What Is ?

Aileron roll: A 360-degree roll accomplished by applying and maintaining coordinated aileron pressure. The maneuver is begun with the nose slightly raised, because, as the airplane rolls, its lift vector is no longer countering its weight, so the nose of the ariplane drops significantly during the maneuver. Back stick pressure is maintained throughout,so that even when the aircraft is upside down, positive seat pressure of about1g(1 times the force of gravity) will be felt. As the airplane approaches wings-level at the end of the maneuver, aileron pressue is removed and the roll stops.

Ailerons: Control surfaces located on the outer part of the wing of an airplane, used to help the airplane turn. As the ailerons hinge down on one wing, they push the air downward, making that wing tilt upward. This motion tips the airplane to the side and helps it to turn, a process also known as banking. The pilot manipulates the ailerons from the cockpit by moving the control column or stick left and right. Right movement rolls the airplane to the right, and left movement rolls the airplane to the left.

Air density: The product of altitude and air temperature.

Airfoil: A structure designed to obtain reaction upon its surface from the air through which it moves. Early airfoils typically had little more than a slightly curved upper surface and a flat undersurface. Over the years, airfoils have been adapted to meet changing needs. By the 1920′s, airfoils typically had a rounded surface, with the greatest height being reached in the first third of the chord line, or width. In time, both upper and lower surfaces were curved to a greater or lesser degree, and the thickest part of the airfoil gradually moved backward. By moving forward in the air, the wing’s airfoil obtains a reaction useful for flight from the air passing over its surface. In flight, the airfoil of the wing normally produces the greatest amount of lift, but propellers, tail surfaces, and the fuselage also function as airfoils and generate varying amounts of lift. If the velocity of air is increased over a certain point of an airfoil, the pressure of the air is decreased. Air flowing over the curved top surface of the wing’s airfoil moves faster than the air flowing on the bottom surface, decreasing the pressure on top. The higher pressure from below pushes or lifts the wing up to the lower-pressure area. Simultaneously, the air flowing along the underside of the wing is deflected downward, providing an equal and opposite reaction and contributing to total lift.

Airplane: Any of a class of heavier-than-air, fixed-wing aircraft propelled by a screw propeller or by a high-velocity jet, and supported by the dynamic reaction of the air against its wings.

Airspeed: Wind velocity.

Bank: The angle between an aircraft’s wings and the horizon, as viewed from the rear of the aircraft. An airplane with its wings level has zero degrees of bank.

Banking: The turning of an airplane by pushing the control stick in the cockpit to the left or right, which makes the ailerons on one wing go down and the ailerons on the other wing go up and makes the airplane tip to the left or right.

Biplane: An airplane with two sets of wings, one above the other. Between 1903 and 1909, the Wright brothers’ biplanes inaugurated the era of powered flight, and biplanes predominated in military and commercial aviation from World War I through the early 1930′s. However, the biplane’s greater maneuverability could not offset the speed advantage of the lighter monoplane, with one set of wings. After World War II, biplanes were used only for special purposes such as crop dusting and sport flying. A biplane with one much smaller, usually lower, wing is called a sesquiplane.

Civil aircraft: All nonmilitary airplanes, including private and business planes and commercial airliners. Private aircraft are personal planes used for pleasure flying and are often single-engine monoplanes with nonretractable landing gear. They can be very sophisticated, however, and may include such variants as “warbirds,” ex-military planes flown for nostalgic reasons; primary trainers; large bombers; and homebuilts, aircraft built from scratch or from kits by the owner.

Business aircraft are used to generate revenues for their owners and include everything from small single-engine aircraft used to train pilots or to transport small packages over short distances to four-engine executive jets that can travel across continents and oceans. They are used by salespeople, prospectors, farmers, doctors, missionaries, and many others, and their primary purpose is to free their users from airline schedules and airport operations. They also serve as executive perquisites and as sophisticated inducements for potential customers. Other business aircraft include those used for agricultural operations, traffic reporting, forest-fire fighting, medical evacuation, pipeline surveillance, and freight hauling.

Commercial airliners are used to haul passengers and freight on a scheduled basis between selected airports. They range in size from single-engine freight carriers to Boeing 747 jumbojets and in speeds from less than 200 miles per hour to those greater than the speed of sound.

Cockpit: The pilot’s seat in an airplane, where all of the controls and instruments are located.

