Aileron Arm Bearings -- S-2A

Discussion in 'Pitts Miscellaneous' started by cwilliamrose, May 7, 2018.

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  1. May 7, 2018 #1

    cwilliamrose

    cwilliamrose

    cwilliamrose

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    I have a question that can't be answered by the parts book or any S-2 assembly drawings I have;

    The upper arms on my airplane have a KSP3L on the right side and a K3L (not KP3L) on the left side. I noticed there was some rotational freedom on the right side slave strut and none on the left side. I figured it might be a bearing going bad but most likely it was a different bearing on that side because there was no free play in the ailerons. That turned out to be the case.

    I know it doesn't really matter for the round slaves and maybe the factory was just using a cheapest option or the best 'in stock' option. Or maybe that bearing was replaced and the wrong one was used?? If/when I put streamline slaves on the airplane that bearing will have to be replaced anyway so I'm doing it now.

    So, does anyone know if it is common to see a spherical bearing in the upper arms? It seems odd to me even with round slaves. I intend to replace that bearing with a KP3L which I happen to have in stock and is called out, along with the K3L, as the proper bearing in the S-1S plans......
     
  2. May 7, 2018 #2

    PittsDriver68

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    Bill,

    That does not sound right. There should be no rotational freedom on the slave struts. I will be flying today and I can look at both the round slave struts hanging on my hangar wall and the streamlined ones on the airplane that I did a Field Approval for. Will report back.

    Best of luck,

    Wes
     
  3. May 7, 2018 #3

    cwilliamrose

    cwilliamrose

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    Thanks Wes. Did you have to use different aileron arms for the streamline struts?
     
  4. May 7, 2018 #4

    PittsDriver68

    PittsDriver68

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    The streamlined slave struts are simply installed on the S-2A upside down from their installed orientation on the S-2B. Re-use the original hardware and no other change to the aircraft. Good for 12mph.

    Best of luck,

    Wes
     
  5. May 7, 2018 #5

    PittsDriver68

    PittsDriver68

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    Went flying. Took a couple of pictures of the upper aileron slave strut attach on the S-2A. First, my airplane has plain bearings not spherical bearings in the aileron arms. No rotational motion of the slave struts. I will note that the bearings are pressed into the aileron arms. The slave struts just have a fork on each end.

    Pics below.

    Wes

    20180507_144155.jpg

    20180507_144140.jpg
     
  6. May 7, 2018 #6

    Morphewb

    Morphewb

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    I would guess the S2B slave rods would fit a later model symmetrical aileron S2A then?
     
  7. May 8, 2018 #7

    cwilliamrose

    cwilliamrose

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    Very interesting Wes. That angle the machined fork is mounted on is normally there to help the strut clear the lower rear spar. Having it at the top seems like it would put the edge of the slot in the fork awfully close to the arm at full deflection. No marks on your aileron arm so it must be OK.

    There needs to be a spherical bearing at one end or the other of the slave strut. The upper wing's sweep angle causes the upper arm to try to rotate the slave strut as the ailerons are deflected. Normally that spherical bearing is placed at the bottom end which I think is bass-akwards since the slave strut would stay aligned nicely if the lower arm was in charge. The lack of clearance between the welded fork on the slave strut end to the upper arm is probably the reason the upper arm dictates alignment.

    Many thanks Wes!
     
  8. May 8, 2018 #8

    PittsDriver68

    PittsDriver68

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    I can take a picture from a different angle but I believe that the upper aileron arm is bent so that it is aligned with the lower aileron's arm. Which allows plain bearings to be used in both arms. The slave strut has a fork on each end and no bearings.

    Wes
     
  9. May 8, 2018 #9

    cwilliamrose

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    I was unable to make that happen in SWx. The rotation angle was small but, in my efforts anyway, unavoidable.
     
  10. May 8, 2018 #10

    gmann750

    gmann750

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    I had streamline struts on my Freise aileron s-2s and did not have to invert them. Maybe the other end differed from what you guys have, it was basically a U shape that attached to the top ailerons.
     
