contributions of the autogyro
Vice-Marshall Sir Safton Brancker (left) with Captain Rawson just before
the famous Cierva autogiro in a successful test flight over Heston Air
Park, London, England.
Spanish engineer Juan de la Cierva's
development of rotor blade design and articulated (hinged) rotor blades in
1923 was the technical breakthrough that led to the first successful
helicopter in 1936. Cierva developed the autogyro, which resembled the
helicopter, but used an unpowered rotor. This rotor autorotated as the
autogyro was pulled through the air by a separate powered propeller. The
craft required only a short takeoff run to build up sufficient speed to
lift off the ground.
Cierva's first successful autogiro, flown in Spain in January 1923.
1923, Cierva successfully flew his C.4 autogyro, which incorporated
hinged, or articulated, rotor blades. The blades were attached to the
shaft by a flexible hinge for cyclic pitch control to balance the
amount of lift and torque caused by the rotating blades and produce a
stable ride. The articulated rotor blade
is used today on all helicopters.
By 1925, his
development aircraft had become reliable, and he began to demonstrate it
in France, England, and the United States. On October 20, 1925, his
pilot Frank T. Courtney flew the autogyro at Britain's Royal Aircraft
Establishment near Farnborough during tests for the British Air Ministry.
Later that year, Cierva formed the
Cierva Autogiro Company, Ltd., in Great Britain. Courtney toured Europe,
and early in 1926, he demonstrated the gyro for the French at Villacoublay
Airdrome with at least one crash. In September 1926, he flew at Tempelhof
near Berlin. On September 18, 1928, Cierva flew an improved autogyro 25
miles (40 kilometers) across the English Channel from Croydon to Le
Bourget Airfield near Paris in 18 minutes at 4,000 feet (1,219 meters). He
then took a leisurely trip 3,000 miles (4,828 kilometers) across Europe
that drew crowds everywhere.
A crash in February 1927, led to an
improvement in rotor hub design. A "drag hinge" was incorporated at the
hub to allow each blade to drag back a little or pivot forward slightly as
it rotated. This relieved the stresses and was another step in developing
the fully articulated hub used on many modern helicopters. Another
innovation was the development of a mechanical starter to bring the rotor
up to the necessary speed for takeoff.
During the next decade, some 500 gyros
were built around the world. In Britain, the A.V. Roe, de Havilland, Weir,
and Westland companies produced them. In Germany, Focke-Wulf built the
crafts; in France, it was the Loire Company, and in Russia, The Central
Aerohydrodynamic Institute (TsAGI). In 1928, Harold Pitcairn, who had been
involved with aviation in the United States since 1914, negotiated
successfully with Cierva, purchased a Cierva model C-8 autogyro, and
brought it to the United States for test and evaluation. It flew at Bryn
Athyn (Pitcairn Field), Willow Grove, Pennsylvania, on December 19, 1928.
In February 1929, Pitcairn purchased the
U.S. rights to Cierva's inventions and the autogyro patents then existing
and established the Pitcairn-Cierva Autogiro Company for licensing its
manufacture in the United States. Kellett, another U.S. aviation company,
also manufactured gyros in the United States.
Pitcairn PAA-1 autogiro was flown at Langley for the NACA
investigation of an experimental cantilevered three-bladed rotor.
Pitcairn-Cierva built three prototypes
in the fall of 1929. These were the first autogyros manufactured in the
United States. Two of the prototypes had all-steel, fabric-covered
fuselages and one had an aluminium structure. One prototype crashed during
takeoff on October 10, 1929, with Cierva piloting. The crash badly damaged
the aircraft, but Cierva was unhurt.
In August 1929, the first public
demonstration of a Cierva machine took place in the United States at the
Cleveland Air Races. The two-person open cockpit aircraft cruised at 75
miles per hour (120 kilometres per hour) and had a top speed of 90 miles
per hour (145 kilometres per hour). In 1930, an autogyro led an "air
parade" during an airshow at Newark Airport in New Jersey. Later, a
special demonstration was given for Thomas Alva Edison, who was
enthusiastic about the device.
