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

radial Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric), a line * Radius, adjective form of * Radial distance (geometry), a directional coordinate in a polar coordinate system * Radial set * A ...

aero engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbin ...

designed and built by the

Curtiss Aeroplane and Motor Company The Curtiss Aeroplane and Motor Company (1909–1929) was an American aircraft manufacturer originally founded by Glenn Curtiss, Glenn Hammond Curtiss and Augustus Moore Herring in Hammondsport, New York. After significant commercial success in ...

in the mid-1920s.Gunston 1989, p. 46 In contrast to most multi-row radials, where the cylinders in the rows are staggered to present better airflow for cooling, the Chieftain used the inline radial arrangement with the cylinders behind each other to allow pairs of cylinders to share a cast

cylinder head In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern ...

and

camshaft A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition syst ...

s. The design saw some use in the 1920s but was quickly passed by newer designs.

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

s shared a single

overhead camshaft An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustio ...

and the propeller was directly driven. By aligning the cylinders the effective diameter and frontal area of the engine was less than more conventional radial engines, and it was thought that the use of a

Townend ring A Townend ring is a narrow-chord (aircraft), chord cowling ring fitted around the cylinders of an aircraft radial engine to reduce drag and improve cooling. It was patented in 1929, and found use on various aircraft of the 1930s and into the 1940s ...

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 although this engine had 16 aligned cylinders, forming an

octagon In geometry, an octagon () 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, which alternates two types of edges. A truncated octagon, t is a ...

. Further similar engines are the

Armstrong Siddeley Hyena The Armstrong Siddeley Hyena was a British aero engine developed by Armstrong Siddeley. Designed in the 1930s, it was an unusual experimental radial engine with inline cylinder banks. It was flown using an Armstrong Whitworth A.W.16 fighter ...

and the much larger Armstrong Siddeley Deerhound.

Applications

* Curtiss XP-22 Hawk *

Curtiss YP-20 The Curtiss YP-20 was an American biplane fighter project developed by Curtiss for the United States Army Air Service. Design and development In 1929, three Curtiss P-11 Hawks were ordered with 600 hp (447 kW) Curtiss H-1640 Chieft ...

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 United States, 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 deve ...

Specifications (H-1640)

References

Notes

Bibliography