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A BRIEF
HISTORY OF AIR CARS
For half
a century the air-powered locomotive was a serious contender for the top
spot in transportation because of its obvious advantages: simplicity,
safety, economy, and cleanliness. Air engines were commercially
available and used routinely, first as metropolitan street transit and
later for haulage in mines.
The term
"air engine" disappeared from engineering textbooks after the 1930s and
the second world war. Gas engines had been perfected, the oil
industry was established, and gas was cheap.
Serious
interest in air cars was rekindled by the energy glitches of the 1970s.
Dozens of inventors have patented designs for hybrid, closed cycle, and
self-fueling air cars, as well as conversions for existing engines and
designs for air cars meant to stop at air stations for refueling.
(click picture for full size view)
The
Pneumatic Railway, 1880s to today
 Like modern electric subway
trains, the power supply was provided continuously by a pipeline laid
along the track. This concept was not practical at the time it was
invented (1820s) because the materials were not available to make it work
reliably. A modern version appeared in Brazil in the 1980s, invented
by Oskar H. W. Coester, and developed by Aeromovel Global Corp.
The Mekarski Compressed Air
Locomotive, 1886-1900
 The Mekarski air engine was used
for street transit. It was a single-stage engine (air expanded in
one piston then exhausted) and represented an advance in air engine
technology that made air cars feasible: the air was reheated after leaving
the tank and before entering the engine. The reheater was a hot
water tank through which the compressed air bubbled in direct contact with
the water, picking up hot water vapor which improved the engine's
range-between-fill-ups.
The
Hardie Compressed Air Locomotive, 1892-1900
 Robert Hardie's air engine was a going
concern in street transit in New York City. Air car advocate General
Herman Haupt, a civil engineer, wrote extensively about the advantages of
air cars, using the Hardie engine as his source material and providing
much of the impetus for the New York experiment to gain support and
succeed. The engine was a one-stage expansion engine using a more
advanced type of reheating than the Mekarski engine. One of its new
features was regenerative braking. By using the engine as a
compressor during deceleration, air and heat were added to the tanks,
increasing the range between fill-ups. A 1500 horsepower
steam-powered air compressor station was built in New York City to supply
the Hardie compressed air locomotives and the Hoadley-Knight pneumatic
locomotives.
The
Hoadley-Knight Compressed Air Locomotive, 1896-1900
 The Hoadley-Knight system was
the first air powered transit locomotive that incorporated a two-stage
engine. It was beginning to be recognized that the longer you keep
the air in the engine, the more time it has to absorb the heat that
increases its range-between-fill-ups. Hoadley and Knight were also
supporters of Nikola Tesla's disc turbine, for which they formed a
propulsion company that didn't get off the ground.
The H. K. Porter Compound Air
Locomotives, 1896-1930
 Inventor Charles B. Hodges became
the first and only air car inventor in history to see his invention become
a lasting commercial success. His engine was two-stage and employed
an interheater between the two piston stages to warm the partially
expanded compressed air with the surrounding atmosphere. A
substantial gain in range-between-fill-ups was thus proven attainable with
no cost for the extra fuel, which was provided by the sun. The H. K.
Porter Company in Pittsburgh sold hundreds of these locomotives to
coal-mining companies in the eastern U.S. With the hopeful days of
air powered street transit over, the compressed air locomotive became a
standard fixture in coal mines around the world because it created no heat
or spark and was therefore invaluable in gassy mines where explosions were
always a danger with electric or gas engines.
The European Three-Stage Air
Locomotive, 1912-1930
 Hodges' patents were improved
upon by European engineers who increased the number of expansion stages to
three and used interheaters before all three stages. The coal mines
of France and Germany and other countries such as Belgium were swarming
with these locomotives, which increased their range-between-fill-ups 60%
by the addition of ambient heat. It might have become obvious to the
powers-that-be that these upstarts were a threat to the petroleum takeover
that was well under way in the transportation industry; after world war
two the term "air engine" was never used in compressed air textbooks and
air powered locomotives, if used at all, were usually equipped with
standard, inefficient air motors.
