Developing The Jet Engine

By May 1941, Glosters had made the E. 28/39 test aircraft – a single-engine, single-seater machine – and the engine was deemed to be ready for flight at about 800 lb of thrust. The first flight trials were so successful and dramatic that Whittle’s programme was stepped up by the Government and the design of the Meteor, known as the F. 9/40, was pushed ahead. Whittle was asked to design the W. 2 engine with a thrust of 1,600 lb for this new twin-engined fighter.

At the same time, arrangements for the production of the W. 2 were put in hand. The Rover Company was asked to tool up at Bankfield Shed, Barnoldswick, on the Yorkshire/Lancashire border, to produce 20 engines per month. Design, development and all technical details were to remain with Whittle at Lutterworth.

The only changes that Rovers were allowed to make were modifications to ease production.

The established engine makers – Rolls-Royce, Bristol, Armstrong Siddeley – took little interest in Whittle’s work, largely because they were used to thinking in terms of horsepower, whereas the jet engine gave thrust. One thousand horsepower sounds an awful lot more than 1,000 lb of thrust, but at 300 mph and with the current propeller efficiency of around 75 per cent, the two are identical – 1 lb of thrust equals 1 bhp.

The penny dropped with Rolls-Royce in 1940. In August of that year, the director and general manager of Rolls-Royce, Ernest Hives (who later became Lord Hives and chairman of the company) visited Lutterworth and offered to help Whittle in the manufacture of components. Thus, the collaboration between Power Jets and Rolls-Royce began.

At this time, Whittle’s new engine, the W. 2, was beset by compressor surging. This prevented the full 1,600 lb design thrust of the engine from being achieved. In fact, Whittle was unable to run the engine above about 1,000 lb of thrust.

Surging is caused by the capacity of the compressor not matching the requirements of the turbine: as the throttle is opened a point is reached when the airflow through the compressor reverses itself and flows backwards out of the intake. The result is a fearful bang and flames from the intake. There is also a sharp rise in jet pipe temperature which is bad for the turbine blades.

No test rig in the country was capable of running Whittle’s compressor independently of the engine to determine its characteristics, as was the normal procedure on piston engine superchargers. Consequently, Whittle was working in the dark and was reduced to making ad hoc modifications to the compressor in an effort to cure the problem. That he finally succeeded speaks volumes for his powers of analysis and his grasp of the fundamentals of compressor performance.

To assist him, Rolls-Royce built a compressor test rig at Derby in 1941. On this, the W. 2 compressor could be driven at 17,000 rpm by a 2,000 hp Vulture piston engine via a step-up gear. This rig made the first practical contribution by Rolls-Royce to the development of the jet engine.

Eliminating production problems

The year 1942 was not a good one for Whittle. Not only was he beset by compressor surging but he also had many mechanical problems, the chief of which was the failure of turbine blades after a few hours’ running. The Rover Company was waiting for an engine specification to be produced at Barnoldswick and was breathing down his neck. Contrary to their terms of reference, Rovers began to modify the engine in an effort to get it right. This was unsuccessful and led to very strained relations with Whittle.

Although most changes made by Rovers did not improve the performance, they necessitated a new nomenclature for the engine. It became known as the W2B/23 – or, locally, the 8. 23. This engine was later named the Welland. One move put in hand by Rovers – namely, skewing the turbine blades 5° in the disc – did have a beneficial effect on performance and in March 1943 an engine completed a satisfactory 25-hour test at the full design rating of 1,600 lb.

Lord Hives was watching from the sidelines and in November 1942 he made his move. He was a great friend of S. B. Wilks, the managing director of the Rover company. At dinner at the Swan & Royal Hotel at Clitheroe, he arranged with Wilks to swap the Rolls-Royce tank engine factory at Nottingham for the jet engine activities at Barnoldswick.

Both men were well satisfied with the deal. It allowed Rolls-Royce to take over Barnoldswick on April 1, 1943, although in practice the company took control earlier, in January. Rover staff were given the option of going with their parent company or joining Rolls-Royce; about half opted to stay.

The next move by Lord Hives was equally dramatic. He decreed that the Whittle W2B/23 engine was far from ready for production and that the factory at Barnoldswick should concentrate entirely on the finalisation of the engine and further developments. When production of the engine became possible, this would be done elsewhere.

The first flight tests

Rolls-Royce had always laid great emphasis on the necessity for testing in flight any aero-engine and its installation features. To this end, the Hucknall flight test establishment had been formed prior to World War II – primarily, of course, to test the Merlin in its various aircraft.

The Whittle engine first flew in May 1941 in the single-engined Gloster E. 28/39 aircraft. Although very suitable for demonstrating the remarkable advantages of the gas turbine combined with jet propulsion, the E. 28/39 was not suitable for endurance testing or for the measurement of engine performance.

