15.3 Inlet (Level 2, 3 Questions)

Question 1

What is the purpose of the engine inlet in a turbine engine?

A. To provide distortion-free airflow to the compressor in the required amount.
B. To provide cooling airflow to the turbine blades during operation.
C. To increase the overall efficiency of the turbine engine system.

Answer 1

A. To provide distortion-free airflow to the compressor in the required amount.

Question 2

What is the purpose of Inlet Guide Vanes (IGV) in many engines?

A. To straighten airflow and direct it into the first stages of the compressor.
B. To increase the pressure of the airflow entering the engine.
C. To cool the airflow before it reaches the compressor.

Answer 2

A. To straighten airflow and direct it into the first stages of the compressor.

Question 3

Why is a uniform and steady airflow required in a turbine engine?

A. To increase the speed of airflow through the engine.
B. To enhance fuel efficiency and reduce emissions.
C. To avoid compressor stall and excessive turbine temperatures.

Answer 3

C. To avoid compressor stall and excessive turbine temperatures.

Question 4

What is the air-inlet duct considered as?

A. A part of the engine.
B. An airframe part.
C. A part of the fuel system.

Answer 4

B. An airframe part.

Question 5

Why is the air-inlet duct important to the engine?

A. It improves the fuel efficiency of the engine.
B. It helps the engine produce an optimum amount of thrust.
C. It reduces the noise produced by the engine.

Answer 5

B. It helps the engine produce an optimum amount of thrust.

Question 6

Compared to reciprocating engines, gas turbine engines:

A. Consume considerably more airflow.
B. Consume less airflow.
C. Consume about the same airflow.

Answer 6

A. Consume considerably more airflow.

Question 7

The size of the air entrance passage in gas turbine engines is:

A. Smaller and less important.
B. Larger and critical to engine and aircraft performance.
C. The same size as in reciprocating engines.

Answer 7

B. Larger and critical to engine and aircraft performance.

Question 8

What can inefficiencies in the inlet duct cause?

A. Increased fuel efficiency.
B. Performance losses through other engine components.
C. Reduced engine noise.

Answer 8

B. Performance losses through other engine components.

Question 9

Why do many turboprop and turboshaft engines have screens covering the inlet?

A. To improve airflow speed.
B. To prevent Foreign Object Damage (FOD).
C. To reduce engine temperature.

Answer 9

B. To prevent Foreign Object Damage (FOD).

Question 10

What happens to thrust as aircraft speed increases?

A. Thrust tends to increase.
B. Thrust tends to decrease.
C. Thrust remains constant.

Answer 10

B. Thrust tends to decrease.

Question 11

What helps compensate for thrust losses at higher aircraft speeds?

A. Ram recovery.
B. Fuel injection.
C. Exhaust cooling.

Answer 11

A. Ram recovery.

Question 12

What must the inlet do to maintain engine performance at high speeds?

A. Recover as much total pressure of the free airstream as possible.
B. Reduce airflow to the compressor.
C. Increase fuel flow to the engine.

Answer 12

A. Recover as much total pressure of the free airstream as possible.

Question 13

What happens to pressure loss as air molecules are compressed in the inlet?

A. Pressure loss increases significantly.
B. Much of the pressure loss is recovered.
C. Pressure loss stays the same.

Answer 13

B. Much of the pressure loss is recovered.

Question 14

What is the increase in pressure and airflow at the engine inlet called?

A. Total pressure recovery or ram recovery.
B. Fuel injection.
C. Airflow distortion.

Answer 14

A. Total pressure recovery or ram recovery.

Question 15

What must the inlet duct do when delivering air to the compressor inlet?

A. Deliver air with minimal turbulence and pressure variation.
B. Increase turbulence to mix airflow better.
C. Maximize drag to stabilize the aircraft

Answer 15

A. Deliver air with minimal turbulence and pressure variation.

Question 16

What else must the engine inlet duct minimize on the aircraft?

A. Fuel consumption.
B. Drag effect.
C. Noise levels.

Answer 16

B. Drag effect.

Question 17

What causes an air pressure drop in the engine inlet, and how is smooth airflow maintained?

A. Friction along the duct and bends cause pressure drop; smooth flow needs minimal turbulence.
B. Fuel injection causes pressure drop; smooth flow requires higher airspeed.
C. Engine heat causes pressure drop; smooth flow is maintained by increasing turbulence.

