In 1932, the engineers at Lycoming Engines became aware that the United States Army Air Corps (USAAC) wanted a high performance engine that could produce at least one horsepower per cubic inch (46 kW/L) of engine displacement. Determined to become known as a high performance engine manufacturer, Lycoming began an experimental, high-performance engine of its own. After spending US $500,000, and after many attempts to develop a successful engine, it finally came close to the USAAC specifications with the O-1230 engine, which was a 12-cylinder liquid-cooled horizontally-opposed low-profile piston engine. In 1936, the single-cylinder development tests exceeded expectations, passing its 50 hour test requirement. The full-size engine was ready for testing in 1937, and was rated at 1,000 hp. Continued development of the O-1230 reached its peak when the engine was rated at over 1,200 hp (895 kW). The O-1230 was not well received by aircraft manufacturers, because it was not very reliable at that power setting.
It was apparent that the O-1230 engine was uncompetitive with the high performance air-cooled engines that were then becoming available. The US Navy began funding the development of the Lycoming engine. The funding enabled Lycoming's engineers to attempt rescuing the design by proposing a 24-cylinder H-configuration engine made by stacking two of the O-1230 engines, gearing them together to one common output shaft. The new engine was the H-2470. It weighed in at 2,430 pounds and produced 2,300 hp (1,700 kW) at 3,300 rpm.
The Navy specified the H-2470 for the Curtiss XF14C-1 experimental fighter. After some rigorous testing the engine's poor performance led to the substitution, before the aircraft flew, of a Wright R-3350 radial engine, which was also having technical problems but was considered to be more reliable than the H-2470. The testing program was eventually terminated due to the poor performance of the aircraft.
The USAAC was also interested in the H-2470, and installed and flew it in the Vultee XP-54 prototype fighter. The XP-54 was the only aircraft to actually use it for flight, but like the Navy's XF-14C, the XP-54 never went into production.
Type: 24 cylinder, 'H' piston engine
Bore: 5.25 in. (133.35mm)
Stroke: 4.75 in. (120.65mm)
Displacement: 2467.8 cuin (40.44 Li)
Dry weight: 2,430 lb
Cooling system: Liquid-cooled
Power output: 2,300 hp at 3,300 rpm