The Napier Scorpion series of

rocket engine A rocket engine is a reaction engine, producing thrust in accordance with Newton's third law by ejecting reaction mass rearward, usually a high-speed Jet (fluid), jet of high-temperature gas produced by the combustion of rocket propellants stor ...

s are a family of British liquid-fuelled engines that were developed and manufactured by Napier at the Napier Flight Development Establishment,

Luton Luton () is a town and borough in Bedfordshire, England. The borough had a population of 225,262 at the 2021 census. Luton is on the River Lea, about north-west of London. The town's foundation dates to the sixth century as a Saxon settleme ...

, in the late 1950s. The Scorpion range were designed and flight tested as boosters to improve aircraft take-off performance.

Design and development

After

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

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 and civil aviation that existed from 1918 to 1964. It was under the political authority of the ...

issued specifications for a wide variety of rocket engines, both liquid and solid-fuelled. Napier responded with the design of a liquid-fuelled rocket which used catalysed

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

(H₂O₂), in the form of

High-Test Peroxide High-test peroxide (HTP) is a highly concentrated (85 to 98%) solution of hydrogen peroxide, with the remainder consisting predominantly of water. In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with n ...

(HTP) as

oxidiser An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...

and

Kerosene Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...

as fuel. The Scorpion was a regeneratively-cooled HTP (High Test Peroxide/Kerosene) bi-propellant rocket engine. Fuel and oxidiser were pumped by a single shaft turbo-pump driven by super-heated steam, generated by catalysing HTP. Engine starting was achieved by an electric pump supplying HTP to the turbo-pump decomposition chamber. Once started, a bleed off the turbo-pump oxidiser outlet fed the turbo-pump decomposition chamber to maintain flow of fuel and oxidiser. Due to the single-shaft turbo-pump operating both fuel and oxidiser pumps, flow of fuel and oxidiser were automatically maintained at the correct ratio. The Kerosene fuel is ignited thermally by the super-heated steam from HTP, decomposed by passing over a catalyst in a decomposition chamber, which is injected simultaneously into the combustion chamber. First run on 19 May 1956, the N.Sc.1 Scorpion was also fired in the air on the following day, mounted in the bomb-bay of an English Electric Canberra B.2.

Double Scorpion

The Double Scorpion engine was simultaneously developed with the single-chamber Scorpion, consisting of two Scorpion engines mounted together with each unit individually controllable, developing double the thrust. From 1956 Double Scorpion engines were fitted experimentally to three Canberra light bombers, to improve high altitude performance. On 28 August 1957 ''WK163'', fitted with a Double Scorpion, broke the world altitude record, exceeding . The Double Scorpion was also considered for use in the English Electric P.1A interceptor (which gave rise to the

Lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

) and

Aerojet General Aerojet was an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California, with divisions in Redmond, Washington, Orange and Gainesville in Virginia, and Camden, Arkansas. Aerojet was owned by GenCorp, ...

was chosen for projected

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production.

Triple Scorpion

A triple-chamber version was also developed as the Napier Triple Scorpion, emerging as a Double Scorpion with a third chamber mounted centrally under the other two.

Cancellation

The Scorpion project was cancelled in February 1959, at a reported total cost of £1.25 million.

Variants

;Scorpion NSc.1: :Initial development single-chamber engine. ;Double Scorpion NScD.1: :Double-chamber engine. ;Triple Scorpion NScT.1: :Triple-chamber engine.

Engines on display

A sectioned Napier Double Scorpion engine is on display at the

Royal Air Force Museum London The Royal Air Force Museum London (also commonly known as the RAF Museum) is located on the former Hendon Aerodrome, in North London's Borough of Barnet. It includes five buildings and hangars showing the history of aviation and the Royal Air ...

. Another Napier Double Scorpion engine is on display at the

Solent Sky Solent Sky (previously known as the Southampton Hall of Aviation) is an aviation museum in Southampton, England. The museum depicts the history of aviation in Southampton, the Solent area and Hampshire. There is a focus on Supermarine, the air ...

Museum Southampton.

Specifications (Double Scorpion)

Notes and references

{{Aviation rocket engines

Scorpion Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward cur ...

Aircraft rocket engines Rocket engines using hot cycle hydrogen peroxide propellant