Week 2 of building a 20-foot foam cargo plane for aerial combat at Flite Fest. The elevators got finished, the tail learned to come apart for transport, the wing grew 27 laser-cut ribs and aluminum joiners, the nose got a quick-release latch, and the landing gear got custom 12-inch tires. By the end of the week the pile of disconnected foam finally looks like an airplane — and the weight estimate leaves almost no room to finish it under the 55-pound combat limit.
Flite Fest combat has a strict weight limit, and a 20-foot foam plane eats that budget terrifyingly fast. Every decision this week — how the tail joins, how the ribs are cut, what the joiners are made of — happens in the shadow of that number. It's why parts keep getting ovals cut out of their middles, and why "strong enough" always has to be weighed, literally, against "light enough."
The elevators on this thing are enormous, and they hinge into wood hardpoints glued into the foam so the hinges have something solid to bite. That part of the plan worked. What didn't: one side of the tail had wood exactly where the hinge pockets needed to go, and the Dremel couldn't reach deep enough to clear it. After a lot of unproductive carving, an oscillating saw solved in seconds what the rotary tool couldn't do at all — beveled the wood, seated every hinge cleanly. Lesson worth stealing: on big builds, hinge-line problems are tool-reach problems.
A 20-foot airplane doesn't fit in anything, so the tail was redesigned to be removable: a custom plywood-and-foam insert epoxied into the structure, a central rib, and 3 mm pins passing through wood blocks with collets so the horizontal and vertical tail lock together and can't pull apart in flight. The insert itself got an oval hollowed out of the middle — keep the load paths, lose the grams. That's the whole build philosophy in one part.
The wing panels join through a box spar — layers of wood forming a box that captures a removable aluminum tube set at an angle, which is what gives the wing its dihedral. This is the part of the plane where a failure would be catastrophic, and it got treated that way. It also produced the scariest moment of the week: Gorilla Glue expanding in the box very nearly locked the removable joiner tube in permanently. It came free. One side now slides in and out easily and sits rigid with barely any play; the other is tighter than it should be and gets more fitting work before the wing is trusted.
This week is also where the new CO₂ laser cutter (provided by OMTech — disclosure below) went from unboxed to indispensable. The difference from the little diode laser is night and day: where the diode dug divots and left edges that weren't usable for structure, the CO₂ machine cuts pink insulation foam and foam board cleanly in a single pass. That's what made 27 weight-relieved wing ribs practical — every one precise, every one lightened with cutouts, produced in batches instead of traced and knifed by hand. On a build where every part has to be both strong and light, precision fabrication isn't a luxury; it's how you stay under 55 pounds.
The nose has to come off for transport too, and a fistful of bolts at the field gets old immediately. The fix: printed hook latches — a hook that passes through an inch of foam and locks the nose in place, click-on click-off. The proof-of-concept worked well enough that four of them are going on the final airplane.
A plane this size needs landing gear from another category of aircraft. The answer was to 3D-print custom 12-inch tires (printed on the Bambu Lab H2D, along with the build's bolts and wing nuts). When the airframe outgrows the hobby supply chain, the printer becomes the parts shop.
End of Week 2: the disconnected foam pieces finally assemble into something that is recognizably an airplane. The wing structure is mostly glued together — but it isn't skinned yet, the systems aren't in, and the weight estimate says the remaining budget under the combat limit is razor thin. Skinning the wing, finishing the systems, and the Flite Fest attempt are next — with about two weeks left on the clock.
Disclosure: OMTech provided the laser cutter featured in this video. Hot Wire Foam Factory provided the cordless hot knife and StyroGoo adhesive. Some links are affiliate links — they cost you nothing and support the builds.
| OMTech CO₂ laser cutter · sponsor-provided | The machine behind the 27 ribs — cuts foam and thin ply cleanly in one pass. omtech.com/ERICROBBRC — code ERICROBBRC for 5% off. |
| Bambu Lab H2D | Printed the 12-inch tires, bolts, and wing nuts. Bambu Lab store · models on MakerWorld. |
| Hot Wire Foam Factory cordless hot knife · sponsor-provided | Clean freehand cuts in EPS foam. hotwirefoamfactory.com |
| StyroGoo foam adhesive · sponsor-provided | Instant-tack grab for foam-to-foam joints. hotwirefoamfactory.com |
Shopping for your own workshop? My tested picks — including laser cutters and 3D printers for RC work — are in the gear guide.
Nothing to correct yet — this write-up matches the video, and the build is still moving. The wing skinning, the finished systems, and the Flite Fest combat attempt land in the next episode. Spot something off? Tell me and I'll fix it.
