15.7 Flashcards
What does exhaust do in a jet engine
Accelerate airflow from the turbine to efficiently generate thrust
How does APU reduce noise
Mufflers
What does the exhaust do in a turboprop engine
Guide gases overboard
Why does APU exhaust gases go overboard
All gas energy is absorbed by the turbine
Components of exhaust
Cone
Tailpipe
Exhaust nozzle
What does exhaust cone do
Collects exhaust gases from turbine section and gradually confers them into solid flow of gases
Exhaust cone assembly
Outer shell/ duct
Under cone
3/4 radial hollow struts/fins
What do radial struts do
Support inner cone
Straighten swirling exhaust gases that would of came out at a 45 degree angle
What’s the purpose for the hole at the tip of the cone
Allows cooling air to be circulated from the aft end of the cone
How is the tail pipe constructed
So it’s semi flexible in a bellows arrangement
What’s the need for a bellows arrangement
Allows movement in instillation , maintenance and thermal expansion
Two most common methods of protecting the fuselage structure
Blankets and shrouds
What’s the two types of exhaust nozzle designs
Converging for Subsonic gas velocities
Converging-diverging for supersonic gas velocities
What increases exhaust gases velocity
Converging nozzle
What % does thrust increase by increasing velocity
15-20%
How much thrust does a turboprop exhaust nozzle give you
10-15%
Why is the fixed type nozzle simplest
No moving parts
2 types of exhaust nozzle
Fixed or variable
When is a variable nozzle used
Augmenter or after burner is used
After the turbine what duct is there
Divergent to reduce turbulence in the airflow
When exhaust gases exceed Mach 1 what nozzle is would you use
Convergent - divergent
Advantage of convergent divergent nozzle
At high Mach numbers because of the resulting higher pressure ratio across the engine exhaust nozzle
Where does engine noise come from
Fan
Compressor
Air discharge from core of engine
Sources of noise
Air intake
Vibration
Engine exhaust
What happens in terms of noise with more thrust
High gas stream velocity and higher noise levels
What are the two types of noise suppressors
Perimeter type or the multi tube type
What’s the purpose of acoustic linings
Noise absorbing which coverts acoustic energy into heat
(Forms a porous skin)
Where is acoustic linings
In the nacelle between the engine and cowl
How do thrust reverses produce braking force
Deflecting exhaust gas steam in the opposite direction which creates a thrust force in the opposite direction of movement
Where can thrust reversers be used
Only on ground
Where is the deflection mechanism when not in operation
Flush with the wall so it doesn’t disturb normal exhaust gas stream
What aircraft is clamshell doors used on
Older jet engines with a low bypass ratio
How is a clamshell door operated
Pneumatically operated by bleed air from the HP compressor
What’s different about a bucket type door
Found on the same aircraft and clamshell but opened hydraulically
What conditions would thrust reverser be used
Wet , icy or snowy runway
What gives fan reverser its name
The fact that only cold fan air is deflected
What type of thrust reverser is a fan reverser
Cascade type with translating sleeves
Operated either pneumatically (drive motors) or hydraulically (actuators)
How does a pivoting door reverser work
Hydraulically activated
Closes off fan discharge airflow when deployed
When are thrust reverses most efficient
During high speed and shortly after touchdown
Disadvantages to thrust reversers ingesting reversers airflow
Compressor stall and high exhaust gas temperatures
Picks up FOD
How do we minimise disadvantages caused my thrust reverser operation
Reversed airflow is matched to the engine position
What’s an advantage to engines having the same cowlings
Fewer spare parts needed
What must you do with a defective thrust reverser system
Deactivate before flying to ensure it doesn’t deploy unintentionally
What’s thrust vectoring
Moving the direction of the exhaust nozzle to direct thrust to move in your desired path
