Fixed-wing aircraft
 | This article needs additional citations for verification. (December 2006) |
A fixed-wing aircraft is a heavier-than-air craft where movement of the wings in relation to the aircraft is not used to generate lift. The term is used to distinguish from rotary-wing aircraft, or ornithopters, where the movement of the wing surfaces relative to the aircraft generates lift. Modern jet transport aircraft take off at roughly 290 km/h (180 mph), and cruise at over 892 km/h (555 mph). Fixed-wing aircraft are commonly called airplanes in North America (the U.S. and Canada), and aeroplanes in Commonwealth countries (other than Canada) and Ireland. These terms are derived from Greek aéros- ("air") and -plane[1]. Both terms are often shortened to just planes.
Overview
Fixed-wing aircraft include a large range of craft from small training and recreational aircraft to large airliners and military cargo aircraft. Some aircraft use fixed wings to provide lift only part of the time and may or may not be referred to as fixed-wing.
The word also embraces aircraft with folding or removable wings that are intended to fold when on the ground. This is usually to ease storage or facilitate transport on, for example, a vehicle trailer or the powered lift connecting the hangar deck of an aircraft carrier to its flight deck. It also embraces "variable geometry" aircraft, such as the General Dynamics F-111, Grumman F-14 Tomcat and the Panavia Tornado, which can vary the sweep angle of their wings during flight. There are also rare examples of aircraft which can vary the angle of incidence of their wings in flight, such the F-8 Crusader, which are also considered to be "fixed-wing".
Two necessities for all fixed-wing aircraft (as well as rotary-wing aircraft) are air flow over the wings for lifting of the aircraft, and an open area for landing. The majority of aircraft, however, also need an airport with the infrastructure to receive maintenance, restocking, refueling and for the loading and unloading of crew, cargo and/or passengers. While the vast majority of aircraft land and take off on land, some are capable of take off and landing on ice, aircraft carriers, snow, and calm water.
The aircraft is the second fastest method of transport, after the rocket. Commercial jet aircraft can reach up to 900 km/h. Single-engined aircraft are capable of reaching 175 km/h or more at cruise speed. Supersonic aircraft (military, research and a few private aircraft) can reach speeds faster than sound. The speed record for a plane powered by an air-breathing engine is currently held by the experimental NASA X-43, which reached nearly ten times the speed of sound.
The biggest aircraft currently in service is Antonov An-225, while the fastest currently in production is the Mikoyan MiG-31. The biggest supersonic jet ever produced and currently in service is Tupolev-160.
Aircraft parts
A typical fixed-wing aircraft can be divided into the following major parts:
- A long cylinder, called a fuselage, usually with tapered or rounded ends to make its shape aerodynamically smooth. The fuselage carries the human flight crew if the aircraft is piloted, the passengers if the aircraft is a passenger aircraft, other cargo or payload, and engines and/or fuel if the aircraft is so equipped. The pilots, who are members of the flight crew, operate the aircraft from a cockpit located at the front or top of the fuselage and equipped with windows, controls, and instruments. Passengers and cargo occupy the remaining available space in the fuselage. Some aircraft may have two fuselages, or additional pods or booms.
- A pair of long, narrow, flat, nearly horizontal wings, with an airfoil cross-section shape, used to generate aerodynamic lifting force to support the aircraft in flight by deflecting air downward as the aircraft moves forward. The wings are typically symmetrical about the plane of symmetry (for symmetrical aircraft), and are attached to the fuselage roughly at its midpoint in most cases. The wings also stabilize the aircraft about its roll axis and control its rotation about that axis.
- A small wing mounted vertically at the top rear of the fuselage, called a vertical stabilizer. The vertical stabilizer is used to stabilize the aircraft about its yaw axis (the axis in which the aircraft turns from side to side) and to control its rotation along that axis. Some aircraft have multiple vertical stabilizers.
- A pair of small horizontal wings used mainly to stabilize the aircraft about its pitch axis (the axis around which the aircraft tilts upward or downward). The horizontal stabilizers are symmetrical and usually mounted near the rear of the fuselage, or at the top of the vertical stabilizer.
