Before 1800 Dr. Johnson observed that ‘the age is running mad with innovation’ and ‘every Master Manufacturer hath a new Invention of his own and is daily improving on those of others’. By the middle of the 19th century this first industrial revolution had made Britain the world leader in the application of steam power, in railways and in the output of coal, iron, steel, cotton cloth, and other manufactured goods. Yet by 1886 the Commission of Enquiry into the Economic Depression stated ‘We are no longer alone. More active rivals with better equipment are springing up and leaving us behind’. Between the turn of the century and the First World War, some of those rivals—in particular the USA and Germany—had eliminated our earlier lead and had gone ahead in key industrial sectors.

In the early 1970s considerable attention was being given to the possibilities of short-haul aircraft aimed at operating into or near city centres. There was a belief that suitable airfield sites could be found if field lengths no greater than about 2000 ft-3000 ft were required into which the aircraft could operate quietly with steep climb out and approach.

Although the latest aircraft flight simulators incorporate much recent technical development and are becoming increasingly accepted by the world's airlines, government regulatory agencies and air forces for pilot training and checking, there does not exist any completely satisfactory objective method for assessing their realism. If an objective method of measuring the realism of an aircraft simulator could be developed, it might be possible to reduce the often lengthy period needed by the simulator manufacturer in making final adjustments (tweaking) before customer acceptance, or to monitor the realism in service (15 year service life being typical), or to achieve the same degree of realism with equipment of a significantly lower specification and therefore much lower cost.

As early as 1714, when he was 26, Emanuel Swedenborg (1688-1772) showed an interest in the possibility of building a flying machine. Writing from Rostock on 8th September 1714 to his brother-in-law Erik Benzelius, he ambitiously listed 14 inventions which he had under way and about which he had prepared manuscript notes. The projected inventions included ‘a kind of flying chariot, or the possibility of being sustained in the air and of being carried through it’. Two years later, in 1716, Swedenborg founded Sweden's first scientific journal, Daedalus Hyperboreus, in the fourth number of which he anonymously published a short article entitled ‘Utkast til en Machine at flyga i wädret’ (Sketch of a Machine for Flying in the Air).

The intersection of two oblique shock waves of opposite families is a common occurrence in supersonic flows. It can result either in a regular intersection, where the downstream waves are weak shocks and a single slip line emanates from the intersection, or in a form of Mach reflection where a strong shock bridges the gap between two three-shock confluences each of which generates a slip line. The transition between regular and Mach reflection has been discussed for the symmetrical case by Henderson and Lozzi and by Horning et al. The conditions at a three-shock confluence point have been analysed for two-dimensional flow by Henderson and for three-dimensional flow by Hunt and Lamont and by Rudman.

Screens and contraction are used to achieve a low level of free-stream turbulence in the test-section of a wind tunnel. The effect of contraction on turbulence was initially studied, theoretically, by Prandtl, Taylor, Ribner and Tucker and Batchelor and Proudman. The last two theories, called rapid distortion theory, take into account the random nature of turbulence, but assume that the turbulence is initially isotropic, the effect of viscosity is small and the distortion is rapid.