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Helicopter

Helicopter

Background

Helicopters are classified as rotary wing aircraft, and their rotary wing is commonly referred to as the main rotor or simply the rotor. Unlike the more common fixed wing aircraft such as a sport biplane or an airliner, the helicopter is capable of direct vertical take-off and landing; it can also hover in a fixed position. These features render it ideal for use where space is limited or where the ability to hover over a precise area is necessary. Currently, helicopters are used to dust crops, apply pesticide, access remote areas for environmental work, deliver supplies to workers on remote maritime oil rigs, take photographs, film movies, rescue people trapped in inaccessible spots, transport accident victims, and put out fires. Moreover, they have numerous intelligence and military applications.

Numerous individuals have contributed to the conception and development of the helicopter. The idea appears to have been bionic in origin, meaning that it derived from an attempt to adapt a natural phenomenain this case, the whirling, bifurcated fruit of the maple treeto a mechanical design. Early efforts to imitate maple pods produced the whirligig, a children's toy popular in China as well as in medieval Europe. During the fifteenth century, Leonardo da Vinci, the renowned Italian painter, sculptor, architect, and engineer, sketched a flying machine that may have been based on the whirligig. The next surviving sketch of a helicopter dates from the early nineteenth century, when British scientist Sir George Cayley drew a twin-rotor aircraft in his notebook. During the early twentieth century, Frenchman Paul Cornu managed to lift himself off the ground for a few seconds in an early helicopter. However, Cornu was constrained by the same problems that would continue to plague all early designers for several decades: no one had yet devised an engine that could generate enough vertical thrust to lift both the helicopter and any significant load (including passengers) off the ground.

Igor Sikorsky, a Russian engineer, built his first helicopter in 1909. When neither this prototype nor its 1910 successor succeeded, Sikorsky decided that he could not build a helicopter without more sophisticated materials and money, so he transferred his attention to aircraft. During World War I, Hungarian engineer Theodore von Karman constructed a helicopter that, when tethered, was able to hover for extended periods. Several years later, Spaniard Juan de la Cierva developed a machine he called an autogiro in response to the tendency of conventional airplanes to lose engine power and crash while landing. If he could design an aircraft in which lift and thrust (forward speed) were separate functions, Cierva speculated, he could circumvent this problem. The autogiro he subsequently invented incorporated features of both the helicopter and the airplane, although it resembled the latter more. The autogiro had a rotor that functioned something like a windmill. Once set in motion by taxiing on the ground, the rotor could generate supplemental lift; however, the autogiro was powered primarily by a conventional airplane engine. To avoid landing problems, the engine could be disconnected and the autogiro brought gently to rest by the rotor, which would gradually cease spinning as the machine reached the ground. Popular during the 1920s and 1930s, autogiros ceased to be produced after the refinement of the conventional helicopter.

The helicopter was eventually perfected by Igor Sikorsky. Advances in aerodynamic theory and building materials had been made since Sikorsky's initial endeavor, and, in 1939, he lifted off the ground in his first operational helicopter. Two years later, an improved design enabled him to remain aloft for an hour and a half, setting a world record for sustained helicopter flight.

The helicopter was put to military use almost immediately after its introduction. While it was not utilized extensively during World War II, the jungle terrain of both Korea and Vietnam prompted the helicopter's widespread use during both of those wars, and technological refinements made it a valuable tool during the Persian Gulf War as well. In recent years, however, private industry has probably accounted for the greatest increase in helicopter use, as many companies have begun to transport their executives via helicopter. In addition, helicopter shuttle services have proliferated, particularly along the urban corridor of the American Northeast. Still, among civilians the helicopter remains best known for its medical, rescue, and relief uses.

Design

A helicopter's power comes from either a piston engine or a gas turbine (recently, the latter has predominated), which moves the rotor shaft, causing the rotor to turn. While a standard plane generates thrust by pushing air behind its wing as it moves forward, the helicopter's rotor achieves lift by pushing the air beneath it downward as it spins. Lift is proportional to the change in the air's momentum (its mass times its velocity): the greater the momentum, the greater the lift.

Helicopter rotor systems consist of between two and six blades attached to a central hub. Usually long and narrow, the blades turn relatively slowly, because this minimizes the amount of power necessary to achieve and maintain lift, and also because it makes controlling the vehicle easier. While light-weight, general-purpose helicopters often have a two-bladed main rotor, heavier craft may use a four-blade design or two separate main rotors to accommodate heavy loads.

To steer a helicopter, the pilot must adjust the pitch of the blades, which can be set three ways. In the collective system, the pitch of all the blades attached to the rotor is identical; in the cyclic system, the pitch of each blade is designed to fluctuate as the rotor revolves, and the third system uses a combination of the first two. To move the helicopter in any direction, the pilot moves the lever that adjusts collective pitch and/or the stick that adjusts cyclic pitch; it may also be necessary to increase or reduce speed.

Unlike airplanes, which are designed to minimize bulk and protuberances that would weigh the craft down and impede airflow around it, helicopters have unavoidably high drag. Thus, designers have not utilized the sort of retractable landing gear familiar to people who have watched planes taking off or landingthe aerodynamic gains of such a system would be proportionally insignificant for a helicopter. In general, helicopter landing gear is much simpler than that of airplanes. Whereas the latter require long runways on which to reduce forward velocity, helicopters have to reduce only vertical lift, which they can do by hovering prior to landing. Thus, they don't even require shock absorbers: their landing gear usually comprises only wheels or skids, or both.

One problem associated with helicopter rotor blades occurs because airflow along the length of each blade differs widely. This means that lift and drag fluctuate for each blade throughout the rotational cycle, thereby exerting an unsteadying influence upon the helicopter. A related problem occurs because, as the helicopter moves forward, the lift beneath the blades that enter the airstream first is high, but that beneath the blades on the opposite side of the rotor is low. The net effect of these problems is to destabilize the helicopter. Typically, the means of compensating for these unpredictable variations in lift and drag is to manufacture flexible blades connected to the rotor by a hinge. This design allows each blade to shift up or down, adjusting to changes in lift and drag.

Torque, another problem associated with the physics of a rotating wing, causes the helicopter fuselage (cabin) to rotate in the opposite direction from the rotor, especially when the helicopter is moving at low speeds or hovering. To offset this reaction, many helicopters use a tail rotor, an exposed blade or ducted fan mounted on the end of the tail boom typically seen on these craft. Another means of counteracting torque entails installing two rotors, attached to the same engine but rotating in opposite directions, while a third, more space-efficient design features twin rotors that are enmeshed, something like an egg beater. Additional alternatives have been researched, and at least one NOTAR (no tail rotor) design has been introduced.

Raw Materials

The airframe, or fundamental structure, of a helicopter can be made of either metal or organic composite materials, or some combination of the two. Higher performance requirements will incline the designer to favor composites with higher strength-to-weight ratio, often epoxy (a resin) reinforced with glass, aramid (a strong, flexible nylon fiber), or carbon fiber. Typically, a composite component consists of many layers of fiber-impregnated resins, bonded to form a smooth panel. Tubular and sheet metal substructures are usually made of aluminum, though stainless steel or titanium are sometimes used in areas subject to higher stress or heat. To facilitate bending during the manufacturing process, the structural tubing is often filled with molten sodium silicate. A helicopter's rotary wing blades are usually made of fiber-reinforced resin, which may be adhesively bonded with an external sheet metal layer to protect edges. The helicopter's windscreen and windows are formed of polycarbonate sheeting.

The Manufacturing
Process

In 1939, a Russian emigre to the United States tested what was to become a prominent prototype for later helicopters. Already a prosperous aircraft manufacturer in his native land, Igor Sikorsky fled the 1917 revolution, drawn to the United States by stories of Thomas Edison and Henry Ford.

Sikorsky soon became a successful aircraft manufacturer in his adopted homeland. But his dream was vertical take-off, rotary wing flight. He experimented for more than twenty years and finally, in 1939, flew his first flight in a craft dubbed the VS 300. Tethered to the ground with long ropes, his craft flew no higher than 50 feet off the ground on its first several flights. Even then, there were problems: the craft flew up, down, and sideways, but not forward. However, helicopter technology developed so rapidly that some were actually put into use by U.S. troops during World War II.

The helicopter contributed directly to at least one revolutionary production technology. As helicopters grew larger and more powerful, the precision calculations needed for engineering the blades, which had exacting requirements, increased exponentially. In 1947, John C. Parsons of Traverse City, Michigan, began looking for ways to speed the engineering of blades produced by his company. Parsons contacted the International Business Machine Corp. and asked to try one of their new main frame office computers. By 1951, Parsons was experimenting with having the computer's calculations actually guide the machine tool. His ideas were ultimately developed into the computer-numerical-control (CNC) machine tool industry that has revolutionized modern production methods.

