Open-source browser-based simulation engine. Any vehicle is a JSON file. Any mission is a JSON file.

Born 05:32, Sunday 15 March 2026, Zürich. Built with Claude Code.

Realism as respect.

Every aircraft modeled here carried a human being. Every engine sound is calibrated from real recordings. Every mission is set on the right day, over the right place, with the right names.

We do not take sides in history. A nineteen-year-old climbing into a Zero over the Pacific deserves the same accuracy and respect as the one climbing into a Corsair. OpenSim honors duty. Not victory. Not ideology. Duty.

→ MANIFEST.md · CODE_OF_CONDUCT.md

Spotters — open the live radar, watch real flights within 1000nm, color-coded by destination. Click any aircraft and fly it at its current position, altitude, and heading.

Historians — load a mission from 1918, 1942, or 1956. Read the classified briefing document. Hear the crew in the right language. Fly the aircraft with the right physics.

Warbird buffs — the R-2800 Double Wasp fires 18 cylinders in two rows. The DB 601 startup takes 71 seconds from cold. Open the radiator flap too late and the coolant boils; spring a coolant leak and the engine seizes. Every number came from a POH or technical manual. If you've stood next to a running radial at an airshow, you'll know immediately whether it's right.

Space nerds — fly the Falcon 9 Demo-2 from T-3:00 with real webcast audio. Watch stage separation. Track the booster back to LZ-1, or out to the droneship. Fly a 590 km orbit. Deorbit, reentry, splashdown. Apollo 8 to the Moon, Apollo 13 home again, Starship IFT-12 and IFT-13. The physics are real. SpaceX, Apollo, V-2, Vostok, H3 — every program that ever put something into orbit deserves a mission here. Scott Manley would check the Isp. Everyday Astronaut would check the fairing. Check them.

PPL students — circuits at LSZF and LSZG. Full checklists. GPWS callouts. Emergency procedures. Scored debrief: alignment, speed, touchdown point. Engine failure scenarios with virtual ATC Mayday acknowledgement. Real weather via live METAR. No instructor needed to run a session.

Airline pilots-to-be — gate to gate on real SIDs, STARs and approaches. LNAV and VNAV fly the route, the ND draws it, the MCDU and kneeboard brief it — including the missed approach. EGPWS watches the terrain.

Makers — build a Dragon capsule mockup with a table saw, a Bambu A1, and four screens. Wire an ESP32 to a physical altimeter. Add a 6-DOF motion platform. The WebSocket data stream is open.

Anyone with a browser — no install. No login. No fee. Works on a laptop, tablet, or Raspberry Pi.

OpenSim is not a game. It is a modular simulation engine that runs entirely in the browser with zero dependencies and no build step.

• Real aerodynamic physics — lift, drag, thrust, weight from first principles. Not kinematic approximations.
• Procedural sound — engine sounds synthesised from physics. No samples. Wind rises with airspeed. The DB 601 fires 12 cylinders. The NK-12 turboprop beats at 3.8Hz.
• Historically accurate comm chain — every voice passes through the correct radio equipment for its era. VHF aviation, NASA S-band, Soviet VHF, SpaceX IP backbone. Pre-recorded voices, archival recordings, or TTS — all through the same chain.
• Real terrain — Mapbox Terrain-RGB tiles (Copernicus DEM, 30m resolution) projected onto a flat-earth pinhole camera. Mountain silhouettes, elevation-based colour, atmospheric haze, space skybox with stars. 60 fps on M2. A default public token is included — replace it with your own free token in display/terrain.js if you're running a public deployment.
• 3D wireframe aircraft at 60 fps — flat-shaded painter's algorithm in pure Canvas 2D. Back-face culling, depth sorting, light-direction shading. No WebGL. No Three.js. No dependencies. Chase cam · side cam · wing view · plume cam · booster cam. For Falcon 9: engine plumes, LOX vent clouds, grid fins, S2 Merlin Vacuum bell, landing legs that deploy.
• Any aircraft — envelope, performance, handling, sound, crew language, checklists in one JSON file
• Any mission — weather, ATC clearances, classified briefing documents, scripted failures, crew voices in one JSON file
• Data-driven airports — runways, taxiways, gates and terminals derived from OSM + OurAirports. Fly an approach into an airport the sim has never seen and the ground environment is already there.
• Gate-to-gate — pushback, ATC taxi clearances over the taxiway graph, vacate detection, gate assignment, and VDGS docking guidance — both directions of the ground phase.
• Real navigation — SIDs, STARs and approaches from FAA CIFP / X-Plane nav data, airways, navaids. One route (core/route.js) feeds the briefing, the ND, the MCDU and the LNAV/VNAV autopilot.
• EGPWS + CFIT — terrain collision from the Mapbox DEM, reactive and predictive terrain warnings, sink-rate callouts, terrain display on the ND.
• Data-driven cockpit views — each aircraft JSON lists the zones it has: overhead, left, centre, right, pedestal. An airliner has all five; a fighter has its two side consoles; a light aircraft has the pedestal.
• Aircraft systems — fuel, electrical, hydraulics, battery state of charge, a generic engine-cooling heat balance (liquid or air-cooled, driven by real outside-air temperature), autobrake, speed brakes, parking brake.
• Live radar — real flights via OpenSky Network, color-coded by destination, route lines to arrival airport, 150/400/1000nm range
• Runs anywhere — laptop, tablet, Raspberry Pi, custom cockpit panels

