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Thread: [BAC-Mail] Autopilot Question

  1. #1

    [BAC-Mail] Autopilot Question

    Sounds like it could be related to the speed of the
    computer that is doing the processing (the stech
    autopilot). I remember some other comments that this
    is a normal thing (I just can't remember if this is
    normal for just this autopilot, or most that you would
    find in our airplanes).

    Jay

    --- Rich Dahab <rich@dahab.com> wrote:

    > I do not know the STEC 50 unit, but what you are
    > describing is called
    > hunting. It comes from overshooting the heading and
    > oscillating backand
    > forth. A lot of units do it as they pass over an
    > OMNI. It might be
    > adjustable. Usually it is due to the unit putting
    > in too big a correction
    > relative to the error or deflection. That is, if
    > you need a 5degree aileron
    > deflection you are putting in 7 degrees. That puts
    > you on the other side
    > and then you put in too much in the other direction.
    > Or it could be from
    > slow response in taking out the deflection. Either
    > way, I would contact the
    > company directly and get their advise.
    >
    > Rich Dahab
    > A23-24
    > N9119T
    >
    >
    > ----- Original Message -----
    > From: "Mark L Stuckey" <mlstuckey1968@yahoo.com>
    > To: <musketeermail@yahoogroups.com>;
    > <bac-mail@beechaeroclub.org>
    > Sent: Tuesday, November 22, 2005 5:14 PM
    > Subject: [musketeermail] Autopilot Question
    >
    >
    > > Have a 1978 Sierra with an STEC 50 autopilot and a
    > > Garmin 430. When I put the autopilot on heading
    > mode,
    > > she will rock back and forth like we are on the
    > ocean.
    > > If I set the heading bug to 270, then she will go
    > > from 260 to 280 and back again. It is usually
    > pretty
    > > gentle, but sometimes not - and after a while, it
    > gets
    > > annoying. When I have the autopilot on Nav mode,
    > she
    > > rarely has the same problem. My avionics person
    > > cleaned out the autopilot gyros and put it back
    > > together, but it still does the same thing. Any
    > > thoughts?
    > >
    > > Mark Stuckey
    > > N5428M
    > > Macon, Georgia
    > >
    > >
    > > ------------------------ Yahoo! Groups Sponsor
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    > > Join BAC today and be a part of the ONLY Type Club
    > for the Musketeer
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    > > Yahoo! Groups Links
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    > >
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    > >
    > >
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    > >
    > >
    > >
    >
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  2. #2

    [BAC-Mail] Autopilot Question

    Two thoughts:

    If you have the option of a manual sensitivity setting, use the precision
    approach mode. On the 430, scroll to the setup page for CDI, etc. Select
    Manual for range sensitivity (rather than Auto), and select 0.3 (rather than
    5) for the manual range value. Then, if your coupler has a Localizer
    position, use that position rather than Nav or Omni, when you are enroute.
    See how this works out for you, when coupled to the 430 in GPS mode. My
    Century IIB will hunt a bit if set up conventionally (Omni on the coupler
    and Auto/5 miles/enroute in the 430). But if set up as I described, it is
    rock-solid on course; probably within 20-30 feet either side of the
    centerline, with no hunting or wander. The Auto and the 5-mile (enroute
    sensitivity) setting is what the 430 will select for itself, if you don't do
    the Manual over-ride. And despite the over-ride, the 430 will still
    auto-range as you close in on the waypoint. For example, as you pass under
    30 miles out, it will auto-range from 0.3 (where you manually set it), up to
    1.0 (which is its auto-select for Terminal operations). When on a precision
    approach it will auto-range back down to the 0.3 mile setting. Oddly enough,
    once you have been in cruise on the manual 0.3 setting, with the autopilot
    tracking 100% solid, when it auto-switches to the 1.0 range you probably
    won't see any adverse effect on tracking.

    If it persists, I would strongly suspect the roll servo. When it builds up
    brush resistance at the commutator, it requires more and more of a signal
    before it will "break out" and move. Then it goes too far, and the same
    thing happens in the other direction. It requires a servo overhaul to fix
    it. You can search BAC on 'autopilot' for much more info on this.


    -----Original Message-----
    From: bac-mail-bounces@beechaeroclub.org
    [mailto:bac-mail-bounces@beechaeroclub.org] On Behalf Of Rich Dahab
    Sent: Tuesday, November 22, 2005 6:07 PM
    To: musketeermail@yahoogroups.com; bac-mail@beechaeroclub.org; Mark L
    Stuckey
    Subject: [BAC-Mail] Re: [musketeermail] Autopilot Question

    I do not know the STEC 50 unit, but what you are describing is called
    hunting. It comes from overshooting the heading and oscillating backand
    forth. A lot of units do it as they pass over an OMNI. It might be
    adjustable. Usually it is due to the unit putting in too big a correction
    relative to the error or deflection. That is, if you need a 5degree aileron

    deflection you are putting in 7 degrees. That puts you on the other side
    and then you put in too much in the other direction. Or it could be from
    slow response in taking out the deflection. Either way, I would contact the

    company directly and get their advise.

    Rich Dahab
    A23-24
    N9119T


    ----- Original Message -----
    From: "Mark L Stuckey" <mlstuckey1968@yahoo.com>
    To: <musketeermail@yahoogroups.com>; <bac-mail@beechaeroclub.org>
    Sent: Tuesday, November 22, 2005 5:14 PM
    Subject: [musketeermail] Autopilot Question


    > Have a 1978 Sierra with an STEC 50 autopilot and a
    > Garmin 430. When I put the autopilot on heading mode,
    > she will rock back and forth like we are on the ocean.
    > If I set the heading bug to 270, then she will go
    > from 260 to 280 and back again. It is usually pretty
    > gentle, but sometimes not - and after a while, it gets
    > annoying. When I have the autopilot on Nav mode, she
    > rarely has the same problem. My avionics person
    > cleaned out the autopilot gyros and put it back
    > together, but it still does the same thing. Any
    > thoughts?
    >
    > Mark Stuckey
    > N5428M
    > Macon, Georgia
    >
    >
    >
    > Join BAC today and be a part of the ONLY Type Club for the Musketeer
    > series!
    >
    > www.beechaeroclub.org
    >
    >
    > Yahoo! Groups Links
    >
    >
    >
    >
    >
    >
    >
    >

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