15.3 Flashcards
(22 cards)
What happens to air in a convergent and divergent ducts above and below the speed of sound
Bellow
P+
V- Divergent
T+
P-
V+ Convergent
T-
If are is supersonic the above is reversed convergent acts as divergent
What is the function of the engine compressor inlet
To provide smooth uniform distortion free air flow to compressor to prevent stall
What type of duct is a compressor inlet and what are the effects
Divergent duct
Increase in temp and static pressure with a decrease of air speed
Creates more static pressure
Why do divergent duct compressor inlets have a flat spot
Ensure smooth are flow into engine
What is the inlet duct part of
Airframe part
not engine part
As air speed increases thrust decreases how is this effect reduced
RAM air recovery is used to reduce this effect
RAM air to recover thrust
What are the advantages and disadvantages of compressor inlet screens and the types of engines they are used on
Portect engine form fod
Air susceptible to icing
Used on turboprops and turboshaft engines
Pressure losses
What is used to defect ice out of a turboprop and turboshaft compressor inlets
Deflector door
What is a Divided- entrance ducts
Two ducts that feed 1 engine
Can be fitted to fuselage or wings
Used on military aircraft
What is the disadvantages of divided entrance ducts and what is used to get uniform airflow
Gives more drag
Can be bad when performing manoeuvres
They have a Series of turning vanes to achieve uniform flow
Where are variable geometry ducts used
On supersonic aircraft as airflow must always be less then the seed of sound before entering an engine
How does a variable geometry duct work and the three key points
Divergent duct
A diffusers progressively decreases the area in the down stream direction
The duct creates a shock wave in the air stream to decrease the speed of the air
The geometry of the ducts changes
Air is bled off via a bypass
Where and why are bellmouth compressor inlets used
Only found on test cells
Used to have zero duct losses
What can prevent ice build up on turbofan engines
Can be prevented by bleed are or a conical spinner
How does a turbofan engine prevent fod damage
The fan blades are designed to move the fod to the side of the engine and direct it down the bypass
What can turboprop engines use to prevent ice
Warm oil form engine
Bleed air or conical spinner
At what temps can ice spawn in at the inlets
5 C in dry air
7 C in moist air
What does the bleed are come form for anti icing
HP compressor
What indication can be seen on the flight deck for anti icing
Valve not is selected position
Low duct pressure
High duct pressure
Low duct temp
High duct temp
How is the bleed air at A/I valve control and what is the manual override for
Electricaly controlled
Solenoid
Manuel overide used on ground in case of failure (can be locked open of closed)
What is the EEC
Electrical engine control, part of FADEC, it’s only schedules fuel
Where is elector thermal anti icing system found and what does it need
On smaller turboprop and shaft engines
Needs air flow to prevent over heating
