz]

Thanks to Lawrence Doan, the problem is now fixed.

The support produced by the aircraft manufacturer to correct the ADAHRS inclination on the longitudinal axis was mounted in the opposite direction, generating a 15º error of its position.