Helicopters, Industry Sector AEROSPACE

"A helicopter is an assembly of forty thousand loose pieces, flying more or less in formation"

Although fixed-wing aircraft receive all the attention by most historians, helicopter flight was the first flight envisioned by man. In fact, the ancient Chinese were playing with a hand-spun toy that rose upward when revolved rapidly.

mid 1500's The great Italian inventor Leonardo Da Vinci had used his fertile mind to make drawings of a machine that we now know as the helicopter.

"...I have discovered that a screw-shaped device such as this, if it is well made from starched linen, will rise in the air if turned quickly..." Leonardo Da Vinci - Codice Atlantico

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.

1790s Sir George Cayley is famous for his work on the basic principles of flight.

Early 1860s Ponton d'Amecourt of France flew a number of small steam-powered helicopter models. He called his machines helicopteres, which is a word derived from the Greek adjective "elikoeioas" meaning spiral or winding, and the noun "pteron" meaning feather or wing. However, the novelist Jules Verne was still impressed with d'Amecourt's attempts, and in 1886 he wrote "The Clipper of the Clouds" where the hero of the novel cruised around the skies in a giant helicopter-like machine that was lifted by thirty-seven small coaxial rotors and pulled through the air by two propellers.

1880s The well-known scientist and inventor Thomas Alva Edison experimented with small helicopter models in the United States.

The great breakthrough came at the end of the nineteenth century. The invention of the internal combustion engine made it possible for the pioneers to develop full-sized models with an adequate power source. It was then they found the first of many great problems: torque, the effect produced by the rotor to force the fuselage to rotate in the opposite direction as the engine.

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.
 

1922 a Russian émigré to the United States by the name of Georges de Bothezat built one of the largest helicopters of the time under contract to the US Army. De Bothezat's machine was a quadrotor with a rotor located at each end of a truss structure of intersecting beams, placed in the shape of a cross. Each rotor had six wide chord blades.

1930 Corradino d'Ascanio of Italy built a relatively successful coaxial helicopter, which flew under good control. His relatively large machine had two, two-bladed, counterrotating rotors. Following the work of de la Cierva, the blades had hinges that allowed for flapping and a feathering capability to change blade pitch. Control was achieved by using auxiliary wings or servo-tabs on the trailing edges of the blades, a concept that was later adopted by others, including Bleeker and Kaman in the United States.

1929-30 In Belgium the Russian born engineer Nicolas Florine built one of the first successful tandem rotor helicopters. The rotors turned in the same direction but were tilted in opposite directions to cancel torque reaction.

1930--1936 The famous French aviation pioneers Louis Breguet and Rene Dorand made particularly notable advances in the development of a practical helicopter. Their machine of 1935 was relatively large for the era, with a coaxial rotor configuration. Each rotor had two modern looking tapered blades that were mounted to the hub with flap and lag hinges. The blades were controlled in cyclic pitch using a swashplate design. Yaw control was achieved by differential torque on one rotor with respect to the other rotor. Horizontal and vertical tails were used for increased stability. For its time, the aircraft had held several FAI records, including a duration flight of 62 minutes and distance flown of 44 km (27 mi).

1930s Arthur Young began a series of experiments with model helicopters that were ultimately to lead to the design of the renowned Bell-47 helicopter.  

1933 - 1936 Heinrich Focke of the Focke-Wulf Company began his work on rotating-wing aircraft. He acquired a license to build de la Cierva's autogyros, and successfully manufactured the C-19 and the C-30 models. From the experience he gained by working on these machines and after many wind tunnel tests with small models, Focke began developing the FW-61 helicopter in 1934, named after his current company, Focke-Wulf. Later, in early 1936, Focke and Gert Achgelis finally built and demonstrated a successful side-by-side, two-rotor machine, called the Fa-61. The Fa-61 machine is significant in that it was the first helicopter to show fully controlled flight and also to demonstrate successful autorotations.

1938-43 Antoine Flettner, of Germany, developed several helicopter designs. Flettner's success came with using a side-by-side intermeshing rotor configuration, which became known as a synchcropter. . In the synchropter design, the rotor shafts are close together but arranged so that they are at a significant outward angle with the overlapping rotors turning in opposite directions. A gearing system ensures the exact phasing of the rotors. In 1939, Flettner's Fl-265 synchropter flew successfully and was the first helicopter to demonstrate transition into autorotation and then back again into powered flight.

