15.4

Question 1

Primary function of a compressor

Answer 1

Supply right amount of air combustion chamber needs at the right pressure

Question 2

Secondary function of compressor

Answer 2

Supply air to systems that need bleed air

Question 3

Where are bleed ports located

Answer 3

Depends on pressure or temperature of the system required

Question 4

What is a compressor stage

Answer 4

Combination of rotor and stator

Question 5

What is the first part of the compressor stage

Answer 5

Rotor

Question 6

What does a rotor do

Answer 6

Such in air and push it to the outlet side of the rotor which increases energy of the airflow

Question 7

What does a stator do

Answer 7

Guide of slow airflow to cause an increase in pressure

Question 8

What are stator blades called

Answer 8

Stator vanes

Question 9

What are stator vanes at the front of the compressor stage

Answer 9

Inlet guide vanes that improve airflow into the first compressor stage

Question 10

What are the stator vanes in the fan duct called

Answer 10

Outlet guide vanes that improve airflow into fan nozzle

Question 11

What 3 parts does a compressor have

Answer 11

Impeller (rotor)

Diffuser(stator)

Compressor manifold

Question 12

What is the high pressure rise per stage in a centrifugal compressor

Answer 12

8:1

Question 13

What is a centrifugal impeller made of and why is it smoothed

Answer 13

Forged alluminum alloy

Smoothed for minimum flow restriction and turbulence

Question 14

Which impeller entry is more complicated

Answer 14

Double - entry

Question 15

Where are axial flow compressors found

Answer 15

Turbofan engines

Question 16

Where are centrifugal compressors found

Answer 16

Turboprop and turbo shaft engines

Question 17

In an axial flow compressor why does the diameter of the rotating drum gradually decrease

Answer 17

Maintain steady axial velocity as pressure and density of the air increases

Question 18

What does a multi spool compressor consist of

Answer 18

Two or three drums of rotors

Each drum is driven by a separate turbine

Question 19

Why is the compression ratio small

Answer 19

Amount of deflection and degree of deflection is low to minimise loss due to flow separation and stall

Question 20

Why don’t we always add large number of stages to get a high compression rate

Answer 20

Optimising design to be most efficient becomes difficult

Question 21

When do rotors run free of vibration

Answer 21

When Fan blades are opposite each other create identical centrifugal forces

Question 22

What 3 parameters does fan blades depend on

Answer 22

Rotor speed

Blade mass

Distance of CoG of fan blade from rotational axis

Question 23

What is the moment weight

Answer 23

Product of Blade mass and Distance of CoG of fan blade from rotational axis

Question 24

Where is moment weight displayed

Answer 24

At the blade root

Question 25

What is moment weight given in

Answer 25

Gram inches Cm.g Ounce inches

Question 26

What numbers are at the blade root

Answer 26

Part number Serial number Moment weight

Question 27

What is the entire assembly of diffuser and manifold referred to as

Answer 27

Diffuser

Question 28

What is the best method to replace a blade

Answer 28

With a new one with as close moment weight as the old one

Question 29

What are balance weighs used for

Answer 29

When a new blades moment weight larger then specified from the manufacturer

Question 30

Where are balance weights installed

Answer 30

Fan disc or spinner cone

Question 31

What’s the second method of changing fan blades

Answer 31

Change a pair with similar moment weights (The pair would be the damaged blade and the blade opposite it)

Question 32

How do we achieve smooth airflow

Answer 32

Having the correct relationship between inlet velocity and rotor speed

Question 33

What angle of attack do we need to ensure smooth airflow

Answer 33

AoA to the rotor blades is small

Question 34

What makes the AoA increase

Answer 34

Inlet air velocity decreases

Question 35

What is compressor stall

Answer 35

Airflow separation which causes air to slow down, stop or reverse direction

Question 36

What is compressor surge

Answer 36

Severe form of compressor stall

Question 37

Where stages can compressor surge occur

Answer 37

Forward and aft stages

Question 38

How is compressor stall and surge caused

Answer 38

Problems in engine operations or damaged engine components

Question 39

How can we achieve a high compression rate

Answer 39

Large number of stages

Question 40

3 methods to prevent stall and surge

Answer 40

Bleed valves Dual or triple spool rotors Variable compressor stator vanes

Question 41

Where are bleed valves found

Answer 41

Mid section or aft section of engine

Question 42

What do bleed valves do

Answer 42

Open at low engine speeds so excessive airflow can escape overboard

Question 43

What is n1 and n2

Answer 43

N1 - low pressure compressor N2 - high pressure compressor (aft) (Both driven by separate turbine)

Question 44

What’s the most effective method of preventing Stall

Answer 44

Variable stator vanes in the compressor

Question 45

Where are the variable inlet guide vanes and stator vanes found

Answer 45

Fwd stages of high pressure compressor

Question 46

Advantage of variable stator vanes

Answer 46

Optimum AoA on rotor blades for every engine speed

Question 47

Disadvantage of variable stator vanes

Answer 47

Very complicated control mechanism

Question 48

What is compression ratio

Answer 48

Volume of its combustion chamber for largest to smallest capacity

Question 49

Axial flow compressor pressure ratio

Answer 49

1:3:1

Question 50

How are fan blades numbered

Answer 50

Often in direction of rotation

Question 51

Stages in a centrifugal compressor limited to

Answer 51

2 stages

Question 52

What’s a disadvantage of centrifugal flow

Answer 52

Lots of twists and turns

Question 53

What’s the sequence of turbines and compressors in a triple spool engine

Answer 53

LPC - IPC - HPC ~> HPT - IPT - LPT