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Thread: Tailwheel Spring Clamp Failure

  1. #1
    Senior Member jiott's Avatar
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    Default Tailwheel Spring Clamp Failure

    One of our Kitfox SS7 group of 3 had a tailwheel spring clamp bolt failure (maybe Airfox will post details) where the #10 bolt holding the clamp plate sheared off. Apparently from side load. Lots of use on grass and unimproved runways. I am wondering how common this problem is, and if so, what have others done to beef up this area. The Grove main gear is so strong and the AK Bushwheel tailwheel we are using is also very strong, but this spring clamp area appears to be a weak link in an otherwise very sturdy landing gear system.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  2. #2
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    Default Re: Tailwheel Spring Clamp Failure

    Don't know if its still the same setup on the newer airplanes, but on my series 5 AN3 bolts were called for in this area, however I drilled out the holes to accommodate AN 4 bolts , then made a clamp out of a solid block of aluminum , machined to fit around the leaf springs. No problems 11 years and 700 hours later. Bruce

  3. #3
    Senior Member jiott's Avatar
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    Default Re: Tailwheel Spring Clamp Failure

    Yes the new Super Sport still calls for AN3 bolts. I am also thinking about changing to AN4 bolts and new sturdier spacer blocks instead of the tubular sleeves around the bolts. Since the AN3 bolt sheared, I think the only answer is larger bolts with more shear strength.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  4. #4
    Senior Member AirFox's Avatar
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    Default Re: Tailwheel Spring Clamp Failure

    After landing at a strip in Hells Canyon last weekend I discovered a broken bolt in the tailwheel spring attach bracket. Here is a picture of my Back country fix. First I wrapped the spring bracket with steel wire then as a backup I used parachute cord. The AN3 broke just beyond the grip length in the threads. AN3-12A is the origional bolt length. AN3-13A would be a better solution. Flew home and landed with the tailwheel up.
    IMG_0668.jpg

    Here is a picture of my Solution thanks to Kitfox Aircraft!
    DSC_1537 (Large).jpg

  5. #5
    Senior Member jtpitkin06's Avatar
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    Default Re: Tailwheel Spring Clamp Failure

    First let me compliment you on the "back country" engineering. All I would add is duct tape to give it an east Texas look.

    A search on tailwheel problems indicate failures are somewhat common. Failures include broken springs, mountings, tail wheels, steering chains and linkages.

    These problems are not unique to the Kitfox. Discussions on tail wheel failures on other aircraft types are quite common.

    With that in mind it would be advisable for all builders to pay special attention to the tail wheel assembly and mounting. Certainly, larger bolts and brackets are high on my list. There is a lot of strain on the mountings particularly when doing turns on rough fields. When the tail wheel turns there is a lot of torque on the spring assembly. Upping the AN3 bolts to AN4 is a small weight penalty for a big gain in strength.

    JP

  6. #6
    Senior Member jiott's Avatar
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    Default Re: Tailwheel Spring Clamp Failure

    Scott's solution using the Grove one-piece aluminum spring with the beefy brackets looks really good. The only thing that bothers me is that it looks like it still uses the small AN3 bolts to attach the new bracket to the top fuselage plate. This is still a weak point in shear (side) loading, same as before. I think I would up these bolts to AN4 like the others.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  7. #7
    Senior Member jiott's Avatar
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    Default Re: Tailwheel Spring Clamp Failure

    I take back what I just said. Shear loading on that new bracket would have to shear both AN3 bolts for the spring to move sideways. Compared to the old bracket where shearing only one bolt would allow the spring to move sideways. Therefore the new bracket is twice as strong in shear.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  8. #8
    Senior Member jiott's Avatar
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    Default Re: Tailwheel Spring Clamp Failure

    At some point all this strenghtening becomes a moot point because a large impact on the tailwheel assembly will then cause the whole fuselage tail structure to bend; which is much harder to repair. Maybe a bolt that shears before that happens is not such a bad idea. Just thinking.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  9. #9
    Senior Member akarmy's Avatar
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    Default Re: Tailwheel Spring Clamp Failure

    Does this mean John is ready to start selling the Aluminum leaf and brackets? Previously when I checked it was in development undergoing "testing"
    Andy Karmy
    Kitfox 7 - 912S - SOLD
    Auburn, WA

    http://kitfoxflying.com

  10. #10
    Senior Member SkyPirate's Avatar
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    Default Re: Tailwheel Spring Clamp Failure

    I have the solid leaf system on mine, practicing Stol landings and getting the tail wheel on the ground first, no problems yet but i have not had a sideways tail first landing yet either , i have had some 3 point landings where i was landing short and had to set her down a little rough but still with no issues and i have 6x6 with wheel pants on so not allot of give in the tires like a bushwheel tire
    Chase
    Model 5 OutBack
    912 UL

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