Answers - Turbine Engine (Part 2)

61. c
Almost all of the components on a turbine engine, including the hot section, are required to be inspected on a time o? cycle basis. Additional times when a hot section must be inspected include during an overhaul or when an overtemperature or overspeed incident occurs.

62. a
The use of shrouded turbine rotor blades reduces blade vibration and improves turbine efficiency. With shrouded blades, the tips of the blades contact each other and provide support. This added support reduces vibration substantially. The shrouds also prevent air from escaping over the blade tips making the turbine more efficient.

63. a
In a dual spool axial-flow compressor the first compressor (N1) is driven by the second turbine, while the second compressor (N2) is driven by the first turbine.

64. a
If a turbine engine catches fire during an attempted start, you should immediately turn off the fuel and continue to turn the engine with the starter. By continuing to rotate the engine, the fire is likely to be drawn into the engine and discharged out the tailpipe.

65. b
The first step in starting a typical turbine engine is to engage the starter. Once this is done, the ignition is turned on. Then, when the N1 compressor obtains a predetermined rpm, the fuel lever is moved to the idle position. Normal lightoff is indicated by a rise in the exhaust gas temperature (EGT).

66. b
If you operate a turbine engine with a weak or lean fuel to air mixture, you risk encountering what is known as a lean die-out. In other words, the amount of fuel supplied is insufficient to support combustion.

67. b
Airflow through some turbine engines during low thrust operations must be stabilized to prevent the compressor from stalling. To do this, variable inlet guide vanes or compressor bleed valves are used. Variable guide vanes rotate to maintain the correct angle of attack relationship between inlet air flow and compressor speed. Compressor bleed valves, on the other hand, dump away unwanted air.

68. c
Most modern gas turbine engines use a dual-spool compressor that utilizes two axial-flow rotors or one axial and one centrifugal-flow rotor. An advantage of the dual-spool compressor is the ability of the first compressor (N,) to seek its own best operating speed. Therefore, when the engine is operated at altitude where the air is less dense, the reduced drag on the first stage compressor allows the compressor to speed up thereby increasing efficiency.

69. a
The guide vanes direct the airflow into the first stage rotor blades at the proper angle and induce a swirling motion to the air entering the compressor. Answers (B) and (C) are incorrect because inlet guide vanes do not alter the pressure or velocity of incoming air.

70. a
When inspecting the hot section of a turbine engine, the exhaust cone and tailpipe should be inspected for cracks, warping, buckling, or hotspots. Hotspots on the tail cone are a good indication of a malfunctioning fuel nozzle or combustion chamber. For example, if a fuel nozzle is spraying a solid stream of fuel instead of an atomized spray, the fuel continues to bum as it passes through the exhaust section, producing bum marks on the tail cone. By the same token, a combustion chamber which is not properly controlling the flame zone may allow the flame to come in contact with the tail cone.

Answers for questions 71 to 120
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