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NASA Prandtl-D Flying wing

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    #16
    “Name that Tune!” in 30 Watts!
    “Sedate flying from a hand launch requires 35 watts per pound(W/Lb).”

    2.4 meter wing Moment of Inertia
    0.8m from centerline x 9g servo = 7.2 meter grams
    0.8m / 2 from centerline wiring for servo! x 9g??? = 3.6 meter grams
    10.8 meter grams

    0.15m from centerline x 2 x 25g motor = 3.75 meter grams (say, 30 cm between motors)
    = 29% of Moment of Inertia!


    You can't change the design of the printed wing, but you can replace the servos with two motors / propellers, closer to the centerline of the wing.

    Two pusher propellers provide thrust: half throttle for straight and level, full throttle for climb.

    Bank left by reducing power on one motor and increasing power on the other motor.


    Max Power: 30W 25g
    HC2208-1260 Kv = 1260, Rm = .450, Io = 0.50,
    Efficient Operating Current = 1-5.0A, 6.5A Max 15 seconds

    6 x 4 propeller 3 cells @ 3 volt
    9 V x 3.5V = 31.5 Watts

    HC2208 Series Motor
    HC2208-1260
    see graph of Current vs. Voltage with 6 x 4 Propeller
    HC2208-xxxx.pdf

    Doug

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      #17
      Originally posted by derfred View Post
      Following the suggestion of our fellow member my77gmc I´ve designed for 3d printing the NASA Prandtl-D flying wing:
      .

      My model will be 2.4 meter span, probably printable on a Prusa i3, 250X210X200 the chord at root its only 230mm plus a little bit because the wing is swept back.

      Dang derFred, I had no idea this was going on!!!


      congrats on the good work! What's a printed copy of the airframe go for? I need a copy of your 2.4 meter!!!


      for reference, the ailerons should have equal throw up and down, you can increase differential to get less down elevon to increase proverse yaw effect at the cost of some roll authority, or more down to decrease proverse yaw and increase roll authority.

      I would think one pusher motor in the center would be best


      Last edited by my77gmc; 05-09-2018, 12:57 PM.

      Comment


        #18
        Originally posted by Doug 77 View Post
        May I suggest ailerons and servos are unnecessary.
        Two very small motors, controlled differentially, may provide enough thrust to engage proverse roll.
        Enough thrust to climb to 100 feet in 60 seconds.
        Battery sized for 4 minutes flight...to acquire flight experience.
        Doug
        proverse yaw is produced by the wing shape itself, much like a bird does. Elevons are necessary to produce the effect in the way the designers intended, as such tip mounted motors are not necessary.
        Last edited by my77gmc; 05-07-2018, 07:05 PM.

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          #19
          This may help also, to keep cog forward. This is also BSLD but a non swept finless plank, so far called the "MarkoPlank V1" plans are in refinement stages.

          Comment


            #20
            Originally posted by my77gmc View Post


            Dang derFred, I had no idea this was going on!!!

            i let al know about this, he or red Jensen should be able to shed light on your questions.

            congrats on the good work! What's a printed copy of the airframe go for? I need a copy of your 2.4 meter!!!


            for reference, the ailerons should have equal throw up and down, you can increase differential to get less down elevon to increase proverse yaw effect at the cost of some roll authority, or more down to decrease proverse yaw and increase roll authority.

            I would think one pusher motor in the center would be best


            I will give you the files when I finish it, right now it doesn´t have the servo pockets and a few other details. I´ll share everything on thingiverse when I have it done.

            Agree, A pusher at the center shouid be the best and probably it wont even need much power to fly.

            Comment


              #21
              Originally posted by my77gmc View Post
              This may help also, to keep cog forward. This is also BSLD but a non swept finless plank, so far called the "MarkoPlank V1" plans are in refinement stages.
              That twisting wire link it´s interesting, On mine I´ll use abs filament to make the link. The link tubes are printed and the link itself its going to be 1.75mm filament. I+ll also make the link horns in 3d printing.

              Comment


                #22
                Originally posted by aeradmifor View Post

                I will give you the files when I finish it, right now it doesn´t have the servo pockets and a few other details. I´ll share everything on thingiverse when I have it done.

                Agree, A pusher at the center shouid be the best and probably it wont even need much power to fly.
                id be interested in the glider version 👍

                Comment


                  #23
                  This is on Facebook and the RCGroups.com conversation linked on the AMA website:



                  Let's assume for a moment that you want to build an RC model of a flying wing. Like a Horten. But you don't know how to create the twist. Or maybe you've built a few Zagi-like aircraft, and every time you designed something that looked like a Horten it didn't fly well at all ( if it flew at all). What went wrong?