Answer 17

A. Friction along the duct and bends cause pressure drop; smooth flow needs minimal turbulence.

Question 18

What must the duct in turbofan engines have to ensure smooth airflow?

A. A sufficiently straight section.
B. Several sharp bends.
C. Screens to prevent debris.

Answer 18

A. A sufficiently straight section.

Question 19

On engines with low flow rates, why is the airflow turned?

A. To allow the engine nacelle to be smaller and reduce drag.
B. To increase the size of the nacelle and airflow speed.
C. To cool the engine more effectively.

Answer 19

A. To allow the engine nacelle to be smaller and reduce drag.

Question 20

What dictates the choice of configuration for the entrance of the engine inlet duct?

A. Engine location, airspeed, altitude, and aircraft attitude.
B. Fuel type and engine temperature.
C. Pilot preference and maintenance schedule.

Answer 20

A. Engine location, airspeed, altitude, and aircraft attitude.

Question 21

Why is a divided-entrance duct used in some high-speed military aircraft?

A. Because the crew sits low near the nose, making single-entrance ducts difficult to use, so air is taken from both sides of the fuselage.
B. Because it improves fuel efficiency by taking air from the tail.
C. Because it reduces engine noise by directing air overhead.

Answer 21

A. Because the crew sits low near the nose, making single-entrance ducts difficult to use, so air is taken from both sides of the fuselage.

Question 22

What are the two types of divided ducts mentioned?

A. Wing-root inlet and scoop at each side of the fuselage.
B. Overhead duct and tail scoop.
C. Rear inlet and bottom scoop.

Answer 22

A. Wing-root inlet and scoop at each side of the fuselage.

Question 23

Why do divided ducts present more problems to aircraft designers than single-entrance ducts?

A. Because it’s hard to get enough air scoop area without causing large drag.
B. Because they increase engine noise significantly.
C. Because they reduce airflow speed.

Answer 23

A. Because it’s hard to get enough air scoop area without causing large drag.

Question 24

What is a major drawback in designing an entrance duct?

A. Creating a duct with as few bends as possible and reasonable length.
B. Making the duct very short with many sharp bends.
C. Adding multiple scoops to increase airflow.

Answer 24

A. Creating a duct with as few bends as possible and reasonable length.

Question 25

Where are side scoops usually placed on the fuselage? A. As far forward as possible for a gradual bend toward the compressor inlet. B. Near the tail to maximize airflow speed. C. Above the cockpit for better cooling.

Answer 25

A. As far forward as possible for a gradual bend toward the compressor inlet.

Question 26

What is the purpose of turning vanes in side-scoop inlets? A. To straighten incoming airflow and prevent turbulence. B. To increase turbulence for better mixing. C. To cool the air before entering the compressor

Answer 26

A. To straighten incoming airflow and prevent turbulence.

Question 27

What is an advantage of mounting an air inlet duct on each side of an aircraft? A. It shortens the duct length without adding much drag. B. It increases fuel consumption significantly. C. It causes more noise during flight.

Answer 27

A. It shortens the duct length without adding much drag.

Question 28

What disadvantage can sudden flight maneuvers cause with side-mounted air inlet ducts? A. An imbalance in ram air pressure between the two ducts, causing a slight loss of engine power. B. Increased fuel consumption during flight. C. Overheating of the turbine section.

Answer 28

A. An imbalance in ram air pressure between the two ducts, causing a slight loss of engine power.

Question 29

What is the main function of an inlet duct? A. To provide the correct amount of air to the engine inlet. B. To cool the engine compressor. C. To reduce fuel consumption.

Answer 29

A. To provide the correct amount of air to the engine inlet.

Question 30

In turbojet or low bypass turbofan engines, the airflow Mach number ahead of the engine face must be: A. Less than Mach 1. B. Exactly Mach 1. C. Greater than Mach 1.

Answer 30

A. Less than Mach 1.

Question 31

Why must airflow through the engine always be less than Mach 1? A. To prevent shock waves that can disrupt engine performance. B. To increase fuel consumption. C. To maximize noise levels.

Answer 31

A. To prevent shock waves that can disrupt engine performance.

Question 32

What must happen to the velocity of airflow as it enters the air-inlet duct? A. It must be reduced before entering the compressor. B. It must be increased to maximize thrust. C. It remains the same throughout.

Answer 32

A. It must be reduced before entering the compressor.

Question 33

How do inlet ducts achieve the reduction of airflow velocity before the compressor? A. By functioning as diffusers that decrease velocity and increase static pressure. B. By accelerating airflow to increase velocity and decrease pressure. C. By maintaining constant velocity and pressure throughout.