A Wellington bomber was therefore modified by removing the rear gun turret and installing in its place a B. 23 engine with side intakes. Flights of several hours’ duration could be made and the limitation on the possible engine measurements was removed. This modified Wellington first flew at the end of 1942 and the aircraft did sterling work in establishing the flight reliability of the B. 23 engine.

In the meantime, the twin-engined F9/40 – later known as the Meteor – was being made at Gloucester and the B. 23 flew in the Meteor, at 1,400 lb thrust, on June 12, 1943. After that, progress was rapid and the engine was soon flying at its full performance. in October 1943, the B. 23, now named the Welland, was put into small-scale and limited production at Barnoldswick and deliveries began in May 1944. However, a new factory at Newcastle-under-Lyme was completed in 1944 and production was then transferred there. Only about 100 B. 23 engines were produced at Barnoldswick and delivered to Glosters – a small number in comparison with the peak rate of 1,000 Merlins a week that was attained (though not all at the same factory).

The first production squadron of Meteors was delivered to 616 Squadron of the RAF in July 1944. They were deployed against the flying bombs from Manston in Kent and shot their first one down in August 1944.

Developing the Derwent I

As the performance and reliability of the B. 23 engine became established, the company began to consider the next step forward the 2,000 lb thrust B. 37-1, which was named the Derwent I.

Virtually all that was required to increase the thrust of the B. 23 by 25 per cent to 2,000 lb was a new diffuser, which had 20 vanes, and a 25 per cent larger turbine blade to pass the increased airflow. The impeller dimensions were unchanged, but intake swirl vanes were deleted because they had proved unreliable on the B. 23 and they were (erroneously) regarded as unnecessary- not being a feature of any other supercharger.

Their deletion caused a loss of compressor efficiency, from 75 per cent on the B. 23 to 70 per cent on the Derwent I. This necessitated an increase in combustion temperature, which went up from 1,027°K to 1,116°K, and there was a corresponding increase in specific fuel consumption from 1. 083 to 1. 178. Nevertheless, the engine ran satisfactorily and gave the specified 2,000 lb thrust. On later Marks of the engine, the intake swirl vanes were replaced with great benefit to the performance.

It was also decided to adopt straight-through combustion chambers which were a great improvement. The complicated sheet metal components of the reverse-flow type were eliminated and expansion joints were incorporated which eased metal distortion and cracking problems.

Meteors with Derwent I engines at 2,000 lb of thrust were sent to France to back Montgomery’s army and actually got as far as Eindhoven before being stopped so that none would fall into the hands of the Germans or the Russians. They gave a great boost to the morale of the RAF and the British Army – who had already been exposed to the German equivalent, the Me. 262

The speed of the Meteor with the B. 23 was about 420 mph at sea level and this increased to 470 mph with the Derwent I. The design of the B. 37-1 was begun on April 1, 1943 and the first engine went to test on July 29, 1943. The first 100-hour test was completed by October 18, 1943 and consideration was immediately given to its production. These phenomenally short times set the standard for all future work.

Barnoldswick was now wholly engaged in experimental work and the new factory at Newcastle-under-Lyme was tooled to produce the Derwent I. Five hundred Derwent I engines were made there before the factory was closed at the end of the war.

Cheering the Nene

Early in 1944 the Ministry of Aircraft Production asked Rolls-Royce to design an engine of 4,200 lb thrust. The first studies were designated the RB. 40. Following refinement, this became the B. 41 and, ultimately, the Nene. It was aimed at 5,000 lb thrust. The impeller was 28. 8 in. in diameter, compared to the Derwent I of 20. 68 in. , and the airflow was set at 80 lb/sec.

Great credit must go to the designers, because despite the 40 per cent increase in impeller diameter, the engine overall diameter increased only from 41. 5 in. to 49. 5 in. , i. e. by 20 per cent. Otherwise, the engine incorporated all that had been learnt from the Derwent and included a modified compressor casing which eliminated cracking and was more efficient aero-dynamically.

The design of the B. 41 was begun on May 1, 1944 and on October 27 the first engine ran on the test bed. As usual, there were various snags, the principal one being that the engine would not ‘light up’ on the conventional igniter. The igniter was unscrewed and an acetylene welding torch was inserted which did the trick, and thus the idea of a torch igniter was born.

The whole factory turned out to see the first run, which took place at about midnight. The cheer that went up when the engine was opened up slowly to reach 4,000 lb could be heard all over Barnoldswick and at that point, a halt was called. After this, the Nene never looked back. It was type tested at 4,000 lb in January 1945, at 4,500 lb in May 1945 and at 5,000 lb in November 1945.

