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Through the sound barrier without a boom?

May 27, 2002

Supersonic aircraft might not be plagued by the problem of sonic boom if a radical design proposal by a Cambridge academic could be made to work. Professor John Ffowcs Williams, Master of Emmanuel College Cambridge, directed the Concorde Noise Panel in the 1960s and 70s. He now believes it is possible to build an aeroplane that could pass through the sound barrier without generating the characteristic and disturbing sonic boom, which prevents Concorde flying supersonic over land and severely limits its routes.

Professor Ffowcs Williams is a world expert in noise-reduction technology and was prominent in developing the concept of anti-sound now routinely used to silence some aircraft noises. He will receive the Royal Academy of Engineering Sir Frank Whittle Medal at the Academy Awards Dinner tonight (27 May) for his lifelong dedication to understanding the properties of sound, which has enabled huge innovation in international transport.

His concept for avoiding sonic booms was patented in 1986 but it involves a radically new aircraft configuration. "You need an aeroplane that doesn't disturb the air very much because disturbances cause resistance to motion, which produces the sonic boom," he explains. "I envisaged an aeroplane making destructively interfering waves, a double flying wing in fact, based on the disturbance-free biplane proposed by the influential German scientist Adolf Busemann. The upper and lower surfaces of the wing assembly would be formed so that the airflow over them is straight and smooth. It would create no waves as it travelled, eliminating or at least minimising the sonic boom." Concorde is still the only supersonic passenger jet in service but many in the airline industry foresee a market for a supersonic business jet and minimising sonic boom could be crucial to its acceptance.

Professor Ffowcs Williams got involved in Concorde's development in 1964 when he was a Reader in the mathematics department at Imperial College. There was a real risk that Concorde would be too noisy to operate but the noise problem was poorly understood. "Strange things happened," he says. "The propulsive jet makes most of the noise, which increases with speed until at very high speeds it doesn't get any louder, so going faster may be better! We had to rethink the whole physics of the process."

Since then Professor Ffowcs Williams has made an enormous contribution to predicting and reducing sound, both in aircraft and submarines. With his student David Hawkings he developed the deceptively simple and elegant Ffowcs Williams-Hawkings equation describing how surfaces moving at high speed generate sound. This has helped to reduce dramatically the noise from helicopter blades and jet engine fans. A typical passenger plane is now 30 decibels quieter than its 1950s equivalent, even though planes have become much heavier since then.

Professor Ffowcs Williams is justly proud of his achievements - he was born in Wales in 1935, one of three boys. His mother died when he was five and he was sent to a Quaker school in North Yorkshire, despite speaking no English. He left school at 16 and served an engineering apprenticeship with Rolls-Royce and eventually won a scholarship to Southampton University. After working at the National Physical Laboratory and in the US he joined Imperial College, where he was ultimately appointed Rolls-Royce Professor of Theoretical Acoustics before moving to Cambridge University in 1972 as the first Rank Professor of Engineering. He founded a consultancy company in Cambridge, Topexpress Ltd, which pioneered active noise control.

Royal Academy of Engineering