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The Curtiss OX-5 was an early V-8
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liquid-cooled
aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...
built by
Curtiss Curtiss Aeroplane and Motor Company (1909 – 1929) was an American aircraft manufacturer originally founded by Glenn Hammond Curtiss and Augustus Moore Herring in Hammondsport, New York. After significant commercial success in its first decade ...
. It was the first American-designed aircraft engine to enter mass production, although it was considered obsolete when it did so in 1917.Smith, 1981, page 46 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.


Design and development

The OX-5 was the last in a series of
Glenn Curtiss Glenn Hammond Curtiss (May 21, 1878 – July 23, 1930) was an American aviation and motorcycling pioneer, and a founder of the U.S. aircraft industry. He began his career as a bicycle racer and builder before moving on to motorcycles. As early ...
designed V engines, which started as a series of air-cooled V-twins for
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s 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 Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the mass density of the air-fuel mixture drawn into the cylinder at atmospheric pressure (during the intake stroke) to the mass density of the same volu ...
. The
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ordered a version of this basic design in 1912 for its A-1 amphibious aircraft,A reproduction of the A-1 is on display at the
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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
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, whose earlier
Manly–Balzer engine The Manly–Balzer was the first purpose-designed aircraft engine, built in 1901 for the Langley Aerodrome project. The engine was originally ordered from Stephen Balzer (1864–1940) in New York, but his five-cylinder radial engine design faile ...
had held the
power-to-weight ratio Power-to-weight ratio (PWR, also called specific power, or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measuremen ...
record for 16 years.Smith, 1981, page 12 Like most engines of the era, the OX-5's high-temperature areas were built mostly of
cast iron Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
, 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.Fisher, 2009, page 7 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.Gunston, 1995, page 47 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, each operated by a pushrod from a camshaft running between the banks. This arrangement caused the outer exhaust valves to have a rather long rocker arm. 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.Angle, 1940, pages 244-246 The pistons were cast aluminum. The OX-5 was not considered particularly advanced, nor powerful, for its era. By this point
rotary engine The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine's crankshaft remained stationary in operation, while the entire crankcase and i ...
s such as the
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or Gnome-Rhône were producing about , and newer inlines were becoming available with or more. Nevertheless, the OX-5 had fairly good fuel economy as a result of its slow RPM, which made it useful for civilian aircraft. The OX-5 was used on the
Swallow Airplane Swallow The Swallow Airplane Swallow is an American-built general purpose biplane of the mid- to late 1920s. Development The Swallow Airplane Manufacturing Co was formed in 1923 to take over the business of the E.M. Laird Aviation Co. of Wichita, Kansa ...
,
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,
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,
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and 10, the
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, the Buhl-Verville CW-3 Airster, and some models of the Jenny.Smith, 1981, page 47 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, but unreliable is a relative term: aviation engine technology had not fully matured at the end of World War I. Certainly the JN4 with the OX-5 was underpowered, but the OX-5 proved a much better engine than the Hall Scott A7A that was the Achilles heel of the
Standard J The Standard J is a two-seat basic trainer two-bay biplane produced in the United States from 1916 to 1918, powered by a four-cylinder inline Hall-Scott A-7a engine. It was constructed from wood with wire bracing and fabric covering. The J-1 ...
-1, the substitute primary trainer. In particular the valve gear was fragile, and it had no provisions for lubrication other than grease and oil applied by hand, leading to an overhaul interval as short as fifty hours. Additionally the engine featured a single
spark plug A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...
in each cylinder, and a single ignition system, in an era when ignition equipment was less reliable, with
dual ignition Dual Ignition is a system for spark-ignition engines, whereby critical ignition components, such as spark plugs and magnetos, are duplicated. Dual ignition is most commonly employed on aero engines,Crane, Dale: ''Dictionary of Aeronautical Terms ...
already being fitted to more advanced aviation powerplants like the French V-form
Hispano-Suiza 8 The Hispano-Suiza 8 was a water-cooled V8 SOHC aero engine introduced by Hispano-Suiza in 1914, and was the most commonly used liquid-cooled engine in the aircraft of the Entente Powers during the First World War. The original Hispano-Suiza ...
and the inline-six cylinder series of
Mercedes D.I The Mercedes D.I (also known as the Type E6F) was a six-cylinder, water-cooled, SOHC valvetrain inline engine developed in Germany for use in aircraft in 1913. Developing 75 kW (100 hp), it powered many German military aircraft during t ...
through D.III German engines. Built by several contractors in large numbers, the OX-5 suffered from uneven quality control. However, while the overwhelming majority of training accidents in the U.S. were in JN-4s, this was because JN-4s were flown by the vast majority of trainee pilots, and the accident rate in the US for primary training was four times less than the advanced training rate in France (virtually all US airmen getting advanced training in France), approximately 2800 flying hours in the US primarily in OX-5 powered JN-4s per fatality to 761 hours per fatality in France in other types. Very few fatal accidents were caused by engine failure, although the lack of power may have been the cause of the many 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
Wright Aeronautical Wright Aeronautical (1919–1929) was an American aircraft manufacturer headquartered in Paterson, New Jersey. It was the successor corporation to Wright-Martin. It built aircraft and was a supplier of aircraft engines to other builders in the g ...
-built version of the 150 hp Hispano-Suiza HS-8a V8 engine in the nearly 930 examples of the later production
Curtiss JN-4 The Curtiss JN "Jenny" was a series of biplanes built by the Curtiss Aeroplane Company of Hammondsport, New York, later the Curtiss Aeroplane and Motor Company. Although the Curtiss JN series was originally produced as a training aircraft for th ...
H Jenny biplanes.


Engines on display

* A Curtis OX-5 engine is on public display at the
Aerospace Museum of California The Aerospace Museum of California is a private non-profit aviation museum located in North Highlands, California, outside of Sacramento, California, on the grounds of the former McClellan Air Force Base. The museum has a 4.5-acre outdoor Air Park ...
.


Specifications (OX-5)


References


Bibliography

* Angle, Glenn D., ''AEROSPHERE 1939''. New York: Aircraft Publications, 1940. * Gunston, Bill, ''World Encyclopedia of Aero Engines''. Somerset: Haynes Publishing, 1995. * 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.


External links


Curtiss OX-5
{{Curtiss aeroengines
OX-5 The Curtiss OX-5 was an early V-8 American liquid-cooled aircraft engine built by Curtiss. It was the first American-designed aircraft engine to enter mass production, although it was considered obsolete when it did so in 1917.Smith, 1981, page ...
1910s aircraft piston engines