Exhaust Flashcards
Main task of exhaust
Guide exhaust gas from rear of turbine into atmosphere
What does the exhaust do in a jet engine
Exhaust system accelerates airflow from turbine to make thrust
What does the apu do in exhaust
Guides exhaust gases overboard as all gas energy absorbed by the turbine
What is the exhaust system tube called
Exhaust duct or tail pipe
How is the conical tube supported
At its forward end by turbine exhaust
Where is the exhaust nozzle and what does it do
Aft of the exhaust duct and accelerates gasses
What does the exhaust cone do
Guides discharge flow and prevents excessive turbulence of the gases
Prevents reverse flow of exhaust gases into the hub of the turbine rear stage
What’s the exhaust streams of a high bypass turbofan
Primary for hot gas
Secondary for cold air
What aircraft are combined exhaust nozzle used for
Modern long range aircraft
How does a combined exhaust nozzle work
Mixes gasses to reduce velocity
Advantage to common exhaust nozzle
Reduces exhaust gas velocity which higher propolsion efficiency
Disadvantage of common exhaust nozzle
Increases weight of engine
What does the addition mixer do
Improves the mixing of hot and cold gas flow to get higher propulsion efficiency but also adds weight
Why must exhaust gasses expand completely
To achieve optimum thrust from the given mass
Guarantees a laminar vortex-free and axially oriented exhaust gas flow
When is a convergent exhaust nozzle used
For max airflow with a pressure ratio up to 2:1
When is convergent divergent nozzle used
For pressure ratios bigger then 2:1 for aircraft’s to fly faster then speed of sound
Why are high exhaust gas velocities avoided
Decrease the propulsion efficiency
What unit is engine noise reduction
Effective Perceived Noise DeciBel EPNdB
What variable is engine noise dependent on
Velocity of gases
turbofan noise change depends on what ratio
Depending on bypass ratio
How can we suppress noise
Reducing airflow disruption
Airflow lining are equipped with noise absorbing materials
What is a porous surface made of and how does it minimise noise
Supported by honeycomb structures and converts sound energy into heat energy
What are the two types of liner
Single and double
How does a thrust reverser work
Producers a breaking force by deflecting exhaust gas stream to opposite direction
Most ideal deflection angle
180 degrees but causes problems for engine
What is the actual deflection angle
45-60 degrees
What air is used for thrust reverser
Only Bypass air
When are thrust reverses used
Only on ground
How is the bucket on common thrust revereres operated
Hydraulically operated
In a fan reverser what air is used
Cold fan is used which is secondary air
What’s type of reverser is a fan reverser
Cascade type with translating sleeves
How is a fan reverser operated
Pneumatically with drive motors
Hydraulically with actuators
How are pivot door reversers activated
Hydraulically
How can you minimise the disadvantages of reverse thrust
March reverse airflow with engine position
Why is angle of reverse steam important on 4 engine aircraft
Reverse airflow of the inner engines can be ingested by outer engines
What’s the use of a cascade vane
Directs the airflow of a thrust reverser
What advantage do large aircraft’s have in regards to thrust reversers
They use the same cowlings which means they can use less parts
Can aircraft’s be released to service with faulty thrust reversers
Yes
What does the control system do
Actives thrust reverser and increase engine power
What components does a reverser actuation system have
Pneumatic or hydraulic
What does the airflow deflection system do
Directs airflow in optimum direction for safe reverse thrust
What does thrust reverser interlock do
Makes sure engine power can only be increased once reverser is deployed
Where are hydraulic reverser actuation systems used
Reversers with translating sleeves and cascade vanes
What does thrust reverser locking system do
Makes sure reverser is locked and stowed
Where are blocker doors
Linked between the fixed cowl and translating sleeve
What are 4 cascade airflow directions
45 degrees up
45 degrees down
90 degrees straight
Some is blocked
What does reverse unlock message indicate
Reverse is not safe in its stowed position
What colour are reverse unlock messages
Amber & always shows when reverser moves from deployed to stowed
When is the green reverse light show
Reverser fully deployed and throttle interlock is released so engine power can be increased for reverser thrust
