Flight dynamics (preview)

Dawn Engine Flight (planned Gem Gems/FlightDynamics) integrates JSBSim as the sole flight-dynamics authority for aircraft. Dawn owns input, entity lifecycle, large-world transforms, rendering, weather bridging, terrain queries, kinematic collision proxies, editor workflows, and diagnostics.

Maturity: planned / design complete. First ship target: Windows / Linux desktop, single-player authoritative sim, fixed-wing MVP. Rotorcraft, VTOL, rockets, and multiplayer sync are architecturally reserved—outside first-release scope. Baseline: JSBSim v1.3.1 (LGPL-2.1), dynamically linked so users can replace a compatible DLL/SO.

JSBSim owns motion. PhysX does not re-integrate lift, drag, thrust, or gravity; AzPhysics supplies scene queries and optional kinematic proxies only.

What problem it solves

Simulation and training products need a data-driven fixed-wing loop—cold start through landing—without inventing another aerodynamic solver inside the engine. FlightDynamics is intended to provide:

Per-aircraft FGFDMExec instances advanced on a fixed simulation clock (default 120 Hz);
Aircraft / engine / systems / init XML packages—no per-airframe C++ forks for ordinary models;
Stable control, state, and event APIs for C++, Lua, and Script Canvas;
Large-world absolute state on AZ::Vector3d / AZ::TransformD with render-origin-relative GPU transforms;
One-way consumption of Weather atmosphere, wind, and turbulence facts;
Automated regression for units, frames, ground contact, and typical flight cases—plus LGPL-compliant shipping requirements.

Planned first-release scope

In MVP	Deferred
Fixed-wing piston and jet (shared architecture)	Rotorcraft wake / VTOL / rockets / orbital
Cold start → taxi → takeoff → cruise → approach → landing	Full avionics, ATC, weapons, damage, icing accumulation
Single-player authoritative FDM	Multiplayer prediction / rollback
Weather + terrain + kinematic proxy integration	CFD, aeroelasticity, certification training devices
Dynamic JSBSim link + replaceable binary	Static / LTO merge into a monolithic launcher

Realism is declared per aircraft asset (DeclaredRealismLevel). MVP acceptance targets R2 (procedural: mass/fuel, engines, FCS, trim, stall, gear, standard atmosphere and wind)—not FAA/EASA certification.

How it will work

Input / AI / Navigation3D expectations
 │
 ▼
FlightDynamics Gem ◄── Weather FlightBridge (facts only)
 │
 ├─ FGFDMExec (120 Hz fixed steps)
 ├─ Axis / unit adapter (body · NED · ECEF ↔ Dawn +Y forward, +Z up)
 ├─ HighPrecisionTransform (absolute)
 └─ AzPhysics kinematic proxy + terrain / runway queries

Design rules:

Render dt never enters FGFDMExec::Run() directly—only a fixed-step accumulator does.
One adapter layer converts JSBSim frames/units to Dawn conventions.
Weather writes environment; FlightDynamics never drives Weather.
LGPL-2.1 compliance is a release prerequisite: dynamic link, notices, corresponding source offer, and EULA reverse-engineering exception for user-modified JSBSim.

Rollout stages (FD0–FD5)

Stage	Intent
FD0	Version lock, dynamic-link probe, license / asset audit, upstream check cases
FD1	Wrapper, clock, units/coordinates, headless harness
FD2	Components, XML asset pipeline, Prefab, sample fixed-wing
FD3	Weather, terrain, gear / runway friction, collision proxies
FD4	Full-mission E2E under large-world / origin shift
FD5	Performance, Windows/Linux packages, license and compliance checks

Topic	Relationship
Weather (planned)	`WeatherFlightRequestBus` atmosphere / wind / turbulence
Double-precision rendering	Absolute FDM state vs float render origin
Navigation3D	Route / attitude expectations → control adapter (not direct Transform writes)
PhysX Vehicle	Ground vehicles only—not reused for flight FDM
Cesium 3D Tiles	Optional geospatial context for long-range visuals

Status and next steps

This chapter is a product preview. When FlightDynamics ships, expect Quick start (enable Gem, mount sample aircraft Prefab, map input), Registry / packaging notes, and debugging panels consistent with other user-guide chapters.