Hot Air Engines

By Staff
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17333 34th St. Seattle, Washington 98188

On November 16, 1816, Robert Stirling was granted patent #4081
for an engine that ran on a column of air that was continuously
displaced to hot and cold ends of a cylinder. From that time on,
the hot air engine served as a stationary engine. It could not
compete with the more powerful steam engine and soon became
obsolete for industrial use. In more modern times, one of the more
popular uses for small engines was to power home cooling fans in
areas with no electricity.

Hot air engines are currently enjoying a renewed popularity,
mainly as models. This is partially due to the many possible
variations in construction. There are several commercially produced
models on the market, either in kit form or completely assembled
and ready to run. I have seen several models, well constructed in
home workshops, that would rival many commercial models. Of these,
there are many air cooled and water cooled variations. They can be
heated by direct flame, flame injection, sunlight, and various
other means.

Although my design does not equal many of the well-machined
units in appearance, it does rival them in performance, material
cost, and ease of construction. I chose this design because no
special tools or materials are needed. The cylinder and piston are
made from a shock absorber. The water jacket, heat jacket,
displacer cylinder, and displacer piston are all tin cans. The
water level gauge and the oiler are constructed of copper fittings
and glass vials. Everything else is basically welding rod and nuts
and bolts. The flywheel, supports, and frame can be of any
convenient design and material. These engines run quietly at about
200 r.p.m. with a Sterno can or alcohol burner for heat.

I’ve constructed four of these models and I call them
‘Rainy Day Numbers 1, 2, 3, and 4.’ I chose that name
because, with all of the materials prepared, this model is a
satisfying rainy day project.

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