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Resource Group Mod 15 2024 > 15.3 Inlet > Flashcards

15.3 Inlet Flashcards

1
Q

What’s the fundamental purpose of an engine inlet?

A

Designed to provide a relatively distortion-free airflow to the inlet of the compressor in the required quantity.

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2
Q

What is the purpose of Inlet Guide Vanes (IGVs)?

A

To straighten the airflow and direct it into the first stages of the compressor. (prevents comp. stall).

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3
Q

What is the inlet considered a structural part of?

A

The airframe, NOT the engine.

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4
Q

What do many turboprop and turboshaft engines use to protect their inlets from FOD?

A

Inlet Screens

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5
Q

What tends to happen to thrust as airspeed increases?

A

Thrust tends to decrease with increasing airpeed.

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6
Q

What is the definition of Ram Recovery?

A

The added pressure at the inlet of the engine increases the pressure and airflow to the engine

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7
Q

Another name for Ram Recovery?

A

Total Pressure Recovery.

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8
Q

What can cause a drop in air pressure in the inlet duct?

A

Friction against the duct walls, and bends in the duct system.

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9
Q

What factors dictate duct entrance design?

A
  • The location of the engines on the airframe.
  • Intended operation of aircraft airspeed.
  • Intended operation of aircraft altitude.
  • Intended operation of aircraft attitude.
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10
Q

What type of aircraft would you find a ‘Divided-Entrance Duct’ on?

A

High-speed, single or twin engine aircraft.

(Think F35 Lightning side intakes)

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11
Q

Why are the side intakes on a divided-entrance duct placed as far forward as possible?

A

To increase distance from compressor so that the bend angle of the ducting is a gradual as possible.

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12
Q

What assists straightening the airflow into side-scoop inlets?

A

Turning vanes.

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13
Q

What is the disadvantage of using side-scoop inlets?

A

A ram-air pressure imbalance can develop across the two ducts when peforming sudden manoeuvres. Can cause small power-loss.

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14
Q

At what speed must airflow through an engine always be?

A

Below Mach 1.

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15
Q

What happens to supersonic air as it passes through a converging duct?

A

Velocity decreases, pressure increases. (Opposite to subsonic air in Bernoulli’s principle).

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16
Q

What are the 3 methods for slowing down supersonic air as it enters an inlet?

A
  • Variable geometry inlet.
  • Variable airflow bypass arrangement.
  • Using shockwaves in the airstream.
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17
Q

How does a Variable Geometry Inlet slow down supersonic air?

A

By introducing a movable restriction, such as a ramp or wedge, inside the duct.

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18
Q

How does a Variable Airflow Bypass Arrangement slow down supersonic air into the inlet?

A

Extracts part of the inlet airflow from the duct ahead of the engine.

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19
Q

How do shockwaves in the airstream slow down supersonic air into the inlet?

A

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

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20
Q

How are shockwaves in the airstream generated in the inlet?

A

A shockwave is created by a small restriction/obstruction which automatically protrudes into the duct at high speed.

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21
Q

What is the purpose of a Compressor Inlet Screen for turboprop/shaft engines?

A

Prevents FOD from entering and damaging the compressor.

22
Q

Which type of Turboprop/shaft engine especially requires an Inlet Screen?

A

An axial compressor engine with aluminium blades.

23
Q

What are the disadvantages of an Inlet Screen?

A
  • Can cause a loss of inlet duct pressure.
  • Can ice-up.
24
Q

What can result in more damage, a failed inlet screen or having no screen at all?

A

A failed inlet screen can cause more damage than having no screen at all.

25
Q

Why is a mechanically-rectractable inlet screen beneficial?

A

Can be withdrawn from the airstream after take-off or whenever icing conditions are encountered.

26
Q

What are the disadvantages of a mechanically-rectractable inlet screen?

A
  • prone to mechanical failure.
  • add weight to the installation.
27
Q

On what type of engine would an inlet screen not be required?

A

On turbofan engines with steel or titanium compressor (fan) blades.

Disadvantages outweigh the advantages.

28
Q

Where are ‘Bellmouth Inlets’ used?

A

Fitted to the engine inlet during testing.

29
Q

What does a Bellmouth inlet measure?

A

Intake temperature, pressure (total and static), and thrust.

30
Q

Why are Bellmouth inlets used in testing?

A

They reduce aerodynamic losses to zero, so that the most accurate data can be obtained from testing. Can produce the TSFC and Flat Rating.

31
Q

How does a turbofan engine protect its core from FOD damage?

A

The fan takes debris and throws it out and through the bypass duct area.

32
Q

What are the main problems with ice formation at the inlet?

A
  • Disturbs the airflow, reducing performance and may cause compressor stall.
  • Pieces of ice can damage the fan blades and inlet vanes.
33
Q

How can turboprops keep their inlet free of ice?

A

Turboprops use the warm oil from the engine oil reservoir to provide anti-icing, together with a minimum of additional hot air.

34
Q

At what temperature in DRY AIR can ice start to form at the inlet?

A

5 degrees C in dry air.

35
Q

At what temperature in MOIST AIR can ice start to form at the inlet?

A

7 degrees C in moist air.

36
Q

What are the two types of ice protection ‘Thermal’ system?

A
  • Bleed air.
  • Electrical heating.
37
Q

What type of engines use bleed air?

A

High-mass airflow engines.

38
Q

Where is bleed air normally ‘bled’ from?

A

HP compressor, and passed through anti-icing regulator valve.

39
Q

What parts of the engine is the bleed air supplied to?

A
  • Intake lip.
  • Spinner.
  • Surface of inlet guide vanes.
40
Q

What conditions (other than icing) do the anti-ice valves protect against?

A
  • Overpressure.
  • Engine power losses from bleeding too much air.
41
Q

How are the anti-ice valves operated?

A

Electronically controlled, pnematically operated.

42
Q

What type of valve can the anti-ice valve be described as?

A

Solenoid-controlled pressure regulating valve.

43
Q

Where does bleed air that’s used to heat the intake end-up, after its use is completed?

A

It’s ejected overboard.

44
Q

Where does bleed air that’s used to heat the spinner and IGVs end-up, after its use is completed?

A

Returns to the LP compressor intake.

45
Q

What possible indications/cautions are there for the anti-ice valve? (5)

A
  • Valve not in position selected.
  • Low duct pressure.
  • High duct pressure.
  • Low duct temperature.
  • High duct temperature.
46
Q

Which of the 5 cautions/indications causes a system ‘lockout’ and require an ON-OFF reset?

A
  • Low duct pressure.
  • High duct pressure.
  • Low duct temperature.
  • High duct temperature.

(All of them apart from Valve Position).

47
Q

What do all anti-valves have, in a failure situation?

A

A manual override.

48
Q

What do FADEC systems provide for the anti-ice valves?

A

Auto control for flow and temperature, when anti-icing is switched on or detected.

49
Q

What do turboprops/shafts normally use to anti-ice their inlets?

A

Electric-thermal heating. Cycles ON-OFF only when engine is running, to prevent the elements from burning out when there is no airflow.

50
Q

What safety factor should be observed when testing thermal anti-icing systems on the ground?

A

No personnel should be in the test area during ground tests of thermal anti-ice systems.

Resource Group Mod 15 2024 (13 decks)

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