Rivets

Discussion in 'Other Mechanical Systems Tech.' started by VALENGO, Apr 3, 2010.

  1. VALENGO

    VALENGO Member

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    Every single picture of a WWII bird shows lots of rivets, you must not apply much zoom to be striken for hundred of them... until you watch pictures of Me210/Me410. Even in best pictures, and applying a good amount of zoom, barely can be distinguished a few rivets; those planes had almost no rivets!.
    Here, the question: why?.
    Did germans invented the epoxy too? :shock:
     
  2. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    A few things here...

    For the most part rivets actually gave little drag problems in the bigger picture. There were even some rivets that were countersunk, so that's why in some instances you seen aircraft with surfaces that were smooth. The problem with countersunk rivets is they are not as strong as "button" head rivets and will require either a 'dimple' or countersunk to fit into the structure being riveted. Many times engineers made decisions on aerodynamic requirements as opposed to strength to determine where and when countersunk rivets were to be used.

    I don't think the Germans invented epoxy, I believe every country had their own type of epoxy.
     
  3. VALENGO

    VALENGO Member

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    So the reason for the "no rivets look" is that they was countersunk rivets and they were not caught for the camera. I believed that it was due to some different constructive method, other than rivets, the answer was more simple.
    Well, Flyboy, thanks for the answer.
    P.S.: I was kidding about epoxy.
     
  4. sagindragin

    sagindragin New Member

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    because a lot of german aircraft have the rivets covered by filler,
    this was to give a more aerodynamic shape and made them slightly faster.
     
  5. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    #5 FLYBOYJ, Apr 4, 2010
    Last edited: Apr 4, 2010
    Not really true. Filler was tried by almost everyone making aircraft. It was time consuming to put on, came off easy and did not lend itself well for repairs in the field. There was sealants used for lap joints but for the most part you didn't cover up rivet heads.
     
  6. schwarzpanzer

    schwarzpanzer Member

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    Originally the Spitfire was based on the He70. The filler was thrown away, as it added too much weight for the reduction in drag. However, the flush Rivets were copied ( so too was probably the elliptical wing). There are letters to and from Ernst Heinkel and Reginald Mitchells assistants - very friendly ones too, where they happily give away their secrets.

    Domed rivets were also tested on the Spitfire - using Lentils, glued over the flush rivets. The desired goal was reduced production costs and time thugh, not the advantages FlyboyJ suggests (though those may have been advantages too, thanks Flyboy!). The reduction in top speed was considered too great to be worth it though, however.
     
  7. Sweb

    Sweb Member

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    #7 Sweb, Apr 4, 2010
    Last edited: Apr 4, 2010
    Not sure here, memory is getting old so maybe Joe can correct. I think the first use of the flush (100 degree countersunk) rivet was on the Hughes H-1. I think it was Hughes Aircraft that came up with the flush rivet. There are predominantly two types of rivets in use today for most aluminum airframes. They are the MS20470-Series Universal Head and MS20426-Series 100 degree countersunk varieties. Their predecessors, though literally of the same materials depending on part number, were AN470-Series and AN426-Series, respectively.

    Then there were many flush, or recessed head screws used. These can still be bought under the old AN number AN507-Series. The first dash number indicated the screw diameter and the second indicated the length in 1/16 inches. AN507-10-8 indicates a 10-32 screw 1/2 inch long, regular high-tensile slotted steel screw, for example. Replace the first hyphen with a "C", and the second hyphen with an "R" - AN507C10R8 - and we have a corrosion resistant steel, phillips head countersunk screw. The "507" denotes a size 10 screw with 32 threads per inch. The new number for it is MS24693-Series, but the dash number does not directly correspond to the same information as its predecessor. These were used as well as the old Dzus cowling and panel fasteners of varying types both round and flush heads.

    Otherwise, yes, round, or what is now called Universal Head, rivets were used where structural strength was needed most (on pursuits) but flush riveting was the norm. Also, certain planes were spot-welded. The center section/wing stub structure of the F4U-series was spot-welded. It saved a few hundred pounds of weight. Skins might have been nailed on but the internals were all spot-welded.

    Note: Way back the round head varieties of rivets were broken up into two types. One was the Round Head and the other was the Brazier Head. These have been cancelled and replaced by the Universal Head. The Brazier head was a low profile Round Head rivet. The Universal Head splits the difference in the heights of the manufactured heads between the two older, inactive designs.

    Believe it or not, I actually use this knowledge on a daily basis.
     
