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Roberts 4X, In-line 4 Engine


Display Status:

This object is on display in the Early Flight exhibition at the National Air and Space Museum in Washington, DC.

Collection Item Summary:

The Model 4X engine was built by the Roberts Motor Company of Sandusky, Ohio. An important design objective was light weight, which was achieved through the extensive use of aluminum and magnesium alloys in the cylinders and crankcase, and a hollow crankshaft. Also like all Roberts engines it operated on a 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 during this period.

This engine artifact was manufactured about 1911 and powered a Curtiss-type, float-equipped aircraft (hydroplane) built by Harry H. Ford. Mr. Ford was a self-taught pilot and did most of his flying between 1912 and 1913 in the area of the Bridgeport, Connecticut harbor.

Collection Item Long Description:

Data Source

National Air and Space Museum


Do not reproduce without permission from the Smithsonian Institution, National Air and Space Museum

Credit Line

Gift of Harry H. Ford.




  • 3-D: 102.9 × 61 × 63.5cm, 77.1kg (40 1/2 × 24 × 25 in., 170lb.)
  • Support: 114.3 × 58.4 × 39.4cm (45 in. × 23 in. × 15 1/2 in.)

Country of Origin

United States of America



Physical Description

  • Type: Reciprocating, in-line, 4 cylinders, water-cooled, two-stroke cycle
  • Power rating: 37.3 kW (50 hp) at 1,400 rpm
  • Displacement: 5.2 L (318 cu in.)
  • Bore and Stroke: 114 mm (4.5 in.) x 127 mm (5 in.)
  • Weight: 77 kg (170 lb)


PROPULSION-Reciprocating & Rotary

Inventory Number