Exhaust Flashcards
What is the purpose of an exhaust?
Conduct gas flow away from the turbines and clear of the aircraft surface.
What is the purpose of an exhaust in Turbojets, Turboprops and Turboshaft?
Turbojet: Produce thrust
Turboprop: Produce some thrust
Turboshaft: Acts as a diffuser
What are the major components in an Exhaust?
Exhaust Unit:
- Tail cone
- Exhaust cone
- Exhaust fairing/strut
Exhaust Duct
Exhaust Nozzle
What are exhaust components typically made from?
Nickel or titanium due to high temperatures
What are the two ways that the heat from the exhaust is insulated from the aircraft structure
- Passing ventilating air
- Insulation blanket made up of a core of fibrous material wrapped in a dimpled stainless steel outer skin.
How does the exhaust work on Turboshafts helicopters
The nozzle forms a divergent duct to diffuse air
- Does not increase thrust
What are the two types of Turbofan exhausts?
Ducted and Unducted
How does a ducted turbofan exhaust work?
Takes fan airflow and directs it to a common exhaust where the core flow and fan flow mix
How does an unducted turbofan exhaust work?
Has two separate nozzles (one for core, one for fan).
- Both flow to ambient air through separate nozzles.
- Handles high amounts of airflow
- Converging nozzle exhaust produces 15-20% thrust
In a turboprop, what is another word for exhaust duct?
Tailpipe
What does a turboprop tailcone and struts do to the airflow?
Imparts an axial flow onto the air, straightening it.
What percentage of thrust is produced from a turboprop exhaust?
10-15%
On a turboprop, is the fwd section of the tailpipe connected to the exhaust?
No
- Fwd section is funnel shaped and surrounds the exhaust but DOES NOT CONTACT (Annular gap).
Where is the rear section of the exhaust connected to on Turboprops?
Connected to the airframe by two support arms, one on each side.
- Support arms are connected to the wing in a way to compensate for heat expansion.
What is the insulating blanked on a turboprop tailpipe made of?
Stainless steel on the outside and fiberglass on the inside
- Used when the exhaust is located some distance from an aircraft structure.
What is Turbine Discharge Pressure?
Total pressure discharge in an LP turbine in a dual spool axial engine
Where is the Turbine Discharge Pressure measured from in the exhaust?
Immediately aft of the turbine and fwd of the exhaust flange
- Pressure probes inserted.
In large engines where its not practical to measure temperature at the turbine inlet, where is temperature measured?
EGT is measured on the turbine outlet
What is the purpose of an Exhaust Cone (tailcone)
Form a divergent duct to reduce the velocity to Mach 0.5 and increase the pressure.
What is the purpose of an Exhaust Duct?
The convergent duct is used to accelerate the gas to Mach 1 (Chocked Nozzle)
- Usually fixed geometry on subsonic aircraft
When is a Convergent-Divergent (C-D) Nozzle used?
To help produce thrust when the exhaust velocity is higher than Mach 1.
- Best suited for supersonic aircraft due to higher pressure ratios in exhaust.
What is the use of an afterburner limited by?
Fuel consumption
What are some additional components that are needed to make an afterburner?
- Flame stabilizer
- Flame holder
- Fuel manifold
- Igniters
- VARIABLE AREA EXHAUST NOZZLE
When energy and mass are added to fuel an afterburner, what must the exhaust nozzle do?
Widen to allow more fuel
