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171 Cards in this Set
- Front
- Back
- 3rd side (hint)
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The thrust created by a turbine engine is based on Newton’s ____________ law
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Newton's 2nd Law
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F=ma
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What type of gas turbine engine sends all the air from the intake into the engine core for thrust development
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Turbojet
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What type of gas turbine engine would be utilized on a helicopter?
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Turboshaft
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The ________________________ cycle describe the operating principles of a gas turbine engine.
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Brayton Cycle
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The compressor in a gas turbine engine increases the ______________ of the airflow through the engine core.
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pressure
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Which type of gas turbine compressor has a higher compressor ratio per stage?
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Centrifugal compressor
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What is the rotating component of a centrifugal compressor?
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Impeller
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What types of gas turbine engines utilize centrifugal compressors?
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Turboprops
Turboshafts Small turbofans |
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What two components make up one stage of an axial compressor?
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Rotor and stator
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On a 2-spool turbine engine, the low pressure turbine will drive the ________________________.
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low pressure compressor (LPC)
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What is the main function of the turbine in a gas-turbine engine?
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Drive the compressor
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What material is used in the construction of turbine blades?
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Nickel alloys with a ceramic matrix coating
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What type of turbine blade construction is the most resistant to creep?
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Single crystal
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Boeing 767 and Airbus A310
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The fan section of a turbofan engine provides the ____________________ in Newton’s second law relating to jet thrust.
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mass
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On a turbofan engine, the starter engages and directly rotates the ______________.
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High Pressure Compressor (HPC)
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On a two-spool turbofan engine, the N1 tachometer indicates the speed of the ____________________.
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Low Pressure Compressor (LPC)
Fan |
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On a two-spool turbofan, the N2 tachometer indicates the speed of the ____________________.
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High Pressure Compressor (HPC)
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What are the sources of potential energy in a gas turbine engine?
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pressure
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Bernoulli's Principle
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Where is the most kinetic energy produced in a gas turbine engine?
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velocity
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Bernoulli's Principle
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List at least three reasons why turbofan engines are better than reciprocating engines?
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1. Higher altitudes
2. More power 3. Easier maintenance |
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What advantages does a turboprop engine have over a reciprocating engine?
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better performance at lower altitudes
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Which parts of a gas turbine engine provide the “suck”, “squeeze”, “bang” and “blow” respectively?
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Suck = inlet
Squeeze = Compressor Bang = Combustors Blow = Exhaust |
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Why have turbofan engines replaced turbojet engines?
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They are more fuel efficient
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The potential energy in the mass airflow of a gas turbine engine is the ____________ of the air in the engine.
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pressure
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Bernoulli's Principle
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The kinetic energy of the mass airflow of a gas turbine engine is the _____________ of the air in the engine.
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velocity
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Bernoulli's Principle
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Who developed the turbo-supercharger for reciprocating engines?
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Dr. Sanford Moss
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How does a jet engine propel an aircraft forward?
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Forces the motion of air backward
Creates an equal and opposite force propelling the aircraft forward Engine takes in air at the inlet and expels it out the exhaust at a higher velocity |
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How is the amount of force developed by an engine determined?
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The mass of the air
Acceleration of the air |
Newton's 2nd Law
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What is the main disadvantage of using a rocket engine to power a transport aircraft?
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Limited burn time
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What type of jet propulsion is being developed for hypersonic transportation?
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SCRAM Jet
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It's a rocket, combusting air at speeds above the speed of sound
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How do pulse jets work?
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Inlet valves open to allow air, which - combined with fuel - allows for combustion
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What was the first type of turbine engine manufactured? With what commercial aircraft did it first appear?
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Turbojet engine
DeHavilland Comet |
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True or false, a turbofan uses all of the inlet air in the combustion process
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False. Some of the air is bypass air, which helps cool the engine
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True or false, a turbofans, turbojets, and turboprops share the same basic internal components?
