Interesting approaches to cockpit cage construction?

Discussion in 'Tube and Fabric' started by cluttonfred, Jan 13, 2020 at 1:48 PM.

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  1. Jan 13, 2020 at 1:48 PM #1

    cluttonfred

    cluttonfred

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    In the Simple pusher pseudo-jet thread, I described what is basically a pod-and-boom pusher design disguised to look like a generic jet trainer. I had in mind a welded 4130 steel tube, bolted aluminum tube, or riveted aluminum tube and gusset cockpit cage at the center of the design, everything else (wings, boom, landing gear, engine mount, seats, harnesses) attaches to that. A large prewelded cockpit cage is, however, an awkward and expensive thing to ship in a kit.

    Does anyone have any good examples of prewelded or otherwise preformed lightweight steel or aluminum structures (doesn't have to be a kit airplane) shipped in flat subassemblies that are then bolted or riveted together for final assembly? I also wonder if there might be some interesting approaches with CNC-cut flat sheet components that could be bent and welded together to create truss structures faster and cheaper than traditional welded tubing.

    Any ideas?

    Cheers,

    Matthew
     
  2. Jan 14, 2020 at 4:01 AM #2

    lr27

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    If this is going to be a kit, how about a bunch of tubing with all the cuts shaped right, so there's no cutting for the builder, just welding? The welding might be easier with a jig made from NC-routed plywood that slots together. DIdn't FritzW do something like this on one of his projects? I suppose parts of the assembly could be welded in the factory. This method might have the lowest engineering risk, though of course it depends on moderately good welding.

    I wonder how honeycomb panels do in crash situations. Maybe aluminum skinned, preformed panels. Barnaby Wainfan's PAV report discusses how to make airframes from the this stuff.

    I wonder how they make those composite tubs that are used in race cars.
     
  3. Jan 14, 2020 at 4:21 AM #3

    Geraldc

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    This is how the Australian V8 supercars are made.Body panels are welded to this frame.
    Cage can take massive crashes with not much damage to drivers. upload_2020-1-14_17-18-58.png
     
  4. Jan 14, 2020 at 5:31 AM #4

    cluttonfred

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    Yup, welded 4130 is very appealing (see https://vr3.ca/ for beautiful CNC-cut and bent tube structures) but awkward to ship and not everyone wants to (or can) do the welding. I was just wondering if anyone know of any clever ways around the shipping.
     
  5. Jan 14, 2020 at 5:57 AM #5

    BBerson

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    Tubes with thick end tabs factory welded can be easily bolted together. I had a radio tower made with tabs on each diagonal and longeron tube.
     
  6. Jan 14, 2020 at 5:59 AM #6

    cheapracer

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  7. Jan 14, 2020 at 9:20 AM #7

    Chilton

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    Might be worth looking at the DH Tiger Moth forward fuselage, 2 flat welded sides with cross members bolted in place. The rear fuselage is a welded box structure which bolts on at the rear of the cockpits.

    Whether it is much simpler to ship the sides and crossmembers than the full welded cage is another question though!
     
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  8. Jan 14, 2020 at 9:57 AM #8

    henryk

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    Last edited: Jan 14, 2020 at 10:05 AM
  9. Jan 14, 2020 at 1:00 PM #9

    cluttonfred

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    Thanks, all. I may be overcomplicating things here, looking at something like this uncovered Kolb fuselage it may be possible to do lower fuselage, engine mount, and possibly a roll bar/seat harness support as three separate units that could all be shipped if need be.

    uncovered kolb.jpg
     
  10. Jan 14, 2020 at 8:50 PM #10

    Geraldc

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    The Rans S6 is partly there with a steel cage and alloy bolted rear.
    Now all you need to do is design bolted joins into the cage section.
    Question is what size do you need to get down to?
    Here we would need to get down to max length of 6ft under 3.5 cu ft and no heavier than 55lb

    [​IMG]
     
  11. Jan 14, 2020 at 10:08 PM #11

    BBerson

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  12. Jan 14, 2020 at 10:55 PM #12

    cluttonfred

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    Yes, I was thinking of UPS limits as a guideline.
     
  13. Jan 14, 2020 at 11:35 PM #13

    Tiger Tim

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    Does it have to be a cage that goes around the occupants? For a side-by-side pod and boom pusher it may be worthwhile to look into a centre keel to carry the landing gear, controls, seat attach structure, and engine mount. That ought to allow the doors to be absolutely enormous.
     
  14. Jan 15, 2020 at 12:35 AM #14

    Geraldc

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    The original truss and wire system developed by the Wright brothers could be modernised.
    upload_2020-1-15_13-31-16.png
    Long tubes with sockets and loops welded on.Struts fit into sockets.Long tubes are pulled tight together and loads
    are taken by diagonal wires.Wires are tensioned and then eyes nicopressed to hold it all together.
     
  15. Jan 15, 2020 at 1:19 AM #15

    TFF

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    It’s not that it can be designed. The question come to, is it worth the it? The answer can go both ways legitimately.

    In a Western country, the answer is probably no. While it may take a while to find someone to weld something up, it will be cheaper than a low production factory of probably one employee. It’s only a one time job.

    Air dropped in the middle of an African grassland, any prefab will be welcomed.

    It comes down to what does it really save you, because it has to be done somewhere, and what amount of performance are you willing to give up for not having the normal methods.

    It has to be designed. Non standard usually has teething pains.
     
  16. Jan 15, 2020 at 6:26 PM #16

    Riggerrob

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    How about pre-welding the sides of the roll cage?
    They could lay flat for shipping.
    Then bolt in cross-members or flat bulkheads to complete the roll-cage.
     
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  17. Jan 15, 2020 at 6:38 PM #17

    stanislavz

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    Ikarus c42 way :

    [​IMG]

    Plus some panels give you nice in airplane.. All bolted and bended..

    [​IMG]
     
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  18. Jan 15, 2020 at 7:12 PM #18

    cluttonfred

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    I did my microlight training in a C42, nice little plane. Here's a clearer pic to show the structure underneath the fairings.

    stripped c42.jpg
     
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  19. Jan 15, 2020 at 10:13 PM #19

    stanislavz

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    Any hope to know main tube size ?

    A kind of paradox in c42 - slower to modern composite ones, faster to most rag and tube. But sold in huge numbers.

    But c52 was a flop.. More attention to details, better cruise. As read in german forum - a vw golf is an vw golf. Do not try to make luxury car from it.
     
  20. Jan 15, 2020 at 11:27 PM #20

    cluttonfred

    cluttonfred

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    I don't know the main tube size, but I am very leery of designing around a tube of a specific size and alloy unless it is very common and made by multiple manufacturers in the USA and around the world. Does anyone know if there are such common tube sizes available pretty much anywhere?
     

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