Airplanes Essay Research Paper One of the — страница 2

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operations on unimproved fields, because of the added clearance amid the propeller and the ground. However, airplanes with this type of gear are more difficult to handle during ground operations. When the third wheel is located on the nose, it is called a nosewheel. This design is referred to as tricycle gear. An airplane with this type of gear has a steerable nosewheel, which you control through use of the rudder pedals. Landing gear can also be classified as either fixed or retractable. Fixed gear always remains extended, while retractable gear can be stowed for flight to reduce air resistance and increase airplane performance. Just as shock absorbers are needed on a car, some shock absorbing device is needed on the landing gear. Shock struts are designed for this purpose. They

absorb bumps and jolts, as well as the downward force of landing. Airplane brakes operate on the same principles as automobile brakes, but they do have a few significant differences. For example, airplane brakes usually are located on the main wheels, and are applied by separate pedals. Because of this, operating the brake on the left independently of the brake on the right, or vice versa is possible. This capability is referred to as differential braking. It is important during ground operations when you need to supplement nosewheel steering by applying the brakes on the side toward the direction of turn. In fact, differential braking is extremely important on conventional gear airplanes, since some do not have a steerable wheel. In small airplanes, the powerplant includes both

the engine and the propeller. The primary function of the engine is to provide the power to turn the propeller. It also generates electrical power, provides a vacuum source for some flight instruments, and, in most single-engine airplanes, provides a source of heat for the pilot and passengers. A firewall is located between the engine compartment and the cockpit to protect the occupants. The firewall also serves as a mounting point for the engine. During flight, the four forces acting on the airplane are lift, weight, thrust, and drag. Lift is the upward force created by the effect of airflow as it passes over and under the wings. It supports the airplane in flight. Weight opposes lift. It is caused by the downward pull of gravity. Thrust is the forward force which propels the

airplane through the air. It varies with the amount of engine power being used. Opposing thrust is drag, which is a backward, or retarding, force that limits the speed of the airplane. Lift is the key aerodynamic force. It is the force that opposes weight. In straight-and-level, unaccelerated flight, when weight and lift are equal, an airplane is in a state of equilibrium. If the other aerodynamic factors remain constant, that airplane neither gains nor loses altitude. When an airplane is stationary on the ramp, it is also in equilibrium, but the aerodynamic forces are not a factor. In calm wind conditions, the atmosphere exerts equal pressure on the upper and lower surfaces of the wing. Movement of air about the airplane, particularly the wing, is necessary before the

aerodynamic force of lift becomes effective. During flight, however, pressures on the upper and lower surfaces of the wing are not the same. Although several factors contribute to this difference, the shape of the wing is the principal one. The wing is designed to divide the airflow into areas of high pressure below the wing and areas of comparatively lower pressure above the wing. This pressure differential, which is created by movement of air about the wing, is the primary source of lift. The weight of the airplane is not a constant. It varies with the equipment installed, passengers, cargo, and fuel load. During the course of a flight, the total weight of the airplane decreases as fuel is consumed. Additional weight reduction may also occur during some specialized flight

activities, such as crop dusting, fire fighting, or sky diving flights. In contrast, the direction in which the force of weight acts is constant. It always acts straight down toward the center of the earth. Thrust is the forward-acting force which opposes drag and propels the airplane. In most airplanes, this force is provided when the engine turns the propeller. Each propeller blade is cambered like the airfoil shape of a wing. This shape, plus the angle of attack of the blades, produces reduced pressure in front of the propeller and increased pressure behind it. As is the case with the wing, this produces a reaction force in the direction of the lesser pressure. This is how a propeller produces thrust, the force which moves the airplane forward. To increase thrust by using the