15.3 Inlet Flashcards
What are IGVs
Inlet Guide Vanes
What is the purpose of IGVs?
To straighten airflow and direct it into the compressor first stage.
What is the inlet duct a part of?
The airframe, not the engine.
What happens to velocity, pressure and temperature at a divergent duct?
V decrease.
P increases.
T increases.
What happens to velocity, pressure and temperature at a convergent duct?
V increases.
P decreases.
T decreases.
How does supersonic air behave a convergent and divergent ducts?
Oppositely to subsonic air.
On what engines can screens be found?
Turboprop and turboshaft.
What is the purpose of screens?
They cover the inlet to prevent FOD.
On what aircraft are divided entrance ducts found?
High speed military aircraft.
What are the 2 types of divided ducts?
Wing root inlet or scoop inlet.
What is the purpose of the turning vanes in the side scoop inlet?
They assist to straighten air preventing turbulence.
What is the design drawback of divided entrance ducts?
Trying to design them to a reasonable length with as few bends as possible.
Why is it difficult to obtain sufficient air scoop?
High drag.
What is the problem with sudden flight manoeuvres for divided entrance ducts?
They cause imbalance in RAM air pressure between the 2 ducts, causing a slight power loss.
What is the purpose of a variable geometry duct?
To provide the correct amount of air into the engine inlet.
What is the purpose of the inlet duct of a variable geometry duct?
To act as a diffuser= divergent duct.
What does the inlet duct of a variable geometry duct do to airs velocity and pressure?
V decreases.
P increases.
What does the inlet duct of a variable geometry duct do to airs velocity and pressure?
V decreases.
P increases.
How is the inlet of a variable geometry duct designed on a supersonic aircraft?
A sharp lip.
What is the purpose of the variable geometry duct varying the inlet area?
To manipulate the normal shockwave to occur at intake.
In relation to a variable geometry duct, what are the 3 methods to diffuse inlet air to slow air to subsonic speed?
Vary the inlet area.
Use variable airflow bypass arrangement.
A shockwave in the airstream.
On what engines is a compressor inlet screen used?
Turboshaft and turboprop.
What are the problems with the compressor inlet screen?
Causes loss in duct pressure.
Susceptible to icing.
When is the retractable compressor inlet screen retracted?
After take off or in icing conditions.
What is the problem with the retractable compressor inlet stage?
Prone to mechanical failure.
When is the bell mouth compressor inlet used?
During testing only.
What is the purpose of the bell mouth compressor inlet?
To obtain very high aerodynamic efficiency as duct loss is considered zero.
What is the purpose of deflector doors in a turboprop and turboshaft compressor inlet?
To deflect ice and dirt away from the intake.
What is the purpose to the conical spinner?
Doesn’t allow ice to build up.
On what engines the conical spinner used?
Turboprop and turbofan.
What is the purpose of the fan in turbofan engine inlet section?
Reduce engine damage due to FOD.
What is used for inlet lip anti icing in a turbofan engine inlet section?
Warm bleed air draw from LP compressor of engine.
What is used for turboprop inlet area anti icing?
Warm oil from the engine oil reservoir.
What is used if only the engine cowls require anti icing?
Electrical heat strips.
What is the thermal system subdivided into ?
Bleed air and electrical heating.
On what engines is bleed air from the HP compressor used for anti icing?
On engines with high mass airflow.
What does bleed air provide surface heating of?
IGVs, spinner, inlet lip.
What is the purpose of anti ice valves?
Protect against over pressurisation and limit bleed air to prevent engine power loss.
How can anti ice valves be operated?
Mechanically or automatically.
When does the anti ice valve open?
When manually selected or when the ice is detected on the sensor.
Anti icing valves are electrically selected, pressure operated and have cockpit indications for what?
Valve not in selected position.
High pressure.
Low pressure.
High temperature.
Low temperature.
How is the regulator valve controlled?
Solenoid controlled.
What function is available in case of valve or system failure?
Manual override.
Anti icing with electronic engine control is controlled by what?
FADEC.
What is the electro thermal anti icing system?
Electrical heat strips.
When are electrical heat strips designed to operate?
When engine is running without air passing over it.
What effect does increased aircraft speed have on thrust?
Decreases it.
What is RAM recovery/ total pressure recovery?
Added pressure at engine inlet increases pressure and airflow to the engine.
Why must a turbofan engine duct have a sufficiently straight section?
To ensure smooth airflow due to high airflow.
