Key.Aero Network
Register Free

Page 1 of 2 12 LastLast
Results 1 to 30 of 54

Thread: Spitfire wing bolt observation

  1. #1
    Join Date
    Oct 2009
    Location
    Oxfordshire
    Posts
    454

    Spitfire wing bolt observation

    While cleaning some of the wing bolts found, I noticed that some were hollow, and some solid, anyone care to explain why ?
    Also a close up of one shows a 330 part number, Mk3 ?

    Jules
    Attached Images Attached Images  

  2. #2
    Join Date
    Oct 2009
    Location
    Oxfordshire
    Posts
    454
    Another photo, sorry taking a long time to load !
    Attached Images Attached Images  

  3. #3
    Join Date
    Oct 2009
    Location
    Oxfordshire
    Posts
    454
    And another
    Attached Images Attached Images  

  4. #4
    Join Date
    Oct 2009
    Location
    Oxfordshire
    Posts
    454
    Last one !
    Attached Images Attached Images  

  5. #5
    Join Date
    Jan 2000
    Location
    Angels one-five over North Bucks.
    Posts
    10,465
    I suspect that the hollowed out wing bolt is for weight saving.

    On the new Mk VIII/XIV wing the two centre bolts of the four on the lower spars were increased in diameter by a significant and visual amount.

    If the required 'shear modulus' could be maintained with a hollow bolt...every little helps.

    It would be interesting to measure the precise length of the bearing surface diameters. The Mk VIII bolts should be slightly longer by 2 x 16SWG than the Mk V.

    Mark
    "...the story had been forensically examined and was deeply impressive. I knew that the whole story was a load of myth and baloney…"

  6. #6
    Join Date
    Oct 2006
    Posts
    8,142
    You dont think they have had problems getting them out, so have drilled them for an easy out or to relieve there fit?

  7. #7
    Join Date
    Nov 2003
    Location
    SPL Rad112/09DME
    Posts
    1,491
    The holes look too neat for that. That is, I was never able to get a result like this!
    A Little VC10derness - A Tribute to the Vickers VC10 - www.VC10.net

  8. #8
    Join Date
    Oct 2006
    Posts
    8,142
    Lol I do.

  9. #9
    Join Date
    Oct 2009
    Location
    Oxfordshire
    Posts
    454
    no, they are there for a reason, i thought perhaps it was a material reducing exercise late in the war ? remember the early Mk1's had Stainless Steel bolts, sadly we have not found a single one of those.

    looking at some of the threaded ends, you can see where they were belted with a hammer to drift them out !

  10. #10
    Join Date
    Jul 2012
    Location
    Melbourne, Australia
    Posts
    932
    I find these things fascinating. A hollow bolt would be there for a definite reason, and I am not so sure that weight or material saving would be the primary reason. I do not know the reason, but I would throw these guesses out, and would love to follow the story to a definite conclusion.

    1. Interference fit.
    A tight fit for a wing connection is good practice, evidenced by the use of drift to drive it out. The bolt may have been frozen, to aid insertion into a spar fitting at ambient temperature. As it heated up to ambient it would expand to an interference fit. A hollow core bolt may shrink further than a solid bolt. In reverse, the injection of a stream of readily available compressed gas, such as CO2, into the hollow, to freeze the bolt, might have allowed it to shrink and be removed more easily.

    2. Protection against failure.

    The bolt is designed to be stretched as it is torqued up. It might fail in tension at the shoulder, where the threaded, narrower dimension meets the body of the bolt. The difference in mass of a solid bolt body and the shoulder concentrates stress in this point. If the bolt is hollow, the stress is spread over the length of the bolt, as there is less difference in mass. The whole bolt stretches evenly, and deals with service stresses evenly. This is the same principle as the waisted conrod end cap bolt in the Merlin. However, for the spar joint, the connection or surface area meeting between the outside of the bolt and spar fitting is critical, so the waist becomes a hollow.

    Something else is niggling me about even heat treatment, but this would be secondary.

