wreck-fall

A dead aircraft falls. The pure model behind b3d-death's wreckage: a tumbling ballistic descent, an impact, a skid, and a rest. Babylon-free, deterministic, unit tested — the same discipline as fly-by-wire and ballistics, whose ballisticStep does the translation here rather than a second copy of gravity.

Why this exists

A wreck used to stop dead at the point of death and hang in the air. Tonio, from a headset: "I collided with wreckage high up … the wrecked plane hanging in mid-air (it should really tumble to the ground)." Hanging wreckage is worse than untidy — it is a solid object in the sky, so the debris of one death becomes the cause of the next.

It is also the cheapest possible piece of the north star: the unit of progress is a watchable behaviour, and a plane that comes apart, tumbles, slams in and slides to a stop is one, for the price of eleven lines of integration.

The rules

• The spin is DERIVED, never random. Axis from the velocity — a craft tumbles end-over-end about the axis across its flight path — and rate from speed. So a fast crash windmills, a stall drops flat, and the same crash looks the same twice, which matters for a scenario you are trying to tune.
• It bounces once, badly. Real wreckage does not stick where it lands; it slams, hops, and slides. The hop is small and the skid decays, so it settles quickly rather than skating away.
• It stops for good. Below a threshold it is grounded and stays there — no infinite micro-bouncing, and the caller can stop stepping it entirely.

Ground is passed IN, not sampled here

The caller raycasts (that is a scene concern) and hands over a groundY. Which also means a caller holding the wreck's position on a NODE can copy it in and out each frame, so a floating-origin rebase is absorbed for free — the model never holds a world position across a shift.