Armstrong Siddeley Sapphire - Design and Development

Design and Development

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 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 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 late-40s/early-50s British designs.

At about the same time, Metrovick exited the jet engine industry, 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 (33,000 N) 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 (41,000 N) "wet", but doing so in an unreliable fashion that demanded a short period of "no use" while the problems were addressed. 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 (37,000 N), 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 (49 kN) was the first British engine to be rated above 10,000 lbf (44 kN), 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 (55,100 N) wet ASSa.7LR, used on some 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.