Full-scale Economic model

Modeler's Corner

| June 2009

About 10 years ago, while traveling on business, I found myself wandering through a downtown tourist-oriented shopping mall. I was attracted to a small antique shop which proved to have nothing of interest except there, in a glass case, was a Sept. 8, 1883, issue of Scientific American magazine with an engine I had never seen before on the front cover. This I could not resist.

Unraveling the mystery
The engine was described as an Economic Motor Co. engine rated at 1/2 manpower (1/20 of a horsepower), also available in sizes up to 1/2 horsepower. The engine was of noncompression design with a flame ignition. I later discovered that this was the only non-compression engine designed and manufactured in the United States.

Fuel for this engine was illuminating gas, which was available in most large cities. It was manufactured from coal and also known as coal gas. The BTU content of this and similar gases was 1,000 BTUs per cubic foot or less. Illustrations in the magazine showed a rubber hose connecting the engine to a gas lamp on the wall. I recently discovered a patent covering a carburetor for operating this engine on gasoline.

Getting to work
The magazine lay in its protective cover for three or four years while I contemplated how I would obtain this engine. I slowly came to the conclusion that the possibility of any surviving engines was so poor that I had no chance of obtaining an original. The logical conclusion was that I must build a model, but I wanted a full-size engine. My preference was to build one that I could transport to shows without help, but this was complicated by the feeling that the engine would not be historically accurate if displayed on a cart. Another thing influencing my decision was foundry location. The nearest foundry I could locate that would do cast iron was over 400 miles away, while I had a friend with an aluminum foundry only 70 miles from home. The obvious conclusion was to build it mostly from aluminum.

A draftsman and I worked out the dimensions of the engine by scaling items that we recognized in the magazine drawings. This gave us a flywheel diameter of 21 inches. I also obtained copies of four patents filed by a man named Hopkins, which provided additional details on the construction. With this information, the draftsman produced a set of drawings for the major parts. The engine size I decided to make was the 1 manpower version.

Making the patterns
Next came pattern making. The base was fairly easy to make, using plywood flat parts and curved parts cut from cardboard tubing, Bondo and polyester resin, and lots of sanding. The frame was next with plywood parts machined on a Bridgeport mill, more Bondo and more sanding. The flywheel rim provided more of a challenge as no machine was available to build a 21-inch diameter. The problem was solved by making two halves on a CNC milling machine and joining them; the spokes were machined from wood on a Bridgeport mill and the hub on a wood lathe. The real challenge was figuring out how to make a pattern for a cylinder with 12 vertical fins. The first try was a lost plastic foam casting. A fin pattern was produced on the CNC for each end of a block of plastic foam, and a hot wire cutter was used to cut the foam. This did not work well and after several tries only one good part was produced. An aluminum casting was made and sleeved with a piece of hydraulic cylinder tubing with an inside diameter of 3 inches. This bore size proved to be too large when assembled into an engine. When the engine fired, the cylinder pressure was so great that the engine jumped each time it hit and the engine would simply walk off the table if not restrained. A different approach to building a cylinder was necessary.


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