Peter Lynn ARCHIVE
Stirling cycle air engines (especially of the unpressurised variety) are not renowned for power output. Most struggle to overcome their own friction.
They've had very little influence on the world, except for a brief burst of popularity in the 19th century. This was before the advent of IC engines, when not requiring a boiler certificate was enough advantage to offset the fundamental handicap of low specific output (by size and cost).
But, Stirling engines have been fascinating people since Robert Stirling demonstrated his first version in 1816.
And, many engineers and enthusiasts continue to invest lives and fortunes in their design, development, and promotion.
Accordingly:
As the standard power measurement systems by which engines are compared do not show Stirling engines in an advantageous way, I believe they should have their own special power scale (with apologies to Watt and a nod to Beaufort):
To be called: The Jude*Scale
Jude 1: No discernible preference for rotational direction.
Jude 2: Clear rotational direction preference but not self-sustaining.
Jude 3: Almost self-sustaining; tantalisingly close to.
Jude 4: Occasionally self-sustaining, but sometimes stops spontaneously.
Jude 5: Mostly self-sustaining- almost never stops spontaneously.
Jude 6: Easily self-sustaining- with excess enough to run its cooling fan.
Jude 7: Some power: Could spin the "Lotto" wheel (for small numbers).
Jude 8: Useful power; like from half an unfit person on an exercise machine.
Jude 9: Really useful output; enough to power a mobility scooter (but not uphill).
Jude 10: Power commensurate with cost and complexity (Never achieved yet).
*After Saint Jude the apostle- and patron saint of lost causes.
Peter Lynn, Ashburton New Zealand, 2025
PS. Having built 17 original full size Stirling engines since 1969, I have two 8’s and two 9's so far, but also one’s and two’s and have barely averaged Jude 6
