Inlet Flashcards
How does air enter engine
Via intake
2 parts of an intake
Intake nose & inlet duct
What is a divergent
Shape when inlet duct gets wider
What does a divergent do
Increase static pressure of air moving through the duct
What does intake nose do
Smoothens airflow
Why does all air enter the inlet from the front
Ram air effect at high speeds
What velocity to the ensure flow through compressor is smooth
0.4-0.7 Mach
What is a intake designed to do and how
Decelerate flow & convert kinetic energy into pressure energy
How is a subsonic air inlet shaped
To deliver air to front of compressor which gives even pressure distribution
What’s the consequences of poor air pressure and velocity
Compressor stall
What happens to ram pressure as ram velocity increases
Decreases
What happens to air while the aircraft is stationary
Air in duct is accelerated to velocity required by compressor
What does a rounded inlet lip do
Gives it a thicker radius which reduces risk of separation
At high speed what shape inlet lip do we want
Thin
What is a transonic duct practical speed
Up to Mach 1.5
What does a transonic duct use to decelerate supersonic airflow
Shock diffuser
What happens in a normal shockwave
Pressure and temperature increases while velocity decreases to subsonic
What is critical condition
Cross section of the inlet is sufficient to allow max airflow requirements of the engine
What is sub critical
The shockwave is detached from the lip and moves upstream which reduces Mach number
What is super critical
The shockwave is swallowed which makes the airflow in the inlet become supersonic which is unacceptable flow into the compressor
What is diffuser buzz or intake buzz
When extreme pressure fluctuations can severely damage the engine
What happens to kinetic energy in a supersonic inlet duct
Large amount of it turns into unusable heat
What happens in a oblique shockwave
Forced to change direction , the shockwave is inclined at oblique angle which is determined by upstream velocity
Disadvantage of shock diffuser in supersonic duct
Abrupt loss of efficient as Mach number increases such as 30% at Mach 2
What does a oblique shock diffuser do
Reduces supersonic flow progressively by wing , in a series of oblique shock waves
In a normal duct what will an inefficiency of 1% do
Thrust loss between 1% and 4%
Efficiency of pilot design
96-99% efficient
Efficiency of wing root design
87-95% efficient
Efficiency of side design
80-89% efficient
Efficiency of turbo prop annular (Dart)
74-82% efficient
In a transonic duct what lip shape do you want
As thin as possible
In a variable intake what’s the maximum amount of shockwaves
4 , 3 oblique 1 normal
How can we prevent intake buzz
Bleed door
How do we cool the engine bay
With Air bled from ramps used for engine bay cooling
Problems with snow and ice
Cause turbulent flow which can stall
What anti ice system is used
Jet engines have thermal anti - ice systems
What are antennas heated with
Warm air
What’s the purpose of anti ice valves
Protect against over pressurisation
How are anti ice valves operated
Automatically via ice detection system or manually in flight deck
What happens to the air used for anti-icing
Ejected over board via small grills
What are the 2 methods of ice protection
Bleed air & electrical heating
How is the thermal anti ice valve energised
Engine anti-ice switch/ light
When does the amber light turn off
When LP sensor duct pressure is more then 5psi
Where is duct over pressure signalled to
EICAS/ECAM
Why is caution necessary when testing thermal anti Ice system on ground
Air is still hot no personnel should be in the area
Where is electrical ice protection employed
Turbo prop engined aircraft
Are mats supplied with AC or DC
Both
What’s the purpose of the continuously heated element
Prevent formation of ice on leading edge or aircraft engine air intake lip and propeller spinners
Where is a intermittently de-icing element located
Behind continuous heated element
What type of system is a continuous heated element
Anti - icing
What type of system is a intermittent heated element
De -icing
In an intermittently heated element why are they divided into separate segments
To ensure ice breaks away easily
What happens on the FAST cycle
ON/OFF for 2 minutes OAT between -6 & 10 degrees
What is the SLOW cycle
ON/OFF for 6 minutes OAT below -6 degrees
Why does the cycling light glow dim and bright
Indicate timer is rotating
What is a heated mat examined for
Splits , tears , wrinkling and discolouration which happens due to overheating security of the attachment or general condition
Where are anti-corrosion strips placed
Any sign of splitting or corrosion
When should you replace a heated mat
any damage which exposes the heated element
When does a continuity and resistance check need to be completed
Following any repair to heated mats , resistnace valves must be within limits
Why do we need to do insulation resistance checks
To determine any breakdown of insulation between heater mats
Insulation resistance to earth must be checked
What should
