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Thread: Rear Seat Leg Room

  1. #1

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    Rear Seat Leg Room

    Wanted to show how we gained several inches of leg room in our Javron build.

    Most Super Cub kits are built with the rear seat bottom hinge applied at the same point as the rear seat pan hinge. We placed ours back approximately 5-6inches to provide greater leg room and full range of motion for the control stick when applied. Also modified the removable rear seat top cross brace tube to provide favorable lean back alignment. Keep in mind this will have an effect on rear seat GC station #’s.

    Additionally, designed the rear seat back bottom hinge to allow for a flat lay down on the seat pan plywood. This method provides two layers of plywood support.

    Just athought.

    SHEP


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    Last edited by elpcub; 05-07-2019 at 07:40 PM.
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  2. #2
    Steve Pierce's Avatar
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    I figured Javron had copied the Dakota Cub mod that moves the rear seat mounts both top and bottom back. Make a huge difference to the back seat occupant. Looks like you put a jog in the seat back carry-thru tube, interesting.
    Steve Pierce

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  3. #3

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    How's the head room that far back and can you reach the pedals?
    Remember, These are the Good old Days!

  4. #4
    skywagon8a's Avatar
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    Quote Originally Posted by elpcub View Post
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    Quote Originally Posted by Steve Pierce View Post
    Looks like you put a jog in the seat back carry-thru tube, interesting.
    I should point out that crossover tube is more than a seat back support. There are structural loads which are part of the fuselage tubing being carried by this tube. I don't know what those loads are but there is a reason that it must be there. I'm just pointing out that when you place a 90 degree joint in that tube, the ability for it to carry those loads is greatly reduced without any special reinforcement. That reinforcement does not appear to be in this part.

    The original removable cross tube was made to be removed in the ag version when it passed through the hopper and was bolted in place. The non-ag stock Cubs had this tube welded in. A person can easily move the sides of the fuselage in and out without this tube bolted in place. If you can move it easily, what is gong to happen to it during rough air loads being applied? Just food for thought, it's your plane.
    N1PA
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  5. #5
    Gordon Misch's Avatar
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    Agree with Sky. I have the removable tube, and when the plane is loaded heavy, the tube is a bit of a challenge to install. It is definitely structural and I wouldn't do what is shown. I'd expect that right angle arrangement to fail from fatigue, if not outright. Of course that could be over-cautious, but - - - -
    Gordon

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    and if nothing else weld some, say 3 inch triangle gussets on it at the 90.
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  7. #7
    skywagon8a's Avatar
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    Quote Originally Posted by tempdoug View Post
    and if nothing else weld some, say 3 inch triangle gussets on it at the 90.
    At the four 90s.
    N1PA
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  8. #8

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    there would be a thread in itself as to how much pull or pull pressure or movement there actually is on that tube, alot use what a 3/16 pin on each end? to hold it in place. and just for curiousity if you put a 225 guy with a touch of weight in the baggage, back 4-5 inches does it change the cg much? just wonderin. goes back to whats said here long ago, you add here your taking something away there. as long as a guy knows his weights it will be just fine.
    Last edited by tempdoug; 05-09-2019 at 06:54 AM.

  9. #9
    skywagon8a's Avatar
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    Quote Originally Posted by tempdoug View Post
    there would be a thread in itself as to how much pull or pull pressure or movement there actually is on that tube, alot use what a 3/16 pin on each end? to hold it in place.
    Look up the shear strength of a 3/16" steel pin. Double it, as there are two sides of the tube each carrying the shear strength of the pin. One pin is actually doing two separate jobs. That number would be the maximum load which can be carried by that joint. The actual flight loads may be nowhere near that number.
    There are several other calculations which could be made for this purpose. For the purposes of this discussion, just the pin strength will do.
    N1PA
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  10. #10

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    I have the rear seat relocation STC Steve posted about and REALLY like it, especially since I seem to spend a lot of time back there when Molly is home... the way the STC version works also increases the recline of the seat back which really helps. I’m not sure how much further back I could go using my thick OregonAero seat cushion and still have full head room but I’m a short legged 6 footer so I use more than the standard FAA pilot amount of space (in all axis) and as it is now I’m good with a headset but I can’t wear my DC helmet back there without doing the bump (yea I’m old too).

    I tend to agree with the concerns about the offset brace shown in the pics but in reality the normal load is likely somewhat low but in an opps it would easily be very high and the design for the STC version can easily carry a significant load and would likely function beyond a pin deflection failure as it is straight. To be safe I would definitely monitor it for deflection and I if mine I would add a small corner gussets plates on top of the member and they could be even riveted (3/16” SS pops are really stout, if you can pull them) for installation if you can’t easily remove what’s there for welding.

    Kirby

    Ps. That’s a Beautiful interior, good job!
    Remember, These are the Good old Days!

  11. #11
    skywagon8a's Avatar
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    This is an example of a corner gusset. I would place one on top and another on the bottom to eliminate any twisting loads. You would only need them on the two furthest aft corners as they will transfer the loads to the stubs pulling straight. Also you could use AN3 bolts as shown in this drawing. Or you could weld the outside edges.

    Not necessarily those dimensions.
    N1PA
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