Tube construction: Alternatives to conventional welding

Discussion in 'Tube and Fabric' started by Vigilant1, Mar 28, 2017.

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  1. Mar 28, 2017 #1

    Vigilant1

    Vigilant1

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    Okay, I can see the looks of disgust already.
    Welding is a wonderful skill, and many people enjoy it in its own right.
    But, if we want the advantages of a chrome moly tube fuselage but already know in our heart that we do not want to invest the scores of hours needed to master welding and we also don't want to fiddle around with the precise fitting of angled tubes, what are the alternatives? Are there alternatives, assuming we can live with the weight penalties, etc?

    1) Fittings made of stamped/pressed sheet metal, with included gussets (i.e. riveted construction used by some British companies during WW-II). These handled some fairly sizeable loads, we're not talking about a pop-riveted hang glider fuselage)
    2) Internal fittings (forged?), perhaps brazed or riveted into straight-cut tubing. With 3D printers; it would seem practical to rapidly make a mold of any needed angle/cluster. They wouldn't necessarily need to be "solid" parts of cylindrical cross-section, simple metal "webs" would be lighter and just as strong as the tubing, though they'd need enough area to mate with the tubing)
    3) External fittings (forged), brazed or riveted onto straight-cut tubing (similar to the lugs found on some bicycle frames).
    4) Other?

    Obviously, I'm not the first to think of this, so I'm assuming there's something out there, and leads would be appreciated. Obviously, comments (even snarky ones) are appreciated. Some welding-alternatives that might be impractical for a one-off airframe ("just learn to weld, lazy idiot!") could be pretty useful in a kit: Send out the fittings, builders buy the straight tube locally and chop 'em to length from a simple cut list. Without any angles, a monkey could do it. That's me.

    Flame on! (so to speak)

    Mark
     
    Last edited: Mar 28, 2017
  2. Mar 28, 2017 #2

    cluttonfred

    cluttonfred

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    Sorry, but I think I must have missed something. There are dozens if not hundreds of bolted-and-riveted, gusset-and-tube designs in aluminum. Airdrome WWI replicas, Sherwood Ranger, Sky Ranger, Morgan Aeroworks designs from Australia and just about every true dacron sails over aluminum tubes ultralight ever made.

    Did you mean doing the same thing with steel? I suspect that in practice bolted and riveted steel tube fuselages pay more of a weight penalty compared to welding than aluminum ones, though I don't know why that would be. Brazing has fallen out of favor as unreliable and not as easy as it looks. The Hawker-type construction relied on all sorts of special fittings which would be even more difficult and time consuming to make than learning to weld, IMHO.
     
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  3. Mar 28, 2017 #3

    Vigilant1

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    Yes, that's it.

    Or, maybe its just that welding thin AL is difficult enough that fittings are used instead?
    Probably so. But making the fittings would go quickly once a form/master was made, so it would be useful for kits or even for multiple fuselages made in the same shop.
    If brazing is out, it would seem that bolted or riveted connections would do (as they did for Hawker).
    With well-made fittings, the fuselage could be largely self-jigging. And these connections would have the advantage of being relatively easily disassembled and re-fitted if a tube is the wrong length or if a repair is needed later. Once the original investment is made in producing the fittings, the fuselage would go together relatively quickly and the connections are forgiving of error.
    .
     
  4. Mar 28, 2017 #4

    BBerson

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    Heath used wrap around steel sheet and bolts, see below. Cut a 2" long piece of tube next size smaller and slip inside tube end.
    Then heat end to dull red with a torch. A good propane torch can do it sometimes. Then flatten in a vise.


    image.jpg
     
  5. Mar 28, 2017 #5

    Little Scrapper

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    To do what you propose means designing a different airplane. Welding has been a popular method for decades because it's strong, easy, minimal and very very light weight. So really, you'd be designing a airplane for a very very select few people.

    The truth is this, welding is not scary, it's quite easy. But you're correct in saying it requires practice. However, not nearly as much practice as you may think.

    I bet I could type out a syllabus that if followed you'd be extremely competent at around 40 hours. So 40 hours of actual welding. 30 hours of that would be running straight beads.

    I bet at 10 hours you'd really feel good. At 20 hours in to it you'd feel ready, but your not. At 30 hours of actual structured meaninful practice you'd be pretty solid, at 40 there's no reason why you couldn't tackle any steel tube fuselage you wanted. 40 hour investment? Pretty cheap.

