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In my eyes, the autogyro is a very important Diesel Era symbol. For more than a decade it was seen as viable alternative to light airplanes and helicopters.

There were different autogyro designs and makes but the most significant are those of Juan de la Cierva y Codorníu.

Jeff Lewis wrote in his Autogyro History and Theory: "Cierva was born in Murcia, Spain, September 21, 1895. He was only eight years old when the Wright brothers first flew on Dec. 17, 1903. He was a young man on his way to becoming a civil engineer when they first demonstrated their machine to the rest of the world in France in 1908. Cierva was intrigued by this new technology and decided to build his own airplane. His first attempt was to rebuild a Sommer biplane. He fitted it with a new engine and made several modifications to the original airplane. When he completed the project in 1912, he named the airplane the BCD-1 El Cangrejo, Spanish for the BCD-1 Crab.

After tossing a toy helicopter from his parents balcony and studying the flight, Cierva came up with the idea of an autogyro, which he called the autogiro (Notice the spelling with an "i" instead of a "y"). "

Cierva's first attempt at building an autogyro was the C.1. For this prototype which he built at Madrid, he used the fuselage of a Deperdussin, a French monoplane of 1913 vintage, on which were mounted two contra-rotating four-bladed rotors. The C.1 had a vertical surface above the rotor to give lateral control. This model never flew, since it proved impossible to control: the lift from the two rotors was unbalanced because of mutual interference. However, when it was tested, in October of 1920, it did demonstrate successfully the principles of autorotation while taxiing on the ground.

Then came the C.2: above the centre of gravity of a Hanriot fuselage retaining its customary elevators and rudder was fitted a three-bladed rotor, the blades of which incor-porated variation of the angle of incidence. Of this aircraft, La Cierva himself spoke as follows: "My first experiments with this type were encouraging. But after this model had been damaged and reconstructed nine times, it seemed clear that the solution would not be found in such a design." Gyroscopic effects in fact proved virtually unsurmountable.

At the beginning of 1922, the C.3 prototype with five rigid blades was ready for trial. Though its lateral control was improved, it always showed in the inventor's own words "a tendency to fall over sideways". It was damaged on several occasions and rebuilt four times. An end was put to La Cierva's failures by a toy autogyro which he had built. Its engine consisted of a twisted rubber band, and its rotary wings of flexible palm wood. Unlike the full-sized machines, it flew properly. On comparing it feature by feature with the C.3, La Cierva discovered that the flexible rotor blades accounted for the toy's successful flight. This gave La Gierva the idea of articulating the blades so as to overcome the unbalance between the advancing and the retreating blade.

Jeff Lewis: "Cierva's next design, the C.4, incorporated these hinged rotors. For lateral control, ailerons were mounted on outriggers to the side of the aircraft. Yaw and pitch control still came from a rudder and elevators. On January 17, 1923, the C.4 flew, marking the first controlled flight of an autogyro. The C.4 also demonstrated the autogyro's safety in low speed flight.

On January 20, three days after its first flight, the autogiro went into a steep nose-up attitude after an engine failure at about 25-35 ft. In an airplane, this would have almost certainly resulted in an almost unrecoverable stall. But the autogyro just descended gently to the ground without damage to the machine or injury to the pilot. "

In 1928, Harold Pitcairn purchased a Cierva C.8W and the American manufacturing rights from Juan de la Cierva for his autogiro designs for $300,000.

In 1929, Pitcairn formed a separate patent holding company to build autogiros, the Pitcairn-Cierva Autogiro Company, which was later renamed the Autogiro Company of America. As a part of the licensing agreement, Pitcairn used Cierva's copyrighted variant of the name autogiro (spelt with an i) as opposed to the currently more common spelling of autogyro which was initially used to bypass his copyright. Kellett autogyros competed with, and eventually licensed production rights from Pitcairn-Cierva Autogiro Company for $300,000.

The first commercially successful Cierva autogyro was the C.19, built in Great Britain by A.V.Roe & Company as Avro 620 and in Germany by Focke-Wulf as Model C 19. Three prototypes employed with the revolutionary aerodynamic rotor spin system. Fitted with 80 hp Armstrong Siddeley Genet II engines, they appeared underpowered so in the serial aircraft (Mark II to IV) more powerful Genet Major I were installed, developing 105 hp.

In 1931, a single C.24 cabin two-seater was built by de Havilland, using the DH.80A Puss Moth fuselage, a a 120hp Gipsy III engine and Cierva Rotor. It is preserved at the Mosquito Aircraft Museum at Salisbury Hall (Hertfordshire, UK):

The Cierva C.30A marked a major step forward in rotorcraft development, being the first production autogiro in which the engine was geared directly to drive the rotor blades for take-off. The degree of direct control was increased still further by having the control column, which acted directly on the rotor, suspended from the pylon so that the rotor head could be tilted in any direction to produce the manoeuvre desired.

