M15.03 Inlets Flashcards
Air enters the engine via?
The engine air intake
If the air if the air inlet duct gets wider it’s a?
Divergent inlet
A divergent duct does what to the air passing through?
. Velocity decreases
. Static Pressure increases
. Temperature increases
The air intake has a inlet duct and inlet nose, what does the nose do?
Helps smooth out the airflow
Air disturbances can be caused by?
. Damage to the intake nose
. Ice build up
. Cross winds
In order for air to flow smoothly to the compressor, what velocity does it need to be?
Between 0.4 - 07 Mach (307-537mph)
Air intakes are designed to decrease airflow speed by?
Converting kinetic energy to static pressure without shocks or lose of aircraft speed
The condition of an air inlet are present?
In ground and during flight
Subsonic ducts are shaped to ensure?
Even pressure distribution to the compressor
Else could cause compressor stall
What is the most efficient subsonic inlet configuration?
Pitot type quasi-circular diffuser
To reduce the risk of airflow separation, how are the inlets shaped for subsonic?
Inlet lip is well rounded with a thicker radius
(However at high speeds, the inlet lip needs to be thin)
When engines are mounted under the wing, what can happen?
Ground vortex’s (mini tornados) can form, which is swelled by the inlet, further decreases performance.
Another thing that can effect the performance of an inlet is?
Crosswinds
The subsonic air inlet duct form a divergent or convergent duct??
Divergent, which means it gets wider which would increase the static pressure
At transonic speeds the inlet is designed to keep the shock waves out and reduce the speed, how is this done?
By using a normal shockwave diffuser to decelerate the airflow to speed compressor can cope with.
What will the normal shockwave do to the air entering the transonic inlet?
Reduce the velocity to subsonic
Increase pressure
Increase temperature
What is critical condition??
When a Cross section of the inlet must allow the maximum engine airflow requirements at only one specific Mach number and altitude
What is sub-critical condition?
When RPM demand is reduced the shock wave detaches from the inlet lip and moves upstream of inlet, which causes bow wave to form and Mach number to decrease
What is super- critical condition??
When RPM demand is increases to more than the inlet can cope with, it causes a pressure drop which causes the shock wave to be swallowed, which allows supersonic airflow in the inlet. Which results in couples shockwaves and turbulence.
Duct inefficiencies or 1% will cause a loss of thrust of what %?
1-4% of thrust loss
Three types of shock waves that can form on inlets?
. Normal
. Oblique
. Bow wave
What occurs when a normal shock wave takes place??
Velocity abruptly drops to subsonic and pressure rises
During a normal shock wave, a lot of pressure is generated, is this all usable??
No, large amount is turned into heat energy
When would an oblique shockwave take place?
When the airflow is force to change direction
What happens after an oblique shock wave?
Less serve magnitude and flow, decreases a bit but stays supersonic
When do normal shock waves take place?
At low supersonic airspeed and stand perpendicular to the airflow
Bow shock wave?
What does the normal shock inlet employ?
A single normal sock wave at the inlet to slow the air to subsonic
At what speeds can the normal shock inlets work at?
Slow speeds, not suitable for Hugh speeds as it causes a reduction in pressure/ efficiency (30% at Mach 2)
What does the oblique shock inlet do?
Employed a series of external oblique shock waves to slow the supersonic airflow before the normal shock occurs, that way the normal wave would on,y be weak, causing only a small loss of efficiency
What is diffuser buzz?
When a normal shock wave is swallowed and expelled continuously at high speeds
(Buzz due to sound it makes)
How can you overcome a diffuser buzz?
By using a variable geometry inlet
How do variable geometry air inlets work?
. At supersonic - produces multiple oblique shock waves then followed by a normal shock wave.
. At transonic - a normal shock is formed
At a high Mach number how many oblique waves and normal waves are formed??
3 oblique waves and then 1 normal wave
What are the two negative effects of ice in engine inlets?
. Disturbed airflow - decreases performance
. Engine sucks ice up and damages
All jet engine have for ice?
Thermal anti ice systems
What are the requirements of anti ice systems?
. Reliable
. Easy maintenance
. No excess weight
. No reduction of enshrine power
What are the two types of thermal anti ice systems?
. Bleed air
. Electrical heating
What system only protects the engine spinner and intake lip?
Bleed air system
What other methods protect the engine spinner?
. Hot oil pumped around inside the spinner
. Rubber spikes - causes unbalance then spins off
Where is the bleed air from??
Engine HP compressor
What do anti ice valves protect against?
Over pressurisation and limits the bleed air
Where does waste anti ice air go?
Over board via small grills
How are anti ice valves selected and operated?
Electrically selected and pressure operated
On the engine intake thermal anti ice ins, the amber light will illuminate until?
The low pressure switch senses a duct pressure of more than 5 psi
Where is duct over pressure signalled?
ECAM or EICAS
What engine are electrical anti ice systems normally used on?
Turboprop
What is the electrical power supplied to heater mats?
AC or DC
What type of heater mats are there?
Continuous and intermittent
What is the purpose of continuous heated elements?
Prevent ice formation in leading edge, intake and spinners
What is the purpose of intermittent heated elements?
. Situated behind continuous heated mats
. During heat OFF allows thin layer of ice to build up
. During heat ON rapidly melts the ice
To ensure ice breaks off easily on intermittent heat mats, what is there??
The elements are divided into separate segments
At +10 to -6 degrees what ice protection cycle is used and for how long?
. Fast
. 2 minutes
At below -6 degrees what ice protection cycle is used and for how long?
. Slow
. 6 minutes
What are continuity of heater checks?
Check correct resistance, carried our at prescribed inspections and following repairs
What do insulation resistance check for?
To see if there is any breakdown of insulation between heater mats/ elements
What are heater mats examined for?
. Splits
. Wrinkles
. Tears
. Discolouration