# Any static server works
python3 -m http.server 8080
open http://localhost:8080

No build step. No framework. No dependencies. Open index.html and fly.

First time? → docs/quickstart.md — the screens you'll see, a first flight to watch, a first takeoff of your own.

G1000 (C172): Click any switch in the left panel to toggle it. Click the COM1 frequency in the PFD top bar to show/hide the COM panel.

Gamepad: Logitech Extreme 3D Pro out of the box. axes[0]=roll · axes[1]=pitch · axes[2]=rudder · axes[5]=throttle · buttons[1]=flaps · buttons[2]=gear

Airliners here are not shaped by eye. Manufacturers publish airport-planning drawings (DWG) so airports can lay out gates and taxiways — every fuselage station, wing root, gear track and engine position dimensioned to the millimetre. OpenSim reads those numbers.

Each airliner JSON carries a dimensions block of real measurements, and the wireframe geometry is derived from it:

• fuselage diameter sets the model scale
• the wing-to-body fairing is a flat-bottomed super-ellipse from its DWG cross-section
• landing gear from track / wheelbase / strut lengths
• wing position from its root station — move it and the engines, pylons and flap-track fairings follow
• the engine nacelle is a parametric builder — fan-cowl ratio, nacelle profile, stepped core nozzle — so a GE90 reads differently from a CFM56
• cockpit windows as explicit polygons matched to the type

Truth in, truth out. Accuracy is intrinsic, and a wrong number shows up as a visibly wrong shape. The A340-300 HB-JME (Edelweiss) is the reference build; the 777-300ER and A350 follow the same method.

The same idea, one level up: an airport is not modelled by hand either. ICAO Annex 14 standardises how every airport is laid out — and the open data already maps it. So the entire ground environment is derived, not drawn:

• runways from OurAirports (CC0) — thresholds, true bearing, width
• taxiways from OpenStreetMap (ODbL) become a navigable graph — shared nodes are vertices, each way carries its designator (A, B, C…)
• stands / gates from OSM aeroway=parking_position — the painted lead-in line gives the stop point and the nose-in heading for free
• terminals + aprons from OSM aeroway=terminal footprints, extruded to wireframe massing
• jet bridges reach from each gate to the nearest terminal wall; VDGS units, taxiway signs and lead-in lines all fall out of the geometry

Run scripts/build-*.py once to bundle a new airport's OSM data. Then you can fly an approach into an airport the sim has never seen — München, say — and the runway, your taxi-in route, the assigned gate, the VDGS and the taxiway signs are all there, because the standardisation is the model. The drawing is the compression; the sim decompresses it.

One taxiway graph powers the entire ground phase, in both directions.

Departure — request pushback at your stand; a tug walks the aircraft back onto the taxiway. Ground gives a taxi clearance routed over the graph — "taxi to holding point runway 22 via Foxtrot, November" — the green route draws on the map, you hold short of and cross runways on request, then line up and go.

Arrival — after touchdown, vacate detection latches once you turn off the runway and slow to taxi speed. That unlocks the REQUEST → Taxi to gate call. Ground assigns a gate from the arrival dock (random within the dock, or a fixed stand) and reads the full clearance — "taxi to stand E27 via Foxtrot, Delta" — which lands on the kneeboard scratchpad while the green route leads you in. At the stand a VDGS shows your aircraft type, an azimuth dot tracking your offset from the lead-in centreline, the closing distance, and STOP at the parking line. ENG MASTER OFF and the turbofan coasts down by inertia to a descending spool-down whine.

Autobrake (LO/MED/MAX) is armed from pushbuttons on the centre panel and disarms when you touch the brakes. Brake-to-Vacate, the jet-bridge connect and brake temperature are the next links in the chain.

Story missions (Wolfskopf) run with a fixed scenario and skip the scenario chooser.

Press Near me to fetch real flights via OpenSky Network. No account needed.