Control stick: The airplane control, located in the cockpit, to which the ailerons are connected. Pushing the stick to the left or the right makes the ailerons on one wing go down and the ailerons on the other wing go up. This action makes the plane tip to the left or the right and is called banking.

Drag: One of the four principles of flight, along with thrust, weight, and lift. Drag is the force encountered as an airplane pushes through the air, which tends to slow the airplane down. There are two types of drag, and an airplane must fight its way through both kinds in order to maintain steady flight. Profile or parasite drag is the same kind of drag experienced by all kinds of objects in a flow. This type of drag is caused by the airplane as it pushes the air out of the way as it moves forward. This drag can be easily experienced by a motorist if he or she places his or her hand out of the window of a moving vehicle. Induced drag is the result of the generation of lift. This drag is the part of the force produced by the wing that’s parallel to the relative wind. Objects that create lift must also overcome this induced drag.

Elevators: Movable flaps attached to the horizontal stabilizer used to change the angle of attack of the wing which will, in turn, change the pitch, moving the airplane up and down. The angle of attack is the angle between the wing and the relative wind. Moving the control stick forward or backward operates the horizontal stabilizer, which in turn moves the elevator down or up, respectively.

Engine: This part of the airplane produces thrust or forward movement necessary to sustain flight. Thrust is one of the four basic principles of flight, and all aircraft need some type of thrust to propel themselves aloft. The most common means of generating thrust on powered airplanes comes from propellers or jets. Whether an aircraft has a propeller or jet, both of these produce thrust by accelerating a mass of air to the rear of the aircraft. The movement of this air to the rear creates an unbalanced force pushing the aircraft forward. Propellers are essentially revolving wings situated so that the lift that they produce is used to pull or push the airplane. Most modern high-speed aircraft use jet engines rather than propellers. Jets produce thrust by burning propellant or jet fuel mixed with air and then by forcing the rapidly expanding gases rearward. In order to operate from zero airspeed on up, jets use enclosed fans on a rotating shaft to compress the incoming air and channel it into a combustion chamber where fuel is added and ignited. The burning gases keep the shaft turning by rotating a fan before exiting the engine.

In a jet engine, the inlet area is small compared to that of a propeller. As the air exits the compressor section of the engine, it enters the combustion chamber, where fuel is added. This densely packed air-fuel mixture is ignited, and the resultant explosion accelerates the gases out of the rear of the engine at a very high rate of speed. This chemical acceleration of the air or combustion adds to the thrust produced by the engine. Most jet fighter aircraft have afterburners, which add raw fuel into the hot jet exhaust and thereby generate even more thrust through higher accelerations of the air. The jet generates large amounts of thrust by chemically accelerating the air as the result of combustion. The fact that the jet compresses the air as much as 40 times allows the jet aircraft to fly at higher altitudes, where the air is too thin for propellers. Engine thrust is controlled by a throttle for each respective engine. As the throttle is moved forward, more fuel is added and the engine rotates faster and produces more thrust. Thrust is also directly related to engine revolutions per minute (RPM). The amount of thrust is often referred to as percentage RPM.

Flaps: Extensions of the trailing or inner edge of the wing, which can be deflected downward as much as 45 degrees. They help the airplane to fly slower. Many flaps effectively increase the wing area, adding to lift and drag. The angle to which the flaps are deployed determines the relative amount of additional lift or drag obtained. At smaller angles, lift is typically increased over drag, while at greater angles, drag is dramatically increased over lift. The flaps slide back and forth and are controlled by a lever in the cockpit. Flaps come in a wide variety of types, including the simple split flap, in which a hinged section of the undersurface of the trailing edge of the wing can be extended. The Fowler flap extends the wing area by deploying on tracks, creating a slotted effect.

Fly-by-light: Flight control system in which signals pass between computers and actuators along fiber optic leads.

Fly-by wire: Flight control system with electrical signaling, without mechanical interconnection between cockpit controls and control surfaces.

Fuselage: The central body of the airplane to which the wings, tail, and engines are all attached. In a modern passenger airplane, passengers sit only in the top half of the fuselage. The fuselage also houses the cockpit, where all of the controls necessary for operating and controlling the airplane are located. Cargo is housed in the bottom half of the fuselage. The fuselage is generally streamlined as much as possble.

Global Positioning System (GPS): U.S. civil-military satellite-based precision navigational aid.

Gravity: The earth’s attractive force and one of the four forces of flight.

