Development of Jet and Turbine Aero-engines, The

Journal of Transport History, The, Mar 1999 by Lyth, Peter

Bill Gunston, The Development of Jet and Turbine Aero-engines, second edition, Patrick Stephens/Haynes, Yeovil (1997), 239 pp., L19.99.

Richard P. Hallion, Supersonic Flight: breaking the sound barrier and beyond, revised edition, Putnam Aeronautical, London and Washington DC (1997), 268 pp., L25.00.

The jet engine is arguably the most significant innovation in long-distance transport this century. Since it galvanised air travel in the early 1960s it has become so closely identified with aircraft propulsion that one wonders how the aircraft industry managed to make so much progress in its first forty years with piston engines. Compare the swift introduction of the jet in civil aviation with, for example, the ponderous conversion of rail transport from steam to diesel and electric locomotives. Aircraft and jet engines are a technological marriage made in heaven, or at least in the upper atmosphere. By contrast the aeroplane's early liaison with the reciprocating engine, a technology borrowed from the automobile industry, was doomed by the laws of aerodynamics to exhaust itself long before the sound barrier was reached.

There would seem to be at least two good reasons for economic and transport historians to learn more about jet engines or, more precisely, gas turbines. First, for Britain they represent one of the few hightech manufacturing success stories of the last fifty years, and secondly it was technical breakthroughs during the Second World War that transformed air travel in the post-war period from a luxury adventure into a mass transport mode, and chief amongst them was the turbojet. The fall in airline operating costs which began in the 1960s was a direct result of the use of jet engines, in particular by-pass engines like the Rolls-Royce Conway. The international tourist trade as we know it today would be virtually inconceivable without jet passenger aircraft. Put simply, jets have revolutionised individual mobility in the twentieth century.

These two books help us understand how they work and the history of their development. Bill Gunston has a long publishing record on aircraft and aircraft engines and this latest volume provides a detailed introduction to jet engines for those of us who can hardly tell a turbine from a compressor. In the first half he takes us step by step through the workings of a turbojet. Basically it consists of just three elements: compressor, combustion chamber and turbine. Indeed, their elegant simplicity is part of the reason why jets are so much more efficient than reciprocating engines at producing useful power. The turbine drives the compressor by means of a connecting shaft, leaving sufficient energy behind the turbine to provide a high-speed propulsive jet out of the tailpipe. The most complicated part is the compressor, and Gunston is probably right when he claims that, given its rapid development from the centrifugal types of the 1940s to highly sophisticated multi-spool axial units, the advances in compressor design ,are without parallel in engineering'.

In the second half of his book Gunston chronicles the turbojet's sixty-year history, tracing its swift evolution through turboprops to the huge, high bypass ratio turbofans of today's airliners. The first operational engines were built in the late 1930s by a group of men working independently in Britain and Germany. The names of Frank Whittle and Hans von Ohain head the list, but the Germans Herbert Wagner and Helmuth Schelp also played a vital role, as did academics such as Ludwig Prandtl and A. A. Griffith, whose work on fluid mechanics was fundamental to compressor design. In Germany wartime work on jet aircraft was more advanced than in Britain. The Germans not only had three major manufacturers (Junkers, BMW and Heinkel) working on production engines but they were also following at least three different design approaches. The British proceeded on a narrower front, at least until the end of the war, with Whittle's design forming the basic model for Rolls-Royce, de Havilland and Armstrong Siddeley.

Richard Hallion's book, which was first published in 1972, shifts the focus to the United States. The Americans had neglected jet engine research before the war and when the Whittle engine was given to them in 1941 they started from scratch with the British design. The subsequent sale to the Americans of the rights to the engine has been described by Whittle's biographer (John Golley) as `one of the bargains of the century'. Be that as it may, the Americans would undoubtedly have caught up after the end of the war and by the late 1940s both General Electric and Pratt & Whitney were developing their own advanced axial flow turbojets.

With the jet engine came the prospect of aircraft flying faster than sound, i.e. Mach 1.0, or a little under 700 m.p.h. With the exception of the Concorde, it has never been realised for commercial aircraft, so Hallion's story is essentially about military research aircraft, the engineers who built them and the intrepid pilots who flew (and often died in) them.