AIR CDRE SIR FRANK WHITTLE, who has died in America aged 89, was the greatest aero-engineer of the century

Whittle ensured that Britain was the first to enter the jet age when, on May 15 1941, the jet-propelled Gloster-Whittle E 28/39 flew successfully from Cranwell.

During 10 hours of flying over the next few days, the experimental aircraft - flown by the test pilot Gerry Sayer - achieved a top speed of 370 mph at 25,000 ft. This was faster than the Spitfire, or any other conventional propeller-driven machine.

Although this was a moment of triumph for Whittle, it was tinged with some bitterness, for he had had to overcome years of obstruction from the authorities, lack of funding for and faith in his brilliant ideas. He felt, with justification, that if he had been taken seriously earlier, Britain would have been able to develop jets before the Second World War broke out.

As early as October 1932 he had been granted a patent for the first turbo-jet engine, but the Air Ministry's indifference had caused a long delay in realising his ideas. Thus it gave Whittle particular satisfaction when, days after the E 28/39's maiden flight, Sir Archibald Sinclair, the Air Minister, and a gathering of officials, stood stunned as Sayer put it through its paces over Cranwell.

 As John Golley noted in his biography (Airlife, 1987): "Whittle - who had been the first man to get a turbo-jet running - had thrust Britain forward into the Jet Age and stood the aviation industry on its head."

Whittle's engineering genius led to the creation of several other aircraft: the RAF's Gloster Meteor, which saw action during the latter stages of the Second World War; the de Havilland Comet, the world's first passenger jet, and Concorde.

 Concorde's maiden flight in 1969 set the seal on Whittle's endeavours. He maintained that once his system of propulsion was available, no great invention was required for an aircraft to use it.

 Frank Whittle was born on June 1 1907, in the Earlsdon district of Coventry, the son of a foreman in a machine tool factory.

When Frank was four his father, a skilful and inventive mechanic who spent Sundays at a drawing board, gave him a toy aeroplane with a clockwork propeller and suspended it from a gas mantle. During the First World War Frank's interest in aeroplanes increased when he saw aircraft being built at the local Standard works, and was excited when an aeroplane force-landed near his home.

In 1916 the family moved to Leamington Spa, where Frank's father had bought the Leamington Valve and Piston Ring Company, which comprised a few lathes and other tools, and a single-cylinder gas engine. Frank became familiar with machine tools and did piece work for his father.

Frank won a scholarship to Leamington College, but when his father's business faltered there was not enough money to keep him there. Instead he spent hours in the local library, learning about steam and gas turbines.

In January 1923, having passed the entrance examination, Whittle reported at RAF Halton as an aircraft apprentice. He lasted only two days; only five feet tall and with a small chest measurement, he failed the medical.

Six months later, after subjecting himself to an intense physical training programme supported by a special diet, he was rejected again. Undeterred, he applied using a different first name, passed the written examination again and was ordered to Cranwell where he was accepted.

In 1926, strongly recommended by his commanding officer, he passed a flying medical and was awarded one of five coveted cadetships at the RAF College. The cadetship meant that he would now train as a pilot. In his second term he went solo in an Avro 504N biplane after eight hours' instruction.

Whittle graduated to Bristol fighters and, after a temporary loss of confidence due to blacking out in a tight loop, developed into something of a daredevil. He was punished for hedge-hopping. But he shone in science subjects and in 1928 wrote a revolutionary thesis entitled Future Developments in Aircraft Design.

THE PAPER discussed the possibilities of rocket propulsion and of gas turbines driving propellers, although it stopped short of proposing the use of the gas turbine for jet propulsion. However, Whittle launched his quest for a power plant capable of providing high speed at very high altitude.

In the summer of 1928 he passed out second and received the Andy Fellowes Memorial Prize for Aeronautical Sciences. He was rated "Exceptional to Above Average" as a pilot on Siskin operational fighters - but red-inked into his logbook were warnings about over confidence, an inclination to perform to the gallery and low flying.

At the end of August 1928, Pilot Officer Whittle joined No 111, an operational fighter squadron equipped with Siskins and based at Hornchurch, and was then posted to the Central Flying School, Wittering, for a flying instructor's course. In his spare time he conceived a gas turbine to produce a propelling jet, rather than driving a propeller. A sympathetic instructor, Flying Officer Pat Johnson, who had been a patent agent in civilian life, arranged an interview with the commandant.

This resulted in an almost immediate call from the Air Ministry and an introduction to Dr A A Griffith at the ministry's South Kensington laboratory. Griffith was already interested in gas turbines for driving propellers, and scorned Whittle's proposals. The Air Ministry informed Whittle that successful development of his scheme was considered impracticable. Whittle nevertheless took out his jet patent, and qualified as a flying instructor.

Pat Johnson, still convinced by Whittle's ideas, set up a meeting at British Thomson-Houston, near Rugby, with the company's chief turbine engineer. While not questioning the validity of Whittle's invention, BTH baulked at the prospect of spending £60,000 on development.

At the end of 1930 Whittle was posted to test floatplanes at the Marine Aircraft Experimental Establishment at Felixstowe. On leave he publicised his jet engine proposal, unsuccessfully. Fortuitously, a friend from Cranwell days, Rolf Dudley-Williams, was based at Felixstowe with a flying-boat squadron, and his efforts on Whittle's behalf soon bore fruit.

In the summer of 1932 Whittle was sent on an engineering course at RAF Henlow. He did so well that, exceptionally in that period, he was permitted to take a two-year engineering course as a member of Peterhouse College, Cambridge, where in 1936 he took a First in the Mechanical Sciences Tripos.

