By Lieutenant Colonel Ronald J. Brown
U.S. Marine Corps Reserve, Retired
The first rotary-winged aircraft used by naval aviation was not a helicopter. It was an autogiro, an airplane propelled by a normal front-mounted aircraft engine but kept aloft by rotating overhead wings, a phenomenon known as “autorotation.” Although rather ungainly looking due their stubby upturned wings, large tails, and drooping rotors, autogiros took well to the air. Their ability to “land on a dime” made them favorites at air shows and an aggressive publicity campaign touted them as “flying autos, the transportation of the future.” Autogiros, however, turned out to be neither a military nor a commercial success.
The aircraft itself was an odd compilation of a normal front-mounted aircraft engine used to generate thrust and three overhead free-spinning blades attached to a center-mounted tripod to provide lift. The fuselage included a pair of stubby wings that supported the landing gear and had a semi-standard elongated tail assembly. Typical of the day, it had an open cockpit.
Although a rotary-winged aircraft, the OP-1 was not a helicopter. The engine was used to start the rotors moving but was then disengaged and connected to the propeller to deliver thrust. A speed of about 30 miles per hour was needed to generate lift and maintained for controlled flight. The OP-1 could not hover, it required conventional engine power to take off and move forward in the air; the plane could, however, make a vertical landing. This unique feature made the OP-1 attractive to the military.
The specific autogiro model first tested by the Marine Corps was the OP-1 built by Harold F. Pitcarin, who would later found Eastern Airways. His company was a licensed subsidiary of a Spanish firm. All American autogiros were based upon designs formulated by Spanish nobleman Juan de la Cierva. His first successful flight was made near Madrid in 1923. More than 500 autogiros flew worldwide during the next decade. Although his airplanes never lived up to his high expectations, de la Cierva did develop rotor technology and recorded aerodynamic data later applied by helicopter designers Igor Sikorsky and Frank Piasecki.
The Navy purchased three Pitcarin autogiros for extensive field-testing and evaluation in 1931. The only carrier tests were conducted on 23 September of that year, but the OP-1’s performance was virtually identical to that of carrier-borne biplanes then in use. The Marines took one OP-1 to Nicaragua to test it under combat conditions. Again, its performance was disappointing. The pilots of VJ-6M noted it lacked both payload and range. The only practical use they found was evaluation of potential landing areas. This was not enough reason to incorporate the OP-1 into the Marine inventory. Overall, the OP-1 was described as “an exasperating contraption,” not fit for military use. Further trials of a wingless autogiro in 1935 revealed no improvement, so director of aviation Major Roy S. Geiger recommended against adoption of that aircraft type.
In the barnstorming days between the World Wars, autogiros proved to be the ultimate novelty attraction. Aviator Charles A. Lindbergh often put on demonstrations, aviatrix Amelia Earhart set an altitude record in one, and Secretary of the Navy Charles Francis Adams flew in an autogiro to join President Herbert C. Hoover at an isolated fishing camp in Virginia. The Royal Air Force actually used autogiros for convoy escort and observation during World War II, and the Soviet Union developed its own autogiro.
Although the OP-1 never became a mainstream Marine aircraft and was not a true helicopter, some aviation enthusiasts assert that the technology and data developed by de la Cierva was crucial for rotary-winged flight. They, therefore, make the case that the OP-1 should be considered the progenitor of today’s helicopters.