This Week In Aviation History: Why Helicopters Work

In Spain, on November 15, 1922, Juan de la Cierva was granted a patent that led to the birth of the helicopter. The patent was granted for a system of rotor blades that incorporated flapping hinges and immediately led to the advancement of the autogyro — precursor of the helicopter.

Applied for in April of 1922, Spanish patent 81,406 described the concept of having rotor blades that were able to compensate for the unbalanced lift generated by a revolving rotor in forward motion. As the blades move about the rotor head, the lift on each blade changes, becoming greater as it advances in the direction of flight (resulting in an increase in relative wind and therefore, lift) and least as it retreats. This caused unequal forces on the aircraft that would make the craft roll to one side if it attempted to advance in any direction — or even if it was hit by a gust of wind.

De la Cierva was intrigued by flight and the problems associated with making aviation safer. He envisioned an aircraft that could use an unpowered lifting rotor, thrust coming from a conventional powerplant at the nose of the aircraft. The rotor would be tilted slightly back, and the airflow passing through it from below would cause it to turn, providing the lift. In the event of engine power loss, the rotor would continue to turn as the craft descended and air continued to pass through the blades. This added a parachute like effect to the rotorcraft.

The first Autogyro to use this system was Cierva’s C.4, which flew for the first time on January 17, 1923 at Getafe, Spain.

The drawback to the Autogyro was the drag the system produced. Although capable of landing and taking off at slow speeds, cruise speed of an Autogyro was less than a fixed wing craft powered by the same horsepower. But, given the right winds, the low speeds of an Autogyro gave it the advantage of flying in a virtual hover in over a fixed spot on the ground, good for observing or photography.

De la Cierva started work on his craft in Spain but moved to Britain in 1925 and founded the Cierva Autogyro Company Ltd. The company produced several types and de la Cierva was savvy enough to license his patents abroad, including to the United States.

The most notable American licensees were the Kellet Aircraft Corporation and Pitcairn Aviation Company. Both of these firms were located in the Philadelphia, Pennsylvania area, a locale that soon became a hotbed of rotary wing development. Acquiring military contracts, these two firms were major players in the success of the Autogyro. The first rotorcraft to land on a carrier was the naval PCA-2 Autogyro (existing then as the XOP-1). The country quickly became familiar with the aircraft examples too, as examples flew across the American skies in the role of ‘Flying Billboards’. Miss Champion of Champion Sparks Plugs was a Pitcairn PCA-2 Autogyro as was another example flown by The Detroit News.

Kellet craft made their mark with such ships as the Pep Boys Snowman, a Kellet K-3 used by the 2nd Byrd Antarctic Expedition, which was mounted from 1933 to 1935. Loaned to Admiral Byrd by the auto parts chain, it was the first rotorcraft to be flown in the South Polar Region. Unfortunately it was lost due to snow that had collected in the rear of the fuselage — the undiscovered weight moved the center of gravity out of limits and the aircraft crashed.

While others worked on different aspects and approaches for controlling rotary wing flight (Focke and Flettner in Germany, Wilford and Herrick in the United States and Kay and Hafner in England), the accolades for the most important ancestor of the helicopter belong to Juan de la Cierva.

Editor’s note: More information on modern homebuilt autogyros is available from the Popular Rotorcraft Association: