Collection Item Long Description:
Pitcairn-Cierva Autogiro Company of America PCA-1A
In the late 1920's, Harold Pitcairn had established a sterling reputation as a builder of rugged biplanes used by airmail services. He had also founded what would eventually become Eastern Airlines. Yet by 1930, Pitcairn had begun dismantling these enterprises to support the highly speculative venture of developing and producing an American version of Juan de la Cierva's experimental Autogiros. Although, the Autogiro would prove to be a minor player in twentieth century aviation, Pitcairn nonetheless was able to succeed, at least temporarily, in his enterprise and, by 1940, had sold scores of the groundbreaking aircraft. The PCA-1 was Pitcairn's first Autogiro project and successfully demonstrated that he and his engineering staff not only understood Cierva's innovation, but also that they were capable of improving upon it.
The word "Autogiro" is actually a proprietary name coined by Juan de la Cierva. His designs were the first aircraft to fall in the gyroplane category. Nonetheless, nearly all gyroplanes built from the 1920s through the end of World War Two became commonly known as "autogiros" (or the more generic "autogyros"), regardless of the manufacturer. A gyroplane is an aircraft that derives most, if not all, of its lift from the unpowered autorotation of a horizontally mounted rotor or rotors. Unlike a helicopter, an engine does not drive the rotor blades while the aircraft is in flight. Instead, the resultant of the lift and drag forces acts to pull the blade forward in rotation while also creating lift - the same effect that turns the sails on windmills. This state of autorotation is only possible with a sustained airflow through the rotor disc, with the air moving from below and in front of the rotor to above and behind it. The gyroplane requires some propulsive force to maintain sufficient speed to sustain autorotation and hold altitude. In the Cierva and Pitcairn Autogiros, an engine driving a tractor propeller supplied the necessary force. If the pilot reduced throttle while flying, the rotors would begin to slow and the autogiro would descend. The increased airflow of the descent allowed the rotors to continue in autorotation and maintain the blades in an unstalled condition - even without the forward pull of the propeller. Although the pilot still had to keep some forward motion for a landing flare-out, and to maintain airflow over the control surfaces, it allowed for unpowered and near vertical descents ending in a very short landing rollout. This was an excellent safety feature in case of engine failure. Nonetheless, until the advent of direct control gyroplanes, the diminished control effectiveness in slow speed flight required a highly experienced Autogiro pilot to perform minimal rollout landings.
Most of the early gyroplanes were nearly identical to single-engine low-wing monoplanes, with the exception of the rotor mounted on a pylon in front of the cockpit that provided the primary source of lift during slow-speed flight. They employed standard airplane-type control surfaces (elevator, aileron, and rudder) and fixed pitch rotor blades. The stubby monoplane wing did not serve primarily for the generation of lift. Rather, it was a convenient means of mounting the ailerons and providing stability. It also had the unintended benefit of making the aircraft appear more conventional to skeptical airplane operators who were doubtful about flying without fixed wings.
Cierva constructed his first Autogiro, the coaxial rotor C.1, in 1920. As the rotors on the C.1 autorotated at different speeds, rendering the aircraft incapable of controlled flight, he decided to switch to a single rotor design. However, the abortive first flight of the new aircraft revealed a problem that he had not considered. As the Autogiro began to gain speed during its takeoff roll, the rotor blade that was turning towards the front of the aircraft received the benefit of additional airspeed because of the forward motion of the Autogiro. However, the blade retreating towards the rear of the autogiro suffered a loss in its airspeed relative to the oncoming air for the same reason. The net effect was a difference in airspeeds of the two blades that naturally caused dissymmetry of lift between the two sides of the rotor disc (as lift is a function of airspeed). In turn, this resulted in the Autogiro to rolling into the retreating blade side. A subsequent Cierva Autogiro also suffered the same problem and failed to take off successfully.
In 1922, Cierva conceived an inspired solution to his problem. By incorporating a hinge that allowed each blade to "flap" independently at its root, he developed a rotor that equalized lift amongst all of the blades, regardless of whether the Autogiro was flying fast or slow. When the advancing blade generated additional lift because of its higher velocity, the flapping hinge allowed it to rise, which effectively reduced the angle of attack of the blade, thus reducing its lift. On the other side of the rotor, the flapping hinge allow the retreating blade to descend with its reduced lift, which effectively increased its angle of attack, thus generating more lift. This breakthrough was not only an essential component for the Autogiro - it was also necessary for the development of the practical helicopter.