- One or more aircraft engines, propulsion units that provide thrust to push the aircraft forward through the air. The engine is optional in the case of gliders that are not motor gliders. The most common propulsion units are propellers, powered by reciprocating or turbine engines, and jet engines, which provide thrust directly from the engine and usually also from a large fan mounted within the engine. When the number of engines is even, they are distributed symmetrically about the roll axis of the aircraft, which lies along the plane of symmetry (for symmetrical aircraft); when the number is odd, the odd engine is usually mounted along the centerline of the fuselage.
- Landing gear, a set of wheels, skids, or floats (depending on the intended landing surface for the aircraft) that support the aircraft while it is on the ground.
Aircraft controls
A number of fairly standardized controls allow pilots to direct aircraft in the air. The controls found in a typical fixed-wing aircraft are as follows:
- A yoke or control stick, which controls rotation of the aircraft about the pitch and roll axes. A yoke resembles a kind of steering wheel, and a control stick is just a simple rod with a handgrip. The pilot can pitch the aircraft downward by pushing on the yoke or stick, and pitch the aircraft upward by pulling on it. Rolling the aircraft is accomplished by turning the yoke in the direction of the desired roll, or by tilting the control stick in that direction. Pitch changes are used to adjust the altitude and speed of the aircraft; roll changes are used to make the aircraft turn. Control sticks and yokes are usually positioned between the pilot's legs; however, a sidestick is a type of control stick that is positioned on either side of the pilot (usually the left side for the pilot in the left seat, and vice versa, if there are two pilot seats).
- Rudder pedals, which control rotation of the aircraft about the yaw axis. There are two pedals that pivot in such a way that pressing one forward moves the other backward, and vice versa. The pilot presses on the right rudder pedal to make the aircraft yaw to the right, and on the left pedal to make it yaw to the left. The rudder is used mainly to balance the aircraft in turns, or to compensate for winds or other effects that tend to turn the aircraft about the yaw axis.
- A throttle, which adjusts the thrust produced by the aircraft's engines. The pilot uses the throttle to increase or decrease the speed of the aircraft, and to adjust the aircraft's altitude (higher speeds cause the aircraft to climb, lower speeds cause it to descend). In some aircraft the throttle is literally a single lever that controls thrust; in others, adjusting the throttle effectively means adjusting a number of different engine controls simultaneously in a coordinated way. Aircraft with multiple engines usually have individual throttle controls for each engine.
- Brakes, used to slow and stop the aircraft on the ground, and sometimes for turns on the ground as well. In most aircraft the brakes are controlled by movable portions of the rudder pedals.
Controls that are used in many aircraft, but are not as universal as the above, include:
- Flap levers, which are used to control the position of flaps on the wings.
- Spoiler levers, which are used to control the position of spoilers on the wings, and to arm their automatic deployment in aircraft designed to deploy them upon landing.
- Trim controls, which usually take the form of knobs or wheels and are used to adjust pitch, roll, or yaw trim.
- A tiller, a small wheel or lever used to steer the aircraft on the ground (in conjunction with or instead of the rudder pedals).
- A parking brake, used to prevent the aircraft from rolling when it is parked on the ground.
Many aircraft also include controls that allow full or partial automation of flight, such as an autopilot, a wing leveler, or a flight management system. Pilots adjust these controls to select a specific attitude or mode of flight, and then the associated automation maintains that attitude or mode until the pilot disables the automation or changes the settings. In general, the larger and/or more complex the aircraft, the greater the amount of automation available to pilots.
Control duplication
More often than not, aircraft are designed so that either of two people (a pilot and copilot, for example) can fly the aircraft without changing seats. The most common arrangement is two complete sets of controls, one for each of two pilots sitting side by side, but in some aircraft (military fighter aircraft, some taildraggers and aerobatic aircraft) the dual sets of controls are arranged one in front of the other. A few of the less important controls may not be present in both positions, and one position is usually intended for the pilot in command (e.g., the left “captain's seat” in jet airliners). Some small aircraft use controls that can be moved from one position to another, such as a single yoke that can be swung into position in front of either the left-seat pilot or the right-seat pilot.
