Radial: the R-2800 Double Wasp, taken apart - #3

What was built

machines/radial/: the Pratt & Whitney R-2800 Double Wasp, an 18-cylinder twin-row radial, modelled as a C-series CB16 (DC-6B) from public sources. It is not affiliated with Pratt & Whitney, and both the page and REFERENCES.md say so.

• One input. The crank angle is integrated once from a planned run: starter → magnetos on → first firings missed, then caught → idle → 2,700 rpm → idle. Every pose is read from that angle: pistons, master and articulated rods (exact geometry), cam rings (4 lobes, ⅛ crank speed, turning against the crank), tappets, rockers, valves, magnetos, planetary reduction gear, impeller and propeller. The sparks, gauges, propeller blur and score come from the same angle.
• Film (40 s): thumbnail at 3/4 front → starter → coughs → firing order going round the star, seen from the front in slow motion → a row in section (master rod vs articulated rod, panel included) → rows pulled apart (20° offset, crankpins at 180°) → a cam ring lifting a valve → climb to take-off rpm in real time → full power from the front → throttle back.
• Live page: starter, magnetos, throttle, slow motion, pause. Seven subsystems: rods & crank, cylinders & fins, cam rings, ignition, supercharger (air particles), gear & propeller, lubrication (oil particles). Cutaways: glass, section, solid. Views: face, ¾ front, profile, inside a cylinder. Cowling and label layers, orbit and zoom. An auto tour with a cursor plays when the visitor is idle. The page uses createChrome({slug: 'radial', ...}) and has quality tiers.
• Look: distinct from Spindl and Quantum. A 1940s airfield: pale sky dome, a warm horizon, concrete apron, a hard sun from the upper left. The console is styled as a period manual plate: paper panels with double rules, numbered figures, Barlow Condensed with a Saira Stencil title (both latin-subset @fontsource, SIL OFL), and round needle dials drawn from the model. The only accent is flame blue #0a8fe0, used for the firing cylinder, the pushing cam/tappet/valve and the compressed air.
• Three languages (en, fr, es) through makeT(). check.mjs is wired into npm run check. Also added: REFERENCES.md, FILM.md, og.png (1200×630, -map_metadata -1), a README row and the gallery description.

Figures checked (node machines/radial/check.mjs)

• Displacement π/4 × 5.75² × 6 × 18 = 2,804.5 in³ (45.96 L).
• Firing order from the FAA handbook's +11/−7 rule = 1-12-5-16-9-2-13-6-17-10-3-14-7-18-11-4-15-8. Every cylinder appears once, consecutive firings are 40° apart, the rows alternate, and the crankpin points at each cylinder at its firing TDC. In the film, each cylinder sparks once every 2 turns.
• Master stroke 152.40 mm. Articulated strokes run 152.41–153.08 mm. Articulated TDC is up to 3.7° early or late and up to 2.45 mm lower, which gives a compression ratio of 6.27–6.75.
• The lift read off the turning cam ring equals the valve timing for all 36 valves (error 0), and each valve opens once per 720°.
• Take-off 2,050 hp at 2,700 rpm, 55.0 inHg (exact, from the FAA TCDS 6A3); torque 5,407 N·m; 405 firings/s; mean piston speed 13.7 m/s; propeller 1,215 rpm (0.45:1); impeller 19,683 rpm (7.29:1). The same model gives 1,702 hp at the METO point, against 1,800 hp in the TCDS (−5.4 %, the check allows ±7 %).

npm test passes. Each page is about 975 KB, under the 1 MB budget, and the CI check of CSP hashes against inline scripts passes locally. In headless Chrome on an M1 (an integrated GPU), the live page renders WebGL at about 60 fps (quality tier 1) in en/fr/es. The only console errors are the favicon and the Cloudflare beacon failing under file://.

Decisions

• Series: CB16. The brief said C-series. Its primary public source (FAA TCDS 6A3) gives dry take-off at 2,700 rpm, which matches the brief, plus wet 2,400 hp / 2,800 rpm, a single-stage two-speed supercharger (7.29 / 8.58) and 0.45:1 reduction. The NASM record gives the weight, 1,068 kg.
• Power law: the propeller absorbs P ∝ N³, calibrated to the take-off point. Manifold pressure comes from bmep = k·MAP − friction − pumping, with k set by the take-off point. This is quasi-steady, with inertia neglected.
• Slow motion is a separate map from film time to physical time. The rpm shown is always the physical rpm, and the panel says how much the film is slowed.
• Run-up stand: the engine sits on a tall test stand so the true ~4 m three-blade propeller clears the concrete.
• Scope: I touched scripts/build.mjs only to add loader: {'.woff2': 'base64'}. I added two font dependencies to package.json. kit/, shared/, spindl and quantum are untouched.
• Callout names are 24 px on the 900-px layout (≈29 px at 1080). That is a little under the skill's 34 px, so the leaders don't cover the engine.

Known limitations / not confirmed from a primary source

• Not public, estimated, and listed under [E] in REFERENCES.md: master rod length (292 mm), knuckle-pin circle (60.3 mm), and which cylinders carry the master rods (13 rear, 8 front).
• The knuckle pins are placed at exact 40° steps. Real engines trim these positions, so the articulated-piston spread shown is the uncorrected geometry.
• The cam ring's 4 lobes, ⅛ speed and reversed rotation come from the FAA handbook's nine-cylinder example plus P&W's "same as the Twin Wasp". I found no R-2800-specific statement.
• The firing order is derived from the handbook rule, not taken from an R-2800 manual.
• Also estimated: valve timing and lift, spark advance, idle and cranking speeds, propeller diameter, and the reduction gear tooth counts (72 / 88, which give exactly 0.45).
• The geometry is simplified: pushrod tube routing (the far tube wraps around the barrel), the harness lead paths, the supercharger internals, and a generic cowling shape. Rocker boxes are capsules.
• The film's cross-fades into and out of the cam-ring view pass through about 1 s of ghosted parts.

🤖 Generated with Claude Code

https://claude.ai/code/session_01BzxZC5aA7ZkPTd3m9Kq4wy