composite longerons and ribs

Discussion in 'Composites' started by jthntrmn, Jul 14, 2008.

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  1. Jul 14, 2008 #1

    jthntrmn

    jthntrmn

    jthntrmn

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    I am considering building a KR2S "Super" due to its low cost and easy build process. I was wondering if anyone had attempted to make the boat frame out of carbon fiber tubes and if it would have any weight savings benefit. I was really wondering about building the KR2S Super out of as much cf as possible due to increased strenght and reduced weight. I know the cost will be more but I feel it would justify the better constructed airframe. Thanks, JT
     
  2. Jul 14, 2008 #2

    Scott

    Scott

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    Johnathn,

    I do not see the advantage of building the KR2S Super2 fuse (www.KRSuper2.com) from Carbon Fiber. The fuselage is made of a fiberglass/foam/fiberglass sandwich, one layer fiberglass BID on the inside and then a double Fiberglass layer on the outside, one UNI and one BID. This results in a structure that is amazingly strong, much stronger than is required by the stresses of full aerobatic flight.

    Carbon Fiber really shines when you are replacing many layers of Fiberglass with fewer layers of Carbon fiber. It would not buy you anything to replace the inner layer of Fiberglass BID with Carbon fiber, and you would not want to replace the two outside layers with a single layer of BID CF as it would be too thin and brittle. In my opinion, the fuselage is not the best place the use Carbon Fiber. There are areas of the Super2 that utilize Carbon Fiber--nose gear reinforcement, the control surfaces and of course the wing spar.

    If you calculate the amount of Carbon Fiber you are talking about and then calculate the cost, I think you are going to be amazed--spend that money on a nice EFIS.

    Just my opinion, :)
     
  3. Jul 16, 2008 #3

    wsimpso1

    wsimpso1

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    +1 on Scott.

    In order to do the job right, you would have to derive the loads and design a new fuselage. As long as you are solving your equations for carbon, check them out for glass too, and compare them to each other and to the factory way of building. I would be willing to bet that the KR2S, like many other little airplanes, has its skin and structure designed as much to stand building and then ground abuse more than to survive flight loads. Which means a certain thickness of composite, no matter how you do it.

    One of the things about carbon is that it is frequently only a little stronger than glass in a home layup. The fantastic numbers we see for carbon strength are usually obtainable with pre-pregs, vacuum bagging, and an autoclave.

    Now, even then, carbon will save you some weight relative to glass, just not a lot... In my bird, one where the pragmatist went with fiberglass, my wing will weigh a lot more than my fuselage. So, if you are still in love with carbon, you might be better off to redesign the wing structure in carbon.

    Billski
     
  4. Jul 16, 2008 #4

    Rom

    Rom

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    In my tadpole shaped fuseloge I am using two layers of e-glass inside and out. Carbon fiber for strength as previously mentioned in a hand layup is not much better than fiberglass. If you want the advantage of carbon, pultruded carbon rods in lieu of unidirectional fiberglass spar caps would give the benefit of additional strength/weight.
     
  5. Jul 22, 2008 #5

    Midniteoyl

    Midniteoyl

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    Besides, you'd then have to have external antennae as opposed to internal for a glass bird.
     

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