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True
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How much of the thrust in a turbofan engine is generated from the initial fan stages?
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Up to 80%
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What is a bypass ratio? What is considered a high bypass ratio?
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The ratio of bypass air to combusted air.
A high bypass ratio is 5:1 (a Boeing 777 with GE engines is 9:1) |
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How is a propeller driven in a turboprop?
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The horsepower from the turbine-compressor shaft drives the propeller via a reduction gear.
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How much of the exhaust gas energy is used to spin the propeller?
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90%
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Aside from a helicopter rotor, what else does a turboshaft drive?
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Auxiliary Power Units (APUs)
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What do planes use on the ground when engines are turned off?
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How do turbines create thrust?
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Turbines manipulate gas with pressure, temperature, and volume to create useful work
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True or false: the compressor decreases pressure
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False. The compressor increases pressure
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What is Boyle's Law?
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Volume of a confined body of gas varies inversely as its absolute pressure changes with the temperature remaining constant
P1V1 = P2V2 |
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What is Charles' Law?
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Volume of a gas varies in direct proportion to the absolute temperature
V1/T1 = V2/T2 |
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What is the Combined Gas Law?
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(P1V1)/T1 = (P2V2)/T2
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What is the 1st law of Thermodynamics?
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Conservation of Energy:
Energy is neither created nor destroyed. Energy changes from one state to another. |
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What is the second law of thermodynamics?
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Heat cannot be transferred from a colder body to a hotter body
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What is pressure?
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Pressure = force/area
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What types of pressures are used in describing turbine engine parameters, and how are they referenced?
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Absolute pressure = referenced from zero pressure (vacuum)
Gage pressure = referenced from existing atmospheric pressure Differential pressure = difference between two pressures |
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What types of pressures are used for measuring?
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Static pressure = pressure of still air
Ram pressure = increase of pressure from the motion of air Total pressure = static + ram pressure |
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What is Bernoulli's principle? Is it a direct or inverse relationship?
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Total energy in a column of Moving fluid remains constant throughout the column
It is an inverse relationship between these two forms of energy: Potential energy = pressure Kinetic energy = velocity |
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Where is a converging duct used? What is the relationship between pressure and velocity here (assuming subsonic airflow)?
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It is used in the exhaust nozzle
Velocity increases Pressure decreases |
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Where is a diverging duct used? What is the relationship between pressure and velocity here?
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Used for the air intake of an engine
Velocity decreases Pressure increases |
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What is Newton's 1st Law of Motion?
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A body at rest stays at rest and a body in motion stays in motion in a straight line unless acted on by an external force
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What is Newton's 2nd Law of Motion?
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F = ma
F = force m = mass a = acceleration |
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What is Newton's 3rd Law?
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Every action has an equal and opposite reaction?
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What is the cycle that describes power in a reciprocating engine?
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Otto Cycle
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Power events happen in one area in a sequence
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What is static thrust?
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Amount of thrust developed when the engine is NOT moving through the air (i.e. taxi)
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What is net thrust?
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Amount of force developed when the aircraft is in flight
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What is thrust?
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weight per unit time of the airflow through the engine
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What factors can have an effect on thrust?
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Altitude
Ram effect Engine speed Humidity Temperature Water injection (rain) Afterburning |
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What is the altitude effect?
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Mass air flow into the engine is determined by the density of air
Altitude increases, air density decreases and thrust output decreases |
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What is the ram effect, and what does it increase?
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Aircraft's airspeed increases as air enters the divergent inlet duct
Increase in density and thrust |
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What effect does engine speed have on thrust?
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At low engine speeds, increasing RPM means low thrust increase.
At high engine speeds, small increases of RPM mean large increases of thrust |
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What effect does humidity have on thrust?
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Air density is decreased, so horsepower and thrust decrease as the air is more humid.
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What effect does air temperature have on thrust?
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Thrust output has an inverse relationship with air temperature
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What effect does water injection (i.e. rain) have on thrust?
