Term Paper on "Evolution of Rotorcraft"

/>This form of play aircraft engaged the attentions of Leonardo da Vinci as it related to his fascination with the phenomenon of flight

. 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 and another that resembled a hang-glider. However, his designs were impractical and could not provide lift. His sketches of the "aerial-screw" or "air gyroscope" device date back to 1483 but were not published until nearly three centuries later

Figure 2: Da Vinci's design for a flying machine c. 1488

Even into the nineteenth century these toys were sold in the U.S.A. As Wooden Puddle Jumpers, and they were studied by Sir George Cayley in 1809 to play a role in the birth of modern aviation. However, It wasn't until the early 1900's that the first helicopter took flight

II. Early Developments

More than 2,000 years after Leonardo Da Vinci's sketches, the latter half of the eighteenth century marked the beginning of the industrial revolution and of the continued search for manmade flight. In 1754, Mikhail Lomonosov of Russia developed a small coaxial rotor modeled after the ancient Chinese toy but powered by a wound-up spring device

. The device flew freely and climbed to a reasonable altitude

. In 1783, the French naturalist Christian de Launoy used a coaxial version of the Chinese toy in a model consisting of a counter-rotating set of turkey feathers powered by a string wound around the rotor shaft and tensioned by a crossbow

. When the tension was released, the blades whirled to climb the device high into the air. The scientific stir created by these early successes inspired the French mathematician A.J.P. Paucton in 1786 to publish one of the first scientific papers on the dilemma of rotating wings entitled "Theorie de la vis D'Archimede."

III. The first Helicopters

Even before the Wright Brothers first airplane took flight, Igor Sikorsky was building a coaxial helicopter in Russia.

. Into the early twentieth century, there were more attempts to build helicopters than fixed wing aircrafts

. However, these early models, developed around 1907 were not able sustain flights as we know it today; they merely just hopped of the ground

. The failure of these early pioneers and their designs is due in part to a failure to truly understanding of the nature of lift and their heavy weight-to-power ratio from inadequate motor use. The development of the engine is fundamental to any form of flight. While airplanes could fly with engines of relatively lower power, the success of the helicopter's hover abilities required aircraft engine technology that could build much more powerful and lightweight engines. A look at the historical record shows that the need for engines of sufficient power-to-weight ratio was really a key enabling technology for the success of the helicopter

Prior to 1870, the steam engine was all that was available for engineers and mechanics to use in most mechanical devices. The steam engine is a relatively primitive external combustion engine. It requires a separate boiler, combustor, recirculating pump, condenser, power producing piston and cylinder and well as a fuel and an ample supply of water

. All of these heavy components weigh down the steam engine and create a power-to-weight ration that is unsuitable for aeronautical use. Nonetheless, the innovations of James Watt greatly improved on the steam engine making it relatively practical for use in early helicopters. In the 1920's, when lighter gas engines were developed, engineers were able to achieve a more balanced weight-to-power ratio necessary for sustained flight

Then the problem of torque arose to confound early pioneers until the introduction of swashplate. Torque is the effect produced by the rotor to force the fuselage to rotate in the opposite direction as the engine

. Due to dissymmetry of lift the early single-rotor helicopters tended to flip over when changing between hovering to forward movement

. The swashplate provides a means of varying the pitch of the blades in a cyclic fashion as they rotate around the central shaft to create the freedom of independent blade motions. Cyclic pitch control equalized the lift on each side of the shaft and eliminated the tendency to tip over sideways. Gaetano A. Crocco was one of the first designers to propose cyclic pitch for rotor control in 1906 Italy

. Crocco, who pioneered the idea of hydrofoil boats, recognized that proper forward flight in a helicopter required a means of changing the pitch on the blades to account for dissymmetry of the lift

The coaxial design's basic simplicity further reduced torque issues. By placing two rotors on top of each other with counter-rotation, the power train remains short and the airframe can take many shapes. Counter-rotation eliminated the need to force torque into the airframe. In hovering flight the lift force is only vertical without a tail rotor producing a side force that requires constant pilot intervention to avoid tip-over. This design was originally produced by the Russian Kamov helicopter design bureau

. Well-known names in coaxial designs include Cornu, Asboth, Pescara, De Bothezat, Berliner, Bendix, Hiller and others.

On November 13, 1907, the French pioneer Paul Cornu lifted a coaxial rotor helicopter into the air for a few seconds

. The airframe was very simple, with a rotor at each end and two large blades set at the periphery of a spoked wheel. Power was supplied to the rotors by a gasoline motor and belt transmission. Also in the early 1900's, Henry Berliner created the first powered coaxial rotorcraft 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

The VS-300, the first practical helicopter was designed by Sikorsky in 1939

. The VS-300 was a single rotor (as opposed to the coaxial rotor discussed above) with an open cockpit welded together by steel tubing frame. 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 redesign the safety quotient of the aircraft, 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

. 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

IV. The Autogiro

During the roaring twenties, Juan de la Cierva developed an aeronautical design independent of the contemporary engineering paradigms

. This design led to the Autogiro, the first successful rotating -- wing aircraft to demonstrate a useful role in aviation

. However, it wasn't until hinged rotor blade and the swashplate, discussed above, that design was laid out for the helicopter as a practical form of air-transport.

Cierva's Autogiro differed from the later helicopter in that the Autogiro rotor was not run by a motor (which removes the power-to weight ration problem that many developers struggled with approximately fifteen year later) such that the rotor movement came from a flow of air directed upwards through the rotor disk

. However, only a very small flow is necessary to turn the rotor, so as long as the machine continues to move through the air, the rotor will continue to turn

. Therefore, the early… READ MORE