Aircraft that require more than one pilot usually have controls intended to suit each pilot position, but still with sufficient duplication so that all pilots can fly the aircraft alone in an emergency. For example, in jet airliners, the controls on the left (captain's) side include both the basic controls and those normally manipulated by the pilot in command, such as the tiller, whereas those of the right (first officer's) side include the basic controls again and those normally manipulated by the copilot, such as flap levers. The unduplicated controls that are required for flight are positioned so that they can be reached by either pilot, but they are often designed to be more convenient to the pilot who manipulates them under normal condition.
Aircraft instruments
Most aircraft have a large number of instruments that provide important information to the pilot. When these instruments are electronic, they are often called avionics. An aircraft that uses electronic displays almost exclusively is said to have a glass cockpit; mechanical instruments are sometimes referred to as steam gauges in comparison, even though they don't actually run on steam.
Basic instruments that are present in almost all aircraft include:
- An airspeed indicator, which indicates the speed at which the aircraft is moving through the surrounding air.
- An altimeter, which indicates the altitude of the aircraft above the ground or above mean sea level (MSL).
- An attitude indicator, sometimes called an artificial horizon, which indicates the exact orientation of the aircraft about its pitch and roll axes.
Most aircraft have many other instruments as well, including (but not limited to):
- A Turn coordinator, which helps the pilot maintain the aircraft in a coordinated attitude while turning.
- A rate-of-climb indicator, which shows the rate at which the aircraft is climbing or descending
- A horizontal situation indicator, existing in many different forms, all of which show the position and movement of the aircraft as seen from above with respect to the ground, including course/heading and other information.
- Various instruments showing the status of each engine in the aircraft (operating speed, thrust, temperature, and other variables).
- Combined display systems such as primary flight displays or navigation displays.
- Information displays such as on-board weather radar displays.
Types of fixed-wing aircraft
Gliders
Gliders or sailplanes are aircraft designed for unpowered flight. Most gliders are intended for use in the sport of gliding and have high aerodynamic efficiency: lift-to-drag ratios may exceed 70 to 1. The energy for sustained gliding flight must be obtained through the skillful exploitation of naturally occurring air movements in the atmosphere. Glider flights of thousands of kilometres at average speeds over two-hundred kilometres per hour have been achieved.
Military gliders have been used in war for delivery of assault troops, and specialized gliders have been used in atmospheric and aerodynamic research. Motor gliders equipped with engines (often retractable), some capable of self-launching, are becoming increasingly common, though most have to be pulled up in the air by a tug plane (often a Cessna or a Maule Air of some kind). The glider is attached to the tug plane by a tow rope, which can be released at the flip of a switch by the pilot. Though the cost of a tug plane is high, compared to oil prices, a glider is actually often considered the cheapest type of aviation, short only of ultralight aircraft.
Propeller aircraft
Smaller and older propeller aircraft make use of reciprocating internal combustion engines that turns a propeller to create thrust. They are quieter than jet aircraft, but they fly at lower speeds, and have lower load capacity compared to similar sized jet powered aircraft. However, they are significantly cheaper and much more economical than jets, and are generally the best option for people who need to transport a few passengers and/or small amounts of cargo. They are also the aircraft of choice for pilots who wish to own an aircraft.
Turboprop aircraft are a halfway point between propeller and jet: they use a turbine engine similar to a jet to turn propellers. These aircraft are popular with commuter and regional airlines, as they tend to be more economical on shorter journeys.
Jet aircraft
Jet aircraft make use of turbines for the creation of thrust. These engines are much more powerful than a reciprocating engine. As a consequence, they have greater weight capacity and fly faster than propeller driven aircraft. One drawback, however, is that they are noisy; this makes jet aircraft a source of noise pollution. However, turbofan jet engines are quieter, and they have seen widespread usage partly for that reason.
The jet aircraft was developed in Germany in 1931. The first jet was the Heinkel He 178, which was tested at Germany's Marienehe Airfield in 1939. In 1943 the Messerschmitt Me 262, the first jet fighter aircraft, went into service in the German Luftwaffe. In the early 1950s, only a few years after the first jet was produced in large numbers, the De Havilland Comet became the world's first jet airliner. However, the early Comets were beset by structural inadequacies discovered after numerous pressurization and depressurization cycles, leading to extensive redesigns.
