The science
A displacer shuttles a fixed gas charge between the hot and cold ends; the power piston, 90 degrees behind, converts the resulting pressure swing into shaft work. In this teaching model the gas temperature seen by the power space is T(θ) = Tc + ΔT (0.5 + 0.4 cosθ), the volume is V = 1 + 0.18 sinθ, and the pressure follows the ideal gas law P ∝ T/V. Shaft torque is (P - Pref) dV/dθ; the net work per cycle is the area of the P-V loop, ∮ P dV.
The flywheel obeys J ω' = τgas - friction - load. The Carnot limit 1 - Tc/Th is shown for reference; an ideal regenerative Stirling cycle reaches it.
Simplifications (stated by the original page too): lumped gas, no regenerator or dead-volume model, no heat-transfer delay, pressure in calibrated kPa units, torque in arbitrary units. It is explicitly approximate and does not predict real engine power.
Made with ChatGPT · 2D companion of the 3D page; same solver and numbers.