Module 15.3 Inlet

Question 1

Engine inlets are what kind of duct and what do they do?

Answer 1

Divergent ducts. This increases the RAM recovery.

Question 2

When the aircraft is stationary, all the suction is done by what?

What does this mean?

Answer 2

The engine, meaning there’s no RAM effect.

Question 3

If there is no RAM effect at the inlet, what does this mean for air pressure?

Answer 3

Air pressure at the inlet will be lower than ambient air pressure.

Question 4

The engine inlet of a turbine engine is designed to do what?

Answer 4

Provide a relatively distortion-free airflow to the inlet of the compressor.

Question 5

What do many engines use to straighten the airflow and direct it into the first stages of the compressor?

Answer 5

Inlet Guide Vanes (IGV)

Question 6

What is needed to avoid compressor stall?

Answer 6

A uniform and steady airflow.

Question 7

Is the air-inlet duct is considered an engine part or airframe part?

Answer 7

An airframe part.

Question 8

What can inefficiencies of the inlet duct result in?

Answer 8

Performance losses through other components of the engine.

Question 9

What is used to prevent Foreign Object Damage (FOD) getting into the engine when the aircraft is stationary?

Answer 9

Screens

Question 10

What happens to thrust as aircraft speed increases?

Answer 10

It decreases

Question 11

What does RAM recovery compensate for?

Answer 11

Losses caused by reduced thrust due to the increase of speed.

Question 12

What is RAM recovery?

Answer 12

The process of converting the kinetic energy of incoming air (RAM effect) into potential (static) energy at the engine inlet.

Question 13

The inlet must be able to recover as much what from the free air stream?

Answer 13

Total pressure.

Question 14

What does the added pressure at the inlet increase?

Answer 14

The pressure and airflow to the engine (RAM recovery).

Question 15

What is an air pressure drop at the inlet caused by?

Answer 15

Friction of air along both sides of the duct and by the bends in the duct system.

Question 16

What does an engine with low flow rates turning the airflow’s nacelle need to be?

Answer 16

Smaller

Question 17

On turbofan engines, what must the duct have

Answer 17

A straight section to ensure smooth airflow.

Question 18

What is the configuration to the entrance of the duct dictated by?

Answer 18

Location of the engine and the airspeed, altitude, and attitude the aircraft is designed to operate at.

Question 19

What two effects can ice have on an engine?

Answer 19

Disturbed air flow that reduces the performance.

Pieces of ice can damage fan blades or inlet vanes.

Question 20

What do turboprops do to prevent ice build up?

Answer 20

Warm oil from the engine oil reservoir together with a small amount of hot air.

Question 21

Where is hot air taken from to provide anti-icing protection for the inlet?

Answer 21

From the compressor or diffuser.

Question 22

How is hot air used to protect against ice?

Answer 22

It’s sprayed in a high-pressure pattern to heat all the surfaces where ice is likely to form.

Question 23

At what temperatures can ice form on the inlet?

Answer 23

5 °C in dry air and at 7 °C in moist air.

Question 24

What are the most common ice protection systems known as?

Answer 24

Thermal systems

Question 25

Thermal anti-ice systems can be subdivided into what two categories?

Answer 25

Bleed Air and Electrical Heating.

Question 26

Bleed air ice protection is generally used on what engines?

Answer 26

Those with high mass airflows (turbofan engines).

Question 27

Where is hot air bled off from in the bleed air anti-ice system?

Answer 27

The engine HP compressor and passes through a pressure regulating bleed valve (anti-icing valve).

Question 28

Bleed air provides surface heating to which parts of the engine?

Answer 28

Inlet Guide Vanes (IGVs), the spinner and the intake lip.

Question 29

What are anti-ice valves used to protect against?

Answer 29

Over-pressurisation

Question 30

How can anti-ice valves be operated?

Answer 30

Automatically via the ice detection system, or manually from the flight deck.

Question 31

What is done with air used for the intake lip anti-icing?

Answer 31

Ejected overboard through small grills.

Question 32

What is done with air used for the nose cone and inlet guide vanes

Answer 32

Directed overboard or back into the LP compressor intake.

Question 33

Which valves provides the anti-ice connection between the compressor and where the air's sent?

Answer 33

The anti-ice valve.

Question 34

What happens when the anti-ice valve opens?

Answer 34

The hot air enters the anti-ice duct. The hot air sprays through small holes in the anti-ice duct into the engine cowling.

Question 35

What safety precaution should their be in place during ground tests of thermal anti-ice systems.

Answer 35

No personnel should be in the test area.

Question 36

How is the regulator valve controlled?

Answer 36

Solenoid-controlled

Question 37

Other than anti-ice valves, what other valve is found in the anti-ice system?

Answer 37

Solenoid-controlled pressure regulating valves.

Question 38

All thermal anti-ice valves have what?

Answer 38

A manual override function.

Question 39

When is the manual override function of anti-ice valve used?

Answer 39

When there is a valve or system failure.

Question 40

What is the anti-ice system linked to?

Answer 40

Electronic Engine Control (EEC) as part of a Full Authority Digital Engine Control (FADEC) system.

Question 41

Once the flight crew makes the choice to turn on anti-icing, what does the Electronic Engine Control (EEC) do?

Answer 41

Controls the flow of hot air to the engine inlet.

Question 42

What is used as anti-icing on smaller turboprop and turboshaft engines?

Answer 42

Electric heat strip systems, which are classed as electro-thermal anti-icing systems.

Question 43

Where are electric heat strip anti-ice systems located?

Answer 43

At the lip of the nacelle inlet.

Question 44

What does a divided duct do?

Answer 44

Takes air from either side of the fuselage.

Question 45

What are two types of divided duct?

Answer 45

Wing-root inlet or scoop

Question 46

Which type of divided duct is often used

Answer 46

Scoops

Question 47

Where are divided inlet side scoops placed and why?

Answer 47

As far forward as possible to permit a gradual bend toward the compressor inlet.

Question 48

Why are a series of turning vanes sometimes placed in the side-scoop inlet?

Answer 48

To assist in straightening the incoming airflow.

Question 49

What is a disadvantage to a divided inlet arrangement?

Answer 49

Some sudden flight manoeuvres can cause an imbalance in ram air pressure between the two ducts. This can result in slight power loss.

Question 50

Through all flight conditions, what must be done to the velocity of the airflow as it enters the air-inlet duct?

Answer 50

It must be reduced through the duct before the airflow enters the compressor.

Question 51

How are inlet ducts designed to decrease velocity and increase static pressure before air gets to the compressor?

Answer 51

They are designed to function as diffusers.

Question 51

With supersonic flight aircraft, what does the fwd portion of the duct do?

Answer 51

It acts as a diffuser by progressively decreasing in the area in the downstream direction. This decreases the velocity of the airflow to Mach 1.0. Pressure is also increased

Question 52

With supersonic flight aircraft, what does the aft portion of the duct do?

Answer 52

It increases in area as this part must act as a subsonic diffuser. This decreases air velocity further and increases pressure further.

Question 53

What do stronger shockwaves do?

Answer 53

Produce larger changes in the properties of the air or gas. E.g. slow the air down more.

Question 54

Where are shockwaves created?

Answer 54

In the supersonic flow of the air entering the duct.

Question 55

what do shockwaves result in?

Answer 55

The diffusion of the airflow, which, in turn, decreases the velocity of the airflow.