GAS TURBINES DEVELOPED IN URMSTON ?

By Terry Burnett

The introduction of Gas Turbines for model aircraft propulsion has generated considerable interest in these highly stressed aerodynamically complex IC engines.

Development of the Gas Turbine is a complicated, and, chronologically difficult story. I will attempt to whet your appetite by explaining the 'local connection,' however a brief historical overview of gas turbine development may be of interest.

Many engineers had considered the theoretical possibility of an open cycle gas turbine as a prime mover, though one of the many practical problems which dogged engineers from as early as the 17^th century was the availability of materials which could withstand temperatures in excess of 1800 degrees centigrade, together with production techniques and machining accuracy which would allow rotational speeds in excess of 10,000rpm (120,000 + in model engines); at these elevated temperatures. The late 1930's saw the development of Nimonic alloys which have high creep resistance coupled with the required mechanical strength needed at high temperatures and rotational speeds, the engineer was now encouraged to consider the possibility of the development and manufacture of a practical self-sustaining gas turbine.

A Gas Turbine is an open cycle IC engine consisting of a compressor, a combustion chamber and a turbine, this works on the principle of suck, squeeze, burn and blow.

In essence the sequence is as follows. A compressor delivers compressed air through a combustion chamber, fuel is injected into the airstream and ignited, the expanding gas is directed through a turbine wheel which rotates, as this turbine wheel is on the same shaft as the compressor the turbine drives the compressor. This is the closed loop which results in a self-sustaining gas turbine. It is the thrust from the exhausting gases, which propels the aircraft, according to Newton's law. Interestingly early schemes only considered the gas turbine as a driver for the conventional aircraft propeller.

Sir Frank Whittle is acknowledged as the first person to design and run a self sustaining gas turbine engine, his WU (Whittle Unit) spooled up for the first time on 12 April 1937, by an amazing coincidence Dr. Hans Von Ohain of Germany successfully test ran his first engine HeS1 on the test bed of the Heinkel factory a few months later, this was one night in September 1937; according to Heinkel's autobiography.

Whittle was well aware that the axial flow compressor had the potential for a mass flow far in excess of the centrifugal compressor, however as engineers and scientists had not resolved the complex aerodynamic problems the axial flow presented he took the decision to use the proven centrifugal compressor as the Herculean task achieving a self sustaining Gas turbine was all he could realistically cope with.

We will start with 'suck and squeeze': The Compressor

A compressor used in a gas turbine is not the positive displacement reciprocating type used by garages and the like, it is an 'open' type compressor, and is categorised as either centrifugal or axial flow. A centrifugal compressor impeller looks very similar to the impeller found in a domestic washing machine water pump, where as the axial flow is radically different in design, aerodynamically more complex, and will never be found in a water pump! The centrifugal compressor is limited in performance in terms of mass flow of air at discharge, where as the axial flow is only limited by aerodynamic development.

Whittle choice of a centrifugal compressor for the WU (Whittle Unit) was influenced by his association with BTH (British Thompson Houston) of Rugby who built WU, as BTH were in a position to assist with compressor design data.

It is of interest to note that by 1942 centrifugal compressors were reaching the limits of efficiency due to the efforts of a fine engineer who specialised in aerodynamics, Dr. Stanley Hooker.

Aerodynamisist Dr. Stanley Hooker hired by Ernest Hives of Roll-Royce was given the responsibility for the development of superchargers (centrifugal compressors) for aircraft engines such as the Rolls-Royce Merlin. I recommend Hookers autobiography entitled 'Not much of an engineer' this title came from a statement made by Hives during Hookers interview, reading Hookers formidable academic qualifications the plain speaking Hives remarked, “you are not much of an engineer Hooker”. Those of a certain age will remember Stanley Hooker being brought our of retirement by Rolls-Royce in 1970, this drastic move was in order to resolve the aerodynamic problems of the RB211 which pushed Rolls-Royce into near bankruptcy.

Burn : The combustion chamber.

Combustion chamber design falls into two categories, Multiple Chamber, Tubo Annular and Annular. Model engines use an annular combustion chamber and may use kerosene, diesel oil, or gas (gas is now discouraged for safety reasons). Full size engines use a form of Kerosene and in the main employ the 'Tubo Annular' combustion chamber. The combustion chamber used by Whittle was multiple chamber with reverse flow and presented tremendous challenges such as aerodynamic internal design for maximum flame temperatures and expansion of gas, materials which could withstand temperatures up to 2000 degrees centigrade. An issue was finding craftsmen who could construct the chambers from new lightweight and as yet untried materials. Fortunately Laidlaw of Glasgow who were manufacturers of steam boiler burners came up with a solution and although Whittle was reluctant to disclose the application. Laidlaw had an idea of what Whittle was up to but kept his own council. The final design was a masterpiece of the sheet metal workers art, being a reverse flow chamber, which reduced the turbine shaft length avoiding rotor transverse vibration at certain critical speeds, (due to shaft natural frequency of vibration). A later example of the Whittle engine with a sectioned view of the combustion chamber is located in the Air & Space Gallery of the Science and Industry Museum Manchester.

Blow :The Turbine wheel.

The first mention of a turbine principle comes from 'Hero' of Alexandria, circa 150BC who described an apparatus in which air or steam was forced by expansion from nozzles attached to a rotatable drum. The reaction of the departing gas exerted force on the nozzles and rotated the drum, this formed the basic principle of reaction.

