Juan de la Cierva y Codorníu, 1st Count of la Cierva, was a Spanish civil engineer, pilot, and self-taught aeronautical engineer. He was born on September 21, 1895, and died on December 9, 1936. His most important achievement was inventing a rotorcraft called an autogiro in 1920. This aircraft had a single rotor and was later called an autogyro in English. In 1923, after four years of testing, De la Cierva created an articulated rotor, which led to the first successful flight of a stable rotary-wing aircraft. This flight used his C.4 prototype.

Early life

Juan de la Cierva was born into a wealthy Spanish family. His father once worked as the minister of war. At age eight, he used his allowance to buy supplies for experiments with gliders in one of his father's work sheds. During their teenage years, he and his friends built an airplane using parts from a crashed plane they purchased from a French pilot. The final airplane used wood from a bar counter in Spain for the propeller. He later earned a degree in civil engineering and, after successfully building and testing the first autogyro, moved to the United Kingdom in 1925. With the help of Scottish industrialist James G. Weir, he founded the Cierva Autogiro Company.

At the start of the Spanish Civil War, De la Cierva supported the Nationalist forces. He helped the rebels obtain the De Havilland DH-89 "Dragon Rapide," an airplane used to transport General Franco from the Canary Islands to Spanish Morocco. His brother was executed by the Republican army in Paracuellos del Jarama.

The gyroplane (autogyro)

In 1912, De la Cierva began building aircraft. In 1914, he designed and built a three-engine airplane that the Spanish government accepted. In 1919, he started studying how to use a rotor to create lift at low speeds and avoid stalling.

To achieve this, he used a feature called autorotation. When the rotor blades are set at the right angle, they can spin on their own without needing a motor, because the forces of lift and drag balance each other. In De la Cierva’s autogyro, a regular propeller turned the rotor, allowing it to create enough lift for flight, climbing, and descending.

Before this worked well, De la Cierva faced problems during takeoff. Uneven lift between the rotor blades caused unbalanced movement. This issue was solved by adding a flapping hinge. In 1923, his first successful autogyro was tested at Getafe aerodrome in Spain by Lt. Gomez Spencer.

This work took place in Spain, where De la Cierva was born. In 1925, he brought his C.6 model to Britain and showed it to the Air Ministry in Farnborough, Hampshire. This machine had a four-blade rotor with flapping hinges and used standard airplane controls. It was built on the frame of an Avro 504K airplane, and the rotor started spinning when a rope wrapped around the blades was quickly unwound.

The Farnborough demonstration was successful, leading to an invitation to continue work in the UK. With help from Scottish industrialist James George Weir, the Cierva Autogiro Company, Ltd., was formed in 1926. De la Cierva focused on designing rotor systems, while other companies, like A.V. Roe, built the airplane bodies.

The Avro-built C.8 improved on the C.6, using a more powerful engine. The C.8R had drag hinges to reduce stress on the rotor blades, but this caused new problems, such as ground resonance, which was fixed with dampers.

Solving these rotor issues led to progress. After several flights, a C.8L4 autogyro entered the 1928 Kings Cup Air Race. Though it had to leave the race, it later flew 4,800 km (3,000 mi) across the British Isles and flew from London to Paris, becoming the first rotating-wing aircraft to cross the English Channel. The tour later included Berlin, Brussels, and Amsterdam.

A major challenge was starting the rotor before takeoff. Methods like the rope system could reach 50% of the needed speed, but ground movement was still required. Another idea was tilting the tail to direct engine airflow through the rotor. The best solution came with the C.19 Mk.4, which used a direct drive from the engine to the rotor. The rotor could then be disconnected before takeoff.

As De la Cierva’s autogyros gained success, others began building similar machines. A key innovation was direct rotor control through cyclic pitch changes. This was first done by tilting the rotor hub and later improved by Raoul Hafner with a spider mechanism that adjusted each blade. The C.30, made by Avro, Liore et Olivier, and Focke-Wulf, allowed movement in any direction using horizontal rotors and reduced the need for traditional controls. This development was also influenced by Albert Gillis von Baumhauer, who used a swashplate in his designs.

Another improvement was the jump takeoff method. The rotor was accelerated to flight speed with no lift, then disconnected. The loss of torque caused the blades to move forward, increasing lift and making the aircraft leap into the air. With the engine now powering the propeller, the autogyro could fly forward with the rotor spinning on its own. The C.40 was the first autogyro to use this method.

Autogyros were built in many countries under De la Cierva’s licenses, including France, Germany, Japan, Russia, and the United States.

De la Cierva aimed to create an aircraft that would not stall. Later in life, he recognized the benefits of helicopters and began work on them. In 1936, the Cierva Autogiro Company, Ltd., responded to a British Air Ministry request by designing the gyrodyne, a helicopter-like aircraft for the Royal Navy.

Death

On the morning of December 9, 1936, he entered a Dutch DC-2 airplane operated by KLM at Croydon Airfield, heading to Amsterdam. A delay occurred due to thick fog, and the airplane took off around 10:30 a.m. Shortly after takeoff, the plane went off course slightly and crashed into a house on slightly hilly ground near the airport. The crash killed 15 people, including de la Cierva.

Legacy

Juan de la Cierva's research on how rotor wings work made it possible to create modern helicopters. Before this, helicopters could not be built because people did not understand how rotor wings functioned. The knowledge he developed applies to all rotor-winged aircraft. Although autogyros cannot fly vertically, work on them helped engineers study and improve helicopter designs.

Cierva died in a plane crash in December 1936 before he could complete a project to build a reliable aircraft for the Royal Navy that could take off and land straight up and down. However, his work on the autogyro was used to achieve this goal. Technology from the autogyro was used in the Fw 61 helicopter, which was tested in 1936 by a company that had permission to use Cierva's designs. His early work also inspired the creation of a third type of rotorcraft, the gyrodyne, which was developed by Dr. James Allan Jamieson Bennett, a former assistant and later leader of Cierva's company.

In 1966, Juan de la Cierva was honored in the International Aerospace Hall of Fame for his improvements to rotor blade technology, which helped generate lift and control an aircraft's movement. A scholarship from the Spanish Ministry of Science is named after him to recognize his contributions.