The earliest attempts at helicopter design can be traced back to the days of Leonardo da Vinci in 1486, although some people attribute it to the Chinese Flying Top designed by Ko Hung around 320 AD. Davinci’s notes and drawings of the ‘Helical Screw’. He had the idea that a large helical screw would literally pull his flying machine into the air as it turned. Although we now know that his design would not work, except perhaps under water (hardly the right place for a flying machine !), his perception that vertical flight was a possibility was, as always, very correct and way ahead of his time.
A copy of the original drawings and notes by the great Leonardo da Vinci. Between the mid 1700’s until the early 1900’s, quite a large number of designs and proposals were put forward for helicopters. The majority of these designs and proposals, some of which were very grandiose, never progressed beyond the initial concept. Additionally, because of the lack of an engine with a suitable power to weight ratio, all helicopters built up till 1907 were essentially toys, or large models which were not capable of lifting more than their own weight.
Power was derived from a number of sources such as electric motors, clock-springs and elastic bands. In some cases, the rotors were turned by ‘steam-jets’ at the end of each rotor blade. The first successful steam-driven model was built by an Englishman named Phillips in 1842; the model managed an uncontrolled flight across two fields.Launoy and Bienvenu based their idea on the Chinese Flying Top, using four feathers for each rotor at either end of a short stick. The device was rotated by means of a bow string. Several ‘designers’ tried variations on this theme, but the machines did not progress beyond the toy stage.
An Italian, Enrico Folanini, is credited with building the first shaft-driven steam-powered helicopter to fly. The model weighed only 8 pounds, weight being saved by boiling water in a cylinder before attaching it to the helicopter and opening the ‘throttle’.
Those of you familiar with Newton’s Laws of Motion will recall that “To every action there is an equal and opposite reaction”. For helicopters this law manifests itself by the desire for the body of the helicopter to rotate in the opposite direction to the rotors. This is because the rotors are turned by the engine which is fixed to the body of the machine. Most of the early designs therefore incorporated two rotors turning in opposite directions to counteract this effect. The rotors were either mounted on separate outriggers or co-axially (on the same drive shaft). The first designer to make use of a separate tail rotor to counteract the turning effect (torque reaction) was a German named B.R.Beenan who, in 1897, built a model which also incorporated variable pitch control of the main and tail rotor blades as well as a method of tilting the rotor.
Although Lift can be controlled by varying the Rpm of the rotor, this method is not very efficient as the inertia of the rotor system means that the Rpm is slow to react to changes in throttle setting. By maintaining the rotor Rpm and varying the angle of attack of the rotor blades (changing the pitch) more positive control of Lift can be achieved.
Between 1909-10, Igor Sikorsky built two machines, one of which was powered by a 24 hp Anzani engine. Neither machine was capable of lifting more than the weight of the entire machine off the ground and, for the next 30 years, Sikorsky gave up his initial attempts at vertical flight to concentrate on designing fixed-wing aircraft. However, he was sure that the concept was feasible but knew that technology had a long way to go before any further advances could be made.
Apart from the lack of a suitable engine, powerful, and light enough to enable the helicopter to lift more than its own weight, the principle problem which all the early pioneers encountered was of controlling the helicopter. Helicopters did not really progress until the arrival of a certain Senor Juan de la Cierva who experimented with Autogyro’s. His designs made use of freely rotating rotor systems with independently articulated rotor blades. Although Cierva is generally credited with inventing the articulated rotor system, it was originally conceived by a Frenchman named Renard in 1904.
The overall weight of Cierva’s autogiro’s was much less than that of a helicopter because there was no need for a large engine and drive system to turn the rotor(s); this also meant that it was not necessary to fit dual rotors or a tail rotor to counteract the torque reaction. The best known of Cierva’s designs was the C-30, pictured right, of which several hundred examples were built in the 1930’s. One of his earlier models, the Cierva No4, is pictured left. In 1928, using one of his C-30 Autogiro’s, Cierva became the first rotary-wing pilot to cross the English Channel.
Focke-Achgelis designed an autogiro for use as an aerial spotting device in the Second World War. The Fa 330 was a small autogiro which could be stored on board German U-boats. When it was required for service, the blades were re-attached and the autogiro was towed behind the U-boat. The pilot was able to communicate with the U-boat by means of a telephone line running along-side the towing wire.
One unfortunate problem with this method of aerial spotting was that it also enabled the enemy to sight the U-boats more readily. The effect of this was that sometimes the U-boat had to crash-dive, cutting the Autogiro adrift in the process, leaving the poor pilot to drown in the conventional manner.
The complicated task of altering the pitch of the rotating blades and the direction of tilt of the whole rotor system was successfully tackled by the Marquis de Pescara, an Argentinean working in Paris. He designed and built a helicopter with two contra-rotating bi-plane rotors which were powered by a 170 hp La Rhone engine.