William S. Pretzer

Airframe: Preparing the tubing

  • 1 Each individual tubular part is cut by a tube cutting machine that can be quickly set to produce different, precise lengths and specified batch quantities. Tubing requiring angular bends is shaped to the proper angle in a bending machine that utilizes interchangeable tools for different diameters and sizes. For other than minor bends, tubes are filled with molten sodium silicate that hardens and eliminates kinking by causing the tube to bend as a solid bar. The so-called water glass is then removed by placing thebent tube in boiling water, which melts the inner material. Tubing that must be curved to match fuselage contours is fitted over a stretch forming machine, which stretches the metal to a precisely contoured shape. Next, the tubular details are delivered to the machine shop where they are held in clamps so that their ends can be machined to the required angle and shape. The tubes are then deburred (a process in which any ridges or fins that remain after preliminary machining are ground off) and inspected for cracks.
  • 2 Gussets (reinforcing plates or brackets) and other reinforcing details of metal are machined from plate, angle, or extruded profile stock by routing, shearing, blanking, or sawing. Some critical or complex details may be forged or investment cast. The latter process entails injecting wax or an alloy with a low melting point into a mold or die. When the template has been formed, it is dipped in molten metal as many times as necessary to achieve the thickness desired. When the part has dried, it is heated so that the wax or alloy will melt and can be poured out. Heated to a higher temperature to purify it and placed in a mold box where it is supported by sand, the mold is then ready to shape molten metal into reinforcement parts. After removal and cooling, these parts are then finish-machined by standard methods before being deburred once again.
  • 3 The tubes are chemically cleaned, fitted into a subassembly fixture, and MIG (metal-arc inert gas) welded. In this process, a small electrode wire is fed through a welding torch, and an inert, shielding gas (usually argon or helium) is passed through a nozzle around it; the tubes are joined by the melting of the wire. After welding, the subassembly is stress relievedheated to a low temperature so that the metal can recover any elasticity it has lost during the shaping process. Finally, the welds are inspected for flaws.

Forming sheet metal details

  • 4 Sheet metal, which makes up other parts of the airframe, is first cut into blanks (pieces cut to predetermined size in preparation for subsequent work) by abrasive water-jet, blanking dies, or routing. Aluminum blanks are heat-treated to anneal them (give them a uniform, strain-free structure that will increase their malleability). The blanks are then refrigerated until they are placed in dies where they will be pressed into the proper shape. After forming, the sheet metal details are aged to full strength and trimmed by routing to final shape and size.
  • 5 Sheet metal parts are cleaned before being assembled by riveting or adhesive bonding. Aluminum parts and welded subassemblies may be anodized (treated to thicken the protective oxide film on the surface of the aluminum), which increases corrosion resistance. All metal parts are chemically cleaned and primer-painted, and most receive finish paint by spraying with epoxy or other durable coating.

Making the cores of composite components

  • 6 Cores, the central parts of the composite components, are made of Nomex (a brand of aramid produced by Du Pont) or aluminum "honeycomb," which is cut to size by bandsaw or reciprocating knife. If necessary, the cores then have their edges trimmed and beveled by a machine tool similar to a pizza cutter or meat slicing blade. The material with which each component is built up from its cores (each component may use multiple cores) is called pre-preg ply. The plies are layers of oriented fibers, usually epoxy or polyimide, that have been impregnated with resin. Following written instructions from the designers, workers create highly contoured skin panels by setting individual plies on bond mold tools and sandwiching cores between additional plies as directed.
  • 7 Completed layups, as the layers of prepreg affixed to the mold are called, are then transported to an autoclave for curing. An autoclave is a machine that laminates plastics by exposing them to pressurized steam, and "curing" is the hardening that occurs as the resin layers "cook" in the autoclave.
  • 8 Visible trim lines are molded into the panels by scribe lines present in the bond mold tools. Excess material around the edges is then removed by bandsawing. Large panels may be trimmed by an abrasive water-jet manipulated by a robot. After inspection, trimmed panels and other composite details are cleaned and painted by normal spray methods. Surfaces must be well sealed by paint to prevent metal corrosion or water absorption.

Making the fuselage

  • 9 Canopies or windscreens and passenger compartment windows are generally made of polycarbonate sheet. Front panels subject to bird strike or other impact may be laminated of two sheets for greater thickness. All such parts are made by placing an oversized blank on a fixture, heating it, and then forming it to the required curvature by use of air pressure in a freeblowing process. In this method, no tool surface touches the optical surfaces to cause defects.

Installing the engine, transmission,
and rotors

  • 10 Modern helicopter engines are turbine rather than piston type and are purchased from an engine supplier. The helicopter manufacturer may purchase or produce the transmission assembly, which transfers power to the rotor assembly. Transmission cases are made of aluminum or magnesium alloy.
  • 11 As with the above, the main and tail rotor assemblies are machined from specially selected high-strength metals but are produced by typical machine shop methods. The rotor blades themselves are machined from composite layup shapes. Main rotor blades may have a sheet metal layer adhesively bonded to protect the leading edges.

Systems and controls

  • 12 Wiring harnesses are produced by laying out the required wires on special boards that serve as templates to define the length and path to connectors. Looms, or knitted protective covers, are placed on the wire bundles, and the purchased connectors are soldered in place by hand. Hydraulic tubing is either hand-cut to length and hand-formed by craftsmen, or measured, formned, and cut by tube-bending machines. Ends are flared, and tubes are inspected for dimensional accuracy and to ensure that no cracks are present. Hydraulic pumps and actuators, instrumentation, and electrical devices are typically purchased to specification rather than produced by the helicopter manufacturer.

Final assembly

  • 13 Finished and inspected detail airframe parts, including sheet metal, tubular, and machined and welded items, are delivered to subassembly jigs (fixtures that clamp parts being assembled). Central parts are located in each jig, and associated details are either bolted in place or, where rivets are to be used, match-drilled using pneumatically powered drills to drill and ream each rivet hole. For aerodynamic smoothness on sheet metal or composite skin panels, holes are countersunk so that the heads of flat-headed screws won't protrude. All holes are deburred and rivets applied. A sealant is often applied in each rivet hole as the rivet is inserted. For some situations, semi-automated machines may be used for moving from one hole location to the next, drilling, reaming, sealing, and installing the rivets under operator control.
  • 14 After each subassembly is accepted by an inspector, it typically moves to another jig to be further combined with other small subassemblies and details such as brackets. Inspected "top level" subassemblies are then delivered to final assembly jigs, where the overall helicopter structure is integrated.

    Upon completion of the structure, the propulsion components are added, and wiring and hydraulics are installed and tested. Canopy, windows, doors, instruments, and interior elements are then added to complete the vehicle. Finish-painting and trimming are completed at appropriate points during this process.

  • 15 After all systems are inspected in final form, along with physical assemblies and appearance aspects, the complete documentation of materials, processes, inspection, and rework effort for each vehicle is checked and filed for reference. The helicopter propulsion system is tested, and the aircraft is flight-tested.

Quality Control

Once tubular components have been formed, they are inspected for cracks. To find defects, workers treat the tubes with a fluorescent liquid penetrant that seeps into cracks and other surface flaws. After wiping off the excess fluid, they dust the coated tube with a fine powder that interacts with the penetrant to render defects visible. After the tubular components have been welded, they are inspected using X-ray and/or fluorescent penetrant methods to discover flaws. Upon completion, the contours of sheet metal details are checked against form templates and hand-worked as required to fit. After they have been autoclaved and trimmed, composite panels are ultrasonically inspected to identify any possible breaks in laminations or gas-filled voids that could lead to structural failure. Prior to installation, both the engine and the transmission subassemblies are carefully inspected, and special test equipment, custom-designed for each application, is used to examine the wiring systems. All of the other components are also tested before assembly, and the completed aircraft is flight-tested in addition to receiving an overall inspection.

The Future

Manufacturing processes and techniques will continue to change in response to the need to reduce costs and the introduction of new materials. Automation may further improve quality (and lower labor costs). Computers will become more important in improving designs, implementing design changes, and reducing the amount of paperwork created, used, and stored for each helicopter built. Furthermore, the use of robots to wind filament, wrap tape, and place fiber will permit fuselage structures to be made of fewer, more integrated pieces. In terms of materials, advanced, high-strength thermoplastic resins promise greater impact resistance and repairability than current thennosets such as epoxy and polyimide. Metallic composites such as aluminum reinforced with boron fiber, or magnesium reinforced with silicon carbide particles, also promise higher strength-to-weight ratios for critical components such as transmission cases while retaining the heat resistance advantage of metal over organic materials.

