15.1 Fundamentals Flashcards
What is a change of state in terms of airflow through the engine?
A thermal process which entails a transformation of heat energy into mechanical
What are the four ideal changes of state and which are of importance in gas turbine engines?
-isobaric
-isochric
-isothermal
-isentropic
(Isobaric isentropic)
What is the compressors function?
To increase static pressure
What turns the compressor?
The turbine
What is potential energy?
Energy contained virtue of its position
What is kinetic energy?
Energy contained virtue of its motion
What is the formula for potential energy?
PE = mgh
Mass = M
Gravity = gravitational constant
Height = height
What is the formula for kinetic energy?
2
KE = 1/2 mv
Mass = m
Velocity = v
What is Newton’s first law?
The law of inertia
What is Newton’s second law?
Force = mass x acceleration
What is Newton’s third law?
Every action has an equal and opposite reaction
What are the stages of the Brayton cycle?
-intake
-compress
-combust
-exhaust
What is the working fluid in a gas turbine engine?
Air
What is isobaric heating?
Volume increases pressure remains the same
Where does isobaric heating occur?
The combustion chamber
Where is the highest pressure in the engine?
The inlet of the combustion chamber
Where is the highest temperature in the engine?
Rear of the combustion chamber/ the first stage nozzle guide vane
What is isentropic compression?
Pressure increases volume decreases
What is a brayton cycle?
The thermodynamic cycle of a gas turbine engine
What is the formula for work?
Force x distance
Expressed in joules or nm
What is the formula for power?
Work/time
Expressed in watts
What is motion?
A continuous change of position or place
What is acceleration?
The rate of change of velocity
What is the formula of acceleration?
Change in velocity (m/s) / time (s)
What is speed?
How fast an object is moving/ the time it takes for an object to mover a distance
What is velocity?
Speed with direction
What are the characteristics of a turbojet engine?
Good
-efficient at high speed
-compact
Bad
-high fuel consumption
-poor performance at low speed
-limited range and endurance
What are the characteristics of turbofan engines?
Good
-They produce 80% of their thrust with front mounted fans
-They are more efficient then turbojet
Bad
-inefficient at high altitudes
-heavier
-large frontal area
What are the characteristics of turboprop engines?
-Using the turbo jet principle and applies the force to a propellor for small commuter aircraft
-it has additional turbines to try and produce shaft horsepower only
-very fuel efficient
-most efficient at mid altitude and mid speed
-the gearing systems are heavy
What are the characteristics of turboshaft engines?
-It uses the shaft to power machinery
-small and light (APU)
-high power to weight
-smaller than a piston engine
-loud
-the gear systems can be complex
What are the characteristics of piston engines?
Fuel efficient
Poor at high altitudes
In very small aircraft
What is a twin spool vs a three spool turbine arrangement?
A twin spool has a turbine powering the low pressure compressor and the fan with a turbine powering the high pressure compressor
A three spool has a third spool dedicated to the fan
What is important to remember regarding spools?
-They operate independently
-it’s effectively a turbine powering a compressor
What is the gas generator in turbo prop engine?
The compressor, combustor and turbine
Where are cobalt materials used?
Hot areas
What are the characteristics of materials used in engines that are most desirable?
Strong enough and cheap
