Turbine Engines
Which statements are true regarding aircraft engine propulsion? 1. An engine driven propeller imparts a relatively small amount of acceleration to a large mass of air. 2. Turbojet and turbofan engines impart a relatively large amount of acceleration to a smaller mass of air. 3. In modern turboprop engines, nearly 50 percent of the exhaust gas energy is extracted by turbines to drive the propeller and compressor with the rest providing exhaust thrust.
1, 2
Which of the following factors affect the thermal efficiency of a turbine engine? 1. Turbine inlet temperature. 2. Compression ratio. 3. Ambient temperature. 4. Speed of the aircraft. 5. Turbine and compressor efficiency. 6. Altitude of the aircraft.
1, 2, 5
During inspection, turbine engine components exposed to high temperatures may only be marked with such materials as allowed by the manufacturer. These materials generally include 1. layout dye. 2. commercial felt tip marker. 3. wax or grease pencil. 4. chalk. 5. graphite lead pencil.
1, 2, and 4
Which of the following can cause fan blade shingling in a turbofan engine? 1. Engine overspeed. 2. Engine overtemperature. 3. Large, rapid throttle movements. 4. FOD.
1, 4
Which of the following variables affect the inlet air density of a turbine engine? 1. Speed of the aircraft. 2. Compression ratio. 3. Turbine inlet temperature. 4. Altitude of the aircraft. 5. Ambient temperature. 6. Turbine and compressor efficiency.
1, 4, 5
Standard sea level pressure is
29.92" Hg
Which of the following may be used to accomplish internal inspection of an assembled turbine engine? 1. Infrared photography. 2. Ultrasound. 3. A borescope. 4. Fluorescent penetrant and ultraviolet light.
3
Turbine engine components exposed to high temperatures generally may NOT be marked with 1. layout dye. 2. commercial felt tip marker. 3. wax or grease pencil. 4. chalk. 5. graphite lead pencil.
3 and 5
Using standard atmospheric conditions, the standard sea level temperature is
59 degrees F
What is meant by a double entry centrifugal compressor?
A compressor with vanes on both sides of the impeller
What is the profile of a turbine engine compressor blade?
A reduced blade tip thickness
What is the first engine instrument indication of a successful start of a turbine engine?
A rise in the exhaust gas temperature
What is meant by a shrouded turbine?
A- The turbine blades are shaped so that their ends form a band or shroud.
Newton's Law of Motion, generally termed the "Law of Momentum," states:
Acceleration is produced when a force acts on a mass. The greater the mass, the freater the amount of force needed.
Where do stress rupture cracks usually appear on turbine blades?
Across the leading or trailing edge at a right angle to the edge length
At what point in an axial-flow turbojet engine will the highest gas pressures occur?
At the compressor outlet
Which statement is true regarding jet engines?
At the higher engine speeds, thrust increases rapidly with small increases in RPM
Which of the following influences the operation of an automatic fuel control unit on a turbojet engine?
Burner pressure
In which type of turbine engine combustion chamber is the case and liner removed and installed as one unit during routine maintenance?
Can
What turbine engine section provides for proper mixing of the fuel and air?
Combustion section
At what stage in a turbine engine are gas pressures the greatest?
Compressor outlet
What is one purpose of the stator blades in the compressor section of a turbine engine?
Control the direction of the airflow
A turbine engine hot section is particularly susceptible to which kind of damage?
Cracking
What term is used to describe a permanent and cumulative deformation of the turbine blades of a turbojet engine?
Creep
One function of the nozzle diaphragm in a turbine engine is to
Direct the flow of gases to strike the turbine blades at the desired angle
What is the function of the inlet guide vane assembly on an axial-flow compressor?
Directs the air into the first stage rotor blades at the proper angle
What is the possible cause when a turbine engine indicates no change in power setting parameters, but oil temperature is high?
Engine main bearing distress
Newton's First Law of Motion, generally termed the Law of Inertia, states:
Every body persists in its state of rest, or of motion in a straight line, unless acted upon by some outside force
In what section of a turbojet engine is the jet nozzle located?
Exhaust
What is the primary advantage of an axial-flow compressor over a centrifugal compressor?
Greater pressure ratio
How does a dual axial-flow compressor improve the efficiency of a turbojet engine?
Higher compression ratios can be obtained
What type of turbine blade is most commonly used in aircraft jet engines?
Impulse-reaction
Where is the highest gas pressure in a turbojet engine?
In the entrance of the burner section
Main bearing oil seals used with turbine engines are usually what type(s)?
Labyrinth and/ or carbon rubbing
Which of the following types of combustion sections are used in aircraft turbine engines?
