Turbojet development at the RAE
Encyclopedia
Between 1936 and 1940 Alan Arnold Griffith
designed a series of turbine
engines that were built under the direction of Hayne Constant
at the Royal Aircraft Establishment
(RAE). The designs were advanced for the era, typically featuring a "two-spool" layout with high- and low-pressure compressors that individually had more stages than typical engines of the era. Although advanced, the engines were also difficult to build, and only the much simpler "Freda" design would ever see production, as the Metrovick F.2
and later the Armstrong Siddeley Sapphire. Much of the pioneering work would be later used in Rolls-Royce
designs, starting with the hugely successful Rolls-Royce Avon
.
Laboratory in South Kensington wrote a report in response to an Aeronautical Research Committee
(ARC) request about the possibilities of developing a gas turbine engine to drive a propeller
. His report was extremely negative. Given the performance of existing turbocompressors, such an engine appeared to be mechanically inefficient. In addition to high weight and poor fuel efficiency
, Stern was skeptical that there were materials available that would be suitable for use in the high-heat areas of the turbine.
Griffith, who was at this point the senior scientific officer at the RAE at Farnborough, read Stern's report and responded with a request that the National Physical Laboratory should study the materials problem. Griffiths, meanwhile, started studying the issues with compressor design. In 1926 he published An Aerodynamic Theory of Turbine Design, which noted that existing compressor designs used flat blades that were essentially "flying stalled
" and that efficiency could be dramatically improved by shaping them aerodynamically
.
In October, Griffith presented the paper to a small group from the Air Ministry and the RAE. They unanimously supported starting a development project to study Griffiths' compressor designs. Initial work started in 1927, and by 1929 this project had progressed to the point of building an extremely simple 4 inches (101.6 mm) "engine" consisting of a single-stage compressor and turbine with a single row of stators in front of each. Designed solely to test the basic concept, the rig nevertheless demonstrated superb aerodynamic efficiencies as high as 91%.
At the same the RAE team introduced the "cascade", consisting of multiple rows of compressor blades attached to flat plates. Unconvinced that the aerodynamics of a single blade in a wind tunnel
would match the real world performance of a multi-stage compressor, the cascade allowed various compressor layouts to be tested simply by moving the plates on a mounting plate inside the wind tunnel. This also allowed the angle of attack
to be easily varied by rotating the plates with respect to the airflow. According to NASA
, one of the reasons UK engine design remained ahead of the US into the 1950s was that the cascade tests and theory were widely used in the UK, while generally ignored in the US.
During this period Griffith was promoted to principal scientific officer at the Air Ministry's South Kensington Laboratory. Here he returned to theoretical work and published a report in November 1929 that outlined the design and theoretical performance of a 500 hp turbine engine driving a propeller. Contrary to Stern's earlier report, Griffith demonstrated that if the existing testbed design could be scaled up successfully, it would have performance far superior to existing piston engines.
The engine outlined in the report was quite complex, consisting primarily of a fourteen-stage "contra-flow" gas generator
. Each stage combined a compressor disk, on the inside, with a turbine, on the outside, and were free to rotate relative to each other on a central shaft. Air would enter at the front of the engine in the center where the compressor half was located, passing through the contra-rotating stages until it reached the other end of the engine where it was ignited. The airflow then reversed direction at the back of engine and flowed back through the outer half of the disks, powering the turbines, eventually flowing out of a front-mounted exhaust. Each turbine stage powered only its associated compressor, and as they were free to rotate on the central shaft, no mechanical power was produced. Power would have to be extracted externally through a free turbine.
In April 1930 Griffith proposed building a testbed version of his design, but the ARC concluded that it was simply too far beyond the current state of the art
. In 1931 Griffith returned to the RAE. At some point during this period he was given Frank Whittle
's engine design using centrifugal compressor
s and returned a negative response; after pointing out minor errors in the calculations he stated that the centrifugal design was inefficient and its large frontal size would make it unsuitable for aircraft use. He also stated that Whittle's idea of using the hot exhaust directly for thrust was inefficient and would not match the performance of existing engines, in spite of Whittle concentrating on high-speed use where it would be more effective (propellers suffer a dramatic drop in efficiency below the speed of sound
(M.1
)).
