Curtiss OX-5

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OX-5
Preserved OX-5 engine
Type V-8 piston engine
National origin United States
Manufacturer Curtiss Aeroplane and Motor Company
First run 1915
Number built 12,600
Developed from Curtiss O

The Curtiss OX-5 was an early

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.

Design and development

The OX-5 was the last in a series of Glenn Curtiss designed V engines, which 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 valve arrangement, which eventually gave way to a cross-flow cylinder with overhead valves in 1909, leading to improved volumetric efficiency. By this point engine design was a team effort; the team included Charles M. Manly, whose earlier Manly–Balzer engine had held the power-to-weight ratio record for 16 years.[2] Curtiss continued the development of their V8 engines with demand for higher power outputs being largely driven by the US Navy’s requirement for seaplanes. By 1912 Curtiss V8’s were developing 75 hp and were known as the Curtiss Model O. The Curtiss O was further developed into the 90 hp Curtiss OX. OX series production began in 1913. The OX-5 was built between 1915 and 1919 and was by far the most popular OX variant.[3]

Curtiss OX-5 at Canada Aviation Museum

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.[4] 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.[5] 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 near each other. The cylinders had one intake and one exhaust valve, the exhaust valve operated by a pushrod from a camshaft running between the banks and inlet valve operated by a pull rod/tube working from the same camshaft. This arrangement caused the outer exhaust valves to have a rather long rocker arm. The push/pullrods were arranged one inside the other, the exhaust valve rod being on the inside and the intake valve rod a tube around it.[4] The aluminum camshaft bearings were a split type bolted together and held in place by lock screws.[6] The pistons were cast aluminum.[6]

The OX-5 was not considered particularly advanced, nor powerful, for its era. By this point

Swallow Airplane Swallow, Pitcairn PA-4 Fleetwing II, Travel Air 2000, Waco 9 and 10, the American Eagle, the Buhl-Verville CW-3 Airster, and some models of the Jenny.[7]
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.

Reliability

The engine was considered unreliable,

stall and spins that took about forty five percent of training lives. Anyone seeing a JN-4 today struggling into the air with an OX-5 can see very quickly that the JN-4 had to be flown in a narrow envelope. Also, the replacement of the A7A in Standard J-1s was contemplated, but the cost of $2,000 per aircraft compared with the need (by the time the J-1s were grounded in June 1918 JN-4s were in sufficient supply) led to the rejection of this idea. The successful civilian post-war use of the OX-5 (even in civilian purchased and converted J-1s) was due to its relative reliability in the more aerodynamically advanced designs of the 1920s, its simplicity of operation, and its low cost. By comparison the Hall Scott A7A
created such a bad impression during the war that very few, if any, were used by civilian operators.

The OX-5 itself would be replaced by the well-proven

Curtiss JN-4
H Jenny biplanes.

Engines on display

Specifications (OX-5)

Top overhead view of OX-5 at Lone Star Flight Museum

General characteristics

Components

Performance

  • Power output:
  • 90 hp (67 kW) at 1,400 rpm[4][5]
  • 105 hp (78 kW) at 1,800 rpm for brief periods
  • Specific power: 0.21 hp/in3 (9.5 kW/L)
  • Compression ratio: 4.9:1
  • Fuel consumption: 8.0 US gal/h (30.8 L/h) at 75% power[4]
  • Specific fuel consumption
    :     0.53 lb/(hp·h) (0.32 kg/(kW·h)) at 75% power
  • Oil consumption: 0.5 US gal/h (1.9 L/h) at 75% power
  • Power-to-weight ratio: 0.27 hp/lb (440 W/kg)

References

  1. ^ a b c d Smith, 1981, page 46
  2. ^ Smith, 1981, page 12
  3. ^ Rinek, Larry (1994). "Glenn H. Curtiss: An Early American Innovator in Aviation and Motorcycle Engines". SAE Transactions. 103: 927–945. Retrieved 31 Dec 2022.
  4. ^ a b c d e f g h i j k Fisher, 2009, page 7
  5. ^ a b c d e f Gunston, 1995, page 47
  6. ^ a b c d e f g h i j Angle, 1940, pages 244-246
  7. ^ Smith, 1981, page 47

Bibliography

External links

Wikimedia Commons has media related to Curtiss OX-5.
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