The Gas Turbine Engine

Question 1

The brayton cycle

Answer 1

Compression
Combustion
Expansion
Exhaust

Question 2

The compressor

Answer 2

Air pressure steadily increases

Entire unit is contained within a divergent duct

Question 3

Why the compressor contained within a divergent duct

Answer 3

Maintain constant axial velocity whilst pressure increases

Question 4

Diffuser

Answer 4

Divergent duct between the compressor and the combustion section

Highest pressure occurs here

Question 5

Combustion section

Answer 5

Continuous combustion at constant temp - highest gas temp occurs here

The exit from the combustion section is a convergent duct - gas velocity increases as it exits the combustion chamber and enters the nozzle guide vanes

Question 6

Flat rated

Answer 6

Below ISA + 15 = thrust limited

Above = temp limited

Power curve is flat

Question 7

Specific fuel consumption

Answer 7

Ratio of fuel mass consumed to produce a unit of thrust per unit of time

Lower the SFC = the better

Question 8

What engines have the lowest SFC

Answer 8

Engines with the higher pressure ratios

Question 9

Propulsive efficiency

Answer 9

Efficiency with which kinetic energy is translated into propulsive force

Low speeds - high velocity exhaust wastes more energy than slow slipstream of a prop
Prop systems are more efficient at low speeds

Question 10

When does ram effect start to take force

Answer 10

Mach .3

Question 11

Effect of thrust above the tropopause

Answer 11

Trust will reduce quicker due to the temp remaining constant - temp will not be able to offset the reduction in density with altitude

Question 12

Effect of bleed air on thrust

Answer 12

Reduces mass flow and reduces thrust

Question 13

Some engines can provide ?% efficiency

Answer 13

80-90%

Question 14

Single spool axial flow turbo jet

Answer 14

Only efficient at high speed

Small frontal area

Inefficient and nosey

Question 15

Spool

Answer 15

Assembly consisting of a compressor and turbine linked by a shaft

Question 16

Axial flow

Answer 16

Passage of air through the turbine parallel to the axis of rotation

Question 17

Twin spool low bypass

Answer 17

Improves efficiency

Same air bypasses the inner core - given only a small acceleration by the LP compressor

LP compressor works most efficiently at low rpm

Question 18

Advantages of bypass engine

Answer 18

Bypass air is cold - more thermally efficient

Small core section

Bypass air is given a smaller acceleration - greater propulsion efficiency

Question 19

Twin spool low bypass - bypass ratio

Answer 19

0.8 - 1

= 1 bucket of air though the compressor while 0.8 is accelerated around the outside

Question 20

Twin spool high bypass

Answer 20

Very efficient - 70% of thrust is created from the bypass

Accelerate a much larger proportion and overall mass of air through the bypass duct

Question 21

Twin spool high bypass - bypass ratio

Answer 21

5:1 - 70% N1 70% of thrust is created from the bypass

Question 22

Three shaft high bypass ratio

Answer 22

9.3:1

Question 23

High bypass multiple spool

Answer 23

Each spool rotates at a diff speed

Indicators separately display the speed of the fan

Question 24

Reduction gearbox - turboprop

Answer 24

Reduces the RPM of the engine for the prop via sun and planet gear train

Turbine needs to run quickly - prop needs to run slowly

Question 25

Functions of the air intake

Answer 25

Min drag

Supply or turbulent free air, evenly distributed to the face of the compressor

Question 26

Subsonic pitot intake

Answer 26

Presents air at 0.5mach

Max ram effect - Minimise the loss of ram with alt

Question 27

Strong x wind at t/o can cause

Answer 27

Inlet instability and surge

Question 28

Possible effects of low airspeed and a high pressure setting

Answer 28

Air entering may app mach 1 - inlet can get chocked

Question 29

Effects on the inlet above mach .85

Answer 29

Shockwaves may form

Excess air spills over the lip

Question 30

Effects of inlet icing

Answer 30

Disrupt the laminar flow into the engine

Can starve the engine - cause a flame out

Can damage blades if it breaks away

Lip is heated with bleed air