European Helicopters - Early Developments
In its first form, the helicopter was conceived by Leonardo da Vinci, back in the middle ages, and a rough sketch with notes described his idea. In his notes he used the Greek word “helix” meaning a spiral, and he is believed to have combined this word with ‘e‘Pteron,” meaning wing. It is from this combination of Greek words that our word “Helicopter” is derived. If the development of the idea of vertical flight had proved as simple as the idea itself, the helicopter would undoubtedly have been the first practical airplane in the field. But the development, instead of being simple, proved extremely complicated and difficult.
Even after the introduction of the internal combustion engine, lack of sufficient power was a common cause of failure. It took many trials and many failures to convince the early experimenters that the then existing 25 or 50 horsepower engines were not powerful enough to insure lfight, even under the most favorable conditions. It was this lack of power that was responsible for the failure of Paul Cornu’s two-rotor helicopter, which he built in France, in 1907. It was powered by a 24-horse-power gasoline engine. With full power, Cornu was able to get the helicopter off the ground, supporting its own weight alone. With the weight of the pilot added, it could not be made to rise. Control was poor, and the machine could remain airborne for only about 20 seconds.
In 1907, the year of Cornu’s experimental model, and four years after Wright’s flight at Kittyhawk, the French engineer Louis Breguet succeeded in flying a helicopter of his own design. The machine was built in the form of a cross with a biplane rotor at the end of each arm. It was powered by an engine with sufficient horsepower to enable the helicopter to lift itself with a pilot aboard. The machine was unstable, had no satisfactory means of control, and was not practical as an apparatus for vertical lfight. But its brief flight distinguished Breguet as the first man to leave the ground in a helicopter.
At the time of these experiments, the captive balloon was considered necessary for observation, gunfire spotting, and other military uses. It was only natural that the idea of replacing such balloons with the much discussed helicopter should be considered. In such an application the matter of control would be greatly simplified. The rotor blades could be placed at a fixed angle and the only control needed would be the throttle to provide more or less engine power as conditions required.
Proposed in 1915 by Lieutenant Petroczy of the Austrian Army, the concept of the captive helicopter was developed by Professor Theodore von Karman, who was then a professor of aerodynamics at Aix-la-Chapelle. The helicopter of his design was provided with coaxial propellers, turning in opposite directions. Power was supplied by three 120 hp Le Rhone engines which were connected to the propellers by shafts and gears. The weight of the helicopter was approximately 3,200 pounds, and there was sufficient lift to carry the pilot, an observer, a machine gun and fuel for an hour of flight. In tests carried on with this captive helicopter, several ascents were made to an altitude of approximately 150 feet. A feature of this helicopter was the position of the crew. They were to be stationed on top of the rotors, with full visibility above.
The captive helicopter held promise as a replacement for the captive observation balloon, and appeared to be less vulnerable to fighter attack. Tests of the captive helicopter were carried on for several months, but the inventors failed to find anybody who would serve as an observer. In its final ascent the engines began to misfire; the machine oscillated violently, and crashed to the ground. The destruction was complete and the idea of a captive helicopter was never revived. In spite of the discouragements and failures up to this time, there were many who still believed that the helicopter was the most practical form of airplane.
Through experiments carried on from 1920 to 1928, Juan de Cierva of Madrid discovered auto-rotation in which the movement of the craft through the air keeps the rotor turning, and dis-symmetry of lift, or the difference in lift between the blade moving into the airstream and the one moving with the airstream. He had already built a conventional sportplane which had become popular in Europe. In a crash of one of these airplanes the pilot was killed, and de la Cierva began the development of an idea for an airplane which could fly safely at low speeds. Realizing that there was a critical value below which the lift of an airfoil is lost, he conceived the idea of using rotating airfoils instead of fixed wings. The plan he worked out caused the airfoils to rotate automatically and to act as wings for the plane. De la Cierva’s first autogiro utilized a system of counter-rotating rotors, but failed to fly because of the interference of one rotor with the other. In the year following his initial trial, he made another attempt, using a single five-bladed rotor. In 1928 de la Cierva built an autogiro with a four-blade, fully-articulated rotor, which was a complete success.
