Predicting the future for Agricultural Aviation is rendered even more uncertain than predictions for most forms of aviation because in this case the future depends on two entirely separate sets of unknowns. These are the normal unknowns affecting aeronautical development but, more important, there are the unknowns affecting the development of agricultural chemicals. Also, in predicting the future evolution of any activity one must normally look back over the rate and the trend of developments in the activity, so far as they are relevant, from the past and then project this rate and trend into the future, bending and extending the line of projection in accordance with known or foreseeable influences. Here again we get a third set of unknowns related to future farming techniques, although these unknowns are perhaps less significant because the main expansion in agricultural aviation will probably lie in the vast undeveloped regions of the world where the farming techniques will merely be brought up to present standards, or just introduced where there was literally no agriculture before.

Aviation has become a great international utility, and as the scale of investment has grown innovation is increasingly dominated by economic considerations. The time needed to bring research, development and design to fruition is lengthening and economic and technical trends must be appraised tor many years ahead. Of the various parameters defining aircraft design and performance, speed is the most fundamental. The speeds of both military and civil aircraft have been doubling every decade for over 50 years; but the factors which contributed to this exponential growth have changed and a new basis for prediction must be established.

Above high subsonic speed transport efficiency remains sensibly constant although with pronounced optima around Mach 0.8 and Mach 3. In future, aircraft will tend to fall into distinguishable speed regimes; but application will be determined by their economic productivity rather than by small differences in transport efficiency. Subsonic aircraft will remain the mainstay of civil and military aviation for many years, with supersonic aircraft meeting a growing civil demand on the longer international routes and military requirements tor fighters, bombers and reconnaissance aircraft. In neither field is there any imminent demand for hypersonic aircraft.

But if the quest for higher speed is no longer the dominant incentive in aeronautics, there are new in:tiatives at the low speed end of the flight envelope, and continued improvements are foreseeable in the efficiency of propulsion, structure, and avionics. If these opportunities are seized there is a challenging and rewarding future for European aviation.

It is always an honour to be invited to give a lecture, and particularly a memorial lecture to a man so outstanding in his own field.

I knew Roy Chadwick and liked him. I admired, too, his working ability and his professionalism. He was a natural born designer, and I need not list here his attainments and successes since these were very adequately dealt with by Rogerson in the First Memorial Lecture to him.

I thought long about the subject of my talk this evening and finally decided that, at my time of life, it might be appropriate if I were to give a sketch of my accumulated experience, and experiences, over more than fifty active years—divided between marine diesel engines and automobile and aviation engines.

The theme of this lecture on Helicopter All-Weather Operation is a discussion of the equipment requirements for the helicopter in the transport role.

I have to say at the outset and possibly somewhat provocatively, that I believe that there are no real problem areas left, as far as the equipment means are concerned, between us and the realisation of a good all-weather capability in a transport helicopter. By this I mean that virtually all the basic work has been done in the main fields of guidance and control. Much of the equipment is already produced or in an advanced stage of development and most of that outstanding has already been defined and the feasibility of meeting the requirements examined. Thus, I believe, all that is required is a determination to achieve all-weather operation and to set in hand the processes of procuring the equipment. This means that the requirement has to be firmly stated and the price paid to meet it. It is idle to think that an all-weather capability can be achieved without an adequate equipment standard. However, it is reasonable to expect that its achievement should cost no more in the transport helicopter than for an equivalent standard in the transport aeroplane.

The problem of a two-dimensional pressure field moving over a free surface is analysed by dynamic modelling techniques. Using a simple second order linear differential equation, it is possible to obtain all the classical theory rersults for a uniform field in deep water. Squire’s results for the non-uniform pressure field of a planing wedge are also duplicated. Further results, not hitherto obtained with classical theory, may explain some anomalies associated with the classical theory. The method has the advantage that results for a large number of “pressure field distributions” have already been tabulated by workers studying the response of simple lumped parameter mechanical dynamic systems.

A conclusion of some practical importance in applied hydrodynamics is that the wave drag of a pressure field varies with its distribution. The more non-uniform a pressure field the greater its wave drag. The theory also gives insight into the occurrence of “humps and hollows” in model resistance curves, and gives some insight as to why a minor change in form may cause a major change in wave resistance.

Pressure recovery measurements in a straight pipe with crossflow-generated entry velocity distributions suggested substantial effects of inflow distortion on the pressure recovery downstream of a sudden enlargement in area. This note reports results of actual measurements in the same pipe equipped with entry sections of various reduced diameters providing sudden area enlargement ratios of 1.33, 1.71, 2.04, and 3.52. The results have practical bearing on the performance of settling pipes located at diffuser exits where, in general, velocity distributions are significantly non-uniform. In addition, the results provide information on the momentum content of the crossflow-generated velocity distribution.

It is generally accepted that the displacement patterns chosen to represent the deformation of a finite element should be such that there is complete compatibility with adjacent elements. Although some writers have doubted the necessity for the complete satisfaction of compatibility away from the reference nodes, provided the displacement pattern is capable of assuming certain uniform strain states, the desirability of complete compatibility is not in question. The displacement fields suggested in this note satisfy complete compatibility.

The drag at cruise CL of a number of recent aircraft—mostly large subsonic transports—has been analysed in terms of figures-of-merit derived from Melvill Jones’ original concept of a streamline aeroplane. The values have been compared with those for some representative aircraft from the 1930-1940 period. The paper then proceeds to highlight some of the main sources of excess drag; for the recent aircraft, these are grouped under broad headings such as “excrescences”, “Mach-number effects” and “nacelle installation or interference”.

The results of the analysis are somewhat disturbing. Perhaps the most striking feature, bearing in mind that only a restricted class of aircraft have been considered, is the very wide spread between the figures for the poorest and the best of the recent aircraft. Also, the detailed drag breakdown varies widely from one aircraft to another. The evidence in the paper suggests that, in many cases, present drag standards can and should be improved.

This work is concerned with the side force produced in rocket nozzles by secondary gas injection. A new theory for determining the side force is presented for two-dimensional flow and this is considered to be an important step towards a theory applicable to three-dimensional flow. The proposed theory is based on a double wedge model for the separated region upstream of the secondary port. The principal feature of the model is that it accounts tor the fact that the angle of the shock wave, originating from the separated region, is observed to increase with increase in secondary mass flow rate. Theoretical side force results are shown to compare favourably with experimental results obtained using two-dimensional nozzles and a comparison is made between the proposed theory and the theories of other workers.