A most important aspect of space technology is the development of methods for atmospheric re-entry. In this phase of flight very severe structural and material requirements exist. The origin of the problem lies in the intense aerodynamic heating which occurs as the body enters the denser regions of the atmosphere. High stagnation temperatures at the nose, shear effects in the boundary layer, radiation from the hot gas in the shock wave, and heat liberated by the recombination of dissociated and ionised gases give rise to conditions which will result in the destruction of the body unless some form of heat protection is provided.

The speaker has no specialist knowledge of agricultural aviation and will therefore briefly describe the aircraft, and provide thoughts on possible uses in aid of agriculture.

The ultra-light autogyro is probably the smallest practical aircraft of any type. Happily it does not need to be correspondingly fragile or delicate and it is little affected by turbulence or inclement weather, in the air or on the ground.

Some thought has already been given to an agricultural autogyro, although a somewhat larger machine than the Wallis autogyro was envisaged. While advantages would undoubtedly ensue from the larger size, such an aircraft would probably be in competition with comparable helicopters and fixed - wing machines. By the time development was complete there might be no great saving in first cost or maintenance.

The phrase “Air-Cushioned Vehicle” describes the complete range of vehicles which obtain some or all of their support from a free pressurised cushion of air contained between the vehicle and the ground.

Vickers’ interest in air cushion vehicles stems directly from the basic work carried out on the Hovercraft—one type of air cushion vehicle—by Mr. C. S. Cockerell and the initiative and encouragement displayed by the N.R.D.C. through its subsidiary Hovercraft Development Ltd.

A Great deal of information is available today which cannot over-emphasise what is at the moment, the serious plight of millions of people in the world and which will become more serious unless agriculture and science can continually develop new techniques to increase production.

There is more than enough land in the world if only it can be developed and farmed. What is needed is capital, work and new ideas for its means, so that, if all are to be fed enough food, the grain production of the world must be doubled and the animal production tripled.

My Subiect is a highly specialised and rather adventurous one—the practice of night spraying of trees and agricultural crops from aircraft.

It may sound hazardous, as it is, and of course it is at present only attempted when biological or climatic factors make spraying by daylight undesirable or ineffective. It is also dependent on a favourable terrain, and the development of better equipment. Where these conditions are fulfilled, in certain cases night spraying may become part of the armoury of a number of spraying contractors, mainly in Africa and America.

Following the Second World War, agricultural aircraft use increased rapidly in the United States, but appears to have levelled off in the past five years. California is one of the largest users of agricultural aircraft of any State, with an estimated 8 million acres treated per year. This figure includes all applications of insecticides, fungicides, and herbicides, plus seeding, fertilising, and defoliation of agricultural crops, grasslands and forest areas. Also, this figure represents acres covered and includes duplicated applications. Certain crops, such as cotton, may have as many as four or five separate treatments during the season.

Rotary atomisers, initially of brush and disc design, but subsequently superceded by a rotating cage device , have for some while been used with fixed-wing aircraft for producing relatively finely dispersed homogeneous liquid sprays. Common to all these types is rotation in the vertical plane with axial liquid feed intended to give uniform discharge from the rotor periphery. Atomisation, for a given liquid and a fixed rotor diameter, is a function both of the rotor speed and also of the airspeed of the aircraft. In combination these two factors determine the resultant shear force producing break-up of the discharging liquid filaments. With fixed-wing aircraft, having a minimum forward speed of, say, 60 mph, it is ultimately this velocity which determines a theoretical upper limit to the size of droplet which may be produced, but in practice drop size also varies with throughput, and, in connection with anti-Locust spray work, Sayer has found that the normal droplet spectra may be considerably coarsened by dispensing with the orifice feed restrictors and non-drip valves, thus allowing the rotor feed rate to rise to three to four times the design figure.

The following are various aircraft requirements which, it can be said, a pilot considers in the course of his employment in agricultural aviation.

• 1. Physical comfort.

• 2. Accident protection.

• 3. Operating, performance and flying requirements.

• 4. Work capacity and operational efficiency.

The Agricultural pilot looks for the following qualities in his aircraft, and I suggest that he looks for them in this order of importance:

Lively performance

Docile handling

Personal protection in an accident

Reliability of both aircraft and agricultural gear.

I said that performance should be lively. Perhaps it should be not far short of exhilarating. Certainly in many cases in current operations it can barely be described as adequate. Of course, some conditions of work call for a higher performance than others, and it is not possible to talk about ideal figures without relating them to a specific operation. Compromise is inevitable, but the most exacting types of work must be kept always in mind. Admittedly, most suggestions for performance minima made by a pilot may call for engines and power loadings which will seem quite uneconomical to the operator, particularly as engine overhaul costs often appear to increase as the square of the engine power.

