What material/method would you prefer to use if you were building an ultralight?

Discussion in 'The light stuff area' started by Head in the clouds, May 27, 2012.

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For developing an improved ultralight, what material would you prefer to use?

  1. Pop-rivetted aluminum tube and gusset truss fuselage, fabric covering

    39.2%
  2. Welded chromoly truss fuselage, fabric covering

    26.6%
  3. Wood truss, ply or fabric covering

    19.0%
  4. Other - please tell us more in the 'A challenge to you all' thread

    15.2%
  5. Pop-rivetted aluminum tube and gusset truss fuselage, fabric covering

    39.2%
  6. Welded chromoly truss fuselage, fabric covering

    26.6%
  7. Wood truss, ply or fabric covering

    19.0%
  8. Other - please tell us more in the 'A challenge to you all' thread

    15.2%
  1. May 27, 2012 #1

    Head in the clouds

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    A group is working on developing an improved ultralight, please let us know what materials and method you would prefer if you were to build one. If you choose the last answer please tell us more in the 'A challenge to you all' thread in the General Experimental area. Or just come and have a look anyway and tell us what you think, we need all the help we can get!
     
  2. May 27, 2012 #2

    BBerson

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    I voted for welded 4130 because I enjoy welding and I believe a welded structure is best for crashworthiness, inspection and cost.
    But some builders don't want to or perhaps feel they cannot weld safely.
    I am working on methods to produce adequate welds by an average person. Any less than perfect weld (but still adequately welded steel frame) is preferred, compared to an imperfect glue joint in wood or composite, in my opinion.

    But the designer needs to think of easier ways for a non-professional to weld the joints.
     
    Last edited: May 27, 2012
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  3. May 29, 2012 #3

    pwood66889

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    I submit that all designers have to have joints that the non-professional can construct correctly every time!
    Percy in SE Bama
     
  4. May 29, 2012 #4

    Hot Wings

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    Consider brazing. There are brazing alloys available that develop the same, or better strength (the fit needs to be very good for this to happen), than normalized 4130. It can be done with less expensive torches and there is little danger of creating a brittle HAZ zone. For added insurance, 22 gauge mild steel cuts real easy and can be folded by hand for gussets, similar to what is used in tube and gusset aluminum tube ultralight fuselage construction.
     
  5. May 29, 2012 #5

    larr

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    Well, my vote goes to wood. I've been around the block on this several times, and for me wood is the best compromise.
    Everything in aviation is a compromise of one kind or another, you have to pick what you're comfortable with and go with it.
     
  6. May 29, 2012 #6

    BBerson

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    I prefer welding over brazing for several reasons.
    But your suggestion for gussets is what I had in mind (and other ideas).
    The problem is welding the cut off butt ends of thin tubes is difficult because the thin metal melts away. Gussets are easy to weld.

    No one would suggest butt end glue joints for wood truss where gussets are required. Why should steel tube be restricted to butt welds only? Lots of options exist, such as gussets, flat ends, plate inserts, etc.

    I don't have the solution yet, but am doing some experiments.
     
  7. May 29, 2012 #7

    Hot Wings

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    I prefer welding over brazing for several reasons.

    Why? I find that when it's appropriate that it is quicker and easier.

    But your suggestion for gussets is what I had in mind (and other ideas).


    Here is a quick sketch if what I think would be possible. These tabs could be stamped out in 2 or 3 sizes by the thousands pretty cheaply, or just make the basic lower tab by hand. If they were stamped nice little details like the tabs for ply formers and holes for good braze flow would be very easy to incorporate. If you don't need the tab, just clip it off.

    braze tab.jpg
     
    Last edited: May 29, 2012
  8. May 30, 2012 #8

    BBerson

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    I think welding is quicker and stronger than brazing. And braze must be cleaned if welded in the future. I think braze is not advised in AC43.13 (but have not looked recently). I guess i don't have enough experience with brazing to comment much more.
    But new ideas are needed. It needs to be tested.

    I am working on methods for the MIG welder for the homebuilder. The MIG is used in airplane factories (with professional welders), but for a homebuilder lots of practice is needed on thin tube ends.
    That's because of the open ends, as I mentioned. But the ends could be designed for easier MIG welding.
     
  9. May 30, 2012 #9

    Head in the clouds

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    All the airframes of the Skyfox (JAR23 certified version of the Kitfox) were MIG welded. There was a lot of scepticism at first about the proposal to use MIG, and the welds were pretty messy but they went to testing and found the frame to be stronger than if it was TIG welded, so that destroyed the DoA's argument altogether.

