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When an electrical de-icing system is operating, what happens to thrust?
When an electrical de-icing system is operating, what happens to thrust?
What is the purpose of a divergent pitot intake?
What is the purpose of a divergent pitot intake?
What method is used for anti-icing inlet guide vanes?
What method is used for anti-icing inlet guide vanes?
How is a divergent intake characterized?
How is a divergent intake characterized?
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What operates the variable inlet guide vanes?
What operates the variable inlet guide vanes?
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What does a well-designed intake do with forward speed?
What does a well-designed intake do with forward speed?
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What is the primary design goal of intakes?
What is the primary design goal of intakes?
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What is the function of the stator vane assembly in an axial flow compressor?
What is the function of the stator vane assembly in an axial flow compressor?
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In an axial flow, dual compressor forward fan engine, which component turns at the same speed as the fan?
In an axial flow, dual compressor forward fan engine, which component turns at the same speed as the fan?
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Which measurement unit is typically used to assess aircraft noise levels?
Which measurement unit is typically used to assess aircraft noise levels?
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What component is essential for the efficient burning of gases in a gas turbine engine?
What component is essential for the efficient burning of gases in a gas turbine engine?
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What characterizes a turbojet engine compared to a piston engine?
What characterizes a turbojet engine compared to a piston engine?
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Where is the jet nozzle located in a turbojet engine?
Where is the jet nozzle located in a turbojet engine?
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Which of the following correctly describes the Brayton cycle?
Which of the following correctly describes the Brayton cycle?
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In a ducted fan engine, what drives the fan?
In a ducted fan engine, what drives the fan?
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Which theorem is related to the energies present in fluid flow?
Which theorem is related to the energies present in fluid flow?
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What is the major function of the turbine assembly in a turbojet engine?
What is the major function of the turbine assembly in a turbojet engine?
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What advantage do shrouded blades provide in gas turbines?
What advantage do shrouded blades provide in gas turbines?
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What is the principle of jet propulsion based on?
What is the principle of jet propulsion based on?
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What effect does forward speed have on the efficiency of a jet engine?
What effect does forward speed have on the efficiency of a jet engine?
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What type of failure is most likely when turbine blades are subjected to excessive heat stress?
What type of failure is most likely when turbine blades are subjected to excessive heat stress?
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How does thrust change with high temperatures in a jet engine?
How does thrust change with high temperatures in a jet engine?
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What purpose do nozzle guide vanes serve in a gas turbine engine?
What purpose do nozzle guide vanes serve in a gas turbine engine?
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What is creep in the context of turbine operation?
What is creep in the context of turbine operation?
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The efficiency of converting kinetic energy into propulsive work is known as what?
The efficiency of converting kinetic energy into propulsive work is known as what?
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Which condition is most likely to lead to creep in turbine blades?
Which condition is most likely to lead to creep in turbine blades?
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What happens to thrust when an aircraft's forward speed increases and the engine experiences ram effect?
What happens to thrust when an aircraft's forward speed increases and the engine experiences ram effect?
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What is a common method to compare engine efficiencies?
What is a common method to compare engine efficiencies?
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What is the primary role of the turbine section in a jet engine?
What is the primary role of the turbine section in a jet engine?
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How does the passage between adjacent nozzle guide vanes in an impulse-reaction turbine function?
How does the passage between adjacent nozzle guide vanes in an impulse-reaction turbine function?
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Which component experiences the highest heat in contact within a jet engine?
Which component experiences the highest heat in contact within a jet engine?
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At what Mach speed does ram pressure recovery typically begin to take effect?
At what Mach speed does ram pressure recovery typically begin to take effect?
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What is the maximum practical angle through which the gas flow can be turned during thrust reversal?
What is the maximum practical angle through which the gas flow can be turned during thrust reversal?
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What happens to pressure and velocity in the first part of the exhaust duct when an exhaust cone is placed aft of the turbine?
What happens to pressure and velocity in the first part of the exhaust duct when an exhaust cone is placed aft of the turbine?
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What is the consequence of having an exit area of the nozzle that is too large?
What is the consequence of having an exit area of the nozzle that is too large?
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How can exhaust noise be effectively reduced?
How can exhaust noise be effectively reduced?
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What should be done if damage is found to the reverse thrust cascade vanes?
What should be done if damage is found to the reverse thrust cascade vanes?
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Through what angle are exhaust gases turned in a clamshell type thrust reverser?
Through what angle are exhaust gases turned in a clamshell type thrust reverser?
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What type(s) of main bearing oil seals are typically used with turbine engines?
What type(s) of main bearing oil seals are typically used with turbine engines?
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Why are oil seals pressurized in turbine engines?
Why are oil seals pressurized in turbine engines?
