15.03 Inlets

Question 1

Definition of Total Head pressure

Answer 1

Pressure of the air when brought to rest in front of the wings and intakes.

Question 2

Definition of recovery

Answer 2

To regain as much of the ram air velocity as possible, and convert it into pressure at the face of the engine.

Question 3

Definition of intake momentum drag

Answer 3

As forward speed increases, thrust decreases. Momentum of the air passing into the engine in relation to the forward speed of the aircraft.

Question 4

Definition of ram ratio

Answer 4

Ratio of total pressure at the inlet to the compressor, to the static pressure at the entrance to the air intake.

Question 5

What two parts make up the air intake?

Answer 5

The intake nose and inlet duct.

Question 6

What is an inlet duct that gets wider, known as?

Answer 6

Divergent.

Question 7

What is the job of the intake nose?

Answer 7

Smooth the airflow to prevent disturbances.

Question 8

What should air intakes be (in general) ?

Answer 8

• As straight as possible.
• As smooth as possible.
• Designed to decelerate the airflow.

Question 9

What does the inlet duct convert in-flight?

Answer 9

Kinetic energy of the air stream into pressure energy.

Question 10

What is the most efficient inlet type for subsonic aircraft?

Answer 10

The pitot type quasi-circular diffuser. 😂

Question 11

How is the inlet lip designed to reduce the risk of flow separation?

Answer 11

It’s well-rounded, has a thicker radius and thin lips for high speed flight.

Question 12

What is nose suction?

Answer 12

A suction effect from a drop in pressure in front of the inlet, acting in the direction of engine thrust.

Question 13

What is the ‘super-critical condition’ in supersonic inlets?

Answer 13

Where airflow demand is greater than the inlet can provide, resulting in shockwaves and turbulence that affect the flow into the compressor.

Question 14

What are the five types of intake loss?

Answer 14

1. Frictional losses due to skin friction.
2. Frictional losses at the intake duct walls.
3. Turbulence losses due to structures in the intake.
4. Turboprop drag and turbulence from the spinner and blade roots.
5. Divided intake suffers losses due to boundary layer problems, and loss of ram pressure on one side when yawing.

Question 15

What are the efficiency percentages of the different intake designs?

Answer 15

• Pitot, 96-99% efficient.
• Wing root, 87-95% efficient.
• Side, 80-89% efficient.
• Turbo Prop annular, 74-82% efficient.

Question 16

How does a ‘normal shockwave inlet’ function?

Answer 16

Employs a single normal shockwave at the front of the inlet to slow the air to subsonic velocity.
Not suitable for higher speed supersonic flight.

Question 17

How does an oblique shockwave inlet function?

Answer 17

This design employs an external oblique shock wave to slow the supersonic airflow before the normal shock occurs.

Question 18

How does a variable supersonic inlet function?

Answer 18

Equipped with actuated panels that change angle based on Mach number. Usually, higher Mach number means more closure of the intake.

Question 19

What are the two negative effects of ice on engine intakes?

Answer 19

• Disturbed airflow that can affect performance and cause compressor stall.
• Physical damage.

Question 20

What do engines have to prevent ice buildup?

Answer 20

A thermal anti ice system on each engine.

Question 21

What are the requirements of the anti ice system? (4)

Answer 21

• Reliable
• No weight penalty
• No loss of power
• Ease of maintenance.

Question 22

What are the two types of heating system for the INTAKE?

Answer 22

Bleed air and electrical heating.

Question 23

What are the two types of spinner ice protection?

Answer 23

Hot oil and rubber spike.

Question 24

Where is bleed air bled from?

Answer 24

The HP compressor.

Question 25

How does the bleed air de-ice the engine?

Answer 25

The hot air sprays through small holes from the anti ice duct and enters the engine cowling.

Question 26

What are the two types of electrical anti ice system?

Answer 26

Continuously heated elements and intermittently heated elements.

Question 27

What is the typical ice protection cyclic sequence?

Answer 27

• Fast, ON/OFF 2 minutes, between -6°C and 10°C.

- Slow, ON/OFF 6 minutes, below -6°C.

Question 28

When must functional tests of anti icing systems be carried out?

Answer 28

• Periods specified in the approved maintenance schedules.
• When a system malfunction occurs.
• When a new or overhauled heater mats has been installed.
• After replacement of a component (e.g. a cyclic timer or heater element).
• After repairs to a heater mat.