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Aircraft

2007 Schools Wikipedia Selection. Related subjects: Air & Sea transport

   An Airbus A380, currently the world's largest passenger airliner
   Enlarge
   An Airbus A380, currently the world's largest passenger airliner

   An aircraft is any vehicle or craft capable of atmospheric flight.

Categories and classification

   Aircraft fall into two broad categories:
   A hot air balloon takes off from Royal Victoria Park, Bath, England
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   A hot air balloon takes off from Royal Victoria Park, Bath, England

Heavier than air

   Heavier than air aircraft, or aerodynes, include autogyros, helicopters
   and gyrocopters, and conventional fixed-wing aircraft (aeroplanes).
   Fixed-wing aircraft generally use an internal-combustion engine in the
   form of a piston engine (with a propeller) or a turbine engine (jet or
   turboprop), to provide thrust that moves the craft forward through the
   air. The movement of air over the wings produces lift that causes the
   aircraft to fly. Exceptions include gliders which have no engines and
   gain their thrust, initially, from winches or tugs and then from
   gravity and thermal currents. For a glider to maintain its forward
   speed it must descend in relation to the air (but not necessarily in
   relation to the ground). Helicopters and autogyros use a spinning rotor
   (a rotary wing) to provide lift; helicopters also use the rotor to
   provide thrust. Gyrodynes are aircraft intermediate between helicopters
   and autogyros, whose rotor is sometimes powered (often by a jet at its
   tips) but which do not have a tail rotor. Heliplanes are combination
   aircraft with both a rotor and wings; they can take off and land
   vertically, and hover, like a helicopter, but use their wings for high
   speed flight. The abbreviation " VTOL" is applied to aircraft that can
   take off and land vertically. " STOL" stands for Short Take Off and
   Landing.

Lighter than air

   Lighter than air aerostats: balloons and airships. Aerostats use
   buoyancy to float in the air in much the same manner as ships float on
   the water. In particular, these aircraft use a relatively low density
   gas such as helium, hydrogen or heated air, to displace the air around
   the craft. The distinction between a balloon and an airship is that an
   airship has some means of controlling both its forward motion and
   steering itself, while balloons are carried along with the wind.

Types of aircraft

   There are several ways to classify aircraft. Below, we describe
   classifications by design, propulsion and usage.

By design

   A size comparison of some of the largest aircraft in the world. The
   Airbus A380-800 (largest airliner), the Boeing 747-8, the Antonov
   An-225 (aircraft with the greatest payload) and the Hughes H-4 "Spruce
   Goose" (aircraft with greatest wingspan).
   Enlarge
   A size comparison of some of the largest aircraft in the world. The
   Airbus A380-800 (largest airliner), the Boeing 747 -8, the Antonov
   An-225 (aircraft with the greatest payload) and the Hughes H-4 "Spruce
   Goose" (aircraft with greatest wingspan).

   A first division by design among aircraft is between lighter-than-air,
   aerostat, and heavier-than-air aircraft, aerodyne.

   Examples of lighter-than-air aircraft include non-steerable balloons,
   such as hot air balloons and gas balloons, and steerable airships
   (sometimes called dirigible balloons) such as blimps (that have
   non-rigid construction) and rigid airships that have an internal frame.
   The most successful type of rigid airship was the Zeppelin. Several
   accidents, such as the Hindenburg fire at Lakehurst, NJ, in 1937 led to
   the demise of large rigid airships.

   In heavier-than-air aircraft, there are two ways to produce lift:
   aerodynamic lift and engine lift. In the case of aerodynamic lift, the
   aircraft is kept in the air by wings or rotors . With engine lift, the
   aircraft defeats gravity by use of vertical thrust. Examples of engine
   lift aircraft are rockets, and VTOL aircraft such as the
   Hawker-Siddeley Harrier.

   Among aerodynamically lifted aircraft, most fall in the category of
   fixed-wing aircraft, where horizontal airfoils produce lift, by
   profiting from airflow patterns determined by Bernoulli's equation and,
   to some extent, the Coanda effect.

   The forerunner of these type of aircraft is the kite. Kites depend upon
   the tension between the cord which anchors it to the ground and the
   force of the wind currents. Much aerodynamic work was done with kites
   until test aircraft, wind tunnels and now computer modelling programs
   became available.

