A period of extended disillusionment followed this brief initial run of the 50cc yoke drive engine. My stirling work continued, however, and considerable time was spent thinking of ways to create extended surface area in heaters. Eventually, I decided to at­tempt an investment cast, externally and internally finned, stainless steel heater head. After overcoming the usual unforeseen difficulties, several successful multipart alumi­num dies were made to produce the wax patterns necessary for the casting process. To my dismay, the internal fins of the patterns, being 0.020 inch (.5 mm) wide, 0.060 inch (1.5 mm) deep and 0.020 inch (.5 mm) apart, proved to be uncastable by the very firm that had previously assured me they would be "no problem". These parts were eventu­ally successfully and consistently cast by another firm using vacuum investment and a newly developed ceramic. Indicative of my sagging morale at the time, however, this successful work was never followed up by actually testing one of these elegant heaters on an engine.

Another project undertaken during this period was a machine to dynamically test gas flow losses through heat exchangers. This machine was painstakingly designed and constructed, and then, for lack of interest, never used and eventually scrapped.

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