Long Earth Society01 · Engineering
Heat in.
Electricity out.
Nothing in between.
Stirling-class engines that turn a temperature difference into motion, and then into power, with no valves, no combustion inside, and almost no moving parts.
The lab
Builds & tests
Stirling-class engines only; everything else lives in Misc. Every build and test gets a page: the question, what was built, the data, the answer. Logs download as CSV where they exist.
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NASA-style
Free-piston Stirling engine (FPSE)
The architecture behind NASA's radioisotope Stirling convertors. Two pistons, no crankshaft: the gas itself and a set of springs keep everything in time.
The cycle
Displacer moves cold
Gas is pushed through the regenerator into the hot end. It absorbs heat and pressure rises.
Piston expands
High pressure drives the power piston outward. The magnets cross the coils: this is the power stroke.
Displacer moves hot
Gas returns through the regenerator to the cold end, dropping heat into the regenerator on the way. Pressure falls.
Spring returns piston
Low pressure plus the gas spring and planar spring pull the piston back. The cycle repeats at the system's resonant frequency.
- →No crankshaft. Piston and displacer are tuned mass-spring systems; the gas pressure wave keeps them 90° apart.
- →No contact. Gas bearings or flexures keep moving parts off the walls. NASA units have run for over a decade without wear.
- →Any heat source. Radioisotope, solar, propane, wood stove. The engine doesn't care what's on the hot end.
- →Hermetic. Sealed helium charge, electricity leaves through the wall. Nothing to leak, nothing to refill.
What LES builds
Thermoacoustic Stirling engine
Take the Stirling cycle and remove the displacer too. A sharp temperature gradient across a porous stack makes the gas oscillate on its own, producing a standing sound wave that pushes a linear alternator.
Why it's interesting
One moving part (the alternator piston), no precision bores, no seals under load. It trades power density for radical simplicity.
What limits it
Stack geometry, the gradient you can hold across it, and losses in the tube. Most of the experiments on the channel are about those three things.
Where it's going
Current work: replacing the diaphragm alternator coupling with a more heat-tolerant drive, and logging output vs. heater temperature for every build.
Components
Linear alternator
Converts the piston's back-and-forth motion directly into AC. Magnets on the mover, coils on the stator, no gearbox.
Tri-clamp nodes
Sanitary tri-clamp fittings make the engine modular: swap stacks, lengths and heater heads with a single clamp.
Custom valve
Vents hot air to regulate the hot-end temperature and protect the stack.
High-temp silicone diaphragm
Flexible coupling between the acoustic field and the alternator. Strong, but the weak link under sustained heat.
Products
In stock and sold through the LES Etsy shop.
Thermal Acoustic Stirling Engine
Complete thermoacoustic engine on tri-clamp hardware.
$249.99
High-Performance Ceramic Stack
Regenerator stack for thermoacoustic engines.
$29.99
Tri Clamp Copper Magnet Wire Spool
Coil spool for linear alternator builds.
$24.99
High-Temp Silicone Diaphragms (10)
Custom high-temperature silicone diaphragms.
$19.99