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Study Notes
Gas Turbine Engine Fundamentals
- Axial flow, dual compressor forward fan engines have a fan that rotates at the same speed as the low-pressure turbine.
- Turbine discharge pressure is often identified using Pt7.
- Turbojet and turbofan engines accelerate a smaller mass of air, while turboprop engines accelerate a larger mass of air.
- Effective perceived noise decibels (EPNdB) are used to measure aircraft noise.
- The combustion section is responsible for mixing fuel and efficiently burning gases.
- Turbojet engines are smoother than piston engines because they lack reciprocating parts.
- The jet nozzle is located in the exhaust section of a turbojet engine.
- The Brayton cycle is a constant pressure cycle.
- The highest pressure in a gas turbine occurs just after the last compressor stage, before the burner.
- In a ducted fan engine, the fan is driven by the turbine.
- Bernoulli's theorem relates kinetic, pressure, and potential energy in a fluid flow.
- The Brayton cycle describes the continuous combustion cycle in a gas turbine engine.
- High bypass ratio turbofan engines have smaller compressors and combustion chambers compared to turbojet engines.
- Jet propulsion is based on the principle of action and reaction.
Engine Performance
- Ram effect increases engine efficiency due to aircraft forward speed.
- Ram effect does not change engine thrust.
- The highest heat to metal contact in a jet engine occurs at the turbine inlet guide vanes.
- Thrust increases with low temperature.
- Specific fuel consumption is used to compare engine efficiencies.
- Mechanical efficiency measures the conversion of kinetic energy into propulsive work.
- Engine rating plugs control thrust rating on FADEC-controlled engines.
- With increasing forward speed, engine thrust decreases slightly but recovers due to ram effect.
- Thrust increases at low temperatures.
- Ram pressure recovery generally takes effect at speeds between Mach 0.1 and 0.2.
- To maintain selected RPM at altitude, fuel is automatically reduced during climbs.
- Ram Recovery is a measure of intake efficiency.
- Gas turbine efficiency is greatest at cold temperatures.
Engine Inlet
- Electrical de-icing systems do not affect thrust.
- A pitot intake is divergent to maximize ram compression.
- Inlet guide vanes are anti-iced using engine bleed air.
- A divergent intake is divergent from front to rear.
- Variable inlet guide vanes are operated by fuel pressure.
- Intakes are designed to convert kinetic energy into pressure energy through forward speed.
- Intakes decelerate the free air stream flow.
- De-icing systems break up ice formations on turboprop engine nose cowls.
Engine Compressors
- A bypass engine LP compressor supplies more air than needed for combustion.
- A bypass ratio of 5:1 signifies the bypass flow is five times the hot stream.
- During high RPM operation, variable guide vanes are at minimum swirl and bleed valves are closed.
- Stator vanes straighten airflow after the axial flow compressor to reduce turbulence.
- Variable guide vanes and compressor bleed valves help stabilize compressor airflow.
- The boundary layer is the thin layer of air that adheres to a surface.
- The boundary layer flow is most affected by the surface along the leading edge, parallel to the edge.
Engine Turbines
- The turbine assembly provides power to rotate the compressor in a turbojet engine.
- Shrouded blades allow for thinner, more efficient blade sections.
- Shrouded turbine rotor blades reduce vibration and improve airflow characteristics.
- Excessive heat stress in turbine blades can lead to stress rupture.
- Shrouding rotor blade tips minimizes vibration.
- Nozzle guide vanes are fitted to increase the velocity of gas flow.
- Turbine rear struts straighten the gas flow.
- Creep is a permanent deformation of turbine blades.
- Creep can occur due to prolonged over-temp with excessive centrifugal loads.
- Cracking is a common occurrence in the turbine section of a jet engine.
- The turbine section converts dynamic pressure into mechanical energy.
- The passage between nozzle guide vanes in an impulse-reaction turbine forms a convergent duct.
- Secondary creep is a slow and constant growth in a turbine blade.
Engine Exhaust
- The exhaust cone assembly straightens and collects exhaust gases into a solid jet.
- The maximum practical angle for thrust reversal is 135 degrees.
- An exhaust cone increases pressure and decreases velocity in the first part of the exhaust duct.
- A nozzle exit area that is too large lowers exit velocity, reducing thrust.
- Exhaust noise can be reduced by increasing the mixing rate.
- Replace damaged reverse thrust cascade vanes with new ones that match the original part.
- Clamshell door thrust reversers redirect the exhaust stream 45 degrees to the thrust line.
Bearings and Seals
- Main bearing oil seals in turbine engines are typically labyrinth and/or carbon rubbing types.
- Indentations on bearing races caused by high static loads are called brinelling.
- Oil seals are pressurized to minimize oil loss.
- Some labyrinth seals control the outflow of air at the turbine.
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