1935 Sikorsky was issued a patent, which showed a relatively modern looking single rotor/tail rotor helicopter design with flapping hinges and a form of cyclic pitch control. Although Sikorsky encountered many technical challenges, he tackled them systematically and carefully. To the workers at the Sikorsky plant in Connecticut, the machine was known as "Igor's nightmare" and reflected the mechanical complexity of his early prototypes. Sikorsky's first helicopter, the VS-300, was flying by May 1940. His first machine had one main rotor and three auxiliary tail rotors. Powered only with a 75 hp engine, the machine could hover, fly sideways and backwards, and perform many other manoeuvres. Yet it could not easily fly forward, exhibiting a sudden nose-up pitching characteristic at low forward speeds. This was traced to the downwash of the main rotor wake, which as airspeed built, blew back onto the two vertically thrusting tail rotors and destroyed their lift. The main lifting rotor of the VS-300 was used in the later VS-300A with a more powerful 90 hp engine, but only the vertical (sideward thrusting) tail rotor was retained out of the original three auxiliary rotors. In this configuration, longitudinal and lateral control was achieved by tilting the main rotor by means of cyclic-pitch inputs; the single tail rotor was used for antitorque and directional control purposes. This configuration was to become the standard for most modern helicopters.

1941 Before long, Sikorsky had refined his first machines and had already started production of the R-4.

1943 Sikorsky developed the R-5, which, although still only a two-seater helicopter, was much larger, more powerful, and more capable than the R-4, which became used extensively for pilot training. T

1944 the Cierva-Weir Company, prompted by the initial success of Sikorsky's R-4 and R-5, proposed a rather large single-rotor machine called the W-9. This machine was rather unique in its use of jet thrust to counteract rotor torque reaction.

The early 1950s Helicopters quickly matured into safe, successful, and highly viable aircraft that were easier to fly and more comfortable for crew and passengers alike. This era is marked by significant mass production of helicopters by various manufacturers in the United States and in Europe. The Sikorsky S-55 and S-58 models made great advances in helicopter design. These aircraft had a large cabin under the rotor, and to give a wide allowable centre of gravity position, the engine was placed in the nose. Westland also maintained their relationship with Sikorsky and built versions called the S-55 Whirlwind and S-58 Wessex.

1959 The success with the Model-47 led Bell Helicopter to develop the UH-1 Huey. The Bell 212 was a two-engine development of the UH-1D, and proved to be a successful military and civilian machine. The Huey-Cobra also grew out of the UH-1 series, retaining the same rotor components, but having a more streamlined fuselage with the crew seated in tandem. The type is still in production in 1999 as the AH-1W Super-Cobra, which uses an advanced composite four-bladed rotor.

1960s The development of the Sikorsky S-61 Sea King, the heavy-lift S-64 Sky Crane, and the larger five- and seven-bladed CH-53 models. Later, the S-70 (UH-60) Blackhawk was to become the mainstay of the Sikorsky company, and the machine is expected to remain in production well into the twenty-first century. The latest Sikorsky machine, the civilian medium lift S-92 Helibus, flew for the first time in 1998.

After 1960 The European manufacturers Aerospatiale, Agusta, MBB, and Westland have produced many successful helicopter designs since the 1960s. Augusta and Westland have also license-produced helicopters designed in the United States, such as those of Sikorsky and Bell. The Aerospatiale (formally Sud-Aviation) Alouette was one of the most successful European helicopters, and in 1955 it was one of the first machines to be powered by a gas turbine. The Aerospatiale Super Frelon was a large transport machine, first flown in 1962. In the early 1970s the Aerospatiale/Westland SA330 Puma became Europe's best selling transport helicopter. The Aerospatiale/Westland Gazelle was a successful successor to the Alouette, first flown in 1967, and it introduced the fenestron tail rotor.

Westland Helicopters (now GKN-Westland) has been a key player in British aviation since the 1930s.The earliest helicopters built by Westland were under license from Sikorsky, but these were significantly modified to meet British airworthiness standards. Skeeter was a small two-seat trainer, which led to the bigger and relatively successful Wasp in 1962. The Westland Wessex was a development of the Sikorsky S-58, which was built in many configurations through 1970. The Sea King and Commando were derived from the S-61, which were steadily improved upon since the first models flew in the late 1960s. The latest versions of the Sea King sold through 1990 have used composite rotor blades and various airframe improvements. Westland designed its own line of helicopters, starting with the military Lynx, which first flew in 1971.

Crazy Facts Corner

• Helicopters are fundamentally safer than airplanes.
• If the engine stops, the helicopter rotor continues to spin allowing the machine to slowly land, generally with out crashing to the ground. 
• Over 3 million lives have been saved by helicopters in both peacetime and wartime operations since the first person was rescued from the sea in 1944.
• If you include military helicopters it is estimated that there are more than 45,000 operating worldwide.
• If you want to travel 300 to 400 miles the helicopter is often the quickest means of transportation.
• Tilting the main rotors enables the helicopter to lift, go forward, backwards or sideways.  The power provided by the engine is principally used to turn the rotors.

Links:

http://www.helis.com/pioneers/

http://www.enae.umd.edu/AGRC/Aero/history.html

http://www.vtol.org/helifact.html

Researched by Angua-