Where To Learn More

Books

Basic Helicopter Handbook. IAP Inc., 1988.

Seddon, J. Basic Helicopter Aerodynamics. American Institute of Aeronautics & Astronautics, 1990.

Periodicals

"Rotary-Wing Technology Pursues Fixed-Wing Performance Capabilities." Aviation Week & Space Technology. January 19, 1987, p. 46.

"Advanced Technology Prompts Reevaluation of Helicopter Design." Aviation Week & Space Technology. March 9, 1987, p. 252.

Brown, Stuart F. "Tilt-rotor Aircraft." Popular Science. July, 1987, p. 46.

"Graphite Tools Produce Volume 'Copter Parts." Design News. February 17,1986, p. 30.

"Researchers Work on Noise Reduction in Helicopters." Research & Development. January, 1986, p. 55.

Smith, Bruce A. "Helicoptor Manufacturers Divided on Development of New Aircraft." Aviation Week & Space Technology. February 29, 1988, p. 58.

Phillip S. Waldrop

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Helicopters

Helicopters. With its ability to hover, take off and land rapidly, and fly close to the world's land and seas, the helicopter has extended the efficacy of air power by bringing it down to earth. In contrast to many other aviation developments which seemed focused on creating an independent role for airpower, for most of its existence helicopter aviation has concentrated on intimate involvement with land and sea forces.

The first complete helicopter (“gyroplane”) performance was accomplished by Louis‐Charles Breguet in 1935. Four years later, Igor Sikorsky captured the imagination of the military with several demonstrations of his VS‐300, XR‐4, and XR‐6 helicopters before high‐ranking officials of various U.S. and British defense units. After developing Sikorsky's ideas, the U.S. military put helicopters into service at the end of World War II, primarily for air rescue. In the Korean War, the United States expanded on tactics developed by the French during their involvement in Algeria, and began experimentally to arm its helicopters. These innovations, along the with deployment of troops by U.S. Marine Corps helicopters, and medical evacuations (medevacs) were key developments in helicopter applications. Helicopters were also used for resupply and observation; and the potential for command and control from above became clearer. The introduction of the helicopter into the battlefield gave the United States a valuable new offensive weapon.

The experiences with helicopters in the Korean War provided impetus for postwar experimentation. Several attempts were made to integrate offensive armaments with other helicopter systems. The U.S. Army, in particular, led by Brig. Gen. Carl I. Hutton, Commandant of the Army Aviation School at Fort Rucker, Alabama, aided by Col. J. D. Vanderpool, sought to construct and employ helicopters which could perform in the traditional cavalry roles, including reconnaissance, flank security, and shock as well as transportation of ground troops.

There was great resistance in political and military circles towards the development of a large, sophisticated, or autonomous army aviation element. One of the main sources of this antipathy was the feeling that all air operations belonged to the air force. Many in the army feared the consequences of a bitter schism similar to that which occurred when the air force itself became autonomous from the army in the previous decade. Proponents, however, argued that army aviation was necessary to fulfill the close air support mission; there was a pervasive feeling, felt most strongly in the army, that the air force was simply not interested in supporting small ground units in close combat.

The development of the UH‐1 “Huey” helicopter gave proponents of an airmobile division the craft, which ultimately persuaded policymakers that such an organization, within the Army, could flourish. Originally planned as an air ambulance, the Huey was later rigged as a gun ship and a troop carrier. The presence of the Huey in all of its multiple roles allowed the army to ask for a division‐sized airmobile unit and to press for the infusion of helicopters into already existing ground units.

Within the army hierarchy individuals such as former paratroop commander Gen. James Gavin were advocates of an increasing role for army aviation. One of Gavin's proteges, Gen. Hamilton Howze, was a Director of Army Aviation and the chief of the Army Tactical Mobility Requirements Board, which during the Kennedy administration advocated an Airmobile Division. Tests for a new 11th Air Assault Division, which largely used UH‐1 Hueys, under Gen. Harry Kinnard began in earnest with a key evaluator being an ardent army aviation supporter, Gen. Robert R. Williams.

In 1965, the army and the air force reached an understanding in which responsibility for helicopter operations were assigned to the army. At approximately the same time the 11th Air Assault Division was redesignated the 1st Cavalry Division (Airmobile), and with its 16,000 troops and more than 400 helicopters was assigned to Vietnam. A second Army division (101st Airborne) became airmobile and aviation assets were assigned to other army and Marine units in large numbers. In many respects the Vietnam War was a “helicopter war” and by 1970 the U.S. Army operated about 12,000 aircraft, the overwhelming majority of which were helicopters.

Helicopters provided American commanders in Vietnam a great deal of flexibility in their operations. They enabled the quick evacuation of wounded troops from the battlefield and saved thousands of lives, thereby holding the politically important death statistics down. Paradoxically, helicopters enabled U.S. troops to engage in combat in areas that otherwise would be inaccessible. The ability to land helicopters in any area with a small cleared space enabled the United States to establish bases known as LZs (landing zones), which produced a battlefield which distinctly lacked a clear demarcation between the friendly and enemy lines. The airmobile capability of helicopters created a more effective fighting force for Vietnam, but it also limited the imagination of tacticians who used this asset in cases where helicopters may not have been the wisest choice to employ. Nevertheless, the sound of helicopters became associated with the Vietnam War in the nightly news and motion pictures.

In 1983, army aviation became a separate branch within the United States army. This was a step along the way toward demand for greater autonomy for army aviators. The Marine Corps organizational structure also promotes considerable autonomy for their aviation forces. Following Vietnam, the army acquired an advanced attack helicopter, the AH‐64 Apache, a modern multi‐purpose craft, the UH‐60 Black Hawk, and an armed reconnaissance craft, the OH‐58D Kiowa Warrior. Other services use, among other helicopters, variants of these craft.

Operation Desert Storm, the American‐led assault to evict Iraqi forces from Kuwait, was initiated in early 1991 by Apache attacks on Iraqi long range radar. The Persian Gulf War presented army aviation with the opportunity to use airmobile tactics to the fullest. The strategic scheme of maneuver for the final assault on Iraqi troops in both Kuwait and Iraq was a flanking attack from the west, known as the “left hook.” The execution of the “left hook,” deep into Iraq, confirmed the faith of military planners who believed in the centrality of helicopters for cavalry and logistical missions.

Over the years the primary criticism of helicopters has been their vulnerability to ground fire. This vulnerability was made clear, once again, when two Black Hawks were shot down in Mogadishu, Somalia almost three years after the Persian Gulf War. Though helicopters may be somewhat vulnerable to ground fire, they are still feared by opposition forces because their ability to fly along the nap of the earth makes them difficult to track via electronic methods. The enemy's frequent inability precisely to locate a helicopter via electronic means contributes to the helicopter's effectiveness and the ground troops' terror. For example, the fear of U.S. helicopters by opposition forces has been noted by implementation force (IFOR) peacekeeping soldiers who served during the Bosnian Crisis in the late 1990s.
[See also Rivalry, Interservice; Vietnam War, U.S. Air Operations in.]

Bibliography

Frederic A. Bergerson , The Army Gets an Airforce: Tactics of Insurgent Bureaucratic Politics, 1980.
Eugene H. Grayson . Where do we go from here? U.S. Army Aviation Digest, March/April 1992, pp. 44–47.
James L. Cox , The Decline of Marine Helicopter Aviation, Marine Corps Gazette, December1994, pp. 47–48.
David S. Harvey , The Choppy World of Army Aviation, Air Force Magazine, January1994, pp. 56–60.
Marvin Leibstone , U.S. Military Helicopter Programmes, Military Technology, June1994, pp. 53–57.

Frederic A. Bergerson and and Jason E. Trumpler

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Helicopters

HELICOPTERS

HELICOPTERS. Few inventions have changed transportation and military aviation as rapidly and dramatically as the helicopter. The quest for powered flight assumed two forms—horizontal takeoff and vertical take-off—and helicopters and their cousins autogiros, emerged as solutions to the problem of vertical flight. Researchers who pursued vertical flight options sought to capitalize on the increased battlefield surveillance and reconnaissance potential that such craft could provide. Additionally, helicopters promised to offer an inexpensive method of maintaining liaison between central command centers and subordinate units. Experiments with autogiro and helicopter designs occurred throughout Europe, Russia, and the United States from the early 1900s through the interwar years. In 1939, Igor Sikorsky successfully tested his VS 300, the first helicopter with a main rotor that provided lift and a tail rotor that provided directional stability. Sikorsky's solution to the problems of simultaneously lifting and controlling the aircraft launched the helicopter industry in the United States.

