Tapered rod tailspring question

Discussion in 'Pitts Model 12' started by lakeracer69, Nov 21, 2017.

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  1. Nov 21, 2017 #1

    lakeracer69

    lakeracer69

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    I am wondering what kind of "fit" is acceptable for the tapered rod tailspring/ fuselage socket tube connection?

    I want to use the same type of system for my build. Say if the tapered rod tailspring is .875 where it slides into the tube, and the tube is .885 I.D. Would the .005 per side all around be too loose? I ask because I bought a piece of 1.000 4130 tube with an .063 wall hoping I would have to ream it after welding. The tubing I got was more like .058 wall nominal thickness.

    I'm also looking for a couple of pics where people drilled the parts for attachment. One bolt, two bolts, holes drilled 90 degrees apart, etc?
     
  2. Nov 21, 2017 #2

    PittsDriver68

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    I believe that there is an old thread here somewhere that shows via CAD simulation that you want to drill your holes horizontally. The highest stress is on the top and bottom of the rod and drilling vertical holes results in fatigue cracking and eventual failure.

    The search function might dig up that thread.

    Best of luck,

    Wes
     
  3. Nov 21, 2017 #3

    ioneater

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    lakeracer69 likes this.
  4. Nov 21, 2017 #4

    lakeracer69

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    Thanks Greg, that helps a lot.

    Still looking for some accurate "fit" numbers of the tubing "socket" and rod/spring.
     
  5. Nov 21, 2017 #5

    planebuilder

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    Lakeracer69, are you certain they shipped you the correct tube? I have never found .063 wall tube to allow the next smaller size to fit inside without reaming? Sounds like they sent you .058 by mistake.
     
  6. Nov 21, 2017 #6

    smizo

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  7. Nov 21, 2017 #7

    lakeracer69

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    This is what I am thinking. I got it two weeks ago from ACS. No markings on the tube and I just got around to measuring it last night. Arrrgggggg!
     
  8. Nov 21, 2017 #8

    lakeracer69

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    Thanks Chris
     
  9. Nov 21, 2017 #9

    cwilliamrose

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    Mine is just barely a slip fit. No hammer required but twisting back and forth as you push it into the tube works well. You can see evidence for that same type of fit in the Kimball document.

    I wish I could remember what size tube I used and all the steps involved, it has been too long ago but I'm certain it was reamed after welding. I have a single 3/8" bolt and the spring has a double flat machined on the end with a 3/8" vertical hole. The flats take the torsional loads and the bolt only holds the spring in place and clamps the flats tightly with matching features in the socket tube.

    Tailwheel Mount X-section.jpg

    Tailwheel Mount0.jpg

    Tailwheel Mount Assy.jpg
     
    Last edited: Nov 21, 2017
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  10. Nov 21, 2017 #10

    jrs14855

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    The Haigh tailspring used on many aircraft did not use a socket. Flats on the forward end and a short adapter at the tailpost to bolt to the standard Pitts tailpost fitting. There were some problems with bending the forward attach bolt. I solved that on new construction by welding a 1/2" x .058 bushing into the square tube. I think I also used a custom washer to allow the tailspring flat to fit tight against the square tube. This setup allows reverting back to a flat tailspring if you break a tailspring in East Bum----. From the pictures Raven appears near identical to Haigh.
    On the Wittman Tailwind the forward bolt is vertical, spring diameter 3/4". No problems despite a lot more weight on tail than S1S.
    I use .058 wall socket tube. By the time you are done welding it will require honing to get the spring to fit. Long slotted tube with some strips of course emery wrapped around the slot.
     

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