Curtiss OX-5 Engine

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The OX-5 was an early V-8 American liquid cooled aircraft engine built by Curtiss. It was the first US-designed engine to enter mass production, although it was considered obsolete when it did so in 1917. It nevertheless found widespread use on a number of aircraft, perhaps the most famous being the JN-4 “Jenny”. Some 12,600 units were built through early 1919. The wide availability of the engine in the surplus market made it common until the 1930s, although it was considered unreliable for most of its service life. Today the engine can be found powering many Edwardian automobile racing specials on the historic racing scene.

Design and development

The OX-5 was the last in a series of Glenn Curtiss designed V engines, which had started as a series of air-cooled V-twins for motorcycles in 1902. A modified version of one of these early designs was sold as an aircraft engine in 1906, and from then on the company’s primary market was aircraft. The basic design had slowly expanded by adding additional cylinders until they reached the V-8 in 1906. They also started enlarging the cylinders as well, but this led to cooling problems that required the introduction of water cooling in 1908. These early engines used a Flathead engine valve arrangement, which eventually gave way to a cross-flow cylinder with overhead valves in 1909, leading to improved volumetric efficiency. The US Navy ordered a version of this basic design in 1912 for its A-1 amphibious aircraft, which Curtiss supplied as the OX. These improvements and others were worked into what became the OX-5, which was first built in 1910. By this point engine design was a team effort; the team included Charles Manley, whose earlier Manley-Balzer engine had held the power-to-weight ratio record for 16 years.

The OX-5 was used on the Laird Swallow, Travel Air 2000, Waco 9 and 10, the American Eagle, the Buhl-Verville CW-3 Airster, and some models of the Jenny. The primary reason for its popularity was its low cost after the war, with almost-new examples selling as low as $20. It was often used in boats as well as in aircraft.

General characteristics

* Type: 8-cylinder water-cooled 90° Vee piston engine
* Bore: 4.0 in (102 mm)
* Stroke: 5.0 in (127 mm)
* Displacement: 503 in³ (8.2 l)
* Length: 56.75 in (1441.45 mm)
* Width: 29.75 in (755.65 mm)
* Height: 36.75 in (933.45 mm)
* Dry weight: 390 lb (177 kg)


* Power output:
o 90 hp (67 kW) at 1,400 rpm
o 105 hp (78 kW) at 1,800 rpm for brief periods