  11. May 8, 2018 #11

    PittsDriver68

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    It all depends on how the fabric is installed. I found that I did not have to cut fabric on my S-2A if I installed them inverted from the standard S-2B installation. Since this is an alteration to a certificated aircraft requiring additional FAA approval, I took the easy installation. Someone else, working their own approval with the FAA, could put the slave struts in using the "normal" orientation. The struts don't care.

    And Exp-Exhibition aircraft don't need to do paperwork, making life much simpler.

    Question though - I think the S-2S moves the top wing to accommodate the weight and balance change due to the installation of the 6 cylinder engine. Yes? If so, that might account for the better installation geometry.

    Best of luck,

    Wes
     
    Last edited: May 8, 2018
  12. May 8, 2018 #12

    Morphewb

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    Ok, Wes got slave rods from a symmetrical aileron S2B and put them on the old style frieze style ailerons. Do I have that right?
     
  13. May 8, 2018 #13

    cwilliamrose

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    At some point the factory seems to have taken the original streamline slaves and modified them for the S-2B/S-2S. What they did was to take a 5/8" chunk out of the aft portion of the welded/fabricated fork end of the strut to provide clearance for the aileron (??) and they run this design inverted such that the fabricated end attaches to the lower aileron.

    Slave End, S-2B_2.JPG

    Slave End, S-2B_1.JPG

    At this point I'm planning to reproduce the original design SL strut and run them right side up (fabricated fork attaching to the upper aileron).
     
  14. May 8, 2018 #14

    PittsDriver68

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    Ben, you have a correct understanding of how the S-2B aileron slave struts are installed on my friese aileron S-2A.

    "the original streamline slaves" - Did any S-2A's have streamlines slave struts. The parts books suggests not.

    Best of luck,

    Wes
     
    Last edited: May 8, 2018
  15. May 8, 2018 #15

    cwilliamrose

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    Yes, the older S-2A's had streamline slaves, then the AD came out......

    EDIT: The AD affected the first 25 airplanes built.
     
    Last edited: May 8, 2018
  16. May 8, 2018 #16

    Morphewb

    Morphewb

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    Thanks Wes.

    Three of the original S2A's I was involved with were all early models with streamline slave rods.
     
  17. May 10, 2018 #17

    cwilliamrose

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    Upper Aileron Arm Bearing.JPG


    This is the bearing I question. It certainly appears to be a factory installed and staked part. I asked Janette about what bearing is being used in this part but she was not able to answer me. I asked that maybe someone could look at the one in stock and see which bearing was used. Hopefully they can do that. The price is just under $200 for that new one sitting on the shelf.


    Given the 'roller stake' done at the factory I'm not sure what will happen if I try to replace this bearing with the KP3L I happen to have in my stash. Since this one isn't very well seated and square maybe they use these spherical bearings for good reason. :eek:
     
  18. May 11, 2018 #18

    PittsDriver68

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    When you call Aviat, the guy you want to talk to is Danny Adams. If he does not know the answer, he can find the person who does.


    Best of luck,


    Wes
     
  19. May 11, 2018 #19

    cwilliamrose

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    Thanks Wes. I don't know Danny personally but I have heard his name around here for several years.
     
  20. May 15, 2018 #20

    cwilliamrose

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    I called the factory and asked for Danny Adams. He no longer works there. :(
    I talked to Bob Wells and he's going to check the one they have in stock to confirm it has the straight bearing installed instead of the spherical one. It's a $200 part which is about half of what I guessed they might charge.

    Since the bearing in my arm was going bad anyway and adding some lube didn't bring it back I decided to try pressing it out gently with some special tools I made. The arm, or more specifically, the roll stake, did not survive -- about 25% of it broke off. I think I could maybe press the KP3L into the arm and it would stay put since most of the roll stake is still there but I'll feel better with a new part.
     

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