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Thread: Composite Spec'ing

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    steveinindy's Avatar
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    Composite Spec'ing

    Does anyone know a good introductory to intermediate-level source of information on how to choose particular composite materials (as in the specific brand and model of fabric, epoxy, etc) for specific applications?

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    AviationSpruce or Wicke's?

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    steveinindy's Avatar
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    I am looking for stuff more technically oriented than what they have to offer or more so how to interpret things that are more technically oriented than what they have to offer since the decision is coming down not "Do I use Kevlar or E-Glass here?" but to "What grade/type/etc of carbon fiber do I want for this particular application?". I have a lot of the technical specs for things but I have little specific experience in these particular aspects (my area of knowledge is injury biomechanics, not materials science at this level).

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    Mike Switzer's Avatar
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    Steve - take the Sportair composite workshop at IUPUI (or Versailles or whatever they are calling it now, on the north side of the big airport) next time they have it

    I took it several years ago, it was taught by an engineer that worked for Rutan (cant remember his name off the top of my head) & Troy Grover from Danville / Avon helped out some, pretty good, I learned a lot & it convinced me I did NOT want to use fiberglass composite construction for the structure on my project...

    My project will look a lot like a Long EZ but it will be tube & fabric......

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    steveinindy's Avatar
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    Steve - take the Sportair composite workshop at IUPUI (or Versailles or whatever they are calling it now, on the north side of the big airport) next time they have it
    Oh, the Vincennes University "campus" up here? LOL

    I took it several years ago, it was taught by an engineer that worked for Rutan (cant remember his name off the top of my head) & Troy Grover from Danville / Avon helped out some
    Ah....OK. I think I have met Troy before.

    pretty good, I learned a lot & it convinced me I did NOT want to use fiberglass composite construction for the structure on my project...
    Why is that? Granted, I want to stay away from the standard foam core composite technique that a lot of homebuilders use since it's not the best thing for occupant protection but I would be interested in hearing your reasoning for choosing a more traditional method of construction.

    My project will look a lot like a Long EZ but it will be tube & fabric...
    Very interesting. Mine will look like a traditional aircraft. After a conversation with Rutan, I decided to ditch the idea of a pusher configuration although I might come back to it in a later design just for the challenges involved.

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    Mike Switzer's Avatar
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    Quote Originally Posted by steveinindy View Post
    Why is that? Granted, I want to stay away from the standard foam core composite technique that a lot of homebuilders use since it's not the best thing for occupant protection but I would be interested in hearing your reasoning for choosing a more traditional method of construction.
    While i wanted to be a design engineer for Ford, I couldn't because 1) my grades weren't real great & 2)the year I graduated they laid off 6000 engineers

    So I went to work for ADM, got lots of training as a maintenance engineer & went on to do that as a consultant for a lot of similar companies.

    Foam core composite is easy to build in your garage, but it is a real pain to ever fix in the future. It is also pretty much impossible to determine if it was constructed properly without doing destructive tests.

    With Tube & fabric, I can design all the structural elements, then add all the controls BEFORE I cover it, makes it real easy to work on, plus the guy that taught the composite class told me tube & fabric was the lightest construction method out there.

    And if it ever gets screwed up. get out the carpenter's knife, cut off the fabric, fix it & re-cover it.


    Edit - plus I'm scared of fire & I know what a foam core does when it gets hot....

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    steveinindy's Avatar
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    Edit - plus I'm scared of fire & I know what a foam core does when it gets hot....
    Well....two things:

    1. Ever seen a Piper Cub burn? Fabric isn't exactly something I would want to be riding to the ground on with a fire on board. Then again, there's a reason why parachutes would work
    2. It depends on what you're using for the core. There are core materials available that are pretty resistant to burning or melting. They aren't as inexpensive as the glorified Styrofoam a lot of folks use so they aren't common, but they are available if someone is building with safety in mind.

    Taking that into account with my design. Welcome to the wonderful world of building a fire suppression system into the cowling as well as the landing gear wells.

    Foam core composite is easy to build in your garage, but it is a real pain to ever fix in the future.
    Yeah, it might be useful for skin panels (which could be designed in such a way to be replaceable; such a design would also make other forms of maintenance as well as the later stages of construction easier) but not for anything structural.

    plus the guy that taught the composite class told me tube & fabric was the lightest construction method out there
    It is....but there are some trade-offs just as with any other method. Personally, I love Piper Cubs, Aeroncas, etc but at the same time, I think I'm better suited to something a little more sporty. That said, my next design will be an LSA. It'll be a good way to figure out how scale down the things developed from a safety aspect for the first design to something to help protect a broader audience.

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    Quote Originally Posted by steveinindy View Post
    1. Ever seen a Piper Cub burn? Fabric isn't exactly something I would want to be riding to the ground on with a fire on board.
    Fabric coatings and finishes have come along way since the days of Grade A cotton and nitrate dope.

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    I know but unless they've started making the stuff out of Nomex, P84 or something similar, I'm still not fond of the idea. Actually, regardless, if I were in something small enough to be made out of fabric the first sign of a serious fire, I'm bailing. There are three things that scare the crap out of me when it comes to flying:
    1. Fire
    2. Drowning after a ditching
    3. In-flight breakup

  10. #10
    Yeah, maybe Boeing should go back in time to caveman construction and use tube and fabric. I'll point out to them they are really off base with that composite stuff....... Maybe someone should tell Burt too?
    PS: foam core composite is the easiest structure out there to repair. Really easy.
    Last edited by flyingriki; 09-12-2011 at 09:44 AM.

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