   In a "conventional" configuration, the lift surfaces are placed in
   front of a control surface or tailplane. The other configuration is the
   canard where small horizontal control surfaces are placed forward of
   the wings, near the nose of the aircraft. Canards are becoming more
   common as supersonic aerodynamics grows more mature and because the
   forward surface contributes lift during straight-and-level flight.
   A collection of NASA test aircraft
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   A collection of NASA test aircraft

   The number of lift surfaces varied in the pre-1950 period, as biplanes
   (two wings) and triplanes (three wings) were numerous in the early days
   of aviation. Subsequently most aircraft are monoplanes. This is
   principally an improvement in structures and not aerodynamics.

   Other possibilities include the delta wing, where lift and horizontal
   control surfaces are often combined, and the flying wing, where there
   is no separate vertical control surface (e.g., the B-2 Spirit).

   A variable-geometry wing (or " swing-wing") has also been employed in a
   few examples of combat aircraft, such as the F-111, Panavia Tornado,
   F-14 Tomcat and B-1 Lancer, among others.

   The lifting body configuration is where the body itself produce lift.
   So far, the only significant practical application of the lifting body
   is in the Space Shuttle, but many aircraft generate lift from nothing
   other than wings alone.

   A second category of aerodynamically lifted aircraft are the
   rotary-wing aircraft. Here, the lift is provided by rotating aerofoils
   or rotors. The best-known examples are the helicopter, the autogyro and
   the tiltrotor aircraft (such as the V-22 Osprey). Some craft have
   reaction-powered rotors with gas jets at the tips but most have one or
   more lift rotors powered from engine-driven shafts.

   A further category might encompass the wing-in-ground-effect types, for
   example the Russian ekranoplan also nicknamed the "Caspian Sea Monster"
   and hovercraft; most of the latter employing a skirt and achieving
   limited ground or water clearance to reduce friction and achieve speeds
   above those achieved by boats of similar weight.

   A recent innovation is a completely new class of aircraft, the fan
   wing. This uses a fixed wing with a forced airflow produced by
   cylindrical fans mounted above. It is (2005) in development in the
   United Kingdom.

   And finally the flapping-wing ornithopter is a category of its own.
   These designs may have potential, but currently have no major practical
   applications.
   Gossamer Albatross, a human-powered aircraft
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   Gossamer Albatross, a human-powered aircraft

By propulsion

   Some types of aircraft, such as the balloon or glider, do not have any
   propulsion. 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). For gliders, takeoff takes place from a high location, or
   the aircraft is pulled into the air by a ground-based winch or vehicle,
   or towed aloft by a powered "tug" aircraft. Airships combine a
   balloon's buoyancy with some kind of propulsion, usually propeller
   driven.

   Until World War II, the internal combustion piston engine was virtually
   the only type of propulsion used for powered aircraft. (See also:
   Aircraft engine.) The piston engine is still used in the majority of
   aircraft produced, since it is efficient at the lower altitudes used by
   small aircraft, but the radial engine (with the cylinders arranged in a
   circle around the crankshaft) has largely given way to the
   horizontally-opposed engine (with the cylinders lined up on two sides
   of the crankshaft). Water cooled V engines, as used in automobiles,
   were common in high speed aircraft, until they were replaced by jet and
   turbine power. Piston engines typically operate using avgas or regular
   gasoline, though some new ones are being designed to operate on diesel
   or jet fuel. Piston engines normally become less efficient above
   7,000-8,000 ft (2100-2400 m) above sea level because there is less
   oxygen available for combustion; to solve that problem, some piston
   engines have mechanically powered compressors (blowers) or
   turbine-powered turbochargers or turbonormalizers that compress the air
   before feeding it into the engine; these piston engines can often
   operate efficiently at 20,000 ft (6100 m) above sea level or higher,
   altitudes that require the use of supplemental oxygen or cabin
   pressurization.
   A turboprop-engined DeHavilland Twin Otter adapted as a floatplane
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   A turboprop-engined DeHavilland Twin Otter adapted as a floatplane

   During the forties and especially following the 1973 energy crisis,
   development work was done on propellers with swept tips or even
   scimitar-shaped blades for use in high-speed commercial and military
   transports.