Multiple-can, annular, and can-annular
In a dual axial-flow compressor, the first stage turbine drives
N(2) compressor
In the dual axial-flow or twin spool compressor system, the first stage turbine drives the
N(2) compressor
What is the primary factor which controls the pressure ratio of an axial-flow compressor?
Number of stages in compressor
When the leading edge of a first-stage turbine blade is found to have stress rupture cracks, which of the following should be suspected?
Overtemperature condition
Some engine manufacturers of twin spool gas turbine engines identify turbine discharge pressure in their maintenance manuals as
Pt7
What must be done after the fuel control unit has been replaced on an aircraft gas turbine engine?
Retrim the engine
Which two elements make up the axial-flow compressor assembly?
Rotor and stator
What type igniter plug is used in the low tension ignition system of an aircraft turbofan engine?
Self-ionizing or shunted-gap type plug
Which turbine engine compressor offers the greatest advantages for both starting flexibility and improved high-altitude performance?
Split-spool, aacial-flow
What is the proper starting sequence for a turbojet engine?
Starter, ignition, fuel
What are the two basic elements of the turbine section in a turbine engine?
Stator and rotor
When aircraft turbine blades are subjected to excessive heat stress, what type of failures would you expect?
Stress rupture
What is the major function of the turbine assembly in a turbojet engine?
Supplies the power to turn the compressor
Who establishes mandatory replacement times for critical components of turbine engines?
The engine manufacturer
Who establishes the recommended operating time between overhauls (TBO) of a turbine engine used in general aviation?
The engine manufacturer
What is the purpose of the dump valve used on aircraft gas turbine engines?
The fuel is quickly cut off to the nozzles and the manifolds are drained preventing fuel boiling off as a result of residual engine heat
Why do some turbine engines have more than one turbine wheel attached to a single shaft?
To extract more power from the exhaust gases than a single whell can absorb
What is the purpose of the diffuser section in a turbine engine?
To increase pressure and reduce velocity
What is the function of the stator vane assembly at the discharge end of a typical axial-flow compressor?
To straighten airflow to eliminate turbulance
Dirt particles in the air being introduced into the compressor of a turbine engine will form a coating on all but which of the following?
Turbine blades
Which of the following engine variables is the most critical during turbine engine operation?
Turbine inlet temperature
Which of the following is the ultimate limiting factor of turbine engine operation?
Turbine inlet temperature
A gas turbine engine comprises which three main sections?
Turbine. compressor, and combustion
What should be done initially if a turbine engine catches fire when starting?
Turn off the fuel and continue engine rotation with the starter
What is used in turbine engines to aid in stabilization of compressor airflow during low thrust engine operation?
Variable gude vanes and/or compressor bleed valves
Hot spots on the tail cone of a turbine engine are possible indicators of a malfunctioning fuel nozzle or
a faulty combustion chamber
Compressor stall is caused by
a high angle of attack airflow through the first stages of compression.
When starting a turbine engine,
a hot start is indicated if the exhaust gas temperature exceeds specified limits.
A weak fuel to air mixture along with normal airflow through a turbine engine may result in
a lean die-out
A condition known as 'hot streaking' in turbine engines is caused by
a partially clogged fuel nozzle
Generally, when starting a turbine engine, the starter should be disengaged
after the engine has reached self-accelerating speed
A cool-off period prior to shutdown of a turbine engine is accomplished in order to
allow the turbine wheel to cool before the case contracts around it
(1) Accumulation of contaminates in the compressor of a turbojet engine reduces aerodynamic efficiency of the blades. (2) Two common methods for removing dirt deposits from turbojet engine compressor blades are a fluid wash and an abrasive grit blast. Regarding the above statements,
both No. 1 and No. 2 are true
(1) In a turbine engine axial-flow compressor, each consecutive pair of rotor and stator blades constitutes a pressure stage. (2) In a turbine engine axial-flow compressor, the number of rows of stages is determined by the amount of air and total pressure rise required. Regarding the above statements,
both No. 1 and No. 2 are true
If the RPM of an axial-flow compressor remains constant, the angle of attack of the rotor blades can be changed by
changing the velocity of the airflow
If a turbine engine is unable to reach takeoff EPR before its EGT limit is reached, this is an indication that the
compressor may be contaminated or damaged
The stator vanes in an axial-flow compressor
convert velocity energy into pressure energy
Continued and/or excessive heat and centrifugal force on turbine engine rotor blades is likely to cause
creep
Stator blades in the compressor section of an axial-flow turbine engine
decrease the air velocity and prevent swirling
The compressor stators in a gas turbine engine act as diffusers to
decrease the velocity of the gas flow
The pressure of subsonic air as it flows through a convergent nozzle
decreases
The pressure of supersonic air as it flows through a divergent nozzle
decreases
A turbine engine compressor which contains vanes on both sides of the impeller is a
double entry centrifugal compressor
The turbine section of a jet engine
drives the compressor section.