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Water injection increases the mass airflow and the fuel flow
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What does afterburning do?
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It increases thrust
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What is Thrust Specific Fuel Consumption (TSFC)?
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Amount of thrust divided by fuel consumption
Main measurement of turbine efficiency amount of fuel in lbs required to produce 1lb/hr in thrust the more thrust obtained per lb of fuel, the greater the efficiency |
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What is propulsive efficiency (PE)?
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Amount of thrust developed by the jet nozzle compared to the energy supplied to it in usable form
work completed / work completed + exhaust waste PE = 2V/(V+Vj) V =aircraft speed Vj = jet velocity @ propelling nozzle |
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What is thermal efficiency?
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Heat energy output/heat energy input
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Do higher turbine inlet temperatures equal a higher or lower thermal efficiency?
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Higher thermal efficiency (limited by metals in the engine)
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True or false, TE improves with the ram effect?
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True
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What is the average thermal efficiency for gas turbine engines?
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45-50%
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What type of gas turbine sends air through large fans around the core of the engine?
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Turbofan
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Boeing 777 (triple seven)
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The pressure of the air through a turbine engine increases each time it passes through a ________________ blade of an axial compressor.
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(blank)
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What three things are necessary to start a turbine engine?
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1. Airflow at correct pressure/volume
2. Spark (ignition) 3. Fuel flow via fuel nozzles |
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Turbofan engines with over 6,000 lb-thrust rating will use what type of starter?
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Air turbine starter
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When starting a turbine engine, what is introduced first, fuel or ignition?
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Ignition. If fuel is introduced first, it will pool up and cause an explosion in the engine, likely damaging it.
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On a turbofan engine, the starter engages and directly rotates the ______________.
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High Pressure Compressor (HPC)
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An N1 tachometer indicates the speed of the ____________________.
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Low Pressure Compressor (and fan)
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An N2 tachometer indicates the speed of the ____________________.
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High Pressure Compressor (HPC)
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The ____________________ is an indicator of thrust for turbofan engine.
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Engine Pressure Ratio
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What are the fan blades of the GEnX video made of?
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Carbon fiber with a titanium leading edge
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What two things does a high-bypass fan design reduce?
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Fuel consumption and engine noise
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Which kind of rotating does the turbine sections do?
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counter-rotate
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What does the TAPS acronym stand for? What does it allow?
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Twin
Annular Pre-Mixed Swirlers allow for consumption at reduced temperatures by 205C/401F |
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What are the three bladed disks in the compressor called on the GEnX?
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blisks
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What are the two modules of the engine?
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Fan and propulsor
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What do turbines in the GEnX do?
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Extract energy from the core flow
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What is the pressure ratio of the High Pressure Compressor (HPC) in the GEnX?
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23:1
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What is at the core of the GEnX engine?
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A 10 stage High Pressure Compressor (HPC)
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What is the fan of the GEnX made of? What is the advantage of the material used?
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composites
They are lighter and more durable than metals |
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How many sections are the RR turbofan engines built from, and what are they called?
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8 modules
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What are the fan blades made of for RR Trent engines?
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Hollow titanium
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Besides directing air into the engine, what’s the other purpose of the fan case on a turbofan engine?
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Contains engine failures and fan blades
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What is the operating environment for the turbines with respect to their material's melting point?
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300C/572F above the material's melting point
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temperature
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Why is it important to manufacture turbine blades from a single crystal of metal?
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Increases the blade’s durability, and makes it more creep-resistant
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After production, the turbine blades are visually inspected, dimensions checked by a computer and inspected by what other method?
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X-ray
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What was the first commercial aircraft to fly with RR engines? What is the most commonly RR powered plane now?
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1. Lockheed L1011 Tristar
2. Airbus A330 |
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What type of spool is the RR Trent engine turbofan?
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triple spool
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What is the Trent engine's fan case made of?
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Aluminum with kevlar
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What is the purpose of releasing a fan blade when testing a turbofan engine?
