15.1 Flashcards
What is the definition of energy?
Something that gives us the capacity to perform work
What is kinetic energy?
Energy in motion
What is the formula for kinetic energy?
1/2 x M x V^2
What is potential energy?
Stored energy or energy at rest
What is the formula for potential energy?
M x G x H
What is kinetic energy measured in?
Joules
What is the unit for potential energy?
Joules
What is Newtons first Law?
The law of Inertia
What is Newtons second Law?
It covers the interplay between force and motion which allows us to analyse the motion of an object
What is Newtons Second Law expressed using what formula?
Force = Mass X Acceleration
What is Newton’s third law?
Action and reaction
What is the name given to the thermodynamic cycle of a gas turbine engine that produces thrust?
The Brayton Cycle
What are the 4 stages of the Brayton cycle?
Suck, squeeze, bang, blow
Using its volume and pressure to describe it, what is the Brayton Cycles features?
Constant pressure cycle and variable volume
What is the Brayton cycle also known as?
Continuous combustion cycle
In the intake of a GTE, at what pressure and what volume does air enter?
Ambient pressure at a constant volume
How does air leave the intake in terms of pressure and volume?
At increased pressure and a decrease in volume
After going through the compressor, what happens to the air?
Pressure increases and volume decreases.
Where does expansion take place?
In the combustion chamber where it heats the air which expands it.
What happens to pressure velocity and volume in the combustion chamber?
Pressure remains relatively constant if not decreases but velocity increases. Volume increases
What does the turbine do?
Converts velocity energy into mechanical energy to drive the shaft connected to the compressor turbines.
What type of duct is on the rear of the engine?
Convergent duct
What does the convergent duct increase?
Velocity
What are the 4 ideal changes of state and which of these are used on a gas turbine engine?
Isobaric (Used)
Isochoric
Isothermal
Isentropic (Used)
The changes of state are put on a graph that represents what two features?
Pressure and Volume
What was point 0 represent?
Atmospheric conditions
Along the lines 0-2, what takes place and what does this cause?
Isentropic compression of the air meaning the pressure increases and volume decreases
What happens in stages 0-1?
Ram or dynamic compression in the air intake
What happens In stages 1-2?
Compression in the compressor
What stage is also known as isobaric heating?
2 to 3
What is isobaric heating?
When heat is added to the air in the combustion chamber by using fuel to burn it
What does the line from 3-5 represent?
Isentropic expansion which results from combustion expanded through the turbine to drive the compressor
What are stages 4-5?
The remaining energy
What is the formula for force?
Force = Mass x Acceleration
What is force?
The intensity of an input
What is force measured in?
Lbs (English system) and N (Metric)
What is work?
A measure of energy transferred during a force over a distance.
What is work measured measured in?
Joules
What is the formula for work?
Work = Force x Distance
What needs to happen in order for work to be done?
The object victimised under work needs to be moved against a restrictive force
What is the formula for power?
Power = Work / Time
What is the SI unit for power?
Watts
What is motion?
The continuing change of position or place when a body undergoes displacement
When is motion uniform?
When an object remains the same for a given period of time
What will happen if a moving object is in uniform?
It remains at constant speed
What is speed?
How fast an object is moving or how far it’ll travel in a specific amount of time
What is velocity?
The quantity that describes both speed and direction
What is acceleration?
The rate of change in velocity
What is the formula for acceleration?
Change in velocity (m/s) / time (s)
What are the three main functions of an aircraft’s engine?
Hydraulic power, Bleed air and electrical power
What are the 2 different types of aircraft engines?
Piston and Gas
2 advantages of piston type engines that turn a propellor?
Fuel efficient and simple designs
What are the disadvantages of piston engines?
- Performance decreases at high temperatures as the air is thinner.
- The ratio of weight and power decreases regarding size.
- Only used on small aircraft
Where are piston engines often used?
Small aircraft
Where are piston engines often used?
Small aircraft
What are gas turbines engines good for?
At high altitudes
What was the first type of a gas turbine engines?
Turbojet
Advantages of turbojet engines?
- Relatively simple designs
- Capable of high speeds
- Take up little space
Disadvantages of turbojet engines?
