AP 74 in Esqual VM1

[coopjim]

I had a local avionics tech install the AP 74 (with new servos for pitch and roll and the interface module) in my 2005 VM1 and we've been test flying it. It's connected to a Dynon remanufactured D10A. The heading hold works just fine but the Altitude hold is not holding present or selected altitude. I'm able to toggle thru the Heading, Alt and Baro settings and adjust the heading bug which is followed well and it couples to the Garmin 796 GPS just fine. I can adjust the Barometer setting which seems to be off in the D10A Efis and I can select/adjust altitude but no matter which altitude I select, the AP74 is not capturing or climbing/descending to that altitude.
I'm looking for suggestions please.
Thanks
Jim Coop Indianapolis

 

[led]

Hi Jim,

The first thing to verify is that the pitch servo is engaging and not slipping,

- Verify ALT is illuminated on the AP74 and on the EFIS screen.  (The autopilot is actually in the EFIS; so it's the primary thing to check.)
- Verify in the servo test menu (on the ground) that all controls move the correct directions
- Verify in flight that the ALT indication is not turning yellow.  If it is, that indicates a slipping servo.  Turn the torque up.

Also, make sure you're got the vertical speed set to a value you want the plane to use when climing and descending.

Have a look at the AP turning guide - it's aimed at Skyview, but most of it applies to the D10A, especially the troubleshooting.

In particular, look at the Altitude Hold and Capture procedure.  You can't do the IAS procedure, but you can get a similar result by asking the AP to climb at a fixed power setting and tuning for a smooth transistion to vertical speed.

http://www.dynonavionics.com/downloads/Install_Guides/SkyView_Autopilot_In-Flight_Tuning_Guide-Rev_A.pdf

Hope that helps!

 

[coopjim]

Thanks for the ideas and the link to the tuning guide. We will have a look. I can tell you that the lights are on in both the AP74 panel and the EFIS. No Yellow lights. I'm not sure what vertical speed is set for climb or decending. This plane had a simple Tru Trak installed when I bought it and the tech left it installed as a turn coordinator. I don't know how it's wired with the Dynon but I am suspicious that the old TT is part of the problem. It was a heading only AP and never worked for me.
I'll let you know.

 

[coopjim]

Looks like the aluminum rod (as supplied in the kit) that connects the pitch servo to the elevator control has stripped threads. Since this is a new installation, we're replacing the aluminum rod with a custom made steel threaded rod. Expect to test it tomorrow.
Does that sound like the right thing to do Lawrence?

 

[led]

Hi Jim,

As long as you're satisfied that the rod is strong enough, won't bind or jam etc; I leave that to you and your mechanic.

We would like to see the rod that stripped though; please get in touch with our support folks:
support@dynonavionics.com

 

[coopjim]

I'm happy to arrange to return the pitch control rod to you or send you pictures. Meantime we're experiencing an intermittent problem with the AP74 panel. It won't always engage when the AP button is pushed. If we turn off the Alt and push the AP button it will track heading but when we turn on ALT it wants the aircraft to descend rapidly regardless of the altitude set in the EFIS alt bug. What's going on?

 

[Dynon]

So first of all, know that the AP74 is just a set of buttons/knobs/lights, and doesn't command/control the servos. So first off: is the ALT light on the AP74 lighting up / are you seeing the ALT mode engage on the AP status area of the EFIS? A picture of both the AP74 and the display when the aircraft is in this odd state may help a lot. What are your pitch servo settings? If you can get a picture, you should email that, a link to this thread, and a list of your pitch axis settings to support at dynonavionics dot com for further support (we can track issues easier via email).