D100/AP74 problems

[Rivieraaero]

Hi everyone,
I’m not sure if this is the right place to try solve this problem as I’ve sent 3 messages to tech support without any reply.
I have a 2007 P92 Tecnam with a D100 coupled to a AP 74 which has not had any updates due to it working perfectly up until now.
Problem, I’ll trim the aircraft to fly straight and level, engage the autopilot, set it to Nav and Alt Hold, it will track a straight line but will not hold altitude, the trim warning comes on saying trim up and it goes into a steady gentle climb, even if I dial up a lower altitude and trim down it just keeps climbing.
It behaves the same if I use Track and Alt.
This is a hire aircraft and it is possible that someone has had a fiddle in the AP setup menu.
Does anyone know how to fix this problem ?
Cheers Martin

 

[Raymo]

Martin,

Check to see if your pitch servo shear pin has broken. If it has, the AP will not be able to properly control your altitude.

 

[djones]

Hi everyone,
I’m not sure if this is the right place to try solve this problem as I’ve sent 3 messages to tech support without any reply.
I have a 2007 P92 Tecnam with a D100 coupled to a AP 74 which has not had any updates due to it working perfectly up until now.
Problem, I’ll trim the aircraft to fly straight and level, engage the autopilot, set it to Nav and Alt Hold, it will track a straight line but will not hold altitude, the trim warning comes on saying trim up and it goes into a steady gentle climb, even if I dial up a lower altitude and trim down it just keeps climbing.
It behaves the same if I use Track and Alt.
This is a hire aircraft and it is possible that someone has had a fiddle in the AP setup menu.
Does anyone know how to fix this problem ?
Cheers Martin

Martin,
I apologize for not getting back sooner, I haven't found the messages you refer too, perhaps they are hung up in cyberspace.  The fastest way to get a replacement shear screw (which definitely sounds like it could be the problem) is by going to dynonavionics.com/shearscrew 
Fill out the form and we will ship you a replacement asap.
If you would like to do further diagnostics give me a call at 425-402-0433 and I would be happy to talk you through it.

 

[Rivieraaero]

Hi Don, thanks for the quick reply.
I don’t think that it is the shear pin as when I’m flying the servo appears to be engaging and I can feel the resistance on the controls and I can feel when the servo clutch suddenly release when I apply a small amount of force and I can also feel the difference in the clutch slippage when I adjust the torque settings from 0 to 100
At the moment I’m in the aircraft, stationary on the ground, when I turn on the autopilot, the trim indicator shows it needs up trim and the control stick is moving to full back elevator , even if I dial the AP altitude to a lower altitude it’s still shows it needs up trim and the servo is moving the elevator to full back stick.
Hope this observation helps
Martin.

 

[djones]

Hi Don, thanks for the quick reply.
I don’t think that it is the shear pin as when I’m flying the servo appears to be engaging and I can feel the resistance on the controls and I can feel when the servo clutch suddenly release when I apply a small amount of force and I can also feel the difference in the clutch slippage when I adjust the torque settings from 0 to 100
At the moment I’m in the aircraft, stationary on the ground, when I turn on the autopilot,  the trim indicator shows it needs up trim and the control stick is moving to full back elevator , even if I dial the AP altitude to a lower altitude it’s still shows it needs up trim and the servo is moving the elevator to full back stick.
Hope this observation helps
Martin.

Martin,
I would suggest you give us a call when you are at the airplane and let us talk you through a couple of things. Call me at 425-402-0433

 

[DBRV10]

Do a AP calibration just in case someone has filed with it.

You can have a broken screw and it still grips enough to give you a feeling of it not being broken.

 

[Rivieraaero]

I have done the calibration a couple of times and pulled the servo arm off checking the shearscrew, all appears ok.
I’m thinking it might be a software problem