AIRCRAFT
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.[1]
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Although rockets and missiles also travel through the atmosphere, most are not considered aircraft because they do not have wings and rely on rocket thrust as the primary means of lift.
The human activity that surrounds aircraft is called aviation. Manned aircraft are flown by an onboard pilot. Unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Aircraft may be classified by different criteria, such as lift type, propulsion, usage, and others.
[]History
Flying model craft and stories of manned flight go back many centuries, however the first manned ascent - and safe descent - in modern times took place by hot-air balloon in the 18th century. Each of the two World Wars led to great technical advances. Consequently the history of aircraft development can be divided into five eras:
- Pioneers of flight, from the earliest experiments to 1913.
- First World War, 1914 to 1918.
- Inter-war, sometimes called the Golden Age, 1919 to 1938.
- Second World War, 1939 to 1945.
- Postwar era, also called the jet age, 1946 to the present day.
[edit]Methods of lift
[edit]Lighter than air – aerostats
Main article: Aerostat
Aerostats use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large gasbags or canopies, filled with a relatively low-density gas such as helium, hydrogen, or hot air, which is less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, it adds up to the same weight as the air that the craft displaces.
Small hot-air balloons called sky lanterns date back to the 3rd century BC, and were only the second type of aircraft to fly, the first being kites.
A balloon was originally any aerostat, while the term airship was used for large, powered aircraft designs – usually fixed-wing[citation needed] – though none had yet been built. The advent of powered balloons, called dirigible balloons, and later of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by a rigid outer framework and separate aerodynamic skin surrounding the gas bags, were produced, the Zeppelinsbeing the largest and most famous. There were still no fixed-wing aircraft or non-rigid balloons large enough to be called airships, so "airship" came to be synonymous with these aircraft. Then several accidents, such as the Hindenburg disaster in 1937, led to the demise of these airships. Nowadays a "balloon" is an unpowered aerostat, whilst an "airship" is a powered one.
A powered, steerable aerostat is called a dirigible. Sometimes this term is applied only to non-rigid balloons, and sometimes dirigible balloon is regarded as the definition of an airship (which may then be rigid or non-rigid). Non-rigid dirigibles are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back. These soon became known as blimps. During the Second World War, this shape was widely adopted for tethered balloons; in windy weather, this both reduces the strain on the tether and stabilizes the balloon. The nickname blimp was adopted along with the shape. In modern times, any small dirigible or airship is called a blimp, though a blimp may be unpowered as well as powered.
[edit]Heavier than air – aerodynes
Heavier-than-air aircraft must find some way to push air or gas downwards, so that a reaction occurs (by Newton's laws of motion) to push the aircraft upwards. This dynamic movement through the air is the origin of the term aerodyne. There are two ways to produce dynamic upthrust:aerodynamic lift, and powered lift in the form of engine thrust.
Aerodynamic lift involving wings is the most common, with fixed-wing aircraft being kept in the air by the forward movement of wings, androtorcraft by spinning wing-shaped rotors sometimes called rotary wings. A wing is a flat, horizontal surface, usually shaped in cross-section as an aerofoil. To fly, air must flow over the wing and generate lift. A flexible wing is a wing made of fabric or thin sheet material, often stretched over a rigid frame. A kite is tethered to the ground and relies on the speed of the wind over its wings, which may be flexible or rigid, fixed, or rotary.
With powered lift, the aircraft directs its engine thrust vertically downward. V/STOL aircraft, such as the Harrier Jump Jet and F-35B take off and land vertically using powered lift and transfer to aerodynamic lift in steady flight.
A pure rocket is not usually regarded as an aerodyne, because it does not depend on the air for its lift (and can even fly into space); however, many aerodynamic lift vehicles have been powered or assisted by rocket motors. Rocket-powered missiles that obtain aerodynamic lift at very high speed due to airflow over their bodies are a marginal case.
[edit]Fixed-wing
Airplanes or aeroplanes are technically called fixed-wing aircraft.
The forerunner of the fixed-wing aircraft is the kite. Whereas a fixed-wing aircraft relies on its forward speed to create airflow over the wings, a kite is tethered to the ground and relies on thewind blowing over its wings to provide lift. Kites were the first kind of aircraft to fly, and were invented in China around 500 BC. Much aerodynamic research was done with kites before test aircraft, wind tunnels, and computer modelling programs became available.
The first heavier-than-air craft capable of controlled free-flight were gliders. A glider designed byCayley carried out the first true manned, controlled flight in 1853.
Besides the method of propulsion, fixed-wing aircraft are in general characterized by their wing configuration. The most important wing characteristics are:
- Number of wings – Monoplane, biplane, etc.
- Wing support – Braced or cantilever, rigid, or flexible.
- Wing planform – including aspect ratio, angle of sweep, and any variations along the span (including the important class of delta wings).
- Location of the horizontal stabilizer, if any.
- Dihedral angle – positive, zero, or negative (anhedral).
A variable geometry aircraft can change its wing configuration during flight.
A flying wing has no fuselage, though it may have small blisters or pods. The opposite of this is alifting body, which has no wings, though it may have small stabilising and control surfaces.
Wing-in-ground-effect vehicles may be considered as fixed-wing aircraft. They "fly" effeiciently close to the surface of the ground or water, like conventional aircraft during takeoff. An example is the Russian ekranoplan (nicknamed the "Caspian Sea Monster"). Man-powered aircraft also rely on ground effect to remain airborne with a minimal pilot power, but this is only because they are so underpowered — in fact, the airframe is capable of flying higher.
[edit]Rotorcraft
Main article: Rotorcraft
Rotorcraft, or rotary-wing aircraft, use a spinning rotor with aerofoil section blades (a rotary wing) to provide lift. Types include helicopters, autogyros, and various hybrids such as gyrodynes and compound rotorcraft.
Helicopters have a rotor turned by an engine-driven shaft. The rotor pushes air downward to create lift. By tilting the rotor forward, the downward flow is tilted backward, producing thrust for forward flight. Some helicopters have more than one rotor and a few have rotors turned by gas jets at the tips.
Autogyros have unpowered rotors, with a separate power plant to provide thrust. The rotor is tilted backward. As the autogyro moves forward, air blows upward across the rotor, making it spin. This spinning increases the speed of airflow over the rotor, to provide lift. Rotor kites are unpowered autogyros, which are towed to give them forward speed or tethered to a static anchor in high-wind for kited flight.
