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Thread: Resources for designing a primary glider?

  1. #1

    Resources for designing a primary glider?

    Howdy from Texas, new member to the EAA here, I've joined up for my passion for aviation but also because I am pursuing the design of an ultralight primary glider.

    Now I'm no stranger to conceptual design, I've competed in a couple design competitions before, however, these were all theoretical (I just fleshed out ideas in CAD).

    I have chosen to design a primary glider on the premise that my design will be:
    -extremely light (less than 300 pounds empty weight)
    -constructed using composites (I plan to use fiberglass in the wings and control surfaces, and spruce for everything else)
    -capable of being winch launched (i.e. from the hitch of a truck)
    -relatively cheap

    I have Daniel Raymer's Conceptual Aircraft Design for Homebuilders and his actual textbook (Aircraft Design: A Conceptual Approach), I am also going through the FAA's Glider handbook. I feel that these resources might be sufficient enough, considering that many concepts from powered aircraft design carry over to glider design. I am wondering if there are any online resources or textbooks I can find specifically for glider design.

    Specifically, I'm having trouble with sizing the fuselage and the wingspan.

    Thank you all for your help in advance, I look forward to being a part of this community.

  2. #2

    Join Date
    Aug 2017
    Location
    Greece
    Posts
    16
    Dear friend,
    Hello from Greece! I had spent a lot of time on research previous years. I design an all composite 2 seat airplane.
    I am a civil engineer and i will be glad to help you if you need a hand of help in fea structure analysis.
    Before choosing a composite structure, keep in your mind that it will be more expensive and maybe more complex (if you build only one)
    Best regards!

  3. #3

    Join Date
    Aug 2011
    Posts
    257
    I’d be glad to help with whatever you need. The soaring industry needs more people like you.

    Check out Barnaby Wainfan’s current design series in Kitplanes. He’s a great guy.

    Start with your payload (people, ballast, avionics, battery, etc.). Contour a fuselage around it. Figure the CG of the fuselage and contents. Place the wing 1/4 chord at the CG of the fuselage (the wing CG will be close to 1/4 chord, too). Wing size will be determined by your estimated gross weight.

    FIY, your statement of “primary” glider conflicts with having an enclosed fuselage. And an empty weight of 254 lbs for an ultralight glider is ~100 lbs. over the legal US limit.

    Keep going; you’ll get there!

  4. #4
    Quote Originally Posted by Ron Blum View Post
    I’d be glad to help with whatever you need. The soaring industry needs more people like you.

    Check out Barnaby Wainfan’s current design series in Kitplanes. He’s a great guy.

    Start with your payload (people, ballast, avionics, battery, etc.). Contour a fuselage around it. Figure the CG of the fuselage and contents. Place the wing 1/4 chord at the CG of the fuselage (the wing CG will be close to 1/4 chord, too). Wing size will be determined by your estimated gross weight.

    FIY, your statement of “primary” glider conflicts with having an enclosed fuselage. And an empty weight of 254 lbs for an ultralight glider is ~100 lbs. over the legal US limit.

    Keep going; you’ll get there!
    Thank you very much stranger! what all can I expect from subscribing to KITPLANES? Will I find the necessary equations to properly estimate my craft’s wingspan?

    And thanks for the headsup, I got my terminology confused, but I definitely would like to have a closed fuselage on my glider.

  5. #5

    Join Date
    Oct 2011
    Location
    WA
    Posts
    1,085
    Most primary ultralight gliders are aluminum tube and fabric around 36' span.
    Plans for the "Bloop" series of gliders is free online.

    The Part 103 empty weight limit is 155 pounds for gliders.
    Last edited by Bill Berson; 01-03-2019 at 11:32 PM.

  6. #6
    Quote Originally Posted by Bill Berson View Post
    Most primary ultralight gliders are aluminum tube and fabric around 36' span.
    Plans for the "Bloop" series of gliders is free online.

    The Part 103 empty weight limit is 155 pounds for gliders.

    Howdy pardner, thanks for the response, I’ve heard most gliders with the specifications I’m looking at are around 36’, I guess I’m just trying to find the math behind that.

    Also where is a good place to find aircraft fabric covering, can’t I just use fiber glass?

  7. #7

    Join Date
    Oct 2011
    Location
    WA
    Posts
    1,085
    Ultralights can use heat shrink-able uncertified polyester fabric from Aircraft Spruce and Specialty Company.
    Or some ultralights use the heavier marine sail fabric that doesn't shrink.

  8. #8

    Join Date
    Aug 2011
    Posts
    257
    Quote Originally Posted by Braxton Hornbuckle View Post
    Also where is a good place to find aircraft fabric covering, can’t I just use fiber glass?
    You will find that fiberglass is very heavy. A structure covered in cloth will be much lighter.

    EVERYTHING in design is a trade off. Your wingspan question is a good example. A longer wingspan is desirable from a reduction in induced drag (drag due to lift), but as the wingspan increases (wing chord will decrease to keep the same wing area), wing weight will go up significantly because the spar height is decreasing so the spar caps have to get much thicker. Design is not easy; it is the result of what you determine to be the best compromise.

    BTW, if you try to do it all, you will probably end up with a design that is poor at everything.

    Get a book/magazine of existing gliders (or look online). Simple gliders like the “Bug” and “Goat” come to mind. See how you can improve on those designs. There are also some really cool foot-launch sailplanes (but you’ll need a cliff (hill) to run off to start. The more high tech the design; the more it will cost, too.

    Look online at what are called “secondary gliders”, too. They are primary gliders with a shell (or canoe) for the fuselage.

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