The prototype C.30 (G-ACFI) differed chiefly in having a tripod rotor pylon and dihedral on the tailplane tips; the fuselage was modified by Airwork from a standard Cierva C.19, and assembly was undertaken by National Flying Services at Hanworth, where G-ACFI made its maiden flight early in April 1933. Take-off run of the C.30 was about 30 yards (27.43m), while the landing was achieved in about 3 yards (2.74m) with the rotor blades autorotating.

Another 1933 prototype was G-ACKA, the first C.30P, with 140hp Genet Major 1A, folding rotor blades and other improvements. First customer for the production C.30A was the Royal Air Force, for whom the type was built by Avro and given the name Rota. One twin-float Sea Rota and ten standard Rotas with wheeled undercarriages were completed to Specification 16/35, and were delivered to the School of Army Co-operation from December 1934.

One other military C.30A was K4775, a Civet Major-engined machine sent to the Royal Aircraft Establishment in 1935 for blade-flexing tests. Avro production of C.30 types was in the region of seventy aircraft, three of which were C.30P's. Thirty-seven C.30A's appeared on the pre-war British civil register, and others were completed for customers in Europe, India, China, Australia and South Africa.

In Britain the C.30A, like the C.19 before it, was used for traffic reporting duties at major sporting and similar events, and one aircraft (G-AGUT) was used for filming the 1936 F.A. Cup Final.

During 1933 the C.30 prototype, G-ACFI, was converted for jump-start trials with a modified rotor head, and in 1936 a perfected form of this was fitted to G-ACWF when it made the first genuine vertical take-off by an autogiro, by keeping the engine and rotor system engaged throughout the take-off sequence. This machine was, in effect, the prototype for the C.40, five of which were ordered for the R.A.F. as the Rota II to Specification 2/36.

These were built by the British Aircraft Manufacturing Co., having side-by-side seats, wooden semi-monocoque fuselages and 175hp Salmson 9NG engines. Two of the original five Rota II's were diverted to civilian customers, replacements being built in 1938-39. The R.A.F. C.40's served with No.1448 Flight (later 529 Squadron).

On the outbreak of World War 2 over a dozen civil C.30A's were impressed for military service; these and the surviving Rota I's were allocated singly to R.A.F. radar stations in the United Kingdom for calibration duties.

Jeff Lewis: "... we can ask the question of why autogyros were never widely accepted. Just about every aviation historian has their own answers to this question, but here is this author's opinion. Early autogyros, although they had a higher speed envelope than airplanes, had a higher drag and so were not as efficient at higher speeds, and absolutely could not attain the maximum speeds of the faster airplanes. Also, the early autogyros did not have the vertical takeoff and landing capabilities that would have made them more attractive to potential buyers. When the C.30 finally demonstrated a successful jump takeoff in 1934, it was less than a year until the first successful helicopter flew, and only a few more years until the very successful Sikorsky V.S.300 and VS-316. Although helicopters had a smaller speed envelope than autogyros, they were capable of hovering, and their envelope could fill the role that airplanes couldn't. In other words, anything an autogyro could do could be done by another aircraft. Also, Cierva, who was doing most of the development of autogyros, was funding much of the development on his own. When the army ordered the VS-316, that money went in to Sikorsky's company. This gave Sikorsky the funding for development that Cierva was running out of. Without the money, Cierva just couldn't fund the research. And then, on December 9, 1936, Cierva was killed in a plane crash (a DC-2 operated by KLM). He was only 41 years old. There were other people developing autogyros, but Cierva had been one of the main driving forces behind the movement. Much was lost when he was killed.

Another factor that kept the autogyro from being accepted was purely psychological. Even though helicopters weren't successful until 1935, they had been under development for as long as airplanes. The general public knew about helicopters, and understood the principle of a powered rotor. Autogyros had an unpowered rotor that spun due to aerodynamic forces. Most people did not understand how it worked and so did not trust it. Although it is actually safer than either helicopters or airplanes, people did not realize this. They wanted something powered. "

Watch the video:

See a restored C.30 fly (1999):

Sources: Cierva aircraft @ aviastar.org; Jeff Lewis, Autogyro History and Theory

Headline picture: James C. “Jim” Ray taking off with passenger Juan de la Cierva from Pier 38 in Manhattan in a PCA-2 Autogiro in 1931.

More pictures of Cierva Autogiros in my Flickr photostream

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