- High fuel consumption
- Loud
- Poor performance at slow speeds
- Limited in range and endurance (0.8 Mach)
What are the advantages of a turbofan engine? (improvement from turbojet)
- Makes high aircraft speed possible with good engine efficiency
- Quiter
-Better fuel consumption
What principle do turbofan engines work off of to produce thrust?
They turn a large fan or set of fans to produce 80% of thrust
What does a spool consist of?
A turbine driving a compressor through a shaft
Advantages of turbofan engines?
- Fuel efficiency
- Quieter than turbojets
- Streamlined
Disadvantages of turbofan engine?
- Heavier than turbojets
- Larger frontal area
- Inefficient at high altitudes
What are turboprop engines specifically used for?
To produce shaft horsepower only which is used to drive a prop
What is the primary difference between the turboprop and the turbojet?
It has additional turbines, power shafts and a reduction gearbox to drive the propellor
Advantages of a turboprop engine?
- Fuel efficient
- Most efficient at mid range speeds and altitudes
What are the disadvantages of turboprop?
- Heavy so can break down
- Limited forward airspeed
What are the disadvantages of turboprop
What are the disadvantages of turboprop engines?
- Limited forward airspeed
- Heavy so can break down
What is the purpose of the turboshaft engine?
Produces shaft power to drive machinery not thrust
What engine is used for the APU and helicopters to provide pneumatics and electric power?
Turbo shaft
Why are turboshafts used for helicopters and APU?
A small, but powerful lightweight engine
What are the 2 advantages of turbo shaft engines?
Smaller and much higher power to weight ratio
What are the two ways of describing the various sections of a turbine engine?
Cold and hot sections
What is an advantage of modular designs in engines?
They are classed as minor repairs so work can be done via a maintenance organisation.
Where is the highest temp of the combustion chamber?
Rear if combustion chamber or the 1st stage nozzle guide vane
Where is the highest static temperature located?
Inlet of combustion chamber but outlet of the compressor
What are the stationary vanes (Stators) used for?
To straighten air prior to the compressor to guide to the rotor blade
Where has the highest static pressure?
The inlet of the combustion chamber
What are the resultant features of a convergent duct?
Decreases temp, increases dynamic pressure, reduces pressure
Why would you use convergent duct?
To increase thrust
How does air move in a turbofan engine?
Large amounts of air slowly
How does air move in a turbojet engine?
Small amounts of air quickly (makes it noisy and less fuel efficient)
What does the twin spool arrangement consist of?
High pressure turbine driving the high pressure compressor and a low pressure turbine driving the low pressure compressor and a fan
What does a three spool arrangement consist of?
A high pressure turbine driving the high pressure compressor, an intermediate pressure turbine driving the intermediate compressor and a low pressure turbine driving the low pressure compressor and fan
How are spools connected?
Aerodynamically
Do spools run independently?
Yes
How do you slow the fans down and why?
You give it its own turbine so it doesn’t affect the compressor speed. (You can put a reduction gearbox to do this) so the propellers don’t flutter and break
What regarding spools in the engine are primary indications in the cockpit?
N1 n2 and n3 which is the rotational frequency.
What is the gas generator in turboprop engines?
The core. Compressor, turbine and combustion chamber
How do you drive a propellor in a turboprop?
You add extra turbines
2 functions of APU?
Pneumatic air and electricity
How many spools means they run at the same speed?
2
What pressure spool is the gearbox connected to?
High pressure spool
What is the stator motor connected to that turn the gears in the gearbox to turn the shaft that spins the compressor? (Spins HP first)
The gearbox
What does the gas generator consist of?
A compressor combustion and turbine
What are the 4 advantages of a modular engine for the manufacturer?
Rotating module parts can be pre-balanced
Fewer spare engines are needed in stock
More flexibility when changes are made to individual engine parts
Main engine modules can be easily stored and transported
What are the 5 advantages of a modular engine for the operator?
Modules can be replaced with minimum disturbance to other nearby engine parts
No re-balancing is required after a module change
Most modules can be replaced while the engine remains on the aircraft
Less need for spare parts and modules can be easily transported
Work can be done by a maintenance organisation instead by an engine overhaul organisation, as a module replacement is considered a minor repair not a shop repair