• Range: 150nm (local) · 400nm (regional) · 1000nm (intercontinental)
• Color coding: each destination airport gets a color. All flights going there share it.
• Routes: callsign lookup via adsbdb.com — LSZH → JFK, ORD → EDDM
• Click: spawn the sim at that aircraft's current position, altitude, and heading.

OpenSim uses a real aerodynamic force balance — point-mass wind axes:

L = q × S × CL(α, flaps)
D = q × S × (CD₀(flaps) + k × CL²)
T = throttle × Tmax × ρ/ρ₀ × enginePower
W = mass × g

dv/dt  = (T·cos(α) − D − W·sin(γ)) / m
dγ/dt  = (L − W·cos(γ)) / (m·v) − 0.4·γ + trim × 0.0015

ISA density: ρ = 1.225 × (1 − 2.2558e⁻⁵ × alt_m)^4.2559

Angular inertia — PD controller with momentum (τ_roll = 0.18s, τ_pitch = 0.30s). Stall — high-alpha snap + energy stall (progressive sink at low speed). Gyroscopic precession — rotary engines precess when pitch or roll rate changes.

Point-mass gravity turn, programmed FPA profile, extended ISA through 140 km. Thrust interpolated sea-level ↔ vacuum.

Orbit-targeting guidance — the upper stage steers to a target orbit and cuts off on velocity, not on a clock. Callouts fire on events, not timestamps. tools/booster-descent-sim.mjs simulates ascent and booster descent offline and reports each mission's reachability.

Staging — cold-staged vehicles show a visible separation gap during the coast (hot-stagers and the Saturn V don't). Upper-stage thrust spools up. Dragon separates from Stage 2 with drift and a Draco ΔV.

Orbital propagation — Velocity Verlet integrator in ECEF. Energy conserved < 0.01% over 30 minutes. Dragon / Stage 2 propagate independently after separation.

Deorbit + reentry — retrograde ΔV at deorbitT, drag below 140 km, drogue at 5 500 m, mains at 1 800 m, terminal ~6 m/s.

Booster recovery — flip → boostback → coast → entry burn → glide → landing burn, engine-first. Single engine proportional throttle v²/2h. Grid fins deploy after separation; 3D landing legs deploy over 5 s and cast a ground shadow. Two recovery modes, set per vehicle in the JSON:

• RTLS — boostback to the landing zone (Demo-2 → LZ-1).
• ASDS — no boostback; the booster lands on a droneship at the real landing point (Inspiration5). Predictive landing guidance, and a ship cam (mode 6) that shows the full booster coming down onto the deck.

The booster cam (mode 5) auto-activates during boostback, entry burn, landing burn, and landing, then restores the previous camera.

Time warp — w steps 1× → 2× → 5× → 10× → 100× → next mission event; j jumps straight to the next event. A 3-day Inspiration5 orbit passes in minutes.

The Cessna 172 uses a three-zone canvas layout matching the real G1000 NXi installation:

┌─────────────┬───────────────────────┬───────────────────────┐
│ Switch panel│       PFD             │       MFD             │
│  (14%)      │  attitude · tapes     │  engine strip         │
│             │  HSI · ILS · COM      │  EGT/CHT/OIL · fuel  │
│  MASTER     │                       │  map overlay          │
│  AVIONICS   ├───────────────────────┴───────────────────────┤
│  FUEL PUMP  │   Analog backup: ASI · AI · ALT               │
│  MAGNETO    │   (always powered — vacuum / standby)         │
│  LIGHTS     │                                               │
└─────────────┴───────────────────────────────────────────────┘

Cold-dark startup sequence:

1. MASTER BAT → ON
2. AVIONICS → ON (powers both screens)
3. FUEL PUMP → ON (boost pump audible)
4. MAGNETO → click to cycle: OFF → R → L → BOTH → START
5. START fires the engine lifecycle — whirr → catch → idle → running
6. MAGNETO snaps back to BOTH when engine catches
7. FUEL PUMP → OFF after engine running

COM panel: click the COM1 frequency in the PFD top bar to show/hide the full COM + transponder panel. Real mission frequencies from the mission JSON. Appears on the right side of the screen.

All engine sound is synthesised. No samples.

See docs/db601-synthesis.md for the full DB 601 physical impulse model.

Every voice in a mission passes through the correct radio equipment for its era. The voice source and the comm chain are decoupled:

[voice source]           [commProfile chain]
ElevenLabs MP3      ──►  bandpass + presence boost
Archival recording  ──►  noise floor + crackle
H4n Pro WAV         ──►  carrier hum + squelch tail  ──►  speakers
Web Speech TTS      ──►
                    ↑
          environment bleed
          (engine tap from sound.js)