The ability of the helicopter to hover and therefore to take-off and land in confined areas has proven to be of significant value in an increasing range of applications. Rotorcraft have now established a significant role for specialist aeronautical applications both in the civil and military field.

Figure 1(a) shows a graph of the increase of helicopter usage in the civil market. To the traditional roles of point to point transport and special purpose public service operations has been added a massive increase in energy related use, particularly for off-shore oil exploration. Present fleet growth rate in the civil area is about 15% p.a. There is no sign that this demand will abate. There has also been a substantial increase in helicopter use on military operations, as illustrated in Fig. 1(b). Helicopters now account for between 40–50% of all service aircraft (excluding training and liaison) in both the United States and Britain. The flexibility offered by the helicopter has been critical in its tactical value for land operations. The ability of the helicopter to operate from small ships at sea in all weathers, and at night, has provided it with a unique role in naval applications. In Britain over 80% of naval aircraft are now helicopters.

Traffic growth and the replacement of the older, less efficient and noisier aircraft—60% of Western World capacity may be regarded as in this category—provide the opportunity for applying new technologies to subsonic commercial transports. Reduction of operating cost continues to provide the major incentive, though increasing emphasis is being placed on low fuel consumption and low noise.

In this paper, the term ‘advanced technology’ is taken to embrace significant engineering advances which are not commonplace on aircraft flying today. In general, it is wrong to think of such advances as new inventions. Almost without exception they have evolved over the years, with few quantum jumps. There are, of course, exceptions to this and a recent example as regards engine development might be the introduction of high bypass ratio engines in the late 1960s, which brought about a 25% improvement in specific fuel consumption. However, even this major step could be regarded as an evolutionary development from engines of bypass ratio about 1·0, which themselves had conferred significant gains relative to the straight turbo-jet engines of the late 1950s.

Nobody would deny that a major objective of the peoples of the world is to improve standards of health and hygiene and an essential part of this must be to increase the quantity of food produced. To do this it is essential to use supplementary nutrients and exercise effective pest management. It has been shown that the yields of basic foods, such as rice, can be doubled by using the right seed strains, fertilisers and crop protection techniques. Crop yield losses because of insects alone are estimated at 5% in Europe where insecticides are used widely and as much as 21% in Asia where insecticides are used only in a few of the better organised cultural areas.

Experiments in the wake of a circular rod at a Reynolds number Re=5·104 have shown that single vortex-like structures can leave the wake and may be detected in the ambient potential flow. This experimental finding suggested the theoretical investigation of the interaction between a vortex and a shear flow. Lin has calculated the average acceleration acting on the vortex at the time t = 0. In the following a finite-difference scheme is described which, in detail, determines the local components of the acceleration and the temporal development of the flow.

The phenomenon of aerodynamic coupling between the longitudinal and lateral motion at high incidence is well known. In recent years, there have been a number of attempts to analyse the behaviour of aircraft allowing for this coupling. One of the more practical methods of approach is that of Kalviste, in which the aircraft rotary motion alone is considered, the aircraft having a certain angle of sideslip in the steady state. However, that method is essentially based on linearised equations. In this note, we show how Kalviste's analysis can be modified to include certain non-linear aerodynamic effects. In particular, some unstable modes only become apparent on introducing the non-linear terms.