easa part 66 module 15.2 : engine performance
Post on 20-Jan-2015
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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
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.
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)
SPECIFIC FUEL CONSUMPTION
• Amount of fuel required in a time to produce specific thrust output
• Normallt compare during cruise condition
ENGINE EFFICIENCIES
• Thermal efficiencies : KE ÷ Fuel EnergyRatio of convertion of heat energy to kinetic energy (thrust)
• Propulsive efficiencies :Ratio of convertion of kinetic energy(thurst) to do the work(pushing aircraft)
• Overall efficiency : TE + PE
_________Work done____________Work done + Work wasted in exhaust
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
P(intake)P(exhaust)
EPR = P(intake) P(exhaust)
PERFORMANCE GRAPH
Velocity
PressureTemperature
Peak temp at begining of combustion chamberPeak pressure at the end of compressor sectionPeak velocity at begining of turbine inlet
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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