Green aircraft: Unpainted flyable aircraft that are furnished with only basic equipment.

Horizontal stabilizer: A fixed-position airfoil that stabilizes the pitch of the airplane. When a wing produces lift, it also develops a force that tries to pitch the airplane forward. The horizontal stabilizer prevents this unwanted pitch from occuring.

Landing gear: On conventional aircraft, the landing gear consists of wheels or tires with supports and shock absorbers that assist in takeoffs and landings. To reduce drag while the airplane is flying, most wheels fold up into the body of the airplane after takeoff. On many smaller aircraft, the wheels do not fold up after takeoff.

Lift: An upward force that causes an object to rise. In aircraft it may be produced by downward-facing propellers, or by a moving wing with an airfoil shape, or the specially curved shape of an airplane wing. Lift is one of the four basic principles of flight. Forces are produced by the wing as the air flows around it. Lift is the part that is perpendicular to the relative wind. The other part contributes to drag.

Loop: A 360-degree change in pitch. Because the airplane will climb several thousand feet during the maneuver, it is started at a relatively high airspeed and power setting. The pilot, once satisfied with the airspeed and throttle setting, will pull back on the control stick until about 3 gs are felt. The nose of the ariplane will go up and steadily increasing climb will be established. As the maneuver continues, positive g is maintained by continuing the pull. The airplane continues to increase its pitch until it has pitched through a full circle. When the world is right-side-up again, the pilot releases the back stick pressure and returns the aircraft to level flight.

Mach number: The ratio of the speed of the aircraft to the speed of sound, named after the Austrian physicist Ernst Mach.

Maneuverability: The ability to change the speed and flight direction of an airplane. A highly maneuverable airplane, such as a fighter, has the ability to accelerate or to slow down very quickly and also to turn sharply. Quick turns with short turn radii place high loads on the wings as well as on the pilot. These loads are referred to as g forces and the ability to “pull g’s” is considered one measure of maneuverability. One g is the force acting on the airplane in level flight imposed by the gravitational pull of the earth. Five g’s in a maneuver exerts five times the gravitational force of the earth.

Monoplane: A type of aircraft with a single pair of wings. The monoplane design has been nearly universally adopted over multiplane configurations, because airflow interference between adjacent wings reduces efficiency. The first monoplane was constructed by the Romanian inventor Trajan Vuja, who made a flight of 40feetonMarch 18,1906. Louis Bleriot of France built a monoplane in 1907 and flew it across the English Channel two years later. Monoplane design proved itself conclusively during World War II, and since then the craft has completely supplanted the biplane except for special purposes such as crop dusting.

Payload: In civil aircraft, a disposable load generating revenue such as passengers, cargo, mail, and other paid items. In military aircraft, payload loosely refers to the total load of weapons, cargo equipment, or other mission equipment carried.

Performance: The motion of the airplane along its flight path, how fast, slow, high, and far an aircraft can fly. In a general sense, performance may also refer to the ability of an airplane to accomplish the different aspects of its mission. Included in such a comprehensive designation are minimum and maximum speed, maximum altitude, maximum rate of climb, maximum range and speed for maximum range, rate of fuel consumption, takeoff and landing distance, and weight of potential payload. Differences in weather conditions such as temperature, pressure, humidity and winds strongly affect these performance indices.

Pitch: The angle between the airplane’s body (lengthwise) and the ground. An airplane going straight up would have a pitch attitude of 90 degrees and one in level flight, about zero degrees.

Propeller: The part of the airplane that produces thrust or forward movement necessary to sustain flight. This turning blade on the front of the airplane moves it through the air. Propellers are basically rotating airfoils, and they include two-blade fixed-pitch, four-blade controllable- (variable) pitch, and eight-blade contrarotating-pitch propellers. The blade angle on fixed-pitch propellers is set for only one flight regime, and this restriction limits their performance. Some fixed-pitch propellers can be adjusted on the ground to improve performance in one part of the flight regime. Variable-pitch propellers permit the pilot to adjust the pitch to suit the flight condition, using a low pitch for takeoff and a high pitch for cruising flight. Most modern aircraft have an automatic variable-pitch propeller, which can be set to operate continuously in the most efficient mode for the flight regime. If an engine fails, most modern propellers can be feathered or mechanically adjusted so that they present the blade edgewise to the line of flight, thereby reducing drag.

