Strix

What it is

A four-stroke pusher mounted between twin booms, with the pilot and engine in a chined centre-section pod, fixed tricycle gear, a ballistic airframe parachute, and a fixed-pitch propeller. The engine runs for the whole flight, so the glide ratio is a performance number rather than the mission.

Looks are a stated requirement, not an afterthought: few edges, each one continuous and aligned with the planform, near-planar panels between them. There is a written surface-discipline reference the geometry is measured against.

I am not an aerospace engineer. What I am is someone who will not accept a number he cannot trace, which turns out to be most of the job.

The current airframe

These are renders of the same model in the viewer above. The surface lines are the CAD face boundaries and construction stations, left visible on purpose — they are how you see whether a surface is actually fair or merely looks it from one angle.

The decision worth explaining

The design has been reframed twice, and each reframe meant deciding which constraints were real and which had merely become habits.

It began under an ultralight category with a hard empty-weight limit, a stall ceiling and a fuel cap. Released from that, it became a self-launching sailplane — soar with the engine off, retractable monowheel, folding propeller. Then it was reframed again for the pilot who will actually fly it: engine on throughout, fixed gear, a parachute, a simpler propeller.

Three things are open, and the page says so

This is a design in motion, not a finished object. As of September 2026:

• Span. The CAD exploration and the airflow cases use an 11.0 metre wing; the handling, stability, performance and weight studies all use 14.2 metres. Which one the aircraft has is an open decision, and the two halves of the project currently disagree.
• Weight. Sourced equipment plus a measured centre-section structure put it at 333 to 419 kilograms with a pilot and full fuel, against the 320 the spar was sized for. Either the structure is re-sized or weight comes out.
• Pitch stability. Counting the pod as a lifting body, the aircraft is unstable at today's centre of gravity. The fix being sized moves the wing and tail aft with a larger stabiliser; only a handful of the grid points evaluated so far satisfy the targets across the full pilot-weight range.

Naming the open items is not modesty. A design where the unresolved parts are written down is one you can hand to someone else; a design where they live in the author's head is not.

The number I refused to publish

The engine cooling installation is undersized. A fully-fed duct needs roughly 1400 square centimetres of radiator face. Three concepts were built and measured against the real bay; the best reached about 904. That is approximately 83 percent of required flow, which sustains around 36 kilowatts continuous instead of 43 — a real climb-power limitation, recorded as one.

The tempting move was to write the cooling factor as though the duct were fixed, which would have published a noticeably better glide ratio.

The ceiling turned out to be aerodynamic rather than geometric — the volume that looks free is the path the air-cooled cylinders need. The remaining recovery is a closable inlet door, which the design promises and has not yet drawn. That sentence is in the project's own README, in bold, near the top.

Everything regenerates

The geometry, the structural layout, the weight statement and the performance figures all come out of scripts. Change the engine and the weight, the balance, the climb rate and the glide all move together. There is no drawing updated by hand and no spreadsheet holding a stale number.

A contract-test harness runs over the model and fails the build on geometry that is physically wrong — surfaces folding through themselves, sections crossing themselves. Bad shapes are caught by a gate rather than by my eyes at midnight.

The published performance table carries an explicit warning that it is the previous configuration, before the tricycle gear, the parachute and the fixed propeller, and has not been regenerated. Stale numbers are labelled stale instead of quietly presented as current.

Honest limits

• This is a design. Nothing has been built or flown, and nobody should treat these figures as engineering advice.
• The analysis is estimation calibrated against a known sailplane, not certification work.
• Span, weight and pitch stability are unresolved, as described above.
• The cooling shortfall is unresolved.
• The repository still carries the old project name in its directory, filenames and presets — the debris a long redesign leaves behind.

Seeing the code

The repository is private. If you are evaluating me and want to read the code or walk through the architecture, ask me and I will arrange read access or a screen share.