1881 LEHMAN HOT AIR ENGINE

1881 LEHMAN HOT AIR ENGINE
75mm bore, 35mm stroke, 155 cc, beta

Sir Julius von Haast commissioned Paul Lochmann of Zeitz in Germany to make this engine for the for the heat engines laboratory at Canterbury College (which later became Canterbury University) in Christchurch New Zealand.  It is a small version of a distinctive style of Stirling cycle engine developed from 1867 by Wilhelm Lehman of Nuremberg Germany and patented in 1869.

Lehman’s are horizontal beta style engines, generally coal fired, and were built in the range 0.5hp to 4hp.  They have a distinctive mechanical linkage connecting the crankshaft (which is mounted on top of the cylinder) to the piston and displacer.  Because they use unpressurised air as their working gas, they may also be called hot air engines (modern Stirling cycle machines use other gases- hydrogen and helium being optimum for power and efficiency- and at high pressure).  

Gustav Schmidt used a Lehman engine for the first thermodynamic analysis of Stirling Cycle machines in 1871.

Lochmann is best known for his now highly collectable hot air engine driven decorative fountains, excellent examples of quality German engineering from the era.  This Lochmann version of a Lehman is the only one known and is nearly identical to a small Lehman in the Deutsch’s Museum Munich.  Lochmann’s workshop later became home to Jost, well known for hot air engine fans- of which there’s also an example in the Mahan Stirling engine collection. 

It remained with the Canterbury University Engineering School for 130 years- until approximately 2010.  I first saw it while attending a conversazione there in 1962 when I was 15 years old, and it was stored in a cupboard under a lab bench while I was a student there from 1965 to 1968.  The interest I developed in this engine, and a Phillips 102C which was running during the 1962 conversazione, led directly to the 1987 beginnings (with Don Clucas) of what later became WhisperTech.   WhisperTech developed and manufactured WhisperGen Stirling engine powered combined heat and power units from 1988 until just after the 2011 Christchurch earthquake.

It has unfortunately lost its governor and water pump at some stage but is in excellent running condition.  
             
PETER LYNN, ASHBURTON, NEW ZEALAND 2025