Design and sizing of composities wing and fusolage

Discussion in 'Composites' started by Albert80, Jul 5, 2009.

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  1. Jul 5, 2009 #1

    Albert80

    Albert80

    Albert80

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    Dear Friends,
    My name is Alberto, I'm new of this wonderful site.....

    I have need your help because I want understand better how I can sizing a composite wing from size of the main spar or box spar to what are the common materials that I can use like foam, prepeg or fiber and their orientation....another thing is know how drawing a composite fusolage with wing attached point.

    If somebody know some composite plan that is possible purchase for increase the knowledge of the composite drawing is well accept!!!

    Thanks a lot...
    Alberto
     
  2. Jul 6, 2009 #2

    orion

    orion

    orion

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    Good morning and welcome.

    The problem with your question is that it's so broad that I'm not sure how we would actually provide you with an answer that did you any good. I think it's best to ask about a specific area or design detail, rather than asking about the whole assembly.

    Like any other material, you design with composites so that the material properties serve the purpose of the airplane. When dealing with composites, the designer needs to understand a few more fundamental details of the material in question since it's not orthotropic in nature (like metal), but otherwise the issues of loads, stresses, deflections and so on, are pretty much similar to that of a metal or wood assembly. Yes, there are a few specific areas of behavior and application that have to be part or the designer's experience when dealing with laminates, but that can be learned by looking at previous examples of the application and by a whole lot of reading and analysis.

    Your question is also broad in the sense that you're asking about very basic items (like materials used for aircraft application), along with some very advanced concepts like design with respect to fiber orientation. While we can answer some of these things, we cannot design the airplane for you, nor can we teach you how to do what is essentially a fairly involved analysis. That is well beyond the scope of this board and certainly well beyond most people's patience for typing. But, as a start, you may want first to use the search function herein and look at several previous discussions that have dealt with this subject, especially as it relates to reference materials, technical papers and readily available publications.

    You can also look at previous building projects for which plans or instructions are available, but with that I would urge a whole lot of caution since what may work for one airplane may (and most likely, wont) work for what you have in mind. Each application should be analyzed on its own.

    So, as a start, I'd suggest reading through the structural posts herein, especially as they pertain to composites, and then obtain as many reference texts as you can stand or afford. Getting a plan set for a VariEze or a Vision might be a good idea also. Another good assembly manual is one for the Glasairs. None of these will teach you how to design an airplane but they should give you a pretty good insight into the various details and types of structures. The Glasiar manual is especially good in that it contains many excellent illustrations and photos you can reference - I think the best of the line is for the later Glasair III or the IIS models.
     
  3. Jul 6, 2009 #3

    Albert80

    Albert80

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    Thanks a lot Orion,
    One more thing, I have found on many web site different books of composite and I don't know whether choose for beginning. are you able to tell me a good book for start?
    I do not know "Vision might" do you have a web site?

    thanks
    Alberto
     
  4. Jul 6, 2009 #4

    orion

    orion

    orion

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    The Vision web site is at: American Affordable Aircraft, Vision, Experimental Aircraft, Sport Aircraft,homebuilt aircraft,vision or Pro-Composites Home of the Personal Cruiser Kit Aircraft

    Coincidentally, one of the web sites sells a couple of basic books that might get you going in the right direction. It looks to be fairly "entry-level" yet it seems to cover the key subjects as they relate to composite fabrication. It just might give you enough information to where you might be able to ask more specific questions.

    Personally, I haven't seen any books dealing specifically with composite design - maybe some other folks here can chime in on that one. The couple of books I have are fairly advanced and are probably beyond the scope of information that you might be after.
     
  5. Jul 7, 2009 #5

    Albert80

    Albert80

    Albert80

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    Thanks a lot for your help!
    Alberto
     
  6. Jul 7, 2009 #6

    wsimpso1

    wsimpso1

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    Alberto,

    Responding to this is also a problem for me. It seems that you are at the entry point for your knowledge and yet you are asking questions that will ultimately require much more sophisticated knowledge.

    Use the Search function. These topics have been talked about before. You will find a lot of material already written there.

    Depending upon your background, learning this stuff might be straightforward, or it might be impossibly complicated. The conventional way to learn this stuff is to learn basic mechanics, design and analysis for sheet metal structures, and then to add in the mechanics of composites. This is because metals are assumed to be homogeneous so a lot of simplifications of the math occur, and the learning of all of the concepts is easier. And since steel is ubiquitous in engineering, those skills are very useful. Then for composites, many of the assumptions are dropped, and things get much more complicated...

    Now in little airplanes, a fair amount of monkey-see, monkey do engineering exists. Many of the things that the airplane has to survive are not based in carrying flight loads, but are instead set by handling, building, bird strikes, and air-show morons who will use your airplane as a desk or a place to set a squalling toddler. GRRRR.

    Exterior skin of many wings and fuselages is 1 UNI the long way on the part (spanwise on wings and tails, along the length of the fuselage), 1 UNI at +45 deg, 1 UNI at -45 deg. Another common exterior skin is 22 Triax run the long way on the part (open layups in triax will be heavy, much better to vacuum bag this stuff). Either way, you end up with 21 or 22 ox/square yard of fabric. This skinning is common and it works. Similarly, if you have foam cored skin sections, 2 BID is on the inside surfaces is common. 18 oz/square yard of glass. Going to graphite fiber will likely not change the thickness of material needed to prevent bird bones and pencil points from poking holes in you airplane skin.

    One other thing that makes things easier to design with is virtually all practical structures for little airplanes are made from either woven cloths, or the stitched fabrics. So fiber directions are 0 degrees (the long way), 90 degrees (across the long way), or +/-45 degrees.

    Now once you have that done, you still have to figure out spars and attachments for spars, seats, seat belts, control systems, engine mounts, and on and on.

    Sizing at a basic level for many of these things seems simple at first, but then, you end up upsizing many items because the various loads interact. For instance, spar shear webs not only carry shear, but they move with the caps, and that distortion has to be added into the failure check. And the strange thing is that the light way to passing the failure checks is to beef up both the caps and the web...

    I learned mechanics of solids from Timoshenko and Gere Mechanics of Materials, and composites from Tsai and Hahn Introductions to Composite Materials. The other primary composities book is Jones Mechanics of Composite Materials. Timoshenko will give you some basics of beam theory, shear theory, etc, and either of the composites books will take it from there. The first book is the basis for a sophomore level engineering class that takes a semester. The other two are the basis for a senior/grad level class that takes a semester...

    Then there are the aero structures books by Peery and Bruhn... Both are long out of print, but available if you spend enough money. My copy of Bruhn just arrived, and it has margin notes from a student who used it long ago in a class. Composites were not part of the world when these books were written, so I imagine there will also have to be engineering interpretation...

    Billski
     

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