, returned to the turbine engine concept after learning that Whittle was going ahead with his designs at his new company, Power Jets
. Tizard convinced Hayne Constant
to return to the RAE from Imperial College to assist with the development of Griffith's designs. They set about building a 6 inches (152.4 mm) version of the inner portion of the Griffith engine, known as Anne, consisting of the hub and eight compressor stages without the outer turbine portions. On its first run a faulty seal allowed the oil to drain from the engine, and the blading was stripped off after only 30 seconds of running. In 1937, while Anne was being built, Griffith visited Jacob Ackeret of Brown Boveri, another turbine pioneer, and became convinced that the compressor/stator design was superior to his own contra-rotating "all compressor" concept. After it was damaged, Anne was rebuilt using the new layout and started running again in October 1939. It continued to be used in tests until it was destroyed in a German bombing raid by KG 54 on 13 August 1940, "Eagle Day".
At this point there was some debate as to how to proceed after Anne. The team, which included Griffith, Constant, Taffy Howell and D. Carter, studied a number of approaches to building a complete engine, as opposed to the compressor-only Anne. They decided that the only reasonable solution to low compressor efficiency was to use what would today be referred to as a "two-spool" design, with separate high and low-pressure compressors. However the team considered the concentric shafts needed for this layout to be too complex (although the reasons for this are not clear), and there was some consideration of using two completely separate compressor/turbine sections "side-by-side". Eventually they settled on building one of the two engines that would be used in such a layout, in order to study the mechanical problems.
The resulting Betty design consisted of a nine-stage compressor 1 ½ feet in diameter attached through a coupling to a four-stage turbine. A considerable amount of design effort went into various devices to relieve mechanical stress due to thermal expansion. For instance, the compressor and turbine blading was attached to large hollow rotors which they felt would expand and contract more like the outer engine casing than a series of solid disks as used in Anne. The ends of the turbine rotor were closed with double-cones, which had enough flexibility to expand with the rotor while still remaining solidly attached to the power shaft. The compressor and turbine were attached to each other through another rotor, allowing the two sections to be easily separated. The compressed air output was piped to an inlet cage on the turbine section. Finally the turbine was water-cooled, as it was believed that even the latest high-temperature alloys like Hadfield's ERA/ATV would eventually deform under constant operation.
Betty, also known as B.10, was first tested as separate compressor and turbine sections using steam to power them. In October 1940 they were run as a single complete engine for the first time. During testing it was decided that the water cooling was not needed, and was replaced by an air cooling system, and the turbine was allowed to run red hot at 675 C. Experiments with Betty convinced the team that any sort of piping between sections led to unacceptable losses, so the "distributed engine" concept Betty was built to test would likely be inefficient. At the same time it was decided that overall pressure ratio
s on the order of 5:1 would be sufficient for near-term engines, so it was decided to abandon the two-spool approach for the time being.
that would outperform existing piston engines except at very low altitudes. Further, continued improvements in these metals would allow improvements in compression ratio
s that would lead to it being completely superior to piston engines in all ways. The report also pointed out that such an engine would be considerably less complex than a piston engine of similar power, and therefore more reliable.
Based on the work with Betty and Constant's report, ARC gave the team the go-ahead to build a complete turboprop engine. The new D.11 Doris design consisted of an enlarged Betty-like 17-stage compressor/ 8-stage turbine section, and a mechanically separate 5-stage low-pressure turbine to drive the propeller. Designed to provide about 2,000 hp, construction of Doris started in 1940.
By this point in time Whittle's centrifugal-compressor designs were fully operational, and plans were underway to start production of early models. The progress had been so swift that Whittle's argument that the centrifugal layout was mechanically superior than the axial designs appeared to be borne out. Adding to their problems, in June 1939 Griffith left the team and started work at Rolls-Royce. At Rolls he returned to his earlier "contraflow" designs and eventually produced such a design in 1944, but the concept was abandoned as being too complex.
So even while Doris was being built, Whittle's successes meant it was considered outdated, and work proceeded slowly. It was not until 1941 that the Doris compressor started running, and in testing it demonstrated a number of problems related to high-speed airflow that could not be tested in the earlier cascade wind tunnel system. A new high-speed version was constructed to test these issues, and new blading provided to address the problems were added later in 1941. The Doris concept was then abandoned.
