Bolted Connections / Gussets.

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by proppastie, Sep 15, 2016.

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  1. Sep 15, 2016 #1

    proppastie

    proppastie

    proppastie

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    Peery has an easy explanation of a bolted fitting example Fig 12.22 attached. The question comes up as to how is this handled if the fitting is attached to 2 parts as in a gusset. Are the loads on either of the parts the same as calculated or are these loads handled differently or separately. I have highlighted perhaps relevant sentence in PDF but not sure how that would effect the loads on the sub structure.

    Peery fitting2.jpg
     

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  2. Sep 15, 2016 #2

    Matt G.

    Matt G.

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    I'm not sure I understand the question. The method assumes both pieces are infinitely rigid and that fastener loads developed are due to the relative position of the fasteners with respect to each other and the applied load. The part you highlighted basically means that you make assumptions to deviate from the 'rigid body' assumption based on the configuration of the joint.

    I'm not sure what "the fitting is attached to 2 parts as in a gusset" has to do with the example you provided. In a gusset, the axial (and bending, if applicable) load in each member is transferred to other members via the gusset. If you take an imaginary section cut between the two members of the joint, the load is the same. The sum of the forces must equal zero. Can you provide an example of what you are actually trying to analyze? I'm not sure you're asking the right question or if I'm providing the right answer, or neither...
     
  3. Sep 15, 2016 #3

    proppastie

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    rather than use my design I decided to modify the worked example. The plate in the modified example would be a gusset and join two flat plates shown in red. I think you have answered my question in that the loads in the example say for Rivet 6 of 440 # are only good for the plate/gusset, and that 440# would not be the load on the red plate under the gusset for rivet 6. I am trying to size gussets and bolts.

    pod2.jpg
     
  4. Sep 16, 2016 #4

    Autodidact

    Autodidact

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    I don't see how
    is saying
    If a rivet or bolt connects two pieces, such as a gusset to a plate, then the load on each piece that is transferred from one to the other by that rivet or bolt is the same. A gusset may need to take into account buckling in addition to bearing strength to determine its size, but the load should be the same IIRC. Does Peery say different somewhere?
     
  5. Sep 16, 2016 #5

    Matt G.

    Matt G.

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    Proppastie, let's back up a step and get the cart behind the horse where it belongs.

    Draw a free-body diagram with the bolted/riveted joint you are trying to size, including the applied load and all necessary dimensions. If you want advice on a specific example, provide the specific example...
     
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  6. Sep 16, 2016 #6

    proppastie

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    It is unreasonable to expect someone to check this. Peery example lines 1-10, gusset lines 12-28....
     

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  7. Sep 16, 2016 #7

    proppastie

    proppastie

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    4 bolts aft pipe
     

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  8. Sep 17, 2016 #8

    proppastie

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    See post 6 and 7 and that is the question I asked....if I knew the answer I would not ask. Matt says the method assumes rigidity. The calculated load for rivets 5,6,9,10 are different post 6 & 7...looking at post 3 that gusset is the bottom gusset. The reference system is rotated to match the example. The load is 2100 lb (6g Ultimate gear load) located 1/2 between wheel and skid. Per Glider Criteria Page 39. I show the gusset for post 7 however I really am looking at the load on the Tube from those bolts as per the title of the post 7. And assuming the method, assumptions and calculations are correct this design fails in bearing on the aft tube.
     
  9. Sep 17, 2016 #9

    Autodidact

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    OK. I think I may be confused by your syntax; are you saying that the load on a gusset and plate connected by the same rivet is different for the gusset than it is for the plate? Or are you referring to a rivet #6 on two different connections altogether?

    If you have a gusset that connects two plates together, then you have two connections - one plate to the gusset, and then the other plate to the gusset, and I believe you would calculate the loads for each of those two connections separately, instead of assuming that one is a mirror image of the other. Or am I still not understanding the question?

    On the other hand, were you asking if the calculated load in the example from Peery could be valid/correct for the load on your design, which is almost certainly different than the Peery example?
     