    As I understood it, the reason was that they were running the MIG a bit cool to prevent blowing holes in the tubing and so the welds tended to not have much penetration, particularly in the acute-angled fillets, so there was a lot of buildup of filler material which was messy. But - because they were forming the welds very quickly and with low heat, the heat affected zone never got very hot and so the usual failure zone of a non stress-relieved frame was avoided.
     
  10. May 30, 2012 #10

    Head in the clouds

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    Except for one I built all my 4130 fuselages with brazing. I didn't use brass because in testing it wasn't very strong. Instead I used nickel-bronze alloy (here they call it bronzing) and it was very strong. The frame was stronger overall than a TIGd frame because the heat affected zone (weakest part) wasn't so affected as with TIG. But it was easy to make it worse. You had to get the brazing right, in particular avoiding overheating (cooking) the bronze, all heat must come from the parent material to the filler, any attempt to heat the filler instead was a complete disaster.

    The worst aspect was cleaning the flux off which goes into a hard varnish but maybe there are chemicals for that.

    I used a Dillon torch which was just awesome, so small you could get it right into tight corners and it used half the gas of the 'normal' torches.

    I'd still use TIG now though, since I have one, and have the proficiency to work fast, but for a beginner I would suggest bronzing, with plenty of practice first. I like your tabs concept but how will you attach the crossmembers?
     
  11. May 30, 2012 #11

    Head in the clouds

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    Yes, flattening the tube end is a good option and a hell of a lot quicker than grinding fishmouths and makes the weld really easy to do. Also your suggestion of cutting a slot in the tube end and welding in a plate is accepted practice in the structural field but usually requires endcapping each side of the fin plate which is a lot of work but if you don't do it, the tube would rust out from the inside. Both of these are OK structurally though as long as the cluster is all resolved to a nodal point.
     
  12. May 30, 2012 #12

    Hot Wings

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    Except for one I built all my 4130 fuselages with brazing. I didn't use brass because in testing it wasn't very strong. Instead I used nickel-bronze alloy (here they call it bronzing) and it was very strong.

    This is the reason so many people have poor results using brass. Hardware store brazing rod is fine for fixing a broken leg on the barbeque grill, but thin wall tube, like airplanes and bicycles need something else. Your use of an alloy with nickel in it is going in the right direction. The old nickel/cadmium containing ones, I think, were nicer to use (you can still find old stock if you look). Next time try going down the heat scale a bunch and get some silver/nickel rod. It is still generically called "brazing" but is several hundred degrees below the critical temp of 4130N so overheating isn't a problem if you are paying even a bit of attention to the color of the base metal. Start with some BAg-3 to see if you like it.

    For those that haven't looked into some of the subtleties of welding 4130 here is a good web site to start. And this one.
     
  13. May 30, 2012 #13

    Himat

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    I would go for aliminium sheet and maybe some tubing put together with blind (pop) rivets.
    An alternative is steel tubing bolted togheter, but that might bring a weight penalty thats to heavy. Look at the Martin Baker MB5 design for reference.
     
  14. May 30, 2012 #14

    litespeed

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    Alloy sheet, and square alloy tube all riveted with gussets.

    Seems cheap and easy.

    Litespeed
     
  15. May 31, 2012 #15

    bmcj

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    Unobtainium!
     
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  16. Jun 1, 2012 #16

    litespeed

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    **** I suugeested that.......................said it was over budget.
     
  17. Jun 3, 2012 #17

    clanon

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    Couldn't find it on Aircraft Spruce...:gig:
     
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  18. Jun 3, 2012 #18

    Sir Joab

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    When it comes to cheap steel welding I've found that with a bit of practice you can use flux-core wire and possibly eliminate the gas bottle from your expenses. Burn-through is even more of a problem on edges, but if you start the weld a little ( about 1/8 inch) inboard and walk it out to the edge it works great.

    EDIT: I'm talking about MIG welding here... forgot to mention that.
     
    Last edited: Jun 3, 2012
  19. Jun 4, 2012 #19

    PaulS

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    Actually you are talking about wire feed flux core...
    And it is not what most would use on steel tube for strength ot weld quality.
    The gas is cheap compared to your life.
    Paul
     
  20. Jun 4, 2012 #20

    Sir Joab

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    Sorry about that... I have a bad habit of calling any any wire feed welding "MIG". I do know there's a difference. :nervous:

    Just throwin' it out there... I've been very satisfied with the welds I've gotten using this system. (On non-aircraft applications.) I've been welding with a gas bottle for years, I just recently started experimenting with flux core.
     

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