Compound rotorcraft have wings that provide some or all of the lift in forward flight. They are nowadays classified as powered lift types and not as rotorcraft. Tiltrotor aircraft (such as the V-22 Osprey), tiltwing, tailsitter, and coleopter aircraft have their rotors/propellers horizontal for vertical flight and vertical for forward flight.
[edit]Other methods of lift
- A lifting body is an aircraft body shaped to produce lift. If there are any wings, they are too small to provide significant lift and are used only for stability and control. Lifting bodies are not efficient: they suffer from high drag, and must also travel at high speed to generate enough lift to fly. Many of the research prototypes, such as the Martin-Marietta X-24, which led up to theSpace Shuttle, were lifting bodies (though the shuttle itself is not), and some supersonicmissiles obtain lift from the airflow over a tubular body.
- Powered lift types rely on engine-derived lift for vertical takeoff and landing (VTOL). Most types transition to fixed-wing lift for horizontal flight. Classes of powered lift types include VTOL jet aircraft (such as the Harrier jump-jet) and tiltrotors (such as the V-22 Osprey), among others.
[edit]Propulsion
[edit]Unpowered
Main article: Unpowered aircraft
Gliders are heavier-than-air aircraft that do not employ propulsion once airborne. Take-off may be by launching forward and downward from a high location, or by pulling into the air on a tow-line, either by a ground-based winch or vehicle, or by a powered "tug" aircraft. For a glider to maintain its forward air speed and lift, it must descend in relation to the air (but not necessarily in relation to the ground). Many gliders can 'soar' - gain height from updrafts such as thermal currents. The first practical, controllable example was designed and built by the British scientist and pioneer George Cayley, whom many recognise as the first aeronautical engineer.[2] Common examples of gliders aresailplanes, hang gliders and paragliders.
Balloons drift with the wind, though normally the pilot can control the altitude, either by heating the air or by releasing ballast, giving some directional control (since the wind direction changes with altitude). A wing-shaped hybrid balloon can glide directionally when rising or falling; but a spherically shaped balloon does not have such directional control.
Kites are aircraft[3] that are tethered to the ground or other object (fixed or mobile) that maintains tension in the tether or kite line; they rely on virtual or real wind blowing over and under them to generate lift and drag. Kytoons are balloon-kite hybrids that are shaped and tethered to obtain kiting deflections, and can be lighter-than-air, neutrally buoyant, or heavier-than-air.
[edit]Powered aircraft
Main article: Powered aircraft
[edit]Propeller aircraft
Main article: Propeller aircraft
A propeller or airscrew spins on an axis aligned in the direction of travel to create thrust in a forward direction. The propeller is usually mounted in front of the power source in tractor configuration but can be mounted behind in pusher configuration. Variations of propellers layout include contra-rotating propellers and ducted fans.
Many kinds of power plant have been used to drive propellers. Early airships used man power andsteam-power. The more practical internal combustion piston engine was the power source used for virtually all fixed-wing aircraft until World War II and is still used in many smaller aircraft. Many larger aircraft use turbine engines to drive a propeller in the form of a turboprop or propfan. Human-powered heavier-than-air flight has been achieved, but has not become a practical means of transport. Unmanned aircraft and models have also used other power sources such as solar-powered electric motors and rubber bands.
[edit]Jet aircraft
Main article: Jet aircraft
Airbreathing jet engines take in air, burn fuel with it in a combustion chamber, and accelerate the exhaust rearwards at high speed to provide thrust. Turbojet and turbofan engines use a spinning turbine to drive one or more fans, which provide thrust. An afterburner may be used to inject extra fuel into the hot exhaust, especially on military "fast jets".
Jet engines can provide much higher thrust than propellers, at higher speeds, and are at their most efficient at higher altitudes, being able to operate above 40,000 ft (12,000 m), and there their fuel efficiency is about the same as the best piston and propeller engines.[4] They are also much more fuel-efficient than rockets. As a consequence, nearly all public transport liners, high-speed and high-altitude aircraft, use jet engines. Use of a turbine is not absolutely necessary: other designs include the pulse jet and ramjet. These mechanically simple designs cannot work when stationary, so the aircraft must be launched to flying speed by some other method. Other variants have also been used, including the motorjet and hybrids such as the Pratt & Whitney J58, which can convert between turbojet and ramjet operation.
[edit]Rotorcraft
Main article: Rotorcraft
A helicopter obtains lift from a powered rotary wing or rotor, which acts much like an upward-pointing propeller. Forward propulsion is provided by angling the rotor disc slightly forward so that a proportion of its lift is directed forward to provide thrust. The rotor may, like a propeller, be powered by a variety of methods such as a piston engine or turbine. Experiments have also used jet nozzles at rotor blade tips.
[edit]Other methods of propulsion
- Rocket-powered aircraft have occasionally been experimented with, and the Messerschmitt Komet fighter even saw action in the Second World War. Since then, they have been restricted to research aircraft, such as the North American X-15, which traveled up into space where air-breathing engines cannot work (rockets carry their own oxidant). Rockets have more often been used as a supplement to the main powerplant, typically for the rocket-assisted take off of heavily loaded aircraft, but also to provide high-speed dash capability in some hybrid designs such as the Saunders-Roe SR.53.
- The ornithopter obtains thrust by flapping its wings. It has found practical use in a model hawk used to freeze prey animals into stillness so that they can be captured, and in toy birds.
[edit]General construction
The parts of an aircraft are generally divided into three categories:
- The airframe comprises the mechanical structure and associated equipment.
- The propulsion system comprises the engine or engines and associated equipment.
- The avionics comprise the electrical flight control and communication systems.
[edit]Airframe
Main article: Airframe
The airframe of an aircraft is its mechanical structure,[5] which is typically considered to exclude the propulsion system. Airframe design is a field of engineering that combines aerodynamics,materials technology, and manufacturing methods to achieve balances of performance, reliability, and cost.
The main parts of the airframe are the fuselage, wing and tail.
[edit]Fuselage
The fuselage is an aircraft's main body section containing the crew cockpit or flight deck, and anypassenger cabin or cargo hold. In single- and twin-engine aircraft, it will often also contain the engine or engines. The fuselage also serves to position control and stabilization surfaces in specific relationships to lifting surfaces, required for aircraft stability and maneuverability.