    Seriously, it's not as difficult as it appears I had formal education which is highly efficient but I bet if I add up the Oxyacetylene part of my schooling (years ago - no longer taught) there's no way it was more than 6 hours of classroom instruction. The rest was taking key elements and practice practice practice.

    This is why these designers designed in welded structures. They knew it was simple, strong, light, and when it comes to risk management a very safe bet.

    You and I both know there's some horrible airplane welds on home built airplanes flying around. How many have crashed because the welds broke? Very very few, probably almost none.
     
  6. Mar 28, 2017 #6

    cheapracer

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    Have spent a lot of time and money in the last few years considering and experimenting exactly what you are proffering.

    Is there a case for it, yes, worth it, no, unless you were actually going to sell hundreds per year.

    Stick to basic sheet gussets hand cut or better still, cnc cut and holed, with a little creativity you can use them to self jig, I'm doing it now.

    The only alternate on the theme that I would and did consider, was cutting the gussets from perforated mesh, with the hole size according to your rivets, lets say 3mm or 1/8th". Can use a slightly thicker mesh because of the lightening holes.

    Using that avoids all the measuring and marking, simply lay the mesh gusset on the job piece and drill away then rivet. The hole distances and alignment are a simple matter of being able to count.

    round-hole-perforated-sheets.jpg
     
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  7. Mar 28, 2017 #7

    cheapracer

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    Oh and of course using square tube will make your life considerably easier for this type of build.
     
  8. Mar 28, 2017 #8

    Little Scrapper

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    Welding aluminum for aircraft structures is not advised at all. Mechanical fasteners on aluminum makes much more sense. I'm the further thing from an engineer but I'd suspect mechanically fastened aluminum like a RV, Sonex or Cheapracers bird is highly predictable when it comes to calculating loads? Welding aluminum for structures like airplanes requires a very skilled welder and some witchcraft.

    The original Apollo space capsules, weren't those assembled with fasteners?
     
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  9. Mar 28, 2017 #9

    BoKu

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    Step 1: Cut and fit tubes so gaps are less than tube thickness

    Step 2: Tack weld sparingly with $100 Harbor Freight MIG box

    Step 3: Transport structure to TIG shop, have them weld it
     
  10. Mar 28, 2017 #10

    Vigilant1

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    I'm not opposed to welding, per se, it obviously works well. And I'm not ruling out learning to weld. But even if I invested 40 hours to learn it, many people would not want to do that (40 hours could be quite conservative--if you'd seen some of the copper pipes I've sweated, you'd double your estimate! "More solder, that should do it!"). Welding requires the builder to have some expensive equipment and some hard-won skills. And, it's not just the welding itself, it is also the cutting and fitting of the tubing into a 3D fuselage. As you know, both ends of the tubing often need to be notched to a precise length and at a precise 3D orientation to each other. Having the tube separate from the fitting eliminates all of this fitting: Maybe both ends can be square cut (if we have a solid joint fitting), and the orientation of the tube is not critical.
    Here's another idea: Welded connections, but all of them are made in a jig (like your practice jig in the recent thread). Just 2" long tubes that are slightly larger (slip fit) than the ones used in the fuselage. The jigs result in easily-made precision connections (short tubes are easier to heat, good lighting, repeatable, easy to inspect inside and out), and the main tubes can slip right in, secured by bolts or solid rivets. After a welding jig is made and a jig is made to cut the parts, it's fast to make 10 such fittings. Yes, it'll be heavier than welding the actual fuselage tubes, but one person can crank out the fittings needed for 10 fuselages in a couple of days, and they mail in a 20lb box the size of a file box. I'm not sure it won't even result in a stronger fuselage (larger tubing where stresses are greatest, easily inspectable welds, etc).

    I know you could hammer out a really good syllabus, but am I wrong in thinking this is a hands-on skill that needs hands-on instruction? How the puddle looks, how to know if penetration is sufficient, etc--I'd think it would be like trying to learn golf from a book.
     
  11. Mar 28, 2017 #11

    Himat

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    Alternatives?
    Yes, study the Martin Baker MB 5. I did once read an article about the construction of the MB 5 fuselage on the internet, but can’t now find it. Anyway, as far as I remember the fuselage was all tubes flattened at the ends and bolted together. A guess is that the weight penalty get worse for a lighter airplane, and then there is the risk of the nuts and bolt working lose
     
  12. Mar 28, 2017 #12

    cluttonfred

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    That's a neat idea, cheapracer, has anyone actually tried it and tested the strength and measured the weight against sheet gussets? Especially with square tubes and a design that favors easy angles, it would be very fast to build.