Although U.S. forces gained some experience with helicopters late in World War II, the first substantial use of the vertical-takeoff craft came in the Korean War. Between 1950 and 1953, helicopters proved their worth in casualty evacuation, search and rescue, troop insertion, cargo transport, and reconnaissance. In 1950, General Douglas MacArthur requested an increase in the number of helicopters for use as organic aircraft within division, corps, and army headquarters units. U.S. Marine Corps units also used helicopters as organic airlift and combat support assets to bolster tactical combat effectiveness. Perhaps the greatest contribution helicopters made to the war effort in Korea came in the form of aeromedical evacuation. Countless numbers of wounded soldiers owed their survival to dedicated helicopter crews who carried them to field hospitals for emergency medical care. By the end of the Korean War, the U.S. military was committed to developing the helicopter's potential for nearly every conceivable mission.

After the war, helicopter designers concentrated on developing powerful craft that could carry greater payloads over longer distances. Certain industries—oil exploration, for example—came to depend on the economical transportation ability inherent in helicopter technology. The military concentrated on making helicopters an integral


maneuver element of land warfare. The French use of helicopters to patrol and pacify large territories in the Algerian War foreshadowed the U.S. Army's airmobile concepts that came to typify the Vietnam War between 1964 and 1973. Moreover, U.S. army doctrine contained an implicit comparison between lightly armed, mobile guerrilla forces and the mobility that conventional forces obtained using heliborne troops. With this in mind, the army created air cavalry divisions with an assortment of assault, attack, heavy and medium transport, command and control, search and rescue, and medical evacuation helicopters.

The vision of helicopters as organic aviation assets in nearly every army echelon characterized U.S. involvement in the Vietnam War. Army leaders attempted to use helicopters to achieve "vertical envelopments" of Vietcong and North Vietnamese regular forces. According to this concept, ground reconnaissance missions would locate and fix enemy forces until air cavalry units arrived to launch the main American assault. The strategy first emerged in the dramatic Battle of the Ia Drang Valley in 1965, involving the First Cavalry Division (Airmobile) in which U.S. forces engaged and defeated two North Vietnamese army regiments in South Vietnam's central highlands.

Heroic search and rescue crews penetrated heavily defended Vietcong and North Vietnamese positions throughout the war to pluck downed aircrews and wounded soldiers from certain imprisonment or death. Fittingly, the last images of U.S. involvement in Vietnam included helicopters evacuating embassy personnel and refugees from the roof of the U.S. embassy in Saigon (now Ho Chi Minh City) as the South Vietnamese government collapsed in March 1975. In the post-Vietnam era, the U.S. military continued to develop robust helicopter forces. The U.S. Navy in the twenty-first century continued to rely on a wide range of helicopters to support fleet operations in such roles as antisubmarine warfare, troop insertion, countermine operations, search and rescue, and cargo movement. U.S. Air Force special operations units relied on the high-tech Sikorsky MH-53 J/M aircraft, and the U.S. Army developed the Boeing AH Apache Longbow to dominate the combined arms battlefield.

Civilian use of helicopters exploded after the Vietnam War. The same characteristics—speed, mobility, and vertical takeoff and landing—that made helicopters attractive to military forces also appealed to police, emergency services, and firefighting institutions. Law enforcement helicopters from federal to local levels assisted ground units in surveillance and pursuit operations. Emergency service helicopters supported myriad tasks that produced dramatic lifesaving results. Helicopters enhanced firefighting efforts whether in large-scale wildfires or in combating hazardous industrial fires.

BIBLIOGRAPHY

Allen, Matthew. Military Helicopter Doctrines of the Major Powers, 1945–1992. Westport, Conn.: Greenwood Press, 1993.

Boyne, Walter J., and Donald S. Lopez, eds. Vertical Flight: The Age of the Helicopter. Washington, D.C.: Smithsonian Institution Press, 1984.

Fay, John. The Helicopter: History, Piloting, and How It Flies. 4th ed. New York: Hippocrene, 1987.

Francis, Devon F. The Story of the Helicopter. New York: Coward-McCann, 1946.

Futrell, Robert Frank. The United States Air Force in Korea, 1950–1953. Rev. ed. Washington, D.C.: Office of Air Force History, 1983.

Momyer, William W. Airpower in Three Wars: World War II, Korea, Vietnam. Washington, D.C.: Department of the Air Force, 1978.

Anthony ChristopherCain

See alsoAir Cavalry ; Air Power, Strategic .

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helicopter

helicopter, type of aircraft in which lift is obtained by means of one or more power-driven horizontal propellers called rotors. When the rotor of a helicopter turns it produces reaction torque which tends to make the craft spin also. On most helicopters a small rotor near the tail compensates for this torque. On twin-rotor craft the rotors spin in opposite directions, so their reactions cancel each other. The helicopter is propelled in a given direction by inclining the axis of the main rotor in that direction. The helicopter's speed is limited by the fact that if the blades rotate too fast they will produce compressibility effects on the blade moving forward and stall effects on the rearward–moving blade, at the same time.

The method of flight used by the helicopter was considered by Leonardo da Vinci, in the 16th cent., who described its possibilities but could not provide a propulsion system. Best known among its developers are the French inventor Louis Breguet and the engineers Igor Sikorsky of the United States and Juan de la Cierva of Spain. The helicopter has become very popular for short-distance transportation, because of its maneuverability and ability to land and take off in small areas; it has been adopted for a wide range of services, including air-sea rescue, fire fighting, traffic control, oil platform resupply, and business transportation.

Helicopters have been widely adopted by the military since their first appearance during the Korean War. During the Vietnam War, they became the preferred platforms for transporting troops and evacuating wounded; in the Persian Gulf conflict helicopter gunships provided air cover for advancing tanks. Beginning in early 21st cent. some military helicopters were modified with stealth technology to make them more difficult to track on radar.

See A. Gessow and G. C. Myers, Aerodynamics of the Helicopter (1967); W. Johnson, Helicopter Theory (1984).

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helicopter

hel·i·cop·ter / ˈheliˌkäptər/ • n. a type of aircraft that derives both lift and propulsion from one or two sets of horizontally revolving overhead rotors. It is capable of moving vertically and horizontally, the direction of motion being controlled by the pitch of the rotor blades. Compare with autogiro. • v. [tr.] transport by helicopter: the Coast Guard helicoptered a compressor to one ship. ∎  [intr.] fly somewhere in a helicopter: the inspection team helicoptered ashore. ORIGIN: late 19th cent.: from French hélicoptère, from Greek helix ‘spiral’ + pteron ‘wing.’

helicopter

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helicopter

helicopter Aircraft that gains lift from rotors (rotating aerofoils), and is capable of vertical takeoff and landing, hovering, and forwards, backwards and lateral flight. At take-off, all blades have a steep pitch in order to achieve maximum lift. The circular movement of the blades generates an opposite, reactive force on the helicopter that is overcome by another set of opposite-turning rotors, or by another small rotor in the tail generating thrust in the opposite direction. Igor Sikorsky (1889–1972) built the first successful helicopter in 1939.

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helicopter

helicopter XIX. — F. hélicoptère, f. Gr. heliko- (see HELIX) + pterón wing.

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helicopter

helicopterall-nighter, biter, blighter, fighter, igniter, inciter, indicter, inviter, lighter, mitre (US miter), overnighter, reciter, righter, sighter, smiter, writer •shyster • rhymester • backbiter •expediter • prizefighter • dogfighter •bullfighter • gunfighter • lamplighter •highlighter • downlighter •moonlighter • uplighter • firelighter •screenwriter • scriptwriter •copywriter • signwriter • typewriter •songwriter • ghostwriter •underwriter •blotter, cotta, cottar, dotter, gotta, hotter, jotter, knotter, otter, pelota, plotter, potter, ricotta, rotter, spotter, squatter, terracotta, totter, trotter •crofter •concocter, doctor, proctor •Volta • prompter • wanter •adopter, dioptre •Costa, coster, defroster, foster, Gloucester, impostor, paternoster, roster •lobster, mobster •oxter • monster • songster •witchdoctor • helicopter •teleprompter • globetrotter

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Helicopters

Helicopters

INDUSTRIAL CODES

NAICS: 33-6411 Aircraft Manufacturing

SIC: 3721 Aircraft Manufacturing

NAICS-Based Product Codes: 33-64113014 and 33-64113017

PRODUCT OVERVIEW

No one knows how long humans have dreamed of flying, but this concept informed some of Western culture's earliest stories. Around the time BC became AD, the Roman poet Ovid told the tale of Daedalus and his son Icarus. The first storytellers as well as their audiences could see snow persisting on the highest mountain peaks during warm weather; clearly, air did not grow warmer with altitude, so the sun would not have melted the wax holding Icarus's feathers to his wings. This tale appeals to the emotions, not to reason.

