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A "glider" is an unpowered aircraft. The most common types of glider are today used for sporting purposes. The design of these types enables them to climb using rising air. This has created the sport of gliding. Although many gliders do not have engines, there are some that use engines occasionally.

Early gliders had no cockpit and the pilot sat on a small seat located just ahead of the wing. These were known as "primary gliders" and they were usually launched from the tops of hills, though they are also capable of short hops across the ground while being towed behind a vehicle. To enable gliders to soar more effectively than primary gliders, the designs minimized drag. Gliders now have very smooth, narrow fuselages and very long, narrow wings with a high aspect ratio.

The early gliders were made mainly of wood with metal fastenings, stays and control cables. New materials such as carbon-fiber, glass-fiber and Kevlar have since been used with computer-aided design to increase performance. Drag has also been minimized by more aerodynamic shapes and retractable undercarriages.

With each generation of materials and with the improvements in aerodynamics, the performance of gliders has increased. One measure of performance is the glide ratio. A ratio of 30:1 means that in smooth air a glider can travel forward 30 meters while only losing 1 meter of altitude.

Due to the critical role that aerodynamic efficiency plays in the performance of a glider, gliders often have state of the art aerodynamic features seldom found in other aircraft. The wings of a modern racing glider have a specially designed low-drag laminar flow airfoil. After the wings' surfaces have been shaped by a mold to great accuracy, they are then highly polished. Vertical winglets at the ends of the wings are computer-designed to decrease drag and improve handling performance. Special aerodynamic seals are used at the ailerons, rudder and elevator to prevent the flow of air through control surface gaps. Turbulator devices in the form of a zig-zag tape or multiple blow holes positioned in a span-wise line along the wing are used to trip laminar flow air into turbulent flow at a desired location on the wing. This flow control prevents the formation of laminar flow bubbles and ensures the absolute minimum drag. Bug-wipers may be installed to wipe the wings while in flight and remove insects that are disturbing the smooth flow of air over the wing.

Modern competition gliders are also designed to carry jettisonable water ballast (in the wings and sometimes in the vertical stabiliser). The extra weight provided by the water ballast is advantageous if the lift is likely to be strong, and may also be used to adjust the glider's center of mass. To avoid undue stress on the airframe, gliders must jettison any water ballast before landing.

Pilots can land accurately by controlling their rate of descent using spoilers, also known as air brakes. These are metal devices which extend from either the upper-wing surface or from both upper and lower surfaces, thereby destroying some lift and creating additional drag. A wheel-brake also enables a glider to be stopped after touchdown, which is particularly important in a short field.

UNIT 6

AIRPLANE COMPONENTS

Preparing to Read

Airplanes have many applications in a variety of fields. Brainstorm as many uses of the airplane as possible.

Look at the picture of an airplane. Name the airplane components you know, share the terms with your partner.

Reading

Read the text and try to guess the meaning of underlined words from the content of the text.

AIRPLANE COMPONENTS

A. The airplane consists of six principal structural units, namely, the power plant, the fuselage, the wing, the tail unit (or empennage), flight controls and the landing gear

( undercarriage ).

B. The power plant is a source of power. It provides power and propels the airplane. Nowadays there are many types of aircraftengines. These engines have one thing in common. The energy is derived from a chemical reaction which takes place inside the engine itself. Nacelles are compartments housing the power plant or engine and its accessories. The engine is really the heart of the airplane.

C. The fuselage is the main body of the airplane which is divided into some cabins (compartments). A nose cabin is a pilot’s cabin (cockpit). The cockpit houses the crew, the flight controls and flight instrument panels. The next section of the fuselage is a wing centre-section. Passenger compartments are situated there. The rear part of the fuselage is designed for cargo rooms and for mounting a tail unit on it.

D. The wing is the main lifting surface of sweptback shape. Its function is to support the aircraft in flight producing lifting force. There may be different arrangement, shapes and number of the wings. At the trailing edge of the wing there are movable parts which are called ailerons, flaps and trimmer tabs (trimmers).

E. The tail unit (empennage) provides the necessary stability and consists of vertical and horizontal control surfaces. The vertical plane is called a fin. It has a movable part – a rudder. The horizontal plane is a stabilizer. The movable part at the trailing edge of the stabilizer is an elevator.

F. Three basic flight control surfaces are the ailerons, the elevators, and the rudder. They are hinged so to move and thus to deflect the air stream passing over there. The ailerons are located at the trailing edge and near the tips of the wings. They control the motion of the plane about the longitudinal axis. The elevators are hinged to the horizontal stabilizers and control the airplane's movement up and down about the lateral axis. The rudder is hinged to the vertical stabilizer (fin), and it controls the movement of the airplane around the vertical axis.

J. The landing gear (undercarriage) carries the wheels on which the aircraft moves on the ground. Struts attach it to the fuselage. Two different arrangements of landing wheels are in use today. They are conventional tricycle gears and the landing gear with a skid. The landing gear may be retractable and non-retractable.

Comprehension Check