    For example, this place offers 3003-H14 aluminum sheet with 1/8" holes on staggered 3/16" centers in .032, .050, .063, and .125 thicknesses. The cost is $3.62-12.52 per sq foot in 4' x 10' full sheets. That's not nothing but it might still be worth it.

    http://www.mcnichols.com/products/perforated/round-hole/material/aluminum?navCode=avc:AV-127091
     
  13. Mar 28, 2017 #13

    Vigilant1

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    Cheapracer--are you referring to AL tubing and gussets, or steel ones? I'll have to spend some time looking at your build.
     
  14. Mar 28, 2017 #14

    cheapracer

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    Hell of a lot of work.

    A few years back I experimented with a tube car chassis by using a hole saw instead to avoid this, simply cut the hole in one tube and slipped the over-length tube into the hole, worked a treat.

    Surprising how great an angle you can cut on as long as the pilot drill is long enough to stay in the pilot hole.


    Oh, another one I did intentionally had 50mm main tubes, 30mm secondary tubes and 20mm braces, each tube size could be simply cut off and the gaps were fine for welding, eg; no fishmouthing required.


    Material doesn't matter, same processes apply.
     
  15. Mar 28, 2017 #15

    Swampyankee

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    Brazing is used quite a lot, not just on steel bike frames, but in places like hot end vane assemblies in gas turbines. If you go to lugged construction, like a steel bike frame, the lugs need to be carefully designed and made to tight tolerances, as brazing is more analogous to a glue joint than a weld. It's fairly normal for the lugs for custom frames to be investment cast and, I suspect, reamed to the right size.
     
  16. Mar 28, 2017 #16

    Hot Wings

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    Maybe not scary for you, I, and a bunch of others, but the very fact that threads like this exist implies that it IS scary for some. "Easy" is also relative. There are builders out there that don't have the eye/hand coordination needed and some, even with practice, can't seem to get the basics. My step-son is one of those..... :ermm:

    Another factor to consider is that in some municipalities/condos/apartments welding and gas bottles are forbidden.
     
  17. Mar 28, 2017 #17

    Himat

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    In the same sense as building an airplane of wood is easy. After all woodworking is easy.;)
    Like riveting together an aluminium plane is. Or make the airplane in carbon and/or glass composite. It does take some practice, planning and require some tools, but difficult no.:gig:
     
  18. Mar 28, 2017 #18

    lathropdad

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    In England during WWII they developed a low temperature welding process to build airplanes with the available steel. The steel was not very good when welded and this process over came that issue. The alloy is nickel bronze. The actual alloy can be imported from England. It is gas welded and the flux is mixed with the acetylene during welding.

    This process is used today to build race cars in England. It has the advantage that is a very fast welding process and not difficult to learn. The process requires special attention to joint preparation to eliminate any potential for contamination. However, I was taught that is should not be used with 4130 alloy tubing.

    One post suggested tacking a fuselage together with a MIG gun and then finish the job with TIG. I have been doing TIG welding for 40 years and I have never been able to carry a TIG weld through a MIG weld without contamination issues. My experience is that the 2 systems are absolutely incompatible.
     
  19. Mar 29, 2017 #19

    blane.c

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    I worked in a motorcycle fab shop for a short while in the 70's. The construction technique for frames was mild steel tubing and brazing with fingerjoints in critical stress areas. These bikes were on the track with the Kawasaki H2R, a 750cc three-cylinder driven by Yvon Duhamel and other famous bikes and racers of the day. They performed respectfully against the two strokes of the time while they were running but suffered from the timing chain stretching as it was the week link in the engine at the time. The frames were brutally tuff and could stand the riggers of going over 160mph on the straightaways and hard braking into and acceleration out of the corners of world class road racing courses. I asked Ted Hansen the engineer and owner of the shop why he chose mild steel and brazing? He explained to me that a properly brazed mild tube steel frame was more forgiving of vibration than a welded frame. While it is not "classic tube construction" there is nothing wrong fundamentally with properly fingerjointed and brazed mild steel tubing.
     
  20. Mar 29, 2017 #20

    cluttonfred

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    OK, I'll bite, I know what finger joints are in wood but how do you finger join steel tubes at an angle?
     

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