No British aircraft had been designed for the Nene at this time but, in the US, Lockheed had built the P. 80A Shooting Star, which was the first American jet aircraft to go into production and the first aircraft on the Allies’ side to exceed 500 mph. It is interesting to remember that the P. 80 was originally designed for the de Havilland H1 engine and first flew in June 1944. It was later modified to take the General Electric I 40, which became the production version.

A P. 80 was modified to take the Nene and first flew on July 21, 1945. By October 16, 50 hours’ flying at maximum thrust of 5,000 lb had been completed and aircraft speeds above 500 mph had become commonplace.

World records for the Derwent V

Towards the end of 1944, we entertained Frank Whittle to dinner to celebrate the successful running of the Nene. All mourned the fact that there was no aeroplane suitable for it- nor any on the stocks. It looked as if the masterpiece was doomed to take no part in the war effort.

On the other hand, the Meteor was in full production with the Derwent I at 2,000 lb thrust and someone posed the question: “What would happen if the Nene were scaled down to fit the Meteor nacelle?” A quick sum showed that the scale engine would give 3,650 lb of thrust. Everyone was astounded by this answer which was a consequence of the superior performance that the Nene had already established.

Clearly, there was no point in pursuing the step-by-step development of the Derwent I to 2,200 and 2,400 lb of thrust; the right course was to go straight for the scaled-down Nene. And thus the Derwent V was conceived.

On January 1, 1945 the design work started, making the Derwent V a photographic copy of the Nene, with a scale factor of 0. 855. With the usual tremendous effort, the first engine was ready for test on June 7, and was an immediate success, achieving exactly the scaled Nene performance. It also had the Nene reliability and completed a 100-hour Type Test in June 1945.

On August 15, 1945 a Meteor equipped with two Derwent V engines and longer, streamlined nacelles, was ready to fly at Moreton Valance with Eric Greenwood as the pilot. When Éric took off, the increased thrust of the engine was immediately apparent and when he landed he handed over to his second pilot with the words: “At last we have got a real aeroplane. ”

August and September were exciting months as the throttles of the Derwent Vs were opened further and further and the speed of the Meteor exceeded 500 mph and crept up towards the magic figure of 600 mph. Since the thrust of the Derwent was 2. 25 times that of the B. 23, the aircraft speed (which, apart from drag rise due to Mach number, goes as the square root of the thrust) was 50 per cent greater than the Meteor Is with B. 23 engines, i. e. increased from over 400 mph to approximately 600 mph.

A happy, productive period

The Derwent V and the Nene engines were the world’s preeminent jet engines in 1945 and, with them, the further development of the Whittle type centrifugal engine ceased at Barnoldswick and the development of the Avon axial flow engine began.

To us all, the ending of the epic period 1943/1945 at Barnoldswick brought great sadness. Looking back over these years, it is impossible to avoid nostalgia but one is repeatedly struck by the great amount of work got through and the tremendous progress achieved. One is thankful to have been one of a small team of dedicated people given the opportunity to work in the new and exciting field of jet propulsion and the gas turbine engine.

The short time in which engines were designed, made and tested to a standard suitable for service in the RAF has never been equalled and it is salutary to review the conditions that allowed this to take place.

Rolls-Royce had adequate manufacturing and testing capacity, staffed by men expert in the use of the machine tools and all aspects of the manufacture of aero-engine components. Whittle was never provided with this capacity or staff and, as a consequence, was badly handicapped in developing his remarkable concepts.

The final decision on all engineering matters was vested in one man the chief engineer at Barnoldswick. Lord Hives gave complete autonomy and there were no committees or other management devices to delay things.

Work proceeded by consensus, of course, but once a decision had been taken, it was implemented immediately without question or argument.

The enthusiastic support of the workforce at all levels was vital to our success. No effort was spared and there was no such thing as a ‘working day’. Young men, girls and their elders worked day and night until their assignments were finished. Engines were tested ’round the clock when they were ready. regardless of what time that might be. Above all, we felt that this was our contribution to the war effort and to the continuing supremacy of the Royal Air Force.

One wonders if such an opportunity will ever come again to such young men.

One of the foremost figures in British aviation, Sir Stanley joined Rolls-Royce in January 1938 and in the course of 40 years has held a succession of senior appointments, finally becoming group technical director. As chief engineer at Barnoldswick during the war he was responsible for design and development of early jet engines. Later, at Bristol, he was closely involved in the development of the two-spool Olympus engine and pioneered the vectored-thrust Pegasus. A Fellow of the Royal Society, Sir Stanley has received many awards and decorations. He was knighted in 1974.