[edit]Wing
The wings of an aircraft produce lift. Many different styles and arrangements of wings have been used on heavier-than-air aircraft, and some lighter-than-air craft also have wings. Most early fixed-wing aircraft were biplanes, having wings stacked one above the other. Most types nowadays aremonoplanes, having one wing each side. Wings also vary greatly in their shape viewed from above.
[edit]Control surfaces
Flight control surfaces allow a pilot to control an aircraft's flight attitude.
Development of an effective set of flight controls was a critical advance in the development of aircraft. Early efforts at fixed-wing aircraft design succeeded in generating sufficient lift to get the aircraft off the ground, but, once aloft, the aircraft proved uncontrollable, often with disastrous results. The development of effective flight controls is what allowed flight.
[edit]Horizontal and vertical stabilizers
In spite of effective control surfaces, many early aircraft were virtually unflyable.
The horizontal and vertical stabilizers of most aircraft[6][7] give stability, in a similar way to the feathers on an arrow.[8] Most aircraft feature empennage (a tail section) incorporating vertical, andhorizontal stabilizing surfaces which allow equilibrium of aerodynamic forces, stabilize the flight dynamics of pitch and yaw,[6][7] as well as housing control surfaces.
Today, only a few (often relatively less stable) heavier than air aircraft are able to fly 'tailless' without specific horizontal stabilizers.
[edit]Undercarriage
The undercarriage or landing gear, is the structure that supports an aircraft on the ground and allows it to taxi, take off, and land. In the typical undercarriage, wheels are used, but skids, floats, or a combination of these and other elements can be used, depending on the surface. Many aircraft have undercarriage that retracts into the wings and/or fuselage to decrease drag during flight.
Flying boats are supported on water by their fuselage and hence have no undercarriage, except for amphibians, which have retractable undercarriage allowing them to take off from and alight on both land and water.
[edit]Other
Other structural and aerodynamic components are often present, canards are wings situated near the nose of the vehicle, notably on fighter jets. Booms and other unusual components such as external drop tanks.
[edit]Engines
Main article: aircraft engine
Powered aircraft have one or more engines. Most aircraft engines are either lightweight piston engines or gas turbines. The fuel is usually kept in tanks around the vehicle. Most aircraft store the fuel predominantly in the wings, but may have additional fuel tanks elsewhere.
[edit]Avionics
Main article: Avionics
The avionics comprise the flight control systems and other electronic equipment, including the cockpit instrumentation, radar, andcommunication systems.
[edit]Performance
[edit]Flight envelope
Main article: Flight envelope
The flight envelope of an aircraft refers to its capabilities in terms of airspeed and load factor or altitude.[9][10] The term can also refer to other measurements such as maneuverability. When a plane is pushed, for instance by diving it at high speeds, it is said to be flown "outside the envelope", something considered unsafe.
[edit]Range
Main article: range (aircraft)
The maximal total range is the distance an aircraft can fly between takeoff and landing, as limited by fuel capacity in powered aircraft, or cross-country speed and environmental conditions in unpowered aircraft. The range can be seen as the cross-country ground speed multiplied by the maximum time in the air.
Ferry range means the maximum range an aircraft can fly. This usually means maximum fuel load, optionally with extra fuel tanks and minimum equipment. It refers to transport of aircraft for use on remote location.
The combat range is the maximum range an aircraft can fly when carrying ordnance. The combat radius is somewhat less.
The fuel time limit for powered aircraft is fixed by the fuel load and rate of consumption. For unpowered aircraft, the maximum flight time is limited by available daylight hours, weather conditions, and pilot endurance.
[edit]Flight dynamics
Main article: Flight dynamics (aircraft)
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the vehicle'scenter of mass, known as pitch, roll, and yaw (quite different from their use as Tait-Bryan angles).
- Roll is a rotation about the longitudinal axis (equivalent to the rolling or heeling of a ship) giving an up-down movement of the wing tips measured by the roll or bank angle.
- Pitch is a rotation about the sideways horizontal axis giving an up-down movement of the aircraft nose measured by the angle of attack.
- Yaw is a rotation about the vertical axis giving a side-to-side movement of the nose known as sideslip.
A fixed-wing aircraft increases or decreases the lift generated by the wings when it pitches, respectively, nose up or down by increasing or decreasing the angle of attack. A fixed-wing aircraft usually "banks" to change the horizontal direction of flight. To maintain direction, efficiency, and controllability of flight the sideslip angle must remain near zero, though there are instances when an aircraft may be deliberately "sideslipped," for example, a slip in a fixed-wing aircraft.
Besides lift, the other main aerodynamic force on an aircraft is drag opposing its motion through the air. An aircraft is usually streamlined from nose to tail to reduce drag.
- Flight control
Aerospace engineers develop control systems for a vehicle's orientation (attitude) about its center of mass. The control systems include actuators, which exert forces in various directions, and generate rotational forces or moments about the aerodynamic center of the aircraft, and thus rotate the aircraft in pitch, roll, or yaw. For example, a pitching moment is a vertical force applied at a distance forward or aft from the aerodynamic center of the aircraft, causing the aircraft to pitch up or down. Control systems are also sometimes used to increase or decrease drag, for example to slow the aircraft to a safe speed for landing.
[edit]Areas of use
The major distinction in aircraft types is between military aircraft, which includes not just combat types but many types of supporting aircraft, and civil aircraft, which include all non-military types.
[edit]Military
Main article: Military aircraft
A military aircraft is any fixed-wing or rotary-wing aircraft that is operated by a legal or insurrectionary armed service of any type.[12] Military aircraft can be either combat or non-combat:
- Combat aircraft are aircraft designed to destroy enemy equipment using its own armament.[12]Combat aircraft divide broadly into fighters and bombers, with several in-between types such asfighter-bombers and ground-attack aircraft (including attack helicopters).
- Non-Combat aircraft are not designed for combat as their primary function, but may carry weapons for self-defense. Non-combat roles include search and rescue, reconnaissance, observation, transport, training, and aerial refueling. These aircraft are often variants of civil aircraft such as the Douglas DC-3 airliner.
Gliders and balloons have also been used as military aircraft; for example, balloons were used for observation during the American Civil War and World War I, and military gliders were used during World War II to land troops.
[edit]Civil
Main article: Civil aviation
Civil aircraft divide into commercial and general types, however there are some overlaps.
