‘‘In 1914 Daimler provided the Imperial Air Service with what was to be their most prolific and successful engine, the Mercedes D.III.’’
When introduced this engine was too powerful for most aircraft and was not put into service until 1916 with the Albatros series of single seat aircraft. Originally rated at 150 hp, by the war’s end this unit produced 217hp @ 1,750 rpm. Following the design philosophy first introduced by Daimler with the D.1 of 100hp, the Mercedes provided a robust, light and powerful design. The ‘D’ series engines are water cooled, in-line six cylinder, upright engines. Early engines had three sets of paired cylinders. With the introduction of the D.III, the design changed to individual cylinders allowing for more economic repair. Cylinders are machined steel with two piece fabricated steel water jackets. Each cylinder is bolted to the upper crankcase with four studs that engage flanges on each cylinder base.
The crankcase is cast in two halves split along the crankshaft centreline. The upper half is quite complex providing the top half of the main bearing journals, mounts for the twin magnetos, plenum for the carburettors and mounts for the vertical jackshaft that drives the camshaft and ancillaries. In addition, each of the six engine mounts are cast into the upper case. Some late model engines also had a mount for a generator cast onto the port side, at the rear. The bottom half is the primary reservoir for the wet sump lubrication system. With the D.III series the sump sloped to the rear where the oil pump is situated unlike the D.I and D.II that had a centralized sump cavity and pump. There is an external oil tank that allows for a replenishment of the oil.
The D.III engine line utilised a series of common elements:
1.Overhead camshaft with rocker fingers operating directly onto the single inlet and exhaust valves. The camshaft was driven by the crankshaft using a series of bevel gears and a vertical jackshaft at the rear of the engine. Ancillary equipment, while changing position over the variants, were all driven from the jackshaft. These ancillaries included: oil pump; water pump; magnetos; compression release.
2. Individual steel cylinders bolted to the upper crankcase. In an era of cast iron or iron lined aluminium cylinders, the use of steel created a much lighter cylinder. Each cylinder had a sheet steel water jacket that enclosed it. Water jackets were interconnected with flexible lines to provide a continuous water flow
