This document discusses various aspects of engine performance including: - Thrust is generated through momentum thrust, net thrust accounts for momentum drag, and choked nozzles add pressure thrust. - Thrust distribution varies across engine sections and can be calculated based on exit area, pressure, velocity and mass flow. - Horsepower calculations relate thrust to aircraft speed or shaft power for different engine types. - Specific fuel consumption measures the fuel required to produce thrust during cruise conditions.

1. 15.2 : ENGINE PERFORMANCE
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2. THRUST
• Gross Thrust = Total thrust = Momentum Thrust by engine(F=ma)
• Net Thrust = Gross thrust – momentum drag(flying speed)
= mv2 – mv1
• Chocked Nozzle Thrust = Pressure thrust(venturi)
= P2 – P1(area nozle)
• Resultant Thrust = Net Thrust
= Mom thrust + Mom drag + Prss thrust

3. THRUST DISTRIBUTION
• Distribution of thrust vary in every section of
engine.
• It can be calculated base on exit duct area(A), exit
presssure(P), exit air velocity(v) and air mass
flow(w)
• Thrust Load(sect2) = ((AxP) + WV/g) – thrust
load(sect1)
• Value is (+ve) for convergence exit and (-ve) for
divergence exit
• Resultance thrust is sum of all trust load in every
section.

4. HORSE POWER
• 1HP = 746watt
• Thrust Horse Power(jet engine):
THP = Thrust(Ib) x Aircraft speed(ft/s)
550ft/s
• Actual horsepower engine-propeller unit found
less compare to jet engine
• Equivalent Shaft Horse Power(turboshaft engine):
ESHP = SHP + (jet thrust ÷ 2.5)

5. SPECIFIC FUEL CONSUMPTION
• Amount of fuel required in a time to produce
specific thrust output
• Normallt compare during cruise condition

6. ENGINE EFFICIENCIES
• Thermal efficiencies : KE ÷ Fuel Energy
Ratio of convertion of heat energy to kinetic
energy (thrust)
• Propulsive efficiencies : _________Work done____________
Work done + Work wasted in exhaust
Ratio of convertion of kinetic energy(thurst) to
do the work(pushing aircraft)
• Overall efficiency : TE + PE

7. RATIO
• By-pass ratio is a ratio mass of air bypasses
engine core and air passing through the
engine core.
• Engine pressure ratio is ratio between Turbine
exit pressure to the engine intake pressure
By-pass air
EPR = P(intake)
P(exhaust)
P(exhaust)
P(intake)

8. PERFORMANCE GRAPH
Velocity
Pressure
Temperature
Peak velocity at begining of turbine inlet
Peak pressure at the end of compressor section
Peak temp at begining of combustion chamber

9. FACTOR EFFECTING THRUST
• Temperature :
Thrust increase with decreasing in temperature (air density
increase at low temp)
• Air Pressure :
Thrust increase with increasing air pressure
(air density increase by pressure)
• Altitude :
Thrust decrease with increase in altitude
(change rate after 36kft = temp constant)
• Airspeed :
Thrust decrease initially then increase back due to ram air
effect on jet engine