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Thread: Spitfire wing bolt observation

  1. #31
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    The bolt is designed to be stretched as it is torqued up...
    Interesting theory, but it falls down (as mine does) by the lack of critical (or any) torque figures for the nuts!
    Last edited by Creaking Door; 14th May 2017 at 15:23.
    WA$.

  2. #32
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    Looking at moment but to me bolts are in sheer so nut torque would be negligible..Having them shouldered down is a tell on the torque they need..
    "If the C.O. ask's you to be Tail End Charlie...just shoot him!!!....A Piece of Cake.
    http://spitfirea58-27.blogspot.com.au/

  3. #33
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    To be civilised, this conversation really needs a pub, with a publican that doesn't like to sleep !
    On the lack of torque data and bolts in shear - bolt stretch is how bolts work and bolts are not designed to take shear loads as their primary design function. Without getting the ouija board out and calling up Barnes Wallis I assume that the shouldered bolt acts as a STOP, in other words you can tighten up the nut as much as you want but once it hits the shoulder, that's it. I am not too familiar with the ridiculous telescoping spar design of Heinkel elliptical wing designed Spitfire (just getting your beer frothed up), but I assume the shouldered bolt was designed to stop the chance of tube crush in the spar. If you kept on tightening it once it hit the shoulder, the bolt would eventually break at thinnest point, but I do not think the form was dictated by this function.

    There would have to have been mechanical torque ratchets in Grandpa's hands. There would have to have been a tightening sequence in a group of bolts. How all this translated to a field depot in the middle of the night in the middle of winter might have been quite different.

    A bolt that was more elastic, that could store more energy, would maintain it's clamping force as the stresses of flight impacted on the joint, like the waves of phosphorescence giddying through the translucent body of some disturbed deep sea jellyfish. (the beer is taking effect). It's like squeezing a rubber ball in one hand, and a cricket ball in the other, then getting an eight year old to try and chop either of the balls out of your hands. The less elastic joint is easier to work apart.

    The way to test this theory is to take a hollow bolt, and a solid bolt, and clamp two separate test pieces together, using the same torque, and measure the stretch in each bolt.
    I actually think you could test this theory out with a CAD model on Solidworks, and run some analysis over it, where the metallurgy is the same.
    Got some dimensions?

  4. #34
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    There is no crush on the tubes, as the nested tubes have a solid machined centre at this point.

  5. #35
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    Ed
    A row shouldered bolts each with a transition fit are designed to only take shear. Ref. http://digital.lib.lehigh.edu/fritz/pdf/271_13.pdf. Tension bolts are another way to bolt things together.

    The hole in the bolt is to tune the stiffness so to prevent the slightly larger oversized i.e reworked bolt, attracting a disproportionate amount of load. If the rework is in specific locations in the row, a different size hole is required thus you will notice several different hole sizes.
    Last edited by Vega ECM; 15th May 2017 at 20:50.

  6. #36
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    As Bruce says the tubes can't crush
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  7. #37
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    Great photographs! Can you do me one of one of the bolts in position but in front of the end of the spar-boom; I've always wanted to know just how much of the spar-boom is cut-through by the bolt holes?
    Last edited by Creaking Door; 15th May 2017 at 23:09.
    WA$.

  8. #38
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    A row shouldered bolts each with a transition fit are designed to only take shear...

    http://digital.lib.lehigh.edu/fritz/pdf/271_13.pdf
    That would seem to fly-in-the-face of all I thought I knew about bolted joints on structural steelwork!

    For example, the bolts in the bolted joint at the bottom of one of those old skyscrapers would need to take the weight of everything above it; all the steelwork, all the concrete, all the brickwork, everything! Unless the steel columns are formed end-to-end into one continuous column and the bolted joints just hold these in place?
    WA$.

  9. #39
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    TDP, yes, great photo ! It gets me thinkin' that the spar design was kind of like an old school automobile leaf spring, the telescoping tubes sliding inside each other as the wing bent up and down. In this case each tube is stretching along its length, and a buckling tube face is opposed by a face in tension, creating ying yang serendipity. Somebody in China should now build the world's tallest skyscraper using a telescoping shell central lift well as a structural spine, on the Spitfire spar principle.

    In this case the shouldered bolts are acting in shear, to anchor, all tubes, as the external clamping force might not be reliably transferred through a number of wall thicknesses, in the nightmares of the designer, but I still think this is secondary 'belts and braces'. The placement of a solid core implies the joint was meant to be 'clamped up', transmitting friction love across all tube faces, and the friction forces resulting are quite incredible. There is an idiot here, I mean Aussie, who has done some good broadcasting work recently testing scientific theories with his life. One example was bungee jumping with only an interleaved telephone book in the line, where the simple friction of the pages arrested his fall. Luckily there are a lot of Smiths in the book !

    I still think the shoulder was meant to stop you over tightening, as the aluminium would squeeze out like toothpaste under the clamping force of a steel bolt, and, over time, reduce joint effectiveness. As the evidence of wings coming off in belly up landings past the joint indicates, it was a very effective joint, probably over engineered, as high speed monoplanes were all new in 1936. It looks like there was room for a straight through conventional bolt and larger nut. In earlier pin jointed structures a straight through bolt would be used with a ferrule - so the Spitfire bolt and its reaming kit is kind of the same thing.

    I'm not trying to be a smart **** but I can't slot this away until definite dimensional proof blows the theory out of the water that the cross sectional mass of the hollow shaft equals the cross sectional mass of the threaded section to allow even bolt stretch. Consequently more load put into the bolt, as distinct from a solid shaft bolt of the same metallurgy.

