CAP 11 GAS TURBINE PRINCIPLE

Question 1

Thrust formula

Answer 1

Thrust= mass x velocity

Question 2

Jet thrust

Answer 2

T= m(Vj-Vv) + A (Pj-P0)
T=thrust
M=mass air flow
Vj=velocity of exhaust
Vv= true air speed
A=cross sectional area of exhaust
Pj=jet efflux static pressure
P0= ambient pressure at station 0 air inlet

Question 3

Gross thrust

Answer 3

Is produced when the engine is not moving through the air and presents the greates thrust value
Once TAS increases,thrust decreases
Fg=(Wa(Vo-Vi))/g

Wa= mass flow of air in ft/sec
Vo=exit velocity of air in ft/sec
Vi=inlet velocity of air in ft/sec
G=gravitational force,32.2 ft/sec

Is SI (kg/sec and metres/sec) units are given,conversion is already factored and do not divide by g

Question 4

Net thrust

Answer 4

Allows the calculation to be adapted to show the thrust reduction as airspeed increases
Fn=(Wa(V0-Vi))/g

Vo =exhaust outlet velocity ft/sec
Vi= tas in ft/sec

Question 5

Fan engine trust

Answer 5

~as engine is producing thrust in two ways the formula needs to be applied to be applied for both core and by pass streams and then added togheter
In which case mass flow and velocity would be given at each section

Thrust Fan = (Wa(Vo-Vi))/g

Thrust core= (Wa(Vo-Vi))/g

Total= Fan + core

Question 6

Simple thrust calculation
Pressure thrust(Pf)

Answer 6

Pressure thrust can be considered when the exhaust nozzle become chocked.
Under high thrust conditions the gas velocity reaches the speed of sound and cannot be accelerated further
This causes nozzles pressure to increase above atmospheric this pressure difference across the nozzle produces pressure thrust
Pressure thrust is produced in addition to momentum thrust and most turbojet engines operate a chocked nozzle in hogh power conditions

Pf =(P -Po)x A

P= enigne pressure
Po =ambient pressure

Question 7

Equivalent shaft hosepower

Answer 7

Shaft horse power of the propeller + the jet exhaust power of the turbine after had propelled the propeller

ESHP=SHP + HP (from any jet thrust)

Question 8

Gas turbine enigne

Answer 8

turbine engine is considered a constant pressure engine

Stages :intake,compression,combustion,exhaust

Modules:
~intake
~compressor
~combuster
~turbine
~exhaust

Question 9

THRUST VS TAS

Answer 9

Thrust VS TAS
Thrust lost due to momentum drag
Thrust gained due to ram effect

Overall thrust variation with speed is (a shallow line)

Question 10

FACTORS AFFECTIN THRUST

Answer 10

~ ALTITUDE
~SPEED > above M 0.4
~AMBIENT TEMPERATURE

Question 11

FLAT RTED TEMP

Answer 11

IS THE REDUCTION OF THE THRUST POWER AVAILBLE DUE TO ISA TEMP DEVIATION

Question 12

FACTORS AFFECTING THRUST

Answer 12

~ENGINE BLEED
~INTAKE HEATING

MAX THRUST IS PRODUCED WHE NA/C IS STATIONARY ON THE GROUND (static thrust) because:
~the difffernce between V jet and Vflight is at its greates
~the air is most dense

Question 13

Thermal efficiency

Answer 13

~a long trail of hot exhaust gas left in the wake represents thermal inefficiency
~gas turbine engines are about 30% thermally efficient
~a gas turbines thermal efficiency is primary based the ratio of compression within the compressor

Modern engines can as high as 50% thermally efficient
(Compression rate 30 :1)

Question 14

Propulsive efficiency

Answer 14

~is the efficient with which kinetic energy is translated into propulsive force
~at low speed the high velocity exhaust wastes moe energy than the slow slipstream from the propeller.so prop are more efficient at low speed
~at higher speeds exhaust gas velocity is much reduced relative to the air flow speed
~some engines propulsive efficent up to 80-90%

Question 15

Engine pressure ration

Answer 15

Compares intake pressure to exhaust outlet pressure FADEC can determine the thrust produced by an engine.many operators find this method favoureable than N1 POWER SETTING
FADEC MAY BE CONFIGURED TO USE EOTHER N! OR EPR AS A THRUST SETTINGS METHOD