Construction (exhaust System) Flashcards
What happens to exhaust gases after leaving the turbine?
The exhaust gases pass into the exhaust system and exit through the propelling nozzle, converting energy in the gas stream into velocity to produce thrust.
How much thrust is produced at the end of the exhaust in turboprop and turboshaft engines?
Very little thrust is produced at the end of the exhaust because the majority of the energy in the gas stream has already been extracted by the turbine.
What is the purpose of the exhaust cone?
The cone protects the rear face of the turbine disc from overheating.
How does the shape of the exhaust unit affect gas flow?
The conical shape creates a divergent duct that decelerates the gas flow, thus reducing pressure losses.
What do the struts attached to the exhaust unit walls do?
The struts hold the cone in place and act as straightener vanes to remove any swirl present in the gas flow.
How do helicopter exhaust systems differ from other exhaust systems?
Helicopter exhaust systems are slightly divergent as most of the energy has been taken from the gas stream to drive the turbine/rotors, resulting in very little thrust.
What are the types of exhaust duct configurations?
The types of exhaust duct configurations are divergent, straight, and convergent.
What is the effect of a divergent duct on velocity?
A divergent duct causes the velocity to decrease.
What is the effect of a straight duct on velocity?
A straight duct causes no change in velocity.
What is the effect of a convergent duct on velocity?
A convergent duct causes the velocity to increase.
What are thermocouples used for in jet engines?
Thermocouples are used to measure the average temperature in the jet pipe, which is important for indicating Turbine Entry Temperature (TET).
What are the different names for Turbine Entry Temperature (TET)?
Turbine Entry Temperature has several names:
- JPT - Jet Pipe Temperature
- TET - Turbine Entry Temperature
- EGT - Exhaust Gas Temperature
- TGT - Turbine Gas Temperature
- TIT - Turbine Inlet Temperature
- By notation T4, T6 (etc.)
What are some typical temperature values for jet engines?
Typical temperatures are:
- Starting: 700°C Peak
- Ground Idle: 500°C
- Max Take Off: 690°C
- Max Continuous: 610°C
How do temperatures in turbo prop and turbo shaft engines compare to jet engines?
Temperatures on turbo prop and turbo shaft engines are approximately 90°C - 100°C lower due to most of the energy being extracted to drive the propeller or main rotor gearbox.
What materials are commonly used in jet engine construction?
Materials are mostly Nimonic alloys with specifications similar to those used in combustion chambers. Mild steel or alloys may be used for outer casings and shrouds.
What is the purpose of stiffening in jet engine components?
Stiffening is provided to prevent buckling, along with various sliding and expanding joints and attachments.
What type of insulation is used to protect the aircraft structure against heat?
An insulating blanket or air is used, which has an inner layer of fibrous insulating material contained by an outer skin of thin stainless steel, dimpled to increase strength.
What are common maintenance issues for jet engines?
Common maintenance issues include:
- Cracking around the welds due to vibration fatigue
- Corrosion
- Security of attachment (KLP 37.02.05)
Exhaust unit what happens to duct type and velocity
Divergent and velocity decrease
Jet pipe what happens to duct type and velocity
Straight and no change in velocity
Propelling nozzle what happens to duct type and velocity
Convergent duct and increase in velocity
