M15.3 Flashcards
What does the air intake have to allow for smooth airflow?
A intake nose
What is the shape called when the air inlet duct gets wider?
A divergent duct
What does the divergent duct use to increase static pressure?
Bernoulli principle
What happens with supersonic airflow?
It’s compressible so engine parameters are reversed
What speed should the airflow be at the compressor inlet?
Between Mach 0.4 and 0.7
How do air intakes convert decelerate airflow?
By converting kinetic energy to pressure energy
What happens to velocity and pressure in subsonic inlet ducts?
Velocity decreases
Pressure increases
What is the most efficient inlet configuration for subsonic flight?
The pitot type quasi - circular diffuser
When do you get problems with subsonic inlet ducts?
When a/c on ground with max thrust because of core depression
What does making the inlet lip rounded result in?
A thicker radius
What does having a thicker radius inlet do?
Reduces the risk of flow separation
Why are large inlet lips avoided?
Because it hinders performance at high speeds
What is fitted to an intake to minimise the issues with crosswind?
With cross wind components which are fitted to the intake
What speeds is the pitot type intake good up to?
Mach 1.5
What does the pitot tube do at transonic speeds?
And how is this done?
Keeps shock wave out
By using a normal shock diffuser
What does a normal shock wave do?
Increase temp pressure and decrease velocity
What happens when rpm is reduce?
The pressure in the inlet rise allows less air in.
What must the cross sectional area of a transonic duct allow?
And what is this called?
Max airflow requirements that apply to only 1 Mach number and altitude
Critical condition
What is super critical condition?
When pressure in the diffuser is decreased causing normal shock to be drawn further to the inlet
What is sub critical?
When the normal shock wave is expelled due to an increase of pressure in the diffuser
What is diffuser buzz?
Caused when there is extreme pressure fluctuations
What happens to the shock wave in super critical, sub critical and critical?
Super critical = moves closer to intake
Sub critical = moves further from intake
Critical = perfect position
When does a normal shock wave occur?
When a/c at low supersonic speeds and stands perpendicular to airflow.
What happens to velocity and pressure in a normal shock wave?
Velocity drops from supersonic to sub sonic
Pressure rises
When will a oblique shock wave occur?
If the airflow is forced to change direction then the shock wave will form at an inclined oblique angle
Intake efficiency for pitot intake?
96 - 99%
Intake efficacy for wing root?
87 - 95%
Intake efficacy for side?
80 - 89%
Intake efficacy for turbo prop annular?
74 - 82%
What is the disadvantage of the normal shock diffuser?
Has a abrupt loss of efficiency as the Mach number increases
How is buzz overcome?
With a variable geometry intake
How is a variable geometry intake controlled?
With the use of a air data computer
Where is a normal shock inlet used?
In low supersonic speeds
What does a oblique shock inlet do?
Employs an external shock wave to slow supersonic airflow before the normal shock occurs
What does a variable geometry air intake do?
Uses actuators to operate panels to employ 3 oblique shock waves and 1 normal shock wave
What type of anti icing do engines have?
Thermal
What are the 2 types of ice protection for engines?
Bleed air
Electrical heating
What are the 2 types of ice protection for the spinner?
Hot oil
Rubber spikes
What do anti icing valves protect against?
Over pressurisation
And prevent loss of power
How is the bleed air anti icing system operated?
Automatically or manually
What happens to air used for anti icing?
Ejected overboard via small grills
What happens to bleed air used for anti icing in the nose cone and inlet guide?
Sent either to LP compressor or overboard
How are anti icing valves operated?
Electrically selected, pressure operated
The anti icing valve give indications for what?
Valve not in position selected
Low/ high duct pressure
Low/ high duct temp
When is the amber light shown on the anti ice valve?
Until low pressure switch senses a duct pressure more then 5psi
What a/c is the electrical ice protection system found on?
Turboprop a/c
What is the electrical ice protection system used on?
Air intake cowlings, propeller blades, spinners and oil coolers
What is electrical power supplied to in the electrical ice protection system?
Heater mats (AC or DC)
What do continuously heated elements do?
Prevents ice build up on engine intake and propeller spinners
What is intermittent heating elements?
Behind continuously heated elements and keeps heating whilst continuously heated is switched off
How long does fast mode on the anti ice system work?
2 mins when OAT is between -6c and 10c
How long does slow mode work in the ice protection system?
6 mins with OAT bellow -6c
When does the cycling light on the anti ice system glow dim and bright?
To show the timer is rotating
What are heater mats examined for?
Splits
Winkles
Tears
Discolouration
Security of attachment
When must continuity and heater resistance checks be made?
After any repair to heater mats
When must insulation resistance checks be made?
To determine if there’s any break down of insulation between heater mats
