16 Apr 2024, 16:55 [ UTC - 5; DST ]
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Post subject: KFC250 autopilot oscillating  Posted: 19 Oct 2017, 12:53 |
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Joined: 08/20/11
Posts: 314
Post Likes: +265
Location: Kennewick, WA
Aircraft: Piper Cheyenne I
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I have a KFC250 autopilot in my Cheyenne. Recently I have been seeing a pretty rapid roll oscillation that lasts about 12-14 seconds and then stops. This happens in perfectly smooth air and always in only cruise and descent. (Like it takes a while to start seeing it). Sometimes it will happen when I initiate a turn with the heading bug but not always. Yesterday on a 3 hour flight it must have happened 30-40 times. Nothing stops it from a button pushing standpoint unless I shut off the autopilot. I did have it happen once from a pitch standpoint with the same oscillation speed but only once about 8 months ago. This roll oscillation thing is getting much more frequent. My avionics shop is looking into it but he wasn't super confident that he knew what is going on. Anyone have any ideas that I could use to trouble shoot this further so i have better info for the avionics people? https://youtu.be/xssN6LsvEqM[youtube]https://youtu.be/xssN6LsvEqM[/youtube]
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Coop
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Post subject: Re: KFC250 autopilot oscillating Posted: 19 Oct 2017, 20:48 |
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Joined: 08/20/11
Posts: 314
Post Likes: +265
Location: Kennewick, WA
Aircraft: Piper Cheyenne I
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Username Protected wrote: If you put it in FD only mode, are the command bars cueing the roll? I will try it in FD mode only. It does not look like the FD bars move at all during these events.
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Post subject: Re: KFC250 autopilot oscillating Posted: 19 Oct 2017, 20:49 |
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Joined: 08/20/11
Posts: 314
Post Likes: +265
Location: Kennewick, WA
Aircraft: Piper Cheyenne I
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Username Protected wrote: Most likely the tach generator inside the roll servo. Good rule of thumb, any quick 1 second or less oscillations are because the tach gen is bad Thanks for the insight. I will pass that along to my avionics shop.
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Post subject: Re: KFC250 autopilot oscillating Posted: 21 Oct 2017, 02:54 |
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Joined: 02/10/12
Posts: 1321
Post Likes: +213
Location: Albuquerque,NM KAEG
Aircraft: 1991 AA F33A 550R
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Username Protected wrote: Most likely the tach generator inside the roll servo. Good rule of thumb, any quick 1 second or less oscillations are because the tach gen is bad +1
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Post subject: Re: KFC250 autopilot oscillating Posted: 25 Oct 2017, 01:07 |
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Joined: 02/10/12
Posts: 1321
Post Likes: +213
Location: Albuquerque,NM KAEG
Aircraft: 1991 AA F33A 550R
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Username Protected wrote: tach generator as they say. bh I just went through this. It's the tach generator. You can check cable tensions but experience tells me it's never that simple or cheap to fix. 
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