Commercial aircraft include types designed for scheduled and charter airline flights, carrying both passengers and cargo. The larger passenger-carrying types are often referred to as airliners, the largest of which are wide-body aircraft. Some of the smaller types are also used in general aviation, and some of the larger types are used as VIP aircraft.
General aviation is a catch-all covering other kinds of private (where the pilot is not paid for time or expenses) and commercial use, and involving a wide range of aircraft types such as business jets (bizjets), trainers, homebuilt, aerobatic types, racers, gliders, warbirds, firefighters, medical transports, and cargo transports, to name a few. The vast majority of aircraft today are general aviation types.
[edit]Experimental
Main article: Experimental aircraft
Experimental aircraft are one-off specials, built to explore some aspect of aircraft design and with no other useful purpose. The Bell X-1 rocket plane, which first broke the sound barrier in level flight, is a famous example.
[edit]Model
Main article: Model aircraft
A model aircraft is a small unmanned type made to fly for fun, for static display, for aerodynamic research or for other purposes. A scale model is a replica of some larger design.
Fixed-wing aircraft
"Aeroplane" and "Airplane" redirect here. For other uses, see Aeroplane (disambiguation) and Airplane (disambiguation).
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A fixed-wing aircraft is an aircraft capable of flight using wings that generate liftdue to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.
A powered fixed-wing aircraft that is propelled forward by thrust from a jet engine orpropeller is typically called an aeroplane, airplane, or simply plane. Other types of powered fixed-wing aircraft include powered paragliders and ground effect vehicles. Unpowered fixed-wing aircraft, including gliders, paragliders, hang gliders and kites, can use moving air to gain height.
Most fixed-wing aircraft are flown by a pilot on board the aircraft, but some are designed to be remotely or computer-controlled.
First attested in English in late 19th century, the word aeroplane derives from the French aéroplane, which comes from the Greek ἀήρ (aēr), "air"[1] + πλάνος (planos), "wandering".[2][3] An ancient Greek term coined from these two words was ἀερόπλανος (aeroplanos), "wandering in air".[4][edit]Etymology
In the United Kingdom and most of the Commonwealth, the term "aeroplane" is used. In the United States, the term "airplane" is applied to these aircraft. The form "aeroplane" is the older of the two, dating back to the mid- to late-19th century.[5]The spelling "airplane" was first recorded in 1907.[6]
[edit]History
Main articles: Aviation history and First flying machine
Many stories from antiquity involve flight, such as the Greek legend of Icarus andDaedalus, and the Vimana in ancient Indian epics. Around 400 BC in Greece,Archytas was reputed to have designed and built the first artificial, self-propelled flying device, a bird-shaped model propelled by a jet of what was probably steam, said to have flown some 200 m.[7][8] This machine may have been suspended for its flight.[9][10]
Some of the earliest recorded attempts with gliders were those by the 9th-century poet Abbas Ibn Firnas and the 11th-century monk Eilmer of Malmesbury; both experiments injured their pilots.[11] Leonardo da Vinci researched the wing design of birds and designed a man-powered aircraft in his Codex on the Flight of Birds (1502).
In 1799, Sir George Cayley set forth the concept of the modern aeroplane as a fixed-wing flying machine with separate systems for lift, propulsion, and control.[12][13]Cayley was building and flying models of fixed-wing aircraft as early as 1803, and he built a successful passenger-carrying glider in 1853.[14] 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.[citation needed] In 1883, the American John J. Montgomery made a controlled flight in a glider.[citation needed] Other aviators who made similar flights at that time were Otto Lilienthal, Percy Pilcher, and Octave Chanute.
Sir Hiram Maxim built a craft that weighed 3.5 tons, with a 110-foot (34-meter) wingspan that was powered by two 360-horsepower (270-kW) steam engines driving two propellers. In 1894, his machine was tested with overhead rails to prevent it from rising. The test showed that it had enough lift to take off. The craft was uncontrollable, which Maxim, it is presumed, realized, because he subsequently abandoned work on it.[15]
In the 1890s, Lawrence Hargrave conducted research on wing structures and developed a box kitethat lifted the weight of a man. His box kite designs were widely adopted and became the prevalent type of aircraft until 1909.[verification needed] Although he also developed a type of rotary aircraft engine, he did not create and fly a powered fixed-wing aircraft.[16]
The Wright brothers flights in 1903 are recognised by the Fédération Aéronautique Internationale(FAI), the standard setting and record-keeping body for aeronautics, as "the first sustained and controlled heavier-than-air powered flight".[17] By 1905, the Wright Flyer III was capable of fully controllable, stable flight for substantial periods.
In 1906, Alberto Santos Dumont made what has been claimed as the first airplane flight unassisted by catapult[18] and set the first world record recognised by the Aéro-Club de France by flying 220 metres (720 ft) in less than 22 seconds.[19] This flight was also certified by the FAI.[20][21]
An early aircraft design that brought together the modern monoplane tractor configuration was the Bleriot VIII design of 1908. It had movable tail surfaces controlling both yaw and pitch, a form of roll control supplied either by wing warping or by ailerons and controlled by its pilot with a joystick and rudder bar. It was an important predecessor of his later Bleriot XI Channel-crossing aircraft of the summer of 1909.[22]
World War I served as a testbed for the use of the aircraft as a weapon. Initially seen by the generals as a "toy", aircraft demonstrated their potential as mobile observation platforms, then proved themselves to be machines of war capable of causing casualties to the enemy. The earliest known aerial victory with a synchronised machine gun-armed fighter aircraft occurred in 1915, by German Luftstreitkräfte LeutnantKurt Wintgens. Fighter aces appeared; the greatest (by number of air victories) was Manfred von Richthofen.
Following WWI, aircraft technology continued to develop. Alcock and Brown crossed the Atlantic non-stop for the first time in 1919. The first commercial flights took place between the United States and Canada in 1919.
Aircraft had a presence in all the major battles of World War II. They were an essential component of the military strategies of the period, such as the German Blitzkrieg or the American and Japanese aircraft carrier campaigns of the Pacific.
The first jet aircraft was the German Heinkel He 178, which was tested in 1939. In 1943, the Messerschmitt Me 262, the first jet fighter aircraft, went into service in the German Luftwaffe. In October 1947, the Bell X-1 was the first aircraft to exceed the speed of sound.[citation needed]
In 1948-49, aircraft transported supplies during the Berlin Blockade. New aircraft types, such as the B-52, were produced during the Cold War.