Most wide-body aircraft can carry hundreds of passengers and several tons of cargo, and are able to travel for distances up to 17,000km. Aircraft in this category are the Boeing 747, Boeing 767, Boeing 777, the upcoming Boeing 787, Airbus A300/A310, Airbus A330, Airbus A340, Airbus A380, Lockheed L-1011 TriStar, McDonnell Douglas DC-10, McDonnell Douglas MD-11, Ilyushin Il-86 and Ilyushin Il-96.
Jet aircraft possess high cruising speeds (700 to 900 km/h, or 400 to 550 mph) and high speeds for take-off and landing (150 to 250 km/h). Due to the speed needed for takeoff and landing, jet aircraft make use of flaps and leading edge devices for the control of lift and speed, as well as engine reversers (or thrust reversers) to direct the airflow forward, slowing down the aircraft upon landing.
Supersonic jet aircraft
Supersonic aircraft, such as military fighters and bombers, Concorde, and others, make use of special turbines (often utilizing afterburners), that generate the huge amounts of power for flight faster than the speed of the sound. The design problems for supersonic aircraft are substantially different to those for sub-sonic aircraft.
Flight at supersonic speed creates more noise than flight at subsonic speeds, due to the phenomenon of sonic booms. This limits supersonic flights to areas of low population density or open ocean. When approaching an area of heavier population density, supersonic aircraft are obliged to fly at subsonic speed.
Due to the high costs, limited areas of use and low demand there are no longer any supersonic aircraft in use by any major airline. The last Concorde flight was on 26 November 2003. It appears that supersonic aircraft will remain in use almost exclusively by militaries around the world for the foreseeable future, though research into new civilian designs continues.
Rocket-powered aircraft
Experimental rocket powered aircraft were developed by the Germans as early as World War II (see Me 163 Komet), although they were never mass produced by any power during that war. The first fixed wing aircraft to break the sound barrier in level flight was the rocket powered Bell X-1. The later North American X-15 was another important rocket plane that broke many speed and altitude records and laid much of the groundwork for later aircraft and spacecraft design. Rocket aircraft are not in common usage today, although rocket-assisted takeoffs are used for some military aircraft. SpaceShipOne is the most famous current rocket aircraft, being the testbed for developing a commercial sub-orbital passenger service; another rocket plane is the XCOR EZ-Rocket; and there is of course the Space Shuttle.
Ramjet aircraft
Ramjet aircraft are mostly in the experimental stage. The D-21 Tagboard was an unmanned Mach 3+ reconnaissance drone that was put into production in 1969 for spying, but due to the development of better spy satellites, it was cancelled in 1971. The SR-71's Pratt & Whitney J58 engines ran 80% as ramjets at high-speeds (Mach 3.2). The SR-71 was dropped in the early 70's and then brought back during the cold war. They were used also in the Gulf War. The last SR-71 flight was in October 2001.
Scramjet aircraft
Scramjet aircraft are in the experimental stage. The Boeing X-43 is an experimental scramjet with a world speed record for a jet-powered aircraft - Mach 9.6, nearly 12,000 km/h (≈ 7,000 mph) at an altitude of about 36,000 meters (≈ 110,000 feet). The X-43A set the flight speed record on 16 November 2004.
History
The dream of flight goes back to the days of pre-history. Many stories from antiquity involve flight, such as the Greek legend of Icarus and Daedalus. Leonardo da Vinci drew an aircraft in the 15th century. With the first flight made by man (Francois Pilatre de Rozier and Francois d'Arlandes) in an aircraft lighter than air, a balloon, the biggest challenge became to create other craft, capable of controlled flight.
First attempts
Sir George Cayley, the inventor of the science of aerodynamics, was building and flying models of fixed-wing aircraft as early as 1803, and he built a successful passenger-carrying glider in 1853 [citation needed]. In 1856, Frenchman Jean-Marie Le Bris made the first powered flight, by having his glider "L'Albatros artificiel" pulled by a horse on a beach. On 28 August 1883, the American John J. Montgomery made a controlled flight in a glider. Other aviators who had made similar flights at that time were Otto Lilienthal, Percy Pilcher and Octave Chanute.
