Oehmichen (France)

Etienne Oemichen, a young engineer with the Peugeot motor car company, began to experiment with rotating-wing designs in 1920, and in all designed and built six different vertical take-off machines. When the first of these failed to develop enough lift from its twin rotors and 25hp engine to rise off the ground, he added a hydrogen-filled balloon on top of it to give it added stability and lift. The most noteworthy – and most striking – of his aircraft was the helicopter No.2, which had no less than 4 rotors and 8 propellers, all driven by a single 120hp Le Rhone rotary engine when it flew for the first time on 11 November 1922. A 180hp Gnome engine was substituted later. The Oemichen No.2 was basically a steel-tube framework of cruciform layout, with 2-blade paddle-shaped rotors at the extremities of the four arms. The angle of these blades could be varied by warping. Five of the propellers, turning in a horizontal plane, served to stabilise the machine laterally; another propeller mounted at the nose was for steering the helicopter; and the remaining pair acted as pusher propellers for forward propulsion. The opposing pairs of rotors were of slightly different diameters. The Oemichen No.2 exhibited, for its time, a considerable degree of stability and controllability, and in all made more than a thousand test flights during the middle 1920s. By 1923 it was able to remain airborne for several minutes at a time, and on 14 April 1924 it established the first-ever FAI distance record for helicopters of 360m. Three days later it increased this to 525m and on 4 May was airborne for 14 min, flying more than a mile and completing in the process the first 1km closed-circuit flight by a helicopter in 7 min. 40 sec. Oemichen was, however, dissatisfied with the modest heights to which No.2 was able to fly, and from the third machine onward he adopted a single main rotor layout, accompanied by two smaller anti-torque rotors. His last design, in 1938, reverted to the balloon-assisted principle of his first aircraft.

In France, Etienne Oemichen, a young engineer at Peugeot, began rotary wing experiments in 1920, building a total of six different machines. His second machine flew unassisted on 11 November 1922. The Oemichen No. 2 had an “X”- shaped, tubular frame with a wide two-bladed rotor at the end of each arm. For control and lateral movement, eight small propellers were used: five horizontal propellers with variable and reversible pitch for lateral stability, another propeller at the nose for steering, and another pair of pushers for forward motion. By 1923, the Oemichen No. 2 was able to remain airborne for several minutes and on 14 April 1924, it established the first rotary wing distance record: 360m. On 4 May, it completed the first 1km closed circuit flight by a rotary wing vehicle in 7 minutes 40 seconds to win a 90,000 franc prize. Maximum endurance was 14 minutes. Despite the fact that it was able to demonstrate sufficient controllability and power in ground effect for this historic flight, it was not a practical flying machine. In recognition of the impracticality of the machine, Oemichen began pursuing a series of aircraft with a single-main rotor and two anti-torque rotors, but had little success.

Pescara No.3 (Spain)

It is unfortunate that more complete records have evidently not survived of the later Pescara helicopters, for despite their apparent clumsiness they represented for their time an important step forward in helicopter design technology that deserves recognition. The Spanish Marquis Raul Pateras Pescara built his first helicopter in Barcelona in 1919-20. It was a clumsy machine, weighing some 600kg without fuel or pilot and powered by a 45hp Hispano engine. Each of the 2 co-axial rotors had a diameter of 6.40m and was made up of 6 biplane pairs of blades giving a total of 24 lifting surfaces, but the little Hispano was not powerful enough to raise the machine off the ground. A modified form of this aircraft, with a 170hp Le Rhone rotary engine, did just get off the ground in May 1921, but it was far from being a stable or satisfactory design. In 1922 Pescara moved to France, where the No.2 did succeed in rising some 1.5m during tests carried out for the Service Technique de I’Aeronautique.

Pescara’s most successful helicopter was the No.3, which was built in 1923 and by January 1924 was capable of making flights of some 10 minutes’ duration. The same co-axial rotor system was employed, larger twin rotors each with 4 pairs of blades turning around a ‘totem pole’ rotor mast. A 180hp Hispano-Suiza engine, for which the Lamblin radiator was situated at the rear of the craft, provided the power. Although a heavy and cumbersome machine the Pescara No.3 was a simple design when compared with its closest contemporary, the Oemichen No.2, and makes an interesting comparison with the Breguet-Dorand of some ten years later. On 18 April 1924 Pescara flew the No.3 at Issy-les-Moulineaux for a distance of 736m, handsomely beating the record set up by the Oemichen only the day before.

The significance of this achievement lay in the fact that Pescara’s machine, unlike the Oemichen or any other rotorcraft up to that time, did not rely on conventional propellers rotating in the vertical plane to give the aircraft forward motion. Instead, the pitch of the 16 lifting surfaces could be altered in flight by warping them, and the rotor head could be tilted to give the blades a degree of forward thrust. The speeds thus achieved were extremely modest, but the Pescara No.3 exhibited the first convincing demonstration of the principles of cyclic and collective pitch control. Autorotation of the rotors was also provided for in the event of engine failure.

Reference is made in some quarters to the Pescara No.3F, which was possibly a modification of the No.3 and not a new machine. This appeared in the early part of 1925 and had a 250hp engine, with a cut-down propeller fulfilling a cooling function only. It offered no great improvement over the No.3, and later that year Pescara returned to Spain and entered the motor car industry. He seems to have been discouraged from further serious helicopter development by the emergent success of Cierva with the autogiro, though he was associated with the little French-designed Pouit S-4 later in the 1920s.

Pescara’s No. 3 machine, completed in 1923, used four 7.2m diameter 4-blade biplane rotors and no other propulsion mechanisms: the pitch of the 16 lifting surfaces could be altered in flight by wing warping. This was the first credible use of cyclic and collective pitch control, the essential ingredients of a helicopter. The rotor hub could be tilted for some measure of forward motion, but speed was only about 13km/h. This slow speed was one of the main reasons that the early “helicopters” used auxiliary propellers for forward propulsion. In September 1923, Pescara almost became the first person to complete a 1km circuit, but the machine crashed and was severely damaged. The next spring, four days after Oemichen’s first FAI distance record, Pescara doubled it to 736m.