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To ensure the engine can contain the damaged fan blade and not damage the rest of the airframe
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What instrument is used in the final inspection of a RR Trent engine?
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a periscope
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This instrument can look inside the engine
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What parts make up the engine's cold section? Hot section?
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Cold section = inlet, compressors, diffuser
Hot section = combution, turbine nozzle, turbines, exhaust systems, thrust reversers |
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What's the difference between an inlet on a subsonic aircraft vs. a supersonic aircraft?
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subsonic = smooth and rounded with a slightly diverging inlet
supersonic = rectangular shaped with a retractable cone |
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What is one unique characteristic of turboprop inlets
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They incorporate dust, snow and ice separators for extreme conditions
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What do blow in doors do?
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allow more air into the engine and prevent compressor stalls
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What must supersonic inlet ducts do? What ways do they do it?
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The inlet nozzle is variable (both convergent and divergent). At the transition point, there is a shock wave created by a wedge that extends/retracts
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What type of attachment is used to attach the fanblades to a disk in a turbofan?
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Dovetail
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What are the disks in a turbofan made of?
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titanium (formerly steel)
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What does a wide-chord fan blade do?
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Eliminates need for mid-span supports
Fewer blades More thrust Greater fuel burn |
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What does a compressor do?
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Increases air pressure (mass) entering the combustor
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What are the two compressor types?
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Axial and centrifugal
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What is pressure ratio?
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outlet pressure/inlet pressure
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What is the efficiency factor?
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Actual compressor performance / theoretical performance
expressed as a percentage or decimal less than 1 |
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What are the components of a centrifugal compressor?
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Impeller
Diffuser Compressor manifold |
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What does a centrifugal compressor do?
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takes in air at the hub,
impeller spins and accelerates the air outward air enters diffuser section and exchanges velocity for pressure compressor manifold directs air into the combustion chamber |
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What is the compressor ratio for a centrifugal compressor?
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normally 6:1 to 8:1, sometimes higher
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What are the advantages of a centrifugal compressor?
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high compressor ratio
less expensive than axial compressors |
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What are the disadvantages of centrifugal compressors?
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Less efficient than axial compressors
Large frontal area Limited to two stages Direction changes of airflow |
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What two types of centrifugal compressors exist?
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double entry
single entry = seen in turboprop/turboshaft |
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Why are the clearance dimensions in the compressor critical?
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too much = inefficient
too little = rubbing of impeller blades |
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What do axial flow compressors do?
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Flows air in a straight path through the engine
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What are the components of an axial flow compressor?
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rotor and stator
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what is the compressor pressure ratio per stage for an axial flow compressor?
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1.2-1.3 per stage
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What are the advantages of an axial flow compressor?
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Straight path airflow with little energy loss
Use as many stages as necessary to achieve overall high pressure ratio Smaller frontal area than centrifugal High peak efficiency |
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What are the disadvantages of an axial flow compressor compared to a centrifugal one?
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weight and cost
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What materials are sued to make the axial flow rotor's disks? Blades?
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Disk
-Steel -Titanium Blades -steel -titanium -titanium w/ honeycomb core |
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What ways can axial flow rotors be attached?
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dovetail
fir tree centrifugal force |
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What is the angle of incidence and what happens to it along the blade's length?
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Angle of incidence = angle between blade chord line and longitudinal axis of engine, changing along the blade from the tip (highest) towards the root (lowest)
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What is angle of attack?
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angle between blade chord line and relative wind
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What are the two determinants to a blade's angle of attack?
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Velocity of airflow through compressor
Rotational speed of the compressor |
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What does a compressor stator do?
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Directs air onto the rotor blades at the correct angle
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True or false: each stator acts as a divergent duct
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true
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What are the first and last stators known as?
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first = inlet guide vane
last = exit guide |
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What type of ducts are guide vanes?
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Converging duct
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What do axial flow compressors do?
