Sonic Bangs Research Articles

Sonic Bang Simulation by a New Explosives Technique

Sonic Bang Simulation by a New Explosives Technique

Experience in the United Kingdom on the effects of sonic bangs.

Over the past five years, a number of exercises involving the making of bangs have been staged in the United Kingdom. The bangs have been made both by flying aircraft at supersonic speeds and by firing explosive charges. From this work, information has been obtained on the intensities and waveforms of aircraft sonic bangs as measured outdoors, on the nature of the disturbances that are recorded inside buildings, and on the subjective reactions of people to these bangs. The paper summarizes the results of this work.

Experience in the United Kingdom on the Effects of Sonic Bangs

Over the past five years, a number of exercises involving the making of bangs have been staged in the United Kingdom. The bangs have been made both by flying aircraft at supersonic speeds and by firing explosive charges. From this work, information has been obtained on the intensities and waveforms of aircraft sonic bangs as measured out of doors in the open at ground level, on the nature of the disturbances that are recorded inside buildings, and on the subjective reactions of people to these bangs. The paper summarizes the results of this work.

Subjective measurements of the relative annoyance of simulated sonic bangs and aircraft noise

Experiments were conducted on a total of seventy-nine subjects, in which they were asked to estimate the relative annoyance of the sound of a jet aircraft, a piston-engined aircraft, and sonic bangs, each of which was reproduced electronically at various levels. For the sonic bangs, a sound typical of that received inside a building was chosen. The results are generally consistent with those of earlier experiments using different scaling techniques, and in the case of the jet and piston aircraft sound broadly support the method of calculating perceived noise levels. The increment necessary to double annoyance is about 13 PNdB. The rate of increase of annoyance with level is greater in the case of the sonic bangs, about 10 dB for doubling. By relating the reproduced noise levels to their original values it is concluded, with some reservations due to experimental limitations, that the upper limit of acceptable sonic bangs (as heard in domestic interiors) is about 1·9 lb/ft 2 initial pressure jump measured on the ground in the open. This figure is based on the value of 110 PNdB for conventional aircraft sounds.

A note on the refraction of sound in a moving gas

The object of this note is to draw attention to the correct form of the theory of the refraction of sound in a moving gas in which the speed of sound varies from point to point. The correct theory is firmly established but appears to be insufficiently well-known. The results are of practical importance in predictions of the intensity of sonic bangs from aeroplanes in supersonic flight and of the intensity of blast waves.

A correction to “The theory of sonic bangs”

A correction to “The theory of sonic bangs”

A Note on the Sonic Bang Waveform of an Aircraft with Lift

It is well-known that, at large distances from the flight path, the waveform of the sonic bang from an aircraft, without lift at any rate, has the characteristic N-wave shape, as illustrated in Fig. 1. When we depict a waveform such as this we are stating what would occur at large distances in the absence of viscosity and other diffusive effects, such as turbulence. We know, of course, that in reality, because of these effects, the bow and stern shocks will be “softened”, i.e. the pressure jumps associated with them will not be instantaneous, but will have a finite, but small, “rise time”. However, this is not the matter under discussion. The essential feature of the N-wave illustrated in Fig. 1 is that the pressure jumps associated with the bow and stern shocks are equal, and that the positive and negative phases are of equal duration. The arguments for the waveform to take up this shape at large distances are put in a classical paper by Whitham.

Lower Bounds for Sonic Bangs

Lower bounds for the intensity of the sonic bang of a slender aircraft configuration with various constraints are given in this note which is a condensed version of Ref. 1. Although these lower bounds cannot be achieved in practice the method of obtaining them demonstrates how low values can be obtained. Special emphasis is given to a possible supersonic transport.

The theory of sonic bangs

The pressure disturbances from an aircraft in supersonic flight manifest themselves aurally as “sonic bangs”. The theory of sonic bangs attempts to answer two questions. How do the disturbances propagate, and how do their intensities vary during propagation? The first question is a simple problem in the theory of acoustics. The second, more difficult, question is answered for quite general aircraft motions (including flight with lift). The variations of density and speed of sound in the terrestrial atmosphere are allowed for. The outstanding problem is the behaviour of disturbances when the rays, along which they are propagated, intersect.

The Noise From Aircraft

A general expression is obtained for the potential of sound or aerodynamic disturbance from a source moving with variable vector velocity, based on linear theory. Knowing the space time curve for the source, the Doppler frequency corrections and intensities can be determined. If in any part of its trajectory the aircraft exceeds the velocity of sound, the number of sonic bangs and the times of occurrence can be calculated. A numerical example is given. The following conclusions are deduced: (i) If at any point of its trajectory, the component of the aircraft velocity in the direction of the observer is equal to the velocity of sound, a sonic bang is propagated to the observer with the velocity of sound. This has been previously postulated by C. H. E. Warren. (ii) A bang as determined by conclusion (i) comprises two components and in certain circumstances the components in some of the bangs may be acoustically separable, thus giving rise to double bangs.