I found old plans for a plane called the Mugi Evo, which looked to be a pretty easy build. The original plane was built from something called Plastic Twin Wall Flute Board, but I decided to try and make it from a simple sheet of Dollar Tree foamboard. I knocked together a quick prototype to convince myself that it would, indeed, fly. It did - video of the maiden below - so I set about to try and put together a slightly less sloppy version of the plane.
I scaled the plans down to 95% to allow the plane to be cut from a sheet of 20″ x 30″ foamboard.
The plans call for the wing to be folded over without cutting but that wasn’t gonna happen with my Dollar Tree foam. Instead, I stripped of the paper from one side, then cut along the wing fold line. Next, I reattached the severed corners with some fiber-reinforced duct tape (which will give just enough to allow me to bend the foam board when the time comes.
I cut a 5″ x 5″ square of foamboard and glued it to the very front of the inside of the bottom half of the wing/fuselage. This will strengthen the nose area a bit, and give me somewhere to mount my servos and battery.
I decided to cover the paper-free side of the foamboard with colored packing tape before going any further.
I’m going to try to give the plane a ‘flame’ paint job, so I tried out my technique on the prototype, which is going to be torn down, anyway. It doesn’t look as good as I dreamed, nor as bad as I feared.
Testing out some LED strip lights in one of the stabilizer fins. The fin has had all the paper stripped off, and been covered in colored packing tape.
Moving on. I cut out pockets for the servos to sit in. A little dab of hot glue helps seat them. Then I ran a small zip-tie around them and out of the plane on the bottom. I used some leftover plastic from a GWS Pico Moth to give the zip ties something to grab onto that wouldn't just tear, which the foam would do. That's probably not very clear, so hear are some pix:
Zip tie running out the bottom of the wing and back in again:
I'm trying to get all the wiring squared away before I fold the wing up, as there's no good way to get at things afterward. One final test of the LEDs. I was thinking of adding more but I think this will probably be enough, actually.
I've got all the electronics squared away. Soon, it'll be folding time.
And ... I screwed up. Seems inevitable somehow. Despite my best efforts to get everything set up before folding and gluing the wing, I placed the servos slightly farther forward than in the original, prototype build.
As a consequence, the pushrods are now too short. And access to the servos is pretty much non-existent. I knew I might have to cut holes and some point to replace a servo, etc., but I'd hoped it would at least be sometime after the maiden.
On those size foamies, I've had good luck with using pushrods made from paper clips. I know there are all different sizes , but the medium ones from Wallyworld work good as long as you keep the length reasonable. And instead of EZ connectors , they are easy to bend into a z . Since you already have an existing rod , make the z by first bending a 90, then move down roughly the thickness of the horn, plus a little radius room, then another 90 ( here is the trick) sideways to the first bend! It's not a Z untill you twist it straight, but the metal is malleable to do so without breaking. Now join the two pieces of wire w heat shrink and a dab of glue....
It's a solid non adjustable length now, but if you ever need to move it an exacto will get them apart. I've never seen a 900g servo break that sheer bond.
The lights are cool, And I love wings.. Let us know how it acts in HI-ALPHA...
After slicing open some access to get at the servos. I actually had to cut even farther to pull the bad servo out.
Gluing up the bent nose doubler. Bending this bad boy was extremely trying. I must have snapped a dozen test pieces before I got one to come out. The secret turned out to be applying a layer of packing tape to the outside surface of the foam before bending.
Gluing the nose doubler in place, after applying a layer of red tape.
Getting ready to glue the underbelly doubler in place. I've removed the packing tape where it's going to go, to give me a foam-to-foam glue bond.
Adding the spine piece which runs behind the hatch.
It is flying well, got a few questions. Could you have made the hatch out of foam and not affected your CG or weight much? Great idea putting packing tape on the front fold first, would a little heat work too? Power system?
Thanks, Don. Sure, you could make a hatch from foam; that was my original plan but then I went through my big box of 'plastic crap that I should throw away except that it might be useful on an airplane at some point' and found that ... whatever it is, which looked perfect for my needs.
I suspect that heat would help the bending, but I've never actually tried it. (I've only used heat to straighten unwanted bending, post-crash.)
My current setup is:
24 gram 1700 kV KEDA motor from Strong RC
18-22 Amp HobbyKing SS ESC
(2x) 5 gram servos
Final AUW is 347 grams - up about 40 grams from my naked prototype, thanks to the addition of packing tape covering and LED lights.
My first one from Dollar Tree foam was a shade over 11 ounces, without the LEDs and other fancy stuff.
I left the paper on one half of the foamboard for strength, but I'm not sure that was necessary. Leaving it off would drop the weight of the empty wing by about 26%. That would shave off another ounce, at least.
This one flies pretty well at 12 ounces and a bit.
As I said previously, scale it down slightly - to 95% of the plan size - and you can almost pull the whole plane out of a single sheet of DTF.