Self-powered aircraft were designed and constructed by Clément Ader. On October 9, 1890, Ader attempted to fly the Éole, which succeeded in taking off and flying uncontrolled a distance of approximately 50 meters before witnesses. In August 1892 the Avion II flew for a distance of 200 metres, and on October 14, 1897, Avion III flew a distance of more than 300 metres. Richard Pearse made a poorly documented uncontrolled flight on March 31 1903 in Waitohi, New Zealand, and on August 28 1903 in Hanover, the German Karl Jatho made his first flight.
The Wright Brothers are commonly credited with the invention of the aircraft[1], theirs was the first sustainable and well documented attempt; the first to fly what in modern terms would be considered an airplane instead of a glider or an animal pulled flying device. They made their first successful test flights on December 17 1903 and by 1905 Wright Flyer III was capable of fully controllable, stable flight for substantial periods. Strictly speaking, the Flyer's wings were not completely fixed, as it depended for stability on a flexing mechanism named wing warping. This was later superseded by the development of ailerons, devices which performed a similar function but were attached to an otherwise rigid wing.
Alberto Santos-Dumont a Brazilian living in France, built the first practical dirigible balloons from the end of the nineteenth century. In 1906 he flew the first fixed wing aircraft in Europe, the 14-bis, which was of his and Gabriel Voisin's design. It was the first aircraft to take off, fly and land without the use of catapults, high winds, or other external assistance. A later design of his, the Demoiselle, introduced ailerons and brought all around pilot control during a flight. Santos-Dumont is put forward as the true inventor of the aircraft, but owing to the competing claims, the concept of the invention of the first flying machine has substantial ambiguity.
Wars in Europe, in particular World War I, served as initial tests for the use of the aircraft as a weapon. First seen by generals and commanders as a "toy", the aircraft proved to be a machine of war capable of causing casualties to the enemy. In the first world war, the fighter "aces" appeared, of which the greatest was the German Manfred von Richthofen, commonly called the Red Baron. On the side of the allies, the ace with the highest number of downed aircraft was René Fonck, of France.
After the First World War, aircraft technology continued to develop. Alcock and Brown crossed the Atlantic non-stop for the first time in 1919, a feat first performed solo by Charles Lindbergh in 1927. The first commercial flights took place between the United States and Canada in 1919. The turbine or the jet engine was in development in the 1930s; military jet aircraft began operating in the 1940s.
Aircraft played a primary role in the Second World War, having a presence in all the major battles of the war, especially in the attack on Pearl Harbor, the battles of the Pacific and D-Day, as well as the Battle of Britain. They were also an essential part of several of the military strategies of the period, such as the German Blitzkrieg or the American and Japanese Aircraft carriers.
In October 1947, Chuck Yeager, in the Bell X-1, was the first recorded person to exceed the speed of sound. However, some British Spitfire pilots claimed to have exceeded Mach 1 in a dive. The Boeing X-43 is an experimental scramjet with a world speed record for a jet-powered aircraft - Mach 9.6, or nearly 7,000 mph.
Aircraft in a civil military role continued to feed and supply Berlin in 1948, when access to railroads and roads to the city, completely surrounded by Eastern Germany, were blocked, by order of the Soviet Union.
The first commercial jet, the de Havilland Comet, was introduced in 1952. A few Boeing 707s, the first widely successful commercial jet, are still in service after nearly 50 years. The Boeing 727 was another widely used passenger aircraft, and the Boeing 747, was the biggest commercial aircraft in the world up until 2005, when it was surpassed by the Airbus A380.
Designing and constructing an aircraft
Small aircraft can be designed and constructed by amateurs as homebuilts. Other aviators with less knowledge make their aircraft using pre-manufactured kits, assembling the parts into a complete aircraft.
Most aircraft are constructed by companies with the objective of producing them in quantity for customers. The design and planning process, including safety tests, can last up to four years for small turboprops, and up to 12 years for aircraft with the capacity of the A380.
