15.3 - Inlet

Question 1

State the purpose of an engine air inlet.

Answer 1

The purpose of an engine air inlet is to provide a uniform and steady airflow to the compressor, avoiding compressor stall and excessive internal engine temperature at the turbine.

Question 2

Define Ram Ratio.

Answer 2

Ram ratio = Compression inlet pressure / ambient pressure

It is the pressure rise in the intake due to ram effect.

Question 3

What are the two main groups of air inlets?

Answer 3

1. Those that maintain optimum airflow condition up to high Subsonic speeds
2. The second group have to fulfil the requirements of the first group but in addition have to operate efficiently at aircraft speeds exceeding Mach 1

Question 4

What happens pressure and velocity of the air in a subsonic air inlet?

Answer 4

Velocity decreases (increase in pressure) – divergent flow

pic shows pitot intake which is most common on wing mounted and tail mounted engines

Question 5

What type of intake is a variable geometry intake and explain briefly how it works?

Answer 5

It is a supersonic type of intake

This supersonic intake is only efficient at sonic and low supersonic speeds. As aircraft speed increases further causing Mach number and Ram ratio to also increase, a variable throat area along with spill valves are necessary to cope with the changing volume and weight of the air.

Question 6

Where is a bellmouth type intake used?

Answer 6

Helicopters (Ram Recovery / Ram Ratio insignificant)

Question 7

Name 3 types of subsonic air inlet.

Answer 7

1. Pitot
2. S-duct
3. Bellmouth

Question 8

Define ram ratio

Answer 8

The pressure rise in the intake due to ram effect is known as the Ram Ratio.

Ram Ratio = Compression inlet pressure / Ambient pressure

Question 9

What is Ram Recovery?

Answer 9

Recover as much of the total pressure of the free airstream as possible and deliver this pressure to the face of the engine compressor with the minimum loss.

(Ram recovery = total pressure recovery)

Question 10

Where is a pitot intake used?

Answer 10

Wing or aft mounted engines

Question 11

Which type of duct is best for a supersonic engine?

Answer 11

Convergent-Divergent intake

Variable geometry intake

Moveable wedge intake

Question 12

Where is a bellmouth intake used?

Answer 12

Helicopters

Question 13

What is a bifurcated duct (what is it used on)?

Answer 13

type of intake

used for transonic military aircraft

Question 14

Where is nose cowl anti-icing heat normally taken from (how is it controlled)?

Answer 14

It is normally taken from compressor bleed air

It is controlled from the cockpit electronically by opening and closing a valve