Bending-beam spar carry through schemes

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cluttonfred, Nov 21, 2017.

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  1. Nov 22, 2017 #21

    cluttonfred

    cluttonfred

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    And if they can do it with the wings on a 15m span sailplane, just think how much easier it will be on a 9m span sport plane. ;-)


     
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  2. Nov 22, 2017 #22

    Victor Bravo

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    Yes... the total experience of owning and flying the aircraft is somehting that the European sailplane guys have nearly mastered. Now if we can just get the Euro to be like it was back when the Deutschmark was 25 cents, guys like me could buy another sailplane :) Sailplanes were ahead of their time for another reason; landing out in a field at the end of the day, and having to get the glider disassembled and into the trailer as quickly as possible, was one of the reasons that the sailplane designers so thoroughly developed their wing attach method. Now that the powered aircraft owners are paying attention to trailerability and storage space, the sailplane method is being seen as forward thinking and "my, what a clever idea!". The Spacek SD-1 is using this method very successfully.

    For Matthew's comment about wood and fabric, I can only point out what he already knows very well. Look at the Jodel, Chilton, KR-1, and so many other small cantilever wing wooden aircraft, and it will be clear how this has been done successfully in the past by experienced designers. There are an awful lot of straight one-piece center section airplanes out there, and this stuff is the primary reason why.
     
    Last edited: Nov 22, 2017
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  3. Nov 23, 2017 #23

    wsimpso1

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    Now on to BoKu's post. If one of your requirements is that assembly/disassembly be quick and bombproof simple because you will do it every time you fly, well then, that should drive your design schemes to ones that allow that. If on the other hand, it would only be assembled once or a few times in the plane's existence, convenient assembly should have much lower importance... Our Cherokee is damnably inconvenient to remove a wing, but it has only been done once in the 38 years the airplane has been flying.

    Again, among design schemes that meet your requirements, you should pick the lightest one that does everything you need it to do.

    Billski
     
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  4. Nov 23, 2017 #24

    pictsidhe

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    Wise words, BoKu. I'm pondering how to ditch the tape on folding wings. Neoprene foam gaskets stuck to one surface and trimmed with a razor blade should seal well, and not be excessively draggy? It would need a wing locking mechanism that compresses the gaskets a bit.
     
  5. Nov 23, 2017 #25

    wsimpso1

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    Interesting. From helping rig and de-rig a couple sailplanes, I knew about using two big pins at the main wing spars and fixed pins that automatically connected the leading and trailing spars. I was of the distinct impression that the big main pins simultaneously connected the wing spars together and the wings to the fuselage. I was also of the distinct impression that the fixed pins only reacted loads from pitching moments, and that abutments reacted loads from drag/antidrag moments. This simple coupling was quick and painless to put together and take apart.

    Now I am seriously wondering if I got it wrong. For a year or more, I thought that the HP24 was done the same way, and now BoKu is telling us that the main wing spars only connect to each other, and wing lift is carried to the fuselage through the leading and trailing fittings... Looks like I had that wrong. Big question is: Did I misinterpret the wing attach on the other sailplanes I have had the privilege to fuss over? Are both schemes used?

    Billski
     
    Last edited: Nov 23, 2017
  6. Nov 23, 2017 #26

    jsoar

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    My 2 cantilevered Graphlite based spars meet in the middle of the fuselage where the spar caps are joined with bolted-on aluminum (electrically isolated) transfer plates (no dihedral) thru wider bonded-on carbon fiber plates to form in effect a 40' long beam. The fuselage load is picked up by two bolts thru the beefed up spar shear web. A hassle to assemble but I thought simpler for a home-builder to engineer and build. The pic shows proofed-loading to 5.5G. View attachment 67381 015 5G plus.jpg
     
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  7. Nov 23, 2017 #27

    cluttonfred

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    Neat, jsoar, but it looks like one of your attachments didn't come through.
     
  8. Nov 23, 2017 #28

    BBerson

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  9. Nov 27, 2017 #29

    BoKu

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    Just tuning back into this thread.

    Yes, in the vast majority of composite sailplanes, the wing spar stubs connect only to each other, and not to the fuselage. All of the shear due to lift is extracted at the lift pins, and the spar stubs react only moment into each other. There are exceptions, of course, but they are rare.

    Of course, there are also several variations on the basic theme:

    * Wing thrust is usually reacted as a couple between the wing main spar and the forward lift carrythrough. That is, a forward pull at the wingtip pulls outboard on the wing spar, and presses inboard on the lift fitting near the leading edge of the wing. Likewise, wing drag is reacted as a couple between the wing spar and the aft lift fitting.

    * As noted earlier, Grob tends to use these funky ball-capture fittings like air compressor connectors at their lift pins. So unlike most gliders, they do react spanwise tension due to thrust or drag at the lift pins, not just compression. But Grob is also renown for complicating their gliders with odd mechanicals and lots of aluminum castings. Look no further than the sideways-folding gear on the first-generation Twin Astir to see no end of gear sectors and racks and castings and other fiddly bits that go wonky after only a few seasons of indifferent maintenance.

    * Some two-seaters don't have enough space between the main spar and the forward lift carrythrough to react thrust loads, so they cross-pin the aft lift pin. An example is the ASK21 trainer. I used to make a special tool for extracting the ASK21 cross-pin, until I sold two sets to clubs that consequently declined to pay and ceased all communication.

    * The two common ways of arranging the spar stubs are A) simple overlap in which a single stub on each wing overlaps its counterpart from the opposite wing, and B) a forked pair of spar stubs on one wing, between which the single spar stub of the opposite wing fits. The latter scheme has the advantage of not imparting any torsion into the spar stubs due to bending, but it is also harder to manufacture. The HP-24 uses scheme A; both right and left spars are identical and made in the same molds. The right wing spar is displaced forward, and the left spar is displaced aft. So far as I know, nobody goes to the extreme of having forked spars in both wings.

    * The two common ways of reacting moment between the wing main spar stubs are: A) two large removable longitudinal main pins that join the stubs and B) A transverse pins anchored to the end of each spar stub that engages a corresponding bushing in the root rib of the opposite wing. With B, the wings are generally kept engaged with a single longitudinal pin that passes through the middle of both spar stubs. This pin and its anchors reacts shear that results when tip drag and thrust loads try to pull the main spar outboard. The HP-24 uses scheme A.

    --Bob K.

     
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  10. Nov 28, 2017 #30

    DaveD

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    Something along these lines? (Drawing is still not one of my strong points!)

    Spars.jpg
     
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  11. Nov 28, 2017 #31

    Topaz

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    Pin set "B" (green) is the one I've seen most-often, and what I'm considering for my own projects.
     
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  12. Nov 28, 2017 #32

    BBerson

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    The drawing is very to close to Grob G109, except no " blue" pins on Grob. The Grob has grip connectors on the "red" pins instead.
    Drawing looks more like a RV-12, I think.
     
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  13. Nov 28, 2017 #33

    BoKu

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    Just so. Nice drawing!
     

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