Freda proved successful, and in December 1939 was fitted with a turbine section to become the first self-running axial turbojet in England, the F.1, providing 2,150 lbf. Attention immediately turned to a slightly larger design, the F.1A of 2,690 lbf. There were a number of detail changes including the removal of water cooling for the turbine and various enlargements to increase the mass flow from the F.1's 38 lb/s to 47.5 lb/s, closer to the original Freda design concept.
As attention turned to a production design, Constant started organizing industrial partners with the manufacturing capability to set up serial production. In July 1940 Metropolitan-Vickers
(Metrovick) joined the effort, as they were a major steam turbine manufacturer and would be ideally suited to rapid scale-up. The F.1A was turned over to Metrovick in July 1940, and a production effort started as the F.2.
, and eventually became the ASX. They also worked with the British General Electric Company on a series of axial compressor designs for other uses, and there was some exploration of axial-compressor based supercharger
s known as E.5. By this point, however, the British industrial companies had taken over much of the research and development effort, and the RAE team was no longer vital to continued development. It was later folded into the nationalized Power Jets to form the National Gas Turbine Establishment
.
None of the RAE designs would go on to be a success on their own. The F.2 design was not put into production, although an enlarged version was very successful as the Armstrong Siddeley Sapphire. Griffith's complex designs at Rolls never worked properly and were abandoned, but he turned his attention to the simpler F.2-like AJ.65 design and produced the even more successful Rolls-Royce Avon
, and later to the world's first turbofan
, the Rolls-Royce Conway
.
Alan Arnold Griffith
Alan Arnold Griffith was an English engineer, who, among many other contributions, is best known for his work on stress and fracture in metals that is now known as metal fatigue, as well as being one of the first to develop a strong theoretical basis for the jet engine.-Early work:A. A...
designed a series of turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
engines that were built under the direction of Hayne Constant
Hayne Constant
Hayne Constant, C.B., C.B.E., F.R.S, F.R.Ae.S. was an English mechanical and aeronautical engineer who developed jet engines during World War II....
at the Royal Aircraft Establishment
Royal Aircraft Establishment
The Royal Aircraft Establishment , was a British research establishment, known by several different names during its history, that eventually came under the aegis of the UK Ministry of Defence , before finally losing its identity in mergers with other institutions.The first site was at Farnborough...
(RAE). The designs were advanced for the era, typically featuring a "two-spool" layout with high- and low-pressure compressors that individually had more stages than typical engines of the era. Although advanced, the engines were also difficult to build, and only the much simpler "Freda" design would ever see production, as the Metrovick F.2
Metrovick F.2
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...
and later the Armstrong Siddeley Sapphire. Much of the pioneering work would be later used in Rolls-Royce
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....
designs, starting with the hugely successful Rolls-Royce Avon
Rolls-Royce Avon
|-See also:-Bibliography:* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:**** a 1955 Flight article on the development of the Avon...
.
Early work
In 1920 W.J. Stern of the Air MinistryAir Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...
Laboratory in South Kensington wrote a report in response to an Aeronautical Research Committee
Aeronautical Research Committee
The Aeronautical Research Committee was a UK government committee established in 1919 in order to coordinate aeronautical research and education following World War I...
(ARC) request about the possibilities of developing a gas turbine engine to drive a propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
. His report was extremely negative. Given the performance of existing turbocompressors, such an engine appeared to be mechanically inefficient. In addition to high weight and poor fuel efficiency
Fuel efficiency
Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...
, Stern was skeptical that there were materials available that would be suitable for use in the high-heat areas of the turbine.
Griffith, who was at this point the senior scientific officer at the RAE at Farnborough, read Stern's report and responded with a request that the National Physical Laboratory should study the materials problem. Griffiths, meanwhile, started studying the issues with compressor design. In 1926 he published An Aerodynamic Theory of Turbine Design, which noted that existing compressor designs used flat blades that were essentially "flying stalled
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
" and that efficiency could be dramatically improved by shaping them aerodynamically
Aerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
.
