Need info on composite

Discussion in 'Composites' started by brandon81, Mar 2, 2010.

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  1. Mar 2, 2010 #1

    brandon81

    brandon81

    brandon81

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    I have been working on a design and I am trying to find a good construction method to use. The plane I am designing is go to be a pretty fast design with a lot of power . It is going to be a 2 place side by side with a 502 big block chevy or 0-540 I haven't decided . I want it to be pretty curving the best way to describe it would be sort of a Cory Bird Symmetry and Nemesis Nxt .I think I would build the wing soild foam hot wired.But I am trying find info on figuring how many piles to use and stuff like I have some books on composite construction like Composite Construction by Jack Lambie ,Advanced Composite Techniques by Zeke Smith ,and Composite Airframe Structures by Michael C.Y.Niu .I think I want to carbon fiber to make it as strong and little as possible.Any ideas and opinions would greatly appericated .Thanks Brandon
     
  2. Mar 3, 2010 #2

    brandon81

    brandon81

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    Nobody has any ideas
     
  3. Mar 3, 2010 #3

    Autodidact

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    Patience, and I think you will get some opinions about this from other people much more qualified than me. But in my opinion, solid core is sort of a waste with all carbon fiber. Volume increases with the cube of length and I've heard it said that the bigger a wing is, the heavier solid core is compared with sandwich. There is a saying that goes something like "safe, light, cheap - pick two", or something like that anyway. I'm really tired from making a circus tent peg mallet out of a log with a drill and a chisel so I might not be thinking right.:bored:
     
  4. Mar 3, 2010 #4

    lr27

    lr27

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    Unless you just modify an existing design to use the engine you have in mind, this is going to be a pretty heavy engineering project. And even if you're going to change an existing design to use this engine, you're going to have to do some homework.

    I don't know those books in particular, but another set of books that are interesting are the Strojnik books, Laminar Aircraft ______. There are three. He may convince you that you can go fast on a smaller engine, BTW.

    Still, you're going to need info on structural engineering of composites, and I don't know where you'd find that. Someone else probably does. Prepare for a bit of math!

    BTW, how fast do you need to go? How far? A Cozy will cruise at over 200 mph on 180hp. With up to four people on board. Seems like there are a bunch of kit planes that will carry two people and go very fast as well. I imagine you're going for a design of your own because it's got to have something different. What?
     
  5. Mar 3, 2010 #5

    lr27

    lr27

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    For skinny wings, solid core foam may make sense. For long chords and thick airfoils, they'd be heavy. For instance, if I'm not mistaken a Long EZ canard core might be around 4 lbs. The wing cores might be around 50 or 60 lbs. (Both of these numbers contain some guesswork, but they shouldn't be too terribly far off if made from 2.2 lb foam. I'm assuming the airfoils are something like 15 percent thick and I'm taking the airfoil as 80 percent of the rectangular cross section, although perhaps 65 or 70 percent might be more accurate. As I said, a bit of guesswork. A Double Eagle core, if you were crazy enough to do one that way, might be more like 150 lbs!
     
  6. Mar 3, 2010 #6

    orion

    orion

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    Inquiries like this bring up many questions that may need to be answered before we can really give you an intelligent reply that makes sense to your problem. Discussion boards such as this one cannot teach you how to design an airplane nor any major part of it since that is often a rather lengthy engineering dissertation and in even the simplest of cases, requires a substantial amount of engineering analysis. And of course all this is true in your case, especially for the subject that you mention since there really are no useful books on how to design with composites for the lay person. The design of laminate structures requires a specific background in structural design/modeling/analysis, which even today is gained mainly through work experience.

    Now, that's not to say it can't be done - there are several here who are designing their own - but we can all warn you that you have a long road ahead of you and a fairly huge learning curve if you don't have the applicable education, background, and most importantly, experience behind you.

    So, using your inquiry, let me ask you a few things:

    Configuration, performance and structure are closely related disciplines in the design of any airplane. Your question therefore leads me to guess that you are only at the very beginning of the process, well before your being able to gel your ideas. Correct?


