Module 15.1 Fundamentals Flashcards
Define energy.
Something that gives us the capacity to perform work.
Work and energy are measured in what unit?
Joules
What are the two types of energy?
Potential and Kinetic energy.
Define potential energy.
Energy at rest or energy that is stored.
What is the formula for potential energy?
Potential Energy (PE) = Mass x Gravity x Height
Define kinetic energy.
Energy that is in motion.
What is the formula for kinetic energy?
Kinetic Energy (KE) = ½ x Mass x Velocity squared.
What is Newton’s first law?
An object will remain at rest or continue moving at a constant speed in a straight line unless an external force acts upon it.
The law of inertia.
What is Newton’s second law?
Force = Mass x Acceleration.
What is Newton’s third law?
For every action, there is an equal and opposite reaction.
How does Newton’s second law link to a Gas Turbine Engine (GTE)?
Thrust is proportional to the mass of the airflow multiplied by the acceleration of the air through the engine.
How does Newton’s third law link to a Gas Turbine Engine (GTE)?
Thrust moving rearwards at high speed produces an equal and opposite reaction, which propels the engine and the aircraft forward.
What is the Brayton cycle?
The name given to the thermodynamic cycle of a gas turbine engine that produces thrust.
What is the thermodynamic cycle?
A variable-volume constant pressure cycle of events.
What are the four stages of the Brayton/thermodynamic cycle?
Intake (suck), compression (squeeze), expansion (bang), and exhaust (blow).
What happens to the air at the intake (suck) stage?
Air enters at ambient pressure and constant volume. Its pressure is slightly increased and volume is decreased.
What happens to the air at the compression (squeeze) section?
It gets compressed. There’s a large increase in pressure and a decrease in volume
What happens to the air at the expansion (bang) stage?
Pressure remains relatively constant, but there’s a small increase in volume.
What does the turbine assembly do the expanding gases?
It converts it from velocity energy to mechanical energy.
This drives the turbine.
What happens to the air at the exhaust (blow) stage?
It converts the expanding volume and decreasing pressure of the gases to a final high velocity.
What type of duct does the exhaust use?
A convergent duct.
What type of process is the Brayton cycle?
An isobaric constant pressure process (specific to the combustion section).
The thermal processes are known as what?
‘Changes of state’.
What are changes of state caused by?
Heating or cooling as well as expansion or compression.
What is the Isobaric process?
Constant pressure process.
What is the Isochoric process?
Constant volume process.
What is the Isothermal process?
Constant temperature process.
The Brayton cycle process from stage 2 to 3 is called what?
Isobaric heating (constant pressure).
This would occur in the combustion chamber.
Define force.
The intensity of thrust or input
What is the formula for force?
Force = Mass x Acceleration.
What is thrust expressed in?
Pounds
What is 1 pound equal to in newtons?
4.448 newtons
Define work?
A measure of the energy transferred when a force is moved through a distance.
What is 1 joule in newton meters?
1 Nm
What is the formula for work?
Work = Force x Distance.
Define power.
How long it takes to accomplish the work.
What is the formula for power?
Power = Work ÷ Time
What is speed?
How fast an object is moving, or how far the object will travel in a specific time.
What does the speed of an object not tell you?
The direction an object is moving.
What is velocity?
Both the speed of an object and the direction it’s moving in.
Velocity is also described as being what?
A vector quantity.
Define acceleration.
The rate of change of velocity.
What is the formula for acceleration?
Acceleration = Change in Velocity ÷ Time.
Before air gets to the combustion section, what needs to be done to it?
It needs to be compressed by the spinning compressor section.
What is some of the energy from the air combustion section also used to drive?
The turbine.
What is the turbine also used to turn?
The spinning compressor.
All gas turbine engines easily provide what?
Thrust or torque (depending on the engine) and bleed air
What four types of gas turbine engine are there?
Turbojet engines (thrust)
Turbofan engines (thrust)
Turboprop engines (torque)
Turboshaft engines (torque)
A turboshaft engine that drives the propeller is now what?
A turboprop engine.
A turboshaft engine that drives anything other than a propeller is what?
A turboshaft engine.
How do turbojet engines generate thrust?
By pushing air through the exhaust nozzle.
In what speed range do turbojet engines have a problem with noise and fuel consumption?
In the range of Mach 0.8.
What is the two major disadvantage of turbojet engines?
Poor performance at slow speeds.
Limited in range and endurance.
A turbofan being bigger than a turbojet engine allows for what?
More mass flow.
What does the fan section also do to the air?
Accelerates it slightly.
More mass flow and acceleration allows for what?
Greater thrust
What is the first part of the low pressure (LP) compressor
The fan
After the fan, air is separated into what two areas?
Bypass (cold) and core (hot) flow.
More air goes to the bypass than core (compression & combustion etc).
What is bypass ratio?
The ratio between core and bypass flow.
In turbofan engines, what percentage of the thrust is produced from the bypass?
80%
What are the two arrangements of turbofan engines called?
Twin spool or three spool arrangement.
What does a spool consist of?
A turbine that drives a compressor through a shaft.
What does a twin-spool arrangement have?
A high pressure turbine driving the high pressure compressor.
A low pressure turbine driving the low pressure compressor and fan.
What does a three spool arrangement have?
A high pressure turbine driving the high pressure compressor.
An intermediate pressure turbine driving the intermediate compressor.
A low pressure turbine driving the fan.
Which shaft is the outer and which is the inner most?
HP shaft is the outermost shaft. LP shaft is the innermost shaft.
Where would the intermediate shaft be in a three spool arrangement?
In the middle.
Which shift is the longest and which is the shortest?
LP shaft is the longest shaft. HP shaft is the shortest shaft.
What is the major disadvantage to turbofan engines?
Inefficient at very high altitudes.
What do turboprop engines generate to drive the propeller?
Torque. The propeller creates the thrust.
What are the primary differences between a turboprop and turbojet engines?
Additional turbines, a power shaft, and a reduction gearbox.
Why is a reduction gearbox incorporated into a turboprop engine?
To drive the propeller.
What is the most efficient mid-range speed of turboprop engines?
Between 250 - 400 knots
What is the most efficient mid-range altitude of turboprop engines?
18 000 - 30 000 feet
What do turboshaft engines produce?
Shaft power (torque) drive machinery.
A turboshaft engine in large aircraft is known as what?
An Auxiliary Power Unit (APU).
The Auxiliary Power Unit (APU) is used to supply the aircraft what?
Electric and pneumatic power if the main engines are not available.
What is the main advantage of turboshaft engines over piston engines?
Much higher power-to-weight ratio.
What are the separate sections in the engine dedicated to perform?
Each function simultaneously without interruption (modular engine construction).
What is another way of describing the various sections of a turbine engine?
The “cold section” and the “hot section”.
What does the cold section refer to?
Parts of the engine from the inlet, to the compressors and/or diffusers.
What does the hot section refer to?
Areas past the compressors from the combustion chambers through to the exhaust.
What is the major advantage of a modular engine construction for the manufacturer
The rotating module parts can be pre-balanced.
What is the major advantages of a modular engine construction for the operator.
Most modules can be replaced while the engine remains on the aircraft.
