Turbine Engines Flashcards
At what point in an axial-flow engine will the highest gas pressures occur?
At the compressor outlet.
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 profile of a turbine engine compressor blade?
A reduced blade tip thickness.
The fan rotational speed of a dual axial compressor forward fan engine is the same as the what?
low-pressure compressor.
The abbreviation P(t7) used in turbine engine terminology means what?
the total pressure at station 7.
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.
What turbine engine section provides for proper mixing of the fuel and air?
Combustion section.
In a gas turbine engine, combustion occurs at a constant what?
pressure.
Which statement is true regarding jet engines?
At the higher engine speeds, thrust increases rapidly with small increases in RPM.
Some high-volume turboprop and turbojet engines are equipped with two-spool compressors. When these engines are operated at high altitudes, the what?
low-pressure rotor will increase in speed as the compressor load decreases in the lower density air.
Turbine nozzle diaphragms located on the upstream side of each turbine wheel, are used in the gas turbine engine to what?
Increase the velocity of the heated gases flowing past this point.
Where is the highest gas pressure in a turbojet engine?
In the entrance of the burner section.
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 what?
Increase and the velocity to decrease.
What is the function of the stator vane assembly at the discharge end of a typical axial-flow compressor?
To straighten airflow to eliminate turbulence.
The turbine section of a jet engine…
drives the compressor section.
When starting a turbine engine, …
a hot start is indicated if the exhaust gas temperature exceeds specified limits.
In the dual axial-flow or twin spool compressor system, the first stage turbine drives the what?
N2 compressor.
Which of the following may be used to mark turbine engine components exposed to high temperatures?
Layout dye.
When starting a turbine engine, a hung start is indicated if the engine what?
fails to reach idle RPM.
What are the two basic elements of the turbine section in a turbine engine?
Stator and rotor.
Which of the following acts as a diffuser in a turbine engine and converts velocity to pressure?
Stators.
The function of the exhaust cone assembly of a turbine engine is to what?
straighten and collect the exhaust gases into a solid exhaust jet.
What are the two functional elements in a centrifugal compressor?
Impeller and diffuser.
What must be done after the fuel control unit has been replaced on an aircraft gas turbine engine?
Retrim the engine.
If, during inspection at engine overhaul, ball or roller bearings are found to have magnetism but otherwise have no defects, they what?
must be degaussed before use.
A turbine engine compressor which contains vanes on both sides of the impeller is a what?
double entry centrifugal compressor.
What is the first engine instrument indication of a successful start of a turbine engine?
a rise in the exhaust gas temperature.
Some engine manufacturers of twin spool gas turbine engines identify turbine discharge pressure in their maintenance manuals as what?
P(t7)
Who establishes the recommended operating time between overhauls (TBO) of a turbine engine used in general aviation?
The engine manufacturer.
The basic gas turbine 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 1 nor 2 is true.
(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 1 nor 2 is true.
Turbine engine components exposed to high temperatures generally may not marked with what?
wax, grease pencil, or a graphite lead pencil.
Who establishes mandatory replacement times for critical components of turbine engines?
The engine manufacturer.
Main bearing oil seals used with turbine engines are usually what type(s)?
Labyrinth and/or carbon rubbing.
How does a dual axial-flow compressor improve the efficiency of a turbojet engine?
Higher compression ratios can be obtained.
Three types of turbine blades are what?
impulse, reaction, and impulse-reaction.
Which statement is true regarding aircraft engine propulsion?
An engine driven propeller imparts a relatively small amount of acceleration to a large mass of air.
An advantage of the axial-flow compressor is its what?
High peak efficiency.
What is one purpose of the stator blades in the compressor section of a turbine engine?
Control the direction of the airflow.
What is the purpose of the diffuser section in a turbine engine?
To increase pressure and reduce velocity.
Where do stress rupture cracks usually appear on turbine blades?
Across the leading or trailing edge at a right angle to the edge length.
In which type of turbine engine combustion chamber is the case and liner removed and installed as one unit during routine maintenance?
Can.
The diffuser section of a jet engine is located between what?
the compressor section and the burner section.
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.
Turbine blades are generally more susceptible to operating damage than compressor blades because of what?
exposure to high temperatures.
Which of the following is the ultimate limiting factor of turbine engine operation?
Turbine-inlet temperature.
The recurrent ingestion of dust or other fine airborne particulates into a turbine engine can result in what?
erosion damage to the compressor and turbine sections.
Which of the following engine variables is the most critical during turbine engine operation?
Turbine-inlet temperature.
Reduced blade vibration and improved airflow characteristics in gas turbines are brought about by what?
Shrouded turbine rotor blades.
Which turbine engine compressor offers the greatest advantages for both starting flexibility and improved high-altitude performance?
split-spool, axial-flow.
Jet engine turbine blades removed for detailed inspection must be reinstalled in what?
The same slot.
An advantage of the centrifugal-flow compressor is its high what?
pressure rise per stage.
The highest heat-to-metal contact in a jet engine is the what?
turbine inlet guide vanes
Which two elements make up the axial-flow compressor assembly?
Rotor and stator
The two types of centrifugal compressor impellers are what?
single entry and double entry.
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 what?
stators.
Standard sea level pressure is what?
29.92” Hg.
Using standard atmospheric conditions, the standard sea level temperature is what?
59 degrees F.
When aircraft turbine blades are subjected to excessive heat stress, what type of failures would you expect?
Stress rupture.
