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James Clerk Maxwell
James Clerk Maxwell
3 stage air engine

click photos to enlarge

The most efficient air engine ever marketed, the European compound engine based on Charles B. Hodges' patents increased its range between fill-ups up to 60% by absorbing free ambient heat from its surroundings. There were probably a few thousand of these partially solar-powered locomotives in the coal mines of France, Germany and Belgium during the 1920s, most of them destroyed during World War II.

Burt air drive patent illustration

Robert Cady Burt's air car was a good example of two air engine technologies: closed cycle (recompressing air exhausted from engine) and hybrid (on-board compressor run by small gas engine). His patent is explicit and scientific, a good document to study.

picture of air car from Compressed Air Magazine

This picture of an air car from the olden days appeared in Compressed Air magazine's 100th anniversary issue, along with a promise to publish an article about air cars "soon". But "soon" never happened and the magazine was discontinued after 104 years in print.

injector concept by Scott Robertson

My goal with this design was to show an infallible means of injecting atmosphere into a pressurized tank without dissipating the energy already in the tank. The drawing shows a compressor in a full tank boosting tank air which drives a jet pump to induce atmosphere into the tank through a double bank of check valves. A Roots blower supercharges the atmospheric intake line. Both compressors are driven by an air engine using air from the tank. The injection method was suggested by General Herman Haupt in 1893. More description is given on the injector page.

New York City air station

During the 1890s, General Herman Haupt spearheaded a drive to make air cars a reality. He supported the work of inventor Robert Hardie, whose air powered locomotives ran on the streets of New York City for several years. This Scientific American front cover shows the 1500 horsepower compressing station (steam-powered) that was built to provide compressed air for the Hardie locomotives and for the Hoadley-Knight locomotives. The locomotives' tanks could be filled in a few minutes at the air station.

Bob Neal's self-filling air tank

From U.S. Patent #2,030,759 (1936). Bob Neal was a shoemaker from Arkadelphia, Arkansas who had to take his engine to the patent office to prove that his invention was not a perpetual motion machine; he was granted a patent based on the fact that his engine worked. The Pneumatic Options Research Library catalog is full of information related to our search for how it was possible for a series of check valves to allow low pressure air to be pumped into a high pressure air tank against a very small resistance. See especially the Acoustic Power section.

Bill Truitt with a picture of his 1920 air car

Bill Truitt is shown here holding up a picture of the air car he built in 1920. He perfected his design in the 1970s and gave the rights to NASA and the Army. Bill was from McKees Rocks, Pennsylvania. His design disclosure was fairly complete with the exception of one or two aspects which he said were top secret.

I built this go-kart in the late 1980s. It consisted of a scuba tank, an old wood boring drill, and a valve. From a dead stop headed up a steep hill, it accelerated so fast that it was hard to steer. On a straight, flat sidewalk its range on a scuba tank of 125 psi air was about 25 feet. This is the only air car I have ever built, a situation which I am eager to correct.

E A Rix signature in North Star Mine guestbook Jan 1 1899

A photo of the guest register of the North Star Gold Mine, January 1, 1899. Edward A. Rix was the founder of Rix Compressor Co., which still exists in Oakland, California. He designed air powered locomotives for the gold mines in Grass Valley, California, and held dozens of patents on pneumatic machinery. He also wrote a compressed air textbook with another compressor engineer, A. E. Chodzko.

resonance in closed-end tubes

My catalog contains hundreds of pages of information on the behavior of waves in compressed air and other fluids, because of my search for the working principles of Bob Neal's mysterious equalizer. This diagram was made by a mechanical engineer who got me started on the search for the sound wave solution when he suggested looking into the workings of the pulse jet engine. The diagram illustrates the building-up of pressure variations due to the reflection of compression and rarefaction waves in a closed-end cylinder of the right length.

solar pneumatic power plant by Scott Robertson

My concept design (1987) for a linear air engine/compressor unit with interheaters to absorb ambient heat and compression heat. Based on a type of air engine patented by Charles B. Hodges in 1907. I put this on the cover of a newsletter I tried to put out (Issue One) but it wasn't till they came up with the internet that I had a chance of getting this information into the right hands.

Ricardo Perez Pomar air car 1987 photo by David London

1987 photo by David London. Engineer Ricardo Perez Pomar's free-range air car was dismissed by a flippant newspaper article claiming that any such thing is impossible. After the inventor and his backer put $250,000 into completing a working model, the backer later backed out due to personal problems. People always ask me, "Why didn't this get to market?" The best answer is, "How could you possibly market something like this?" There are more ways to stop inventions, than there are inventions. As Bill Truitt said to the young reporter who later became executive editor of USA Today, "Those oil companies will break you before you cross the street."

Hardie compressed air locomotive

During the 1890s, General Herman Haupt championed the air car cause by finding investors for Robert Hardie's locomotive design for street transit.  One of the concepts proven by their effort was that of regenerative braking, that is, using compressors to slow the vehicle down while heating and compressing the tank contents to increase the range.

30-foot Pelton wheel ran 1000 hp compressor, Grass Valley, California

This 30-foot diameter Pelton water wheel was used in Grass Valley, California to run a 1000 horsepower compressor that provided tool air and ventilation to two of the largest gold mines in the world. The spokes of the Pelton wheel are seen in the background. It is one of the largest water wheels in the world, with a compressed air museum built around it. Mr. Pelton lived a few miles away in Camptonville. The shape of the water cups was inspired when Mr. Pelton squirted one of his cows in the face with a hose. I'd like to see you generate gasoline or diesel fuel with a jet of water piped in from Wolf Creek.

Terry Miller inventor, Scott Robertson, driving

Terry Miller invented the term "air car advocate". This photo shows me driving Terry in his first air car, Air Car One. Terry showed his air car from coast to coast, including Times Square, and I learned of him from an article in People magazine. This photo was taken by Terry's wife at the Wichita Energy Expo in 1985. While the shiny electric car at the booth next to us sat idle, we gave free rides on Air Car One nonstop for three days.


People love air cars!