By the late 1920s, Cierva was close to achieving production of the Autogiro. Harold Pitcairn had been fascinated with the possibilities of rotary-wing flight since his youth and had avidly followed Cierva's progress. He had already established himself as a successful manufacturer of rugged airmail aircraft, such as the PA-5 Mailwing (see NASM collection), and as owner of an airmail service that would eventually become Eastern Airlines. Still unable to shake the desire to experiment with helicopters, which had little success up to that time, Pitcairn made two trips abroad to evaluate the licensing the Cierva technology as the basis for his own line of helicopters. By 1928, Pitcairn had decided to risk everything, phase out his fixed-wing production and airmail operations, and produce license-built versions of Cierva Autogiros. He returned to Cierva's facility in England and bought a C.8 equipped with a Wright Whirlwind J-5, designated C.8W (see NASM collection), and had it shipped to his Bryn Athyn, Pennsylvania airfield. On December 18, 1928, one day after the twenty-fifth anniversary of the Wright brothers' first powered flight, the C.8W became the first successful rotary-wing aircraft to fly in America.
Pitcairn's first step in building his own Autogiros was to acquire the American patent rights to Cierva's innovations and to manage and license them under the direction of the Pitcairn-Cierva Autogiro Company of America. This enterprise, later renamed the Autogiro Company of America, would remain separate from the production side of Pitcairn Aircraft, which would become the Pitcairn Autogiro Company, Inc. in 1933. Cierva, when he had sold the patent rights to Pitcairn, had yet to place any aircraft into production, and was naturally elated at the potential American market for his products.
Pitcairn began flying the C.8W around the Northeast and successfully generated a wave of enthusiasm for the aircraft. Meanwhile, his senior engineer, Agnew Larsen, was hard at work evaluating improvements for Pitcairn's own line of Autogiros, designated the PCA-1 (Pitcairn-Cierva Autogiro). In July 1929, Larsen was ready to begin construction on the first three prototypes.
Originally, Pitcairn and Larsen had intended to use the rugged Pitcairn PA-5 Mailwing (see NASM collection) for the tandem open cockpit fuselage and then mate it with Cierva's latest rotor design. However, the biplane fuselage structure clearly carried weight in places that were not necessary for the monoplane, and Larsen designed a new fuselage that was similar in form to the PA-5's, but differed substantially in the structural details. The front cockpit contained room enough to seat two adult passengers side-by-side, while the pilot occupied the rear cockpit.
One area that required special attention was the landing gear that needed to take the punishment of hard landings and the heavy side loads imposed by near-vertical, minimal rollout landings. Larsen thus settled on a wide-track conventional configuration with high-travel struts. This arrangement would also help to eliminate the ground resonance problems encountered by some of the late Autogiros.
The PCA-1 was a larger, more rugged aircraft than the earlier Cierva designs with a more powerful engine, though its gross weight was similar. The welded square steel tube fuselage that Pitcairn perfected on his Mailwings undoubtedly accounts for much of this accomplishment. The design of the rotorhead resulted in further weight savings, though the RB-55 rotor blades came directly from Cierva and were the same ones used on the C.19, his first production model and consisted of two layers of mahogany. The rotorhead attached to the fuselage with a four-strut pylon, centered over the front cockpit windscreen.
Many Autogiro and helicopter designs utilized fully-articulated rotorheads that incorporated a lead-lag or drag hinge that allowed the blades to pivot slightly fore and aft during rotation to relieve stresses. The PCA-1 and concurrent Cierva designs employed rudimentary drag hinge designs that, in combination with clunky, dynamically unbalanced rotor blades, led to excessive structural loadings in the rotor. The variations in centrifugal forces had to be borne by the blades themselves, which would have resulted in frequent structural failures had an external bracing system not been adopted. Rubber shock-cord bracing wires connected each of the blades and attached to a point almost halfway out along their length. Additional bracing wires, running from a mast on top of the rotorhead, acted as stops to keep the blades from drooping too low and striking the fuselage. As blade and drag hinge design improved in the latter part of the 1930s, along with Pitcairn's discovery of hydraulic dampers, Autogiro manufacturers dispensed with external bracing.
Pitcairn had hoped to enter the PCA-1 in the National Air Tour and the Guggenheim Safe Aircraft Competition, both showcases of the latest advances in light aircraft design, but the Autogiro was not ready for its first flight until October 1929 - too late for entry. Amazingly, Cierva himself performed the first flight of the PCA-1. However, he was only able to fly the aircraft for less than a week before he suffered a substantial crash. A second setback followed, when a devastating fire in the Pitcairn factory destroyed the airframe. Fortunately, the second of the PCA-1 airframes, designated PCA-1A, was nearly ready for flight and indeed took to the air with Cierva at the controls less than a month after the first PCA-1. Cierva had brought a C.19 prototype with him to the United States and used it to drum up enthusiasm for Pitcairn's forthcoming products. The C.19 was similar to the PCA-1 in design, but smaller and considerably lighter.
The PCA-1A was cosmetically similar to its forerunner, but contained some notable structural differences. It was considerably lighter, as duralumin tubing replaced the heavier steel construction and fabric covered the wings instead of plywood. The landing gear underwent further refinement and employed larger "balloon" tires to further ease the jolt received when performing minimum ground-roll landings.
The PCA-1 and PCA-1A incorporated an unusual "box" tail design that deflected propwash into the aft section of the rotor disc to bring the rotor rpm up without the need for excessive high-speed taxiing by bringing the blades into autorotation before takeoff. After Pitcairn realized that the solution to the rotor spin-up problem was a power-takeoff controlled by a clutch, he modified the PCA-1A to incorporate a much lighter tail structure with a single vertical stabilizer to replace the original design.