During this process, the objectives and design specifications of the aircraft are established. First the construction company uses drawings and equations, simulations, wind tunnel tests and experience to predict the behavior of the aircraft. Computers are used by companies to draw, plan and do initial simulations of the aircraft. Small models and mockups of all or certain parts of the aircraft are then tested in wind tunnels to verify the aerodynamics of the aircraft.
When the design has passed through these processes, the company constructs a limited number of these aircraft for testing on the ground. Representatives from an aviation governing agency often make a first flight. The flight tests continue until the aircraft has fulfilled all the requirements. Then, the governing public agency of aviation of the country authorizes the company to begin production of the aircraft.
In the United States, this agency is the Federal Aviation Administration (FAA), and in the European Union, Joint Aviation Authorities (JAA). In Canada, the public agency in charge and authorizing the mass production of aircraft is Transport Canada.
In the case of the international sales of aircraft, a license from the public agency of aviation or transports of the country where the aircraft is also to be used is necessary. For example, aircraft from Airbus need to be certified by the FAA to be flown in the United States and vice versa, aircraft of Boeing need to be approved by the JAA to be flown in the European Union.
Quieter aircraft are becoming more and more needed due to the increase in air traffic, particularly over urban areas, as noise pollution is a major concern. MIT and Cambridge University have been designing delta-wing aircraft that are 25 times more silent (63dB) than current craft and can be used for military and commercial purposes. The project is called the Silent Aircraft Initiative, but production models will not be available until around 2030.[2]
Industrialized production
There are few companies that produce aircraft on a large scale. However, the production of an aircraft for one company is a process that actually involves dozens, or even hundreds, of other companies and plants, that produce the parts that go into the aircraft. For example, one company can be responsible for the production of the landing gear, while another one is responsible for the radar. The production of such parts is not limited to the same city or country; in the case of large aircraft manufacturing companies, such parts can come from all over of the world.
The parts are sent to the main plant of the aircraft company, where the production line is located. In the case of large aircraft, production lines dedicated to the assembly of certain parts of the aircraft can exist, especially the wings and the fuselage.
When complete, an aircraft goes through a set of rigorous inspection, to search for imperfections and defects, and after being approved by the inspectors, the aircraft is tested by a pilot, in a flight test, in order to assure that the controls of the aircraft are working properly. With this final test, the aircraft is ready to receive the "final touchups" (internal configuration, painting, etc), and is then ready for the customer.
Safety
Statistics show that the risk of an airliner accident is very small, so small that the chance of having an accident while driving to the airport in a car is higher than having an accident during the flight. Many people have a fear of flying because they erroneously believe that the risk of death in the event of an aircraft accident is extremely high, when in fact a study of 583 accidents between 1983 and 2000 show that over 96% of those involved survived.[1] Furthermore, car crashes rarely feature outside local news whereas air crashes are reported internationally, making the risk seem greater.
Aircraft are the second safest way to travel long distances after railway trains. The per-trip safety of aircraft is somewhat safer than cars, but over the long distances aircraft cover, they are much safer than other types of transport.
The majority of aircraft accidents are a result of human error on the part of the pilot(s) or controller(s). After human error, mechanical failure is the biggest cause of air accidents, which sometimes also can involve a human component; e.g., negligence of the airline in carrying out proper maintenance. Adverse weather is the third largest cause of accidents. Icing, downbursts, and low visibility are often major contributors to weather related crashes. Birds have been ranked as a major cause for large rotor bursts on commercial turboprop engines, spurring extra safety measures to keep birds away. Technological advances such as ice detectors also help pilots ensure the safety of their aircraft.
Environmental impact
Aircraft have a particularly marked impact on the environment, compared with other commonly used vehicles. Their contrails contribute to global dimming, and their noise is often significant. However, the most significant impact of such aircraft upon the environment is their contribution of greenhouse gases. They are responsible for emitting a great deal of carbon monoxide and nitrogen dioxide, and they distribute the gases more evenly on a global level and far higher in the atmosphere than any other commonly used vehicle type.
See also
References
- Blatner, David. The Flying Book : Everything You've Ever Wondered About Flying On Airplanes. ISBN 0-8027-7691-4
Notes
- ^ "Aeroplane", Oxford English Dictionary, Second edition, 1989.
External links
