C (thrust Augmentation) Flashcards
What is thrust augmentation?
Thrust augmentation is the additional boost of thrust required during critical phases of flight, such as take-off, particularly for older and smaller aircraft engines.
What factors affect thrust and power in a gas turbine engine?
Thrust and power are affected by the density of air, which changes with temperature and altitude.
What is the basic formula for engine momentum thrust?
Thrust = Mass Airflow Rate x (Velocity Out - Velocity In)
How can thrust be increased?
Thrust can be increased by either increasing the mass airflow or increasing the exit velocity of the exhaust gases.
What are the two methods to increase mass airflow?
Mass airflow can be increased by injecting water into the compressor or into the combustion gas flow.
What is compressor water injection?
Compressor water injection involves spraying water into the compressor, where it evaporates, cools the airflow, and increases its density.
What is combustion system water injection?
Combustion system water injection cools the gases, allowing additional fuel to be burned without exceeding temperature limits, thereby increasing mass flow.
What is reheat in the context of gas turbine engines?
Reheat, also known as afterburning, is a method to increase exhaust gas velocity, primarily used in military aircraft during take-off, climb, and combat.
Why is reheat limited in use?
Reheat is limited to short periods of use due to increased fuel consumption.
What types of aircraft still use water injection systems?
Water injection systems are now primarily found on some older types of Turbo-Prop aircraft.
What limits the combustion chamber temperature rise in an engine?
The temperature limitations of the turbine blade material limit the combustion chamber temperature rise.
What happens to the air in the combustion chamber?
Only a certain percentage of the air is burned.
How is thrust increased in an engine?
Mixing and burning fuel with unburnt air further accelerates the gases, providing an increase to the basic thrust.
What are the two main areas where gas turbines produce noise?
Gas turbines predominantly produce noise around the Fan/Compressor and the Jet Pipe/Exhaust.
What causes fan noise in gas turbines?
Fan noise is caused by the sound of rotating assemblies in their bearings and complex aerodynamic interactions.
How can fan noise be reduced?
Fan noise can be reduced by installing noise suppressing acoustic liners or by changing the intake design to create a scarfed intake.
What is a scarfed intake?
A scarfed intake reflects fan noise upwards away from the ground by creating an extended lower lip.
What is a Noise Suppressing Liner?
A component designed to reduce noise in gas turbine engines.
What is a Scarfed Intake?
An intake design that helps in noise suppression for gas turbine engines.
How can exhaust noise be suppressed?
By changing the way the gas mixes with ambient or bypass air.
What type of exhaust duct was used in early turbojets?
‘Lobe’ type exhaust duct that mixed ambient air with exhaust gas.
What is a modern method for reducing exhaust noise in fan engines?
Using serrations in the trailing edges of the Nacelle and Nozzle.