The first jet airliner, the de Havilland Comet, was introduced in 1952. The Boeing 707, the first widely successful commercial jet, was in commercial service for more than 50 years, from 1958 to 2010. The Boeing 747 was the world's biggest passenger aircraft from 1970 until it was surpassed by the Airbus A380 in 2005.
[edit]Overview
[edit]Structure
The most common configuration of a fixed-wing aircraft includes:
- A fuselage, a long, thin body, often cylindrical, and usually with tapered or rounded ends to make its shape aerodynamically smooth. The fuselage may contain the flight crew, passengers, cargo or payload, fuel and engines the aircraft is designed for or they may be attached to it. The pilots of manned aircraft operate them from a cockpit located at the front or top of the fuselage and equipped with controls and usually windows and instruments. An aircraft may have more than one fuselage, or it may be fitted with booms with the tail located between the booms to allow the extreme rear of the fuselage to be useful for a variety of purposes.
- A large horizontal wing with an airfoil cross-section shape. The wing deflects air downward as the aircraft moves forward, generating lifting force to support the aircraft in flight. The wing also stabilises the aircraft's roll (tilt left or right), and the wing-mounted ailerons control rotation about the roll axis. A wide variety of wing configurations (e.g., multiplane aircraft and delta wingplanform) have been used.
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- A vertical stabiliser a vertical surface mounted at the rear of the aircraft and typically protruding above it. The vertical stabilizer stabilises the aircraft's yaw (turn left or right) and mounts therudder which controls its rotation along that axis.
- A horizontal stabiliser or elevator, or tailplane, mounted at the tail of the aircraft, near the vertical stabilizer. The horizontal stabilizer is used to stabilise the aircraft's pitch (tilt up or down) and mounts the elevators which provide pitch control. A fixed portion of the elevators may be omitted in which case it is termed an all flying tail. Some aircraft use a front-mountedcanard instead of a rear-mounted horizontal stabilizer.
- Powered aircraft have one or more engines that provide thrust to push the aircraft forward through the air. The most common propulsion units are propellers (powered byreciprocating or turbine engines) and jet engines (which provide thrust directly from the engine and usually also from a large fan mounted within the engine).
- Landing gear, a set of wheels, skids, or floats that support the aircraft while it is on the surface. On seaplanes the bottom of the fuselage or floats (pontoons) support it while on the water. On some aircraft the landing gear retract during flight to reduce drag.
There are many different configurations of airplanes. An aircraft may have two or more fuselages, or additional pods or booms. Some aircraft have more than one horizontal or vertical stabilizer, while V-tail aircraft combine the horizontal and vertical stabilizers into a pair of diagonal surfaces. While all of the above items are essential - there have been aircraft flown that have dispensed with any one of the components listed, by modifying other components to fulfill the missing components function. A flying wing aircraft has no discernible fuselage structure and horizontal or vertical stabilizers, though it may have small blisters or pods. The opposite of this is a lifting body which has no wings, though it may have small stabilising and control surfaces. Delta wing aircraft often dispense with the horizontal stabilizer and a few aircraft have even dispensed with the vertical stabilizer.
Most aircraft are largely symmetrical along a plane of symmetry.
[edit]Controls
Main article: Aircraft flight control system
A number of controls allow pilots to direct aircraft in the air. The controls found in a typical fixed-wing aircraft are as follows:
- A yoke or joystick, which controls rotation of the aircraft about the pitch and roll axes. Ayoke resembles a kind of steering wheel, and a control stick is just a simple rod with a hand grip. 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 so that when one is pressed forward the other moves 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. Several aircraft including the Ercoupe dispensed with rudder pedals by linking the rudders to the ailerons for simplicity.
- A Throttle or thrust lever for each engine. These control the power produced by the engines and hence airspeed. On piston-engine powered aircraft Engine Mixture Control levers will also be present.
- Brakes, used to slow and stop the aircraft on the ground, and sometimes for turns on the ground.
These were largely standardized during World War I - prior to which many aircraft manufacturers had their own systems.
Other controls can 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. The spoilers reduce lift for landing.
- Trim controls, which usually take the form of knobs or wheels and are used to adjust pitch, roll, or yaw trim. These are often connected to small airfoils on the trail edge of the control surfaces called 'trim tabs'. Trim is used to reduce the amount of pressure on the control forces needed to maintain a steady course.
- A tiller, a small wheel or lever used to steer the aircraft on the ground in conjunction with or instead of the rudder pedals (primarily found on larger aircraft).
- Undercarriage retraction levers, to raise or lower the undercarriage, for reduced drag while in flight.
- A parking brake, used to prevent the aircraft from rolling when it is parked on the ground.
The controls may 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.
On an aircraft with a pilot and copilot, or instructor and trainee, the aircraft is made capable of control without the crew 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 (militaryfighter aircraft, some taildraggers and aerobatic aircraft) the dual sets of controls are arranged one in front of the other (in tandem). 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 (e.g., Beechcraft Bonanza).
Aircraft that require more than one pilot usually have controls and displays intended to suit each pilot position, but still with sufficient duplication so that any of the 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 conditions.
An unmanned aircraft is controlled remotely or via means such as gyroscopes or other forms of autonomous control.
[edit]Instruments
Instruments provide information to the pilot and the co-pilot. Flight instruments provide information about the aircraft's speed, direction, altitude, and orientation. Powerplant instruments provide information about the status of the aircraft's engines and APU. Systems instrumentsprovide information about the aircraft's other systems, such as fuel delivery, electrical, and pressurisation. Navigation and communication instruments include all the aircraft's radios. Instruments may operate mechanically or electrically, requiring 12VDC, 24VDC, or 400 Hz power systems.[23] An aircraft that uses computerised CRT or LCD displays almost exclusively is said to have a glass cockpit.
The Six Basic instruments (sometimes referred to as the six pack) include:[24]
- An Airspeed Indicator, which indicates the speed at which the aircraft is moving through the surrounding air.
- An Altimeter, which indicates the altitude or height of the aircraft above mean sea level.
- A Heading Indicator, (sometimes referred to as a "directional gyro (DG)"), which indicates the magnetic compass heading that the aircraft's fuselage is pointing towards. The actual direction the aircraft is flying towards is affected by the wind conditions.