The German Diesel-Pneumatic
Hybrid Locomotive, 1930
 Just
before technical journals stopped reporting on compressed air locomotives,
they carried stories on a 1200 horsepower full-size above-ground
locomotive that had been developed in Germany. An on-board
compressor was run by a diesel engine, and the air engine drove the
locomotive's wheels. Waste heat from the diesel engine was
transferred to the air engine where it became fuel again. By
conserving heat in this way, the train's range-between-fill-ups was
increased 26%. A modern train engineer tells me that all train
engines these days are hybrids: diesel-electric. And we are supposed
to consider the Toyota Prius a miracle of modern invention?
Terry Miller, the Father of the
Modern Air Car Movement
 In 1979, Terry Miller set out to
design a spring-powered car and determined that compressed air, being a
spring that doesn't break or wear out, was the perfect energy-storing
medium. From there he developed his Air Car One, which he built for
$1500 and patented. He showed his air car from coast to coast and
then went on to other things. In 1993 he picked up his air car
project again with the help of Toby Butterfield of Joplin, Missouri.
They developed the Spirit of Joplin air car with parts mostly donated by
manufacturers. Terry's air engines demonstrated the feasibility of
building air engines with off-the-shelf parts on a small budget. His
engines used up to four consecutive stages to expand the same air over and
over. They ran at a low speed so there was plenty of time for
ambient heat to enter the system and the possibility of low-tech
developers to build engines cheaply at home. Terry was instrumental
in educating the founder of Pneumatic Options on air car fundamentals.
Terry's greatest contribution--and what makes him an air car advocate, not
just another inventor--was that he published and made easily available the
complete details on how to build an engine like his. No other
inventor has done this. Shortly before his death in 1997, Terry
Miller gave all rights to his invention to his daughter and to Toby
Butterfield. Mr. Butterfield died in 2002.
Guy
Negre and MDI
 Currently
a French inventor named Guy Negre is building an organization to market
his air car designs in several countries. A web search for air cars
will turn up hundreds of references to his company, Moteur Developpment
International (MDI). His website is at www.mdi.lu. Mr. Negre
holds patents on his unique air engine in several countries. Plans
are underway to build air car factories in Mexico, South Africa, Spain and
other countries. We wish him success and encourage you to visit his
website (or one of his licensees in Spain, Portugal, and Great
Britain,
theaircar.com) and support his good work.
C.
J. Marquand's Air Car Engine
 Dr. Marquand has
taken the highly commendable step of incorporating heat pipes into his air
engine design for the recovery of compression heat. He also plans to
use regenerative braking. It is not clear whether his engine has
been tested in a car yet. Professor Marquand is a scientist with a
number of published research articles to his credit. For further
information contact: C. J. Marquand or H. R. Ditmore, Dept. of Technology
& Design, Univ. of Westminster, 115 New Cavendish St., London W1M 8JS,
Tel. 0170 911 5000.
Tsu-Chin
Tsao's Hybrid Air Engine for Cars
 Tsu-Chin Tsao is a distinguished professor of mechanical
and aerospace engineering at UCLA. He has invented a camless
gasoline engine that does not idle; it uses compressed air to start the
car, and when the air is gone the engine runs on gasoline. During
deceleration, braking energy operates a compressor to fill the air tank
for the next start. This brings to mind Buckminster Fuller's
reminder in his magnum opus Critical Path, wherein he tells us how
many horses (as in horsepower) could be jumping up and down going nowhere
for all the gasoline being pointlessly burned by cars sitting at red
lights at any given time. We have nothing but admiration and respect
for Professor Tsao's serious step in a perfectly good direction, and
apparently Ford Motor Company is in agreement: they are working with
Tsao's team to look into the viability of putting a pneumatic hybrid on
the road to compete with the Toyota Prius and other electric hybrids.
The pneumatic hybrid is expected to save 64% in city driving and 12% on
the highway.
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