The History of Rotorcraft

Although fixed-wing aircraft receive all the attention by most historians, helicopter flight was the first flight envisioned by man. The ancient Chinese played with a hand-spun toy that rose upward when revolved rapidly. The word "Helicopter" is derived from the Greek term "helix" (spiral) and "pteron" (wing).

This form of aircraft engaged the earliest attentions of one of the great figures in the dawn of flight, Leonardo da Vinci. In 1490 Leonardo da Vinci was the first to put down on paper a design for a man powered spiral winged device that resembled the modern helicopter. The explanation for his keen interest is simple. For ages man has wished not merely to fly but to be able to lift himself vertically from the earth and set himself down again without forward run; and this is exactly what a helicopter, with the power-driven rotor or rotors which stamp it as a member of the "rotary-wing" family of aircraft, enables him to do.

Even before the Wright Brothers flew the world's first airplane, Igor Sikorsky was building a coaxial helicopter in Russia. There are many famous names in coaxial helicopters: Cornu, Asboth, Pescara, De Bothezat, Berliner, Bendix, Hiller and others. Coaxial designs are attractive for their basic simplicity. The power train is short and the airframe can take many shapes. Counter-rotation eliminates feeding torque into the airframe. In hovering flight the lift force is only vertical, there is no tail rotor producing a side force requiring constant pilot intervention.

In the early helicopter period many extraordinary models were developed by an ever increasing number of great thinkers, but all the pioneers were missing two essentials: a true understanding of the nature of lift and an adequate motor. The breakthrough came at the end of the nineteenth century. The invention of the internal combustion engine made it possible to develop full-sized models with an adequate power source. Then the first of many problems arose: torque, the effect produced by the rotor to force the fuselage to rotate in the opposite direction as the engine. Dissymmetry of lift, the action that tended to cause the early single-rotor helicopters to flip over when translating from hovering to forward flight, confounded early pioneers until the introduction of independent freedom of blade motions made possible by the invention of the swashplate. The swashplate provides a means of varying the pitch of the blades in a cyclic fashion as they rotate around the central shaft. The provision of cyclic pitch control allowed the lift to be equalized on each side of the shaft and eliminate the tendency of the helicopter to tip over sideways. There were many other problems to be worked out.

Then on November 13, 1907, the French pioneer Paul Cornu lifted a twin-rotor helicopter into the air entirely without assistance from the ground for a few seconds. In the early 1900's Henry Berliner created the first powered rotor craft that successfully made a controlled flight. Berliner's helicopter only traveled about 100 yards at an altitude of about 15 feet, but the flight was successfully controlled by a pilot. Later, the invention of the hinged rotor blade, by Juan de la Cierva, coupled with the incorporation of a swashplate, laid out the basis for the eventual development of the helicopter as a practical form of air-transport.

It was not until Sikorsky came along that the first practical helicopter, the single rotor VS-300, came into existence. The VS-300 was first flown on 14 September 1939 with Sikorsky himself as the test pilot. The original VS-300 was powered by a 75 HP engine. The aircraft's body was nothing more than an open cockpit with a welded steel tubing frame. Later versions acquired a frame covering and finally a covered cockpit. On its first flight the VS-300 was tethered to concrete blocks, the first untethered flight was performed on 13 May 1940. Although the VS-300 could ascend vertically and could also fly sideways and to the rear, it could not fly safely forward.

Sikorsky continued to perfect and redesign the aircraft and on May 6, 1941 he set a new world helicopter endurance record by flying the VS-300 for 1 hour, 32 minutes and 26 seconds. On December 8, 1941, the VS-300 was flown in its final modern configuration; it had a single lifting rotor with a cyclic-pitch control for roll and pitch and also included a single tail rotor for use in both directional control and anti-torque. In May of 1942, Sikorsky made the first cross-country helicopter flight from Stratford, Connecticut to Dayton, Ohio, a distance of about 761 miles.

From the VS-300 was developed the R-4, more than 400 of which served in China, Burma, India, the Pacific, Europe and Alaska in the second World War and afterwards.

There are four principal helicopter designs which have been developed and produced in the United States: the most common is the tail rotor design, more popularly known as the single rotor design, which has one main rotor and a small tail rotor; the tandem rotor design, which has two rotors, one in the front and one in the rear of the aircraft; the syncropter design which has two intermeshing rotors, one located on each side of the aircraft; and the coaxial design which has two rotors mounted one above the other on a single axis and rotating in opposite directions. The single main rotor and a small anti-torque rotor dominate modern helicopter design through today.

Gyrodyne Company of America, Inc. engaged extensively in the design, development, testing, and production of coaxial helicopters starting in the late 1940s. From the mid-fifties to the early seventies, Gyrodyne manufactured and sold approximately 800 coaxial helicopters. The Gyrodyne designs varied in size and complexity and ranged from its first small one-man helicopter, dubbed Rotorcycle, through its remotely piloted models QH-50A through QH-50D turbine-powered target and utility platforms. Gyrodyne ceased development on coaxial designs in the mid 1970s due to financial difficulties and government cutbacks. Gyrodyne ushered in numerous technological milestones including the world's first successful coaxial flight test, first convert-a-plane, first free drone helicopter flight, and first fully composite rotor blade. Since that time most focus in coaxial design has been concentrated primarily in the UAV military arena.

Other designs such as the Bensen Little Zipster of the 1950's employed coaxial, counter-rotating rotors and employed a tilting rotor head.

Due to complexity, difficulty of learning to pilot and cost and regulation, the helicopter has never reached a mass consumer market although futurists have predicted from time to time that it will become a mass market product.