It's a Kellett!

Air Classics, Jun 2002 by O'Leary, Michael

AT MOJAVE AIRPORT, AL LETCHER HAS RESTORED AN INCREDIBLY RARE PIECE Of AMERICAN AERONAUTICAL HISTORY

During the 1920s and 1930s, the concept of the "Autogiro" fascinated American aviation enthusiasts. Today, the basic concept of the Autogiro lives on in many different homebuilt aircraft designs but, commercially, the original Autogiro was never a real success. Basically, the Autogiro is a heavier-- than-air craft which derives its lift from the rotary movement of its supporting surfaces through the air. The Autogiro primarily differs from the aircraft in that its supporting surfaces - the blades - are free to move at a speed independent of the machine as a whole, thereby introducing flying characteristics which had previously been impossible. Thus, the Autogiro can takeoff at a low speed after a very short run and immediately assume a sharp angle of climb - it can fly at either low or high speeds and can momentarily be brought to a standstill in the air.

Juan de la Cierva, the acknowledged inventor of the Auto giro, began his study and development of the Autogiro in 1920. Prior to this time, he had been concerned with gliders and fixed-wing aircraft and, in 1918, designed a tri-motor bomber for the Spanish Air Force. This machine, in many respects considerably advanced for its time, proved entirely successful. However, it did not overcome the aircraft's limitations and crashed, due to pilot error, during a low altitude stall.

Cierva's work with conventional aircraft convinced him that safety in flight must, in some manner, be divorced from the necessity for continuous high speed before flying would become universally adopted. This led him to the consideration of many systems of flight, including helicopters and ornithopters (devices with flapping wings) and ultimately to his first theoretical concept in 1920 of the idea of freely rotating wings.

The aircraft type of Autogiro tested was fitted with two four-blade rotor systems mounted one above the other to turn in opposite directions to equalize the dissymmmetry of lift. This did not solve the problem and the idea of dual or multiple rotors was abandoned.

The second type had a single rotor system of three blades, capable of being set at varying incidences by a mechanical device, to compensate for the difference in lift. The machine was an improvement over the first model but the mechanism proved cumbersome and substantially ineffective.

The third type of Autogiro was fitted with a rotor system of five rigid blades and was the first full-sized machine to actually leave the ground. However, gyroscopic action on the rigid blades proved too strong a force to overcome and this type was also abandoned.

The fourth machine embodied the previously described principle of horizontal articulation and was notably successful. In this design, lateral control was provided for by tilting the axis of the rotor to the right or left - a method found impractical because of operating difficulties. Although previous and subsequent Autogiros have all seen many modifications in the course of experiment, this particular machine was reconstructed or modified no less than 15 times! Finally, a better system of lateral control was evolved and, in January 1923, the fifth model made a successful flight of about 200 yards at the Getafe Airdrome near Madrid. Subsequently, the Autogiro accomplished an officially observed flight on a closed course at the Quatro Ventos Airdrome.

From this milestone, experimental work was continued without interruption. In 1925, an Autogiro was built and exhibited at Britain's 1926 Hendon Air Pageant and during that year the Cierva Autogiro Company Limited was formed to develop Cierva's principle and to work with him in further experimentation. An Autogiro built in 1928 was flown some 3000 miles around Great Britain and from London to Paris, Berlin, Rotterdam, and Brussels.

In the United States, Harold F. Pitcairn, whose active interest in aviation dated back to 1914, recognized the limitations of flying in the fixed-wing form. This conviction became more conclusive after his activities as a manufacturer of rugged biplanes often used on air mail routes.

After considerable independent experimentation and research over a period of years with rotary wing direct lift machines, Pitcairn's attention was directed toward the development of Cierva's machine from its beginning. Finally convinced of its practicality, Pitcairn shipped the Autogiro to the States in the fall of 1928 and it was flown at Pitcairn Field, Willow Grove, Pennsylvania, for the first time in America on 19 December of that year.

After considerable practical demonstration and testing of this particular machine, Pitcairn acquired - in February 1929 - the United States rights to the Autogiro patents and formed the Pitcairn-Cierva Autogiro Company of America for the licensing and manufacture of the Cierva Autogiro in this country. Pitcairn would go on to build a series of Autogiros that achieved some success but the company was not without rivals.