    A higher performance airframe as this requires a relatively specific bit of knowledge regarding not only the aero aspects but those of structure also. Since your question about composites is rather basic, I'm going to hazard a guess that you do not have much structural design experience either, especially as that relates to aircraft. If so, this lack of experience should not be take lightly since if you do build your bird, even a minor oversight can lead to a dangerous design. For instance, a high performance design can be subject to numerous effects of structural flexibility, the two key areas of concern being things like control effectiveness or possibly, control force reversal, and of course, flutter. These are subjects that are taught at the university level but very little published reference exists outside of those curriculums.

    This is where opinions stop being useful and hard analysis becomes the key. This requires not only intimate knowledge of composites and their behaviors but also of the techniques used in their analysis. This is something that we cannot teach you here. Yes, with enough digging, reading and learning you should be able to gain a good bit of knowledge on your own but I'd still strongly recommend a good and experienced engineer to be looking over your shoulder before you ever cut your first piece of fabric.

    For example, saying that you want to use carbon fiber is fine but is about as meaningful as saying you want to design out of aluminum. Since there are many forms of aluminum and also ways of forming the net shapes, the general statement is relatively meaningless. With graphite you will have different formulations of the graphite yarn itself. Then there are different yarn makeups, different material grades, and of course different weaves and weights of fabric. All of these affect the final structural properties greatly so choosing the right combination of materials is critical to each specific application.

    In short, all we can do here is barely scratch the surface of a complex subject as this - your questions will have to be much more detailed and specific in order for any of us to be able to provide you with anything but general answers or opinions.

    And finally, don't be so impatient for answers. Some inquiries may sit for days or longer before just the right person comes across it.
     
  7. Mar 3, 2010 #7

    Tom Nalevanko

    Tom Nalevanko

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    Hi Brandon,

    Foam is not the way to go for an airplane with lots of power. Your best bet is to copy the Lancair IV / ES / Stallion fuselage / wings design. They are written up in Martin Hollmann's books (many drawings with loads and BID schedules) . The books are pretty poorly written but then he is an engineer, not a grammarian and English is not his first language. The essential is there in the books if you read and think hard enough. The books tell you how to do it as opposed to talking about doing it. You can find these at Aircraft Designs, Inc. Some people on this forum denigrate Martin's work but most of them have never designed and flown an aircraft while Martin had done quite a few... I flew his Stallion which I built, taking off at well over 4,000 lbs. and 200 knots cruise from Camarillo, CA to La Paz in 4:30. My daughter thought that was cool until I told her it was La Paz, Mexico and not Bolivia!

    You will need to do molds and it is a big job.

    The books you looked at are pretty worthless for other than some general concepts. But it is good to understand general concepts; I have read these books too. The Nui book has lots of errors making me wonder if he ever designed anything in Composites. His approach is to mimic an aluminum plane in composites.

    You might consider buying the kit for this plane when it becomes available. The design and build approach are exemplary. ALGIE COMPOSITE AIRCRAFT It might give you some ideas also for your design as it is primarily carbon fiber.

    I hope that this helps and does not start a flame war.