Anti-icing of jet engine air inlets is commonly accomplished by
engine bleed air ducted through the critical areas
The recurrent ingestion of dust or other fine airborne particulates into a turbine engine can result in
erosion damage to the compressor and turbine sections
Turbine blades are generally more susceptible to operating damage than compressor blades because of
exposure to high temperatures
When starting a turbine engine, a hung start is indicated if the engine
fails to reach idle RPM
The procedure for removing the accumulation of dirt deposits on compressor blades is called
field cleaning
Severe rubbing of turbine engine compressor blades will usually cause
galling
An advantage of the axial-flow compressor is its
high peak efficiency.
The exhaust section of a turbine engine is designed to
impart a high exit velocity to the exhaust gases
What are the two functional elements in a centrifugal compressor?
impeller and diffuser
Three types of turbine blades are
impulse, reaction, and impulse-reaction.
An exhaust cone placed aft of the turbine in a jet engine will cause the pressure in the first part of the exhaust duct to
increase and the velocity to decrease
The stators in the turbine section of a gas turbine engine
increase the velocity of the gas flow
Turbine nozzle diaphragms located on the upstream side of each turbine wheel, are used in the gas turbine engine to
increase the velocity of the heated gases flowing past this point
The velocity of subsonic air as it flows through a convergent nozzle
increases
The velocity of supersonic air as it flows through a divergent nozzle
increases
The fan rotational speed of a dual axial compressor forward fan engine is the same as the
low-pressure compressor
Some high-volume turboprop and turbojet engines are equipped with two-spool or split compressors. When these engines are operated at high altitudes, the
low-pressure rotor will increase in speed as the compressor load decreases in the lower density air
Hot spots in the combustion section of a turbojet engine are possible indicators of
malfunctioning fuel nozzles
If, during inspection at engine overhaul, ball or roller bearings are found to have magnetism but otherwise have no defects, they
must be degaussed before use
(1) Welding and straightening of turbine engine rotating airfoils does not require special equipment. (2) Welding and straightening of turbine engine rotating airfoils is commonly recommended by the manufacturer. Regarding the above statements,
neither No. 1 nor No. 2 is true
The basic gas turbine engine is divided into two main sections: the cold section and the hot section. (1) The cold section includes the engine inlet, compressor, and turbine sections. (2) The hot section includes the combustor, diffuser, and exhaust sections. Regarding the above statements,
neither No. 1 nor No. 2 is true
The compression ratio of an axial-flow compressor is a function of the
number of compressor stages
Hot section inspections for many modern turbine engines are required
on a time or cycle basis
In a gas turbine engine, combustion occurs at a constant
pressure
The Brayton cycle is known as the constant
pressure cycle
An advantage of the centrifugal-flow compressor is its high
pressure rise per stage
Compressor field cleaning on turbine engines is performed primarily in order to
prevent engine performance degradation, increased fuel costs, and damage or corrosion to gas path surfaces
A purpose of the shrouds on the turbine blades of an axial-flow engine is to
reduce vibration
In a turbine engine with a dual-spool compressor, the low speed compressor
seeks its own best operating speed
The blending of blades and vanes in a turbine engine
should be performed parallel to the length of the blade using smooth contours to minimize stress points
Reduced blade vibration and improved airflow characteristics in gas turbines are brought about by
shrouded turbine rotor blades
The two types of centrifugal compressor impellers are
single entry and double entry
The non-rotating axial-flow compressor airfoils in an aircraft gas turbine engine, are called
stator vanes
Between each row of rotating blades in a turbine engine compressor, there is a row of stationary blades which act to diffuse the air. These stationary blades are called
stators
The function of the exhaust cone assembly of a turbine engine is to
straighten and collect the exhaust gases into a solid exhaust jet
In an axial-flow compressor, one purpose of the stator vanes at the discharge end of the compressor is to
straighten the airflow and eliminate turbulence
The diffuser section of a jet engine is located between
the compressor section and the burner section
Jet engine turbine blades removed for detailed inspection must be reinstalled in
the same slot
The abbreviation Pt7 used in turbine engine terminology means
the total pressure at station No. 7
The highest heat-to-metal contact in a jet engine is the
turbine inlet fuide vanes
The air passing through the combustion chamber of a turbine engine is
used to support combustion and to cool the engine
The purpose of a bleed valve, located in the beginning stages of the compressor, in an aircraft gas turbine engine is to
vent some of the air overboard to prevent a compressor stall