The autogyro had a few years of
popularity in the United States. On February 12, 1931, the Detroit News
placed the first order for a commercial autogyro in the United States, the
Pitcairn PC A-2. On April 8, 1931, Amelia Earhart set a world's altitude
record for autogyros, climbing to 18,415 feet (5,615 meters). And on April
22, the autogyro received more publicity when veteran Pitcairn pilot Jim
Ray landed on the White House lawn and took off again for the ceremony at
which President Herbert Hoover presented the Collier Trophy to
manufacturer Harold Pitcairn "for the greatest achievement in aviation,
the value of which has been demonstrated by actual use in the preceding
year." Pitcairn built 51 autogyros in 1931 and developed a number of
models for the U.S. Navy as well as some models intended for private
The development of the "direct control"
rotor on a modified Cierva C-19 in 1932 led to the elimination of ailerons
and stub wings. With this system, the rotor was mounted so that it could
be tilted, resulting in a force that would pull the gyro in that
direction. This was a great advance over the existing airplane-type
The next major improvement occurred in
1934. A Cierva autogyro was developed with a device to produce a vertical
"jump" takeoff. This brought the gyro's design much closer to the design
of the true helicopter. The new device was successful, and for the first
time, a rotating-wing flying machine existed that could actually lift
itself vertically into the air.
In 1935, Austrian experimenter Raoul
Hafner created the AR III Hafner Gyroplane, first flown in Britain. This
vehicle had hinged rotors and featured both cyclic control and collective
control, in which the pitch of all rotors was changed simultaneously to
increase or decrease lift. The Hafner gyro could rise and continue to
climb at a fairly steep angle.
The development of cyclic pitch control
was a major improvement. Instead of "rocking" the rotor head, this
approach called for feathering—increasing or decreasing the pitch of the
blades in cycles as they turned. Each blade would assume a high pitch
position on the advancing side of the rotor's circle and a low pitch on
the retreating side. This meant an increase in lift on one side and a
decrease in lift on the other side. Feathering eliminated the need for
hinges so that the blades could move up and down and allowed for a rigid
Cierva and Pitcairn licensed the Kellett
Autogyro Corporation of Philadelphia to build autogyros for the U.S. Army.
Kellett developed the YG-1 in 1935, which became the Army's first
rotary-winged aircraft. Although autogyros saw little service with the
U.S. military. Cierva autogyros did see some limited service in the armed
forces of France, the Soviet Union, and Japan for forward observation and
artillery spotting during World War II. They also played a small but
important role in Britain where they were useful in calibrating the vital
air-defence radar network.
The autogyro saw some use for airmail.
On July 6, 1939, Eastern Air Lines began the world's first scheduled air
mail service by a rotary winged aircraft, using a Kellet gyro to fly from
the roof of the Philadelphia Post Office to the airport at Camden, New
Jersey. This experimental service lasted about one year.
While still used to some extent,
autogyros have been plagued by one major problem that contributed to their
limited acceptance. The phenomenon called ground resonance develops when
the rotor blades move out of phase with each other and cause the rotor
disc to become unbalanced. If not corrected, serious damage can take place
in only a few seconds. Ground resonance can occur only when the gyro is on
the ground and happens when a shock, such as from a hard landing, is
transmitted to the rotor system. If the centre of gravity moves from the
centre of rotation, the entire vehicle can become unbalanced.
The various improvements to the gyro had
allowed the development of the true helicopter. By the mid-1930s, the
helicopter had incorporated the rotors and other components that had first
appeared in the gyro. The gyro eventually faded away—replaced by true
helicopters. But perhaps the true end to the gyro ended on December 9,
1936, when Cierva, who himself might have one day perfected the
helicopter, died in an airplane crash.