The OX-5 was an early V-8 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". Just over 12,600 were built, production ending in late 1918 or early 1919. The wide availability of the engine in the surplus market made it extremely common until the 1930s, although it was considered unreliable for most of its service life. Today the engine can be found powering many Edwardian 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 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 F-head valve arrangement, which eventually gave way to a cross-flow cylinder with overhead valves in 1909, leading to greatly improved volumetric efficiency. The US Navy ordered a version of this basic design in 1912 for their A-1 amphibious aircraft, which Curtiss supplied as the OX. All of these improvements, and more, were worked into what became the OX-5, which was first built in 1910. By this point, detailed design was a team effort, including Charles Manley, whose earlier Manley-Balzer engine had held the power-to-weight ratio record for 16 years.
Like most engines of the era, the OX-5's high-temperature areas were built mostly of cast iron, using individual cylinders bolted to a single aluminum crankcase, wrapped in a cooling jacket made of a nickel-copper alloy. Later versions used a brazed-on steel jacket instead. Cylinder heads were also attached to the crankcase, using X-shaped tie-downs on the top of the head attached to the block via four long bolts. Fuel was carbureted near the rear of the engine, then piped to the cylinders via two T-shaped pipes, the cylinders being arranged so the intake ports of any two in a bank were beside each other. Each cylinder had a single intake and exhaust valve, each operated via a pushrod mounted between the banks, the outer exhaust valves requiring a rather long rocker. Interestingly the pushrods were arranged one inside the other, the exhaust valve rod being on the inside and the intake valve rod a tube around it. The aluminum camshaft bearings were a split type bolted together and held in place by lock screws. The pistons were cast aluminum.
The OX-5 was not considered particularly advanced, nor powerful, for its era. By this point the average rotary engine, like the Oberursel or Gnome-Rhone, was producing about Template:Convert, and newer inlines were just starting to become available with Template:Convert or more. Nevertheless the OX-5 had fairly good fuel economy as a result of its slow RPM, and this made it especially popular for civilian aircraft. The OX-5 could be found on the Laird Swallow, Travel Air 2000, Waco 9 and 10, the American Eagle, the Buhl-Verville CW-3 Airster, as well as some models of the Jenny. Of course the primary reason for its popularity was its low cost after the war, with almost-new examples selling as low as $20. It was not only used in aircraft, but was a common boat engine as well.
Unfortunately the engine was also considered unreliable, and as it was used on many primary trainers, it has been suggested it was responsible for a number of prospective pilot's deaths. In particular the valve gear was fragile, and it had no provisions for lubrication other than grease and oil applied by hand, leading to overhaul times as short as fifty hours. Additionally the engine featured a single spark plug and ignition system, in an era when neither could really be relied on. Built by numerous contractors in vast numbers, it suffered from appaling quality control.
- Smith, 1981, page 46
- Smith, 1981, page 12
- Fisher, 2009, page 7
- Gunston, 1995, page 47
- Angle, 1940, pages 244-246
- Smith, 1981, page 47
- Fisher, 2009, page 10
- Angle, Glenn D., AEROSPHERE 1939. New York: Aircraft Publications, 1940.
- Gunston, Bill, World Encyclopedia of Aero Engines. Somerset: Haynes Publishing, 1995. ISBN 1-85260-509-X
- Fisher, Scott M., The Curtiss OX-5, Aircraft Maintenance Technology. Cygnus Business Media, July 2009.
- Smith, Herschel, Aircraft Piston Engines. McGraw-Hill Book Company, 1981. ISBN 0-07-058472-9
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It uses material from the Wikipedia article "Curtiss OX-5".