In October, Griffith presented the paper to a small group from the Air Ministry and the RAE. They unanimously supported starting a development project to study Griffiths' compressor designs. Initial work started in 1927, and by 1929 this project had progressed to the point of building an extremely simple 4 inches (101.6 mm) "engine" consisting of a single-stage compressor and turbine with a single row of stators in front of each. Designed solely to test the basic concept, the rig nevertheless demonstrated superb aerodynamic efficiencies as high as 91%.
At the same the RAE team introduced the "cascade", consisting of multiple rows of compressor blades attached to flat plates. Unconvinced that the aerodynamics of a single blade in a wind tunnel
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
would match the real world performance of a multi-stage compressor, the cascade allowed various compressor layouts to be tested simply by moving the plates on a mounting plate inside the wind tunnel. This also allowed the angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
to be easily varied by rotating the plates with respect to the airflow. According to NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
, one of the reasons UK engine design remained ahead of the US into the 1950s was that the cascade tests and theory were widely used in the UK, while generally ignored in the US.
During this period Griffith was promoted to principal scientific officer at the Air Ministry's South Kensington Laboratory. Here he returned to theoretical work and published a report in November 1929 that outlined the design and theoretical performance of a 500 hp turbine engine driving a propeller. Contrary to Stern's earlier report, Griffith demonstrated that if the existing testbed design could be scaled up successfully, it would have performance far superior to existing piston engines.
The engine outlined in the report was quite complex, consisting primarily of a fourteen-stage "contra-flow" gas generator
Gas generator
A gas generator usually refers to a device, often similar to a solid rocket or a liquid rocket that burns to produce large volumes of relatively cool gas, instead of maximizing the temperature and specific impulse. The low temperature allows the gas to be put to use more easily in many...
. Each stage combined a compressor disk, on the inside, with a turbine, on the outside, and were free to rotate relative to each other on a central shaft. Air would enter at the front of the engine in the center where the compressor half was located, passing through the contra-rotating stages until it reached the other end of the engine where it was ignited. The airflow then reversed direction at the back of engine and flowed back through the outer half of the disks, powering the turbines, eventually flowing out of a front-mounted exhaust. Each turbine stage powered only its associated compressor, and as they were free to rotate on the central shaft, no mechanical power was produced. Power would have to be extracted externally through a free turbine.
In April 1930 Griffith proposed building a testbed version of his design, but the ARC concluded that it was simply too far beyond the current state of the art
State of the art
The state of the art is the highest level of development, as of a device, technique, or scientific field, achieved at a particular time. It also refers to the level of development reached at any particular time as a result of the latest methodologies employed.- Origin :The earliest use of the term...
. In 1931 Griffith returned to the RAE. At some point during this period he was given Frank Whittle
Frank Whittle
Air Commodore Sir Frank Whittle, OM, KBE, CB, FRS, Hon FRAeS was a British Royal Air Force engineer officer. He is credited with independently inventing the turbojet engine Air Commodore Sir Frank Whittle, OM, KBE, CB, FRS, Hon FRAeS (1 June 1907 – 9 August 1996) was a British Royal Air...
's engine design using centrifugal compressor
Centrifugal compressor
Centrifugal compressors, sometimes termed radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.The idealized compressive dynamic turbo-machine achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller...
s and returned a negative response; after pointing out minor errors in the calculations he stated that the centrifugal design was inefficient and its large frontal size would make it unsuitable for aircraft use. He also stated that Whittle's idea of using the hot exhaust directly for thrust was inefficient and would not match the performance of existing engines, in spite of Whittle concentrating on high-speed use where it would be more effective (propellers suffer a dramatic drop in efficiency below the speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
(M.1
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
)).
Early designs
In 1936 ARC, now under the direction of Henry TizardHenry Tizard
Sir Henry Thomas Tizard FRS was an English chemist and inventor and past Rector of Imperial College....
, returned to the turbine engine concept after learning that Whittle was going ahead with his designs at his new company, Power Jets
Power Jets
Power Jets Ltd was a United Kingdom company set up by Frank Whittle for the purpose of designing and manufacturing jet engines.-History:Founded on January 27, 1936, the company consisted of Whittle, Rolf Dudley-Williams, James Collingwood Tinling, and Lancelot Law Whyte of investment bankers O T...
