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ON MAY 31, 1918, a German Rumpler two-seat aircraft was shot down in combat. The Rumpler’s six-cylinder Bassé & Selve engine was retrieved by British Intelligence and subjected to intensive analysis. What a treasure trove of aero engineering!
Despite its French-sounding name, Bassé & Selve was a Westphalia, Germany, company founded in 1908 as the Selve Automobilewerke AG. During World War I, the company designed engines along the lines of those from Mercedes and Benz (two separate companies until 1926).
As described in eight pages of Jane’s All The World’s Aircraft 1919, much of the Bassé & Selve design was conventional aero engineering for 1918. The engine had six individually-cast cylinders, inline and water-cooled, with a single overhead camshaft actuating four valves per cylinder.
The intelligence report noted that damage to the powerplant precluded testing of its output. However, a plate on its crankcase cited a nominal rating of 270 hp at 1400 rpm. Its bore of 155 mm and stroke of 200 mm gave a displacement of 22.6 liters. Estimates of its cylinder clearance volume suggest a compression ratio of around 4.3:1, “which is lower than any of the previous enemy engines,” Jane’s observes.
One feature that set the Bassé & Selve design apart from those of Benz or Mercedes is its valve actuation. Though its rocker arms are conventional, the tappets between rocker arms and camshaft lobes are decidedly not.
Each tappet is in the shape of a stirrup encircling its cam lobe, with these stirrups riding vertically on bronze bushings. It’s not recorded why this peculiar tappet design was chosen.
Another innovative feature of the Bassé & Selve design was its means of compression release, used to facilitate swinging the propeller in startup. Jane’s notes that other aero engines accomplished this with “the usual half compression cams and mechanism.” With this approach, the camshaft was shifted longitudinally so that different cam lobes actuated the rocker arms to keep the exhaust valves half-open.
Instead, the Bassé & Selve used a rod aligned longitudinally outside the camshaft casing and directly beneath the exhaust valve rocker arms.
The rod, partially rotated by a hand-lever at startup, had slots that raised these rocker arms and thus achieved compression release. Clearly, this was considerably less complex than other compression releases requiring longitudinal shifting of the camshaft.
The intelligence report cited in Jane’s offered extensive details, including metallurgical data on the pistons and crankshaft. For instance, the pistons were aluminum, alloyed with silicon (0.45 percent), iron (1.06 percent), copper (1.90 percent) and zinc (15.62 percent). The crankshaft was of nickel-chromium steel.
Bassé & Selve continued to build engines until 1932. Selve Automobilwerke AG closed in 1934. The former Bassé & Selve factory in Altena, Westphalia, is now a Cultural Heritage building. ds
© Dennis Simanaitis, SimanaitisSays.com, 2016