An Airbus A340 of SriLankan Airlines. This is a wide_bodied long_haul aircraft
, with _24 Business Class seats and 288 Economy Class seats.
A hot air balloon seen from directly below. The burner flame is firing into the envelope
Bell 206B Jet Ranger III helicopter
This article refers to the tool of travel. For other meanings, see aircraft (disambiguation).
An aircraft is any machine capable of atmospheric flight.
Categories and classification
Aircraft fall into two broad categories:
Heavier than air
- Heavier than air aerodynes, including autogyros, helicopters and variants, and conventional fixed-wing aircraft: aeroplanes in Commonwealth English (excluding Canada), airplanes in North American English. 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 airfoil produces lift that causes the aircraft to fly. Exceptions are gliders which have no engines and gain their thrust, initially, from winches or tugs and then from gravity and thermal currents. That is, in order to maintain their forward speed they 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 both lift and thrust. The abbreviation VTOL is applied to aircraft other than helicopters that can take off or land vertically. Likewise, STOL stands for Short Take Off and Landing.
Lighter than air
- Lighter than air aerostats: hot air balloons and airships. Aerostats float in air in the same way that a ship floats in water, by displacing the air around the craft with a lighter gas (helium or hydrogen), or hot air. The distinction between a balloon and an airship is that an airship has some means of controlling forward motion and steering, while balloons simply drift with the wind.
See also: List of aviation, aerospace and aeronautical terms
There are several ways to classify aircraft. Below, we describe classifications by design, propulsion and usage.
Also see this List of aircraft.
Types of aircraft
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 airships (sometimes called dirigible balloons) such as blimps (that have non-rigid construction) and rigid airships that have a rigid frame. The most successful type of rigid airship was the Zeppelin. The best-known Zeppelin was the Hindenburg which was destroyed in a fire at Lakehurst, NJ, in 1937.
In heavier-than-air aircraft, we can discern two major ways to produce the lift: aerodynamic lift and engine lift. In the case of aerodynamic lift, the aircraft is kept in the air because of aerodynamics, usually by means of wings, or rotors, of some kind. With engine lift, the aircraft defeats gravity by use of vertical thrust, being greater than its weight.
Examples of engine lift aircraft are rockets, and so-called VTOL planes such as the Hawker Harrier.
Among aerodynamically lifted aircraft, the largest number falls in the category of fixed_wing aircraft, where horizontal airfoils produce lift, by profiting from Bernoulli's equation and, to some extent, the Coanda effect (aeroplane or airplane).
The forerunner of these type of aircraft is the kite. Kites have been built which carried a person high up in the air where observation could be made for great distances. Kites depend upon the tension between the cord which anchors it to the ground and the force of the wind currents.
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.
The number of lift surfaces varied greatly in the pre-1950 period, as biplanes (two wings) and triplanes (three wings) were numerous in the early days of aviation. Subsequently most planes 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).
A variable geometry ('swing-wing') has also been employed in a few examples of combat aircraft (the F-111, Panavia Tornado, F-14 Tomcat and B-1 Lancer, among others).
The lifting body configuration where the body itself produce lift has been tested. So far the only significant practical application of the lifting body was in the Space Shuttle and its test vehicles, but many aircraft generate lift from other than wings alone.
A second large category of aerodynamically lifted aircraft are the rotary_wing aircraft. Here, the lift is provided by rotating aerofoils or rotors. The best-known examples of this category 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.
And finally the flapping-wing ornithopter is a category of its own. These designs may have considerable potential but are not yet practical.
- Reference (http://history.nasa.gov/SP-367/appenda.htm)
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. 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). Other designs, like the V engine used in automobiles, have had little success in aviation. 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 MSL because there is less oxygen available for combustion; to solve that problem, some piston engines have turbochargers or turbonormalizers that compress the air before feeding it into the engine; these piston engines can often operate efficiently at 20,000 ft MSL or higher, altitudes that require the use of supplemental oxygen or cabin pressurisation.
Pressurized 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 MSL. 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 planes 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).
The major distinction in aircraft usage is between military aviation, which includes all uses of airplane for military purposes (such as combat, patrolling, search and rescue, reconnaissance, transport, and training), and civil aviation, which includes all uses of airplanes for non-military purposes. In most countries, military and civil aviation operate under different sets of regulations, and sometimes conflicts occur when the two share the same airspace.
When people think of military aircraft, they often think of combat planes like fighters or bombers, but those represent only a small minority of the category. In fact, 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 transport in the U.S. military and the Dakota in Britain and the Commonwealth. Even the little fabric-covered two-seater Piper J3 Cub had a military version, the L-4 trainer. 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 gliders were used to land Allied troops in Europe after D-Day during [[World War II].
Combat aircraft themselves, though used a handful of times for reconnaissance during the Italo-Turkish War, did not come into widespread use until World War I, at first also for reconnaissance and surveillance. Soon they were adapted for attacking the ground or enemy vehicles/ships/guns/aircraft, and the first 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 planes 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 and supporting ground troups.
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. Commercial general aviation pilots (when not flying privately) 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 airplanes (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 Jet Ranger 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.
- Smithsonian Air and Space Museum (http://www.nasm.si.edu/) - Excellent online collection with a particular focus on history of aircraft and spacecraft
- Virtual Museum (http://invention.psychology.msstate.edu/Tale_of_Airplane/taleplane.html)
- Prehistory of Powered Flight (http://www.centennialofflight.gov/essay/Prehistory/PH-OV.htm)
- Aircraft-Info.net (http://www.aircraft-info.net)
- HomebuiltAircraft.com (http://www.HomebuiltAircraft.com)- Information Portal about Homebuilt Aircraft
- The Evolution of Modern Aircraft (NASA) (http://www.hq.nasa.gov/office/pao/History/SP-468/contents.htm)
- Airforces (http://www.DefenceTalk.com)
- Series of Photo Essays on British Aviation (http://www.challoner.com/aviation/index.html)
- Check-Six (http://www.check-six.com) - Information on historic aircraft crashes including the X-15 and Flying Wing