    Blue skies,

    Tom
     
  8. Mar 3, 2010 #8

    Autodidact

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    Thankfully, there doesn't seem to have been too many flame wars on this forum. As far as Hollman's books, I have just recieved my copy of Composite Aircraft Design and have read it right up to the point where the matrix algebra starts :gig:. I bought this book because Raymer recomends it as "a good overview" and my method of learning is to start out with just such a (usually short and succinct) book. It has a few typos, none catastrophic, it seems to give a nice short and to the point description of the different materials and methods and the various reasons for using them and seems very informative in that regard.
    As far as the mathematical analysis, the equations he uses are simplified and were derived by Mr. Hollman. I have no problem with that, but there doesn't seem to be any attempt to compare them with more rigorous methods; specifically, what I'm interested in seeing is how much of an error there is and that it is an erring to the "safe" side of strength. I'm not questioning Hollman's expertise, I just feel a need to see his assertions about the effectiveness of his equations justified with comparisons of other results at least, otherwise I would need to gather that information myself which would involve reading the rigorous and more complex texts. Come to think of it, I need to do that anyway. As it stands so far, all I've read is, to paraphrase, "these equations work, just take my word for it". As I said, though, I'm not finished reading it so this is not my "official" review (I should be so qualified!). This is, I assume, the latest edition and I have no idea how earlier editions may have differed or even how new this one is as it doesn't seem to say.
    Even if the equations in Hollmans book are useable, I would not recommend using it as the sole text from which to design an aircraft, nor would I make that recomendation for any other book either.
    Regardless, you will need to understand the ways of mathematics. This is true for any type of aircraft structure, but most especially for composites. Even Hollmans simplified equations require a knowlege of matrices and trigonometry, radian measure of angles, etc. This is because the strength of a FRP laminate changes with the angle from the fiber direction that the force is applied to it.
    Are you still in school, Brandon? If so, hit those books. The desire to design an airplane should provide the motivation you'll need to overcome a large and tedious subject like mathematics. Even If you find an engineer to work with, I would suggest improving your math skills; it will make it easier to work with the engineer and vice versa.
    Composites - you just wet some cloth out in a mold with plastic resin and let it dry, what could be simpler? A better question would be, "What could be more complex?"
    Not trying to discourage, it's just one of those things.
     
  9. Mar 3, 2010 #9

    lr27

    lr27

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    Another variable factor, which, unless I missed it, hasn't been mentioned above, is exactly how the materials are laid up.

    If they're vacuum bagged instead of a hand layup, more layers are probably needed for stiffness, because the vacuum bagged laminate will be thinner. Since there's more fiber in it, it doesn't have to be QUITE as thick as a hand layup, so it can be lighter and stronger, at least if there are lots of layers so fine adjustment is possible. Then there's infusion, which I haven't messed with.
     
  10. Mar 3, 2010 #10

    brandon81

    brandon81

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    Thanks for the reply s I have been going over the conceptual design.Mostly the sizing of the different areas I have been looking at Martin Hollmann's books he seems to have a lot of different ones on subjects you don't see very often.I am not opposed to working with someone in the field like you Orion I just want to do as much as I can and possibly work together .I think I can figure a lot of the sizing and general layout of how the airplane looks.It just seems that when I look at different plans for airplanes they are not that different .There just isn't any airplane that are made of composite that are available as plans in the size I want the only one I can think of is the Vision and it is not fast enough. I have a lot of books on the design of airplanes I am just trying to figure out what construction method I want to use. In looking at the way a Glassair is made it looks like it use bulkhead in the fuseage and it use ribs and a main and aft spar in the wing.My question is if you look at say a Nemesis Nxt and a Glassiar are the structures going to look very similar in the way of how many piles of glass were used in different areas of the two planes.I have looked at the construction of the Cozy and I like how it is constructed.I seen that Martin Hollmann has plans to his Super Stallion available I was wondering why couldn't you use some of these plans as a guideline .Thanks for all your guys time I appreciate it
     
  11. Mar 3, 2010 #11

    Autodidact

    Autodidact

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    Pictures (or drawings), please!:nervous:
     
  12. Mar 3, 2010 #12

    brandon81

    brandon81

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    What are you asking pictures of?
     
  13. Mar 3, 2010 #13

    Autodidact

    Autodidact

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    ...
     
  14. Mar 3, 2010 #14

    Waiter

    Waiter

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    The LongEZ Wings and Canard are built using a "Moldless" construction.

    With that said, the "Mold" or "Core" actually become part of the structure.

    The wings and Canard both have Spar caps built into them, then the core kind of acts like a continous "Wing Rib", serving to transfer wing loads into the spar caps and shear web.

    You can see how the wings and canard are constructed here:

    I FLY EZ

    and

    I FLY EZ

    Good Luck

    Waiter
     
  15. Mar 3, 2010 #15

    lr27

    lr27

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    Numbers too. How fast? What size? Keep in mind that some allegedly 4 place airplanes are really two place if you want to carry much fuel or large people. For instance, if you put 4 of me in a Cozy I think you could put in about 16 gallons of gas. That's maybe an hour's flight plus reserve. And that's in the summertime with no baggage. Throw in some coats, boots, and a backpack and you'd be lucky to make it to the next county.

