Powered heavier-than-air craft supported in flight by fixed wings. Airplanes can be propelled by the thrust of a jet engine, a rocket engine, or airscrew (propeller), as well as combinations of these. They must be designed aerodynamically, as streamlining ensures maximum flight efficiency. The shape of a plane depends on its use and operating speed—aircraft operating at well below the speed of sound need not be as streamlined as supersonic aircraft. The Wright brothers flew the first powered plane (a biplane) in Kitty Hawk, North Carolina, US, 1903. For the history of aircraft and aviation, see flight.
Efficient streamlining prevents the formation of shock waves over the body surface and wings, which would cause instability and power loss. The wing of an airplane has the cross-sectional shape of an airfoil, being broad and curved at the front, flat underneath, curved on top, and tapered to a sharp point at the rear. It is so shaped that air passing above it is speeded up, reducing pressure below atmospheric pressure. This follows from Bernoulli's principle and results in a force acting vertically upward, called lift, which counters the plane's weight. In level flight lift equals weight. The wings develop sufficient lift to support the plane when they move quickly through the air. The thrust that causes propulsion comes from the reaction to the air stream accelerated backward by the propeller or the gases shooting backward from the jet exhaust. In flight the engine thrust must overcome the air resistance, or drag. Drag depends on frontal area (for example, large, airliner; small, fighter plane) and shape (dr.
ag coefficient); in level flight, drag equals thrust. The drag is reduced by streamlining the plane, resulting in higher speed and reduced fuel consumption for a given power. Less fuel need be carried for a given distance of travel, so a larger payload (cargo or passengers) can be carried.
The shape of a plane is dictated principally by the speed at which it will operate (see aeronautics). A low-speed plane operating at well below the speed of sound (about 965 kph/600 mph) need not be particularly well streamlined, and it can have its wings broad and projecting at right angles from the fuselage. An aircraft operating close to the speed of sound must be well streamlined and have swept-back wings. This prevents the formation of shock waves over the body surface and wings, which would result in instability and high power loss. Supersonic planes (faster than sound) need to be severely streamlined, and require a needle nose, extremely swept-back wings, and what is often termed a “Coke-bottle” (narrow-waisted) fuselage, in order to pass through the sound barrier without suffering undue disturbance. To give great flexibility of operation at low as well as high speeds, some supersonic planes are designed with variable geometry, or swing wings. For low-speed flight the wings are outstretched; for high-s.
peed flight they are swung close to the fuselage to form an efficient delta wing configuration.
Aircraft designers experiment with different designs in wind tunnel tests, which indicate how their designs will behave in practice. Fighter jets in the 1990s are being deliberately designed to be aerodynamically unstable, to ensure greater agility. This is achieved by a main wing of continuously modifiable shape, the airflow over which is controlled by a smaller tilting foreplane. New aircraft are being made lighter and faster (to Mach 3) by the use of heat-resistant materials, some of which are also radar-absorbing, making the aircraft “invisible” to enemy defenses.
Planes are constructed using light but strong aluminum alloys such as duralumin (with copper, magnesium, and so on). For supersonic planes special stainless steel and titanium may be used in areas subjected to high heat loads. The structure of the plane, or the airframe (wings, fuselage, and so on) consists of a surface skin of alloy sheets supported at intervals by struts known as ribs and stringers. The structure is bonded together by riveting or by powerful adhesives such as epoxy resins. In certain critical areas, which have to withstand very high stresses (such as the wing roots), body panels are machined from solid metal for extra strength.
On the ground a plane rests on wheels, usually in a tricycle arrangement, with a nose wheel and two wheels behind, one under each wing. For all except some light planes the landing gear, or undercarriage, is retracted in flight to reduce drag.
Seaplanes, which take off and land on water, are fitted with nonretractable hydrofoils.
Wings by themselves are unstable in flight, and a plane requires a tail to provide stability. The tail comprises a horizontal tailplane and vertical tailfin, called the horizontal and vertical stabilizer respectively. The tail plane has hinged flaps at the rear called elevators to control pitch (attitude). Raising the elevators depresses the tail and inclines the wings upward (increases the angle of attack). This speeds the airflow above the wings until lift exceeds weight and the plane climbs. However, the steeper attitude increases drag, so more power is needed to maintain speed and the engine throttle must be opened up. Moving the elevators in the opposite direction produces the reverse effect. The angle of attack is reduced, and the plane descends. Speed builds up rapidly if the engine is not throttled back. Turning (changing direction) is effected by moving the rudder hinged to the rear of the tailfin, and by banking (rolling) the plane. It is banked by moving the ailerons, interconnected flaps at the re.
ar of the wings which move in opposite directions, one up, the other down.
In planes with a delta wing, such as Concorde, the ailerons and elevators are combined. Other movable control surfaces, called flaps, are fitted at the rear of the wings closer to the fuselage. They are extended to increase the width and camber (curve) of the wings during takeoff and landing, thereby creating extra lift, while movable sections at the front, or leading edges, of the wing, called slats, are also extended at these times to improve the airflow. To land, the nose of the plane is brought up so that the angle of attack of the wings exceeds a critical point and the airflow around them breaks down; lift is lost (a condition known as stalling), and the plane drops to the runway. A few planes (for example, the Harrier) have a novel method of takeoff and landing, rising and dropping vertically by swiveling nozzles to direct the exhaust of their jet engines downward. The helicopter and convertiplane use rotating propellers (rotors) to obtain lift to take off vertically.
The control surfaces of a plane are operated by the pilot on the flight deck, by means of a control stick, or wheel, and by foot pedals (for the rudder). The controls are brought into action by hydraulic power systems. Advanced experimental high-speed craft known as control-configured vehicles use a sophisticated computer-controlled system. The pilot instructs the computer which maneuver the plane must perform, and the computer, informed by a series of sensors around the craft about the altitude, speed, and turning rate of the plane, sends signals to the control surface and throttle to enable the maneuver to be executed.
(Alternate spelling: aeroplane).
An aircraft that has fixed a wing and is powered by propellers or jets; SYN. aeroplane, plane.
Sprava za plovljenje vazduhom teža od vazduha; avion.
Naprava za letenje teža od vazduha; aeroplan.
Aeroplan, vazduhoplov, mašina za letenje.
Sprava za letenje.