Cierva C.1

Cierva C.1
Type:	experimental gyroplane
Design country:	Spain
Manufacturer:
First flight:	Start attempts October 1920
Number of pieces:	1 each (C.1, C.2, C.3)

The Cierva C.1 (originally Autogiro No.1 ) was an experimental gyroplane designed by the designer Juan de la Cierva , with whom he carried out the first unsuccessful attempts at starting a gyroplane in 1920. Only a prototype was made. The flight attempts were also unsuccessful with the following developments C.2 and C.3 , each of which was built one copy .

history

Concept presentation

After the experience with the Cierva designed by him three-engine bomber BCD3 that on his first flight in July 1919 due to a stall crashed shortly after takeoff, he turned from now on developing new concepts to secure stable. His simple solution was that of a rotating wing to generate lift, while the rest of the aircraft was to remain "stationary". There should be no connection between the engine and the rotating wings. Since the engine was only responsible for propulsion, a higher speed should be achieved compared to the helicopter models of that time, which made a higher speed and lift of the rotor blades possible. Cierva saw another disadvantage of the helicopters in the fact that if the engine failed, the machine would crash just like a fixed-wing aircraft. According to his theoretical ideas about the aerodynamics of rotating profiled wings, a rotor that would once be "started" by external forces above a minimum speed should continue to run by itself until the engine has accelerated the aircraft to such an extent that it gains sufficient lift and can take off.

Cierva was convinced that the risk of stalling did not exist in its development, as the retained autorotation gave the pilot full control of the aircraft even if the engine failed. But he also recognized early on the problems caused by the asymmetrical lift of the rotor, caused by the higher relative speed of the advancing blades, which receive a higher lift than the retreating blades. In order to put his ideas and concepts to the test in practice, Cierva decided to build a suitable aircraft.

Construction of the first experimental unit

Example photo for a Deperdussin monoplane as used by Cierva

His first machine, the Autogiro No.1, was primarily a full-scale test device for validating his theories. It consisted of the hull of an old Deperdussin monoplane with a 60 HP Rhône radial engine. Cierva installed a mast with two four-blade rotors on top of each other. The Eiffel 101 profile of the blades pointed downwards in one rotor, so that the rotation could take place in opposite directions. The blades were individually clamped firmly against the freely rotatable mounting on the mast. The coaxial arrangement of the rotors should the asymmetry of lift and after Cierva idea gyroscopic effect cancel. The tail unit of the Deperdussin was retained and an additional tail unit was installed on the top of the mast for better controllability around the vertical axis.

Cierva's brother-in-law, Gomez Acebo, made the first flight attempts in October 1920 on the Getafe airfield near Madrid. These attempts were unsuccessful because, due to flow interference between the two rotors, the lower one only rotated at 2/3 the speed of the upper one. Even without the machine taking off, a tendency to roll over due to the asymmetrical lift and the gyroscopic effect could already be determined. The positive result of the tests was that the autorotation was set in the intended direction after the rotor had been set in rotation by hand. Cierva then gave up the design with coaxial rotors and turned to single-rotor solutions.

Autogiro No.2 (Cierva C.2)

For the first "real" gyroplane, Cierva first built a fuselage based on his own designs and equipped it with a 110 hp nine-cylinder Le Rhône rotary engine . As in the previous test device, the individual blades of the five-blade rotor with a flat Eiffel profile were braced with wires in such a way that they could neither move down nor up. Cierva hoped to solve the problem of steering and lateral stability, especially with a large "differential" elevator. The area on the side with the retracting rotor was given a larger setting angle to compensate for the greater lift on the side with the advancing rotor. The construction of the gyroplane was delayed by the late delivery of the duralumin rotor spars made in France, so that Cierva preferred to build a third machine (Autogiro No.3).

After completion, Gomez Spencer tested the C.2 in Getafe in early 1922. At the first attempt to start the machine rolled on its side and the rotor was destroyed. Although the concept of the differential elevator proved to be unusable, it was used again years later in a modified form on the Cierva C.30 .

Autogiro No.3 (Cierva C.3)

The C.3 was completed and tested before the C.2. It consisted of the hull of a summer monoplane with a seven-cylinder 50-hp Gnôme-Rhône rotary engine. A new development, however, was the three-blade rotor with a flat Fokker profile. In the hub of the rotor there was a device to compensate for the differences in lift by twisting the blades, whereby the angle of attack changed cyclically during the rotation. The device in the faired hub consisted of a solid, simple cam disk which actuated a single lever on each trailing edge of the blade as the rotor rotated. Cierva had this "compensation device" patented, but it turned out to be unsuitable for operation under practical flight conditions.

De Lecca made the first test runs with the C.3 in Getafe in June 1921. Although it survived several accidents and was equipped with an 80-hp Le Rhône engine, the C.3 never flew.

Conclusions

With none of the three constructions was Cierva actually able to generate so much lift that a take-off would have been possible. In addition, all test machines showed a tendency to rollover even on the ground. As he thought about solving these problems, Cierva recalled his experiments with a small rubber-motorized model with rotors made of reed. This model showed little tendency to roll to one side. He concluded from this that the flexibility of the tube, which contrasted with the properties of the firmly clamped rotor blades in the test machines, played a decisive role. This led him to develop the flapping hinges , which solved this problem and were first tested in practice on the Cierva C.4 in January 1923 .

See also

• List of gyroplanes

literature

• PT Capon: Cierva's first autogiros Part 1 . In: Airplane Monthly April 1979, pp. 200-205
• Planes from A – Z - Cierva Autogyros . In: AERO - The illustrated compilation of aviation. No. 51, pp. 1424 ff., 1984, Marshall Cavendish.
• TR Hiett: Cierva's rotating wings . In: AIR Enthusiast July / August 2003, pp. 26–31

Web links

• Brief history and photo of the C.1 on aviastar.org (accessed October 3, 2017)

Individual evidence

1. ↑ Description of the summer monoplane