- An Attitude indicator, sometimes called an artificial horizon, which indicates the exact orientation of the aircraft about its pitch and roll axes.
- A Vertical Speed Indicator, which shows the rate at which the aircraft is climbing or descending.
- A Turn Coordinator, or Turn and Bank Indicator which helps the pilot maintain the aircraft in a coordinated attitude while turning.
Other Instruments might include:
- A 2-Way Radio to enable communications with other aircraft and Air Traffic Control. Aircraft before World War 2 may not have been equipped with a radio but they are nearly essential now.
- A horizontal situation indicator, shows the position and movement of the aircraft as seen from above with respect to the ground, including course/heading and other information.
- Instruments showing the status of each engine in the aircraft (operating speed, thrust, temperature, rpms, and other variables).
- Combined display systems such as primary flight displays or navigation displays.
- Information displays such as on-board weather radar displays.
- A Radio Direction Finder which indicates the direction to one or more radio beacons and which can be used to determine the aircraft's position.
- A Global Positioning System which works the same as the previous instrument, but communicates with a variety of satellites automatically to provide an accurate position.
[edit]Design and construction
Main article: Aerospace manufacturer
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 authorises 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 authorising 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 aircraft noise pollution is a major concern.
Small aircraft can be designed and constructed by amateurs as homebuilts. Other homebuilt aircraft can be assembled using pre-manufactured kits of parts that can be assembled into a basic aircraft and must then be completed by the builder.
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 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 is rigorously inspected to search for imperfections and defects. After approval by inspectors, the aircraft is put through a series of flight tests to assure that all systems are working correctly and that the aircraft handles properly. Upon passing these tests, the aircraft is ready to receive the "final touchups" (internal configuration, painting, etc.), and is then ready for the customer.
[edit]Safety
Main article: Air safety
When risk is measured by deaths per passenger kilometer, air travel is approximately 10 times safer than travel by bus or rail. However, when using the deaths per journey statistic, air travel is significantly more dangerous than car, rail, or bus travel.[25] Air travel insurance is relatively expensive for this reason- insurers generally use the deaths per journey statistic.[26] There is a significant difference between the safety of airliners and that of smaller private aircraft, with the per-mile statistic indicating that airliners are 8.3 times safer than smaller aircraft.[27]
[edit]Environmental impact
Main article: Aviation and the environment
[edit]Types
[edit]Overall layout
Main article: Wing configuration
This section discusses the number of wings, which is commonly used means of distinguishing different types. A wing is a single unit that runs from one extremity (called a wingtip) to another. Any interuptions caused by a fuselage or engine is ignored for this purpose. This single wing unit generates lift by creating a high pressure area under it, and a low pressure area above it. When these meet at the wingtips, they mix (much like the water going down a drain), causing considerable drag. The more wings, and hence wingtips, an aircraft has, the more of this type of drag (Induced Drag) is created and so having the least number of wings possible is always the most efficient solution - however there are cases where more than one wing has been necessary.
Aside from the number of wings, the shape the wing forms when seen from above is also used as a distinguishing characteristic.
[edit]Monoplane
Main article: monoplane
A monoplane is a fixed-wing aircraft with one main set of wing surfaces, in contrast to a biplaneor triplane. Since the late 1930s it has been the most common form for a fixed wing aircraft. The earliest monoplanes were braced with wires running outside the wing, however lack of knowledge concerning the stresses a wing was subject to resulted in many failures, and in the United Kingdom the Royal Flying Corps banned their use.
The airfoil sections in use at the time were very thin, and could not have a cantilever structure installed within and so attempts were made to provide a stronger structure by adding an external truss - structurally a biplane, but lacking the lower wing. Unfortunately this adds a lot of drag. Junkers began experimenting with thicker airfoils, which had previously been ignored as being unlikely to be efficient. With the thicker airfoils, a cantilever structure contained entirely within the wing was possible, and it had the added bonus that thick airfoils were more efficient than the thin ones previously in use. The defeat of Germany (where all of the research into cantilever monoplanes was occuring) and conservatism in the aviation industry ensured that biplanes would continue to dominate for the next 20 years.
Monoplanes can be differentiated in where the wings attach to the fuselage: The actual point of attachment is called the wing root.
- low-wing, the wing lower surface is level with (or below) the bottom of the fuselage
- mid-wing, the wing is mounted mid-way up the fuselage
- shoulder wing, the wing is mounted above the fuselage middle
- high-wing, the wing upper surface is level with or above the top of the fuselage
- parasol-wing, the wing is located above the fuselage with structural support being typically provided by a system of struts, and, especially in the case of older aircraft, wire bracing. These were particulary popular in the late 1920s and 1930s.
- gull wing is similar to a parasol wing, but has the roots of the wing drop down to pass the structure through the fuselage reducing the number of struts needed. A variant of the gull wing is the inverted gull wing, in which the lower wing takes the form of a "W" from the front, with the middle peak attached to the fuselage. This has the advantages of shortening the undercarriage, and simplifying the wing root design and was most famously used on the Vought F4U Corsairof World War 2.
[edit]Biplanes
Main article: biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. The primary reason many early aircraft were biplanes was that it had a structural advantage over the monoplanes, since both wings formed a Pratt truss, which was immensely strong, however both the struts, and the extra lifting surface produced more drag and thus tended to be slower. Some later biplanes replaced the Pratt truss with a Warren truss which reduced the drag associated with the struts, however it wasn't enough to keep it competitive with cantilever monoplanes which superseded it for most purposes in the late 1930s. Its compact span for a given lifting area allows for great maneuverability and it is still used for aerobatics aircraft and crop dusting. A sesquiplane is a specific type of biplane, where the (usually) lower wing is significantly smaller than the upper wing.
[edit]Triplanes and Multiplanes
Main article: triplane
A triplane is a fixed-wing aircraft equipped with three vertically-stacked wing planes. Tailplanes and canard foreplanes are not included in this count unless they overlap with other wings, nor usually are airfoil fairing on axles. Only a very small number of triplanes were ever built, but the format does have the advantage of allowing an aircraft a high degree of maneuverability combined with a very good climb rate. Due to the drag however, as with biplanes, this type is obsolete and almost never used anymore except for recreations of early triplanes, such as the Fokker Dr.I and Sopwith Triplane. A multiplane is a fixed-wing aircraft with more than three wings, but is a rarely used format as all of the disadvantages of the triplane are even more pronounced.
