Also called:
aeroplane or plane

The pilot controls thrust by adjustment of the control levers for the engine. In an aircraft with a reciprocating engine these can consist of a throttle, mixture control (to control the ratio of fuel and air going to the engine), and propeller control as well as secondary devices such as supercharger controls or water-alcohol injection. In a turbojet engine, the principal control is the throttle, with auxiliary devices such as water injection and afterburners. With water injection, a water-alcohol mixture is injected into the combustion area to cool it, which allows more fuel to be burned. With afterburners, fuel is injected behind the combustion section and ignited to increase thrust greatly at the expense of high fuel consumption. The power delivered by reciprocating and jet engines is variously affected by airspeed and ambient air density (temperature, humidity, and pressure), which must be taken into consideration when establishing power settings. In a turboprop engine, power is typically set by first adjusting the propeller speed with a propeller lever and then adjusting fuel flow to obtain the desired torque (power) setting with the power lever.

Propellers

Propellers are basically rotating airfoils, and they vary in type, including two-blade fixed pitch, four-blade controllable (variable) pitch, and eight-blade contrarotating pitch. 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 (mechanically adjusted) so that they present the blade edgewise to the line of flight, thereby reducing drag. In large piston engine aircraft, some propellers can be reversed after landing to shorten the landing run. (Jet engines have thrust reversers, usually incorporating a noise-suppression system, to accomplish the same task.)

Instrumentation

The pilot also has an array of instruments by which to check the condition of flight, the engine, and other systems and equipment. In small private aircraft, the instrumentation is simple and may consist only of an altimeter to register height, an airspeed indicator, and a compass. The most modern commercial air transports, in contrast, have fully automated “glass cockpits” in which a tremendous array of information is continually presented on cathode-ray tube displays of the aircraft’s height, attitude, heading, speed, cabin pressure and temperature, route, fuel quantity and consumption, and the condition of the engines and the hydraulic, electrical, and electronic systems. These displays also provide readouts for both routine and emergency checklists. Aircraft are also provided with inertial guidance systems for automatic navigation from point to point, with continuous updating for changing weather conditions, beneficial winds, or other situations. Cockpits have become so automated that training emphasis is focused on “resource management” to assure that the crew members keep alert and do not become complacent as their aircraft flies automatically from one point to the next.

This array of instrumentation is supplemented by vastly improved meteorological forecasts, which reduce the hazard from weather, including such difficult-to-predict elements as wind shear and microburst. In addition, the availability of precise positioning from Earth-orbiting satellites makes navigation a far more exact science. Sophisticated defogging and anti-icing systems complement instrumentation for operation in adverse weather.

Flight simulators

There are three factors that force the increased use of flight simulators in training: the complexity of larger aircraft, the expense of their operation, and the increased complexity of the air-traffic control environment in which they operate. Modern simulators duplicate aircraft exactly in terms of cockpit size, layout, and equipment. They also duplicate the external environment and create a realistic sense of flying by means of the three-axis motion platform on which they are placed. Perhaps the most important use of flight simulators is to train crews in emergency situations, so that they can experience firsthand situations that could not safely be demonstrated in actual flight training. However, the simulator is also far less expensive than using actual aircraft for routine transition and proficiency training. So realistic is simulator training that airline crews are sometimes qualified on a new aircraft in a simulator prior to ever flying the aircraft itself.

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Types of aircraft

There are a number of ways to identify aircraft by type. The primary distinction is between those that are lighter than air and those that are heavier than air.

Lighter-than-air

Aircraft such as balloons, nonrigid airships (blimps), and dirigibles are designed to contain within their structure a sufficient volume that, when filled with a gas lighter than air (heated air, hydrogen, or helium), displaces the surrounding ambient air and floats, just as a cork does on the water. Balloons are not steerable and drift with the wind. Nonrigid airships, which have enjoyed a rebirth of use and interest, do not have a rigid structure but have a defined aerodynamic shape, which contains cells filled with the lifting agent. They have a source of propulsion and can be controlled in all three axes of flight. Dirigibles are no longer in use, but they were lighter-than-air craft with a rigid internal structure, which was usually very large, and they were capable of relatively high speeds. It proved impossible to construct dirigibles of sufficient strength to withstand routine operation under all weather conditions, and most suffered disaster, either breaking up in a storm, as with the U.S. craft Shenandoah, Akron, and Macon, or through ignition of the hydrogen, as with the German Hindenburg in 1937.

Heavier-than-air

This type of aircraft must have a power source to provide the thrust necessary to obtain lift. Simple heavier-than-air craft include kites. These are usually a flat-surfaced structure, often with a stabilizing “tail,” attached by a bridle to a string that is held in place on the ground. Lift is provided by the reaction of the string-restrained surface to the wind.

Another type of unmanned aircraft is the unmanned aerial vehicle (UAV), commonly called drones or sometimes remotely piloted vehicles (RPVs). These aircraft are radio-controlled from the air or the ground and are used for scientific and military purposes.

Unpowered manned heavier-than-air vehicles must be launched to obtain lift. These include hang gliders, gliders, and sailplanes.

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Hang gliders are aircraft of various configurations in which the pilot is suspended beneath the (usually fabric) wing to provide stability and control. They are normally launched from a high point. In the hands of an experienced pilot, hang gliders are capable of soaring (using rising air columns to obtain upward gliding movement).

Gliders are usually used for flight training and have the capability to fly reasonable distances when they are catapulted or towed into the air, but they lack the dynamic sophistication of sailplanes. These sophisticated unpowered craft have wings of unusually high aspect ratio (that is, a long wing span in proportion to wing width). Most sailplanes are towed to launch altitude, although some employ small, retractable auxiliary engines. They are able to use thermals (currents more buoyant than the surrounding air, usually caused by higher temperature) and orographic lift to climb to higher altitude and to glide for great distances. Orographic lift results from the mechanical effect of wind blowing against a terrain feature such as a cliff. The force of the wind is deflected upward by the face of the terrain, resulting in a rising current of air.

Ultralights, which were originally merely hang gliders adapted for power by the installation of small engines similar to those used in chain saws, have matured into specially designed aircraft of very low weight and power but with flying qualities similar to conventional light aircraft. They are intended primarily for pleasure flying, although advanced models are now used for training, police patrol, and other work, including a proposed use in combat.

Experimental craft have been designed to make use of human and solar power. These are very lightweight, sophisticated aircraft, designed with heavy reliance on computers and using the most modern materials. Paul MacCready of Pasadena, California, U.S., was the leading exponent of the discipline; he first achieved fame with the human-powered Gossamer Condor, which navigated a short course in 1977. Two of his later designs, the human-powered Gossamer Albatross and the solar-powered Solar Challenger, successfully crossed the English Channel. Others in the field have carried on MacCready’s work, and a human-powered helicopter has been flown. Solar-powered aircraft are similar to human-powered types, except that they use solar panels to convert the Sun’s energy directly to power an electric motor.