. Tizard convinced Hayne Constant
Hayne Constant
Hayne Constant, C.B., C.B.E., F.R.S, F.R.Ae.S. was an English mechanical and aeronautical engineer who developed jet engines during World War II....
to return to the RAE from Imperial College to assist with the development of Griffith's designs. They set about building a 6 inches (152.4 mm) version of the inner portion of the Griffith engine, known as Anne, consisting of the hub and eight compressor stages without the outer turbine portions. On its first run a faulty seal allowed the oil to drain from the engine, and the blading was stripped off after only 30 seconds of running. In 1937, while Anne was being built, Griffith visited Jacob Ackeret of Brown Boveri, another turbine pioneer, and became convinced that the compressor/stator design was superior to his own contra-rotating "all compressor" concept. After it was damaged, Anne was rebuilt using the new layout and started running again in October 1939. It continued to be used in tests until it was destroyed in a German bombing raid by KG 54 on 13 August 1940, "Eagle Day".
At this point there was some debate as to how to proceed after Anne. The team, which included Griffith, Constant, Taffy Howell and D. Carter, studied a number of approaches to building a complete engine, as opposed to the compressor-only Anne. They decided that the only reasonable solution to low compressor efficiency was to use what would today be referred to as a "two-spool" design, with separate high and low-pressure compressors. However the team considered the concentric shafts needed for this layout to be too complex (although the reasons for this are not clear), and there was some consideration of using two completely separate compressor/turbine sections "side-by-side". Eventually they settled on building one of the two engines that would be used in such a layout, in order to study the mechanical problems.
The resulting Betty design consisted of a nine-stage compressor 1 ½ feet in diameter attached through a coupling to a four-stage turbine. A considerable amount of design effort went into various devices to relieve mechanical stress due to thermal expansion. For instance, the compressor and turbine blading was attached to large hollow rotors which they felt would expand and contract more like the outer engine casing than a series of solid disks as used in Anne. The ends of the turbine rotor were closed with double-cones, which had enough flexibility to expand with the rotor while still remaining solidly attached to the power shaft. The compressor and turbine were attached to each other through another rotor, allowing the two sections to be easily separated. The compressed air output was piped to an inlet cage on the turbine section. Finally the turbine was water-cooled, as it was believed that even the latest high-temperature alloys like Hadfield's ERA/ATV would eventually deform under constant operation.
Betty, also known as B.10, was first tested as separate compressor and turbine sections using steam to power them. In October 1940 they were run as a single complete engine for the first time. During testing it was decided that the water cooling was not needed, and was replaced by an air cooling system, and the turbine was allowed to run red hot at 675 C. Experiments with Betty convinced the team that any sort of piping between sections led to unacceptable losses, so the "distributed engine" concept Betty was built to test would likely be inefficient. At the same time it was decided that overall pressure ratio
Overall pressure ratio
In aeronautical engineering, the term overall pressure ratio is defined as the ratio of the stagnation pressure as measured at the front and rear of the compressor of a gas turbine engine...
s on the order of 5:1 would be sufficient for near-term engines, so it was decided to abandon the two-spool approach for the time being.
A dead-end
During construction, Constant produced a new report, The internal combustion turbine as a prime mover for aircraft, RAE Note E.3546. By this point several high-temperature alloys had become available with creep strength up to 700 °C, and Constant demonstrated that using these materials in an engine would produce what would now be called a turbopropTurboprop
A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...
that would outperform existing piston engines except at very low altitudes. Further, continued improvements in these metals would allow improvements in compression ratio
Compression ratio
The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...
s that would lead to it being completely superior to piston engines in all ways. The report also pointed out that such an engine would be considerably less complex than a piston engine of similar power, and therefore more reliable.
Based on the work with Betty and Constant's report, ARC gave the team the go-ahead to build a complete turboprop engine. The new D.11 Doris design consisted of an enlarged Betty-like 17-stage compressor/ 8-stage turbine section, and a mechanically separate 5-stage low-pressure turbine to drive the propeller. Designed to provide about 2,000 hp, construction of Doris started in 1940.
