Aircraft


Aircraft fall into two broad categories:

   * Heavier than air aerodynes, including autogyros, helicopters and
     variants, and conventional fixed-wing aircraft: aeroplanes in
     Commonwealth English, airplanes in North American English.

     Fixed-wing aircraft generally use a propeller or jet engine to provide
     thrust, which moves the craft forward through the air. The movement of
     air over the wings produces lift, which allows the aircraft to fly.
     Exceptions are gliders which have no engines and gain their thrust from
     gravity. That is, in order to maintain their forward speed they must
     descend in relation to the air (but not necessarily in relation to 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. Similarly, STOL stands for Short Take Off and Landing.

   * Lighter than air aerostats: 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.

Types of aircraft

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

Also see this list of articles on particular aircraft types, and this list
of aircraft.

By design

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

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 (which have a non-rigid construction)
and rigid airships, which have a rigid frame. The best-known type of rigid
airship is the Zeppelin.

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 of some kind. With engine lift, the aircraft defeats gravity by sheer
engine power.

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 surfaces produce lift,
usually by profiting from Bernoulli's principle (aeroplane or airplane).

In a "conventional" configuration, the lift surfaces are placed in front of
a control surface or tailplane. 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.

The reverse configuration is the canard type, where small horizontal control
surfaces are placed forward of the wings, near the nose of the aircraft.

Other possibilities include the delta-wing, where lift and horizontal
control surfaces are 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, 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.

A second large category of aerodynamically lifted aircraft are the
rotary-wing aircraft. Here, the lift is provided by rotating rotors. The
best-known examples of this category are the helicopter, the earlier
autogyro, and the tiltrotor aircraft (such as the V-22 Osprey).

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

By propulsion

Some types of aircraft, such as the balloon or glider, do not have any
propulsion. Balloons drift with the wind. 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.

Most early aircraft used a piston-engine with propeller as propulsion.
Although the configuration of the engine can vary (rotary, radial, inline),
they all work according to the same principles.

Just prior to World War II, the first jet engines emerged. Different types
exist, such as the ramjet, pulse jet, turbojet, and the turboprop, the
latter of which still uses a propeller.

By usage

Three major uses for aircraft may be seen: recreational, military, and commercial.

For recreation, almost any type of aircraft can be used, although they are
usually small ones. Gliders and balloons are used almost exclusively for
recreational purposes although they have been used in times of war in the
past. For instance, balloons were used for observation in the American Civil
War and World War I. Gliders were used to deliver troops into occupied
territory during World War II.

The first widespread use of military aircraft was for reconnaissance and
surveillance in World War I. Soon they were adapted for attacking the ground
or enemy vehicles/ships/guns/aircraft as well, 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.

Eventually, two-seat trainers were developed for the purpose of instructing
new pilots. The use of transport aircraft enabled the rapid movement of
supplies, ammunition, cargo, troops and also casualty evacuation; transport
aircraft were also used to drop paratroopers. Tankers are used to refuel
planes in mid-air, thus increasing their operational range.

Commercial aviation can be divided in passenger transport and cargo
transport. For the former, large planes have been developed that can
transport up to 500 passengers over large distances. Commercial cargo
aircraft are often similar to military transport aircraft, or might be
adapted from the passenger fleets of an earlier era.

Other uses include search-and-rescue operations (especially by helicopters),
border protection and water-bombing (fire-fighting). Further divisions can
be drawn between aircraft designs having a conventional (wheeled)
undercarriage, and amphibious floatplanes or flying boats.