The next milestone which contributed to the development of steam and gas turbines was the impulse principle, this was demonstrated in the early 16^th century by Italian engineer and scientist Giovani Branka. Branka designed a turbine which powered a machine for grinding corn, the principle of reaction was first employed in the flow path of steam turbines perfected by Charles Parsons of Newcastle in 1884, it is interesting to note that the mechanical design, and construction of early gas turbines, owes much to the steam turbine engineer. Gas turbines incorporate both principles of impulse and reaction within the stator and rotor blading.

The writer has built a model of 'Hero' turbine for those who wish to see it, also there is also a 'Hero' turbine located in the electricity gallery of the Science and Industry Museum in Manchester.

The Urmston Connection - a tribute to Dr. David Smith FRS.

Dr.David Smith was a mathematically gifted Scot living in Bowden Cheshire, employed by Metropolitan Vickers Trafford Park Manchester. David Smith had written several mathematical papers on the problems of steam turbine rotor stability and was held in deep respect for his analytical mind and use of the calculus.

The achievement for which David Smith will be best remembered was his role in the development of the first British axial flow jet engine for aircraft propulsion. I was fortunate enough to meet David Smith after his retirement. David passed away in 1986, and was described in his obituary published by the FRS as an 'intellectual giant' praise indeed from the institute.

Although he was a steam turbine design engineer within Metropolitan Vickers, David Smith, and others at the company were aware of the possibilities of the axial flow turbojet engine.

Originally, the first British axial-flow aircraft gas turbine B10 (Betty) was to have been built by the RAE (Royal Aircraft Establishment) the engines compressor was based on test data from experimental compressor 'Anne' built to a design by AA Griffith of the RAE and manufactured by Fraser and Chalmers. A senior scientist within the RAE, A.A.Griffith had published paper on gas turbine development as early as 1926, and together with Hayne Constant also of the RAE considered that the compressors of future gas turbines should be of the axial type; However, the RAE did not have the manufacturing or research capability to make this aerodynamically complex compressor work on a scale sufficient to power an aircraft.

In 1937 discussions took place between the RAE and Metropolitan Vickers chief engineer Dr. Karl Baumann who in turn appointed Dr. David Smith to lead the design, development and manufacturing team. Work started at the company the following year under an Air Ministry Contract.

The experimental non-flight engine B10 had proved successful, with a compression ratio of 2:1. B10 amazed engineers by running happily with the turbine casing glowing with a dull red heat.

As war broke out and the Trafford Park Factory became committed to war work and space was at a premium, B10 had set fire to the research facility so it was decided to extend a small overspeed test cell which had been built in some secrecy on land off Barton Dock Road Urmston Manchester with a view to relocate all gas turbine research and development. For a brief period the salt mines in Wincham had been used for engine testing, however pollution and fog from the nearby industrial town of Northwich caused contamination of the compressor blading which effected performance tests so all efforts were concentrated at 'Barton Test'.

The first flight engine F2 (Freda) ran in a test cell during December 1942, by June 1943 an F2 engine of 1800 lb static thrust was altitude tested in the tail of a Lancaster Bomber. The Lancaster which operated from the RAE Farnborough became the topic of much local discussion as it flew over the Manchester area. Interestingly the aircraft allocated by the ministry was the Lancaster prototype which proved to be most unreliable, much to the frustration of Dr. Smith and the Metrovic team.

The first aircraft to be powered by and axial flow turbojet was a Gloster F/9 40 Meteor aircraft, the flight took place at the RAE on the 13^th November 1943.

Metrovic continued turbojet development, the last flight engine being the F9 Sapphire, the design of which was handed to Armstong Siddley when Metropolitan Vickers decided to opt out of aircraft gas turbines and concentrate manufacturing and development on Industrial and Marine steam and gas turbines.

The test cells at Barton were turned over to steam turbine research and development in the early 1960’s. Dr. Smith returned to steam turbine design, although in great secrecy he was asked to assist Rolls-Royce's Dr. Stanley Hooker when Rolls engineers ran into aerodynamic problems when developing the compressor for the famous Rolls-Royce Avon gas turbine engine.

A Metrovic 'Beryl' engine was chosen by Donald Campbell for his Bluebird K7 waterspeed record attempt on Ullswater in 1955. Campbell unofficially broke the existing world record with the 'Beryl' which incidentally did not reach full power. I was fortunate in the 1970’s to work with a Metrovic ( now AEI ) engineer assigned to overhaul the engines working with the illustrious Leo Villa, Campbell’s chief engineer.

The writer worked at 'Barton Test' up until its closure in 1993, and many times did I gaze in awe at the compressor blades from failed overspeed tests, many of which were embedded 100mm deep into the railway sleepers which lined the walls of the overspeed test cell in order to protect the brickwork, and passers by.

Barton Test is still in existence, although derelict the buildings can be seen from the Parkway whilst travelling to Trafford Park...... its on the left when passing over Barton Dock Road, this building was the first to incorporate acoustic exhaust chambers and air filtration systems which are now commonplace in jet engine manufacture. I often wonder how few know the part Urmston played in the development of the modern turbojet engine.

The original F2 flight engine, experimental compressor B10 (recently refurbished for display by myself) is on show together with a 'Whittle' engine in the Air and Space Gallery of the Science & Industry Museum Manchester.

Compressor 'Anne' is displayed in the Science Museum, South Kensington, London.