At the start of the twentieth
century, aircraft engines were simple, low-powered machines
that were designed and built one by one for specific aircraft.
But very soon, engines started being built in quantity, often
by several manufacturers in different countries who were
licensed by the designer or initial manufacturer. In the
United States, particularly during World War I, automobile
manufacturers dominated the aero-engine field until companies
that specialized in aircraft engines were established in the
A cutaway drawing of
the 1903 Wright Flyer engine.
The earliest aero engines were
stationary—either radial in style or in line. The Antoinette
series was the most commonly used. These were succeeded by the
popular rotary engine. The best known were the Gnome and Le
Rhône, which were used on the majority of aircraft until the
in-line Liberty engine, designed for mass production, started
dominating the aero-engine market. From that point on,
increasingly more sophisticated and powerful stationary
in-line engines were developed until the arrival of the jet
engine a couple of decades later.
advanced aircraft engine early in the century was the
50-horsepower (37-kilowatt) engine designed by Charles Manley
for use on Samuel Langley's aerodromes. But because Langley's
aircraft never succeeded in flying, these engines did not have
the opportunity to demonstrate their potential. The engine
designed and built by Charlie Taylor and the Wright brothers
for their Flyer, although much lower powered, had a greater
place in history because it propelled the first successful
powered flight in 1903. Wright's engine had four inline
cylinders, was water-cooled, generated 12 horsepower (9
kilowatts) (as compared to Manley's 50 horsepower), and had
weighed about 179 pounds (81 kilograms) without the fuel. It
had no fuel pump, carburettor, or spark plugs.
four-cylinder water-cooled engine was America's first military
aircraft engine. It was used to power the 1908 Signal Corps
Dirigible No. 1.
The Curtiss Aeroplane and Motor
Corporation produced two notable engines. A four-cylinder
water-cooled engine used in the 1908 Signal Corps Dirigible
No. 1 was America's first military aircraft engine. It could
generate about 25 horsepower (19 kilowatts) and drove a
22-foot (6.7-metre)-long tubular steel shaft that turned a
Thomas Selfridge designed it. In its speed trial, it reached
19.6 miles per hour (31.5 kilometres per hour). Curtiss also
produced thousands of OX-5 water-cooled engines during World
War I, primarily for the Curtiss "Jenny." It generated only 90
horsepower (67 kilowatts) but, compared to other engines of
the period, was very reliable.
Thousands of Curtiss OX-5 water-cooled engines were produced
in the United States during World War I, primarily for the
Curtiss Jenny airplane.
The Antoinette engine was
designed and built in France by Léon Levavasseur. Named after
the designer's daughter, it was Europe's most widely used
engine until 1909-1910. The first Antoinette engine dated from
about 1901 and was used in a speedboat. By 1905, Levavasseur
had produced a water-cooled engine with eight-cylinders
arranged in a 90-degree "V" and with direct fuel injection. It
was safe, strong, and fairly powerful, generating 50
horsepower (37 kilowatts) and weighing about 110 pounds (50
kilograms). Its power-to-weight ratio was not surpassed for 25
The French and
British-built Anzani 10 was an air-cooled radial engine that
was installed in French Caudron aircraft.
An Anzani engine carried Louis
Blériot's monoplane across the English Channel in 1909. It was
a three-cylinder, air-cooled, semi-radial engine that
developed 25 horsepower (19 kilowatts). It was relatively
low-powered for such a long flight. The engine had automatic
inlet valves and mechanically operated exhaust valves, with
auxiliary exhaust ports in the cylinders. Later Anzani engines
generated 90-100 horsepower (67-75 kilowatts) and were used in
French-produced Caudron aircraft in 1915.
The Gnome 9-N engine
was the first successful air-cooled rotary engine used
extensively in airplanes during the 1909-1910 period. Numerous
types of Gnome engines were designed and built, one of the
most famous being the 165-hp 9-N "Monosoupape" (one valve)
that was used during World War I primarily in the Nieuport 28.
The Gnome 50-horsepower
(37-kilowatt) rotary engine revolutionized aviation. Although
F.O. Farwell developed the first successful air-cooled rotary
engine in the United States in 1896, it was the French-built
Gnome rotary that was first used extensively in airplanes
during the first years of World War I. Designed by the Séguin
brothers and first marketed in 1908, it was the first of a
long line of ever more powerful wartime engines. A typical
rotary engine, it had a fixed crankshaft and rotating
cylinders and crankcase that carried the propeller with them.
of Gnome engines were subsequently designed and built. One of
the most famous was the 165-horsepower (123-kilowatt) 9-N "Monosoupape"
(one valve). The engine had one valve per cylinder. Having no
intake valves, its fuel mixture entered the cylinders through
circular holes or "ports" cut in the cylinder walls. It was
used during World War I primarily in the Nieuport 28, which
the U.S. Air Service purchased from France, and also by the
thousands in other Allied aircraft. This engine, produced
under the names of Bentley Rotary B.R.1 in Britain, the Thulin
in Sweden, and the Oberursel UR.I in Germany, dominated the
industry until 1916.
