Module 15.7 Exhaust Flashcards
What is the main task of the exhaust system on a jet engine?
Accelerate airflow from the turbine to generate thrust
What is the main task of the exhaust on a turboprop and APU?
Exhaust gases overboard
What is an additional feature of an APU exhaust?
Mufflers, for noise reduction
What are the components of the exhaust section?
- Exhaust cone
- Tailpipe
- Exhaust nozzle
The exhaust cone is what, to decrease velocity and increase the static pressure?
Diverging
What does the exhaust cone assembly consist of?
- Outer shell
- Inner cone
- Hollow struts (sole support for the inner cone)
What are the purposes of the radial struts in the exhaust?
- Support the inner cone by connecting it to the outer shell
- Straighten out airflow from the low pressure turbine
How is the tail pipe usually constructed?
Semi-flexible
What does the bellow arrangement allow for?
Movement in installation, maintenance and thermal expansion
What are the two methods for protecting the fuselage structure?
- Insulation blankets
- Shrouds
What are the two types of exhaust nozzle design?
- Converging (Subsonic)
- Converging-diverging (Supersonic)
What effect does a converging nozzle have on exhaust gases?
Increase in velocity, causing an increase in thrust (15-20%)
What are the two types of exhaust nozzle?
- Fixed
- Variable
When is a variable area nozzle used?
When there is an augmenter or afterburner.
Supersonic aircraft, making it divergent allows for supersonic airflow. As after mach 1 divergent ducts increase velocity and decrease static pressure, convergent have the opposite effect
What effect does changing the area/diameter of the exhaust nozzle have?
- Engine performance
- Exhaust Gas Temperature (EGT)
What section of a convergent-divergent exhaust handles air at subsonic speed?
Convergent
GTE’s require what for operations in airports or high population areas?
Noise suppression
What are the 3 sources of GTE noise?
- Air intake
- Engine housing vibration
- Engine exhaust (by far the most)
Noise levels vary with what?
Engine thrust
Why is a turbofan engine quieter than a turbojet?
- Slower moving cooler air
- Greater mass flow of air
What are the two types of noise suppressor?
- Corrugated perimeter
- Multitube
What does the noise absorbing lining convert acoustic energy into?
Heat
What does the noise absorbing lining consist of?
Porous skin supported by honeycomb backing
What do thrust reversers do once operated?
Reduce braking distance
How does a thrust reverser provide braking force?
Deflecting exhaust gas stream in the opposite direction
What airflow is reversed in a high-bypass turbofan engine?
Fan air
When would a bucket type reverser be used?
Low-bypass engines
What do turbofans with a low-bypass ratio usually have?
A common exhaust nozzle
Where are clamshell reversers located on a low-bypass engine?
In front of the exhaust nozzle
Where are the bucket-type reversers located?
After the exhaust nozzle
In clamshell reversers, what do exit ducts have?
Cascade vanes
How are clamshell reversers operated?
Pneumatically
What are fan reversers?
Cascade type reversers with translating sleeves
How may fan reversers be operated?
- Hydraulically
- Pneumatically
What moves rearwards when the thrust reversers are activated in the cockpit?
Translating sleeve
What closes off the fan discharge duct?
Blocker doors
How are pivoting door type reversers activated?
Hydraulically
Where are pivot doors reversers when they are not activated?
Flush with the cowling
How are the disadvantages of reversers minimised?
Reversed airflow is matched to the engine position
On four engine aircraft, why is the angle of reverse stream more important?
Airflow from inner engines can be ingested by outer engines
How is thrust vectoring accomplished?
Relocating/moving the exhaust nozzle
The inward-pointing airflow is directed at such an angle that it cannot blow into what? (Reverse thrust)
Main wheel well
If the engines are far enough apart that the reverse flow does not effect the adjacent engines, what is an advantage of this configuration?
All engines can have the same cowlings, meaning fewer parts
What are some negative effects of reversers?
- Engine compressor can surge and stall
- At very low aircraft speeds the engine can ingest its own reversed airflow
- FOD ingestion