Answer 33

A. By functioning as diffusers that decrease velocity and increase static pressure.

Question 34

In supersonic aircraft, how does the diffuser change in the downstream direction initially? A. It progressively decreases in area to reduce airflow velocity. B. It progressively increases in area to speed up airflow. C. It remains the same size throughout.

Answer 34

A. It progressively decreases in area to reduce airflow velocity.

Question 35

Until what point does the supersonic inlet duct decrease in area? A. Until the airflow velocity is reduced to Mach 1. B. Until the airflow reaches Mach 2. C. Until the airflow is completely stopped.

Answer 35

A. Until the airflow velocity is reduced to Mach 1.

Question 36

What happens to the area of the duct after the airflow velocity reaches Mach 1? A. The duct area increases to act as a subsonic diffuser. B. The duct area continues to decrease. C. The duct area stays the same.

Answer 36

A. The duct area increases to act as a subsonic diffuser.

Question 37

What is the common name for an inlet duct that changes its geometry with speed? A. Variable-geometry inlet duct. B. Fixed-geometry duct. C. Supersonic fixed diffuser.

Answer 37

A. Variable-geometry inlet duct.

Question 38

What are the three methods used to diffuse inlet air and slow airflow at supersonic speeds? A. Varying duct area with movable restrictions, variable airflow bypass, and using shock waves. B. Increasing airflow speed, using fixed ducts, and cooling the air. C. Sealing the duct, increasing fuel flow, and reducing pressure.

Answer 38

A. Varying duct area with movable restrictions, variable airflow bypass, and using shock waves.

Question 39

What is one method to diffuse inlet air and slow airflow at supersonic speeds? A. Varying the duct area by using movable restrictions like ramps or wedges. B. Using fixed ducts with no moving parts. C. Increasing airflow speed inside the duct.

Answer 39

A. Varying the duct area by using movable restrictions like ramps or wedges.

Question 40

What does a variable airflow bypass system do? A. Extracts part of the inlet airflow ahead of the engine. B. Increases the airflow entering the engine. C. Blocks airflow to cool the engine.

Answer 40

A. Extracts part of the inlet airflow ahead of the engine.

Question 41

What happens at a shock wave in the airstream? A. Speed, pressure, density, and temperature undergo a sudden change. B. Airflow becomes smooth and steady. C. Airflow speed increases without any pressure change.

Answer 41

A. Speed, pressure, density, and temperature undergo a sudden change.

Question 42

What effect does a shock wave have on the airflow in the inlet duct? A. It diffuses the airflow and decreases its velocity. B. It increases the airflow velocity. C. It stabilizes airflow with no change in speed.

Answer 42

A. It diffuses the airflow and decreases its velocity.

Question 43

What is the purpose of a compressor inlet screen? A. To prevent the engine from ingesting foreign objects. B. To increase the airflow speed into the engine. C. To cool the incoming air.

Answer 43

A. To prevent the engine from ingesting foreign objects.

Question 44

Where is a compressor inlet screen placed? A. Across the engine air inlet at some location along the inlet duct. B. Inside the combustion chamber. C. At the engine exhaust outlet.

Answer 44

A. Across the engine air inlet at some location along the inlet duct.

Question 45

When is a compressor inlet screen considered necessary? A. When the engine has aluminium compressor blades that are easily damaged. B. When the engine uses steel or titanium compressor blades. C. When the engine operates only at low speeds.

Answer 45

A. When the engine has aluminium compressor blades that are easily damaged.

Question 46

What are some disadvantages of compressor inlet screens? A. They cause pressure loss, can ice up, add weight, and may fail mechanically. B. They improve airflow and reduce weight. C. They prevent fuel consumption.

Answer 46

A. They cause pressure loss, can ice up, add weight, and may fail mechanically.

Question 47

Why are compressor inlet screens usually not used on turbofan engines with steel or titanium blades? A. The blades are tough enough that the disadvantages of screens outweigh the benefits. B. Screens increase the speed of airflow too much. C. Screens cause engines to overheat.

Answer 47

A. The blades are tough enough that the disadvantages of screens outweigh the benefits.

Question 48

Where is a bellmouth compressor inlet usually installed? A. On an engine undergoing testing in a test cell. B. On an aircraft in flight. C. At the exhaust of the engine.

