Roberts 4X In-line 4 Engine

Type: Reciprocating, 4 cylinders, in-line, two-stroke cycle, water cooled

Power rating: 48.5 kW (65 hp) at 1,200 rpm

Displacement: 6.44 L (393 cu in.)

Bore and Stroke: 127 mm (5 in.) x 127 mm (5 in.)

Weight: 77.1 kg (170 lb)

An important objective of the Roberts Motor Company design was light weight, which was achieved through the extensive use of aluminum and magnesium alloys in the cylinders and crankcase, a hollow crankshaft, and two-stroke cycle operation (to reduce parts count). Between 1911 and 1912, Roberts engines were used by many noted exhibition pilots, and more Roberts engines were said to be built than by Hall-Scott and Curtiss combined.

This engine was purchased by Oscar R. Solbrig of Davenport, Iowa, to power the Curtiss-type pusher aircraft he built in 1911-12. Solbrig, who had received aviation training from Curtiss, soloed in his own aircraft in 1912. He later flew exhibition flights and races with it at county fairs, sports events, and exposition parks in Iowa and Illinois. This artifact is apparently rare because the standard Roberts 4X engine used a 114 mm (4.5 in.) bore, resulting in a 5.21 L (318 cu. in,) displacement.