A modern audience could note how the genius of Daedalus, using observation to mimic birds' wing shapes, was rendered irrelevant by his son's reckless behavior. Passion defeated by reality was a lesson that early would-be aeronauts repeatedly rediscover, frequently at a high price. This essay summarizes the history of helicopters.

Helicopters are aircraft characterized by large-diameter, powered, rotating blades. Such a craft can lift itself vertically by accelerating air downward at an angle. The helicopter is the most successful vertical takeoff and landing (VTOL) aircraft yet developed due to its relatively high efficiency in performing hovering and low-speed flight missions.

From the ancient literature cited above, we move forward more than fourteen centuries to the first designs of what human-created flight might look like, and waiting for us is Leonardo da Vinci. His earliest written speculation on human-powered flight dates from 1473, when he was twenty-one, and his notebooks demonstrate that this was a lifelong fascination. Many artists of this period designed theater sets; Andrea del Verrocchio, to whom the young Leonardo was an apprentice, made such sets for the Medici family, and illusionist flying machines were often involved.

Leonardo's first sketch of such a device dates to 1478; today, it would be called a hang glider. The first appearance of a helicopter in Leonardo's notebooks dates to 1490, where a depiction of a large central screw-like device was designed to measure about thirteen feet in diameter. Leonardo intended it to be made of reed and covered with taffeta to make a light, resilient wing. This helicopter is shown as powered by four men who ran on the craft's platform around the central shaft, pushing a bar that would cause the spiral to turn. The helicopter would, at least theoretically, bore its way through the air like a giant corkscrew.

Even as a might-have-been, Leonardo's continuous spiral airfoil offers fascinating possibilities. To find those possibilities realized, we must travel forward four centuries more, to a chilly, windy beach called Kitty Hawk in North Carolina. On December 17, 1903, Wilbur and Orville Wright's 750-pound plane launched from a railroad track at less than seven miles per hour, attained an altitude of perhaps ten feet, and landed about twelve seconds later, having traveled 120 feet. This modest beginning led to a new world in which gravity, while impossible to ignore, could be successfully challenged and, less than seventy years later, overcome as humans traveled to and landed on the moon.

A few decades more and we have arrived at the moment where sufficient power combines with essential materials and human daring. The year is 1939; the place, a Connecticut field; and the person in the well-worn fedora, Igor Ivanovitch Sikorsky, born in Russia and emigrated to the United States in his thirties.

Everything about Sikorsky's VS-300 was bare-boned: the cockpit was only a seat in front of the exposed 75-horsepower engine; belts and pulleys drove the blades; the vertical rotor spun at the end of a spar.

This ungainly machine was an attempt to perfect the helicopter, which Sikorsky and others believed would be the aircraft that brought flight to the masses. The vision was one of backyard and rooftop helipads with commuters taking to the air rather than the road. But engineers had yet to perfect the helicopter. Prototypes lifting off the ground proved too cumbersome for regular service.

The idea of the helicopter was inspired not by nature but the screw discovered by Archimedes approximately 2200 years ago. A screw pump can push water up an incline and a propeller screw can push against water to move a ship forward. Why couldn't a large enough screw pull a machine into the air?

Like hundreds of others in aviation, Sikorsky built on the work of others. In 1919 the Spanish aircraft engineer Juan de la Cierva y Cordonia was studying how aircraft stall. As a propeller pulled a plane down the runway or through the air, the rotor turned, producing lift. Even if the engine failed in flight, the rotor would continue to turn, providing enough lift to enable a slow, controlled descent. Cordonia used this phenomenon to create a freewheeling rotor he used as a crucial part of what he called his autogiro.

The first sustained helicopter flight was not achieved until 1935, with a coaxial model built by Louis Breguet and René Dorand in France. Building partly on that attempt, Sikorsky took out the tandem rotors that canceled the counter-rotation (known as torque) in the French design and used a single main rotor for lift. This greatly simplified the mechanism and made controlling the craft much easier.

The first flight of Sikorsky's VS-300 was something less than astonishing. On Sept. 14, 1939, the craft cleared the ground by just a few inches, probably due to the rotor blowing air downward, and the whole event lasted 10 seconds. This was partly intentional, since the craft had been tethered to the ground in case anything went wrong. For successive flights, the engineers fixed a glitch that shook the machine violently when the rotors whirred at speed and, by November, short one-minute hops were possible.

Test flights through the spring and summer of 1940 helped Sikorsky and his team improve the manner in which aerodynamics applied to the helicopter. They also began practicing some of the three-dimensional feats that make helicopters so useful: landing on a dime, hovering over a single point, even throwing down a rope ladder for a rescue.

Once the control problems were better understood, Sikorsky and his team were able to eliminate first one and then both of the horizontal auxiliary rotors, opting instead for changing the pitch of the main rotor to control longitudinal and lateral motion. The modern helicopter was born.

The helicopter is probably the most versatile instrument ever invented by man. It approaches closer than any other to fulfillment of mankind's ancient dreams of the flying horse and the magic carpet.—Igor Ivanovitch Sikorsky, comment on twentieth anniversary of the helicopter's first flight Sept. 13, 1959

MARKET

The animation company Hannah-Barbera created The Jetsons in the early 1960s. Set in an unspecified future, everyone who wants one has access to a flying car, very much in the spirit of Sikorsky's dream. In the real world, military and other interests reserved helicopters for highly specialized purposes.

Although U.S. forces gained some experience with helicopters late in World War II, the first substantial use of the vertical-takeoff craft came in the Korean War. Between 1950 and 1953 helicopters performed casualty evacuation, search and rescue, troop insertion, cargo transport, and reconnaissance. In 1950 General Douglas MacArthur requested more helicopters for use as organic aircraft within division, corps, and army headquarters units. U.S. Marine Corps units also used helicopters as airlift and combat support. Perhaps the greatest contribution helicopters made to the war effort in Korea came in transporting wounded soldiers to Mobile Army Surgical Hospitals for emergency medical care. By the end of the Korean War, the U.S. military was committed to developing the helicopter's potential for nearly every possible mission.

After the war, helicopter designers concentrated on developing powerful craft that could carry greater payloads over longer distances. Sectors such as oil exploration came to depend on the economical transportation ability provided by helicopter technology. The military concentrated on making helicopters essential to warfare. The French used helicopters to patrol and dominate large territories in the Algerian War foreshadowing the U.S. Army's airmobile concepts typifying the Vietnam War between 1964 and 1973, when the army created air cavalry divisions with helicopters outfitted to specialize in assault, attack, heavy and medium transport, command and control, search and rescue, and medical evacuation. Even the last images of U.S. involvement in Vietnam included helicopters evacuating embassy personnel and refugees from the roof of the U.S. embassy in Saigon (later, Ho Chi Minh City) as the South Vietnamese government collapsed in March, 1975.

Civilian use of helicopters spread widely after the Vietnam War. The speed, mobility, and vertical takeoff and landing that made helicopters attractive to military forces also appealed to police, emergency services, and firefighters, especially in remote areas. Law enforcement helicopters from federal to local levels assisted ground units in surveillance and pursuit operations. Emergency service helicopters made dramatic rescues of hapless hikers and climbers. Helicopters enhanced firefighting efforts whether in large-scale wildfires or in combating hazardous industrial fires.

Though military and commercial aircraft manufacturers dominate the industry in the early twenty-first century, American companies also produced many aircraft for the general aviation and the helicopter market segments, which included fixed wing aircraft and rotorcraft for business transportation, regional airline service, recreation, specialized uses such as ambulance service and agricultural spraying, and training. American manufacturers historically produced approximately 60 percent of the world's general aviation aircraft and 30 percent of the helicopters.

Sales and exports of U.S. civil helicopters surged in 2005 to record levels, according to the U.S. Aerospace Industries Association (USAIA). In its aerospace industry annual review, the trade group reported civil helicopter sales jumped from $515 million to a record $750 million. The U.S. industry shipped 120 more civil helicopters in 2006 than it did in 2004.

Civil helicopter exports also reached record levels, rising 57 percent to $490 million. "Used civil aircraft exports rose 31 percent from already high levels to $2.8 billion," the USAIA said, "helping exports and the trade balance, but not resulting in new production."

According to Flight's HeliCAS database, a healthy 531 turbine helicopters were civil-registered in 2006. The leading helicopter makers also reported strong order backlogs and were planning higher production rates in 2007. While the helicopter industry was riding the same post-9/11 economic recovery that was boosting other sectors of commercial aerospace, it was also seeing strong growth in the offshore support sector, which was re-equipping after years of operating aging but depreciated helicopters. Growth in the law enforcement and emergency medical service sectors was also playing a part.

