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Shock Struts

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  • Shock Struts

    Mark Goldberg says something like "Perfection is the enemy of Completion."

    I have assembled my shock struts, and filled them with fluid. I found some advice on the web that suggested and "Improvement" by installing and sealing a plug (a 1/2" 20 tpi allen head set screw) deep into the Shock Strut Rod before installing the Rod End Bearing. I may be guilty of jumping on any "improvement" that gets suggested. The plug is in place right now with out any sealant and is easily removed. When the strut is layed down horizontally, some leakage occurs over time as I would expect. I expect the same thing to happen after the Rod End is installed.

    But why do I need to worry about sealing this end? After installation the Rod End threads will almost be the high point. The fluid is rarely under pressure, and I don't see it leaking out. So, now question the need for concern about sealing these threads tight. I see some have used EZ Turn in the past...fair enough. The amount of time that the fluid will be under pressure before reaching equilibrium with the spring is a fraction of a second I would guess. Seems like a pretty fool proof design the more I think about it.

    But I want you who are operating this installation to verify this for me. I filled the strut by removing the filler port on the side of the strut cylinder, then poured fluid into the 3/4" tubing until it ran out the filler port which results I think in about 1/2" of air in the top of the strut. As long as the Patrol stays right side up, I can't see where this design is going to be prone to leaking fluid out these threads.

    Am I missing something?
    Screen Shot 2017-04-13 at 5.33.08 PM.png
    Brooks Cone
    Kit Building Patrol #303
    Last edited by Bcone1381; 04-13-2017, 04:50 PM.
    Brooks Cone
    Southeast Michigan
    Patrol #303, Kit build

  • #2
    After I assembled my struts I filled them and stood them out of the way for a few months while the fuselage wasn't on the gear. No sealant on the rod end bearing and there was always just a little fluid on the top of the strut, in the recess around the big C-clip. I would wipe it off and the next week there would be a little fluid again. I got tired of that and put sealant on the rod end. No more leak.
    Rollie VanDorn
    Findlay, OH
    Patrol Quick Build


    • #3
      You can also fill the shock strut that last little bit by unscrewing the rod end bearing and pouring ATF into the piston tube. Mark


      • #4
        Thanks Rollie and Mark. I will be following your advice and example...and will wait until final assembly to adjust and then properly seal the Rod End Bearing. Up to yesterday I wondered if the were ever prone to leaks, and thought about mitigation strategies......

        But, specifically to help confirm my understanding of the wisdom behind Bob's Shock Strut design, I will make a claim that I would like challenged. My claim is: If Rollie had not sealed his threaded Rod End his Shock Struts would have stopped leaking once it was moved from sitting on the workbench to being properly serviced and installed. This is because there is typically no fluid under pressure in the strut and the threaded rod end is at the highest point when moved from the workbench to being installed.

        Shoot away!
        Brooks Cone
        Southeast Michigan
        Patrol #303, Kit build


        • Mark Goldberg
          Mark Goldberg commented
          Editing a comment
          Bob advises putting thread sealant on the 1/8 NPT filler port and also on the rod end bearings threads. Mark

      • #5
        I am trying to locate the slots for the shock struts, and want to adjust the struts accordingly. The fuse in on a rotisserie so the gear is unloaded. Page 28B of the plans call out a length of the strut as "Length to fit with strut extended 1.38 for spring preload". I have no idea what that means.

        I know the final setting depends on the max gear spread. Is there a general starting point for the adjusted length of the strut?


        • Bcone1381
          Bcone1381 commented
          Editing a comment
          Bob is telling the scratch builder to build the shock strut length so that the spread between the center of the tires equals the value in the plans (The Patrol plans value is 72" I don't know what it is for the four place) when the strut is extended 1.38 inches.

      • #6
        The only adjustment is how far the XAM-7 rod end bearing is screwed in. Without the engine & wings in place - the fuselage will be so light that the spring will not compress and the L/G legs will be tucked in tight.

        You will for sure have to adjust this at least one more time when the plane is close to ready. But setting the spread (tire center to tire center) of 66"-68" would be good. Mark