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  1. #1

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    How to draw ribs in CAD?

    I have a pdf of ribs for a Super Kaos 40 I want to get into QuickCad.
    I tried tracing them but that didn't work well.
    Better for the root, terrible for the tip.

    Any suggestions for doing this?

    Thanks,

    KW_Counter

  2. #2

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    If the PDF was created from a vector format file it may be possible to convert it back into a CAD file. (I may be able to help with that) If the PDF was made from a raster file then you're stuck with either tracing or plotting the airfoil based on its ordinates.

  3. #3
    Moderator BMatthews's Avatar
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    Tracing over an image is OK as a start. But at some point you need to clean it up. Also often times the image isn't scanned with the center line exactly horizontal. That adds to the issues.

    If it were me I'd trace over ONE side of the curve if it's a symmetrical airfoil. Or do both sides if it's cambered. Then I'd draw the leading edge stock from scratch to use as a reference and then drop the traced airfoil on the LE rectangular stock item so it lines up. At that point put the reference pivot point at the leading edge or at some point on the rib attached to the leading edge and pivot the angle so the trailing edge ends up on a horizontal line with the center of the leading edge. I'd then draw the spar and trailing edge raw stock sizes from scratch and drop them in place and alter their position as needed to line up like they should. At that point I'd touch up the curved spline lines of the actual airfoil if needed to blend with the wood stock rectangles.

    It sounds like a lot of fiddling around. But if you're fairly comfortable with the CAD you can do all this and have a great looking rib in less time than it takes to read what I typed.
    Witty saying to be plagarized shortly.....

  4. #4

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    I use AutoCAD for design, but I suspect that the features and processes are similar. First, I create the wing plan form. Second, I layout the rib locations. Third, I dimension the chord length for each rib. Now comes the fun part.

    I go to some airfoil data source like http://airfoiltools.com/ and select an airfoil. There are other sites that are just as good, but I find this one fairly easy to get around in. Once you have selected an airfoil, you can download the .dat file for its coordinates. Draw a p-line using these coordinates and then smooth the lines. You will wind up with a rib of your choice with a chord length of one (1). Then all you have to do is to 'insert' the rib into your drawing using the measured chord length as the 'scale' for the 'insert'.

    If you like, I'll be glad to make one for you. Just sent me a PM.

  5. #5

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    I have had some success, dependent on quality of the pdf, with a program called PDF to DWG converter, available at http://anydwg.com/
    The program converts pdf raster to vector dwg or dxf.

  6. #6

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    Awesome, Dude!
    Thanks for the link, I'll play with it this weekend and report back.

    KW_Counter

  7. #7

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    Hi KW,

    I am creating a cadd file for the CG Ultimate 10-300 and what I did for the wing ribs was trace the pdf file using the arc and spline commands.

    Once it was done, I printed it, cut one out and laid it over the original tracing and made any little adjustments needed. First run was really close.

    Email me at abbott10300@gmail.com if you would like some help with it.
    Carl Goldberg Ultimate 10-300 Brotherhood # 51

  8. #8

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    Abbott,

    Thanks for the offer. And thanks to all for your input and suggestions.
    What I finally did was blow up the pdf to about 250%.
    Then using the arc & spline commands, as you suggested, traced the ribs.
    This came out, what seems, very well.
    I'll try the cut outs comparisons.
    Fortunately, I only want the root and tip ribs and don't have to do all 9.

    Thanks,
    KW_Counter

  9. #9

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    Sounds great KW, if you need anything, just let me know and I'll see what I can do to help out.
    Carl Goldberg Ultimate 10-300 Brotherhood # 51

  10. #10
    thailazer's Avatar
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    It's about time some savvy entrepreneur or RC Company realized the need RC hobbyists have for a dedicated aircraft design CAD system that is easy to use and meets the needs of the normal builder and not an engineer. Those needs would include scaling ribs for swept wings while maintaining LE, TE, and spar dimensions. All the development packages can be used but the learning curve is quite steep. If a manufacturer developed a dedicated AC design package, I would be the first to buy one, as long as it works on a Mac!
    Tiger Flyer #49

  11. #11
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    "as long as it works on a Mac!"

    There's the first problem:-)))))))))))

    The second problem, is that we must remember that CAD means Computer AIDED Design. It does not do the design for you.