Range: The distance that an aircraft can fly before running out of fuel. The range of a fighter airplane or bomber, for example, is one-half of its radius. A range of 1,000 miles, then, means that such an airplane can fly from its base for a distance of 500 miles, drop its ordnance, and fly 500 miles back to base. Some of the many factors that influence range are very subtle, such as poor seals on cooling doors or small pockets of disturbed air around the engine inlets.

Reciprocating engine: Often an internal combustion engine; types differ based on the arrangement of the cylinders. Horizontally opposed engines employ four to six cylinders lying flat and arrayed two or three on each side. In a radial engine the cylinders are mounted in a circle around the crankshaft, sometimes inbanks of two or three. Once the dominant piston-engine type, radials are now in only limited production.

Relative wind: The direction that air is going as it passes the airplane relative to the airplane. Relative wind is not related to the wind speed on the ground.

Roll: The tilting motion that the airplane makes when it turns.

Rudder: The hinged part on the back of an aircraft’s tail that helps to turn the aircraft. The vertical part of the tail, the rudder controls the sideways movement of the airplane, called the yaw. The rudder is one of the least frequently used airplane controls, and most flying can be safely accomplished without it.

Seaplane: Any of a class of aircraft that can land, float, and take off on water. Seaplanes with boatlike hulls are also known as flying boats; those with separate pontoons or floats are known as floatplanes. The first practical seaplanes were built and flown in the United States by GlennH. Curtiss in 1911 and 1912. Curtiss’s inventions led to British aircraft called F-boats of World War I. Such boats originated naval air missions such as over-ocean patrol, antisubmarine warfare, mine laying, and air-sea rescue. After the war, commercial versions of the same seaplanes set the range and endurance records of the time. In 1919, the U.S. Navy’s water-based NC-4 made the first crossing of the North Atlantic, via the Azores. By the late 1920′s, the largest and fastest aircraft of the world were seaplanes. Their utility and versatility were dramatized by a 1929 Soviet flight from Moscow to New York City via Siberia of a Tupolev ANT-4 fitted with floats and by fleets of Italian planes that flew from Rome to Rio de Janeiro and from Rome to Chicago in the 1930′s. After the outbreak of World War II, the military and commercial significance of seaplanes gradually diminished, partly because of the increased range of land-based planes and partly because of the construction of land bases and aircraft carriers. Following World War II, the development of water-based aircraft continued, but only on a small scale.

A seaplane must have sufficient buoyancy to float on water and must also have some means for supporting its weight while moving along the water surface at flying speeds. It must be able to take off and land with a margin of stability and control on the part of the pilot. Its structure must be strong enough to withstand the shock of landing, and its water resistance must be low enough to permit reasonably short takeoff runs. Curtiss pro-videdtwo ways of meeting these requirements. First, he developed the float seaplane, which was essentially a land plane with buoyant floats or pontoons substituted for the landing wheels. Second, he created the flying boat, in which the main float and the fuselage are combined in a single boatlike body. In either case, float design includes a stepped bottom to facilitate takeoff. As speed and lift increase, the seaplane lifts onto its step so that it is barely skimming the water with friction at a minimum. Curtiss also added a retractable landing wheel gear to a float seaplane or flying boat, thereby creating the amphibian aircraft capable of operating from land runways or water.

Short takeoff and landing (STOL) aircraft: Any of several fixed-wing aircraft capable of taking off and landing on runways considerably shorter than those needed by conventional aircraft. Most aircraft of this type require a runway no more than 500 feet long, which is about ten times shorter than the average runway. STOL aircraft were developed to meet the needs exemplified by bush or wilderness flying, where steep climb and approach angles and low landing speed are more important than high cruising speeds. These capabilities are provided by a combination of aerodynamic devices, such as the augmentor wing, which was introduced during the early 1960′s. It consists of full span slats at the leading or front edge of the wing and full span double-slotted flaps at the trailing or rear edge. Manipulation of these devices and an air-duct system allow use of air turbulence and prop wash for added lift and drag.

The first version of the STOL was test-flown in 1954 by the U.S. Navy. Since then, the STOL has been adopted by the armed forces of the United States and the United Kingdom for combat operations.

Stall: The reaction of a wing in flight when a given angle of attack is exceeded. The stall is characterized by a progressive loss of lift for an increase in angle of attack.

