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Thread: Lift Strut Attach Bolt

  1. #1

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    Default Lift Strut Attach Bolt

    Would like to get some opinions on the following issue with a PA-22-108.

    Airplane was rebuilt 1997 with around 4000 hours. Appears that original lower lift strut attach bolts were reused at that time and these had a fair amount of surface corrosion. My IA suggested replacing these and I got a set of bolts from Univair, P/N U13241-000. Referenced Piper Service Bulletin No. 1172A and installed new bolts about 12 flying hours ago. The instructions in the service bulletin say to tighten the nut just enough to eliminate axial play in the bolt, then continue tightening as needed to align the cotter pin hole in bolt with the nearest nut castellation and install the cotter pin. We followed these instructions. I found another source that said to tighten to 95-110 in-lb and install the cotter pin at this point.

    Noticed in the last few hours that the right wing has a "pop" when pushing up near the leading edge at or outboard of the upper forward lift strut attach point. No movement is visible, though this is difficult to determine with the airplane rocking on the gear. Finally found that the movement was at the lower fuselage forward lift strut attach point, with a small amount of movement felt at the lower forward lift strut fork where it joins the lower fuselage fitting. Removed the cotter pin of the forward nut only and tightened one more increment on the castellated nut, which appears to have eliminated the play. Have not flown the airplane since, which leads to the following questions...

    1. Is it reasonable to continue at this point and observe whether the strut fork loosens and develops play again?

    2. Is it better to back off the lower strut fork attach bolt, re-torque one increment past "eliminating axial play" per the service bulletin, and accept the wing movement?

    3. Is it necessary to ream/bush the lower strut attach fitting at this point?

    I do not believe that the strut movement was present previously, but this is entirely possible. I can only surmise that this movement would lead to continued wear of the hole in the lower lift strut fuselage fitting, eventually creating a need to ream this oversize and use an oversize bolt (not sure where I would obtain this), or bush the lift strut attachment hole and use a standard bolt.

    I know this subject has been addressed previously and have searched and read previous discussions of lift strut attach bolt installation, but haven't found enough to determine what is acceptable torque to eliminate movement in the wing, and whether some movement in the wing is acceptable in preference to increased torque at the attach bolt.

    Thanks for any help.


    Curtis

  2. #2
    J Ryd's Avatar
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    Default Re: Lift Strut Attach Bolt

    My understanding of this attachment is that the designed forces are "shear" (pulling in line with the strut). Therefore your first tightening procedure would be correct. I dont think you want to put any bending forces on the adjustable clevis ears. (Somebody with more experience might need to correct me)
    Jan

  3. #3
    Stephen's Avatar
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    Default Re: Lift Strut Attach Bolt

    I would remove the strut and check for a possible elongated hole in the fuselage strut bracket.
    "You can only tie the record for flying low."

  4. #4
    Administrator Steve Pierce's Avatar
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    Default Re: Lift Strut Attach Bolt

    If you have gotten rid of the play by tightening then I would operate as normal and keep checking it. I have found several Carbon Cubs with hour glass shaped holes in the strut attach fitting due to a manufacturing issue at Cub Crafters. Their engineering fix was to replace the strut forks with a set that had been reamed, ream the strut attach fittings on the aircraft and install NAS oversized bolts. Issues were the gear had to be removed and wings supported to ream the fittings on the airplane. Very difficult to ream precisely this way. Also the bolts had to be installed upside down because they are longer than the special Piper bolts that have a shorter threaded area. The longer threaded section will hit the landing gear in a bounced landing. The issue there is that the landing gear must be replaced prior to removing the stuts. Hard to do in the field when you are trying to disassemble a wreck. (that is a whole nother story )

  5. #5

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    Default Re: Lift Strut Attach Bolt

    Gents,

    Appreciate the quick replies. The strut hole did not appear elongated or wallowed out when the bolts were swapped, but that is not saying a whole lot given that we did not anticipate measuring the hole during the bolt change, nor was a set of bore gauges readily available.

    I would say the bolt was initially "one finger pulling on the wrench" tight, then moved to the next notch on the castellated nut at that point. It has been torqued 60 degrees since then to the next notch. I wish in hindsight we had put a torque wrench on it while doing so, just to have an idea what the torque range was. Was definitely more than "finger tight", but far from "pulling on the wrench with all your weight" tight, whatever all that means. It eliminated the popping at the wing, so I am inclined to continue fly and monitor as Steve suggests. I do not note any bending, gouging, or deformation at the strut forks - it is a long way from that kind of tight, and obviously that would be something to be more concerned about.

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