    I would be surprised to see stainless steel bolts in this application, given the propensity for work hardening due to cyclical service stresses, and electrolytic corrosion between aluminium spar, unless this was a Seafire type thing.

    Most fascinating. I must light up my pipe and think about this some more. Well done Sir, a bloody good question !

  11. #11
    Join Date
    Jul 2012
    Location
    Melbourne, Australia
    Posts
    932
    Only if it is specified on the drawing as British Standard S2 material, is it possible to get a copy of the drawing specifying this, and a chunk of bolt, to do metallurgical analysis on ? I am punting it is nickel chromium alloy steel. What is the material specification for the bolt ? It may be a later NiCr composition....

  12. #12
    Join Date
    Jan 2000
    Posts
    9,879
    They aren't interference fit - drawing states 'P' fit. You should be able to push them in, and, when required, push them out again!

    Originally manufactured from S1 material. Not heat treated.

  13. #13
    Join Date
    Nov 2008
    Location
    Lancashire
    Posts
    792
    I also understood that the Spitfire wing bolts were required to be interference fit.

    The Mk.3 was the first Spitfire to have the stronger "universal" wing, so it is possible that a change in wing bolt design was required. It was Supermarine's habit to carry forward the designation of parts to later Type Nos, as long as the part itself was unchanged.

  14. #14
    Join Date
    Jan 2000
    Posts
    9,879
    It was a long held misconception. For many years, post service, Spitfires were assembled with frozen bolts, beaten in with a firm hand. Until the original drawing turned up that is, along with an original unused wing reaming kit. Using the original kit, with its Go/No Go gauges, and with a bolt made to the drawing demonstrated the truth of the matter.

  15. #15
    Join Date
    Jan 2000
    Location
    Angels one-five over North Bucks.
    Posts
    10,465
    Quote Originally Posted by Graham Boak
    I also understood that the Spitfire wing bolts were required to be interference fit
    Location or transition fit.

    https://www.google.co.uk/?gws_rd=ssl#q=transition+fit
    "...the story had been forensically examined and was deeply impressive. I knew that the whole story was a load of myth and baloney…"

  16. #16
    Join Date
    Jan 2000
    Location
    Angels one-five over North Bucks.
    Posts
    10,465
    Because of the tolerances, with a 'Transition' fit some bolts will be slightly tighter than others.

    With the worst case, biggest bolt in the smallest hole, we are only talking .0001's". They might drift in but not be so keen to drift out in other climes outside the factory.

    They all come out eventually, usually with bruised ends and sometimes the bore slightly scarred.

    To this end using the special reamer kit mentioned by Bruce the holes are opened up by .004" on diameter and an over size bolt fitted.

    This can be done several times up to at least .016" and possible more.

    Because these over size holes will impact on the fitting and or exchanging of replacement wings, they have to be recorded on a special plate attached adjacent to both the fuselage and the wing.

    For good measure both the RAF serial and the main cockpit c/n are all stamped on the plate and these plates have been a major implement in identifying orphan Spitfires around the world.

    Mark

    Last edited by Mark12; 9th May 2017 at 13:50.
    "...the story had been forensically examined and was deeply impressive. I knew that the whole story was a load of myth and baloney…"

  17. #17
    Join Date
    Jan 2005
    Location
    Glorious Souffff
    Posts
    4,844
    rumour has it the wing bolts on the RAF EF spitties pushed in and out by finger pressure they'd been removed/refitted so often

  18. #18
    Join Date
    Sep 2006
    Posts
    9,396
    There has always been something that has bothered me about the design of the Spitfire wing-fixing (and the design of the spar ends in general): the box-section within box-section design is well-known but at the (crucial) inner-end the wing-fixing bolt-holes are drilled clean through most of these box-sections leaving perhaps only the outer two able to transfer any stress to the fuselage fixing-brackets.

    Also it seems clear to me that the bolts themselves are not supposed to take any stress in shear; in a tension failure of the lower-spar fixing the aluminium alloy spar material above and below the outer bolt will surely fail long before the outer bolt fails (in 'double' shear). And the bolts inboard of this will simply hold the broken end of the spar firmly to the fuselage as it plummets to earth; a chain (of bolts) is only as strong as its weakest link!