    Last edited: Sep 17, 2016
  10. Sep 17, 2016 #10

    Autodidact

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    Ugh. You've clearly done something pretty complex judging from the spreadsheets, so disregard any or all of the above unless it applies in some way. It is almost impossible to tell from the spreadsheets (for me, anyway) what the problem is about. Please try not to take this as ragging on you, but you have a tendency to complicate things; the drawings are difficult to follow and don't look like free body diagrams as I am used to them. I can't see any similarity between the dwg in post #3 and the dwgs in the spreadsheets, and I can't see where the loads are applied.
     
    Last edited: Sep 17, 2016
  11. Sep 17, 2016 #11

    proppastie

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    Guilty...Perry example has nothing to do with my case except to setup and prove the spread sheet.....I will modify and re-post #3 to show the loads and explain hopefully better.....

    "one plate to the gusset, and then the other plate to the gusset, and I believe you would calculate the loads for each of those two connections separately, "

    I believe answers the question.
     
  12. Sep 17, 2016 #12

    Autodidact

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    choppergirl and pictsidhe like this.
  13. Sep 17, 2016 #13

    proppastie

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    to add clarity.....thanks much for the help. Reference system rotated to match example. I think this method requires moment on horizontal or vertical axis.

    peery4.jpg
     
  14. Sep 17, 2016 #14

    Autodidact

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    Wish I'd kept my big mouth shut, now. :whistle: If you're not in a hurry, I'll try to get around to looking through a book or two to see what I can find on this; you've got three members connected by the same gusset, but maybe it's not impossible...There's also the mass of the pilot to consider.
     
  15. Sep 17, 2016 #15

    harrisonaero

    harrisonaero

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    Flabel goes through this. Suggest his book and engineering course (I went through it a long time ago and Mr. Flabel lives in my hometown and publishes the book from here). But when you do please don't post illegal scans from his book. Nor Peery's. When I was looking for an Aircraft Structures answer key I was in contact with the Peery family. They are very nice and the book is still in print and helpful for aero structures engineers so they should be supported. Mods, can you pull the attachment?
     
  16. Sep 17, 2016 #16

    proppastie

    proppastie

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    unless what I did is wrong.... I think it is just a matter of sneaking up on it. The spread sheet really helps. 6x350=2100 (4 g limit) on gear.

    Basic Glider Criteria p39.jpg
     
  17. Jan 27, 2017 #17

    proppastie

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    I am finally getting to the detail design for the boom.....and realize I am missing something that unless is done right will result in another failure in test.

    Shown is the configuration of my gussets joining the tubes. I can easily calculate the stresses on the bolts using the spread sheet however I am not sure what is the correct input. The whole gusset passes as shown and if I analyze the tubes stress underneath the gusset as in case 2 every thing is fine.

    However if I am supposed to analyze only the line of holes for an individual tube as in case 1 ....no good... not enough holes for the moment.

    Which is the right analysis for the tube under the gusset.

    gus1.jpg
    gus2.jpg

    Edit: if post 9 is the answer I am screwed, the gussets will be as big as the tube, twice as many holes? for each tube?
    please forgive if I ask the same thing over, been working 3 days on this.
     
    Last edited: Jan 27, 2017
  18. Jan 27, 2017 #18

    proppastie

    proppastie

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    I have also done this analysis all 80 holes (door # 3)

    gus3.jpg

    and Matt seems to suggest I should do this (door #4)

    View attachment 58431
     

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    Last edited: Jan 27, 2017
  19. Jan 27, 2017 #19

    harrisonaero

    harrisonaero

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    Are you doing your engineering by consensus? May I suggest you take this course? It will answer these questions plus many more and I think you'll find the money *very* well spent (as will your loved ones).

    http://www.psa1.com/distantlearning.html
     
  20. Jan 27, 2017 #20

    proppastie

    proppastie

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    Thanks for the link. Considering this could be the last stress question I need to ask, it might be easier to hire a consultant. Do you know any good consultants?
     

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