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Thread: Dive! Dive! Dive!

  1. #1
    Guest
    Guest

    Dive! Dive! Dive!

    My 1983 Sundowner has a small, but annoying problem. I had a major panel update done last summer. Before it was done, I noticed that when in cruise with the STEC 50 autopilot on and in ALT mode, when I transmitted over the old Collins COMM 2, the aircraft would pitch down strongly. I could hold it level with back pressure if I anticipated the sudden dive, but with a few wobbles.

    After the upgrade, I experience the same thing, only it has switched to COMM 1 (a GNS430W), which of course I use much more. It only happens with the A/P on and engaged in altitude hold mode, regardless of which NAV source it is using.

    Clearly there is some form of electrical coupling between (probably) the PTT switch on the left side yoke and the STEC that only happen with one of the two radios. I don't think the same thing happens using the PTT on the co-pilot side yoke, but I am not sure.

    I don't see how the a/p ALT hold can be coupled to the COMM 1 transmit circuit, but perhaps someone on this group does.....

    One further clue is that I have never seen it pitch up, so I am wondering if it could be a spurious signal to the elevator servos, but then I would expect it to happen with either radio, not just #1.

    Baffled in TX - Paul
    (N6349C)



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  2. #2
    Guest
    Guest

    Dive! Dive! Dive!

    I suspect you might have two comm antennas. It that is the case, one may
    be installed in a fashion in which the STEC is susceptible to RF from the
    offending antenna. The offending antenna itself may have installation
    issues as well.









    From: musketeermail@yahoogroups.com [mailto:musketeermail@yahoogroups.com]
    On Behalf Of Paul
    Sent: Thursday, May 07, 2009 8:22 AM
    To: musketeermail@yahoogroups.com
    Subject: [musketeermail] Dive! Dive! Dive!








    My 1983 Sundowner has a small, but annoying problem. I had a major panel
    update done last summer. Before it was done, I noticed that when in cruise
    with the STEC 50 autopilot on and in ALT mode, when I transmitted over the
    old Collins COMM 2, the aircraft would pitch down strongly. I could hold it
    level with back pressure if I anticipated the sudden dive, but with a few
    wobbles.

    After the upgrade, I experience the same thing, only it has switched to COMM
    1 (a GNS430W), which of course I use much more. It only happens with the A/P
    on and engaged in altitude hold mode, regardless of which NAV source it is
    using.

    Clearly there is some form of electrical coupling between (probably) the PTT
    switch on the left side yoke and the STEC that only happen with one of the
    two radios. I don't think the same thing happens using the PTT on the
    co-pilot side yoke, but I am not sure.

    I don't see how the a/p ALT hold can be coupled to the COMM 1 transmit
    circuit, but perhaps someone on this group does.....

    One further clue is that I have never seen it pitch up, so I am wondering if
    it could be a spurious signal to the elevator servos, but then I would
    expect it to happen with either radio, not just #1.

    Baffled in TX - Paul
    (N6349C)





    [Non-text portions of this message have been removed]



    ------------------------------------

    Join BAC today and be a part of the ONLY Type Club for the Musketeer series!

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    <*> To change settings online go to:
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    (Yahoo! ID required)

    <*> To change settings via email:
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    <*> To unsubscribe from this group, send an email to:
    musketeermail-unsubscribe@yahoogroups.com

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    -----------------------------------------
    This message was automatically imported from BAC-Mail or the Musketeer Mail list. Replies might not be seen by the original author.

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