The Clerget rotary
engine was used in many Allied fighter planes during World War
I. One powered the famous Sopwith Camel.
Around 1911, other engine
manufacturers began building rotary engines. LeRhône and
Clerget engines, both built in France, were used in many
Allied fighter planes.
The LeRhone C-9 was a French air-cooled rotary engine. It was
used in combat airplanes early in World War I, but as larger
and more powerful engines became available, it was relegated
to use in training-type airplanes.
LeRhône engines were quite
reliable and, by the end of the war, were being manufactured
in Britain, Italy, and the United States in addition to
France. The Germans also produced the 110-horsepower
(82-kilowatt) Oberursel, which was practically an exact copy
of the 110-horsepower LeRhône. The Clerget powered Britain's
The Rolls-Royce Hawk was used in World War I British airships
sent against German U-boats.
The British Rolls-Royce Eagle and
its successor, the Falcon, marked the beginning of a famous
line of aviation engines that produced the Merlins and
Griffons of World War II. This liquid-cooled V-12 was
developed in 1915. It was built in several versions that
culminated with the 375-horsepower Mark VII of 1917. It
powered the Vimy plane that John Alcock and Arthur Whitten
Brown flew across the Atlantic in June 1919.
engines powered some of the best-known German fighter planes
in the last two years of the war—the Albatros D.V., Fokker D
VII, and Pfalz D XII. Nearly all German-designed engines were
durable and dependable, with six water-cooled cylinders in
8BE is a V-type liquid-cooled engine. This type of engine was
especially compact for the amount of power it produced and was
used in numerous types of aircraft.
A Swiss engineer of a Spanish car
company, Marc Birkigt, designed a number of Hispano-Suiza
products. These included a large number of water-cooled V-8
and V-12 engines that were made in France, Britain, and the
United States during the war. They were especially compact for
the amount of power they produced.
In 1916 and 1917,
Curtiss produced R-3 and R-4 airplanes that were powered by
the Curtiss V2-3 engine. Because this engine was heavy for the
amount of horsepower it produced, it was replaced during World
War I by the Liberty engine.
By far, the most important of all
Allied engines, and America's most significant contribution to
the war effort, was the Liberty. In May of 1917, Jesse G.
Vincent of the Packard Motor Car Company, and E.J. Hall, of
the Hall-Scott Motor Car Company, took over a hotel room in
Washington, D.C., for nearly a week and designed the eight-
and twelve-cylinder Liberty engines with mass-production in
The Liberty V eight-cylinder engine preceded the Liberty-12.
It was the first Liberty engine tested in an aircraft, on
August 29, 1917.
On June 4, 1917, the Aircraft
Production Board authorized final design, and manufacture.
Assembly of the first eight-cylinder version was completed in
the remarkably short span of less than six weeks.
eight-cylinder version debuted on August 29, 1917. It
generated 270 horsepower (201 kilowatts) initially but its
output was later boosted to 330 horsepower (246 kilowatts).
The initial version vibrated excessively and since another
engine with this capacity had already been perfected, its
development was halted after only 15 had been built.
America's greatest technological contribution during World War
I was the Liberty 12-cylinder water-cooled engine.
The Liberty 400-horsepower
(298-kilowatt) V-12, air-cooled engine, on the other hand, was
one of the war's most powerful engines and one of the
workhorses of the war. Designed to be mass-produced with
interchangeable parts, the Liberty became the standard wartime
aircraft engine, produced by Packard, Lincoln, Ford, General
Motors (Cadillac and Buick), Nordyke, and Marmon. It was used
most often on the DH-4, the only U.S.-made airplane to go into
combat on the Western Front. More than 13,000 engines came off
the assembly line before the Armistice, and more than 20,000
were built by the time wartime production ended early in 1919.
war, the Air Corps used the engine for more than a decade in
numerous types of airplanes. Some were sold to civilians as
war surplus and were illegally used in speedboats for "rum
running" during the Prohibition era of the 1920s. Others
proved their longevity by staying in use much longer, even
being used in Russian and British tanks during World War II.