The Part 103 fleet is mostly 1980s designs. They are cheap, they are buildable in a garage, and they hurt people in a small number of well-understood ways:
- Ground loops, because almost all of them are taildraggers
- Stall-spin departures
- Nothing structural ahead of the pilot's legs
- Lap belts instead of harnesses
- A 7:1 glide, so an engine failure leaves you very few fields to choose from
Every one of those is fixable for roughly 100 build hours and $1,900. Nuthatch is what that looks like.
A single-seat wood-and-steel ultralight derived from the TEAM Sky Pup and Ison Airbike. Plans, drawings, calculations, build log, and measured flight data all live here. So do the mistakes.
Named after the only bird that climbs down a tree headfirst. Small, plain, and does it backwards from everything else in the class.
Status: design phase. Nothing is drawn yet. See docs/open-questions.md for what is still undefined.
| Cost, materials | under $15,000 |
| Build hours | under 750 |
| Takeoff roll | under 200 ft |
| Fits | a 22 ft garage and a 16 ft flatbed trailer |
| Part 103 | a compliant configuration off the same drawings |
Two configurations, one set of drawings. See docs/specs.md.
| EAB build | Part 103 build | |
|---|---|---|
| Empty weight | 296 lb | 250 lb |
| Gross | 580 lb | 450 lb |
| Span / area | 31 ft / 130 ft² | same |
| Stall, with slats | 28.8 mph | 23.8 kt |
| Takeoff roll | 140 ft | ~160 ft |
| Climb | 1,010 fpm | ~500 fpm |
| Glide ratio | 10.7 | 10.7 |
| Cruise | 55–60 mph | 55 kt limited |
| Range | ~150 mi | fuel limited |
| Engine | Hirth F-33, 28 hp | direct-drive, ~16 hp |
| Brakes | yes | yes |
- Welded 4130 steel tube fuselage, all-wood cantilever wing
- Constant chord, 3-piece removable wing, two bolts per cap per joint
- Douglas fir truss ribs, plywood D-tube leading edge, fabric covered
- Aluminum tube spar caps with a wrapped sheet shear web
- Fixed full-span leading edge slats
- Two-axis control: elevator and rudder, roll via spoilerons and dihedral
- Tricycle gear, steerable nose, sprung tube mains, bicycle hydraulic disc brakes
- Structural nose bow ahead of the pedals, rollover hoop, 5-point harness, energy-absorbing seat
- BRS hard points designed in
Glide. 10.7:1 against roughly 7 or 8 for the aluminum-and-Dacron aircraft in this class. That is a safety number as much as an efficiency one: engine-out you reach twice the ground area.
Crash structure. Steel tube nose bow forward of the pedals and a rollover hoop behind your head, so there is a survivable volume rather than fabric.
No ground loop. Tricycle gear with a steerable nose.
No aileron spin mode. Roll comes from spoilerons, which produce proverse yaw and cannot be cross-controlled into a spin.
A fail-safe autopilot path. Spoilerons are single-acting with spring return, so an autopilot servo has no failure mode that takes roll control away from the pilot. See Junco.
docs/ design log, specs, load cases, open questions
analysis/ spar sizing, performance, V-n diagram
drawings/ wing, fuselage, tail, gear, fittings
model/ quarter-scale RC validation aircraft
build-log/ measured weights against estimates, failures
flight-test/ Phase I plan and logged data
docs/design-log.md — every decision and the number behind it, including the configurations that lost and why. Drawings exist for a dozen aircraft in this class. Reasoning does not.
build-log/measured-weights.csv — estimated against actual weight, part by part, as parts arrive. Every published weight in this class is a claim. This one will be a measurement.
Corrections to the analysis are the most valuable contribution, especially on spar sizing, slat geometry, and load cases. Open an issue with your numbers.
Documentation and drawings: CERN-OHL-S v2 (see LICENSE). Firmware and tooling, where present: MIT.
This is an experimental amateur-built aircraft design published as a work in progress. It has never been built or flown.
Nothing here has been reviewed, certified, or validated by any authority. The structural analysis is preliminary and every weight is an estimate until the build log says otherwise. Slat geometry, spar sizing, and load cases are explicitly unresolved.
If you build from this, you are the manufacturer. You are responsible for your own structural analysis, your own airworthiness determination, and your own decision to fly. No warranty of any kind is offered or implied, expressed or otherwise, including fitness for any purpose.
Aircraft built to Part 103 require no pilot certificate. That does not make them safe to fly without training. Get instruction.