POWERPLANT ORAL EXAM ASA FULL
REVISION NOTES WITH RECIPROCATING AND
TURBINE ENGINE CONCEPTS
◉ What is the purpose of the stators in an axial-flow compressor?
Answer: The stators convert some velocity energy into pressure
energy and change the direction of the air so it is proper for the next
stage of rotors.
◉ What are three types of combustors used on aircraft turbine
engines?
Answer: Can-type, annular-type, and can-annular type.
◉ How many igniters are there normally in an aircraft turbine
engine?
Answer: Two.
◉ What is main purpose of the turbine nozzle in an aircraft turbine
engine?
Answer: The turbine nozzle directs the hot gases as they leave the
combustors so they will turn the turbine wheel with maximum
efficiency.
,◉ What is meant by a free-turbine turboshaft engine?
Answer: A turboshaft engine that has a turbine wheel, or stage of
turbine wheels, that is not used to drive the compressor of the gas
generator section of the engine. This free turbine drives the
propeller in a turboprop engine or the transmission and rotor of a
helicopter.
◉ Why do some axial-flow turbine engines have more than one set
of turbines and compressors?
Answer: A two-spool turbine engine has a low-pressure and a high-
pressure compressor, each driven by its own turbine. The two
independent systems operate at the speed at which they are most
efficient.
◉ What kind of bearings are used to support the rotor shaft of an
aircraft turbine engine?
Answer: Anti-friction bearings, such as ball bearings or roller
bearings.
◉ What is meant by a turbofan engine?
Answer: An axial-flow turbine engine in which the first stage of
compressor blades are lengthened, so they can force air around the
outside of the gas generator portion of the engine.
,◉ Where can you find the limits of repair allowed for the
compressor blades of an aircraft turbine engine?
Answer: In the FAA-approved service manual issued by the
manufacturer of the engine.
◉ Why is it important that a turbojet engine be allowed to cool
before it is shut down after it has been operated at a high power
setting?
Answer: If the engine is shut down while it is hot, there is a
possibility that the shroud will contract around the turbine wheel
and seize the rotor.
◉ What is meant by a hung start in a turbine engine?
Answer: A start in which ignition occurs, but the engine does not
accelerate to a self-sustaining speed.
◉ What is meant by a hot start in a turbine engine?
Answer: A start in which ignition occurs, but the internal
temperatures go high enough that they can damage the engine.
◉ What is meant by creep of the turbine blades?
Answer: A condition of permanent elongation of the turbine blades.
Creep is caused by the high temperatures and the high centrifugal
loading imposed on the blades.
, ◉ How is the compressor of a turbine engine cleaned?
Answer: An emulsion-type cleaner is sprayed through the engine
while it is being motored by the starter or operated at a low speed.
The wash is followed by a clean water rinse. More vigorous cleaning
is done by injecting a mild abrasive, such as ground-up apricot pits
or walnut shells, into the engine while it is operating at low speed.
◉ Where is water injected into a turbine engine for cooling
purposes?
Answer: Into the compressor inlet and into the engine diffuser case.
◉ At what point in a turbine engine is the temperature the highest?
Answer: At the inlet to the high-pressure turbine.
◉ What is the function of the interconnect tubes between the cans of
a turbine engine that uses can-type combustors?
Answer: These tubes allow the flame to travel from the cans that
contain the igniters to all of the other cans when the engine is being
started.
◉ What are two types of thrust reversers that are used on turbojet
engines?
REVISION NOTES WITH RECIPROCATING AND
TURBINE ENGINE CONCEPTS
◉ What is the purpose of the stators in an axial-flow compressor?
Answer: The stators convert some velocity energy into pressure
energy and change the direction of the air so it is proper for the next
stage of rotors.
◉ What are three types of combustors used on aircraft turbine
engines?
Answer: Can-type, annular-type, and can-annular type.
◉ How many igniters are there normally in an aircraft turbine
engine?
Answer: Two.
◉ What is main purpose of the turbine nozzle in an aircraft turbine
engine?
Answer: The turbine nozzle directs the hot gases as they leave the
combustors so they will turn the turbine wheel with maximum
efficiency.
,◉ What is meant by a free-turbine turboshaft engine?
Answer: A turboshaft engine that has a turbine wheel, or stage of
turbine wheels, that is not used to drive the compressor of the gas
generator section of the engine. This free turbine drives the
propeller in a turboprop engine or the transmission and rotor of a
helicopter.
◉ Why do some axial-flow turbine engines have more than one set
of turbines and compressors?
Answer: A two-spool turbine engine has a low-pressure and a high-
pressure compressor, each driven by its own turbine. The two
independent systems operate at the speed at which they are most
efficient.
◉ What kind of bearings are used to support the rotor shaft of an
aircraft turbine engine?
Answer: Anti-friction bearings, such as ball bearings or roller
bearings.
◉ What is meant by a turbofan engine?
Answer: An axial-flow turbine engine in which the first stage of
compressor blades are lengthened, so they can force air around the
outside of the gas generator portion of the engine.
,◉ Where can you find the limits of repair allowed for the
compressor blades of an aircraft turbine engine?
Answer: In the FAA-approved service manual issued by the
manufacturer of the engine.
◉ Why is it important that a turbojet engine be allowed to cool
before it is shut down after it has been operated at a high power
setting?
Answer: If the engine is shut down while it is hot, there is a
possibility that the shroud will contract around the turbine wheel
and seize the rotor.
◉ What is meant by a hung start in a turbine engine?
Answer: A start in which ignition occurs, but the engine does not
accelerate to a self-sustaining speed.
◉ What is meant by a hot start in a turbine engine?
Answer: A start in which ignition occurs, but the internal
temperatures go high enough that they can damage the engine.
◉ What is meant by creep of the turbine blades?
Answer: A condition of permanent elongation of the turbine blades.
Creep is caused by the high temperatures and the high centrifugal
loading imposed on the blades.
, ◉ How is the compressor of a turbine engine cleaned?
Answer: An emulsion-type cleaner is sprayed through the engine
while it is being motored by the starter or operated at a low speed.
The wash is followed by a clean water rinse. More vigorous cleaning
is done by injecting a mild abrasive, such as ground-up apricot pits
or walnut shells, into the engine while it is operating at low speed.
◉ Where is water injected into a turbine engine for cooling
purposes?
Answer: Into the compressor inlet and into the engine diffuser case.
◉ At what point in a turbine engine is the temperature the highest?
Answer: At the inlet to the high-pressure turbine.
◉ What is the function of the interconnect tubes between the cans of
a turbine engine that uses can-type combustors?
Answer: These tubes allow the flame to travel from the cans that
contain the igniters to all of the other cans when the engine is being
started.
◉ What are two types of thrust reversers that are used on turbojet
engines?