U.S. manufacturers shipped 4,088 units of complete civilian aircraft (fixed wing, powered craft; helicopters; and non-powered types of civil aircraft) in 2002, valued at approximately $34.7 billion. In terms of unit shipments, this figure represented a decrease from 2001, when the industry shipped 4,541 units valued at 41.8 billion, and from 2000 when shipments numbered 5,162 civil aircraft valued at $38.6 billion.

In use as aerial cranes, firefighting, air ambulances, crop-dusting, search and rescue, law enforcement, a host of military purposes, and the transport of the rich and famous, it may be more appropriate to ask where helicopters are not useful than to list where they are.

KEY PRODUCERS/MANUFACTURERS

Five large-scale firms dominated the helicopter production field in the first decade of the twenty-first century, as can be seen in Figure 108. Each is profiled briefly below.

Eurocopter S.A.

Europe's largest helicopter maker, Eurocopter, makes a full range of civilian and military helicopters and offers helicopter repair, maintenance, and overhaul services.

This premier manufacturer has four plants, two in France and two in Germany, and many offices worldwide. Eurocopter employed a workforce of 10,822 people pro-ducing 57 percent of the civil market and 25 percent of the military market in the middle of the first decade of the twenty-first century. Eurocopter reported revenues of $2.6 billion in 2002. The European firm, with its vast product range, continues to significantly outsell its rivals, claiming to have captured 52 percent of the market in units in 2005 (twice as much as its nearest rival), and 46 percent by value. It has been first in the U.S. market during the period 2000–2005, with a more than 50 percent market share in the EMS, para-public, utility, and tourism sectors.

Like most of its competitors, Eurocopter increased its investment in the Asia Pacific market to the extent that by 2006, it claimed to have captured half of the civil and para-public market in Japan. Eurocopter announced the creation of a Japanese subsidiary in 2006 to coordinate the commercial network in that region. The European firm also views India as a strategic market, and plans to set up a local organization based in Bangalore.

Bell Helicopter Textron Inc.

A subsidiary of Textron, the company makes commercial and military helicopters and tilt-rotor aircraft. Bell's commercial helicopters seat up to 15 passengers and include models designed for transport, emergency medical services, and search and rescue operations. Military models include the venerable UH-1Y Huey, a utility helicopter used for personnel and medical transportation; the AH-1Z Super Cobra reconnaissance/attack helicopter; the Eagle Eye Unmanned Aerial Vehicle (UAV); and the V-22 Osprey tilt-rotor (with Boeing). Bell also makes helicopters through joint venture Bell/Agusta Aerospace and provides repair, maintenance, and overhaul services.

Bell representatives claimed that the company achieved a 23 percent increase in civil helicopter shipments in 2005, compared with the previous year. It continues to build its new offerings on the foundations laid by its older models the Bell 210, a derivative of the Huey, which achieved FAA certification in 2005; and the 407X light single, a 407 refitted with Honeywell's new HTS900 engine and which is the basis for Bell's selection for the Armed Reconnaissance Helicopter (ARH) program—a 368-unit order that has given Bell a new lease of life.

Boeing Company

In 1916 William E. Boeing founded the Boeing Company, then called Pacific Aero Products, in Seattle, Washington. Until 1960 Boeing was only a designer and manufacturer of airplanes. After acquiring Vertol Aircraft Corporation, Boeing became a designer and manufacturer of helicopters as well. On September 21, 1961, the CH-47A Chinook helicopter took its first flight.

At the beginning of the twenty-first century, Boeing Company was the world's largest manufacturer of commercial jetliners and military aircraft, and was NASA's leading contractor. In 2006 its total revenues were $61.5 billion. Boeing Integrated Defense Systems, a division of Boeing Company, manufactures the Apache Longbow, the Chinook, and the Osprey helicopters for the military. This division employed 72,000 people and had revenues of $32.4 billion in 2006. Boeing's headquarters are in Chicago, Illinois.

Sikorsky Aircraft Corporation

Though its legendary founder is long gone, helicopters bearing his name still fly the skies. A subsidiary of United Technologies, Sikorsky Aircraft's military helicopters include the Black Hawk, used for troop assault, combat support, special operations, and medevac operations; and the Seahawk, used for submarine hunting, missile targeting, anti-surface ship warfare, and search and rescue.

The company claimed in 2006 to have logged double-digit growth for the prior three years, with dollar sales leaping from $100 million in 2001 to $600 million for civil aircraft deliveries in 2005. Chief Executive Officer Jeff Pino predicted that billings would be close to those of Eurocopter in 2007. Sikorsky continues to pursue new derivatives, such as the S-76D, scheduled for certification by end-2008. With a maximum takeoff weight of almost 6.6 tons, other features include new composite main and tail rotors offering a 2 decibel noise reduction and a new PW210S engine featuring a dual-channel FADEC and 10 to 20 percent extra power in comparison with the current engine.

The company was also excited about the new Thales Topdeck cockpit, which was being installed on civil helicopter for the first time in 2007. Derived from the cockpit developed for the A380 super jumbo, it features four 6 × 8-inch multifunction screens, an integrated interactive flight management system, synthetic vision interface, and a trackball to interact with the moving map display. Also for the first time on a helicopter, the vehicle includes integrated backup instrumentation giving altitude, attitude, and speed.

AgustaWestland N. V.

One of the world's largest helicopter manufacturers, this company produces a wide range of high-performance rotorcraft for civil and military markets. Of 92 helicopters it delivered in 2004, 66 went to commercial customers. Formed by combining two leading European helicopter manufacturers, AgustaWestland has operations in Italy (near Milan), the United Kingdom (near Somerset, England), and the United States (Fort Worth, Texas, and Philadelphia, Pennsylvania).

AgustaWestland bought out Bell Helicopter's 25 percent stake in the medium twin-turbine AB139 in November, 2005, to improve support and increase sales. Instead of Bell assembling the helicopter in Amarillo, Texas as originally planned, AgustaWestland was expanding its Agusta Aerospace (AAC) subsidiary in Philadelphia, Pennsylvania, to establish production of the AB139 for the North American market. AAC already manufactures the single-turbine A119 and U.S. production of the AB139 was to begin by the end of 2006. AgustaWestland, based at Cascina Costa, Italy, is the second-largest helicopter manufacturer in revenue terms with sales of €2.54 billion in 2004, but around 90 percent of its business is defense. The company responded to the strong interest from the U.S. market by announcing a second production line in Philadelphia, boosting production capacity to 50 units per year. This line, like its twin in Vergiate near Milan, will be directly supplied with structural elements produced by PZL in Poland and TAI in Turkey.

MATERIALS & SUPPLY CHAIN LOGISTICS

Although not quantified until long after the Wright brothers skidded and soared over Kitty Hawk's sand dunes, the ability to fly was eventually rendered as lift plus thrust having to exceed mass (known on Earth as weight) plus drag. All aircraft design must struggle with this reality. The first powered aircraft were largely paper and thin cables, but engineers continue to explore how machines, especially helicopters, can fly more with less.

Some aircraft of composite materials began to appear in the late 1930s and 1940s; these were usually plastic-impregnated wood materials. The largest and most famous example of this design is the Duramold construction of the eight-engine Hughes flying boat, popularly known as the Spruce Goose. A few production aircraft also used Duramold materials and methods.

Fiberglass, fabrics made up of glass fibers, were first used in aircraft in the 1940s and became common by the 1960s. Composite is the term used for different materials that provide strengths, light weight, or other benefits not possible when these materials are used separately. They usually consist of a fiber-reinforced resin matrix. The resin can be a vinyl ester, epoxy, or polyester, while the reinforcement might be any one of a variety of fibers, ranging from glass through carbon, boron, and several other proprietary types.

To these basic elements, strength is often increased by adding a core material, making a structural sandwich. Core materials such as plastic foams (polystyrene, polyurethane, or others), wood, honeycombs of paper, plastic, fabric or metal, and other materials, are surrounded by layers of other substances. This method has been used to create, for example, Kevlar, used in aircraft panels, and Lucite, superior to glass for aircraft windows and canopies.

By the twenty-first century, almost all helicopter parts include composites. The airframe, or fundamental structure, of a helicopter can be made of either metal or organic composite materials, or some combination of the two. Higher performance requirements encourage the designer to favor composites with higher strength-to-weight ratio, often epoxy (a synthetic resin) reinforced with glass, aramid (a strong, flexible nylon fiber), or carbon fiber. Typically, a composite component consists of many layers of fiber-impregnated resins, bonded to form a smooth panel. Tubular and sheet metal substructures are usually made of aluminum, though stainless steel or titanium is sometimes used in areas subject to higher stress or heat. To facilitate bending during the manufacturing process, the structural tubing is often filled with molten sodium silicate. A helicopter's rotary wing blades are usually made of fiber-reinforced resin, which may be adhesively bonded with an external sheet metal layer to protect edges. The helicopter's windshield and windows are formed of polycarbonate sheeting.

