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EASA Part 66 Module 15.2 : Engine Performance

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EASA Part 66 Module 15.2 : Engine Performance

1. 1. 15.2 : ENGINE PERFORMANCE http://part66.blogspot.com/
2. 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. 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. 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. 5. SPECIFIC FUEL CONSUMPTION• Amount of fuel required in a time to produce specific thrust output• Normallt compare during cruise condition
6. 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. 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. 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. 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
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