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Thread: J-3 Airspeed Indicator Mounting....

  1. #1

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    J-3 Airspeed Indicator Mounting....

    Hi All,

    Just purchased my first tail wheel airplane, a 1946 J-3 with C85 engine! The airspeed indicator is loose in the panel, and seems to be missing two screws. Does anyone know the correct length spring clip nut that fits the J-3 airspeed indicator?

    Thanks,

    John

  2. #2
    wireweinie's Avatar
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    I am assuming that you mean the 'grasshopper' nut for the mounting screw. There are several sizes so you'll need to look inside the hole for one of the mount screws. Facing the back of the indicator, measure from the surface of the mounting ear, down to the groove inside the hole. That length is what dictates the size of the grasshopper. It's also a good idea, after installing them, to loosely tie them in the hole with lacing string. Keeps them from falling out when you install the screws.

    Web
    Life's tough . . . wear a cup.

  3. #3

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    Quote Originally Posted by wireweinie View Post
    I am assuming that you mean the 'grasshopper' nut for the mounting screw. There are several sizes so you'll need to look inside the hole for one of the mount screws. Facing the back of the indicator, measure from the surface of the mounting ear, down to the groove inside the hole. That length is what dictates the size of the grasshopper. It's also a good idea, after installing them, to loosely tie them in the hole with lacing string. Keeps them from falling out when you install the screws.

    Web
    Hi Web,

    Yes, that is the type of instrument nut I'm referring to! I'm putting together a Spruce order today, and was hoping to avoid a trip to the hangar to actually measure the thickness of the ASI mounting ear! On the other hand, any trip to the hangar is not such a bad thing!

    John

  4. #4

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    Missing two screws? You mean there are two screws holding it, right? Somebody was "keeping it light". That big heavy tach and temp/press gauge came from the factory with only two screws.

    I too prefer the grasshopper nuts, but piper just used 6-32 brass.

  5. #5
    Gordon Misch's Avatar
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    What the heck is a grasshopper nut?
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

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    Turn one upside down, and with a magnifying glass look carefully. Easier if you find one that mama bit the head off of . . .

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    hotrod180's Avatar
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    Cessna Skywagon-- accept no substitute!

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    I had to look it up. That little nut with the leg/hook things that stick in the hole and hold the nut on instrument screws. Google is your friend.
    DENNY

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    Gordon Misch's Avatar
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    Thanks guys!
    Gordon

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    PerryB's Avatar
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    Quote Originally Posted by bob turner View Post
    Turn one upside down, and with a magnifying glass look carefully. Easier if you find one that mama bit the head off of . . .
    I was late to the game. Could'a had some fun with this one.
    After Monday and Tuesday, even the calendar says WTF !

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    I suck as a comedian. Funniest thread I ever saw was here, discussing throttle balls on a PA-11.

    Am I all wet, or should the OP be happy with two screws holding that presumably plastic case airspeed indicator? My Decathlon does have a couple instruments held with four screws, but they are the ones that have braces at the other end - KI-208, I think, and a pair of vacuum gyros. Am I in trouble with the Feds if I only have two screws on the manifold pressure gauge?

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    wireweinie's Avatar
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    Most instruments are designed to be held in with either three or four screws. I'd always recommend keeping all the screws in place. ezflyr's first post said the instrument is already loose. If it's down to one screw and you lose that, the instrument is just going to be flopping around behind the panel. Don't think the feds will care until it becomes a safety of flight issue.

    Web
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    Hi All,

    As a follow-up, I went to the hangar this morning to determine the proper size for the 'grasshopper' nuts required to secure my ASI. Only the two right side screws were in place, so the instrument was loose in the panel. Anyway, the correct size is 0.375", so I've added those to a Spruce order!

    OK, now I'm not saying the previous owner was half-a$$ed, but I found that the clear plastic tubing from the pitot tube was connected to the ASI with a combination of electrical tape and a ty-wrap.... The ASI has a short piece of copper tubing connected to the input port with an approximately 0.18" OD. The clear plastic tubing has an approximately 0.25" ID, so the copper tube was wrapped with tape to expand the diameter, and the tubing was then held in place with a ty-wrap...... So, what are the proper fittings to make this connection??

    John

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    cubdriver2's Avatar
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    Quote Originally Posted by ezflyr View Post
    Hi All,

    As a follow-up, I went to the hangar this morning to determine the proper size for the 'grasshopper' nuts required to secure my ASI. Only the two right side screws were in place, so the instrument was loose in the panel. Anyway, the correct size is 0.375", so I've added those to a Spruce order!

    OK, now I'm not saying the previous owner was half-a$$ed, but I found that the clear plastic tubing from the pitot tube was connected to the ASI with a combination of electrical tape and a ty-wrap.... The ASI has a short piece of copper tubing connected to the input port with an approximately 0.18" OD. The clear plastic tubing has an approximately 0.25" ID, so the copper tube was wrapped with tape to expand the diameter, and the tubing was then held in place with a ty-wrap...... So, what are the proper fittings to make this connection??

    John
    Go to Ace Hwd and get a nylon fitting with the correct thread and barb size.

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  15. #15
    wireweinie's Avatar
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    Lol! Everyone reading this is laughing and remembering the times we dealt with similar fixes.

    Originally, that copper tube was connected to an aluminum tube with a short piece of rubber hose. The aluminum tube was the conduit to the pitot tube. Sounds like someone replaced the aluminum tube with 'something else'. Is this tubing completely clear or is it whitish in color? If it is clear, I'm not sure what you have but I'd consider replacing it with something else. If it is whitish colored and 1/4" on the O.D., the most secure way to fix this is to go back to the Spruce catalog and get the proper fittings needed for Nylo-flo or Poly-flo tube. But don't over tighten them when you install them.

    All things being equal, I feel that the original aluminum tube is a better set up. But a pain to install if not done during rebuild. Even better if you use AN fittings all the way through. More leak free than rubber or nylon and takes up less room than nylon tube.

    Web
    Life's tough . . . wear a cup.

  16. #16
    cubdriver2's Avatar
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    I think the last 4 planes that I owned had vinyl tubing behind the panel. Barbed nylon fitting. But I've flown a few of these and they work the best



    Glenn

    PS. Just put 2 screws in diagonally and don't worry about the extra weight.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  17. #17

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    First, if you only have two screws, it should be obvious that they must be diagonal. Second, and more important, get a good instructor in the front seat, and have him/her teach you to fly safely without that indicator.

    The original was as described above - no clamps or tape, just copper line and vacuum hose from the Lock Haven Plymouth parts dept. Most now use fish tank hose.

    But just when you think you need it most, the entire system will fail. I broke a rod a while back, and the first thing that happened was the windshield got covered with oil. The second thing, of course, was the airspeed indicator failed. Even then, the two screws did not fail. I think the same screws hold it today! It was the rubber tube in the wing root that failed.

    Make sure the important things are not compromised - check your clevis bolts, particularly the rudder bolts. Check the cables, pulleys, and turnbuckles. Once all that is ship-shape, go back and fill in as many holes as you like with brass 6-32 screws.

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