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Thread: Thanksgiving Scratch-build: 52" Dollar Tree Armin flying wing

  1. #1

    Thanksgiving Scratch-build: 52" Dollar Tree Armin flying wing

    In another thread, I was whining about how I always crash my Sky Surfer because of incompetence/wind/CG/weight/motor. I've been looking at flying wings because of their better handling in high(er) wind conditions, and because I'm getting a little tired repairing my SS.

    Since it was Thanksgiving and I had some time on my hands, I decided to scratch build a flying wing using Dollar Tree foam. Pretty basic flying wing. I used the wing layout from the BajiWing and basically made everything else up.

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    Some stats:
    • Wingspan: 52"
    • Center section: 12"
    • Root Chord: 12"
    • Tip Chord: 6"
    • Aspect Ratio: 5.17
    • CG: ~13% static margin, 7.23" from LE
    • Fully loaded AUW: 3.6lbs (57.6oz)
    • Wing Loading: 15.86 oz/ft^2
    • Theoretical stall speed: 20 mph
    It's a standard cambered Armin-style wing. I wasn't paying attention and totally screwed up the camber. It's huuuge - around 2.5" tall at the root. I honestly have no idea how this will affect flight dynamics. I'm hoping I can overcome aerodynamic inadequacies with a stronger power system (the old "anything can fly with a big enough motor" maxim)


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    (My poor, sad Sky Surfer in the background)


    It came out a lot heavier than I intended. Being sick of repairing my Sky Surfer, and knowing how fragile DollarTree foam is, I reinforced the wing with several layers of bond paper and PVA. Between that and wooden dowel rods...it came out significantly heavier than I expected. Whoops. It is rock solid though, going to take a lot to smash it up.

    The plane holds two 2200mah batteries and a GoPro, but I'm going to leave the GoPro and one of the batteries off until I get a feel for flying. Should help bring some of the weight down.

    These pictures show a 1900kv / 6x4 prop combo because that's what I had laying around. I'm upgrading this to a more legit 1400kv / 9x6 combo which should provide ample power.


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    GPS is mounted on one wing tip. I've had a horrible time getting the GPS to acquire satellites on my SS, so I'm hoping the long distance between VTx and GPS will help. Also all the usual things to help (ferrite rings, LC filter, low pass filter on radio Tx, etc)


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    5.8Ghz cloverleaf mounted on opposite wingtip. The VTx is mounted mid-wing with a little cutout so the heatsink can get adequate airflow.




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    Interior is a bit more cluttered than I would like, but about a gazillion times cleaner than my SS. Everything is relatively easy to reach and service.

    All in all, it was a lot of fun to build. Even if it doesn't fly, or I smash it into pieces, the frame cost roughly $4. I'm planning on getting a real flying wing at some point, but hopefully this tides me over.
    Last edited by polyfractal; 25th November 2012 at 06:42 PM.

  2. #2
    Navigator
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    Outstanding! I can't wait to see the flight video. Do you have any shots of the build? Have done other scratch builds? The BajiWing is on my short list (along with 4 other planes and projects), any pointers would be most helpful. How are the wings reenforced? How are they connected the fuselage?
    Great work! I can't wait to see how it turns out.
    Michael

  3. #3
    Thanks! I'm afraid I don't have any photos of the build itself...got so caught up in building that I forgot to snap some occasional photos.

    The only other scratch build I've done/doing is this one: inverted v-tail pusher. That one is more experimental since I'm doing the design entirely by myself. This flying wing was a lot faster and easier since the design is pretty well established.

    I used this wing layout without modifications:

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    Word of warning: the Armin wing method has you fold the top (yellow) half down onto the red half. Really important...make sure you press down on the camber and flatten it! The sweep angle on this layout makes the camber naturally very tall. If you don't flatten it, you get a ridiculously deep camber like mine (~2"). You can see an example of pressing the camber down in the original Armin wing videos.

    Of course, the tall camber is nice because you can embed everything you need inside the wing itself...but I think the tall camber is going to cause a lot of drag and slow down my wing a lot. We'll see.



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    As far as reinforcements, I have four sections of wooden dowel rod reinforcing the wing. Two thicker dowel rod (7/16") connect the wing sections to the center fuselage section. The upper dowel rod passes through the foam wing formers (blue boxes), while the bottom dowel rod end right at the former. Both rods are gorilla glued + hot glued in place, with a strip of duct tape over top.

    If I were to do it again, I'd move the bottom dowel rod so it was closer to the upperrod . It basically makes a barrier to how far you can move the motor forward, which has made my CG a bit tricky. Even just a few inches forward would have helped a lot.

    Two thinner dowel rods (3/8") run along the wing and are gorilla glued + hot glued into place, in front of the foam former. A lot of people embed them directly in the foam formers...but I was being lazy and this was easier.

    The foam formers themselves are stacks of foam with varying lengths to achieve a taper.
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    Its a crude drawing, but you get the idea The stack is 4 tall at the tip, and 8 tall at the root. The top piece of foam is one continuous piece that bends across the taper to smooth it out.

    After I applied the paper + PVA lamination process, the paper stretched tight as it dried. You can see the foam former pretty clearly on one of the pictures. If I were to do it again, I'd probably make the formers one less tall to account for this effect (although I would just reduce the camber in general).



    The wings are also hot glued to the center section, then bound in duct tape all the way around. We'll see how sturdy it is, but it's survived a few powered tests/crashes and can be shaken around a lot without any visible bending/warping/cracking.

  4. #4
    Instructor Pilot
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    I also built a flying wing using the Armin method and DT foam, only I didn't taper it. I learned a lot from the building process (my first time building a plane) and used some things I learned on my next build. Anyway, mine doesn't fly for crap but it is re-donk-u-lous-ly strong. Covered 100% in Scotch HD packing tape, 3mm plywood spine cut to the shape of the wing root (wings are glued to its faces), and a thin stainless steel wire taped to the length of the LE to absorb sharp impact, coroplast 'bumpers' a la Zephyr 2. It has been thrown into the ground countless times attempting to get it airborne, and only shows a wrinkle on the top of one wing. The stainless wire deflects most of the impact and carries little weight penalty.

  5. #5
    Think I may steal that plywood-at-root chord idea. I've been bothered by the stability at the join between the wings and fuselage. Having a plywood spine would help a lot.

    How heavy is your plane? What kind of wing loading and motor/prop? I've been scouring FPVLab looking for weights so I can compare mine against other planes that work (and don't )

  6. #6
    Instructor Pilot
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    Quote Originally Posted by polyfractal View Post
    Think I may steal that plywood-at-root chord idea. I've been bothered by the stability at the join between the wings and fuselage. Having a plywood spine would help a lot.

    How heavy is your plane? What kind of wing loading and motor/prop? I've been scouring FPVLab looking for weights so I can compare mine against other planes that work (and don't )
    None of this is ideal, just stuff i had lying around from multicopters:
    9x4.7 SF prop
    1050kv 220w motor
    3s 2200 nanotech

    The weight is around 24oz/675g if I remember correctly. Then I added a 2" DT foam tube to give me more CG options (and to absorb more lawndart impact).









    Now it looks like some sort of scifi spacecraft


  7. #7
    Ohh, it's that plane. I think you showed the animated gif in my other scratchbuild thread. Nice to see the rest of the pictures, looks like a clean build. I can see why it would take a pounding...that tube fuselage can probably absorb a lot of damage on impact

    Just received my new motor in the mail: NTM Prop Drive 35-36 1400kv. Going to pair it up with a 9x6 to start, although I ordered a bunch of similar props so I can test them.

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