    Do I read between the lines that you want a conventional configuration? Or is it just that the Q2 and Dragonfly are not fast enough? (Q2 plans appear to be at quickheads.com)

    I take it the KR2 is not fast enough or else not "composite" enough?

    Perhaps it would make sense to start with one of those other plans and just stiffen it up to handle the speed. At least if the engine didn't end up too heavy. I suspect that, although you'd need to do a lot of homework, this might be much easier than starting from scratch. Unless you're like me and it would negate the whole point of the exercise.
     
  16. Mar 3, 2010 #16

    wsimpso1

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    Composites and construction methods and airplane design are all interelated...

    First off, the skin thickness of most of our little airplanes is set mostly by the minimum thickness that can be handled and built and stand airport morons. Serious structures supplement that. Spars in the foils can be substantial, as can structure around the cockpit. In wet layup fiberglass, hotwired cores are the light way to go if your foils are not too thick. If you are willing to use an autoclave to cure prepreg carbon fiber parts in pre-preg carbon fiber molds, you can approach book values for carbon strength and stiffness. Want to do wet layups? Carbon will only be a modest improvement in strength over glass then. And so on.

    You have a lot of homework to do. These threads are a good place to start.

    https://www.homebuiltairplanes.com/...s-anything-i-shouldnt-bother-get-instead.html

    As to Martin Hollmann's books - bad juju. They are just not suitable for designing real airplanes.

    Learn real aerodynamics and real structures and real composites.

    Billski
     
  17. Mar 4, 2010 #17

    brandon81

    brandon81

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    That is what I thought is that the minimum thickest most of the time is set so people can't stick there fingers through it.My thought is if I were to build a plane similar to Cory Bird's Symmetry what steps would I take .From what I read it sounds like he used basic Rutan style moldless construction.He states that that he used long-eze solid hotwired wing type construction and when he started he used moldless construction on the fuselage too but later he used a mold for the fuselage when he changed it to midwing .What I don't understand is why more people don't use these methods .You don't think I would get more strength from the carbon fiber unless I autoclave it .What if I vacuum bagged it and heated it to cure .I am wanting to make it a lot faster than the current few composite planes I least want to get as much speed as Symmetry which is about 270 mph. But I am thinking some where between Symmetry and Nemesis Nxt.I want to use a laminar flow airfoil I have been looking at a lot of different ones at this point .Mike Arnold used a interesting construction method with the hot wired inside and oustside and glassed both.
     
  18. Mar 4, 2010 #18

    orion

    orion

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    I think we have to be a bit careful with terminology - laminate structures don't need an autoclave unless you're doing work for the military or something really weight/strength sensitive. The property difference between an autoclave part and one properly designed for prepregs, vacuum bagged and cooked in a conventional oven, is relatively small (sometimes less than 5%) but keep in mind that that will require molds since most of the mold-less construction techniques use foam that is not too temperature resistant.

    But the differences between a cooked prepreg part and one laid up through wet layup techniques, even when bagged, can be quite significant.
     
  19. Mar 4, 2010 #19

    wsimpso1

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    Orion has been working out some techniques to make parts in molds with pre-pregs of somewhat higher epoxy fraction to eliminate that need for the autoclave. Understand that the autoclave does two things: First it applies several atmospheres outside the bag, which can make for more compaction than an ambient vacumm bag does; Second it raises the cure temperature.

    I did not include Orion's methods as I suspected they might not be ready for the rest of us yet, although I am quite interested in them....

    Billski
     
  20. Mar 4, 2010 #20

    lr27

    lr27

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    Even if you're using a wet layup, I've got to think a fiber that has an elastic modulus over 3 times higher than glass is going to make for a much stiffer part. Especially since it's a bit lighter so you can use more.

    Seems like some of the pultruded rod that's available might be a way to get some of that performance back without going to an autoclave.
     

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