15.3 Flashcards
What do the Inlets guide vanes do?
Straighten the airflow and direct it into the first stages of the compressor
Is the air inlet duct an airframe part, or part of the engine?
Airframe
What does the inlet vary according to?
The type of turbine engine
What do turboprop and turboshaft engines have to prevent FOD from entering?
Screens to cover the inlet
As aircraft speed increases, what happens to thrust? And what compensates for it?
It decreases so RAM air recovers it
What recovers as much of the total pressure of the free airstream as possible? And how?
The inlet by trapping air molecules and compressing it
What is “Ram recovery” or “Total pressure recovery”?
Added pressure at the inlet to increase pressure and airflow
The choice of configuration to the entrance of the duct depends on what?
Airspeed, altitude, attitude, location
Where are divided-entrance ducts located?
Military aircraft on either side of the fuselage
What two things can a divided duct be?
A wing-root inlet or a scoop
Disadvantage of divided ducts?
Drag
What is a major drawback in terms of designing the entrance duct in a divided entrance?
Having a reasonable length with a few bends as possible
Scoops at the side of the fuselage are used in devised entrance air inlets, where are they placed?
As far forward as possible
Why are side scoops placed as far forward as possible?
To permit a gradual bend toward the compressor inlet
What do turning vanes assist with in the side scoop?
The straighten the incoming air and prevent turbulence
What is a major disadvantage of the divided entrance inlets?
After sudden manoeuvres loss of power occurs in one engine so causes a pressure imbalance
In Variable-geometry ducts, what do the inlets act as?
Diffusers so they increase the static pressure but reduce velocity
The aft section of the duct does what to ensure it’s acting as a diffuser?
Increases its area
For very high speed aircraft what changes in order to compensate for the speed?
A variable geometry inlet duct
What are the three methods to diffuse the inlet air and slow it down at supersonic speeds?
Vary the area of the area inlet duct using a ramp or wedge
Use variable bypass arrangement
The use of a shockwave
What is the variable bypass arrangement?
It extracts part of the inlet airflow from the duct ahead of the engine
Why would you use a shockwave in an engine inlet in supersonic aircraft?
To decrease the velocity
What does a compressor inlet screen do?
Stops the engine from ingesting items
What are the disadvantages of inlet screens?
Loss of pressure and they are susceptible to contracting ice.
When are the screens retracted?
After take off and when ice formation is probable
What aircraft are screens not used on? Why?
Turbofan because they weigh a lot and the fan blades do not damage easily
When would you use a bell mouth compressor inlet?
When testing in a test cell
What do the probes measure in a bell mouth duct inlet?
Pressure (total and static) and temperature
What is the bell mouth attached to?
The moveable part of the test stand so moves with the engine
What two parts is the bell mouth made up of?
A moving part and a non moving part so it can measure thrust
What is the duct loss considered as in a bell mouth?
Zero
What is the bell mouth mainly designed to obtain?
Aerodynamic frequency
What does a bell mouth air intake look like?
A bell shaped funnel having carefully rounded shoulders which offer no air resistance
How are inlets in turboprop and turboshaft heated?
By using electrical elements in the lip opening of the intakes
What are deflector doors used for in turboprop and turboshaft?
To deflect ice or dirt away
After the deflector doors where does the air pass through before entering the engine?
A screen
What does a conical spinner do in turboprop and turbofan engines?
Does not allow ice to build up on the surface
In dual spool engines, what allows the fan blades to rotate at low tip speed for best efficiency?
The fan is integral with the low pressure compressor
How does the fan reduce damage from ingested foreign material?
It throws it radially outward and passes through the fan discharge rather than the core
What is drawn from the engines to heat the inlet lip for anti icing?
Bleed air
What prevents ice forming in the fan hub/spinner?
Warm air or uses a conical spinner
What two effects can ice have on the engine inlet?
Disturb airflow so reduces performance on an engine leading to a compressor stall
Suck in ice which can damage the blades or inlet vanes
What do turboprops use to provide anti icing to the inlet area?
Warm oil or hot air
What is hot bleed air extracted from in the inlet extracted from?
The compressor stage of diffuser
What is used if it is only the cowls that require anti icing?
Electrical heat strips
In what pattern is hot air sprayed?
High pressure pattern
What temperature does ice form at?
5 degrees in dry air or 7 degrees in moist air
What can thermal systems be divided into?
Bleed air
Electrical heating
What engines is bleed air extracted from?
High mass airflow engines from the HP compressor
What valve is hot air passed through to provide surface heating to IGV’s, the spinner and the intake lip?
Pressure regulating bleed valve (anti-ice valves)
What do anti ice valves protect against in the anti-ice system?
Over pressurised and limit of bleed air
How can anti ice valve be operated?
Automatically via ice detection system and manually via flight deck
Where is the air used for the aircraft intake anti icing ejected?
Overboard through small grilles
Where is anti icing air ejected when used for the nose cone and IGVs?
Overboard or back to the LP compressor intake
When does a solenoid operated driven air shut off valve open?
When a switch in a flight deck is triggered or ice detector detects a build up of ice
Where does the anti ice system in the engine get air from?
Pneumatic system or directly from engine via engine anti ice valve
What does the hot air flow through in the cowling?
Tiny holes in the Anti ice duct
Where does the hot air leave the leading edge if the engine?
Through openings in the lower part
In a regulator valve what is used to operate the valve when there is a valve or system failure?
Manual override
What positions can the anti ice valves be locked in?
Open and Closed
When the turbine engine is controlled by an ECC, it is linked to the ECC as part of what?
FADEC
On turboprop and shaft engines, what do they tend to use for anti icing?
Electrical heat strips (electrothermal)
When are electrical heat strips designed to operate? Why?
When the engine is running ONLY
They can overheat without air running over it
Are electrothermal systems constantly on when engine is running?
No. They are cycled on and off as required by ambient conditions