By this point in time Whittle's centrifugal-compressor designs were fully operational, and plans were underway to start production of early models. The progress had been so swift that Whittle's argument that the centrifugal layout was mechanically superior than the axial designs appeared to be borne out. Adding to their problems, in June 1939 Griffith left the team and started work at Rolls-Royce. At Rolls he returned to his earlier "contraflow" designs and eventually produced such a design in 1944, but the concept was abandoned as being too complex.
So even while Doris was being built, Whittle's successes meant it was considered outdated, and work proceeded slowly. It was not until 1941 that the Doris compressor started running, and in testing it demonstrated a number of problems related to high-speed airflow that could not be tested in the earlier cascade wind tunnel system. A new high-speed version was constructed to test these issues, and new blading provided to address the problems were added later in 1941. The Doris concept was then abandoned.
The F.2
Before construction started on Doris the RAE team had already turned their attention to the problem of delivering a usable "pure-jet" engine as quickly as possible. The earlier designs had been built with the assumption that overall airflow should be kept as low as possible and that the energy would be extracted through a propeller. This was not appropriate for a pure-jet, where airflow is also providing the thrust. A new 9-stage compressor section known as Freda was designed, increasing in size to just over 22 inches in diameter and providing 50 lb/s airflow and a compression ratio of about 4:1.Freda proved successful, and in December 1939 was fitted with a turbine section to become the first self-running axial turbojet in England, the F.1, providing 2,150 lbf. Attention immediately turned to a slightly larger design, the F.1A of 2,690 lbf. There were a number of detail changes including the removal of water cooling for the turbine and various enlargements to increase the mass flow from the F.1's 38 lb/s to 47.5 lb/s, closer to the original Freda design concept.
As attention turned to a production design, Constant started organizing industrial partners with the manufacturing capability to set up serial production. In July 1940 Metropolitan-Vickers
Metropolitan-Vickers
Metropolitan-Vickers, Metrovick, or Metrovicks, was a British heavy electrical engineering company of the early-to-mid 20th century formerly known as British Westinghouse. Highly diversified, they were particularly well known for their industrial electrical equipment such as generators, steam...
(Metrovick) joined the effort, as they were a major steam turbine manufacturer and would be ideally suited to rapid scale-up. The F.1A was turned over to Metrovick in July 1940, and a production effort started as the F.2.
Further work
The RAE continued working on axial compressor design after the F.2 success. The original Freda compressor was later enlarged into Sarah with the addition of a further five low-pressure stages as part of a collaboration with Armstrong SiddeleyArmstrong Siddeley
Armstrong Siddeley was a British engineering group that operated during the first half of the 20th century. It was formed in 1919 and is best known for the production of luxury motor cars and aircraft engines.-Siddeley Autocars:...
, and eventually became the ASX. They also worked with the British General Electric Company on a series of axial compressor designs for other uses, and there was some exploration of axial-compressor based supercharger
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
s known as E.5. By this point, however, the British industrial companies had taken over much of the research and development effort, and the RAE team was no longer vital to continued development. It was later folded into the nationalized Power Jets to form the National Gas Turbine Establishment
National Gas Turbine Establishment
The National Gas Turbine Establishment in Fleet, part of the Royal Aircraft Establishment , UK was the prime site in the UK for design and development of gas turbine and jet engines. It was created by merging the design teams of Frank Whittle's Power Jets and the RAE turbine development team run...
.
None of the RAE designs would go on to be a success on their own. The F.2 design was not put into production, although an enlarged version was very successful as the Armstrong Siddeley Sapphire. Griffith's complex designs at Rolls never worked properly and were abandoned, but he turned his attention to the simpler F.2-like AJ.65 design and produced the even more successful Rolls-Royce Avon
Rolls-Royce Avon
|-See also:-Bibliography:* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:**** a 1955 Flight article on the development of the Avon...
, and later to the world's first turbofan
Turbofan
The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan...
, the Rolls-Royce Conway
Rolls-Royce Conway
The Rolls-Royce RB.80 Conway was the first by-pass engine in the world to enter service. Development started at Rolls-Royce in the 1940s, but it was used only briefly in the late 1950s and early 1960s before other turbofan designs were introduced that replaced it. The Conway powered versions of...
.