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Thread: landing gear attach reinforcement?

  1. #1
    suntiet's Avatar
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    Default landing gear attach reinforcement?

    I am about to pick up my new to me KF 4-1200 uncompleted kit and have read a bunch about beefing up the landing gear attach points on the fuselage. Is there any how to's out there for this? is it needed with all forms of gear, mine came with grove aluminum spring gear?
    Thanks

  2. #2
    Senior Member 109JB's Avatar
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    Default Re: landing gear attach reinforcement?

    Most weld webs into the door sill tubing area. My opinion is that is not ideal. Webs from an engineering perspective are intended to take shear loads in diagonal tension. The do not take compression well. Many times even heavy steel I-beams have vertical members welded on to prevent web buckling. That said, if you put in a thick web it can take compression without buckling, but at a weight penalty. I've looked at this area and believe that a better solution would be to add diagonal tubes in the opposite direction because tubes can take compression and stiffen this area. As for your grove gear, I would say that gear is the most important to consider reinforcement of that area.

    Stock gear.jpg
    Stock setup

    Stock gear mod.jpg
    Stock setup with additional diagonal tubes opposite to the existing diagonals

    I also have a Kitfox IV project and looked at this area. I wanted a bit wider gear so I decided to build a cabane gear using the stock mount at the rear and the float mount at the front. This provides a more direct load path for the gear loads into the main parts of the fuselage and takes all of the bending out of the door sill area and having the cabane style gear takes the bungees off of the seat truss and hence takes all of the bending off that portion too. It also takes load off the front leg when compared to the stock gear. I didn't know it before I designed mine but it turns out that the TK1 racing guys (aka Monster shock) also make a gear that uses these mounting points. I believe this is the same cabane gear that the Kitfox factory sells. Since I am using this gear arrangement I won't be doing any reinforcement of the door sill area.

    My Gear.jpg
    Gear using stock rear mount and float mount at front

    20201025_150006.jpg
    My gear from front

    20201025_150019.jpg
    My gear from side

    All of this is just my opinion and you can take it or leave it.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  3. #3
    suntiet's Avatar
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    Default Re: landing gear attach reinforcement?

    Thank I saw your paper looks good. Haven’t decided what to do with the gear yet. But I suppose I’ll reinforce the frame before I cover it either way. The green tubes are your suggestion for reinforcement? I like it. Thanks


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  4. #4
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    Default Re: landing gear attach reinforcement?

    I would do some digging in the archives on damage done to the fuselage when the plane wrecked with the grove gear. There was a thread just a month or so ago. Others over the years. You can see what got bent up, and where added strengthening may be appropriate. JImChuk

  5. #5
    Senior Member Maverick's Avatar
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    Default Re: landing gear attach reinforcement?

    Also, consider which model it is. This sounds like it is regarding the 4.
    EAA, AOPA
    KF5 (N49FK & N36KJ)
    Phoenix, AZ

  6. #6
    suntiet's Avatar
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    Default Re: landing gear attach reinforcement?

    It is a four.


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  7. #7
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    Default Re: landing gear attach reinforcement?

    Quote Originally Posted by avidflyer View Post
    I would do some digging in the archives on damage done to the fuselage when the plane wrecked with the grove gear. There was a thread just a month or so ago. Others over the years. You can see what got bent up, and where added strengthening may be appropriate. JImChuk

    Have a look at N195CL revamp. He had damage from hard landing on Grove gear. JImChuk

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