15.3 Inlet Flashcards
What is the primary function of engine inlet ducts in turbine engines?
To provide a relatively distortion-free airflow to the inlet of the compressor in the required quantity.
What are Inlet Guide Vanes (IGV) used for in turbine engines?
To straighten the airflow and direct it into the first stages of the compressor.
Why is a uniform and steady airflow important in turbine engines?
To avoid compressor stall and excessive internal engine temperatures in the turbine section.
Is the air-inlet duct considered a part of the engine?
No, it is considered an airframe part.
What effect do inlet duct inefficiencies have on engine performance?
They can result in performance losses through other components of the engine.
How does the airflow requirement differ between gas turbine engines and reciprocating engines?
Gas turbine engines consume considerably more airflow than reciprocating engines.
What is the significance of air intake size on the Rolls Royce XWB engine?
It is critical in determining engine and aircraft performance, especially at high airspeeds.
What is the purpose of screens on turboprop and turboshaft engines’ inlets?
To prevent Foreign Object Damage (FOD).
What phenomenon compensates for thrust losses as aircraft speed increases?
Ram recovery.
Fill in the blank: The inlet must recover as much of the total pressure of the free airstream as possible, which is known as _______.
ram recovery
What must the engine inlet duct do to minimize drag effect on the aircraft?
Keep the drag effect on the aircraft to a minimum.
What causes an air pressure drop in the engine inlet?
Friction of air along both sides of the duct and bends in the duct system.
How does airflow management affect the size of the engine nacelle in low flow rate engines?
Turning the airflow allows the nacelle to be smaller and have less drag.
What is required in the duct of turbofan engines to ensure smooth airflow?
A sufficiently straight section.
What factors dictate the choice of configuration for the entrance of the duct?
Location of the engine, airspeed, altitude, and attitude at which the aircraft is designed to operate.
What are the different types of inlets discussed?
Divided-entrance duct, variable-geometry duct, compressor inlet screens, bellmouth compressor inlets, turboprop and turboshaft compressor inlets, turbofan engine inlet sections.
What is a divided-entrance duct?
A duct that takes air from either side of the fuselage, widely used in high-speed military aircraft.
What are the main problems faced by a divided duct?
Difficulty in obtaining sufficient air scoop area without causing large amounts of drag and designing an entrance duct of reasonable length with minimal bends.
What is one major drawback of a divided-entrance duct?
Imbalance in ram air pressure between the two ducts during sudden flight maneuvers.
True or False: The airflow through an engine must always be less than Mach 1.
True.
What is the function of a variable-geometry duct?
To provide the correct amount of air to the engine inlet, adjusting for different flight speeds.
Fill in the blank: The aft section of a supersonic inlet duct ________ in area.
increases
What are the three methods to diffuse inlet air at supersonic speeds?
- Vary the area of the inlet duct
- Use a variable airflow bypass arrangement
- Utilize a shock wave in the airstream
What is the purpose of a compressor inlet screen?
To prevent the engine from ingesting items that can cause internal damage.
What are the disadvantages of compressor inlet screens?
- Loss in inlet duct pressure
- Susceptible to icing
- Potential for mechanical failure
- Adds weight to the installation
What is a bellmouth inlet used for?
To test engines in a test cell by allowing outside static air to flow into the engine with minimal resistance.
What is a key design feature of a bellmouth inlet?
It is a bell-shaped funnel with rounded shoulders for high aerodynamic efficiency.
What considerations must be made for turboprop air inlets?
The propeller drive shaft, hub, and spinner must be considered along with other inlet design factors.
What is the best inlet design for turboprop engines?
Ducted arrangement for optimal airflow and aerodynamic characteristics.
What role does the fan play in high-bypass turbofan engines?
It reduces engine damage from ingested foreign material and allows for a conventional air inlet duct.
Fill in the blank: Warm bleed air is circulated on the inside of the inlet lip for ________.
anti-icing
What is a conical spinner used for in turboprop engines?
To prevent ice buildup on the surface.
What is the primary purpose of the inlet cowl in turbofan engines?
To provide the airflow path into the engine.
What is the advantage of using a dual-spool engine in turbofans?
It allows the fan blades to rotate at low tip speed for better fan efficiency.
What is the primary purpose of inlet ice protection?
To prevent ice formation that can disrupt airflow and performance of the engine
What components are typically configured with internal ducting for anti-icing in turbine aircraft?
- Engine cowling
- Fan
- Spinner
- Compressor inlet case
- Nose cowl
What are the potential effects of ice on the engine inlet?
- Disturbed airflow leading to compressor stall
- Damage to fan blades or inlet vanes
How do turboprops provide anti-icing for the engine inlet?
Using warm oil from the engine oil reservoir and hot air to keep the inlet area free of ice
What type of air is used for anti-icing protection during ground and flight operations?
Hot bleed air extracted from the compressor or diffuser
At what temperatures can ice form in the inlet?
- 5 °C in dry air
- 7 °C in moist air
What are the two main types of engine anti-ice systems?
- Bleed Air
- Electrical Heating (thermal)
What is the function of anti-icing valves in bleed air systems?
To protect against overpressurization and limit bleed air from the engine
What triggers the operation of anti-icing valves?
- Automatic via ice detection system
- Manually from the flight deck
What happens when the anti-icing valve opens?
Hot air enters the anti-ice duct and sprays through small holes into the engine cowling
What is a critical warning during ground tests of thermal anti-ice systems?
No personnel should be in the test area due to hot air
What type of valve is commonly used in thermal anti-ice systems?
Solenoid-controlled pressure regulating valves
What is the role of the Electronic Engine Control (EEC) in anti-icing systems?
Controls the flow of hot air to the engine inlet based on sensor inputs
What materials are used in electro-thermal anti-icing systems?
Electrical resistance wire embedded in reinforced neoprene materials
What must be ensured when using electro-thermal systems?
They operate only when the engine is running to prevent overheating
What should be checked if ice forms in the inlet with the anti-icing system turned ON?
Verify the correct power source at the valve and check valve operation
What is a possible cause for compressor stalls at high power settings with the anti-icing system OFF?
Inlet icing during ground run-up
What should be done if the engine is unable to attain full power at EGT limit?
Check for leak-through at the valve and replace if necessary
What could cause fluctuating EGT and engine speed?
Intermittent opening of anti-icing valves when the system is off
What action should be taken if inlet probe icing is suspected during flight?
Turn on anti-ice to remove ice in-flight and inspect after landing
