Initial (virtual) flight tests

Before the TerraHawk leaves the ground, it has flown a lot of air that only exists in a computer. This page is the short, plain version of what the first round of that work found, over the weekend of 2026-09-26 to 2026-09-28. The engineering detail, with every number and its caveats, is on the wing aerodynamics page.

A one-minute spoken summary. The narration is synthesized speech (Kokoro-82M, voice bf_emma); the transcript is below.

The tell-a-friend version

So, the drone project. We’re building a 3D-printed flying wing that takes off like a quadcopter and then flies like a plane, for mapping fields.

This weekend we basically put it in a wind tunnel, except the wind tunnel was software running on an old server in the closet. Fifteen simulations, each one wrapping the whole aircraft in about five million little boxes of air and working out how the air flows round every part.

The fun bit is what it caught. My quick models said the wing tips were doing important work, so we’d kept these little fins on them. The big simulation said nope, the new landing skids underneath were doing that job twice as well, so the fins are gone. It also showed the wing starts to stall at the seams where the printed pieces join, not where I’d guessed. So the fix for a better wing turned out to be a bit of glue and some tape. And one scary-sounding result from the rough first pass, a nose-up tendency near the stall, vanished when we ran it at higher detail.

Meanwhile a whole team of AI sessions was working in parallel: one designing the parts, one flying it in a flight simulator, one building the hangar it lands in, one doing the electronics. They kept each other honest, a couple of them caught my mistakes, and every change rippled through to weight, balance and how many acres it can map on a battery. Right now that’s about a hundred and thirty-five hectares, a bit over three hundred acres, per charge.

(That coverage is an estimate from the mission model. The flight simulator currently reads more energy for the same survey than the model does, and that gap is being worked out.)

Next step is real flying.

What “virtual flight tests” means here

Three kinds of model, each checking the one before it.

Quick models first. A vortex-lattice model of the wing (OpenVSP’s VSPAERO) and 2D section polars (XFOIL) gave lift, drag, trim and stability in minutes per case. They are how the landing gear went from four stilts to a keel under each VTOL spar: dozens of shapes compared in an afternoon. They cannot see the fuselage or the motor pods, and they know nothing about flow that separates from the surface.

Then the full airframe in CFD. OpenFOAM, on a server in the closet, solved the flow round the whole printed aircraft: wing, fuselage, pods, parked propellers and landing gear, from the same 3D models the printer uses. Fifteen cases in two rounds, the second on a mesh fine enough to change several answers. That is where the three findings above come from:

• The keel landing gear gives about twice the yaw stability the quick models credited, so the fins on the wing tips were no longer needed and have been deleted.
• The wing’s first separation appears at the printed joints, which is why the build now seals the wing seams and the elevon hinge lines.
• The nose-up tendency near the stall on the coarse mesh was the mesh, not the aircraft. The aircraft stays stable in pitch through 11°, although its margin shrinks toward zero there, so the stall arrives without a nose-down warning. That is the thing the first real stall test has to watch.

Then flying it in a simulator. ArduPilot’s SITL flight simulator flies the real autopilot software against a model built from these numbers: hangar landings in wind, transitions, gusts, surveys. It found things the aerodynamics alone could not, such as how much the autopilot has to fight the keels to hold a heading across the wind in a hover, and where the speed schedule needed to move up. A standard battery of test flights now runs against every design change.

What is still virtual

Everything on this page. The CFD is a model with known weak spots near the stall, the flight simulator is a model of a model, and the mass is from the slicer, not the scale. The first real flights, and a thrust stand before them, are what turn these numbers into measurements. Some of the figures here will move when they do; the aero page records each change as it happens.