The PCA-1A could carry a respectable payload of 318 kg (700 lb). Its maximum speed was a relatively slow 169 kph (105 mph), but it could maintain altitude at an airspeed of only 32 kph (20 mph). The third of the Pitcairn prototypes, the PCA-1B, was ready for flight a month after the PCA-1A. It was even more advanced than the PCA-1A and illustrated the rapid pace of innovation at Pitcairn's facility, which, in addition to its own talent, benefited considerably from the close oversight of Cierva who observed the experimentation with enthusiasm. The PCA-1B incorporated the revised tail design from the outset. The close association between Cierva and his licensee paid significant dividends for both parties, as their collaboration increased the pace of Autogiro development in both countries. Cierva's C.19 incorporated many of the innovations pioneered on the PCA-1 and entered production concurrently with Pitcairn's initial models.
The PCA-1A and its surviving sibling, rapidly fulfilled their mission and confirmed that the Pitcairn modifications to the Cierva design were sound. Pitcairn began to gear up for production of the PCA-2 - the first Autogiro sold commercially in the Western Hemisphere. In 1930, the National Aeronautic Association awarded Pitcairn the prestigious Collier Trophy because of his pioneering flights in the C.8W and the successful Americanization of the Autogiro in the form of the PCA-1.
The PCA-2 would prove to be a popular aircraft in spite of the fact that the Great Depression was just reaching its stride. While conventional barnstorming had lost its popularity, air races and airshows remained significant draws for a population desperate for distraction and the uniqueness of the Autogiro guaranteed that it would draw crowds wherever it appeared. While the $15,000 price tag was an enormous sum in those troubled times, Pitcairn still sold twenty-one PCA-2s in a two-year period. Many of the operators were pilots who financed their purchase by selling advertising space to corporate sponsors looking for new ways to advertise their products.
Unfortunately, the appeal of the Autogiro as a novelty act did not extend far into the commercial or general aviation fields. While Pitcairn marketed the Autogiro as the ideal personal vehicle for the wealthy, very few went for this purpose. Outside of advertising and exhibitions, some Autogiros performed limited crop-dusting and airmail duties. However, the short takeoff and landing abilities of the type did not compensate for its slower speeds, more limited payloads, and higher acquisition and operating costs relative to conventional aircraft. Despite new innovations, civil sales of the Autogiro had fallen off steeply by the beginning of World War Two. During the war, the introduction of helicopters with true vertical takeoff and landing capabilities and the ability to hover rendered the Autogiro redundant and obsolete. However, the increasing complexity and cost of true helicopters caused a resurgence in gyroplane research in the latter part of the twentieth century.
Pitcairn would die an embittered man, as the patent rights he had owned were usurped by a number of helicopter manufacturers, who, with the exception of Sikorsky, did not pay him any royalties. The helicopter companies had gotten away with this during World War Two because the U.S. Army Air Force had convinced Congress that unless they suspended patent issues relating to helicopter technology, the wartime development of the helicopter would be severely handicapped. After the war, Pitcairn tried to recover his royalties, but the government refused to get involved. Pitcairn filed suit, but the proceedings would came to a conclusion in his favor almost three decades later and several years after his death.
For a brief period, the PCA-1A and PCA-1B continued to serve with Pitcairn as trainers for purchasers of PCA-2s. Pitcairn then donated the PCA-1A to the Franklin institute. In 1955, the Smithsonian Institution acquired the aircraft. In 1997, the National Air and Space Museum loaned the aircraft to Harold Pitcairn's son, Stephen, who fully restored the aircraft to its initial configuration, including the box deflector-tail. In 2000, the aircraft went on temporary display at the American Helicopter Museum in West Chester, Pennsylvania, not far from its original testing ground.
Rotor Diameter:13.11 m (43 ft)
Wingspan:10.05 m (33 ft)
Length:6.60 m (21 ft 8 in)
Height:3.89 m (12 ft 9 in)
Weight:Empty, 998 kg (2,200 lb)
Gross, 1,317 kg (2,900 lb)
Engine, Initial Configuration:Wright R-760-E Whirlwind J-6-7, 225 hp
Engine, Final Configuration:Wright R-975-EG Whirlwind J-6-9, 300 hp
Crew:1 pilot, 2 passengers
References and Further Reading:
Brooks, Peter W. Cierva Autogiros: The Development of Rotary-Wing Flight.
Washington: Smithsonian Institution Press, 1988.
Smith, Frank Kingston. Legacy of Wings: The Harold F. Pitcairn Story. Lafayette Hill,
Pa: T.D. Associates, 1981.
Townson, George. Autogiro: The Story of "the Windmill Plane." Destin, Fl: Aviation
Heritage, Inc., 1985.
Cierva C.8W curatorial file, Aeronautics Division, National Air and Space Museum