The Armstrong Siddeley Deerhound was a large

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 ...

developed by

Armstrong Siddeley Armstrong Siddeley was a British engineering group that operated during the first half of the 20th century. It was formed in 1919 and is best known for the production of luxury vehicles and aircraft engines. The company was created following t ...

between 1935 and 1941. An increased capacity variant known as the Boarhound was never flown,Gunston 1989, p.18. and a related, much larger, design known as the Wolfhound existed on paper only. Development of these engines was interrupted in April 1941, when the company's factory was bombed, and on 3 October 1941 the project was cancelled by the

Air Ministry The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964. It was under the political authority of the Secretary of Stat ...

Design and development

The Deerhound I was a triple-row, 21-cylinder, air-cooled

radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ...

design with the unusual feature of inline cylinder banks. Unlike earlier Armstrong Siddeley engines the Deerhound used

overhead camshaft An overhead camshaft (OHC) engine is a piston engine where 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 combustion cha ...

s to operate its

poppet valve A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usua ...

s, using one camshaft for each bank of three cylinders.Lumsden 2003, p.77. Flight testing began in 1938 using an Armstrong Whitworth Whitley II,

serial number A serial number is a unique identifier assigned incrementally or sequentially to an item, to ''uniquely'' identify it. Serial numbers need not be strictly numerical. They may contain letters and other typographical symbols, or may consist enti ...

''K7243'', during which cooling problems were encountered with the rear row of cylinders. This problem was solved by a 'reversed-flow' cooling system, in which a large air duct at the rear of the

cowling A cowling is the removable covering of a vehicle's engine, most often found on automobiles, motorcycles, airplanes, and on outboard boat motors. On airplanes, cowlings are used to reduce drag and to cool the engine. On boats, cowlings are a cove ...

took in air and directed it forward to exit behind the

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

.Lumsden 2003, p.77. The project suffered a severe setback when the Whitley crashed on

takeoff Takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. For aircraft traveling vertically, this is known as liftoff. For aircraft that take off horizontally, this usually involves starting with a ...

in March 1940, fatally injuring its crew. The accident was attributed to an incorrect elevator trim setting and was not related to the engines.Lumsden 2003, p.77. A single prototype Deerhound III was built and ran, and survived until the late-1970s before being scrapped. Development work on the early engines was cancelled by the Air Ministry on 23 April 1941, but running of the Mk III was allowed to continue until 3 October 1941; at this point all records were ordered to be handed over to

Rolls-Royce Rolls-Royce (always hyphenated) may refer to: * Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct Automobiles * Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...

. A projected increased capacity variant known as the Boarhound was planned but never built, and a related much larger design, the Wolfhound, existed on paper only. The latter engine featured six banks of four cylinders, a displacement of around 61 litres (3,733 cu in) and a projected takeoff power rating of .

Armstrong Siddeley in-line radial engines

The Hyena arrangement of cylinder banks arranged as a radial engine was continued with further designs, but with little commercial success. Only the Deerhound and Hyena were built. ;Hyena: 15 cylinders (5 banks of 3 cyl.) ;Terrier: 14 cylinders (7 banks of 2 cyl.) ;Deerhound: 21 cylinders (7 banks of 3 cyl.) ;Wolfhound: 28 cylinders (7 banks of 4 cyl.) ;Boarhound: 24 cylinders (6 banks of 4 cyl., same format as the later

Junkers Jumo 222 The Jumo 222 was a German high-power multiple-bank in-line piston aircraft engine from Junkers, designed under the management of Ferdinand Brandner of the Junkers Motorenwerke. Such was the projected performance of the engine compared to con ...

) ;Mastiff: 36 cylinders (9 banks of 4 cyl.)

Variants

;Deerhound I:1,115 hp (831 kW): four built. ;Deerhound II:1,500 hp (1,118 kW), capacity enlarged to 41 L (2,509 cu in) by increasing bore and

stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...

: six built. ;Deerhound III:1,800 hp (1,342 kW), major redesign by

Stewart Tresilian Stewart Tresilian (9 January 1904 – 20 May 1962) was a British mechanical engineer, who played a significant role in the early development of British aero engines during World War II. Early life He gained a BA degree in Engineering from the U ...

: one engine built.

Applications

This engine's sole aircraft application was in a modified

Armstrong Whitworth Whitley The Armstrong Whitworth A.W.38 Whitley was a British medium bomber aircraft of the 1930s. It was one of three twin-engined, front line medium bomber types that were in service with the Royal Air Force (RAF) at the outbreak of the Second World ...

which was used as a testbed.

Specifications (Deerhound I)

References

Notes

Bibliography

*Gunston, Bill. ''World Encyclopedia of Aero Engines''. Cambridge, England. Patrick Stephens Limited, 1989. *Lumsden, Alec. ''British Piston Engines and their Aircraft''. Marlborough, Wiltshire: Airlife Publishing, 2003. . * {{ASaeroengines 1940s aircraft piston engines Aircraft air-cooled inline piston engines Aircraft air-cooled radial piston engines Deerhound Inline radial engines