Armstrong Siddeley Sapphire

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This article is about the jet engine. For the Wright engine, see Wright J65. For the vehicle, see Armstrong Siddeley Sapphire (motor car).
Preserved Armstrong Siddeley Sapphire
at the Midland Air Museum
Type Turbojet
Manufacturer Armstrong Siddeley
First run 1 October 1948
Major applications Gloster Javelin
Handley Page Victor
Hawker Hunter
Variants Wright J65

The Armstrong Siddeley Sapphire was a British turbojet engine produced by Armstrong Siddeley in the 1950s. It was the ultimate development of work that had started as the Metrovick F.2 in 1940, evolving into an advanced axial flow design with an annular combustion chamber that developed over 11,000 lbf (49 kN). It powered early versions of the Hawker Hunter and Handley Page Victor, and every Gloster Javelin. Production was also started under licence in the United States by Wright Aeronautical as the J65, powering a number of US designs.

Design and development[edit]

Design evolution of the Sapphire started at Metropolitan-Vickers (Metrovick) in 1943 as an offshoot of the F.2 project. With the F.2 reaching flight quality at about 1,600 lbf (7,100 N), the Metrovick engineers turned to producing larger designs, both an enlarged F.2 known as the Beryl, as well as the much larger F.9 Sapphire. (The names were chosen after a decision to use gemstones for future engine names). The Beryl was soon running and eventually developed 4,000 lbf (18 kN) thrust, but the only project to select it, the Saunders-Roe SR.A/1, was cancelled.

By this point the F.9 MVSa.1 was developing about 7,500 lbf (33 kN), somewhat more than its competitor from Rolls-Royce, the Avon. A number of companies expressed interest in the F.9, and it was considered as either the main or backup powerplant for most British designs of the late '40s and early '50s.

At about the same time, Metrovick exited the jet engine industry,[1][2] and their design team was quickly acquired by Armstrong Siddeley, who already had a turbine development of their own, the ASX, but they were primarily focused on turboprops and the Metrovick team was a welcome addition.[citation needed]

Work on the F.9 continued, now renamed the ASSa.5, and was delivered at 7,500 lbf (33,000 N) ratings. This early engine was used only on the English Electric P.1.A, prototype for the famed Lightning. The fit was not entirely a happy one, and the afterburning ASSa.5R did little to address this, delivering an improved 9,200 lbf (41,000 N) "wet", but doing so in an unreliable fashion that demanded a short period of "no use" while the problems were addressed.[3] Future versions of the Lightning were powered by the Avon instead.

The engine was soon passing tests at ever-increasing thrust settings. The ASSa.6 reached 8,300 lbf (37,000 N), and was used on the Gloster Javelin FAW Mk.1, Hawker Hunter F.Mk.2 and F.Mk.5, and the prototype Sud Ouest SO 4050 Vautour. The dramatically more powerful ASSa.7 at 11,000 lbf (49 kN) was the first British engine to be rated above 10,000 lbf (44 kN), powering the Gloster Javelin FAW Mk.7, Handley Page Victor B.Mk.1 and a prototype Swiss fighter-bomber, the FFA P-16.

Afterburners of limited performance (also known as "re-heat") were also added to the ASSa.7, producing the 12,390 lbf (55,100 N) wet ASSa.7LR, used on some Gloster Javelin FAW Mk.8's. An improved model produced 15,000 lbf (67 kN) above 20,000 ft (6,100 m), appearing on other FAW Mk.8's and all FAW Mk.9's.[4]


Ministry of Supply designation of the original Metropolitan-Vickers F.9 Sapphire, derived from the Metropolitan-Vickers F.2/4 Beryl. Design work on this much larger engine started in 1943.
Metropolitan-Vickers F.9 Sapphire
Company designation for the MVSa.1
Completed a 150-hour Service Type Test in November 1951 at a sea level rating of 7,500 lbf (33.36 kN) at an s.f.c. of 0.91
Early Armstrong Siddeley developed Sapphire engines.[5]
Reheated engines fitted to the English Electric P.1A with limited success.
Later engines developed for the Gloster Javelin FAW Mk.1, Hawker Hunter F.Mk.2, F.Mk.5 and the prototype Sud Ouest SO 4050 Vautour
Rated at 11,000 lbf (49 kN), powering the Gloster Javelin FAW Mk.7, Handley Page Victor B.Mk.1 and the prototype FFA P-16.
Engines with a 12% augmentation reheat system for use above 20,000 ft (6,100 m), powering the Gloster Javelin FAW Mk.8.
Wright J65
Licence production in the United States by Wright Aeronautical



Engines on display[edit]

An Armstrong Siddeley Sapphire is on static display at the Midland Air Museum, Coventry Airport, Warwickshire.

Specifications (ASSa.7 / 7LR)[edit]

Data from [7]

General characteristics

  • Type: ASSa.7 Turbojet, ASSa.7LR Augmented turbojet
  • Length: ASSa.7 125.2 in (3,180 mm), ASSa.7LR 293 in (7,442 mm)
  • Diameter: 37.55 in (954 mm)
  • Dry weight: ASSa.7 3,050 lb (1,383 kg), ASSa.7LR 3,180 lb (1,442 kg)


  • Compressor: 13 stage axial flow
  • Combustors: Annular with 24 hockey-stick vaporisers
  • Turbine: Two stage
  • Fuel type: Aviation kerosene to DERD 2482 or DERD 2486
  • Oil system: Flood feed, minimum oil pressure 12 psi (83 kPa), tank capacity 18 imp pt (10 l), oil grade to DERD 2487.


See also[edit]

Related development
Comparable engines
Related lists



  1. ^ Depending on the sources, Metrovick either left the engine business on their own to concentrate on steam turbines, or were forced from the market by the Ministry of Supply in order to reduce the number of companies they had to deal with.
  2. ^ Gunston 1989, p.102. Note: "...the firm had decided in 1947, under Ministry pressure, to get out of aviation"
  3. ^ English Electric Lightning
  4. ^ Armstrong Siddeley Sapphire
  5. ^ a b c Taylor, John W.R. FRHistS. ARAeS (1955). Jane's All the World's Aircraft 1955-56. London: Sampson, Low, Marston & Co Ltd. 
  6. ^ In many cases the Sapphire was used on early prototypes of these aircraft and was often later replaced by the Rolls-Royce Avon, only the generic aircraft types are given.
  7. ^ Taylor, John W.R. FRHistS. ARAeS (1962). Jane's All the World's Aircraft 1962-63. London: Sampson, Low, Marston & Co Ltd. 


  • Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
  • Kay, Anthony L. (2007). Turbojet History and Development 1930-1960 1 (1st ed.). Ramsbury: The Crowood Press. ISBN 978-1-86126-912-6. 

External links[edit]