Curtiss OX - 5 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 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 . 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 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 . The pistons were cast aluminum . The OX - 5 was not considered particularly advanced , nor powerful , for its era . By this point rotary engines such as the Oberursel or Gnome - Rhone 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 Laird 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 . 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 WWI . 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 - 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 in each cylinder , and a single ignition system , in an era when ignition equipment was less reliable , with dual ignition being fitted to more advanced aviation powerplants like the French V - form Hispano - Suiza 8 and the inline - six cylinder series of Mercedes D . I 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 tailspins 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 . There is no question that 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 of course 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 - built version of the 150 hp Hispano - Suiza HS - 8a V8 engine in the nearly 930 examples of the later production Curtiss JN - 4 H Jenny biplanes . Preservation groups . The OX - 5 Aviation Pioneers is a group of OX - 5 enthusiasts and former barnstormers . The group ' s motto is " Aviation History by those Who Lived It " . " OX5 Aviation Pioneers " PO Box 18533 Pittsburgh , Pa 15236 - 0533 Over 1 , 000 members strong .