Why has no one, that I've seen built one out of foamboard? Granted our passion and love is fixed wings, but that'd be a big "Whoot!"
A foamboard Cobra wouldn't be hard to fabricate. One would have to buy the the rotor, and the linkages would be tough. But It's RC. Surely there are some cheap ways to make that work.
Tell me what I'm missing. Why hasn't anyone done it?
My passion is mainly in scale helis, so I'll give my thoughts. The main issue here is that the mechanics, the "guts" of the helicopter would have to be from something a normal RC helicopter. And to carry the weight of a foamboard fuselage, it would probably have to be around 450 size. I think there was even someone on the FT Fans facebook page who made a Huey fuselage a while back out of foamboard.
The main issue is simply cost. Unless you get an extraordinary deal on finding a heli. the cost of the mechanics/servos/motor/esc isn't cheap. Even using a clone heli with bangood parts, a 450 heli is probably at least $300. And if you have decided to spend that kind of money, most would buy a nice fiberglass fuselage or scratchbuild one out of balsa and traditional materials. That's not to say it can't be done, but it makes it pretty rare.
I could see building a DTFB fuselage for some of those big cheap coaxial choppers. A KA-52 fuselage would look pretty cool on those, and the prices are MUCH lower. They would be restricted to indoor flight or VERY low wind though.