    Les

  12. #12
    thailazer's Avatar
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    Quote Originally Posted by LesUyeda View Post
    "as long as it works on a Mac!"

    There's the first problem:-)))))))))))

    The second problem, is that we must remember that CAD means Computer AIDED Design. It does not do the design for you.

    Les
    I've used a lot of design tools in my life, and personally witnessed and used mechanical and electrical CAD tools. We thought they were the cat's meow in the beginning, but the industry recognized the need for focused RF (radio frequency) design tools. Once that evolution started, the whole radio frequency industry benefited, and today those tools are very easy to use, virtually designing filters, amplifiers, and even complete systems for you. It can happen for the RC aircraft hobby as well if someone invests in it. Designing software for a specific need makes a whole lot of sense Les.
    Tiger Flyer #49

  13. #13
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    ". Designing software for a specific need makes a whole lot of sense Les."

    I concur, whole heartedly. The only requirement is that there is enough market to justify the investment. My experience has been that us modelers are a bunch of tite wads, and would rather spend the hard earned money on a airframe, than on a "tool".

    Les

    p.s. Although I do have a garage full of "tools" that I have used once, for a particular application:-))))))))))))

  14. #14
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    There are programs like CompuFoil and Profili and a couple of others.

  15. #15

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    Quote Originally Posted by saramos View Post
    There are programs like CompuFoil and Profili and a couple of others.
    Actually the most featured and easy to use is devWing, see http://www.devcad.com/eng/devwing.asp

  16. #16

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    I actually draw them using an ellips forward of the high point and blend a radius between the hight point to a straight line forward of the aileron which extends to the trailing edge. To get tapered wing rib profiles I scale the root rib to each cord length. For a non-symetrical I just draw a different bottom. Once I have each rib profile I add internal detail.
    Jim

  17. #17
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    The leading edge to the highest point is easy. Just use an ellipse. From the highest point to the trailing edge (kind of parabola) I found this formula works great for me.

    y=b-(b*(x^1.85/a^1.85)) where y is the desired high to an entered x.

    Click image for larger version. 

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    Last edited by ARillos; 04-02-2014 at 09:40 AM.

  18. #18

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    The conversion programs,converting jpegs and pdfs,result in multiple lines being drawn.Lazer cut files need only one line(polyline) on one plane.So it is better to trace your jpeg,using polylines,and close the result.This insures the correct result,as often,you will not see the flaw,or difference between a closed or open polyline.

  19. #19
    thailazer's Avatar
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    Quote Originally Posted by BMatthews View Post
    Tracing over an image is OK as a start. But at some point you need to clean it up. Also often times the image isn't scanned with the center line exactly horizontal. That adds to the issues.

    If it were me I'd trace over ONE side of the curve if it's a symmetrical airfoil. Or do both sides if it's cambered. Then I'd draw the leading edge stock from scratch to use as a reference and then drop the traced airfoil on the LE rectangular stock item so it lines up. At that point put the reference pivot point at the leading edge or at some point on the rib attached to the leading edge and pivot the angle so the trailing edge ends up on a horizontal line with the center of the leading edge. I'd then draw the spar and trailing edge raw stock sizes from scratch and drop them in place and alter their position as needed to line up like they should. At that point I'd touch up the curved spline lines of the actual airfoil if needed to blend with the wood stock rectangles.

    It sounds like a lot of fiddling around. But if you're fairly comfortable with the CAD you can do all this and have a great looking rib in less time than it takes to read what I typed.
    Been using ViaCAD 2D/3D in the 2D mode and what you say makes a lot sense. Lay out your leading edge, spars, and trailing edge stock and then lay out the air foil using whatever method is easiest on your particular CAD program. (I am still looking for a "smoothing" function on ViaCAD to smooth out some of my segments but it is just a matter of time.) That "fiddling around" takes a long time when you are learning but gets faster as you learn the tool.
    Tiger Flyer #49

  20. #20

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    In autocad,you can smooth your arcs and lines by turning them into splines,with handles that address the direction of smoothing.If you are using planes with known wing profiles,(naca numbers)you can import them directly,generally speaking as a dwg,or dxf.Once you have fixed your airfoil,then you modify its general profile by the balsa rough sizes that you plan on using,as previously noted.In other words,you end up with smaller parts suitable for construction,with notches for spars and stringers,etc.


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