In the United States, Emile Berliner, who held patents for several inventions, turned his attention to the helicopter and, working with his brother [son?] Henry, produced two models; one in 1920 and one in 1923. This later helicopter could rise to about 20 feet, hover briefly, maneuver in a 300 foot radius and proceed at about 40 miles per hour. In the years that followed Berliner’s experiments, work on the helicopter continued in several parts of the world. In France, Oemichen tried to combine a helicopter with a blimp; in Spain, Pescara had some success with a helicopter using counter-rotating rotors. In Holland, von Banhauer built a helicopter in 1930 with a single main rotor and a tail rotor, the configuration found in many helicopters today. In Italy, in the same year, d’Ascanio produced a coaxial helicopter which was able to remain airborne, and on one occasion remained in the air for 9 minutes. The first successful tandem rotor helicopter was flown in Belgium by Florine, also in the year 1930.
By 1935 the helicopter had reached a point where its practical value began to be apparent. Louis Breguet had returned to the helicopter field in 1931. After one unsuccessful attempt, he built a large coaxial helicopter powered by a 350 hp engine. It made use of many of the principles that had been discovered through experimentation with the autogiro. Trials made in 1935 proved that this new helicopter could take off vertically, that it could hover over a spot and that it was able to fly forward, backward or sideways. The machine could be readily maneuvered and could be landed at a selected spot. It not only reached an altitude of 500 feet, but on one occasion remained airborne for more than 45 minutes. It is credited with a forward speed of more than 50 miles per hour. Breguet’s helicopter was overweight, and control at times was marginal, but the record shows that this machine in many ways was a useful and most practical helicopter. Based on the results of his experience with this model, Breguet prepared a scientific paper in which he proposed a gigantic trans-oceanic helicopter. Plans were never completed.
During the 1930s, engineers in both Germany and America were designing and testing the helicopter. Credit for the world's first really practical helicopter must go to Dr. Heinrich Focke of the Focke-Wulf Company, which later produced the German FW-190 fighter plane. Focke had obtained some experience in rotary wing aerodynamics when his company built a version of the de la Cierva Autogyro under license. And in 1937 he designed and built a dual-rotor helicopter which he designated as the FW-61, the world's first practical helicopter. The Focke-Achgeles 61a had two main rotors mounted side-by-side on outriggers extending from an airplane-type fuselage. With the FW-61, many early records were established. Among these were a flight duration of one hour and twenty minutes, a distance of 143 airline miles, an altitude of 11,240 feet, and a speed of 76 mph. The FW-61 is generally considered the world'sfirst practical helicopter, and the records set with it were not broken until Igor Sikorsky returned to the field and again began the development of the rotary wing airplane The machine was demonstrated in a number of European cities and caused wide comment. Its advantage of precision control was demonstrated ; it was once flown inside a 100-by-300-foot exhibition hall in Berlin by the woman pilot, Henna Reitsch. Heinrich Focke designed the Fa 223 Drache which achieved a record altitude of 23,400 feet in 1940. Meanwhile, in the US Igor Sikorsky was developing his own helicopters. Another American company Platt-LePage developed the PL-1.
A relatively new weapon on the battlefield, the attack helicopter has developed in an evolutionary rather than revolutionary manner over the course of fifty years. The Germans were the first in to the field of armed helicopters. Before the end of 1944 the Focke Achgelis Fa-223 Drache, a six-seat military transport helicopter, was equipped with a single Rheinmettal 7.92 mm MG-15 machine gun flexibly mounted in the nose. Despite this effort, helicopter use in World War II was limited, overshadowed by the advances in fixed-wing airplanes, particularly the strategic bomber and the jet fighter.
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