Modern helicopter engines use turbines rather than pistons and are purchased from an engine supplier. The helicopter manufacturer may purchase or produce the transmission assembly, which transfers power to the rotor assembly. Transmission cases are made of aluminum or magnesium alloy.

DISTRIBUTION CHANNEL

Regardless of the kinds of machines in which they are used, most aircraft parts have common origins and distribution channels.

The American aircraft industry can be divided into four segments. In one segment, manufacturers such as Boeing and Lockheed Martin Corp. build the wings and fuselages that make up the airframe. Meanwhile, companies such as General Electric and Pratt & Whitney manufacture the engines that propel aircraft. The third segment covers flight instrumentation, an area where the most profound advances in aviation have taken place. But the fourth segment, broadly defined by the industrial classification "aircraft parts not otherwise classified," includes manufacturers of surface control and cabin pressurization systems, landing gear, lighting, galley equipment, and general use products such as nuts and bolts.

Aircraft manufacturers rely on a broad base of suppliers to provide the thousands of subsystems and parts that make up their products. There are more than 4,000 suppliers contributing parts to the aerospace industry, including rubber companies, refrigerator makers, appliance manufacturers, and general electronics enterprises. This diversity is necessary because in most cases it is simply uneconomical for an aircraft manufacturer to establish, for example, its own landing light operation. The internal demand for such a specialized product is insufficient to justify the creation of an independent manufacturing division.

There is a second aspect to this distribution tier, since aircraft manufacturers have found it cheaper and more efficient to purchase secondary products from other manufacturers, who may sell similar products to other aircraft companies, as well as automotive manufacturers, railroad signal makers, locomotive and ship builders, and a variety of other customers. For example, an airplane builder such as Boeing, Grumman, or Beech might purchase landing lights from a light bulb maker such as General Electric. Such subcontractors supply a surprisingly large portion of the entire aircraft. On the typical commercial aircraft, a lead manufacturer such as McDonnell Douglas may actually manufacture less than half of the aircraft, though it is responsible for designing and assembling the final product.

When a major manufacturer discontinues an aircraft design, as Lockheed did with its L-1011 Tristar, a ripple effect is caused that affects every manufacturer that supplied parts for that aircraft. Therefore, parts suppliers that make up the third tier of distribution strive to diversify their customer base to ensure the decline of one manufacturer will be tempered by continued sales to others. Given the unstable nature of the industry, parts manufacturers also attempt to find customers outside the aircraft business.

In terms of the distribution of helicopters to the end user, most units are produced only after an order has been placed for the vehicle. This is common for large assets that are intended for very specific purposes and therefore often require some level of customization.

KEY USERS

For many practical applications, helicopters are indispensable. They are used to perform important services for cities, industry, and government. Rescue missions and operations depend on the versatility of the helicopter for disaster relief efforts at sea and on land. The Coast Guard uses them regularly, and the ability of the helicopter to hover allows for harnesses to be extended to victims on the ground or at sea, who can then be transported to safety. Helicopters are also useful when rescuing lost or injured hikers or skiers. Hospitals now have helipads so accident victims can be transported as quickly as possible for emergency treatment. Police use them for aerial observation, tracking fleeing criminals, searching for escaped prisoners, or patrolling borders. Police and news agencies use the helicopter to watch for traffic problems in major cities.

Wildlife and forestry employees need helicopters for aerial surveys of animal populations and to track animal movements. Forestry personnel use the helicopter to observe the condition of tree stands and to fight fires. Helicopters transport personnel and equipment to base camps, and spray fires. The agricultural industry engages helicopters to spray fields and to check on and round up cattle.

Helicopters are especially useful to industry, performing jobs that require strength and maneuverability, such as hoisting heavy building materials to the upper levels of a high-rise and hauling awkward or large objects. They have also been used to erect hydro towers and other tall structures. Petroleum industries rely on the helicopter to observe pipelines for damage and to transport personnel to offshore drilling operations.

Helicopters are the prestige vehicle of choice when businesses want to impress clients and employees. Though expensive, helicopter flight is a convenient way to beat the traffic, and downtown businesses in large cities will often have heliports on top of their buildings. Helicopters transport passengers from the airports and are enjoyed recreationally by sightseers and hunters willing to pay for quick transportation to exotic locales.

While helicopters have improved greatly since the first piloted rotary machines of 1907, they are significantly slower than airplanes and cannot reach the same altitudes. Expensive and difficult to fly, helicopters are also highly versatile and can move in ways impossible for fixed-wing craft. This maneuverability makes the helicopter an essential tool for industrial, civil, and military service.

Helicopters in widest use in the U.S. armed services are the Sikorsky UH-60 Black Hawk and the Boeing AH-64 Apache. The Black Hawk, in service since 1978, is designed as a troop carrier and logistical support aircraft, but it can be used for medical evacuation, command and control, search and rescue, armed escort, and electronic warfare missions. The Black Hawk can carry 16 laser-guided Hellfire antitank missiles and a total weapons payload of up to 10,000 pounds of missiles, rockets, cannons, and electronic countermeasures. The helicopter can also transport up to 11 fully equipped soldiers.

Like its predecessor the Black Hawk, the Apache attack helicopter can carry up to 16 missiles as well as 76 aerial rockets for use againt lightly armored vehicles, and other soft-skinned targets. The Apache also boasts state-of-the art sensors that can identify targets in all types of weather during the day or night. Both the Black Hawk and the Apache played critical roles in ground attack, troop support, and supply during the Gulf War of 1991 and the Iraq War of 2003. The flexibility and firepower provided by modern military helicopters make them an indispensable part of the U.S. military arsenal.

ADJACENT MARKETS

Even the simplest modern helicopter contains thousands of parts whose peak functioning is essential to a safe landing. Indeed, a significant part of a helicopter's control panel contains instruments indicating whether the other instruments are working correctly; it is not as though, when something goes wrong, the pilot can pull over to the nearest cloud. The categories considered in this section include instrumentation systems and engine instruments. Products produced by these industry sectors are necessary to getting a helicopter off the ground, keeping it in the air, and touching down gently.

Guidance and Control Instrumentation

The products of this industry relevant to this essay include radar systems, navigation systems; flight and navigation sensors, transmitters, and displays; gyroscopes; and airframe equipment instruments.

The main suppliers of search and navigation equipment are the same contractors who supply the larger U.S. aerospace and defense industries, to which search and navigation equipment contribute significantly. Although not necessarily the most prolific producers of search and navigation instruments, many of the largest and most recognizable corporations in the United States have been involved in the business, including AT&T, Boeing, General Electric, General Motors, and IBM.

A substantial majority of the industry's product types fall into the avionics (aviation electronics) classification, which includes aeronautic radar systems, and air traffic control systems.

Historically, the primary customer for industry products has been the U.S. government—in particular, the Department of Defense and the Federal Aviation Administration.

Search and detection systems and navigation and guidance systems and equipment ($29.1 billion worth of shipments in 2001) constitute 91 percent of the total search and navigation market and include the following product groups: light reconnaissance and surveillance systems; identification-friend-or-foe equipment; radar systems and equipment; sonar search, detection, tracking, and communications equipment; specialized command and control data processing and display equipment; electronic warfare systems and equipment; and navigation systems and equipment, including navigational aids.

During the 1970s development of the Global Positioning System (GPS) satellite network began. Inertial navigators using digital computers became common devices in civil and military aircraft. Industry shipment values for the above products totaled $31.9 billion in 2001, an increase over the $29.9 billion shipped in 2000. Employment in the aircraft components sector in the United States also saw growth in the early 2000s. In 2001 the industry's employment base of 153,710 workers was nearly 12,000 people greater than the previous year. Capital investment, which totaled approximately $1 billion in 2000, had remained relatively constant since 1997.

Aircraft Engine Instruments

The main customers of the aircraft engine instruments segment are General Electric, United Technologies, Rolls Royce, and other aircraft manufacturers. This sector produces temperature, pressure, vacuum, fuel and oil flow-rate sensors, and other measuring devices. Growth in this market is linked to aircraft production.

