The Mercedes D.IVa was a German six-cylinder, water-cooled, inline engine developed in 1917 for use in aircraft and built by Daimler Motoren Gesellschaft (DMG).^[1]

The D.IVa replaced the failed Mercedes D.IV inline eight-cylinder engine. The D.IVa was primarily used to power bombers and large reconnaissance aircraft. Unlike most German designs, the D.IVa was relatively advanced, including four valves per cylinder actuated by a SOHC valvetrain, the same "single-camshaft" arrangement that had also been used on the earlier two-valve per cylinder D.I through D.IIIa powerplants.

Designed specifically to be installed in the fuselage, the engine featured a number of design elements intended to reduce its width. For instance, the carburetor was placed behind the engine, feeding fuel to the cylinders via a long tubular intake manifold. This had the disadvantage of poor fuel distribution. Two versions of the engine were produced in mirror copies, running in opposite directions.

• A Mercedes D.IVa recently restored by the Museum's Friends ASSN. is on public display at the Museo Nacional de Aeronautica (MORON-Argentina).

Data from Jane's all the World's Aircraft 1918,^[2] Jane's Fighting Aircraft of World War One^[3][4]

• Type: 6-cylinder, inline piston engine
• Bore: 160 mm (6.30 in)
• Stroke: 180 mm (7.09 in)
• Displacement: 21.72 L (1,325 cu in)
• Length: 1,168.4 mm (46 in) approx.
• Height: 1,968.5 mm (77.5 in)
• Dry weight: 498.50 kg (1,099 lb)

• Valvetrain: Shaft driven SOHC operating twin exhaust and inlet valves with a half compression setting for starting
• Fuel system: Twin jet Mercedes carburettor with automatic mixture control
• Fuel type: Gasoline
• Oil system: Forced feed to bearings and camshaft
• Cooling system: Water-cooled
• Reduction gear: Direct drive, left-hand tractor

• Power output: 187.92 kW (252 hp) at 1,400 rpm
• Compression ratio: 4.94:1
• Fuel consumption: 125 pints per hour
• Specific fuel consumption: 0.329 kg/kWh (0.541 lb/(hp⋅h)) / 0.461 L/kWh (0.605 imp pt/(hp⋅h))
• Oil consumption: 0.024 L/kWh (0.032 imp pt/(hp⋅h))
• Power-to-weight ratio: 0.376 kW/kg (0.229 hp/lb)
• Bmep: 741.19 kPa (107.5 psi)

Related lists

• List of aircraft engines

• Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
• Jane's Fighting Aircraft of World War I. London. Studio Editions Ltd, 1993. ISBN 1-85170-347-0

• Düsing, Michael (2022). German & Austro-Hungarian Aero Engines of WWI. Vol. 2. n. p.: Aeronaught Books. ISBN 978-1-953201-52-2.

• Tests of the Daimler D-IVa engine at a high altitude test bench (October 1, 1920)