    The nearest thing I can find to this hollow bolt in the detritus of my mind are hollow rivets, which were based on a great deal of 1930's developed science on hollow tube performance. No rivet was primarily designed to act in shear, although it would have a degraded, secondary performance in shear, if the primary tension/friction function failed. I kind of think this hollow bolt came from that.

    I don't see hollow bolts out there today. It's like stumbling onto a lost island and seeing some archaic proto human branch of the bolt family tree. It's fascinating ! So somebody could build the highest skyscraper in the world using articulated joints connected by more ductile hollow bolts - and claim this as an amazing new invention in 2018!

    More beer, wench !

  10. #40
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    The placement of a solid core implies the joint was meant to be 'clamped up', transmitting friction love across all tube faces, and the friction forces resulting are quite incredible...
    That was exactly the way I thought the joint worked, forgetting the lack of any torque-up figures for the nuts, obviously.

    The more I look at this joint the more it confuses me; the spar-boom will always fail above and below the outermost bolt so no matter how good, or how many, bolts there are inboard of this they will not improve the joint one jot! Unless their job is to spread the 'clamping up' forces over a greater part of the in-contact area of the spar-boom and the centre-spar inboard of it?
    Last edited by Creaking Door; 16th May 2017 at 00:17.
    WA$.

  11. #41
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    The hollow bolt is the first one that I have ever seen in 50 years.

    Following assembly of the square tube wing spar booms a press is used to bend the dihedral some inches outboard of the bolts.

    If the clamping loads of the bolts was prime it would put massive loads in compression on the U channel on frame 5 that separates the fuselage carry through spars.

    'Shearly' not.

    Mark
    Last edited by Mark12; 16th May 2017 at 05:51.
    "...the story had been forensically examined and was deeply impressive. I knew that the whole story was a load of myth and baloney…"

  12. #42
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    I can't see how any bolt with a split pin can have a torque figure, especially if it only has one hole, the spar cannot work as a leaf spring, because it has a million bolts through it stopping any internal movement, almost every bolt designed to apply a clamping load would have a proper head not a slot; as I see it, the reduced thread and nut is purely weight saving, (as is the slotted head) of course there will be a clamping load applied with the "shear"number of bolts used.
    Why be your own worse critic, that's what the forum is for.

  13. #43
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    Quote Originally Posted by Stuart Gowans
    I can't see how any bolt with a split pin can have a torque figure, especially if it only has one hole,
    Is the hole not drilled after the nut has been torqued up?
    Martin

  14. #44
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    Personally I have never seen this, especially in mass production, accessibility notwithstanding most aero bolts (indeed all things spitfire) are high tensile making that difficult; Rolls Royce didn't use torque wrenches on the assembly of Merlins (etc) as everything was pre drilled and then hardened.
    Why be your own worse critic, that's what the forum is for.

  15. #45
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    Quote Originally Posted by Stuart Gowans
    Personally I have never seen this, especially in mass production, accessibility notwithstanding most aero bolts (indeed all things spitfire) are high tensile making that difficult; Rolls Royce didn't use torque wrenches on the assembly of Merlins (etc) as everything was pre drilled and then hardened.
    Thanks for the info - I have only seen the post-torque drilling in other industries.
    Martin

  16. #46
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    And the bolt steel is S1 - 35T ultimate strength carbon steel, not hardened, apparently

  17. #47
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    The mounting (tapered?) bolts for the engine-bearers on the Spitfire were tightened-up (torqued?) and then drilled through with the castellated-nut in situ; Guy Martin drilled these on his Spitfire TV show.

    Traditionally when torquing a castellated-nut onto a bolt the nut is torqued and then further tightened to the next alignment of nut and hole so a maximum additional turn of less than 60° Is needed; if the bolt is cross-drilled the additional turn is less than 30°.
    Last edited by Creaking Door; 16th May 2017 at 08:35.
    WA$.

  18. #48
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    If the clamping loads of the bolts was prime it would put massive loads in compression on the U channel on frame 5 that separates the fuselage carry through spars.
    As a u-channel Frame-5 couldn't really resist compression loads well anyway but it wouldn't have to; the bolt compression of the spar-booms would produce very little movement since the spar-booms are solid.

    Again, all this falls down because, apparently, there is no critical requirement to torque-up the nuts anyway!
    WA$.

  19. #49
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    Shouldered bolts prevent overtorquing when "torquing" up an item as it acts as a natural stop. I say "torquing" as in the action of doing up the nut is imparting a torque upon it.

    Last edited by TonyT; 16th May 2017 at 10:27.

  20. #50
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  21. #51
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    Incidentally re torquing and split pinning, the Wessex employed shim washers on some fittings, you peeled layers off the washers until you got the desired position etc.

    interesting read

    http://www.pprune.org/tech-log/44353...e-mustang.html
    Last edited by TonyT; 16th May 2017 at 10:34.

  22. #52
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    [I"Guy Martin drilled these on his Spitfire TV show".
    ][/I]

    Must be true then! I'm sure I'd want bits of swarf floating around the engine bay!
    Why be your own worse critic, that's what the forum is for.

  23. #53
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    This is a slide on photo, but I think it is worth noting that this section of spar came from a BoB crash, I had the whole of both top spar booms with about 3feet of wing spar each side bent like a banana !
    The point being the three bolt holes were still fully bolted and the holes are not fractured or pulled after hitting the ground vertically at high speed.....

    Jules
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  24. #54
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    Thanks for posting that photograph; those holes don't cut through as much of the spar-boom as I thought.

    What I'd really like is some dimensions so I could do some basic calculations: just the diameter of the bolt and the outside size of the outer box-section of the spar-boom.
    WA$.

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