Through the first decade of the twenty-first century, the miscellaneous measuring and controlling devices industry was projected to grow at an annual rate of 3 percent. Aircraft engine instruments were predicted to be one of the industry's faster growing segments. Furthermore, the addition of software and services will contribute to overall industry growth, as will further expansion into overseas markets. The top five export markets in the late 1990s were Canada, Mexico, Japan, United Kingdom, and Germany; these five countries also were the top import countries. Looking into the 2000s, estimates indicated 33 percent of measuring and controlling instrument product shipments would be exported, while 25 percent of U.S. demand would be met by imports.

RESEARCH & DEVELOPMENT

In a sector as competitive as the helicopter industry, it is easy to focus on matters of day-to-day survival. That has never been truer than in the early twenty-first century, when operators have been desperate for aircraft and manufacturers have been under pressure to meet rising demand and demanding production schedules.

What will airframes, power systems, and avionics look like over the next 40 years? That is a more complex question than it would first appear, since even with computer-assisted drawing equipment and high demand, it can take 10 years for a new helicopter to move from the drawing board to the field. Much potential remains for revolutionary advances in the science of vertical flight. Some industry experts feel helicopter technology hasn't advanced significantly since the 1970s; the basic air vehicle performance has remained largely unchanged since the end of U.S. military involvement in Vietnam.

Regardless of how individuals may feel about the need for war, many rotorcraft developments evolve to meet the requirements of the U.S. military. Combat operations in Iraq and Afghanistan, combined with the prospect that they will persist for some time and be coupled with operations elsewhere in the world, confront military and industry leaders with a simple fact: the Pentagon needs an aircraft that can get off the ground and land without requiring a runway but can perform like a fixed-wing airplane in between.

The Bell Helicopter/Boeing V-22 can do that, and was scheduled to go into use in Iraq in 2006, but that process began in the late 1980s. To achieve greater speed, range, and payload, the experts cited the promise of a compound-helicopter design, using an auxiliary propulsion system to supplement the thrust of the rotors for greater forward speed. Fixed wings can provide extra lift. The Piasecki Aircraft, which has long worked on the concept of compound-helicopter design, is preparing its X-49A SpeedHawk for flight tests in 2007.

The Heliplane being developed with funding from the U.S. Defense Advanced Research Projects Agency (DARPA) uses a similar approach. The Salt Lake City-based autogiro maker Groen Brothers Aviation is designing a proof-of-concept, long-range, vertical takeoff and landing aircraft. DARPA's objective is to achieve performance with a rotary-wing aircraft comparable to that of a fixed-wing one.

The Smart Hybrid Active Rotor Control System (SHARCS) integrates actively controlled rotor blades to reduce helicopter noise and vibration. Performance tests of the 6.5-ft rotor were scheduled for early 2007, followed by wind tunnel tests in Milan, Italy. SHARCS is led by the Rotorcraft Research Group at Carleton University in Ottawa, Canada, with funding from the Canadian Natural Sciences and Research Council, AgustaWestland, Manufacturing and Materials Ontario, and Sensor Technology, Ltd.

Developing a low-drag hub alone would be a significant efficiency gain for tomorrow's rotorcraft. Experts said the vertical drag of a rotorcraft's hub is roughly equivalent to the entire drag of a fixed-wing aircraft of a similar gross weight, which greatly limits the performance of helicopters.

Tail rotors are another necessary evil on single main-rotor helicopters. They are critical to controlling torque and directional control, but they also add drag, increase the cost and complexity of maintenance, and generate a lot of noise. Most importantly, tail rotors are a safety weakness. They are a critical flight control that is susceptible to a single-point failure. In the late 1990s, developers and operators of unmanned air vehicles (UAVs) realized they were losing aircraft to single-point flight-control failures. They revised their designs to make them doubly, and lately, triply redundant. As a result, it is difficult to lose a UAV to a flight control failure.

Tomorrow's aircraft also are likely to be less expensive to operate. Since military operators are shifting life-cycle costs to aircraft suppliers through long-term support contracts, suppliers are motivated to maximize aircraft reliability. The United Kingdom has led in this contracting area, but the United States is expanding its use of this practice.

CURRENT TRENDS

Manufacturing processes and techniques will continue to change in response to the need to reduce costs and the introduction of new materials. Automation may further improve quality (and lower labor costs). Computers will become more important in improving designs, implementing design changes, and reducing the amount of paperwork created, used, and stored for each helicopter built. Also, industrial robots that can wind filament, wrap tape, and place fiber will permit fuselage structures to be made of fewer, more integrated pieces. Advanced, high-strength thermoplastic resins promise greater impact resistance and repairability than current materials such as epoxy and polyimide. Metallic composites such as aluminum reinforced with boron fiber or magnesium reinforced with silicon carbide particles also promise higher strength-to-weight ratios for critical components such as transmission cases while retaining the heat resistant advantage of metal over organic materials.

TARGET MARKETS & SEGMENTATION

Helicopters have proven themselves so crucial to so many markets, they would seem to almost sell themselves. In truth there is a great deal of competition among helicopter manufacturers and each must maintain a close relationship with a large variety of institutional buyers.

The major target markets for helicopters are the agencies and organizations that use helicopters as a part of their very function. They include the military, law enforcement, tourism, firefighting, agriculture, construction, the wealthy, and hospitals. Because of the unique functionality offered by the helicopter, it has a built in audience and thus, a capitive market. Even the hazards inherent in all aircraft, particularly acute with helicopters since they often fly at relatively low altitude, with little time to react to a sudden event, do not deter from the popularity of this most useful machine. Air shows remain the most widely attended venues for customers old and new to marvel at the latest advances in aircraft design. Other ways in which helicopters are promoted include through the listings of helicopter charter companies in telephone directories and the plethora of Internet Web sites devoted to the sale, maintenance, supply and repair of helicopters.

RELATED ASSOCIATIONS & ORGANIZATIONS

American Helicopter Society, http://www.vtol.org

Competition Helicopter Association, http://torchs.org/clubs/clubs.htm

Helicopter Club of Great Britain, http://www.hcgb.co.uk

Helicopter Foundation International, http://www.hfi.rotor.com

Naval Helicopter Association, http://www.navalhelicopterassn.org

Popular Rotorcraft Association, http://www.pra.org

Rotor Rats, http://torchs.org/clubs/clubs.htm

Twirly Birds, http://www.twirlybirds.org

Whirly-Girls International, http://www.whirlygirls.org

BIBLIOGRAPHY

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"Airframes: Sleeker, Safer, Friendlier." Rotor & Wing. 15 May 2007.

Allen, Matthew. Military Helicopter Doctrines of the Major Powers, 1945–1992. Greenwood Press, 1993.

Basic Helicopter Handbook. IAP Inc. 1988.

"Boeing in Brief." April 2007. Available from 〈http://www.boeing.com/companyoffices/aboutus/brief.html〉.

Boyne, Walter J., and Donald S. Lopez, eds. Vertical Flight: The Age of the Helicopter. Smithsonian Institution Press, 1984.

Brown, Stuart F. "Tilt-rotor Aircraft." Popular Science. July 1987, 46.

Davis, Kenneth C. Don't Know Much About History, Rev. ed. Harper Collins Publishers Inc., 2003.

Fay, John. The Helicopter: History, Piloting, and How It Flies, 4th ed. Hippocrene, 1987.

Francis, Devon F. The Story of the Helicopter. Coward-McCann, 1946.

Futrell, Robert Frank. The United States Air Force in Korea, 1950–1953, Rev. ed. U.S. Department of the Airforce, Office of Air Force History. 1983.

"Graphite Tools Produce Volume 'Copter Parts." Design News. 17 February 1986, 30.

"History." Available from 〈http://www.boeing.com/history/chronology/〉.

"Integrated Defense Systems." Available from 〈http://www.boeing.com/companyoffices/aboutus/brief/ids.html〉.

Momyer, William W. Airpower in Three Wars: World War II, Korea, Vietnam. U.S. Department of the Air Force. 1978.

Musquere, Anne. "High Times for Helo Makers: This Year's Heli-Expo Saw Record Attendance and Sales." Interavia Business & Technology. Spring 2006, 14.

Nicholl, Charles. Leonardo da Vinci: Flights of the Mind, A Biography. Viking Penguin, 2004.

"Researchers Work on Noise Reduction in Helicopters." Research & Development. January 1986, 55.

"Rotary-Wing Technology Pursues Fixed-Wing Performance Capabilities." Aviation Week & Space Technology. 19 January 1987, 46.

Seddon, J. Basic Helicopter Aerodynamics. American Institute of Aeronautics & Astronautics. 1990.

Smith, Bruce A. "Helicopter Manufacturers Divided on Development of New Aircraft." Aviation Week & Space Technology. 29 February 1988, 58.

"U.S. Civil Helo Sales Hit Record Levels in 2005." Rotor & Wing. 15 February 2006.

see also Airplanes, Jet Aircraft

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