Although this machine actually flew, its highly complicated design made it impracticable for future development. However, the rotor control system pioneered by Pescara has become the basic design used on most modern helicopters. His Model No3, built in 1924, employed collective and cyclic pitch control on the tandem contra-rotating rotors. It is widely believed that Pescara was one of the first pioneers to understand Autorotation and his Model No3 would have been able to descend safely in the event of an engine failure.
In 1907, the Breguet-Richer Gyroplane No. 1, right, with four bi-plane rotors powered by a 40 hp Antoinette engine carried a man into the air for 40 seconds. However, the machine had to be ‘tethered’ by four men to keep it stable, but this was still recorded as the first manned ‘helicopter’ flight.
The tandem-rotor Cornu, powered by a 24 hp Antoinette engine, carried a man into the air during the World’s first recorded untethered helicopter flight in 1907. However, the ‘pilot’ only managed to keep it airborne for 20 seconds and the machine broke up on landing! But, the helicopter had been born.
During the 1920’s, little real progress was made with the development of helicopters; most aviation interest during this period was directed towards the development of better and faster fixed-wing aircraft. Then, in 1931, Bregeut teamed up with Renee Dorand, his technical director, to build a coaxially mounted twin-rotor helicopter which achieved a maximum speed of 61 mph and flew for just over one hour at a height of about 600 feet.
In 1937, Professor Heinrich Focke and another German named Achgelis joined forces to conduct helicopter research. The result was the production of the FW-61, based on the fuselage of a small biplane trainer with two outriggers supporting the contra-rotating rotors. The cut-down propeller mounted on the front of the radial engine was used only for cooling.
The FW-61 rose to fame when it was demonstrated by Flugkapitan Hanna Reitsch inside the Deutschlandhalle stadium in Berlin. Hanna said that the machine was very easy to control, and claimed that she had only 3 hours experience on the machine before she made the first demonstration flight in the stadium. The FW-61 made its first autorotative (descent without power) landing in 1937.
The first, successful British helicopter also flew in 1938. The Weir W.5, designed by C.G. Pullin, weighed only 860 pounds fully loaded and attained a maximum speed of 70mph during 80 hours of test flying. In 1939, the W.5. was followed by a scaled up version, the W.6, which was the first two-seater helicopter in the world. Further progress on this model was prevented by the Second World War.
In the early 1930’s, a German aeronautical engineer named Anton Flettner became interested in helicopter design. He started with autogyro’s and gradually moved towards true helicopters, until in the early 1940’s he designed and built the FL-282 Kolibri, a helicopter with intermeshing, contra-rotating blades, capable of carrying two passengers. The first models were powered by a 160 horsepower, Siemens Halske SH 14A, radial engine. It was successfully operated from boats. The B-model had a top speed of 93 mph and a service ceiling of 10,800 feet.
Around 1931, Igor Sikorsky once again turned his attention to helicopter design. Unlike most other designers he opted for the Main Rotor plus Tail Rotor configuration. However, Sikorsky was not so much an inventor as a designer who made use of the best of all the currently available designs and melded them together into what was the basic ‘mould’ for the majority of his helicopter designs.
The VS-300 was powered by a 75hp Lycoming engine and had two tail-rotors; one for anti-torque and directional control, the other to aid horizontal stability. Later versions of the VS-300 were powered by a 90 hp Franklin engine and the second tail-rotor was dispensed with.
The Sikorsky R-4, as used in the earliest recorded helicopter rescue which took place in Burma in 1944. The R-4 was derived directly from the VS-300 and was powered by a 180 hp Warner Scarab engine. It had a maximum gross weight of 2,503 lb (1130 kg) carrying a payload of one passenger at a maximum speed of 82 mph.
The R-4 was the first helicopter to be manufactured in substantial numbers. It had side-by-side seating for two pilots and was and was extensively used as for pilot training.
It was not until 1943 that the name of Lawrence Bell appeared in the history books with his first successful helicopter. The stabilizer bar, exclusively employed on Bell helicopters was designed by Arthur Young who had initially worked on electrically driven model helicopters.
Although the Bell Aircraft Corporation was formed in 1935, it was not until 1943 that the first Bell Helicopter, the Model 30, was successfully flown. Several modified versions of the Model 30 were built, including Ship 3 which sported the open latticework tailboom more familiarly connected with the arrival of the Model 47 in 1945.
The prototype Bell Model 47 was granted the World’s first Commercial Helicopter Licence. The Bell 47 developed into one of the most successful light-utility helicopters ever. A total of 6,263 variants were built until production of the model was stopped in 1973. A large number of these machines, including many of the earliest versions are still flying today; some at Flying Training Schools, others for agricultural purposes and many as privately owned run-abouts.
The first crossing of the English Channel by a helicopter was in 1945 by the German built Fa 223. This model, also known as the Drache, was originally built in 1940 by the Fokke-Achelis team; in the same year, the Fa 223 achieved record height of 23,924 feet. Progress on this type was held up until after the Second World War.
After 1946, helicopter designs moved forward in leaps and bounds. The majority of the problems which had held up its earlier development were now well catalogued, and modern day helicopters still employ much of the basic designs of the models built during the late 30’s to mid 40’s.
Article by Brian Teeder