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UAA AMT 279 Review 2 Questions and Answers
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UAA AMT 279 Review 2 Questions and Answers
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UAA AMT 279 Review 2 Questions andAnswers
Are cracks acceptable on turbine stator vanes (explain your answer)? - ANSWER-Yes,
if within manufacture's limits
Can turbine engine oils be interchanged with reciprocating engine oils? Why? -
ANSWER-No, turbine oils are a synthetic blend and have properties that reciprocating
oils do not. These properties in general, include; multi-viscosity, higher viscosity index,
greater heat resistance, resistance to coking, and cleaning additives.
Describe at least 2 functions of the pressurization and dump valve. - ANSWER-
Pressurization: through a spring loaded valve fuel is not permitted to flow to the nozzles
until sufficient pressure exists to assure a proper spray pattern from the nozzle (fuel
delivered to the combustion chamber as a fine atomized spray).
Dump: when system pressure drops below the specified value, the pressurization valve
closes and the dump valve (or dump side of the pressurization valve) opens to direct
fuel away from the nozzles and toward a collection tank or back into the fuel system (to
provide a clean shutoff of the fuel and remove residual fuel from the manifold).
Describe at least 3 types of damage/deterioration found in the combustion liner during
hot section inspection. - ANSWER-Hot spots- areas showing heat stress due to over
temperature/momentary flame contact.
Warping-deformation of metal due to uneven expansion and contraction.
Burning- material degradation or loss due to direct flame contact.
Cracking- fracture of metal due to stress imposed during expansion and contraction.
Erosion- loss of material due to friction from passing hot gases.
Describe how a labyrinth oil seal system works. - ANSWER-1)Air from gas path outside
of the bearing compartment bleeds inward across grooves cut in the labyrinth seal. The
seal dams formed by the rings allow for a metered amount of air from the engine gas
path to flow inward.
2)The air entering across the labyrinth seal prevents the oil mist created by the oil jet
spraying on the rotating bearing from exiting the bearing compartment.
3) The seal pressurizing air then leaves the bearing area by scavenge oil system
4) Dead headed air pressure in the balance chamber pushes against the compressor
and prevents sudden thrust loads from being absorbed totally by bearing
How does a flyweight governor determine RPM? - ANSWER-The flyweights are rotated
by a shaft that is connected to the device for which RPM is being monitored. As the
flyweights are rotated, due to their "L" shape, they pivot outward from the axis of
rotation due to centrifugal force. They are restricted from moving outward by a spring
, actin got the lower portion o the "L". A specific RPM will be established when spring
force is balanced by flyweight centrifugal force.
Name three functions of an engine lubricating oil within the engine. - ANSWER-
Lubricate, cushion, cool, clean, corrosion protection, perform hydraulic functions, seals.
The Allison 250 fuel control uses compressor discharge pressure (Pc) for its operation
why? - ANSWER-It provides a working fluid to operate the mechanism in the fuel control
and it is an indication of airflow through the engine.
The fuel control receives numerous inputs to achieve one output what is that output? -
ANSWER-Metering valve position
What are "last chance" oil filters in a turbine engine system? - ANSWER-Filters at, or
close, to the oil jet. Provides filtration if the main filter fails or contamination enters the
system downstream of the main filter. They can provide additional time before failure of
the main filtration system.
What are the inputs used by the Allison 250 fuel control? - ANSWER-Fuel pressure
Compressor discharge pressure (Pc)
Gas producer RPM
Gas producer throttle
Power turbine RPM
Power turbine throttle
What does the governor reset system do in the Allison 250 fuel control? - ANSWER-The
governor reset assembly is the method by which the power turbine governor
communicates power turbine needs to the gas producer fuel control. Through the reset
assembly the power turbine governor can take command or release the gas producer
governor lever to modify gas producer output thereby increasing or decreasing gas flow
to the power turbine dependent on requested power turbine output.
What does viscosity index refer to for lubricating oils? - ANSWER-A measure on the
change in an oil's viscosity for changes in temperature.
What is "creep" at it applies to turbine inspection? - ANSWER-The permanent
elongation which occurs to parts subject to high heat and tensile stress (rotating parts).
Creep is most pronounced in turbine blades due to the high heat and tensile loading
encountered in operation.
What is "stress rupture" as it applies to turbine inspection? - ANSWER-Stress rupture
cracks are perceptible as minute hairline cracks at right angles to the blade length
normally where the blade has narrowed. This condition is a result of creep and can be
an indication of a serious over-temperature.
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