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performance calculations for the Maybach IVa WWI aero engine
Maybach IVa liquid-cooled 6 -cylinder inline engine 245 [hp](182.7 KW)
German engine rating : 248.4 [PS]
introduction : November 1917 country : Germany importance : ***
applications : Rumpler C.VII, Hansa-Brandenburg W.19
max. continuous(take-off) rating : 245 [hp](182.7 KW) at 1400 [rpm] at 1800 [m] above
sea level
high compression engine : cannot run at full power at sea level,
constant power to height : 1800 [m]
no reduction, direct drive, valvetrain : OHV
General information :
Like all engines of that time, the previous Maybach design, the Mb IV, lost at high altitude as much as half of the nominal power of 240 horsepower. The new Maybach Mb IVa of 1916 was the first engine designed to overcome this limitation.[1] It did not use a supercharger, but a much more primitive solution. The engine had purposely "oversized" cylinders, and a significantly higher 6.08:1 compression ratio. It was tested on Wendelstein (mountain) at an altitude of 1800 m and rated there at 245 hp. This would theoretically correspond to rating of about 300 hp at sea level; however, the engine was not designed to withstand such power - it needed to be carefully throttled down at low altitude, so it would not exceed the safe level of 245 hp. It had three carburettor settings, to be changed during the flight depending on the altitude.
The engine was falsely given a rating of 260 hp (190 kW) at sea level, so it would not appear inferior to the engines it replaced.
fuel system : oil system :
weight engine(s) dry : 400.0 [kg] = 2.19 [kg/KW]
bore : 165.0 [mm] stroke : 180.0 [mm]
Mechanical efficiency/mean pressure correction factor : 0.659 [ ]
valve inlet area : 49.9 [cm^2] two inlet and two exhaust valves in cylinder head
gasspeed at inlet valve : 25.3 [m/s]
invloed hoogte > cm : 0.15 [ ]
lean mixture
throttle : 99 /100 open, mixture :13.0 :1
compression ratio: 6.08 :1
calculated compression ratio : 6.08 : 1
high compression engine cannot run with full power/throttle at sea-level (only for short period)
published volume (displacement): 23.100 [litre]
calculated stroke volume (Vs) : 23.093 [litre]
compression volume (Vc): 4.546 [litre]
total volume (Vt): 27.639 [litre]
hoogte motor : 108 [cm]
power / stroke volume (litervermogen Nl): 7.9 [kW/litre]
torque : 1246 [Nm]
engine weight/volume : 17.3 : [kg/litre]
average piston speed (Cm): 8.4 [m/s]
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intake pressure at 1800 [m] altitude Pi : 0.84 [kg/cm2]
mean engine pressure (M.E.P.) at 1800 [m] altitude Pm : 6.27 [kg/cm2]
compression pressure at 1800 [m] altitude Pc: 8.00 [kg/cm2]
estimated combustion pressure at 1800 [m] Pe : 32.01 [kg/cm2]
exhaust pressure at 1800 [m] Pu : 3.29 [kg/cm^2 ]
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compression-start temperature at 1800 [m] Tic: 377 [°K] (104 [°C])
compression-end temperature at 1800 [m] Tc: 575 [°K] (302 [°C])
caloric combustion temperature at 1800 [m] Tec: 2344 [°K] (2071 [°C])
polytroph combustion temperature at 1800 [m] Tep : 2299 [°K] (2026 [°C])
estimated combustion temperature at 1800 [m] Te (T4): 2286 [°K] (2013 [°C])
polytrope exhaust temperature at 1800 [m] Tup: 1430 [°K] (1157 [°C])
exhaust end temperature at 1800 [m] Tu: 1277 [°K] (1004 [°C])
*********************************************************************************
calculations for take-off/emergency power at sea level
intake pressure at sea level Pi : 0.98 [kg/cm2]
rich mixture 11 : 1 applied for cooling > carburettor adjustable in flight by the pilot
compression pressure (TO power) at sea level Pc: 9.04 [kg/cm2]
estimated combustion pressure at sealevel Pe : 27.19 [kg/cm^2 ]
compression-start temperature at sealevel max rpm Tic:466 [°K] (193 [°C])
compression-end temperature at sealevel max rpm Tc:697 [°K] (424 [°C])
caloric combustion temperature at 1800 [m] Tec: 2233 [°K] (1959 [°C])
mean engine pressure at sealevel max rpm Pm : 7.09 [kg/cm2]
emergency/take off rating at 1414 [rpm] at sea level : 280 [hp]
bruto emergency/take off rating at 1414 [rpm] at sea level : 285 [hp]
Thermal efficiency Nth : 0.363 [ ]
Mechanical efficiency Nm : 0.742 [ ]
Thermo-dynamic efficiency Ntd : 0.269 [ ]
design hours : 808 time between overhaul : 63
fuel consumption optimum mixture at 1400.00 [rpm] at 1800 [m]: 55.81 [kg/hr]
specific fuel consumption thermo-dynamic : 223 [gr/epk] = 299 [gr/kwh]
estimated specific fuel consumption (cruise power) at 1800 [m] optimum mixture : 302 [gr/kwh]
estimated sfc (cruise power) at 2250 [m] rich mixture : 303 [gr/kwh]
specific fuel consumption at 1800 [m] at 1400 [rpm] with mixture :13.0 :1 : 305 [gr/kwh]
estimated specific oil consumption (cruise power) : 21 [gr/kwh]
Literature :
Smitsonian National air and space museum
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 31 May 2020 contact : info.aircraftinvestigation@gmail.com python 3.7.4