Straight and level flight: Flight maintained at a given altitude, airspeed, and heading. This condition is achieved and maintained by equalizing all opposing forces. Lift must equal weight so that the airplane does not climb or descend. Thrust must equal drag so that the airplane does not speed up or slow down. The wings are kept level so that the airplane does not turn. Any imbalance will result in a change in altitude or airspeed and hence an interruption of straight and level flight.

Tail: The rear section of an aircraft with many movable parts. The pilot controls these parts from the cockpit. The tail includes the rudder and the elevators.

Thrust: The force produced by the engines. Thrust works opposite of and counteracts drag. Thrust is the forward movement that is necessary to sustain flight and is one of the four basic principles of flight.

Trim: When the controls of an airplane are moved from neutral, it takes a certain amount of pressure to hold them in position in the airflow. Trim gets rid of this pressure and effectively changes the center of the controls, or the neutral position where there is no stick pressure.

Vertical stabilizer: The yaw stabilizer of the airplane. This keeps the nose of the airplane pointed into the relative wind.

Vertical takeoff and landing (VTOL) aircraft: Any of several unconventional aircraft with rotating wing systems, such as the helicopter and autogiro. They may also have rotatable jet systems capable of vertical liftoff and landing in areas that only slightly exceed the overall dimensions of the aircraft. The first operational VTOL jet aircraft was the British Royal Air Force Harrier. Its jet engines are mounted horizontally, with their blast deflected downward to effect vertical thrust for takeoff. It achieves high subsonic speeds in level flight.

Weight: The force produced by the mass of the airplane interacting with the earth’s gravitational field. The force must be counteracted by lift in order to maintain flight and is one of the four principles of flight. There are five types of weight. Basic weight is the weight of the basic aircraft plus weapons, unusable fuel, oil, ballast, survival kits, oxygen, and any other internal or external equipment that is on board the aircraft and will not be disposed of during flight. Operating weight is the sum of basic weight and items such as crew, crew baggage, steward equipment, pylons and racks, emergency equipment, special mission fixed equipment and all other nonexpendable items not in basic weight. Gross weight is the total weight of an aircraft, including its contents and externally mounted items, at any time. Landing gross weight is the weight of the aircraft, its contents, and external items when the aircraft lands. Zero-fuel weight is the weight of the aircraft without any usable fuel, determined by structural limitations of the aircraft.

Wing: The appendages or arms of an airplane. Wings provide the principal lifting force of the aircraft. They hold the airplane aloft by creating lift from the air rushing over them. Like all airplane parts, the wings should be light and strong, but also flexible to absorb sudden gusts of wind. The shape of a wing resembles an elongated drop of water lying on its side. Usually the top is curved more than the bottom, making the upper surface slightly longer than the bottom. Since air passing over the top and bottom must reach the rear of the wing at the same time, the air passing over the top must not only travel faster but also changes direction and is deflected downward. It is a wing’s ability to produce efficiently a force perpendicular to the air passing over it that makes heavier-than-air flight possible. All wings essentially produce lift the same way by pushing down on the air.

They thereby force air downward relative to the wing. Most of the time, the top of the wing does the majority of the pushing on the air. The top and the bottom of the wing combine to produce a force, and part of this force perpendicular to the relative wind is lift.

The wing plan form is the shape that it forms when seen from above. Delta wings are triangular wings lying at roughly a right angle to the fuselage. The supersonic Concorde passenger jet airliner features delta wings. Swept wings are angled, usually to the rear and often at an angle of about 35 degrees. Forward-swept wings also are used on some research craft. Some aircraft have wings that may be adjusted in flight to attach at various angles to the fuselage. These are called variable-incidence wings. Variable-geometry wings, or swing wings, can vary their sweep in flight. The sweep is the angle of a wing with respect to the plane perpendicular to the longitudinal axis of the craft. Swept-wing aircraft have military applications. Another configuration limited to military craft is the so-called flying wing, a tailless craft having all of its elements encompassed within the wing structure. One example of such an aircraft is the B-2 bomber of the U.S. Air Force. The lifting-body aircraft, such as the U.S. space shuttle, generates lift in part or totally by the shape of the fuselage rather than the wing, which is consequently severely reduced in size or altogether absent.

Yaw: The angle between the fuselage of the airplane and the relative wind as seen from above the airplane. Yaw is the term that pilots use to describe the turning left or right of the airplane. Yaw is the sideways movement of the airplane. Normally an airplane is flown without yaw.

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