While he was at Cambridge his jet engine patent lapsed; the Air Ministry refused to pay the £5 renewal fee. But in May that year he received an inquiry from Dudley-Williams, who was by then a partner with another former RAF pilot, named Tinling, in General Enterprises Ltd.

The two men undertook to cover the expenses of further patents, to raise money, and to act as Whittle's agents. In the New Year of 1936 an agreement was signed between Dudley-Williams and Tinling, Whittle, the president of the Air Council, and O T Falk & Partners, a firm of City bankers.

A company, Power Jets, was incorporated and Whittle received permission from the Air Ministry to serve as honorary chief engineer and technical consultant for five years, providing there was no conflict with his official duties.

It was as well, because in July, turbo-jet experiments began at Junkers and Heinkel in Germany; at this stage, Whittle's ideas were not subject to the Official Secrets Act. It was a relief when the He 178, after some promise, was scrapped.

Whittle, seeking somewhere to develop his design on modest Power Jets' capital, returned to BTH at Rugby and the company contracted to build a "WU" (Whittle Unit), his first experimental jet engine. At the same time he tried to persuade companies to develop the specialised materials he needed.

First attempts to run Whittle's jet at Rugby in April 1937 produced a series of alarming incidents as it raced out of control and BTH hands bolted for cover. Money was required for further development, but this was scarce, although an Air Ministry contract provided a paltry £1,900.

In 1938 BTH moved the test-bed to its Ladywood works at Lutterworth where, in September, the engine, reconstructed for the third time, was assembled. A further £6,000 of Air Ministry money was pledged and engine tests resumed in December.

WITH THE OUTBREAK of war in September 1939, the project got a further lease of life. The Air Ministry commissioned a more powerful W 2 from Power Jets, and asked the Gloster Aircraft Company for an experimental aeroplane, specified as E 28/39.

With finances more secure, Whittle faced a new threat. Relations with BTH, never easy, deteriorated as the company took the view that the jet engine would not compare favourably with conventional power plants. Whittle was further bedevilled by various strands of officialdom blowing hot and cold about Power Jets' future, and also the politics of possible participation by the Rover motor-car company.

In the event, the Government cut the ground from under Whittle's feet in early 1940, bypassing Power Jets and offering shared production and development contracts direct to BTH and Rover. Power Jets was demoted to the level of a research organisation.

Matters worsened when the Air Ministry, eager to obtain an operational jet fighter, side-stepped Whittle, ignoring the E 28/39 and authorising Glosters to press ahead with a twin-engined jet interceptor specified as F 9/40. This was to become the Meteor. Worse still, in 1941 the ministry's director of engine production was to agree to Rover alterations to Whittle's design behind his back.

But fortunately, on July 9, Lord Beaverbrook, Minister of Aircraft Production, personally assured Whittle that the jet fighter would go ahead.

Whittle was relieved by the reprieve, but agonised over the difficulties of, literally, getting his engine off the ground. He smoked and drank heavily, and the elbowing-out by BTH and Rover further depressed him.

But the events of April and May 1941, when he saw his E 28 test-bed aeroplane flying successfully at Cranwell, lifted his gloom. When Johnson, who had encouraged Whittle for so long, patted him on the back and said, "Frank, it flies," he replied, "Well, that was what it was bloody well designed to do, wasn't it?".

Details of Whittle's inventions were made available both in Britain and America. Rolls-Royce, de Havilland and Metropolitan-Vickers became involved.

In June 1942, Whittle was flown to Boston to help General Electric to overcome problems. They built the engine under licence in America with the astonishing result that Bell Aircraft's experimental Airacomet flew in the autumn of 1942, beating the Meteor into the skies by five months.

Returning home, Whittle arrived at Power Jets' new factory at Whetstone. While it was nothing like the size of the plants devoted to his jet in America, he was astonished by the factory's size after so many years of parsimony, although in practice it could not provide the capacity that would be needed.

Rolls-Royce stepped in and took over work on the W 2B engine, which in 1943 cleared the way for Whittle to plan further improvements which would evolve as later mark numbers. Then, with Rolls-Royce in almost total control of Power Jets, Whittle lost touch for three months while he attended the RAF Staff College.

Fearing in this period that private industry would harvest the pioneering discoveries of Power Jets for nothing, Whittle suggested that it should be nationalised.

By the time Whittle had come to regret this proposal, he was taken up on it by Sir Stafford Cripps, the Minister of Aircraft Production. Cripps imposed a price of £135,563.10s, and renamed the company Power Jets (Research & Development). Whittle received nothing, having earlier handed over his shares worth £47,000 to the ministry.

But six months later Whittle was promoted air commodore and had the satisfaction of knowing that Meteors of No 616 squadron were shooting down V 1 flying-bombs.

In 1946 Whittle accepted a post as Technical Adviser on Engine Production and Design (Air) to the Controller (Air) at the Ministry of Supply. He again became ill, during an American lecture tour, and in 1948 retired from the RAF on medical grounds. Shortly afterwards he was awarded an ex-gratia sum of £100,000 by the Royal Commission on Awards to Inventors, and he was knighted.

Whittle was appointed CBE in 1944, CB in 1947, and KBE in 1948. He was made a Commander, the US Legion of Merit, in 1946. In 1986 he was appointed a member of the Order of Merit. He was a Fellow of the Royal Society, and of the Royal Aeronautical Society.

Whittle settled in America in 1976, and was a member of the Faculty of the Naval Academy, Annapolis, Maryland.

He published Jet (1953), and Gas Turbine Aero-Thermodynamics (1981).

Frank Whittle married, in 1930, Dorothy Mary Lee; they had two sons. The marriage was dissolved in 1976 and that year he married Hazel Hall.