Since it is too complicated to obtain analytically the stress distribution in a plate containing two reinforced circular holes under uniaxial tension, the stress distribution along the inner edge of a reinforcing ring will be determined experimentally in this report.

The relationship between σθ/p at the inner edge of a ring, the dimensions of a ring and the distance between the centres of two holes will be investigated. Experiments are done in the cases when the uniform load is applied in the perpendicular or parallel direction to the centre line (see Figs. 1 and 2).

The revival of flying in the British Army dates from the Air OP flights of the Second World War, manned jointly with the RAF and highly successful in their limited role. In 1957 the Army took over full responsibility for its own aviation and in the previous year had already agreed with the Air Ministry and the Ministry of Supply to purchase the Saunders-Roe Skeeter. This two-seater aircraft had been under development since 1948. It was designed for worldwide use and with its 215 hp Gypsy Major engine it was supposed to have a service ceiling of 10 000 ft and an ability to climb at 180 ft/min outside ground effect at 4000 ft and ICAO + 30°. By 1958 the Skeeter had been accepted into service, but on its tropical trials in Aden in 1959 and 1960 it could produce only marginal power and the cylinder head and oil temperatures were above limits. It was therefore relegated to use in temperate climates and the Army was faced with the situation of still having no helicopters deployed in the Far East and Middle East. We had to make do there with the Auster, a fine, if rather senior reconnaissance aircraft, able to carry out only a few of the many roles required of an Army aircraft. A new aircraft, the Saunders-Roe P531, which became the Westland Scout, was ordered in 1959.

It must be obvious to anyone who has anything to do with agricultural aviation, that the training of agricultural pilots has, lately, received more attention than ever before. There are several good reasons for this and before speaking of the training itself, as it is carried out in the different countries, I feel that it might serve a useful purpose to go into these reasons more deeply.

The first part of the subject, that is, the reason why we are forced to pay more attention to the training of agricultural pilots than we have in the past, I have often mentioned both by word of mouth and in writing. This will not prevent me, however, from doing so again. This whole question is, in my opinion, of prime importance.

The purpose of this note is to present formulae, derived by stationary energy considerations, for the deflection of an arbitrary length of sandwich structure subjected to the three-point bend test, for comparison with experimental results.

In part 1 of this paper the shape of an axially symmetric ducted body, of given length and fineness ratio, having minimum pressure drag was derived using the Newtonian impact pressure law. It was shown that this shape closely approximated that found by a computer method of Guderley, Armitage and Valentine which employed the general flow equations. Indeed the two curves could be distinguished only for values of the diameter ratio Δ=di/df, of the initial and final diameters, so small as to be outside the range likely to be used for cowl shapes.

The principles of the design of spacecraft are well known and it is not the intention of this paper to review them. Rather it is the intention to review the possibilities of special purpose and multi-purpose designs in relation to the boundary conditions established for the creation of the European Space Research Organisation. These boundary conditions are contained in the Convention and the Protocols for the Organisation, which came into force in March 1964, after signature in June 1962.

The Convention states that: “The purpose of the Organisation shall be to provide for, and to promote, collaboration among European States in space research and technology, exclusively for peaceful purposes.” In addition, it states that: “In order to fulfil its purpose the Organisation shall carry out a programme of scientific research and related technological activities” and some of these are listed in the Convention.

The author presented in his recent main lecture to the Society, “The Computer Shapes the Theory”, a number of novel developments in the matrix displacement method. Since the publication of the lecture and discussion will inevitably be delayed and cannot but illustrate the application of the new ideas on a series of examples, he has been repeatedly urged to summarise some of the more important theoretical contributions in the form of Technical Notes. The first deals with the elasto-plastic analysis, in the presence of strain hardening, of arbitrary three-dimensional configurations. The reader is assumed to be familiar with the corresponding elastic analysis given in refs. 2 and 3, where the medium is represented by a suitable assembly of tetrahedra under constant stress and strain. The corresponding two-dimensional case is investigated on the basis of triangles. Arbitrary anisotropic behaviour and large displacements were also included in refs. 2 and 3.

An analysis is presented for equilibrium of yawing moments for a yacht sailing in the displacement mode in smooth water. The geometry of hull form and sail plan are quite unrestricted, although special attention is given throughout to currently popular types.

The free-surface flow is simplified by a reflection technique. In cases where the hull form is appropriate, the hull hydrodynamics are treated by lifting-line theory: in other cases slender-body theory is applied. The sail aerodynamics are treated by methods taken from aerofoil theory. Some design charts are given and computation methods are suggested for practical design calculations.

