Draft:Walter M208

In June 1947, the production of aircraft engines from the Praga factory , including development, was transferred to the Letecké závody np, plant 1 Jinonice (former AS Walter , from 1 January 1948 Motorlet np). The design group of Jaroslav Kruliš developed the flat six-cylinder M208 with an output of 162 kW (220 hp) here, which was produced from 1954 under the Praga Doris brand. The first variant of this engine, designated M-208A with an expected output of 154 kW (210 hp), was created in 1948. It was still being developed and modified to the M-208B version. Many technical difficulties arose during the development and testing of the prototype. Its development was not completed until 1954, simultaneously with another version, the M-208C, which had an extended drive housing. State tests were carried out in 1955. From 1 to 25 February, the first engine completed a 300-hour state test, during which all ICAO requirements were met . This was followed by an internal test of the second engine, which lasted 600 hours. The last variant was the M-208D version, produced from 1958.^[1][2]

Despite constant problems with crankshaft mounting and mixture combustion, 530 of these engines were eventually produced between 1955 and 1962.^[3]

The M208 was a flat-piston, six-cylinder engine with opposed cylinders in two rows. It was a compact engine, and all components of the mixture preparation system, lubrication and ignition systems were installed directly in or on the engine. The propeller was driven from the engine crankshaft through a planetary speed reducer.

All versions of the M208 had the same bore and stroke (115×115 mm) and a cylinder capacity of 7.167 cubic meters. They differed in the reduction ratio of the reducer used, slightly in weight and power. The M-208 engine had a rolling bearing on the crankshaft using rolled-in half-shells and rollers. Originally, the idea was that the bearing on rolling bearings would contribute to the reliable operation of the engine. However, the engine had a number of defects, especially on the aforementioned crank mechanism and in the combustion of the mixture, the elimination of which was only solved during serial production by Ing. Jan Souček. The problem with the rolling bearing of the crankshaft was solved only by changing to a sliding bearing. The engine with this version of the crank mechanism was designated M-208D.^[4][5]

• M208A (1948): with an expected power of 154 kW (210 hp), not produced
• M208B (1954): basic variant
• M208C (1954): rated power 158 kW (215 hp), take-off power 173 kW (235 hp), reduction ratio: 1:1.52, weight: 214 kg
• M208D (1958): rated power 162 kW (220 hp), take-off 184 kW (240 hp), reduction ratio: 2:3, weight: 195 kg