                  The problem is the twist. I spent TWO DECADES figuring this out. There is a precise solution. This isn't precise. But after looking at the numbers, I think this is close enough.

                  A twist approximation

                  This will get you close and will give you a BSLD for a model. Some of this is guess-work on my part. But it shouldn't be too far off.

                  I assume you can do basic aero calculations, like lift coefficient and mean aerodynamic chord. I also assume you're using quite a bit of taper (tip chord is 10% to 50% of the root chord), you're using moderate sweep (15 deg to 25 deg), and fairly high aspect ratio (at least 6 or higher).

                  NEVER NEVER NEVER do this for an aircraft intended to fly a person!!!!! This is a crude approximation to use for a model ONLY!!! If I hear about any one trying to do this for a full size aircraft I will show up at your shop with a saw and cut your mold/wing up into little tiny pieces!!! I don't ever want a single one of you getting hurt flying something this crude!!!

                  First figure out what your design lift coefficient is going to be. This is where your aircraft is going to spend most of its time flying around. Motor aircraft will be somewhat faster (lower CL, like 0.4) than gliders which tend to fly slower (higher CL, like 0.6). This is a critical number, you need to remember this number really well (like your birth date or your wedding anniversary!!!). And I assume you're using thin symmetric airfoils (or nearly so). If you're using a cambered reflexes airfoil at the centerline that tapers linearly to a symmetric at the tip, you need to offset the twist by the zero lift AOA (this is the aerodynamic twist).

                  Second, calculate the total amount of twist you need for your wing. This number is 20 times your design CL. Example: if your glider has a design CL of 0.6 you will need a total twist of 12 degrees.

                  Now comes the hard/weird part. You need four control points on your wing along the span. The four control points are:

                  At the centerline, 0% span
                  At the quarter span, 25% span
                  At the half span, 50% span
                  At the tip, 100% span

                  Now set the twist at the 0% span (centerline) to zero.

                  At the 25% span (quarter span) you need your CL in degrees of WASH-IN. Example: our glider example with a design CL of 0.6 has 0.6 degrees of wash-in.

                  At the 50% span (half span) you need zero washout.

                  At the 100% span (tip) you need 20 times your design CL in degrees of washout. Example: our glider example with a design CL of 0.6 has 12 degrees of washout.

                  Now plot this on a piece of graph paper and get a French curve (I know, that's very old-school and antiquated) and draw a curve through those points. That's your twist you need for a BSLD. If you're fancy with a computer you can draw a cubic-spline through those points and get your twist curve.

                  To build, you can twist your building board or use a curved foam board jig to build on. Or you can make a series of wedges with an inverse twist and hot wire the wing (when you release the foam from the inverse twist, the foam will spring back and have the correct twist). Or you can cut a big fancy mold and lay up skins and build in the mold bed.

                  Make sure your elevons are all in the last 25-30% of the span out towards the tips. Also remember that the elevons needs to have straight hinge lines! Otherwise you won't be able to deflect your elevons.

                  After you get your model built start out with your CG way far forward, maybe set to 10% cmac. As you test fly, move the CG until your trim needed for level flight is with no elevon deflection.

                  Enjoy your BSLD aircraft! Let us know how well this works, and post pictures. A month from now there had better be dozens of baby Hortens flying around!

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                  • Frankensteve
                    Frankensteve commented
                    Editing a comment
                    Al Bowers post.

                  #24
                  Great to see BSLD projects moving along. Finless flying wings area fascinating development in aviation.

                  Comment


                    #25
                    Hey Fred, what was the process you used to get the .igs files to extract? What software did you use?

                    i keep getting error messages, and can't read file type messages

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                      #26
                      Hi!

                      I used fusion360, imported it into the fusion library and they converted it somehow, its not the importing mesh function on the software buttons bar, its on the file browser at the left

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                        #27
                        Originally posted by derfred View Post
                        Will make it glider only and post files on thingiverse.

                        My model will be 2.4 meter span, probably printable on a Prusa i3, 250X210X200 the chord at root its only 230mm plus a little bit because the wing is swept back.
                        Is this still in the works? I keep checking Thingiverse as it's very interesting to me but haven't found it yet.

                        Thankas

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                          #28
                          Yes, I´ve worked a little on it the other day, I will eventually finish it and post on TV.

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                            #29
                            Good day fellas, I recently got a dxf of optimized airfoils from Steven J Seim and a helpful Sketchup pro user helped to convert it to Sketchup and uploaded it to the warehouse. I'll attach the original dxf rendered in rhino version 5 or 6

                            Sketchup model here:
                            https://3dwarehouse.sketchup.com/mod...-120-optimzed#

                            Dxf attached
                            Attached Files
                            Last edited by my77gmc; 11-13-2018, 11:34 PM.

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