Metrovick F.2
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The Metrovick F.2 was one of the earliest jet engines, and the first British design to be based on an axial compressor. Based on design work by A.A. Griffith from ideas he had developed in 1926, serious development of the F.2 didn't start until the late 1930s, by which point Frank Whittle's designs were already running. In the end the F.2 proved to be everything Griffith promised it would be; smaller than Whittle's designs, more powerful and considerably more fuel efficient. However in his drive for perfection he also ended up designing an engine that was far too complex, and it never entered production. Work did not go to waste, however, and eventually resulted in an engine design that was passed on to Armstrong Siddeley, the Sapphire.
Griffith published a seminal paper in 1926, An Aerodynamic Theory of Turbine Design, that for the first time clearly demonstrated that a gas turbine could be used as a practical, and even desirable, aircraft powerplant. The paper started by demonstrating that existing axial compressor designs were "flying stalled" due to their use of flat blades, and that dramatic improvements could be made by using airfoil designs instead, improvements that made a gas turbine practical. It went on to outline a complete compressor and turbine design, using the extra exhaust power to drive a second turbine that would power a propellor. In today's terminology the design was a turboprop. In order to prove the design, Griffith and several other engineers at the Royal Aircraft Establishment built a testbed example of the compressor in 1928 known as Anne, the machinery being built for them by Fraser and Chalmers. After Anne's successful testing they planned to follow this up with a complete engine known as Betty.
In 1929 Frank Whittle's thesis on pure jet engines was published, and sent to Griffith for comment. After pointing out an error in Whittle's math, he went on to pooh-pooh the entire concept, saying that the centrifugal compressor he used would be impractical for aircraft use due to its large frontal area, and that the use of the jet exhaust directly for power would be extremely inefficient. Whittle was heartbroken, but was convinced to patent the idea anyway. Five years later a group of investors convinced him to start work on a testbed, forming Power Jets, Ltd., and starting work on what would be England's first working jet engine.
Griffith continued development of his own concepts, eventually developing an advanced compressor design using two contrarotating stages that improved efficiency. His partner, Hayne Constant, started discussions in 1937 with Manchester-based Metropolitan-Vickers, a maker of steam turbines, to produce the new machinery. Ironically Metrovick had recently merged with British Thomson-Houston, another turbine builder who was supporting Whittle's efforts. A contract for development work was eventually given by the Air Ministry the next year, and work on Betty, also known as the B.10, started. In 1939 the team, including Metrovick engineers led by David Smith, started work on a flyable design, the F.1. Compared to the Whittle designs, the F.1 was extremely advanced, using a nine-stage compressor, annular combustion chamber, and a two-stage turbine (the second driving a propeller).
In April 1939 Whittle gave a startling demonstration of his experimental engine, the WU, running it for 20 minutes at high power. This led to a rash of contracts to build a production quality design suitable for aircraft use. Development had just started on the F.1 when Whittle started building his W.1 design, planning to install one for flight in the Gloster E.28/39 the next year. Smith decided to end development of the F.1 and move on to a pure-jet instead, starting work on the otherwise similar F.2 Freda in July 1940.
Development of the F.2 progressed rapidly, and the engine ran for the first time in November 1941. By this point there were a number of engines in development based on the Whittle concept, but the F.2 looked considerably more capable than any of them. Flyable versions, the F.2/1, received its test rating in 1942 and were flown on an Avro Lancaster test-bed on 29 June, 1943. Production quality versions were installed on the F.9/40 Gloster Meteor and flew in this form on 13 November, 1943. As expected, the engines were more powerful than the Whittle design, first delivering 1,800 lbf (8 kN) but soon scaling up to well over 2,000 lbf.
It would appear that Metrovick had a winner. Nevertheless the Air Ministry didn't order the design into production. Although the engine was technically superior to its Power Jets counterparts, it was also incredibly complex and nowhere near as reliable. In aircraft design reliability trumps performance in almost all cases, and this was one of those cases. The Meteor would be powered by the original Whittle design, now built by Rolls-Royce as the Welland, and later the slightly improved Derwent.
No one wanted the work to go to waste, and development of the F.2 continued on a version using a ten-stage compressor for additional airflow. The new F.2/4 Beryl initially developed 3,250 lbf and was installed in the Saunders-Roe SR.A/1. Thrust had already improved to 3,850 lbf for the third prototype, and eventually settled at 4,000 lbf, making it one of the most powerful engines of the era. Development of the SR.A ended in 1947, ending development of the Beryl along with it. Nevertheless a Beryl was used by Donald Campbell in his famous 1955 Bluebird K7 hydroplane in which he set seven water speed records between 1955 and 1964. Meanwhile the F.3 was developed, adding a turbine-powered fan to the rear of the engine to improve airflow and thrust at low altitudes, producing the world's first turbofan engine.
Metrovick eventually ended development of the F.2 in 1944. Development of the basic concept continued, however, eventually leading to the considerably larger F.9 Sapphire. However in 1947 the Air Ministry demanded that Metrovick get out of the jet engine business, and their design team was quickly snapped up by Armstrong Siddeley. The Sapphire became a successful design, besting its Rolls counterpart, the Avon, and design features of the Metrovick line were worked into Armstrong Siddeley's own line of axial compressor turboprops.
[edit] Notes
Depending on the sources, Metrovick either left the engine business on their own to concentrate on stream turbines, or were forced from the market by the Ministry of Supply.
[edit] Specifications (F.2/4 Beryl)
General characteristics
- Type: Turbojet
- Length: 159 in (4,039 mm)
- Diameter: 36.75 in (933 mm)
- Dry weight: 1,750 lb (790 kg)
Components
- Compressor: Axial compressor
Performance
- Thrust:
- 3,500 lbf (15.6 kN or 1,590 kgf) maximum
- 3,000 lbf (13.3 kN or 1,360 kgf) cruise
- Specific fuel consumption: 1.05 lb/(h·lbf) (107 kg/(h·kN))
- Thrust-to-weight ratio: 2.0:1 (19.6 N/kg)