The agricultural aircraft is a special vehicle with special needs for simplicity in design coupled with interchangeability and accessibility of components and equipment. Cheap price, commercial availability and easily maintained equipment of high reliability, field replacement capability, freedom from the need of special tools and rigs, together with lack of complication, reflect markedly in the economics of operation and provide improved safety in operation.

To establish that these parameters are appreciated and allowed for, it is profitable to consider whether operators themselves give adequate and logical thought to engineering problems in their forward planning, and whether aviation legislation permits an adequate projection of this philosophy rather than reducing true airworthiness, true safety levels, and reasonable economics.

In this paper the emphasis is on safety problems connected with the use of light fixed-wing aircraft for agricultural purposes. Most of the aircraft concerned are between 2000 and 6000 lb all-up weight and are single piston-engined types. About 97 per cent of all hours flown in agricultural aviation all over the world are by such small fixed-wing aircraft, the remainder by larger aircraft such as the DC-3 and helicopters.

The mass of statistics available on this type of flying is therefore confined to the small fixed-wing aircraft and since this type is obviously the most important with respect to this activity, then it is appropriate to concentrate on this type.

A survey of information on laminar separation bubbles and their effect on the stalling characteristics of aerofoils is presented. It is shown that there are two principal kinds of bubbles and that their existence can be predicted. It is believed that their behaviour may be related to the kind of boundary layer transition process present.

It is intended that a second part of this paper will describe the characteristics of aerofoils at Reynolds numbers typical of model aircraft and show how the observed phenomena are related to the behaviour of laminar separation bubbles.

When Man first dreamt of flying, he most probably envisaged himself soaring through the air with wings on his arms, and his legs trailing behind him like a bird's. This mental picture quite likely influenced a good deal of his early aeronautical thinking and it is a curious fact that even in comparatively recent years a number of the more bizarre aircraft have incorporated a prone pilot position as if the designers, having abandoned orthodox practice, had also reverted to what perhaps seemed a more natural position.

Tests at a Mach number of 1·60 show clear evidence of interference on the end tubes of a Pitot rake whose adjacent tubes touch. This effect is increased when the rake is made into a solid rectangular slab by the addition of fillets between the tubes. By making the gap between the tubes equal to one tube diameter the interference is almost eliminated.

The magnitude of the interference on the end tubes is considerably affected by the ratio of the Pitot orifice to the tube diameter; of the three values of this ratio tested the one close to unity (i.e. a sharp-edged Pitot) was found to have the least interference.

I Think Mr. Filleul's main point, (in the November Journal) somewhat hidden behind some obscure comments about Carnot engines and the like, is that in a by-pass engine with heat exchanger, the heat exchange process is making a definite alteration to the thermodynamic cycle efficiency of the whole engine and not just changing the propulsive efficiency. This may or may not be an important point, depending upon the point of view of the expositor of the subject. In fact, even without heat exchange and when the by-pass compressor and turbine have realistic efficiencies, the by-pass process itself does alter in an unfavourable direction the overall thermodynamic cycle efficiency. This is one reason why in a by-pass compressor with separate jets one does not wish to make for optimum performance the by-pass and jet velocities equal.

The Technical Note by C. H. E. Warren in the September Journal raises a question on the transfer of lift, of an aeroplane in supersonic flight, to the ground. This problem was considered in reference 2. It was shown that, as expected, the resultant of the pressure field produced by the aeroplane is equal to its lift. This apparent inconsistency with the N-wave pattern, predicted by Whitham stems from the fact that most applications of Whitham's theory are based on asymptotic forms for the velocity perturbations. Thus, the formula for the axial velocity perturbation is obtained by allowing (M2— l)l/2r/y to tend to infinity, where M is the flight Mach number, r the radial distance away from the aeroplane, y=x—(M2 — l)1/2, and x is the distance along the aeroplane flight direction. This approximation is valid in the vicinity of the shock waves emanating from the aeroplane.

In the October edition of the Journal Bragg and Smith contribute a stimulating article suggesting that in several examples of confined or two-dimensional flow pressure waves have a special velocity of propagation that is not equal to , the wave velocity in an infinite unbounded medium. Moreover phenomena such as choking can be said to occur at the special wave speed appropriate to the particular circumstances, so that it might appear sensible when describing the flow to use a Mach number based on the special wave propagation velocity rather than on They invite comments on this suggestion.

In his note, Forrest compares the results of an experimental investigation of the notched fatigue strength of HE 15 aluminium alloy (L.64/L.65 type) in three conditions of heat treatment with predicted values obtained using the analysis by Gunn. This analysis appears in R.Ae.S. Fatigue Data Sheets A.00.01 and .02.

The analysis requires a minimum knowledge of four parameters, Kt’ the elastic stress concentration factor, ft the tensile strength, ƒp the 0·1 per cent proof stress and Sao the fatigue strength under reversed loading for the specified endurance Ncycles.