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Thread: Aircraft design software

  1. #1
    KDoersom's Avatar
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    Aircraft design software

    All you home builders out there. Is there a good aircraft design software program that you can use to design and. Hold an aircraft before actually. Holding it. Looking for something that will enable me to con up with some basic plans and be able to do some checking on the structural load limits on the airframe.

    Thanks

    Keith

  2. #2

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    What you're describing is several different programs. CAD to design/model/draw your airplane, FEA for structural analysis, and an aerodynamics program to analyze its performance. CAD is approachable for the amateur, ranging from simple drafting programs to professional (and expensive) solid modeling systems. However, FEA is not something that an amateur will be able to get good results with (you need a thorough ground in structural analysis to set it up and interpret the results), and the available aero packages like AirplanePDQ, while useful for preliminary work, make many simplifying assumptions and thus are no substitute for a proper aerodynamic analysis.

  3. #3
    steveinindy's Avatar
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    However, FEA is not something that an amateur will be able to get good results with (you need a thorough ground in structural analysis to set it up and interpret the results),
    The way one of my professors put it to me: "If someone can't do the basic stress calculations by hand and needs a program to do it for them, they have no business even trying to read, let alone run a finite element analysis."

    thus are no substitute for a proper aerodynamic analysis
    Likewise for structural analysis. This is one reason I try to keep an aerodynamicist and structures guy owing me a favor at all times. LOL
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



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    To answer part of the question, I use the low end Autocad to make basic parts drawings, and I use Google Sketchup to do 3-D assembly drawings. Both have a learning curve, but since Sketchup is free, you can give it a try and see if you have an aptitude for that part of the design process. I have to say that since I started drawing assemblies in 3D, I really am hooked on being able to rotate and view all sides of an assembly.

    If you are new to thinking about stress and strain for aircraft structures, I suggests starting simple. Martin Hollman has some books that will introduce you to that sort of stuff. Try Modern Aircraft Design for starters. If you get serious, will will need to find a college level statics text. Perhaps one of the other posters here can reccomend one.

    Best of luck,

    Wes
    N78PS

  5. #5
    Mike Switzer's Avatar
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    Quote Originally Posted by steveinindy View Post
    The way one of my professors put it to me: "If someone can't do the basic stress calculations by hand and needs a program to do it for them, they have no business even trying to read, let alone run a finite element analysis." LOL
    I agree. Since mine is a tube frame I am using MathCad to run the calculations, but you still need to be able to run the calculations on paper to be able to do this. The advantage to MathCad is it gives me the ability to change input variables & quickly get results.

    I have done basic FEA in the past, but I don't know that I would want to attempt it now even with good software. There is a reason most of the guys getting paid to do it at major companies all have masters degrees in mechanical engineering.

  6. #6
    steveinindy's Avatar
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    There is a reason most of the guys getting paid to do it at major companies all have masters degrees in mechanical engineering.
    You mean besides the fact that one has to be a bit masochistic to either enjoy FEA or to get a masters in ME?
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  7. #7

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    Gentlemen,

    You are missing the point that homebuilding is educational. There is more to the educational component than learning to buck rivets and heat shrink fabric.

    I will confess that sitting next to a fresh-out-of-college Mechanical Engineer at work was a great help in remembering the math when I needed it.

    I will suggest that the math is not hard, just tedious. If I can do it and convince the FAA that I produce the right answers, anyone can do it.

    And taking a swing at figuring this stuff out helps you appreciate guys like Burt Rutan who are up to their eye balls in it.

    Best of luck,

    Wes
    N78PS

  8. #8
    steveinindy's Avatar
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    You are missing the point that homebuilding is educational. There is more to the educational component than learning to buck rivets and heat shrink fabric.
    Agreed. The point we are trying to make is not that we shouldn't learn this stuff (if one is so inclined....personally, I'm more inclined to learn FEA than how to work with fabric because I have zero interest in rag aircraft) but just that one has to be damn sure they have done it correctly so looking for shortcuts or software to do it for you isn't a great idea if you don't understand the underpinnings. Even as reasonably knowledgeable about some things as I am, I still double check and sometimes triple or quadruple check my work and then run it by three or four other people who know more about the technique and/or subject matter than I do before finalizing it. My life and the lives of my passengers may well depend upon it.

    And taking a swing at figuring this stuff out helps you appreciate guys like Burt Rutan who are up to their eye balls in it.
    Rutan freely admits that he hands (handed?) the really specialized stuff over to experts in those fields. That's why any of us have heard of John Roncz.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  9. #9
    Mike Switzer's Avatar
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    The math isn't hard, but if one doesn't have a good understanding of trig, vector mechanics, statics, mechanics of materials, etc it is pretty hard to know which formula to use. You need to know when to use Euler, when to use Johnson, or when to use something really obscure from Roark's book.

  10. #10
    KDoersom's Avatar
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    Guys thanks for all the great replies. I would love to build a replica of the Piper Skycycle but as piper drawings were never drafted I am
    On my own to come up with the structure underneath the skin.
    I'm thinking tube construction for the fuselage and tail feathers and aluminum for the wings.

    Al I have to go on are some 3 view drawings. I'll get a copy of that book and start reading. After I get something drawn up maybe someone could take a look at them for me. We are talking a pretty light and slow aircraft. Less than 700-800 pounds and less than 100 mph cruise.

    Thanks again

    Keith.

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