Why did the Vulcan bomber sound so fantastic?

We asked an expert

The Vulcan’s raucous howl was a beguiling thing - but what caused the Vulcan’s wonderful loudness and distinctive howl?

The Vulcan engine is loud because it is small. Jet engines generate thrust from the product of mass flow rate and exhaust velocity. If your engine is small, the exhaust velocity needs to be large for a given thrust, and noise increases very rapidly with jet exhaust speed (that is one reason why modern aircraft use two large engines rather than four smaller ones, if they can).

The howl comes from acoustic resonance in the air intakes. This gets compared to the sound you hear when you blow over the top of a bottle, but a better comparison might be to the sound from the wind when it blows over cavities and round buildings, to the exhaust or intake noise from a high-performance car or bike, or at a push, to some musical instruments. The effect depends on the details of the airflow and the shape of the cavities, but it can have particular psychological effects. The howl you can hear in a cave has similar causes, but isn't as consistent because the wind speed varies in a way it doesn't in an engine intake

Michael Carley, Senior Lecturer in the Department of Mechanical Engineering of the University of Bath, and member of the Aerospace Engineering Research Centre. Main research interests aeroacoustics and numerical modelling of vortex-dominated flows and acoustics.