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Air exits trailing edge of rotor blade and enters stator blades
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What type of duct are the vanes for an axial flow compressor?
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divergent
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True or false: the axial flow compressor continuously decreases the air pressure after each stage
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False
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What causes a compressor stall (surge)?
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The angle of attack becomes too high
obstruction to the inlet airflow excess pressure in the burners abrupt flight maneuvers choking the airflow through the engine high crosswind component at takeoff and low speeds |
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How is compressor stall prevented?
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inlet doors
variable inlet guide vanes interstage bleed vanes |
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What is the cascade effect?
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The cumulative effect that occurs when the output of one series of components serves as the input to the next series
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What is a two-spool compressor?
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Two separate compressor sections are linked with two separate turbine sections
Low Pressure Compressor (LPC) N1 High Pressure Compressor (HPC) N2 |
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What is the configuration for a triple spool compressor?
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N1 = fan section
N2 = Low Pressure Compressor (LPC) N3 = High Pressure Compressor (HPC) |
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What is a diffuser and what type of area (convergent, divergent) is it?
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Bridge between compressor and combustion chamber, which is a divergent area
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What types of attachments are located at a diffuser?
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Fuel nozzles
Igniter plug Bleed air ports |
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What kind of requirements are there for combustion sections?
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Minimal pressure loss
high combustion efficiency low smoke emission low risk of flames combustion only in the chamber uniform temperature of gases |
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What is primary flow? How much does it make for total airflow?
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It is the combusted air, making up for 25-30% of total air
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What is secondary flow?
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Cooling air, making up 70-75% of total airflow
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What are the three types of combustors?
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Can
Annular Can-Annular |
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What are some characteristics of can combustors?
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Each can has its own combustion and cooling air.
Each can has its own fuel manifold and nozzles Each can is removable |
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Where are Can-Annular Combustors normally seen?
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Large turbofan and turbojet engines
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What makes a can annular combustor unique from a can combustor?
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They share the same airflow, and are interconnected
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What are some advantages of an annular combustor?
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Efficient use of space
Efficient fuel/air mixture Even temperature distribution |
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What are the disadvantages of annular combustors?
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Thin wall, easily damaged
Shorter life than cans More difficult to remove than cans |
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What do reverse flow annular combustors do?
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They shorten the overall length of the engine
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What do turbine nozzles do?
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Control speed, direction and pressure of hot gases
Provide the most effective flow for turbine section |
Where are they located?
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What type of duct does a turbine nozzle create?
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Divergent
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What does the turbine airflow in a turbine rotor blade do?
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Changes direction of airflow
Increases velocity Reduces pressure and temperature |
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What are the three types of turbine rotor blades?
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Impulse = direction changes only
Reaction = velocity of gases increases Reaction-Impulse = both |
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How are turbine blades attached?
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Fir tree style (groove)
Rivet or locking pin Expansion/contraction within groove |
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What does a higher Turbine Inlet Temperature (***) allow for? How is it achieved?
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Higher thrust
Higher horsepower Increased efficiency Achieved via cooling from HPC air |
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What do shrouded tip blades allow for?
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Reduced vibration
Minimal airflow loss |
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What is creep?
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the gradual, permanent deformation of a body produced by a continued application of heat or stress
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How is investment casting performed? What does it produce?
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Molten metal is poured into a ceramic mold under pressure or vacuum. Cooled to produce the single crystal
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Boeing 767
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What is hot isostatic pressing used for?
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Used for applying thermal barrier coatings on turbine blades
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What does an exhaust cone do?
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Directs exhaust air out of the turbines
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What are the three different types of exhaust nozzles?
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Convergent
Convergent-divergent Variable opening |
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Where are convergent exhaust nozzles commonly seen?
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turbojet and low bypass turbofan engines
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Where are CD exhaust nozzles normally seen?
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supersonic aircraft
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What do variable nozzles do?
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They maintain proper back pressure for engines (seen with afterburning engines on fighter jets)
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