Helicopters

Origins

Helicopters are among the earliest type of flying vehicle that humans attempted to construct. Rotary-wing toys have been successfully flown since ancient times, and the seeds of some plants, including the tipu tree, maple tree, box elder tree, and gyrocarpus nut, have distinctive wings that cause them to rotate in the air in a manner similar to helicopters, which inspired many early designs long before the physics of flight were well understood. The most famous designs are those of Leonardo da Vinci, the Renaissance man who in the 15th century designed a rotary-wing aircraft whose mechanics were inspired by the screw, though he seems never to have constructed his flying machine.

The word helicopter was coined in the 19th century, when Industrial Revolution engineers experimented with various forms of heavier-than-air vertical flight at a time when lighter-than-air flight in the form of hot air balloons had captured the popular imagination. Successful helicopter flights were made in the first decade of the 20th century, around the same time as the first successful airplane flights. Further developments were slower to come, and the helicopter industry did not really begin until the late 1930s. Both Germany and the United States developed helicopters for military use during World War II, with the latter effort leading to the Sikorsky R-4, the first mass-produced helicopter, released in 1942.

Innovations

The R-4 used the rotor configuration that has become standard in the industry, consisting of a single, centrally positioned, lifting rotor (with three rotor blades) and a vertical tail rotor. Igor Sikorsky was the first to successfully use a tail rotor for antitorque, which has become part of the standard design for single-rotor helicopters. The tail rotor stabilizes the helicopter by generating thrust in the same direction as the rotation of the lifting rotor, which counters the torque created by the lifting rotor. The amount of antitorque created is controlled by pedals in the pilot's seat, which adjust the pitch of the tail rotor.

The tail rotor is one of the defining features of the modern helicopter and is important enough to safe flight that in most jurisdictions, and in the procedures followed by most aviation companies, it is one of the life-limited parts of the aircraft. Life-limited parts are routinely replaced with new parts after a predetermined number of flight hours, rather than relying on the subjective criteria of an inspection. Tail rotors, as well as elements of the drive system, are also inspected through fluorescent penetrant inspection (FPI) between replacement cycles. FPI is a chemical method of revealing—through use of a fluorescent dye—defects that would otherwise not be apparent in a naked-eye inspection.

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