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The Armstrong Siddeley Sapphire Engine & The Wright J65 Engine

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The Armstrong Siddeley Sapphire Engine

The Saphire was a well-proven turbojet in the 8,000 lb (3,630kg) to 11,000 lb (4,990kg) thrust class and was produced in large quantities. It was the largest turbojet developed by the then Armstrong Siddeley. In the United Kingdom it was in service with the Royal Air Force on the Handley Page Victor B Mk1 bombers, all marks of the Gloster Javelin all weather fighter and also on the Hawker Hunter Mks 2 and 5 fighters. Well over 12,000 Saphires were built under license in the United States of America as the Wright J65. In service, the Saphire proved to be robust and reliable, with excellent handling qualities. Rolls Royce Saphire

The Sapphire was a 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 (71 kN). It powered versions of the Gloster Javelin, Hawker Hunter and Handley Page Victor. Production was also started under license in the United States by Curtiss-Wright as the J65, powering a number of US designs.


Design & Development


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Sapphire Engine

Design of the Sapphire started at Metropolitan-Vickers (Metrovick) in 1943. With the F.2 reaching flight quality at about 1,600 lbf, 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 being chosen after they decided 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 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 late-40s/early-50s British designs.

At about the same time Metrovick exit the industry,[1] with their design team being quickly acquired by Armstrong Siddeley. Although Armstrong Siddeley already had a turbine development of their own, the ASX, they were primarily focused on turboprops and the Metrovick team was a welcome addition.

Work on the F.9 continued, now renamed the ASSa.5, and was delivered at 7,500 lbf ratings. This early engine was used only on the EE 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 "wet", but doing so in an unreliable fashion that demanded a short period of "no use" while the problems were addressed.[2] Future versions of the Lightning would be powered by the Avon instead.

The engine was soon passing tests at ever-increasing power settings. The ASSa.6 increased power to 8,300 lbf, and powered the 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 was the first British engine to be rated above 10,000 lbf, powering the Javelin FAW Mk.7, Handley Page Victor B.Mk.1 and a prototype Swiss fighter-bomber, the FFA P-16. Afterburners of limited quality were also added to the ASSa.7, producing the 12,390 lbf wet ASSa.7LR, used on some Javelin FAW Mk.8's. An improved model produced 15,000 lbf above 20,000 ft, appearing on other FAW Mk.8's and all FAW Mk.9's.[3]


License Production

Wright purchased a license for the Sapphire in 1950, with plans to have the production lines running in 1951. However a series of delays led to its service introduction slipping a full two years, by which point the Pratt & Whitney J57 was on the market and took many of the J65's potential sales. Nevertheless once it entered production it proved to be as good as the British versions, and along with the Martin B-57, its original target, the J65 went on to power versions of the Republic F-84, Douglas A-4 and the two Lockheed XF-104 Starfighter prototypes.


Specifications (ASSa.7)

General characteristics

  • Type: turbojet
  • Length:
  • Diameter:
  • Dry weight:


  • Compressor: axial
  • Combustors: annular
  • Turbine: 1 stage


  • Thrust: 11,000 lbf
  • Power-to-weight ratio:



  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. English Electric Lightning
  3. Armstrong Siddeley Sapphire




The Wright J65 Engine


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Air Force Power Plant Laboratory worked on several foreign jet engines, including the British Sapphire (J65) and Olympus (J67), and the French Marbore (J69). The Wright J65 was US-built version of the Armstrong Siddeley Sapphire. In less than five years, the J65 went from powering the hottest American fighter in 1950, the F-84F, to being rejected as under-powered for the XF-104 in 1954.

The Sapphire was a hand tooled production of the British firm Armstrong Siddeley for which the CurtissWright Aeronautical Division at Wood Ridge NJ, had acquired a manufacturing license. However, the J65, as the Air Force version of the Sapphire was designated, was proved initially difficult to adapt to American specifications and manufacturing. Although the Wright production had been set to begin in September 1951, the J65 prototype engines consistently failed to meet USAF requirements. The new engine was also earmarked for the Republic F-84F. Due to the urgent need for improved fighter bombers since the outbreak of the Korean War, the Air Force in December 1950 selected the Buick Division of the General Motors Corporation as the second source for the Sapphire engine. In June 1952, when the Air Force finally accepted the first 2 YJ65-W-1 engines, neither had yet completed the required 150 hour qualification test.

The British Sapphire J65 engine was initially adapted by Curtiss-Wright for use in the F-84F Thunderstreak. The prototype flew in June 1950. The F-84F had a swept wing and tail instead of the straight wing-tail combination on the basic F-84. It also had a J65 turbojet engine with 7,220-pound thrust output, which gave the F model more speed than the F-86H, which was at that time the fastest American jet. Overall, the F-84F, which became operational in January 1954, was a far superior aircraft to its predecessor F-84 models.

As an intended replica of the English Electric Canberra B. Mk.2, the B-57A featured no outstanding innovations. Two Wright Aeronautical J65 turbojet engines were substituted for the Canberra's 2 Rolls Royce Avon turbojets. A Buick-built J65 was also used in the B-57 bomber. As with so many of the early jet aircraft, configuration of the B-57 was similar in concept to contemporary twin-engine propeller-driven aircraft but with jet engines replacing the reciprocating units. Power was provided by two non-afterburning J65-W-5 turbojet engines of 7200 pounds thrust each. Conventional rudders, ailerons, and elevators were used for control of the aircraft. Simple high-lift flaps were located in the wing trailing edge between the engine nacelles and the sides of the fuselage.

The FJ-3 carrier-based variant was powered by a single Wright J65-W-4 engine with 7,800 pounds thrust; it first flew in 1953. The FJ-4B Fighter used a single J-65-W-16A engine.

The A4D-1 "Skyhawk" attack aircraft was powered by a single J65-W-4 engine. The A4D-2 used the J65-W-16A. In February 1959, Douglas submitted a proposal for an A4D-5 as a follow-on to the A4D-2N. Improvements included installation of the lighter weight, 8,500 lb thrust Pratt & Whitney J52-P6A engine.

The F9F-9 was the planned designation for an F9F-8 powered by a Wright J65-W-6 engine. This aircraft was never delivered to the Navy.

The J65 steel-bladed engine had experienced a number of first-stage compressor-blade failures in service by 1955. The failures are the result of the blade ribrations and consistently occur in the second serration of the blade root., Stress analysis of the fir-tree-type roots of the first three stages of the compressor (the most critical stages from the vibration aspect) was undertaken to determine if it was possible to eliminate failures by redesigning the roots.

The XF-104 was fitted with a Wright J65 jet engine. A very long fuselage contained the cockpit and fuel cells, landing gear, and a single Wright YJ65-W-6 turbojet engine. This was supported by a pair of extremely short, anhedral supersonic wings with sharp leading edges that had to be padded to protect ground crews. The first flight was on 5 March 1954. This design had enormous promise, but subsequent flights soon revealed that the J65 could deliver a maximum speed of only Mach 1.79 (1,324 mph), approximately double that of the F-86 but still short of the Air Force’s requirement of Mach 2.0 or better. The designers soon responded with a much-refined version of the troubled plane. They stretched the already-long fuselage by 5 feet, 6 inches in order to accommodate a new General Electric J79 axial-flow engine with 4,000 pounds greater thrust.

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