  8. drgondog

    drgondog Well-Known Member

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    the use of flush rivets is directed whenthe design engineer wishes to maintain laminar flow as much as possible to reduce drag.

    The first consideration fo rhe selection is the required rivet shear capability, matched to the shear stress applied to the skin from the rivet. If the shank of the rivet fails before the skin - you can consider going to next rivet size or plan closer spacing between rivets to get more rivets and less shear per rivet.

    Conversely if the skin 'tear out' shear forces are reached due to a small diameter flush rivet you have a similar choice - up the shank size to increase the surface area of the skin in contact with the rivet shank - or increase the number of rivets to spread the shear loads over more points along the edge of the skin.

    When designing for shear stress of a flush rivet - you may only consider thethickness of the skin to the vertical shank before it (the rivet head) spreads out at a 100 degree angle.

    That 'reduced thickness of the skin' (from the total thickness) multiplied by the diameter of the rivet is the area of calculation for the area and the resultant stress is S/A where S=equal load to be taken out by each rivet and A is the 'reduced area' of actual contact by the shank.

    For a pan head rivet the entire shank up to the base of the head equals the entire skin thickness, therefore a smaller rivet can perform the same job given equivalent rivet diameter and spacing.
     
  9. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Sweb - broke out the "Standard aircraft handbook" - and Bill, spoken like a true engineer!!!!
     
  10. drgondog

    drgondog Well-Known Member

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    Joe - I had to decompose the structural analysis of a Seacobra by 'hand' to validate the results of the first NASTRAN model the Army accepted.

    The one thing NASTRAN didn't do well at first was shear panels because the only 'elements' were 'plates' not panels.

    Yes, I have 'done em'
     
  11. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    ;) :thumbright:
     
  12. clinton78

    clinton78 Member

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    #12 clinton78, Apr 5, 2010
    Last edited: Apr 5, 2010
    Hi guys

    Countersunk flush rivets were used on most German aircraft although the majority still had minimal areas that would have the raised rivets in place. The Germans were very good at riveting and in some places the sunk flush rivets would be almost totally smooth with the aircraft skin. When an aircraft was quite new this would be the case mostly but after some service usage certain manouvers for instance diving would put the aircraft's structure under immense pressures and therefore the skin would become slightly warped and rippled at the points where the skin was fastened to the structure. For a fact Heinkel and Messerschmitt were applying putty to the flush rivet areas of the jet aircraft that they were producing and then sanding it smooth to help with the airflow. Below are some images of the Me262 and the He162 clearly showing the dark strips of sanded putty before primer and camouflage application. I do not know if Arado and Horten were doing the same.
    Me262-3.jpg
    he162-us.sout.JPG.jpeg

    Cheers :)

    Clint
     
  13. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    That could be said for all manufacturers. There was usually a tolerance of +.001 to -.001 if I remember correctly. Additionally a tool was developed to slightly shave the heads of countersunk rivet to meet tolerance requirements.
     
  14. clinton78

    clinton78 Member

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    Quite possible Flyboy.

    Rgds

    Clint
     
  15. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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  16. clinton78

    clinton78 Member

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    Quite definite Flyboy.:D

    rgds

    Clint
     
  17. gumbyk

    gumbyk Well-Known Member

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    I've seen a Corsair in pieces under refurbishment, and from memory, most of the old stucture looked like it was spot-welded. I was told that during the refurb, they were replacing the spot-welds with dimpled flush rivets.
    This was a while ago, and I've got a crap memory, can anyone shed any light on how common this was?
     
  18. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    I'll find that out the next time I go to Westpac as they are in the process of restoring one. One of the owners told me the Corsair is built like a "bridge" with trusses interconnecting girder type structure. It would not surprise me however as another aircraft from Vought, the Kingfisher had most of its primary structure spot welded and was the first aircraft to employ this.
     
  19. clinton78

    clinton78 Member

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    Hi Guys

    Taken from a topic discussing the use of all bare metal Bf109's (paint sanded/buffed off) with the hope of reduced drag/increased speed for catching Mosquitos. Although not a standard procedure:

    "10./JG300 had several machines in the line of intercepting the LSNF Mosquito(s) with the Bf109G-6/AS having the panel lines and rivets puttied over and a spray on polish was put over the A/C then buffed out to get more speed of which it did."

    Quoted from LEMB: Here!

    Rgds

    Clint
     
  20. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Good info - Lockheed did the same thing to the RP-80

    [​IMG]
     
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