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Engine Maintenance
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In order to keep the engine in working condition, it is necessary to provide its inspecting at regular intervals. To provide efficient operation and maintenance of a gas-turbine engine the mechanic should be familiar with the engine design, inspection, starting and overhaul procedures in general; andthe manufacturer's instructions for any specific engine in particular. In performing maintenance operations certain precautions rules should be inspected for foreign objects; in operating the engine at full power it is necessary to remove all inflammable material from the area; no work should be performed on the ignition system or spark plugs during engine running; the hot starts should be avoided as the turbine or other parts overheating usually requires the engine overhaul.
Maintenance of any gas-turbine engine includes operational and periodic maintenance. Operational maintenance is performed prior to every take-off and after the aircraft landing with the view of checking all systems and units for their readiness for flight. It is called pre-flight and post-flight maintenance, correspondingly. Operational maintenance requires checking all the troublesome units and systems of the engine. Engine compartments and nacelles are checked for cleanliness and security of all lines and fittings. All fuel and oil leaks, loose parts, cracks, corrosion, missed rivers, warping, buckling, burning and other undesirable conditions should be revealed and eliminated. Operational maintenance also includes checking the fuel, oil, water and hydraulic fluid level before each flight.
The periodic engine maintenance includes minor inspection (performed every 60 hours of flight) and major inspection (performed every 200 and 600 hours of flight). When the engine was operated during a certain predetermined number of hours it is removed from the aircraft and sent to the overhaul base. The engine overhaul includes complete disassembly, washing, delectation and repair or replacement of worn units or parts.
Lift
It is well-known that all material objects.are attracted to the earth by a force which is in proportion to the mass of the objects; such a force is called gravity. In order for an object to rise from the earth’s surface and to maintain itself in a flight above the surface, the attraction which gravity has for the object must be opposed by the development of a force called lift.
In order to generate the lifting force there must be relative movement between the wing and the surrounding air.
How is the lift created? The air strikes the leading edge of the wing. It divides into a flow over the upper and lower surface of its airfoil sections. There is difference between the amount of air above and beneath the wing and the wing is at an angle of attack, i.e. at an angle relative to the airflow.
The velocity of the airflow over the upper surface will be greater than that of the air flowing along the lower surface. Since the pressure of a fluid (liquid or gas) decreases at points where the velocity of the liquid increases, for an aircraft wing with a small angle of attack the pressure acting on surfaces of the wing will decrease.
The angle of attack is an important factor in controlling the magnitude of lift, generated by a wing, For example, when angle of attack is increased the velocity of the airflow over the upper surface increases at a faster rate than that over the lower surface.
Other important factors which control pressure distribution and lift are the velocity of the free air flow, its viscosity and its density, the shape and thickness of the airfoil section adopted for a wing, the wing form and its area and condition for wing surface.
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