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William Lawrence Saunders photo from his memorial in Compressed Air Magazine 1931
air-powered shop truck

This photo of an air-powered shop truck was used to illustrate an article about pneumatic vehicles by Charles B. Hodges, the owner of several patents on what became the most efficient and most successful commercial air engine ever built. Hundreds of his engines were sold by the H. K. Porter Co., which is still in business.

refueling an air car

Another photo from the article by C. B. Hodges, showing an air-powered locomotive being refueled. Unlike electric cars which take hours to recharge, air cars can be refueled in a minute or two from central stations, or at a gas station if they are hybrid, or continuously if they are self-fueling (solar).

finned engine cylinders absorb ambient heat

Another photo from the Hodges article. This one shows the ribbed cylinders on an air powered locomotive's engine cylinders. The ribs or fins were for the purpose of absorbing heat from the engine's surroundings to warm the engine cylinders and thereby lessen the energy loss due to the cold of expansion. Hodges expanded on this principle in his design and patents for compound air engines using large interheaters between expansion stages.

Charles Hodges' compound air engine

An illustration from one of Charles Hodges' patents for compound air engines. The interheater is shown on the right. The engine's exhaust air was used to drive an ejector (jet pump with no moving parts) that pulled warm atmosphere through heat exchanger tubes surrounded by partially expanded compressed air between engine pistons/expansion stages in the compound engine. In one coal field in Germany, there were 624 three-stage air powered locomotives being used.

Rack-and-pinion crankshaft substitute

This is one type of rack-and-pinion (straight and round gear) crankshaft substitute. Also known as mangle racks, because they were used in the mangle, the early pedal-powered rotary ironing machines, to convert reciprocating motion to the rotary motion of an ironing drum. I've renamed this device the Torquerack. See the next illustration for more information; a video of the torquerack engine I built is also available.

dead center and piston motion

The crankshaft is a lever being used through a 360 degree motion, and is ideally unsuited for engines because it transmits torque completely at only a few positions in its cycle. The torquerack (see above) uses gears to transmit torque evenly throughout the piston's stroke. The unit I built uses two ratchets, two round gears (pinions) and two straight gears (racks) to convert the back-and-forth (reciprocating) motion of an air cylinder to continuous rotary motion of a shaft in one direction. Because of the low speeds required for effective absorption of ambient heat, the reciprocating mass would not be a problem. There are commercial manufacturers of rotary pneumatic actuators that use rack-and-pinion gears to transmit torque through part of a circle. These manufacturers would be ideally suited to design full-size torquerack engines for cars or stationary air engines. If I can do it, anyone can.

French three-stage air engine

This is part of the engine and controls of the compound locomotives used in French coal mines, which were inspired by Charles Hodges' U. S. patents. The article these illustrations are from is the most detailed exposition of air engine design ever published in a technical journal, and the engine it discusses is the most efficient air engine ever built commercially. I translated the article from the French using software and a good dictionary. My translation has been checked by a native speaker.

Hoadley-Knight air powered locomotive

The Hoadley-Knight air powered locomotive, which was developed during and after the Hardie air locomotive in New York.

Hoadley-Knight air powered locomotive
C. B. Hodges patent illustration C. B. Hodges patent illustration C. B. Hodges patent illustration C. B. Hodges patent illustration

Illustrations from Charles B. Hodges' patents.

Air powered locomotive in Haupt article

The two illustrations above are from an article by General Herman Haupt on air powered locomotives. General Haupt was a civil engineer and was in charge of the Union's railroads during the Civil War. He was discussed in the PBS series on the Civil War, where Lincoln called him "that man Haupt," which is also the name of Haupt's biography.


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