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Thread: The kitfox "Jesus Bolt"

  1. #1

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    Default The kitfox "Jesus Bolt"

    Maybe i'm overly cautious, but the idea that a piece of plastic with some hand drilled holes and saw marks on it being the main interface between my control stick and my airframe isnt exactly what I look at as the pinnacle of safety. Soooo..... I machined some aluminum control column bearings with a surface roughness control of 8 at the internal interface. Installation and function report will be following shorty.
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  2. #2
    Senior Member jiott's Avatar
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    Default Re: The kitfox "Jesus Bolt"

    Never heard of that piece of plastic breaking or causing a control problem, but your machined blocks sure have a nice look to them.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #3
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    Default Re: The kitfox "Jesus Bolt"

    A surface finish of 8 is very impressive. Nice work.

    I think that plastic block is glass filled nylon which is pretty tough stuff. I agree with Jim, I don't think there's any history of failure.
    Kitfox 5 (under construction)
    Citabria (sold)
    Commercial SE/ME, CFII

  4. #4
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    Default Re: The kitfox "Jesus Bolt"

    Avid Flyers used an oak piece of wood. Never had any issues with any of mine there either. Wonder which of the three types would wear out first? My Kitfox has 700 something with plastic, and the Avid has 600 something with the wood block. They both will go a long time yet I'm thinking. Your's look nice though. JImChuk

  5. #5
    Senior Member jrevens's Avatar
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    Default Re: The kitfox "Jesus Bolt"

    The aluminum does look nice, but the plastic is absolutely fine. There is more than enough strength, it's self lubricating, and with the small degree of travel it will almost certainly outlast the airframe, IMHO.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE

  6. #6
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    Default Re: The kitfox "Jesus Bolt"

    Wow. Nice!

    My "just in case" isn't as pretty. I added a plate over the top of the plastic bearing. My thought was..... if the plastic did break, the "torque tube" is caged between the bolts and the plate.


    IMG_3557 2.jpg

  7. #7

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    Default Re: The kitfox "Jesus Bolt"

    I do agree with most of you that it shouldnt really be an issue depending on the level of attention to detail was aimed at that effort during installation - sadly whomever did the drilling and install on mine missed the center and then decided to remove as much plastic from the top piece as possible (for reasons I am not quite sure of) - ill post a picture of my stock one here in a bit. Since I am currently re-skinning portions of the plane and redoing the paint on the body, the floors were coming out already and that provided me the opportunity to make these little upgrades to the plane that I felt would help separate it from every other Model 4, while also looking good and increasing safety. When I removed the plastic one from my aircraft, the lower portion of the clamshell can be squeezed with two fingers and will basically fold in on itself - not something I want retaining the main controls of my aircraft. Yes - ill suffer a slight weight increase, but the added strength gives me a bit more piece of mind.

    I do still have 3 remaining setups (ran a batch of 5) so if anyone is interested in swapping over to the aluminum please drop me a PM. Im not looking to profit on them so itll be cost to machine and base material plus shipping.

  8. #8
    Senior Member Maverick's Avatar
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    Default Re: The kitfox "Jesus Bolt"

    I believe that those "plastic" bearings are made of Teflon and will likely outlast the airframe.
    EAA, AOPA
    KF5 (N49FK & N36KJ)
    Phoenix, AZ

  9. #9

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    Default Re: The kitfox "Jesus Bolt"

    Had to do a bit of research before I could make any statement - Seems these bearings are actually made from Delrin. Melting point of delrin is just under 200 degrees F, melting point of Teflon is just above 600 degrees F. Placed a 250 degree heated iron on the block I removed from the plane and sure enough it melted.

    Now with that said, Delrin still has some amazing material properties :

    • Color: White or Black
    • Temperature Range:
    • 6" Lengths: 0 to 180 F
    • All other sizes: -20 to 180 F
    • Tensile Strength: 7,690 psi (Good)
    • Impact Strength: 1-1.5 ft.-lbs./in. (Poor)
    • Hardness: Rockwell R120-R122 (Hard)
    • For Use Outdoors: No


    Some things to note about Delrin - it is not hydrophobic - so it is likely to take in small amounts of water and is typically not recommended for long term exterior exposure. While most of these aircraft are kept indoors, exposure to the elements is guaranteed and as such life expectancy can only be expected to be reduced. The big one to note from the above properties is the tensile stength of the material - due to how these parts are used and exposed to some form of radial forces as the control stick is moved during flight and run up, this tensile strength is of great importance.

    Now lets consider some material properties of 6061-T6:
    • Temp Range: Up to 900 degrees F (depending upon application)
    • Tensile Strength: 42,000 PSI


    With a maximum operating temperature 5 times greater and tensile strength of almost 5.5 times that of Delrin, I am confident that while it may not be ABSOLUTLEY necessary, from a safety standpoint, this upgrade makes sense and provides me a bit more peace of mind.

  10. #10
    Senior Member Eric Page's Avatar
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    Default Re: The kitfox "Jesus Bolt"

    I don't want to be pedantic, but if there's >7,690psi being imparted on the control system, or it's >180F in the cockpit, I'll have bigger worries than the material properties of that Delrin part.

    Delrin has one property that's important in this application, but which is lacking in 6061-T6. Its slippery surface is inherently self-lubricating. In your application, how will the aluminum be kept lubricated where the powder-coated steel control system rotates against it?
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

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