Basic Gas Turbine

Question 1

What is Charle’s Law?

Answer 1

At constant pressure, the volume of a given mass of gas is directionally proportional to its absolute temperature. V/T=’k’

Question 2

Gay-Lussac’s Law

Answer 2

At constant volume, the pressure of a given mass of gas is directly proportional to its absolute temperature. P/T=’k’

Question 3

What is/causes wet start?

Answer 3

If engine fails to start after fuel has been introduced, a wet start has occurred. Usually a problem with the igniters. Indications are the failure of gas temperature to rise and the rpm stabilising at starter limit.

Question 4

What is bypass air and the benefits?

Answer 4

Bypass air is a secondary airflow around the combustion chamber, which generates increased thrust, cools the engine, and aids in exhaust noise suppression, which provides lower fuel consumption.

Question 5

What is bypass ratio?

Answer 5

Ratio of mass flow rate around the engine core with the mass flow rate through the engine core.

Question 6

What is Boyle’s Law?

Answer 6

At constant temperature, the pressure and the volume of a gas are inversely proportional. PV=’k’

Question 7

How to clear a compressor stall/surge

Answer 7

Should clear themselves but if it continues, reduce thrust setting; may be assisted by lowering nose to increase airspeed

Question 8

What is Avogadro’s Law?

Answer 8

Equal volumes of ideal or perfect gases, at the same temperature and pressure, contain the same number of particles or molecules.
V/n = k

Question 9

What is bleed air?

Answer 9

Bleed air is compressed air taken from the engine and used to run systems such as pressurisation and climate control of the cabin.

Question 10

What are the components of axial flow compressors?

Answer 10

Rotors; Stators (or vanes) (each pair is called a stage)

Question 11

What is the ideal gas Law?

Answer 11

In the ideal state of any gas, a given number of its particles occupy the same volume, and that volume changes are inverse to pressure changes and linear to temperature changes.

PV=nRT

Question 12

What is N2

Answer 12

N2 represents the rotational speed of the high pressure compressor and is presented on the indicator as a percentage of design RPM

Question 13

Levers on a turbo prop throttle quadrant:

Answer 13

Power Lever (Sets NG); 
Prop Lever (Sets RPM); 
Condition Lever (ON/OFF valve for delivering fuel - OFF/LOW IDLE/HIGH IDLE)

Question 14

What are the advantages and disadvantages of Axial Flow Compressors?

Answer 14

Provides high compression ratios so suitable for turbo fan engines; allows relatively smaller frontal area meaning less drag; Are sensitive to FOD damage and to ice and bird ingestion.

Question 15

What are some advantages of free turbine turbo props?

Answer 15

Easier starting as started doesn’t need to rotate reduction gearbox, only the compressor; Once started, the gas generator shaft and prop shaft can rotate at their optimum speeds, independent of each other. (Is generally used with reverse flow turbine engines so it’ll have advantages associated with those also).

Question 16

What is the Combined Gas Law?

Answer 16

The ratio between the pressure-volume product and the temperature of a system remains constant. PV/T=’k’

Question 17

What are the advantages and disadvantages of centrifugal compressors?

Answer 17

The impellers are simpler and easier to manufacture, therefore cheaper. More robust and resistant to damage caused by ingestion of FOD, ice or birds. Not suitable for high thrust output turbine engines.

Question 18

What are some advantages of a reverse flow turbine engine?

Answer 18

Shorter/more compact engine; easy to add intake screens/inertial separators to minimise FOD/ice ingestion; Generally allows use of free turbine.

Question 19

What is/causes a hung (false) start?

Answer 19

Where engine rpm doesn’t increase at the normal rate and/or stops increasing at less then idle rpm. Generally due to starter malfunction such as cutting out too early.
(A hung start is when light off occurs and the engine stabilises or “hangs” below starter cutoff speed usually at a higher than normal temperature. It is caused by insufficient airflow due to high altitude or high temperatures with insufficient compression)

Question 20

What should be done in the event of a wet start?

Answer 20

Fuel should be shut off to the engine and engine should be dry motored to purge and blow out any fuel remaining in combustion chamber.

Question 21

What is the specific gravity of AVTUR?

Answer 21

0.8 at +15°C (Specific gravity of AVTUR decreases with an increase in temperature)

Question 22

Fundamentals of starting a turbine engine on the ground:

Answer 22

The engine core is rotated, with a starter motor, until a specified RPM is reached; igniters are activated and fuel is supplied at the appropriate time.

Question 23

Symptoms of compressor stalls:

Answer 23

Engine popping or banging noise; Rapidly rising turbine temperature; Fluctuating engine rpm; Fluctuating fuel flow; reduction in engine thrust

Question 24

Why does a turboprop have a torque gauge?

Answer 24

Engine torque is proportional to the horsepower developed and transmitted through the shaft to the propeller gearbox. It measures the output of the power shaft.

Question 25

What are Stator Vanes?

Answer 25

Stator Vanes diffuse the air, raises its static pressure and directs it to the next stage of compression.
Also, helps guide the incoming air into the rotor blades at an appropriate angle to decrease chance of compressor stall. (Converts kinetic energy to pressure energy)

Question 26

What is NG?

Answer 26

Used in a turboprop, is the rpm of the gas producer (compressor) spool.

Question 27

How to remedy a hot start:

Answer 27

When abnormally fast temperature rise is noted, fuel supply must be cut off immediately. Then carry out motoring cycle (dry motored) until the turbine gas temperature has been reduced to acceptable level.

Question 28

What is NP?

Answer 28

Used in a turboprop, is the rpm of the power (free turbine) spool.

Question 29

What should be done if a hung start has occurred?

Answer 29

Engine should be shut down and dry motored to reduce turbine temperature and to clear unburnt fuel out of combustion chamber.

Question 30

What are the components of a centrifugal compressor?

Answer 30

Impeller (rotor); Diffuser; Compressor manifold

Question 31

FADEC stands for:

Answer 31

Full authority digital engine control

Question 32

What’s the difference between centrifugal flow compressor and axial flow compressor?

Answer 32

The centrifugal flow compressor takes the air and slings it to the outside in a divergent chamber called a diffuser, where the air is slowed in velocity and increasing the air pressure before reaching the combustion chamber.
An axial flow compressor the air is kept parallel to the longitudinal axis of the engine which is made of an alternating series of rotating blades and stationary stator vanes

Question 33

Freezing point of AVTUR

Answer 33

-47°C

Question 34

What are the core sections of a turbine engine?

Answer 34

Air inlet/intake;
Compressor and diffuser;
Combustion chamber;
Turbine;
Exhaust

Question 35

What is/causes a hot start?

Answer 35

Where during start, internal gas temperature rises high enough to damage engine. Could be caused by lag in rpm acceleration or restriction in the airflow or both causing too much fuel for available airflow. RPM lag could be caused by early cut out of starter, light up occurring at too low an RPM. Airflow restriction can be caused by strong tailwind.

Question 36

What is N1?

Answer 36

RPM of the low pressure compressor or fan. (N1 represents the rotational speed of the low pressure compressor, represented by a percentage of RPM on the gauge. The compressor is connected to the N1 turbine wheel through a concentric shaft. N1 is considered to be the primary thrust setting on most jets.)

Question 37

What is EPR?

Answer 37

Engine pressure ratio is the ratio of exhaust gas pressure to compressor intake/inlet pressure.