Metropolitan-Vickers F.2

F.2/Beryl
Beryl engine preserved at Solent Sky Museum
Type	Turbojet
Manufacturer	Metropolitan-Vickers
First run	1941
Major applications	Saunders-Roe SR.A/1

The Metropolitan-Vickers F.2 was an early turbojet engine and the first British design to be based on an axial-flow compressor. It was considered too unreliable for use during the war, and never entered production. The potential of the engine and the investment did not go to waste, however, and eventually resulted in an engine design that was passed on by Metropolitan-Vickers ("Metrovick") when they left the gas turbine business to Armstrong Siddeley; as the Sapphire.

Development

Alan Arnold 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 mathematics, he went on to deride 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 distraught, but was convinced that he should patent the idea anyway. Five years later a group of investors persuaded him to start work on what would be the first working British jet engine.

Griffith continued development of his own concepts, eventually developing an advanced compressor design using two contra-rotating stages that improved efficiency. His partner, Hayne Constant, started discussions in 1937 with Manchester-based Metrovick, a maker of steam turbines, to produce the new machinery. Incidentally, Metrovick had recently merged with British Thomson-Houston, another turbine builder who were supporting Whittle's efforts.

F.1

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 centrifugal-flow Whittle designs, the F.1 was extremely advanced, using a nine-stage axial 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.

F.2 Freda

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 (the first prototype Lancaster, s/n BT308) on 29 June 1943, mounted in the rear fuselage. Production quality versions were tested on the F.9/40M (Gloster Meteor) s/n DG204/G which made its first flight on November 13, 1943. These were installed in Messerschmitt Me 262 type underslung nacelles.

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 (8.9 kN). (Around this time, the Whittle W.2B was developing 1,600 lbf (7.11 kN)). However, the engine suffered from a number of problems that cast doubts on its reliability. These were primarily due to hot spots building up on the turbine bearing and combustion chamber. The latter, in turn, caused warping and fractures of the turbine inlet nozzles.

F.2/2

To address these problems, in August 1942 a minor redesign delivered the F.2/2, which changed the turbine material from Rex 75 to Nimonic 75, and lengthened the combustion chamber by 6 inches (150 mm). Thrust was improved to 2,400 lbf (11,000 N) static, but the problems with overheating remained.

F.2/3

Another attempt to solve the overheating problems resulted in the more highly modified F.2/3 during 1943. This version replaced the original annular combustion chamber with can-type burners like those on the Whittle designs. This appears to have solved the problems, raising the thrust to 2,700 lbf (12,000 N) in the process. However, by this time it was decided to move on to a much more powerful version of the engine.

F.2/4 Beryl

Development of the F.2 continued on a version using a ten-stage compressor for additional airflow. The new F.2/4 - the Beryl - initially developed 3,250 lbf (14.45 kN) and was test flown in Avro Lancaster Mk.II s/n LL735 before being installed in the Saunders-Roe SR.A/1 flying boat fighter. Thrust had already improved to 3,850 lbf (17.1 kN) for the third prototype, and eventually settled at 4,000 lbf (17.8 kN). In comparison, the Derwent developed 10.9 kN in its ultimate form; making the Beryl one of the most powerful engines of the era. Development of the SR.A/1 ended in 1947, ending development of the Beryl along with it. Nevertheless a Beryl from the SR.A/1 prototype was removed and used by Donald Campbell in his famous 1955 Bluebird K7 hydroplane in which he set seven water speed records between 1955 and 1964.

F.3

In 1942 MV started work on thrust augmentation, or what would today be called a turboprop or ultra-high bypass turbofan. Using a stock F.2/2, they added a section to the rear of the engine that contained four contra-rotating turbines attached to two contra-rotating propellers. The project was generally successful, raising thrust from 2,400 lbf (11,000 N) to 4,000 lbf (18 kN) for a relatively small increase in weight. More importantly, specific fuel consumption fell from 1.05 to 0.65, which was the true aim of the project. Additionally, the team noticed that the cold air from the propellers mixed with the hot exhaust from the engine, resulting in a marked decrease in noise levels, the first time this effect was recorded (it was re-discovered during a major NASA project in the 1960s).

Although the F.3 progressed nicely, development was curtailed during the war. When the war ended the F.2/2 was no longer a going concern, so the same ideas were applied to the current F.2/4 instead.

F.5

Following on where the F.3 left off, the F.5 was a version of the F.2/4 with a thrust augmenter added. Thrust for this version was 4,710 lbf (21,000 N), although it weighed 100 lb (45 kg) less than the F.3. The company cancelled development when they sold their gas turbine business to Armstrong Siddeley in 1946.

F.9 Sapphire

Main article: Armstrong Siddeley Sapphire

Development of the F.2 ended in 1944. Development of the basic concept continued, however, eventually leading to the considerably larger F.9 Sapphire. However, in 1947, Metrovick left jet engine production - encouraged or forced by the Air Ministry^{[citation needed]}5.^{[neutrality is disputed]} - and their design team moved to Armstrong Siddeley. The Sapphire matured into a successful design, initially besting the power of its Rolls-Royce contemporary, the Avon. Design features of the Metrovick line were worked into Armstrong Siddeley's own line of axial compressor turboprops, although Armstrong Siddeley dropped Metrovick's use of gemstone names for their engines in favour of continuing with animal names in particular snakes.

An example of the prototype engine can be found in the Science Museum Flight Gallery in London.

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

• Maximum 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)