15.3 Inlet Flashcards
What is the purpose of the inlet?
It must furnish a uniform supply of air to the compressor to ensure it performs a stall-free compressor performance.
What is the inlet duct on a commercial airliner known as?
Pitot type
What does the pitot type engine inlet maximise?
The ram effect; suffering only a minimum loss of ram pressure as the aircraft altitude changes
What can cause pressure losses in an aircraft engine inlet?
Friction (along the walls)
Turbulence
Mach number related shockwaves
What is a vortex dissipater?
A blow away jet (linked to weight on wheels, so only operates on the ground)
It is compressor bleed air
What happens to the air when total ram recovery has been achieved?
The airflow will be faster than the compressor is capable of tolerating. The engine benefits by expanding less mechanical energy for compressor.
It produces a ‘nose suction’ effect.
Where would you see a bell-mouth air inlet?
Engine testing and helicopter turboshaft engines
Why aren’t inlet screens used in modern gas turbine powered aircraft?
They cause more maintenance problems and icing, so have been avoided.
What are the 3 types of turboprop inlet?
Ducted spinner
Conical spinner
Under scoop
What is installed in an APU air intake, incase of a flap actuator failure?
A manual override device
What happens to the conical surface (Mach cone) as an aircraft increases in supersonic speed?
It’s angle gets smaller
What happens in a normal shockwave?
Airflow becomes subsonic. The shockwave is perpendicular to the flow direction.
It’s the strongest of all shockwaves
What happens in an oblique shockwave?
Air speed increases
Slight angle change
What speed is needed for airflow in a jet engine ?
Subsonic, around Mach 0.4
Where would you find a plug intake?
High supersonic speed aircraft.
Where would you find an inlet filter?
Helicopters for prevention of FOD
What is EAPS?
Engine advanced protection system.
Small fans on intake, prevent FOD, ice, less erosion, all weather protection
When are anti-icing conditions deemed to exist?
Below +10°C with visible moisture.
What is a disadvantage of ducted air anti-ice systems?
A slight power loss when in use
Where would you find an electrical heating element system on an engine intake?
Turbo-prop intakes.
How are the electrical heating elements (pads) attached to the engine intake?
Bonded to the outer skin
How are electrical ice protection systems different in operation to a bleed air anti-ice system?
They are intermittently heated, allowing ice to form in the “heat-off” period.
In terms of pressure and kinetic energy, how does the intake take advantage of the Ram Effect?
It converts kinetic energy of the air into pressure energy
What is the purpose of the nose cone on the N1 Fan?
Streamlined fairing only
How much can EGT increase by with using the bleed air anti-ice system?
10 degrees C
When is the inlet door of a variable geometry intake open?
Subsonic speeds. Closed at supersonic speeds
What happens to pressure and velocity in a bellmouth intake?
Velocity increases and pressure decreases
What does increasing ram effect do to the efficiency?
It increases the overall propulsive efficiency
What happens to the aerodynamic efficiency of a pitot type intake when it approaches the transonic range?
Decreases due to the shock waves produced
How does a turboprop engine INLET anti-ice system operate?
Continuously (The propeller blades are intermittent)
What is the Ram Recovery point?
The intake total pressure equals the ambient pressure
What does an increase in the Ram Ratio of an intake do to temperature?
Increases the temperature
What happens to the efficiency of a Pitot inlet as an aircraft approaches the transonic range?
It decreases due to shockwaves in the transonic region
What does intake momentum drag cause?
A decrease in thrust at low airspeeds