In an axial-flow compressor, one purpose of the stator vanes at the discharge end of the compressor is to what?
Straighten the airflow and eliminate turbulence.
Compressor field cleaning on turbine engines is performed primarily in order to what?
prevent engine performance degradation, increase fuel costs, and damage or corrosion to gas path surfaces.
Hot section inspections for many modern turbine engines are required…
on a time or cycle basis.
A purpose of the shrouds on the turbine blades of an axial-flow engine is to what?
reduce vibration.
In a dual axial-flow compressor, the first stage turbine drives what?
N2 compressor.
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 the proper starting sequence for a turbojet engine?
Starter, Ignition, Fuel
A weak fuel to air mixture along with a normal airflow through a turbine engine may result in what?
a lean die-out.
What is used in turbine engines to aid in stabilization of compressor airflow during low thrust engine operation?
Variable guide vanes and/or compressor bleed valves.
In a turbine engine with a dual-spool compressor, the low speed compressor what?
seeks its own best operating speed.
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.
Which of the following is a good indication of a malfunctioning fuel nozzle when inspecting the exhaust section of an aircraft turbine engine?
Hotspots on the tail cone.
The stator vanes in an axial-flow compressor what?
convert velocity energy into pressure energy.
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 pressure of a subsonic air as it flows through a convergent nozzle…
decreases
The pressure of supersonic air as it flows through divergent nozzle…
decreases
Anti-icing of jet engine air inlets is commonly accomplished by what?
engine bleed air ducted through the critical areas.
Generally, when starting a turbine engine, the starter should be disengaged…
after the engine has reached self-accelerating speed.
What is the primary advantage of an axial-flow compressor over a centrifugal compressor?
Greater pressure ratio.
The purpose of a bleed valve, located in the beginning stages of the compressor, in an aircraft gas turbine engine is to what?
vent some of the air overboard to prevent a compressor stall.
What is meant by a double-entry centrifugal compressor?
A compressor with vanes on both sides of the impeller.
What is the major function of the turbine assembly in a turbojet engine?
Supplies the power to turn the compressor.
Stator blades in the compressor section of an axial-flow turbine engine what?
decrease the air velocity and prevent swirling.
A gas turbine engine comprises which three main sections?
Turbine, compressor, and combustion.
What type of turbine blade is most commonly used in aircraft jet engines?
Impulse-reaction
What is the primary factor which controls the pressure ratio of an axial-flow compressor?
Number of stages in compressor.
The non-rotating axial-flow compressor airfoils in an aircraft gas turbine engine, are called what?
Stator vanes.
(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 1 and 2 are true.
The air passing through the combustion chamber of a turbine engine is what?
used to support combustion and to cool the engine.
The stators in the turbine section of a gas turbine engine…
increase the velocity of the gas flow.
The compressor stators in a gas turbine engine act as diffusers to what?
decrease the velocity of the gas flow.
The procedure for removing the accumulation of dirt deposits on compressor blades is called what?
field cleaning.
Which of the following may be used to accomplish internal inspection of an assembled turbine engine?
A borescope.
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.
Newton’s second 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 greater the amount of force needed.
A turbine engine hot section is particularly susceptible to which kind of damage?
Cracking.
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.
Severe rubbing of turbine engine compressor blades will usually cause what?
Galling.
Which of the following influences the operation of an automatic fuel control unit on a turbojet engine?
Burner pressure.
If a turbine engine is unable to reach takeoff EPR before its EGT limit is reached, this is an indication that the what?
compressor may be contaminated or damaged.
The Brayton cycle is known as the constant…
pressure cycle.
Continued and/or excessive heat and centrifugal force on turbine engine rotor blades is likely to cause what?
Creep.
If the RPM of an axial-flow compressor remains constant, the angle of attack of the rotor blades can be changed by what?
Changing the velocity of the airflow.
The compression ratio of an axial-flow compressor is a function of the what?
number of compressor stages.
Which of the following variables affect the inlet air density of a turbine engine?
Compression ratio, turbine inlet temperature, and turbine and compressor efficiency.
Which of the following factors affect the thermal efficiency of a turbine engine?
Turbine inlet temperature, compression ratio, and turbine and compressor efficiency.
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 wheel can absorb.
The exhaust section of a turbine engine is designed to what?
impart a high exit velocity to the exhaust gases.
Which of the following types of combustion sections are used in aircraft turbine engines?
Multiple-can, annular, and can-annular.
A cool-off period prior to shutdown of a turbine engine is accomplished in order to what?
allow the turbine wheel to cool before the case contracts around it.
What type of igniter plug is used in the low tension ignition system of an aircraft turbofan engine?
Self-ionizing or shunted-gap type plug.
What is meant by a shrouded turbine?
The turbine blades are shaped so that their ends from a band or shroud.
What term is used to describe a permanent and cumulative deformation of the turbine blades of a turbojet engine?
Creep.
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.
At what stage in a turbine engine are gas pressures the greatest?
Compressor outlet.
In what section of a turbojet engine is the jet nozzle located?
Exhaust.
(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 1 and 2 are true.
Hot spots in the combustion sections of a turbojet engine are possible indicators of what?
malfunctioning fuel nozzles.
Which of the following can cause fan blade shingling in a turbofan engine?
Engine over speed and/or FOD.
Compressor stalls is caused by what?
a high angle of attack airflow through the first stages of compression.
A condition known as “hot streaking” in turbine engines is caused by what?
a partially clogged fuel nozzle.
