The subject of this paper is the interaction between airborne and ground attack missions by aircraft, and the defence systems now available to deny or counter such attacks. I should like to make it clear from the start that I am restricting myself to air operations in a non-nuclear land battle scenario and I speak not as an expert in attack missions, but rather in a historical and speculative fashion, as one who has been concerned with some of the techniques concerned with air defence.

You may, from me, expect a highly biased approach to the subject of the paper and probably you are right, but I should warn that if you expect me to conclude that the aircraft is doomed then I must reassure you that I believe that the aircraft remains a most flexible instrument of warfare and will for the foreseeable future exercise an extremely important position in the land and air battle.

The subject of the quiet helicopter is receiving increasing attention throughout the world because it is now established that a helicopter can be made quiet. Quietening is also needed as more helicopters are being used over cities and residential areas. To date, little attention has been paid to helicopter quietening because the emphasis has been on achieving maximum payload and other performance. Now that the basic helicopter design has been established, refinements for quietening are becoming practical. The comparison is much like the evolution of the automobile and the truck in the city. Initially these vehicles were noisy. As their number increased and their design evolved, mufflers and sound-deadening materials were skilfully applied to reduce their noise to more acceptable levels for each type vehicle.

You can pick up almost any history of aviation—from the early times to the present—and read of the exploits and adventures of pilots and their planes. Sir Charles Kingsford-Smith and his Fokker, Charles Lindbergh and his Ryan, Amelia Earhart and her Lockheed. We who have technical interests in aviation know that Kingsford- Smith and Lindbergh depended on their Whirlwinds, and Miss Earhart on a Wasp, but the popular stories often fail to make that point.

In more modern times, the engines are equally vital but sometimes get overlooked. Once, when a new jet aircraft was being announced at a press briefing, an airline officer breathlessly described the aircraft, showed artists’ concepts of the cabin and flight deck, and talked at length of the systems and subsystems. After an hour-long description, he called on his audience of reporters, and then he got his come-uppance from an engine man’s point of view. A reporter at the back of the room was recognised, and asked: ‘And what is this aircraft going to be? A glider?’ The by now red-faced official had neglected to mention the powerplants.

The flow along the corners formed by the intersection of two semi-infinite flat plates has been studied by many workers, notably Pearson (1957) and Rubin (1966) who treated the case of a rectangular corner. The situation is characterised by a region of three-dimensional flow in the vicinity of the intersection line bounded by regions in which the usual two-dimensional boundary layer equations are applicable. Within these boundary regions a secondary shear layer exists whose velocity is normal to the ‘two-dimensional’ vector.