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Thread: Wooden prop placement when parked.

  1. #1

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    Wooden prop placement when parked.

    I had heard somewhere along the line that when parked, a wooden prop should be placed horizontal to the ground; I vaguely remember it had something to do with moisture.

    The Champ I fly has a wooden prop, and as I did the post flight I turned it (after triple checking the mags!) to be that way and got a lot of looks like I had a third eye in the middle of my forehead.

    Is this one of those Old Pilot Tales, or was I correct?
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  2. #2

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    This is a good habit to get into. It most likely doesn't do much for a short duration, but, if the prop is left near vertical for months at a time, mosture could settle in the low end cause an out of balance. Pete

  3. #3

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    Well , Sensenich Doc # W69EK7-CF Rev F says
    "Place the propeller in a horizontal position when parked. This will keep the moisture in both blades evenly distributed."

    AC 20-37E says-
    "Leave two-bladed metal propellers in the one o’clock position to minimize bird droppings and water being retained in the spinner. Wood propellers should be stored horizontal to prevent moisture accumulation in one blade, which would cause unbalance."

    Might be a old pilots tale, but looks like its a "official" old pilots tale.

  4. #4
    rosiejerryrosie's Avatar
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    One other point I've been taught - when moving the prop to position it horizontally, turn it backwards (counter to its normal rotation) to further minimize the possibility of an unintended start. (I wish my engine started that easily
    Cheers,
    Jerry

    NC22375
    65LA out of 07N Pennsylvania

  5. #5

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    Wood props should be left in the horizontal position when parked so that moisture won't settle in one blade. actually, it would nice if we could get enough rain for any moisture to settle anywhere!

  6. #6

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    Every one realizes that the holes in the end of each blade is for allowing water to escape, few realize that they work in reverse also. put the blades horizontally when parked for a day or more.

    OK we know water makes a wooden prop un-balanced, what do we do about that? You know it has sat 2 weeks vertical in the rain. Oh My Goodness What now?

  7. #7
    Mike Busch's Avatar
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    Quote Originally Posted by rosiejerryrosie View Post
    ...when moving the prop to position it horizontally, turn it backwards (counter to its normal rotation) to further minimize the possibility of an unintended start.
    This has some validity on engines that use impulse coupling magnetos, not on engines that use shower-of-sparks (retard breaker) magnetos.

    The downside is that if the engine has a dry vacuum pump installed, rotating the prop backwards can theoretically hasten vacuum pump failure (although in my experience the risk is low).

    My rule is never to rotate the prop unless the ignition keys are in your pocket or clearly visible on the glareshield. (Works for most singles that have a key-operated mag switch, doesn't work for twins that use toggle switches.)
    Michael D. Busch A&P/IA CFIA/I/ME
    President, Savvy Aviator, Inc.
    President, Savvy Aircraft Maintenance Management, Inc.
    2008 National Aviation Maintenance Technician of the Year

  8. #8

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    When a vac pump is operating, the angle that the carbon vanes are set into the rotor and centrifugal forces causes the vanes to make a better contact with the walls of the pump. when a vac pump is rotated backwards at the speeds we turn the prop, there is no centrifugal force, so friction on the walls of the pump cause the vanes to be pushed back into the slot they ride in, and away from the pump walls.

    If a pump fails when turned backwards, the vanes were so short they cocked in the slot they ride in. IOWs it was worn out to start with.

    P1010009.JPGP1010010.JPGP1010011.JPG



  9. #9
    rosiejerryrosie's Avatar
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    Quote Originally Posted by Mike Busch View Post

    My rule is never to rotate the prop unless the ignition keys are in your pocket or clearly visible on the glareshield. (Works for most singles that have a key-operated mag switch, doesn't work for twins that use toggle switches.)
    And that's not 'fail safe' either. I've had an engine start with the keys in my pocket. (The mechanic improperly installed the "P" lead.) And one could break or come loose also. Best bet is to treat all props as "live" just as we treat all guns as loaded.
    Cheers,
    Jerry

    NC22375
    65LA out of 07N Pennsylvania

  10. #10
    Mike Busch's Avatar
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    Tom, those lovely photos look like a Sigma-Tek metal-hub vacuum pump which uses non-canted vanes and is bidirectional. Most pumps (Airborne, Rapco, Tempest) use a graphite hub with canted vanes and are designed to turn in only one direction (e.g., 211CCW or 212CW). I've actually never seen a Sigma-Tek pump disassembled before, that metal hub and big ball bearing are impressive. No wonder they cost more. --Mike
    Michael D. Busch A&P/IA CFIA/I/ME
    President, Savvy Aviator, Inc.
    President, Savvy Aircraft Maintenance Management, Inc.
    2008 National Aviation Maintenance Technician of the Year

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