15.3 Inlet Flashcards
What do engines use to straighten the airflow and direct it into the first stages of the compressor?
Inlet guide vanes
What airflow is required to avoid compressor stall?
A uniform and steady airflow
What happens at convergent ducts?
Velocity increases, pressure decreases and temperature decreases
What happens at divergent ducts?
Velocity decreases, pressure increases, temperature increases
Which engine consumes more airflow?
Gas turbine consumes more air than a reciprocating engine
What can inefficiencies of the inlet duct result in?
Performance losses through other components of the engine
Where are divided entrance ducts found?
High speed single or twin military aircraft
Why can’t you use a single entrance duct on military aircraft?
Pilot sits low in the fuselage and close to the nose
What can the divided duct inlet be?
Either a wing root inlet or scoop inlet
Why are the side scoops usually placed as far forward as possible?
To permit a gradual bend towards the compressor inlet
What’s a disadvantage of divided entrance duct?
Some sudden flight manoeuvres can cause an imbalance in ram air pressure
What is the main function of an inlet duct?
To provide the correct amount of air to the engine inlet
Turbojet or low bypass turbofan, what is the max airflow requirements such as Mach number?
Less then Mach 1
In all flight conditions airflow as it enters air inlet must be reduced through the duct before the airflow enters the compressor, how do you achieve this?
Inlet ducts are designed to function as diffusers, decreasing velocity, increasing static pressure
What are the three ways to diffuse the inlet air and slow air down?
1: is to vary the area, or geometry, of the inlet duct either by introducing a movable restriction, such as a ramp or wedge, inside the duct
2: use a variable airflow bypass arrangement, which extracts part of the inlet airflow from the duct ahead of the engine.
3: is the use of a shock wave in the airstream. A shock wave is a thin region of discontinuity in a flow of air or gas, during which the speed, pressure, density, and temperature of the air or gas undergo a sudden change
What are compressor inlet screens used for?
To prevent engine from readily ingesting any items that can be drawn in the intake
Are inlet screens susceptible to icing?
Yes
Do inlet screens cause a loss in inlet duct pressure?
Yes
When are compressor inlet screens used?
On the ground they are retraced in the air
What is the main disadvantage of compressor inlet screens?
They are prone to mechanical failure
Why are compressor inlet screens not used?
Disadvantages outweigh the advantages
Where is a bellmouth compressor inlet used?
Installed on an engine during testing
Where is a bellmouth compressor inlet used?
Installed on an engine during testing
What does a thrust stand do?
A thrust stand is so the moving component can push against a load cell and measure thrust during the testing of the engine
What is the bell mouth designed for?
Obtaining very high aerodynamic efficiency
What is usually considered the best inlet design for turboprop engine?
Ducted arrangement
How are inlets usually anti iced on turboprop engines?
By using electrical elements in the tip opening of the intake
What can be used to deflect ice or dirt away from a turboprop inlet?
Deflector doors
How do turbofan engines deal with FOD?
Takes any FOD and is thrown radially outward and passes through the fan discharge
How is a turbofan engine anti-iced?
Warm bleed air is drawn from the engine and circulated on the inside of the inlet lip for anti icing
What does the fan permit on a turbofan engine?
Conventional air inlet duct resulting in low inlet duct loss
What is configured with internal ducting that permits hot air to circulate for anti-icing purposes?
On the majority of turbine aircraft, the engine cowling, fan, spinner, compressor inlet case and nose cowl
What effect can ice have on the engine inlet?
A disturbed air flow that reduces the performance of the engine leading to a compressor stall
The engine sucks in pieces of ice pieces of ice can damage fan blades or inlet vanes
What do turboprop use for anti-ice?
Oil from the oil reservoir and bleed air
Where, how and why is hot air sprayed?
Hot air is sprayed in a high-pressure pattern to heat all the surfaces where ice is likely to form
What are the two types of engine anti-icing?
Bleed air and electrical heating (thermal)
Where is bleed air usually used for anti-icing?
Engines with big mass airflow
Where does bleed air anti-ice and how?
Takes hot air from HP compressor and passed through the pressure regulating valve to provide surface heating inlet guide vanes (IGVs), the spinner and the intake lip
What are anti-icing valves used to protect against?
Overpressurisation and limit the bleed of air from the engine, thereby preventing a loss of engine power
How can anti-icing valves be operated?
Automatically via the ice detection system, or manually from the flight deck
What happens to air that is used for anti-icing?
Air used for the aircraft intake anti-icing is subsequently ejected overboard through small grills, while air used for the nose cone and inlet guide vanes is either directed overboard or back into the LP compressor intake
The anti-icing valves are normally selected electrically, pressure operated and indications are given for:
Valve not in position selected
Low duct pressure
High duct pressure
Low duct temperature
High duct temperature
What do all thermal anti-ice valves have?
Manual override function used when there is valve or system failure
When is anti-icing with electronic engine control used?
As part of a full authority digital engine control (FADEC) system, the anti-icing system is linked to the ELC
What do turboprop and turboshaft engines used for anti-icing with electro thermal anti-icing systems?
Tend to use electric heat strips which are classed as electro-thermal anti-icing systems