[edit]Canard
Main article: canard (aeronautics)
Canard is an airframe configuration of fixed-wing aircraft in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing. In contrast a conventional aircraft has a small horizontal stabilizer behind the main wing.[28][29][30]
Canard designs fall into two main classes: the lifting-canard and the control-canard.[31] In the lifting canard the weight of the aircraft is shared between the main wing and the canard wing. In the control-canard, most of the weight of the aircraft is carried by the main wing and the canard wing is used primarily for longitudinal control during maneuvering. Thus, a control-canard mostly operates only as a control surface and is usually at zero angle of attack.
[edit]Tandem wing
A tandem wing aircraft is a fixed wing aircraft with two sets of wings, arranged one in front of the other rather than overlapping each other. NASA research has shown that they must be of different lifting characterists otherwise a severe oscillation will develop, which has limited their use. A tandem wing can be distinguished from a canard by the location of the pitch controls (elevators) on the rear flying surface. A tandem wing may have the front wing larger than the rear, or the reverse. They have the advantage of normally using fewer struts than biplanes, but the induced drag of having multiple wings is still present, though interactions between the wings may reduce this over a conventional biplane.
[edit]Flying wing
A flying wing is a tailless fixed-wing aircraft which has no definite fuselage, with most of the crew, payload and equipment being housed inside the main wing structure.[28]
The flying wing configuration was studied extensively in the 1930s and 1940s, notably by Jack Northrop and Cheston L. Eshelman in the United States, and Alexander Lippisch and the Horten brothers in Germany. After the war, a number of experimental designs were based on the flying wing concept, but the known difficulties remained intractable. Some general interest continued until the early 1950s but designs did not necessarily offer a great advantage in range and presented a number of technical problems, leading to the adoption of "conventional" solutions like the Convair B-36 and the B-52 Stratofortress. Due to the practical need for a deep wing, the flying wing concept is most practical for designs in the slow-to-medium speed range, and there has been continual interest in using it as a tactical airlifter design.
Interest in flying wings was renewed in the 1980s due to their potentially low radar reflection cross-sections. Stealth technology relies on shapes which only reflect radar waves in certain directions, thus making the aircraft hard to detect unless the radar receiver is at a specific position relative to the aircraft - a position that changes continuously as the aircraft moves. This approach eventually led to the Northrop B-2 Spirit stealth bomber. In this case the aerodynamic advantages of the flying wing are not the primary needs. However, modern computer-controlled fly-by-wire systems allowed for many of the aerodynamic drawbacks of the flying wing to be minimised, making for an efficient and stable long-range bomber.
[edit]Blended
Main article: blended wing
Blended Wing Body aircraft have a flattened and airfoil shaped body, which produces most of the lift to keep itself aloft, and distinct and separate wing structures, though the wings are smoothly blended in with the body.
Thus BWB incorporates design features from both a futuristic fuselage and flying wing design. The purported advantages of the BWB approach are efficient high-lift wings and a wide airfoil-shaped body. This enables the entire craft to contribute to liftgeneration with the result of potentially increased fuel economy.
[edit]Lifting body
Main article: lifting body
A lifting body is a fixed-wing aircraft configuration in which the body itself produces lift. In contrast to a flying wing, which is a wing with minimal or no conventional fuselage, a lifting body can be thought of as a fuselage with little or no conventional wing. Whereas a flying wing seeks to maximize cruise efficiency at subsonic speeds by eliminating non-lifting surfaces, lifting bodies generally minimize the drag and structure of a wing for subsonic, supersonic, and hypersonicflight, or, spacecraft re-entry. All of these flight regimes pose challenges for proper flight stability.
Lifting bodies were a major area of research in the 1960s and 70s as a means to build a small and lightweight manned spacecraft. The US built a number of famous lifting body rocket planes to test the concept, as well as several rocket-launched re-entry vehicles that were tested over the Pacific. Interest waned as the US Air Force lost interest in the manned mission, and major development ended during the Space Shuttle design process when it became clear that the highly shaped fuselages made it difficult to fit fuel tankage.
[edit]Wing types
Main article: wing
[edit]Straight Wing
A straight wing is a wing planform in which the centre of lift across the wing forms a straight line from wingtip to wingtip, or nearly so. This was the dominant form of wing until early transsonic aircraft adopted swept wings to reduce transsonic drag. Modern fighters were able to readopt straight wings thanks to advances in both aircraft structures and aerodynamic high lift devices.
[edit]Swept Wing
A swept wing is a wing planform is which the wings are angled backwards so that the tips are closer to the tail than the roots, resembling an arrow. This was done to reduce the drag associated when approaching supersonic speeds and is the form primarily used on airliners and other jet trasnports. A variant of the swept wing is the forward swept wing in which the wings are angled forwards. This has serious structural implications and so hasn't been used very much, but has been tried because a regular swept wing has poor stall characteristics. When an aircraft's lift is less than what is required for it to continue flying and stalls, ideally the nose should drop, which allows the aircraft to regain flying speed. In a swept wing aircraft, the normal result of a stall is for the nose to go up, making recovery difficult.
[edit]Variable geometry
Variable geometry aircraft are 'fixed wing' aircraft where the wing configuration can be changed in flight.
A variable-sweep wing is an aeroplane wing that may be swept back and then returned to its original position during flight. While variable-sweep provides many advantages, particularly in takeoff distance, load-carrying ability, and the fast, low-level penetration role, the configuration imposes a considerable penalty in weight and complexity. The advent of relaxed stability flight control systems in the 1970s negated many of the disadvantages of a fixed platform. No new variable-sweep wing aircraft have been built since the Tu-160 (1980).
Variable camber wings aircraft changes the camberof the airfoil (1933), and varies the area and camber of the wing (1937). The various flaps and slats on the control surfaces of modern commercial airliners perform a similar function.
A variable-incidence wing has an adjustable angle of incidence (the angle between the wing and the fuselage) in order to reduce landing and take-off distances.
The necessary components add extra weight to the aircraft and increase maintenance costs. In some aircraft the benefits outweigh the costs, and variable-incidence functionality is incorporated into the design, most notably with the F-8 Crusader, although other designs have used it, such as the Martin XB-51. No modern aircraft has used this design since the F-8.