Answer 48

A. On an engine undergoing testing in a test cell.

Question 49

What measurements can probes on a bellmouth inlet take? A. Intake temperature and pressure (total and static). B. Fuel flow and engine RPM. C. Exhaust temperature and velocity

Answer 49

A. Intake temperature and pressure (total and static).

Question 50

Why must outside static air flow into the engine with little resistance during testing? A. To ensure accurate engine performance measurements. B. To reduce fuel consumption. C. To cool the engine compressor.

Answer 50

A. To ensure accurate engine performance measurements.

Question 51

Why is the bellmouth attached to the movable part of the test stand? A. So it moves with the engine to allow accurate thrust measurement. B. To keep it stationary during testing. C. To reduce noise levels in the test cell.

Answer 51

A. So it moves with the engine to allow accurate thrust measurement.

Question 52

What is the main design objective of a bellmouth inlet? A. To obtain very high aerodynamic efficiency with minimal air resistance. B. To reduce engine noise during flight. C. To increase fuel consumption for testing.

Answer 52

A. To obtain very high aerodynamic efficiency with minimal air resistance.

Question 53

How is duct loss characterized when using a bellmouth inlet? A. Considered zero, meaning minimal airflow resistance. B. Very high, causing reduced engine performance. C. Variable depending on flight speed.

Answer 53

A. Considered zero, meaning minimal airflow resistance.

Question 54

What kind of engine performance data is obtained using a bellmouth inlet? A. Rated thrust and thrust-specific fuel consumption. B. Exhaust temperature and pressure only. C. Noise levels during takeoff.

Answer 54

A. Rated thrust and thrust-specific fuel consumption.

Question 55

Why is the turboprop air inlet more complicated than other turbine engines? A. Because it must consider the propeller drive shaft, hub, and spinner. B. Because it uses less airflow than other engines. C. Because it doesn’t need any anti-icing systems.

Answer 55

A. Because it must consider the propeller drive shaft, hub, and spinner.

Question 56

What inlet design is generally best for turboprop engines? A. A ducted arrangement for optimal airflow and aerodynamics. B. An open inlet without ducting. C. A simple open intake with no screens.

Answer 56

A. A ducted arrangement for optimal airflow and aerodynamics.

Question 57

How is the inlet on many turboprop engines anti-iced? A. By electrical heating elements in the lip opening of the intake. B. By spraying water to keep ice off. C. By using heated fuel only.

Answer 57

A. By electrical heating elements in the lip opening of the intake.

Question 58

What is the purpose of deflector doors on turboprop engine inlets? A. To deflect ice or dirt away from the intake. B. To increase airflow speed. C. To block airflow during engine shutdown.

Answer 58

A. To deflect ice or dirt away from the intake.

Question 59

What function does a conical spinner serve on turboprop and turbofan engines? A. It prevents ice buildup on the surface. B. It increases drag to slow the aircraft. C. It cools the incoming air.

Answer 59

A. It prevents ice buildup on the surface.

Question 60

Where is the fan typically located in a high-bypass turbofan engine? A. At the forward end of the compressor. B. Behind the low-pressure compressor. C. Inside the engine core.

Answer 60

A. At the forward end of the compressor.

Question 61

How does the fan reduce engine damage from ingested foreign material? A. By throwing material radially outward through the fan discharge. B. By redirecting material into the engine core. C. By stopping material at the inlet cowl.

Answer 61

A. By throwing material radially outward through the fan discharge.

Question 62

How is the inlet lip of a high-bypass turbofan engine typically anti-iced? A. By circulating warm bleed air inside the lip. B. By using an electrical heating element. C. By spraying de-icing fluid during flight.

Answer 62

A. By circulating warm bleed air inside the lip.

Question 63

What effect can ice have on the airflow into an engine inlet? A. It disturbs the airflow, reducing engine performance and possibly causing a compressor stall. B. It increases airflow, improving engine efficiency. C. It has no significant impact on airflow.

Answer 63

A. It disturbs the airflow, reducing engine performance and possibly causing a compressor stall.

Question 64

How can ice damage the engine when sucked into the inlet? A. By damaging fan blades or inlet vanes. B. By clogging the fuel injectors. C. By freezing the engine core.

Answer 64

A. By damaging fan blades or inlet vanes.

Question 65

*How do turboprops provide anti-icing for the inlet area? A. By using warm oil from the engine oil reservoir along with a small amount of hot air. B. By circulating coolant fluid through the inlet. C. By using only heated air from the engine.