    I'm willing to bet that the nuts fitted to these bolts are torqued-up to some pretty exact figure?

    The design of the bolts is also rather curious; the shank of the bolts is large (and hollow) and yet the threaded portion is much smaller (and much, much, weaker). And since the whole of the tension in these bolts must be taken by the weakest part, the narrow threaded section, why are the bolts the size that they are at all; the same tension could be taken by a bolt with the same diameter as the threaded portion. Bear in mind also how a smaller hole through the spar to accommodate the smaller bolt would 'improve' the design of the spar.

    So these bolts aren't working, aren't designed to work, in the way we maybe think they are designed to work.

    My guess is that the stress of the wing-load is actually transferred by friction between the outer spar box-section and the fuselage fixing-brackets; the (many) bolts provide the force holding the surfaces in contact and friction does the rest. For this it is essential for the force to be spread to the right areas of the spar, the outer box-section, and for the (solid) spar not to 'crush' under the bolt tension (nor 'fret' over time undermining that tension).

    Just my theory!
    Last edited by Creaking Door; 9th May 2017 at 22:14.
    WA$.

  19. #19
    Join Date
    Jan 2000
    Location
    Angels one-five over North Bucks.
    Posts
    10,465
    Quote Originally Posted by Rocketeer
    rumour has it the wing bolts on the RAF EF spitties pushed in and out by finger pressure they'd been removed/refitted so often
    Here is one from the EF I pressed out earlier, at the RAFMus.

    Mark

    "...the story had been forensically examined and was deeply impressive. I knew that the whole story was a load of myth and baloney…"

  20. #20
    Join Date
    Jan 2000
    Posts
    9,879
    Ouch! Is that the Mk 1 late of the Battle of Britain hall?

    Creaking Door - There is no Torque figure for the nuts. A good nip and fit the split pin. Note - the wing never breaks at this point. Even in a bad accident, this joint tends to stay intact; and the basic design was also used on the Attacker, Swift, and Viscount that I know of.

    About three years ago, I found a reaming kit in a junk shop in Norwich. It was for the larger oversize bolts, +20, +24 etc. It was passed onto one of the restoration shops.

  21. #21
    Join Date
    Sep 2006
    Posts
    9,396
    I think you may have 'bruised' the fixing-bracket slightly!
    WA$.

  22. #22
    Join Date
    Jan 2000
    Location
    Angels one-five over North Bucks.
    Posts
    10,465
    Quote Originally Posted by Creaking Door
    Also it seems clear to me that the bolts themselves are not supposed to take any stress in shear; in a tension failure of the lower-spar fixing the aluminium alloy spar material above and below the outer bolt will surely fail long before the outer bolt fails (in 'double' shear). And the bolts inboard of this will simply hold the broken end of the spar firmly to the fuselage as it plummets to earth; a chain (of bolts) is only as strong as its weakest link!
    Wing separation from the fuselage in duress occurs on the wing spar booms above and below the innermost holes leaving the stubs still bolted to the fuselage carry through spar...the weakest cross section link.

    That is why they fail at quite modest horizontal fore and aft deflection such as an impact load on the leading edge or trailing edge, in reverse, during a wheels up landing.

    The normal vertical loadings on the wing bolts during landing and high G aerial manoeuvres just put the bolts in shear.

    I believe the clamping torque of the bolts is not the prime factor in taking the normal vertical operational loads.

    Mark

    Last edited by Mark12; 9th May 2017 at 16:17.
    "...the story had been forensically examined and was deeply impressive. I knew that the whole story was a load of myth and baloney…"

  23. #23
    Join Date
    Sep 2006
    Posts
    9,396
    Creaking Door - There is no Torque figure for the nuts.
    Really? That's kind-of blown my theory out of the water!
    WA$.

  24. #24
    Join Date
    Nov 2007
    Posts
    1,895
    Does the absence of the original drawings mean that a lot of restorations had the wings fitted incorrectly?

