Although 2000 AD is but 20 years away, even so this is a long period in terms of the rate of recent technological development. My remarks about the possible future state of this subject must therefore be somewhat speculative. The projections will be based, however, on research carried out over the past 10 years, and I hope this will provide an element of usefulness.

I shall refer to both agricultural and forestry crops. Our most extensive agricultural experience has been with cotton and its pests in the Sudan, particularly the cotton bollworm moth; and with cereals in the UK, particularly cereal aphids. Our forestry experience has been with softwoods and the spruce budworm moth in eastern Canada, and with lodge-pole pine forests and the pine beauty moth in Scotland. In terms of techniques our experience has ranged over ground-based and airborne radars, a full range of ground and airborne meteorological instrumentation, the study of insect flight behaviour by sensitive infra-red opto-electronic devices, the turbulent dispersal of spray droplets and their deposition on foliage and insects, the study and quantification of insect population dynamics, and the use of many biological techniques, including suction traps and light traps.

Control of agricultural pests and diseases has been attempted for well over one thousand years, but it is only during the present century that the means have been available to combat the problems on a large scale by the use of pesticides. The contribution which pesticides have made to the reduction of crop losses is enormous. However, the fact that significant losses of production still occur shows that they are not a complete or simple answer to the problems.

When used in the broadest sense the term ‘pest' applies to a wide range of plant and animal organisms which adversely affect the crops grown by man. Attention here will be restricted to invertebrate pests and crop diseases.

The title of this presentation is, perhaps, wider than the title of the section of the symposium within which it is placed. It is intended to move from the general aspects of aerial photography and other airborne remote sensing devices to the particular aspects of pest forecasting and control using this technology.

The quality of aerial photography has doubled every 10 years since the technique was first introduced, and it is believed that this improvement may well continue for the remainder of this century. It is probable that multispectral photography and improved photographic representation of near and far infra-red imagery will greatly improve during the coming decades. As more research is done on more freely available material, so shall we find more applications for it, including, without doubt, those in the field of pest control.

Twenty-one years ago, a small group of people who were very dissatisfied with the state of the art of aerial crop spraying, met over coffee in the sitting room of Mr. Foster's home near Heathrow. Inevitably, one of the topics discussed was the need for better crop spraying aircraft. The most important outcome of that (and several subsequent meetings) was the formation of the Agricultural Aviation Group of the Royal Aeronautical Society, now celebrating its majority. Of that group I was, and still am, the one who knew least about aerodynamics or aircraft design. However, as the last remaining founder member of this Group, perhaps it is not entirely inappropriate that I should take one last look at the future of spray aircraft design, before removing myself from the scene.

The flight test engineer constantly strives to provide solutions to the problems of testing, developing and proving the progressively more complex and accurate navigation and attack systems of modern military aircraft. The biggest such challenge in Europe for some time was probably the flight trials programme on the swing-wing Tornado aircraft which has a digitally based, self contained, al-lweather NAV/ATTACK avionics system. This paper covers the philosophy and techniques adopted for the flight testing and subsequent analysis of major elements of this system.

As we are all aware, an aircraft in flight has six degrees of freedom. Three translational, that is, lateral, longitudinal and vertical and three rotational that is, rotation about the roll pitch and yaw axes. It is the actuation and control of the surfaces which cause rotation that will be discussed.

For the vast majority of aircraft, control in the three axes of rotation is achieved by three distinct movable surfaces which are elevators for pitch control, ailerons for roll control and rudder for yaw control. The effects of these controls are as follows—Fig. 1 the elevators will alter the angle of attack of the aircraft to the air and unless power is increased will result in a reduction in airspeed. If the airspeed is allowed to drop too much there will be a loss of lift on the wing and eventually a stall will occur. The ailerons will cause the aircraft to roll and alter the angle of bank. In so doing however the aircraft will begin to side slip, thus as there is more surface area aft of the cg than before it, the aircraft will turn.

The drag of slant-based three-dimensional bodies such as the upswept rear fuselage of some aircraft (see for instance McCluney and Marshall and Peake) and car shapes (Morel) can be high and it is generally recognised that this high drag is associated with powerful longitudinal vortices in the flow direction. Morel has shown that the formation of these vortices, and therefore the drag, is a function of the slant angle of the base. His experiments were conducted with the body at zero incidence only and it appears that the effect of body incidence on the drag is unrecorded, although Bearman mentions that it has a significant effect.

Nearly 15 methods have been proposed to obtain the shape of an axisymmetric wind tunnel contraction, but only a few have been studied experimentally. Bibliographic details of these methods can be found in Refs. 1, 2 and 3. Of these, the method described by Thwaites has the advantage that the contour and the velocity distributions are given directly by simple series expression. This method also has the criticism that the solution is periodic and does not satisfy near uniform stream condition obtained at inlet and outlet. But such a criticism applies to all methods which assume the length of contraction to be finite (e.g. methods due to Batchelor and Shaw, Chmielewski. Further, an experimental investigation by Klein et al(3) showed that Thwaites’ method with first four terms in solution gave a better performance than the contour given by Batchelor and Shaw.