Answer 65

A. By using warm oil from the engine oil reservoir along with a small amount of hot air.

Question 66

*Under what conditions can ice form in the engine inlet? A. At 5 °C in dry air or 7 °C in moist air such as fog or rain. B. Only when temperatures drop below freezing. C. Only at high altitudes in dry air.

Answer 66

A. At 5 °C in dry air or 7 °C in moist air such as fog or rain.

Question 67

When are electrical heat strips typically used in engine anti-icing systems? A. When only the engine cowls require anti-icing. B. When heating the compressor is insufficient. C. During ground operations at low temperatures

Answer 67

A. When only the engine cowls require anti-icing.

Question 68

What are the two most common types of engine anti-ice systems? A. Bleed air and electrical heating (thermal). B. Hydraulic heating and bleed air. C. Electrical heating and coolant-based systems

Answer 68

A. Bleed air and electrical heating (thermal).

Question 69

How does bleed air provide heating in engine anti-icing systems? A. By passing hot air from the HP compressor through anti-icing valves to heat surfaces like IGVs, the spinner, and the intake lip. B. By directing air from the LP compressor to the entire engine casing. C. By using exhaust gases to heat the engine surfaces.

Answer 69

A. By passing hot air from the HP compressor through anti-icing valves to heat surfaces like IGVs, the spinner, and the intake lip.

Question 70

What is the purpose of anti-icing valves in bleed air systems? A. To regulate pressure, prevent overpressurisation, and limit bleed air loss from the engine. B. To control the exhaust flow during anti-icing. C. To cool the engine core during icing conditions.

Answer 70

A. To regulate pressure, prevent overpressurisation, and limit bleed air loss from the engine.

Question 71

What happens when abnormal conditions like high duct pressure or low duct temperature occur in a bleed air anti-icing system? A. A latched relay is tripped, locking the system out until it is reset by switching OFF and ON. B. The system automatically resets itself to normal operation. C. The flight crew must activate a manual override to restore the system.

Answer 71

A. A latched relay is tripped, locking the system out until it is reset by switching OFF and ON.

Question 72

What is a critical safety precaution during ground tests of thermal anti-ice systems? A. Ensuring no personnel are in the test area due to the hot air. B. Monitoring the pressure in the pneumatic system. C. Keeping the engine at idle speed throughout the test.

Answer 72

A. Ensuring no personnel are in the test area due to the hot air.

Question 73

What happens when the engine anti-ice valve is opened? A. Hot air sprays through small holes in the anti-ice duct into the engine cowling. B. The engine automatically reduces power to prevent overheating. C. The pneumatic system redirects air to the compressor blades.

Answer 73

A. Hot air sprays through small holes in the anti-ice duct into the engine cowling.

Question 74

What triggers the solenoid-operated shutoff valve in an engine anti-icing system? A. A switch on the flight deck or detection of ice build-up by the ice detector. B. High-speed airflow entering the compressor. C. A sudden drop in engine temperature.

Answer 74

A. A switch on the flight deck or detection of ice build-up by the ice detector.

Question 75

What feature do all thermal anti-ice valves have for use during system failures? A. Manual override function. B. Automatic reset system. C. Pressure relief bypass.

Answer 75

A. Manual override function.

Question 76

What system is the Electronic Engine Control (EEC) a part of? A. Full Authority Digital Engine Control (FADEC). B. Hydraulic control system. C. Electrical power distribution system.

Answer 76

A. Full Authority Digital Engine Control (FADEC).

Question 77

What type of anti-icing system is commonly used on smaller turboprop and turboshaft engines? A. Electro-thermal electric heat strip system. B. Bleed air anti-icing system. C. Hydraulic heating system.

Answer 77

A. Electro-thermal electric heat strip system.

Question 78

Where are the electrical resistance wires typically located in electro-thermal anti-icing systems? A. At the lip of the nacelle inlet embedded in neoprene materials. B. Inside the compressor blades. C. Around the engine exhaust.

Answer 78

A. At the lip of the nacelle inlet embedded in neoprene materials.

Question 79

Why must electro-thermal anti-icing systems only operate when the engine is running? A. Without airflow, the electric heat strips can overheat and damage the engine. B. The system requires hydraulic pressure to function. C. The electrical system is disabled when the engine is off.

Answer 79

A. Without airflow, the electric heat strips can overheat and damage the engine.