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performance calculations for the Pratt & Whitney R-985-SB Wasp Jr aircraft engine
Pratt & Whitney R-985-SB Wasp Jr air-cooled 9 -cylinder radial engine 400 [hp](298.3 KW)
gear-driven supercharger, constant power to height : 1500 [m]
introduction : August 1934 country : US importance : ***
applications : Lockheed Model 10A Electra
normal rating : 400 [hp](298.3 KW) at 2200 [rpm] at 1500 [m] above sea level
no reduction, direct drive, valvetrain : 2 overhead valves, pushrod operated
fuel system : oil system :
weight engine(s) dry : 290.0 [kg] = 0.97 [kg/KW]
bore : 132.0 [mm] stroke : 132.0 [mm]
valve inlet area : 26.6 [cm^2] one inlet and one exhaust valve in cylinder head
gasspeed at inlet valve : 34.8 [m/s]
throttle : 86 /100 open, mixture :13.0 :1
compression ratio: 6.00 :1
high compression engine cannot run with full power/throttle at sea-level
(only for short period)
stroke volume (displacement): 16.140 [litre]
compression volume (Vc): 3.252 [litre]
total volume (Vt): 19.509 [litre]
diam. engine : 116 [cm]
engine length: 1.06 [m]
specific power : 18.5 [kW/litre]
torque : 1295 [Nm]
engine weight/volume : 18.0 : [kg/litre]
average piston speed (Cm): 9.7 [m/s]
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intake manifold absolute pressure (MAP) at 1500 [m] altitude Pi : 0.95 [kg/cm2]
mean engine pressure (M.E.P.) at 1500 [m] altitude Pm : 7.74 [kg/cm2]
compression pressure at 1500 [m] altitude Pc: 8.92 [kg/cm2]
estimated combustion pressure at 1500 [m] Pe : 35.64 [kg/cm2]
exhaust pressure at 1500 [m] Pu : 3.73 [kg/cm^2 ]
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compression-start temperature at 1500 [m] Tic: 343 [°K] (70 [°C])
compression-end temperature at 1500 [m] Tc: 527 [°K] (254 [°C])
average engine wall temperature at 1500 [m] : 476 [K] (202 [°C])
caloric combustion temperature at 1500 [m] Tec: 2149 [°K] (1875 [°C])
polytroph combustion temperature at 1500 [m] Tep : 2105 [°K] (1831 [°C])
estimated combustion temperature at 1500 [m] Te (T4): 2101 [°K] (1828 [°C])
polytrope expansion-end temperature at 1500 [m] Tup: 1123 [°K] (850 [°C])
exhaust stroke end temperature at 1500 [m] Tu: 1075 [°K] (801 [°C])
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calculations for take-off/emergency power at sea level
polytrope combustion temperature at sea level Tec: 2199 [°K] (1926 [°C])
caloric combustion temperature at sea level Tec: 2277 [°K] (2004 [°C])
emergency/take off rating at 2333 [rpm] at sea level : 450 [hp]
Thermal efficiency Nth : 0.361 [ ]
Mechanical efficiency Nm : 0.776 [ ]
Thermo-dynamic efficiency Ntd : 0.280 [ ]
design hours : 1529 [hr] time between overhaul : 46 [hr]
dispersed engine heat by cooling air : 5077.91 [Kcal/minuut/m2]
required cooling surface : 13.89 [m2]
weight cooling ribs : 42.46 [kg]
fuel consumption optimum mixture at 2200.00 [rpm] at 1500 [m]: 68.70 [kg/hr]
specific fuel consumption thermo-dynamic : 215 [gr/epk] = 288 [gr/kwh]
estimated specific fuel consumption (cruise power) at 1500 [m] : 305 [gr/kwh]
estimated sfc (cruise power) at 3240 [m] rich mixture : 308 [gr/kwh]
specific fuel consumption at 1500 [m] at 2200 [rpm] with mixture :13.0 :1 : 299 [gr/kwh]
estimated specific oil consumption (cruise power) : 16 [gr/kwh]
Literature :
Wikipedia
DISCLAIMER Above calculations are based on published data, they must be
regarded as indication not as facts.
Calculated performance and weight may not correspond with actual weights
and performances and are assumptions for which no responsibility can be taken.
Calculations are as accurate as possible, they can be fine-tuned when more data
is available, you are welcome to give suggestions and additional information
so we can improve our program. For copyright on drawings/photographs/
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(c) B van der Zalm 22 October 2021 contact : info.aircraftinvestigation@gmail.com python 3.7.4