An oblique wing (also called a slew wing) is a variable geometry wing concept. On an aircraft so equipped, the wing is designed to rotate on center pivot, so that one tip is swept forward while the opposite tip is swept aft. By changing its sweep angle in this way, drag can be reduced at high speed (with the wing swept) without sacrificing low speed performance (with the wing perpendicular).
[edit]Delta Wing
Main article: delta-wing
The delta wing is a wing planform in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ). The primary advantage of the delta wing is that, with a large enough angle of rearward sweep, the wing’s leading edge will not contact the shock waveboundary formed at the nose of the fuselage as the speed of the aircraft approaches and exceedstransonic to supersonic speed. Additionally a canard-delta gives from a smaller shift in the center of lift with increasing mach number than a wing and tail configuration.[32] Another advantage is that as the angle of attack increases, the leading edge of the wing generates a vortex which energizes the flow, giving the delta a very high stall angle but this gives high induced drag. Pure delta-wings fell out of favour somewhat due to their undesirable characteristics, notably flow separation at high angles of attack, and their high drag at low altitudes. Nevertheless, many modern fighter aircraft, such as the JAS 39 Gripen, the Eurofighter Typhoon and the Dassault Rafale use a combination ofcanards and a delta wing.
[edit]Propulsion
See also: Powered aircraft and Aircraft engine
Fixed-wing aircraft can be sub-divided according to the means of propulsion they use.
[edit]Unpowered fixed-wing aircraft
Main article: Glider (aircraft)
Gliders are fixed-wing aircraft that are intended primarily for unpowered flight. Sailplanes, hang gliders, and paragliders are gliders used mainly for recreation. After launch, further energy is obtained through the skillful exploitation of rising air in the atmosphere. Gliders that are used for the sport of gliding have high aerodynamic efficiency. The highest lift-to-drag ratio is 70:1, though 50:1 is more common. Glider flights of thousands of kilometres at average speeds over 200 km/h have been achieved. The glider is most commonly launched by a tow-plane or by a winch. Some gliders, called motor gliders, are equipped with engines (often retractable), and some are capable of self-launching. The most numerous unpowered aircraft are hang gliders and paragliders. These are foot-launched and are in general slower, smaller, and less expensive than sailplanes. Hang gliders most often have flexible wings given shape by a frame, though some have rigid wings. Paragliders have no frames in their wings.Military gliders have been used in war to deliver assault troops, and specialised gliders have been used in atmospheric and aerodynamicresearch. Rocket-powered aircraft and spaceplanes have also made unpowered landings.
[edit]Propeller aircraft
Smaller and older propeller aircraft make use of reciprocating engines (or piston engines) to turn apropeller to create thrust. The amount of thrust a propeller creates is determined by its disk area - the area in which the blades rotate. If the area is too small, efficiency is poor, and if the area is large, the propeller must rotate at a very low speed to avoid going supersonic and creating a lot of noise, and not much thrust. Because of this limitation, propellers are favoured for aircraft which travel at below mach .5, while jets are a better choice above that speed. They may be quieter than jet engines (though not always) and may cost less to purchase maintain and so remain common on light general aviation aircraft such as the Cessna 172. Larger modern propeller aircraft such as the Dash 8 use a jet engine to turn the propeller, primarily because an equivalent piston engine in power output would be much larger are more complex.
[edit]Jet aircraft
Jet aircraft are aircraft propelled by jet engines, which are used because the aerodynamic limitations of propellers do not apply to jet propulsion. These engines are much more powerful than a reciprocating engine for a given size or weight and are comparatively quiet and work well at higher altitude. Most modern jet aircraft use turbofan jet engines which balance the advantages of a propeller, while retaining the exhaust speed and power of a jet. This is essentially a ducted propeller attached to a jet engine, much like a turboprop, but with a smaller diameter. When installed on an airliner, it is efficient so long as it remains below the speed of sound (or subsonic). Jet fighters and other supersonic aircraft that do not spend a great deal of time supersonic also often use turbofans, but to function, air intake ducting is needed to slow the air down so that when it arrives at the front of the turbofan, it is subsonic. When passing through the engine, it is then re-accelerated back to supersonic speeds. To further boost the power output, fuel is dumped into the exhaust stream, where it ignites. This is called an afterburner and has been used on both pure jet aircraft and turbojet aircraft although it is only normally used on combat aircraft due to the amount of fuel consumed, and even then may only be used for short periods of time.Supersonic airliners (e.g. Concorde) are no longer in use largely because flight at supersonic speed creates a sonic boom which is prohibited in most heavily populated areas, and because of the much higher consumption of fuel supersonic flight requires.
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 use flaps and leading edge devices to control of lift and speed. Many also usethrust reversers to slow down the aircraft upon landing.
[edit]Solar-powered aircraft
Solar-powered aircraft use solar cells to generate energy for electric motors which in turn drive propellers. On 8 July 2010, the manned Solar Impulse became the first solar-powered aeroplane to fly through an entire night.[33]
[edit]Rocket-powered aircraft
Main article: Rocket-powered aircraft
In World War II, the Germans deployed the Me 163 Komet rocket-powered aircraft. The first fixed-wing aircraft to break the sound barrier in level flight was a rocket plane – the Bell X-1. The laterNorth American X-15 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, althoughrocket-assisted take offs are used for some military aircraft. Recent rocket aircraft include theSpaceShipOne and the XCOR EZ-Rocket.
[edit]Ramjet aircraft and scramjet aircraft
A ramjet is a form of jet engine that contains no major moving parts and can be particularly useful in applications requiring a small and simple engine for high-speed use, such as missiles. The D-21 Tagboard was an Mach 3+ reconnaissance drone that was cancelled in 1971. The SR-71's engines ran 80% as ramjets at high speeds.
Scramjet aircraft are in the experimental stage. A scramjet has a very simple engine design. It works by air being forced into one side of a tube-like engine. That air is ignited by fuel, causing it to come out hotter and faster on the other side. This engine requires high speed in order to work, but it is suitable for the speeds at which it travels. The NASA X-43 is an experimental unmanned scramjet with a world speed record for a jet-powered aircraft – Mach 9.7, nearly 12,000 kilometres per hour (7,500 mph) at an altitude of about 36,000 metres (118,000 ft). The X-43A set the flight speed record in 2004.
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