DFC90/DFC100 Digital Autopilot - DFC100 pre-flight test

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DFC100 pre-flight test

Printed From: Avidyne
Category: Avidyne General
Forum Name: DFC90/DFC100 Digital Autopilot
Forum Description: Topics on the Avidyne DFC Digital Autopilots
URL: https://avidynelive.com/forum_posts.asp?TID=157
Printed Date: 26 Mar 2026 at 11:48am
Software Version: Web Wiz Forums 12.07 - https://www.webwizforums.com

Topic: DFC100 pre-flight test

Posted By: rdawson
Subject: DFC100 pre-flight test
Date Posted: 17 Jul 2011 at 8:33am

When testing the autopilot prior to flight, I sync the heading bug, engage heading mode, and then move the heading bug. The yoke responds almost imperceptably - it moves but very slowly. Same is true both directions. This has been the case in all but one pre-flight test since the DFC100 was installed. (The VS test works as expected.)

During the pre-flight, the roll trim works normally from the manual trim control.

Of course, when at the avionics shop, it works normally - the yoke moves quickly in response to a heading bug change.

It finally occured to me (after leaving the avionics shop) that the tests at the avionics shop have been done on battery with the engine off and my pre-flights have been done with the engine running and alternator on. Every test I have done with the engine off works as expected.

The shop tells me that the roll trim cartridge is working normally. (Of course, that was observed with the engine off.)

The auto pilot flys just fine, so this may not be critical, but it is still of some concern.

Any ideas?

Replies:

Posted By: AviJake
Date Posted: 17 Jul 2011 at 9:41am

Hi Rick,

Just to be clear, the question is why you didn't see/feel the yoke responding in the roll axis during the one pre-flight where you had the engine running and alternator on, correct?

If so, no immediate explanation (or concern) jumps to mind.

I usually perform those pre-flight tests with the engine running myself and it has always been fine.

I'll spend some time early this week looking into your observation. It is possible that I may ask for a data download via the IFD USB port. If I do, it will be helpful to know what date (and even approximate time) you witnessed this.

More to come early this week but at this point, I'm not concerned about that observation.

Regards,

Steve

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Steve Jacobson
sjacobson@avidyne.com

Posted By: rdawson
Date Posted: 18 Jul 2011 at 5:16am

Not quite. Since the DFC100 was installed, the pre-flight test (engine running) has been what I consider normal (controls move at about the same rate as a manual roll trim) only once. On every other occasion (dozens) the controls move, but very slowly. The motion is almost imperceptable.

Posted By: AviJake
Date Posted: 18 Jul 2011 at 5:31am

Sorry for being dense but your concern is the slow, almost imperceptible motion during some of your preflights, right?

I'm used to very, very slow motion of the flight controls during pre-flight and consider that normal.

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Steve Jacobson
sjacobson@avidyne.com

Posted By: rdawson
Date Posted: 18 Jul 2011 at 5:34am

Right -- really slooooooooow

I'm glad to know that that is normal - Thanks.