   Pressurised aircraft, however, are more likely to use the turbine
   engine, since it is naturally efficient at higher altitudes and can
   operate above 40,000 ft. Helicopters also typically use turbine
   engines. In addition to turbine engines like the turboprop and
   turbojet, other types of high-altitude, high-performance engines have
   included the ramjet and the pulse jet. Rocket aircraft have
   occasionally been experimented with. They are restricted to rather
   specialised niches, such as spaceflight, where no oxygen is available
   for combustion (rockets carry their own oxygen).

By usage

   The major distinction in aircraft usage is between military aviation,
   which includes all uses of aircraft for military purposes (such as
   combat, patrolling, search and rescue, reconnaissance, transport, and
   training), and civil aviation, which includes all uses of aircraft for
   non-military purposes.

Military aircraft

   Combat aircraft like fighters or bombers represent only a minority of
   the category. Many civil aircraft have been produced in separate models
   for military use, such as the civil Douglas DC-3 airliner, which became
   the military C-47/C-53/R4D transport in the U.S. military and the
   "Dakota" in the UK and the Commonwealth. Even the small fabric-covered
   two-seater Piper J3 Cub had a military version, the L-4 liaison,
   observation and trainer aircraft. In the past, 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
   cargo gliders were used during World War II to land troops.

   Combat aircraft themselves, though used a handful of times for
   reconnaissance and surveillance during the Italo-Turkish War, did not
   come into widespread use until the Balkan War when first air-dropped
   bomb was invented and widely used by Bulgarian Air Force against
   Turkey.

   On January 24 1913 the first naval co-operation mission took place by
   Greek Air Force planes above the Dardanelles. During World War I many
   types of aircraft were adapted for attacking the ground or enemy
   vehicles/ships/guns/aircraft, and the first aircraft designed as
   bombers were born. In order to prevent the enemy from bombing, fighter
   aircraft were developed to intercept and shoot down enemy aircraft.
   Tankers were developed after World War II to refuel other aircraft in
   mid-air, thus increasing their operational range. By the time of the
   Vietnam War, helicopters had come into widespread military use,
   especially for transporting, supplying, and supporting ground troops.
   Interior of Qatar Airways flight
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   Interior of Qatar Airways flight

Civil aviation

   Bell 206B JetRanger III helicopter
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   Bell 206B JetRanger III helicopter

   Civil aviation includes both scheduled airline flights and general
   aviation, a catch-all covering other kinds of private and commercial
   use. The vast majority of flights flown around the world each day
   belong to the general aviation category, ranging from recreational
   balloon flying to civilian flight training to business trips to
   firefighting to medevac flights to cargo transportation on freight
   aircraft.

   Within general aviation, the major distinction is between private
   flights (where the pilot is not paid for time or expenses) and
   commercial flights (where the pilot is paid by a customer or employer).
   Private pilots use aircraft primarily for personal travel, business
   travel, or recreation. Usually these private pilots own their own
   aircraft and take out loans from banks or specialized lenders to
   purchase them. Commercial general aviation pilots use aircraft for a
   wide range of tasks, such as flight training, pipeline surveying,
   passenger and freight transport, policing, crop dusting, and medical
   transport ( medevac). Piston-powered propeller aircraft (single-engine
   or twin-engine) are especially common for both private and commercial
   general aviation, but even private pilots occasionally own and operate
   helicopters like the Bell JetRanger or turboprops like the Beechcraft
   King Air. Business jets are typically flown by commercial pilots,
   although there is a new generation of small jets arriving soon for
   private pilots.

Future Developments

   A number of future aircraft development projects are under way, ranging
   from relatively simple aerodynamic enhancements (e.g addition of
   winglets) to the development of new engine technologies (e.g. Pratt and
   Whitney's Geared Turbofan) to all-new designs such as the Blended
   Wing-Body. The Peebles Fanwing is an example of a new approach to lift.

   To date there has been only limited consideration of alternative fuels
   for aircraft. Hydrogen is perhaps the most obvious alternative to
   existing kerosene/ gasoline-type fuels, but the technical and
   infrastructural challenges inherent in developing a commercially usable
   hydrogen-powered aircraft are huge. The Russian manufacturer Tupolev
   built a prototype hydrogen-powered version of the Tu-154 airliner,
   named the Tu-155, which made its first flight in 1989.

   Retrieved from " http://en.wikipedia.org/wiki/Aircraft"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
