M15.4

Question 1

What is the function of a compressor

Answer 1

Supply a quantity of air to satisfy combustion chamber and supply bleed air. Must increase in pressure.

Question 2

What are the 2 components of a compressor

Answer 2

Rotor and stator

Question 3

What is a rotor

Answer 3

1st part, blades rotate around and suck in air to push to outlet. Increases energy

Question 4

What is a stator

Answer 4

Fixed part. Stator vanes to guide and slow airflow to cause an increased pressure.

Question 5

Compressor stage =

Answer 5

Rotor and stator

Question 6

When are stators called IGV

Answer 6

If there are stator vanes in front of a compressor stage. Fixed or moveable.

Question 7

What are stator vanes in fact duct called

Answer 7

OGV which improves airflow into fan nozzle

Question 8

2 types of compressors

Answer 8

Centrifugal and axial

Question 9

What is a centrifugal compressor

Answer 9

Consists of impeller, diffuser and manifold. Used in turboprop or shaft. High pressure rise per stage (8:1)

Question 10

The impeller can either be:

Answer 10

Single or double entry

Double has smaller diameter but operated at higher speeds

Question 11

What is the function of impeller

Answer 11

Pick up and accelerate air outwards to diffuser

Question 12

What is axial flow compressor

Answer 12

Rotating component with self oil shaped blades. Used on turbofan.

Question 13

How is the number of stages determined

Answer 13

Based on desired pressure increase

Question 14

To achieve a high compression rate….

Answer 14

A large number of stages are required

Question 15

Engines are balanced by

Answer 15

Manufacturer

Question 16

How can a rotor run free of vibration

Answer 16

If opposite fan blades create identical centrifugal forces

Question 17

Centrifugal forces depend on

Answer 17

Rotor speed, blade mass, distance of CG from axis

Question 18

Moment weight =

Answer 18

Blade mass x distance of CG from axis

Question 19

Moment weight in

Answer 19

Gram inch
Cm.g
Ounce inch

Question 20

What does blade root display

Answer 20

Part and serial number, moment weight

Question 21

How is blade 1 marked by

Answer 21

Index mark or offset hole. Usually numbered in direction of rotation

Question 22

What are balance weights

Answer 22

Used to balance difference in moment weight of old and new fan blades.

Question 23

Best method of blade change

Answer 23

Replacing blade with new one that has moment weight as close as possible

Question 24

2 reasons for stall/surge

Answer 24

Speed of engine is below designed speed, incorrect acceleration or deceleration

Question 25

Methods to prevent compressor stall/surge

Answer 25

Bleed valves, dual/triple spool rotors, variable compressor stator vanes Most use combination of 3

Question 26

Compressor bleed valves

Answer 26

Mid-afternoon section, open at low speed so excessive airflow can escape

Question 27

Dual/triple spool rotors

Answer 27

Forward part = LP / N1 Aft part = HP / N2

Question 28

Variable stator vanes

Answer 28

Most effective. Move along vertical axis. FWD stage of HP compressor

Question 29

What is the compression ratio

Answer 29

Represents ratio of volume of chamber from largest to smallest capacity. Axial has 1:3:1. Mass flow - pressure ratio - RPM

Question 30

AOA changes if

Answer 30

Velocity changes. AOA increases when Inlet velocity decreases

Question 31

Airflow separation is called

Answer 31

Compressor stall, which changes airflow to compressor which causes flow to stop, slow or reverse direction

Question 32

What is a surge

Answer 32

Severe form of compressor stall. Surge in FWD stage only affects parts of blades.

Question 33

Stall and surge caused by

Answer 33

Problems in engine operation or damaged components