M15.7 Exhaust Flashcards
On a jet engine what is the main task of the exhaust?
To accelerate the airflow coming from the turbine to generate thrust
What is the main task of exhaust on a turboprop?
Safely guide the exhaust gases overboard
What is the one common function of the exhaust on gas turbine engines?
Direct flow of hot gases rearwards to prevent turbulence and impart or exit velocity to the gases
Components of exhaust section?
Exhaust cone
Tailpipe
Exhaust nozzle
What does the exhaust cone do?
Collects the exhaust gases from the turbine and gradually converts them into a solid flow of gases.
This reduces velocity and increases pressure
What type of passage is between the outer duct and inner cone?
Diverging
The cone is supported by what?
Radial struts
How flexible is the tailpipe?
Semi-flexible
What is an insulation blanket used for?
Primarily used to reduce heat loss from exhaust system
Two types of exhaust nozzles?
Converging design for subsonic gas velocities
Converging- Diverging design for supersonic gas velocities
What is a ducted fan engine?
They take the fan airflow and direct it through closed ducts along the engine
What is an unducted fan engine?
They have two nozzles
One for fan airflow and one for core airflow
Both flow to ambient air separately from each other and have separate nozzles
A converging nozzle increases the thrust produced by how much?
15-20%
Turboprop exhaust nozzles provide what amount of thrust?
10-15%
When can more thrust be gained by using a convergent divergent nozzle?
When the engine pressure ratio is high enough to produce gas velocities that exceed Mach 1
Can thrust reversers be deployed in flight?
No
Describe clamshell type thrust reversers?
Found on older jets with low bypass ratio
Pneumatically operated
When doors rotate to reverse position they block off normal flow path and uncover exit ducts with cascade vanes
Describe a Bucket type thrust reverser?
Found on older jets with low bypass ratio
Hydraulically operated by aircraft’s hydraulic system
What type of reverser is found on turbofan engines?
Fan reversers
How are fan reversers operated?
Either pneumatically operated by drive motors
Or hydraulically by actuators in the cowling
Describe how a fan reverser works?
When pulled, the translating sleeve moves rearwards and uncovers cascade vanes
Blocker doors close off fan discharge duct thus all air can only discharge through cascade vanes
Where would you find pivoting door reversers?
Modern turbofan engines
How are pivoting door reversers operated?
Hydraulically
When are thrust reversers most effective (what speed)?
High aircraft speeds
As at low speeds there is a risk of the aircraft ingesting it’s own reversed flow
How are the thrust reversers pointed?
Outward pointing airflow is blown at optimum angle for reverse thrust
The inward is directed at an angle that wont blow into the main wheel well and damage it
What is important about four engine aircraft thrust reversers?
The inner engines can be ingested by the outer unless they are aimed at the perfect position
If there is a large distance between engines on four engine aircraft does the reversed flow affect the neighbouring engine?
No
Can an aircraft be released to service with a defective thrust reverser?
Yes, they are only additional braking support and not integral
What is thrust vectoring?
Used by military aircraft for manoeuvring in flight.
Accomplished by relocating the direction of the exhaust nozzle to direct the thrust to move aircraft to desired path
What type of exhaust nozzle design is used on engines that travel at subsonic velocities?
Converging design
Which thrust reversers are used on engines with low bypass ratio?
Bucket and clamshell
What thrust reversers are used on engines with high bypass ratio?
Fan reverser
Pivoting door
