Purpose of engine inlet ducts?
To supply the compressor with the required quantity of air with minimal distortion.
Why is uniform airflow into the compressor essential?
To prevent compressor stall, airflow reversal, and excessive turbine temperatures.
What are Inlet Guide Vanes (IGVs) used for?
To straighten and correctly direct airflow into the compressor.
Is the inlet duct an engine or airframe component?
It is considered an airframe component.
Why is inlet design critical for gas turbine engines?
They require much greater airflow than piston engines.
Turbofan inlet characteristics?
Large, smooth, relatively straight ducts for high airflow.
Turboprop/turboshaft inlet characteristics?
Smaller inlets, often with protective FOD screens.
What is ram recovery?
Increase in total pressure due to air being trapped, slowed, and compressed in the inlet.
Effect of ram recovery at high speed?
Compensates for inlet pressure losses and improves engine performance.
Causes of inlet pressure losses?
Friction, bends, and changes in duct direction.
How are inlet pressure losses minimised?
Smooth surfaces, low turbulence, minimal pressure variation.
What factors affect inlet configuration?
Engine location, aircraft speed, altitude, and attitude.
What are divided-entrance ducts?
Inlets taking air from both sides of the fuselage.
Advantage of divided-entrance ducts?
Shorter duct length with no major drag penalty.
Disadvantage of divided-entrance ducts?
Unequal ram pressure during manoeuvres causing airflow imbalance.
Purpose of variable-geometry inlets?
To ensure subsonic airflow at the compressor face.
How do subsonic aircraft diffuse airflow?
By increasing duct area downstream.
How do supersonic aircraft diffuse airflow?
Area reduction to Mach 1 then expansion to subsonic.
Methods of diffusing supersonic airflow?
Variable geometry, bypass airflow, shock waves.
Purpose of compressor inlet screens?
To prevent Foreign Object Damage (FOD).
Disadvantages of inlet screens?
Pressure loss, icing risk, added weight, potential failure.
Why are inlet screens not used on turbofans?
Disadvantages outweigh benefits with metal blades.
Purpose of bellmouth inlets?
Ground testing with near-zero inlet loss.
What measurements use bellmouth inlets?
Thrust, intake pressure, intake temperature.