  25. #25
    Join Date
    Oct 2006
    Posts
    8,142
    You think that's bad when I was at Cosford we were having a discussion with one of the staff, when they were prepping the aircraft for the swap round they found some had hardly any bolts fitted indeed I think he said the Dinah only had a couple of engine bolts in lol.

  26. #26
    Join Date
    Oct 2005
    Location
    South Glos
    Posts
    385
    The distribution of load in bolts or pins when you have a number of them in a line is a nightmare;- the problem is that if I have four pins on a row, each designed to take 1/4 of the load, I must prevent one from bearing more than it's fair share I.e should it pick up more than it's designed to take it will fail ........and then so will all the rest. I know a chap who quite literally wrote a book on the subject.......not a prize winner but it shows just how much there is to this subject.

    In essence you have to adjust the stiffness of individual elements, in this case by drilling a hole in the pins, to encourage it to flex slightly in so doing it offloads on to its partners. I suspect there's (or maybe was) a table which details for certain oversize combinations in the row of pins, other locations must have pins which are drilled to certain sizes to ensure the whole joint is correctly balanced.

  27. #27
    Join Date
    Jan 2009
    Location
    In the shed
    Posts
    110
    You appear to have quite a collection of rusty bolts. Do you think you could spare a couple for 'tommytheace' and his splendid Spitfire project?

  28. #28
    Join Date
    Oct 2009
    Posts
    375
    Looking at the "bolt" it appears to be more a retaining pin? when tight do the nut's tighten against the shoulder of the pin or squeeze frame five together? It's a fascinating look at the engineering and thinking of those day's. did any other aircraft of the time use the same wing location scheme?

    I'm sure you've all seen it but in the video at 48 mins is when they fit the bolts discussed. https://www.youtube.com/watch?v=i7Zebpu2nS4
    Last edited by minimans; 9th May 2017 at 23:55.

  29. #29
    Join Date
    May 2005
    Location
    Aerospace Valley
    Posts
    4,247
    Quote Originally Posted by Bruce
    It was a long held misconception. For many years, post service, Spitfires were assembled with frozen bolts, beaten in with a firm hand. Until the original drawing turned up that is, along with an original unused wing reaming kit. Using the original kit, with its Go/No Go gauges, and with a bolt made to the drawing demonstrated the truth of the matter.
    I remember an original kit showing up at the TFC hangar one day. I think some old guy just walked in with it & asked "Is this any use to you?"
    If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: It's all balls. RJM.

  30. #30
    Join Date
    Jul 2012
    Location
    Melbourne, Australia
    Posts
    932
    Jules,
    Is it possible to measure the outside diameter of the 'holey bolts' (there seem to be two sizes) and the inside diameter of the holes to figure out whether the below theory has merit :

    "The bolt is designed to be stretched as it is torqued up. It might fail in tension at the shoulder, where the threaded, narrower dimension meets the body of the bolt. The difference in mass of a solid bolt body and the shoulder concentrates stress in this point. If the bolt is hollow, the stress is spread over the length of the bolt, as there is less difference in mass. The whole bolt stretches evenly, and deals with service stresses evenly. This is the same principle as the waisted conrod end cap bolt in the Merlin"

    If the punt holds then the cross sectional area of the hollow shaft equals the cross sectional area of the threaded end. I would be interested to know how deep the hole goes too, and the length of the shaft and threaded section.


    Understanding that these bolts are a humble carbon steel, they were designed to be quite ductile, which makes me think this is all about bolt stretch. Getting the torque, and stretch, right was critical. Maybe the original design was meant to fail if you over tightened it, in other words the narrow threaded section would fail. Apart from the space limitations of fitting a larger nut, I can't see why they they wouldn't have used a bolt of consistent diameter all the way through, as they do for modern structural bolting applications, assisted with washers that distort and signal correct torque. It's a weird bolt. Where's Barnes-Wallis when you need him !

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

- Part of the    Network -

KEY AERO AVIATION NEWS

MAGAZINES

AVIATION FORUM

SHOP

 

WEBSITES