The Curtiss H-1640 Chieftain was an unusual American 12-cylinder radial

aero 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 ...

designed and built by the

Curtiss Aeroplane and Motor Company 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 decades ...

in the mid-1920s.Gunston 1989, p. 46

Design and development

The H-1640 was an air-cooled 12 cylinder two-row radial with the cylinder rows aligned rather than staggered as in most multi-row radials. One piece

cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ov ...

s shared a single overhead camshaft and the propeller was directly driven. By aligning the cylinders the diameter of the engine was less than more conventional radial engines, and it was thought that the use of a Townend ring could make the engine more aerodynamically efficient than an inline engine. The engine first ran in 1927. The H-1640 was the first airworthy 'inline radial' and was sponsored for flight testing in a range of aircraft by the U.S. Government. Among the types selected were the Thomas-Morse XP-13 and the Curtiss XO-18. Cooling problems with the rear cylinders caused the project to be canceled with few production engines being built. A similar engine is the

Bristol Hydra The Bristol Hydra (also known as the Double Octagon) was an experimental 16-cylinder, twin-row radial aircraft engine built by the Bristol Engine Company. It is a relatively rare example of a radial with an even number of cylinders per rowit ...

although this engine had 16 aligned cylinders, forming an

octagon In geometry, an octagon (from the Greek ὀκτάγωνον ''oktágōnon'', "eight angles") is an eight-sided polygon or 8-gon. A '' regular octagon'' has Schläfli symbol and can also be constructed as a quasiregular truncated square, t, whi ...

. Further similar engines are the Armstrong Siddeley Hyena and the much larger Armstrong Siddeley Deerhound.

Applications

Curtiss XP-22 Hawk The Curtiss XP-22 Hawk was a 1930s American experimental biplane fighter built by Curtiss for evaluation by the United States Army Air Service. Design and development In 1929, the AAC ordered three P-11 Hawks for testing of the 600 hp (4 ...

* Curtiss YP-20 *

Curtiss P-6 Hawk The Curtiss P-6 Hawk is an American single-engine biplane fighter introduced into service in the late 1920s with the United States Army Air Corps and operated until the late 1930s prior to the outbreak of World War II. Design and development Th ...

Thomas-Morse XP-13 Viper The XP-13 Viper was a prototype biplane fighter aircraft designed by the American company Thomas-Morse Aircraft Corporation. The airplane was delivered to the United States Army in 1929, but they did not adopt it. Design and development Th ...

Specifications (H-1640)

References

Notes

Bibliography