Static directional stability is treated theoretically and some general conclusions drawn regarding the influence of various characteristics on stability.

Where the theory has been applied, results have agreed with the available experimental data within the limits normally provided for adjusting balance of helm. Changes of balance with angle of heel and static stability have been given by the theory at least qualitatively correctly; experimental results are, however, not available for comparison.

Ablative cooling is a proven, reliable thermal protection method for entry vehicles with zero to moderate hypersonic lift/drag ratio. Unfortunately, this method becomes impractical for vehicles with lift/drag ratios greater than about 1-0, because of the severe weight penalties which accrue from long glide times and the large surface areas associated with high LID configurations. Moreover, to obtain high hypersonic LID it is necessary to minimise blunting of the nose and leading edges, a condition certainly present when ablation is used to protect the leading edges. This situation is commonly handled by the design of a high temperature radiation cooled structure of refractory metal with supplemental insulative protection in the stagnation region along the leading edges and in areas of local heating such as those resulting from shock impingement. This insulation may take the form of a high temperature foamed ceramic such as zirconia foam.

This note is concerned with the significance of a “hold period” on thermal fatigue endurances and on the use of a frequency exponent to correlate the results of mechanical fatigue tests at various temperatures.

In their note in the January 1965 Journal (pp. 53-55), Coles and Skinner quite rightly pointed out that residual stresses, set up as the result of plastic yielding in compression during an initial heating period, will undergo redistribution during a subsequent “hold period” at an elevated steady temperature. However, it is important to note that the redistributed stress pattern and the associated creep strains at the conclusion of the “hold period” will depend very much on the nature of the applied loading. For example, the compressive strain and the associated tensile stress set up in the rim of the disc will both fall in magnitude if the disc is not rotating and may reach infinitesimal values if the “hold period” is long enough.

Formulae are presented giving the centre of pressure of axi-symmetric bodies at zero incidence having profiles for which the drag is a minimum in Newtonian flow.

Boyd has suggested that a close correlation may exist between such profiles, and profiles derived from exact pressure distributions, in supersonic flow.

The Method employed by Timoshenko for the cylindrical bending of uniformly loaded rectangular plates with various edge conditions, has been extended for the case of pressure linearly distributed across the width of the plate.

Pesticides are commonly applied either as aqueous solutions or emulsions, using spray tips designed to break up the liquid into a relatively fine spray. One consequence of this practice is that a variable proportion of the spray, composed of smaller droplets, drifts out of the target area. Some weedkillers, such as the derivatives of 2,4-D, are effective in minute quantities and a small amount of drifting spray can, therefore, cause considerable damage to sensitive crops grown down-wind. If the spray contains an insecticide the same amount of drift will take place under the same conditions. The insecticide is not likely to damage adjoining crops but it may not be wanted, it may cause undesired contamination of pasture land, it may be harmful to domestic animals or to wild life, and it can be said to contribute to the much-discussed problem of environmental contamination. However, it is not the purpose, here, to pursue the controversy about the use and misuse of pesticides. Sufficient to say that drift always results in some wastage of valuable spray liquid, it detracts from the efficiency of spraying operations and it is a problem which everyone would like to overcome.

A decade has elapsed since triangular elements under constant strain and stress were independently introduced within the matrix Displacement Method by the Turner group at Boeing and the Aeronautical Structures Department at Imperial College. They proved a considerable success in the practical analysis of complex membrane shapes as occur in modern aircraft wings. However, the original formulation based on a local cartesian system of axes and the classical concept of stress and strain inevitably leads to an unsymmetrical and aesthetically (as well as computationally) unfavourable expression for the stiffness matrix k. Moreover, the method was restricted to isotropic media. The necessity of extending the theory to finite displacements ultimately showed the inadequacy of the past approach and guided the writer to the creation of new concepts, e.g. the natural stiffness of an element. This natural stiffness, which ignores the rigid body motions and is hence of dimensions (3 X 3) for a triangle with three nodal points, relates in a concise manner the nodal force components parallel to the sides and the elongations of the sides themselves. A powerful tool in its derivation and further development was a new definition of stress and strain vectors which excludes shearing contributions and only works with direct components parallel to the sides. The idea has also been extended to tetrahedra and many standard elements which are incorporated as a basic feature in the structural language ASKA (Automatic System for Kinematic Analysis) developed at ISD by the Applied Programming Group under Dr. H. Kamel. These fundamental ideas were emphasised in the author's recent lecture to the Society.

An established method is used to find the stresses in a square plate pierced by a central circular hole. Although the method is not new, the problem is a practical one which has attracted some interest and for which some excellent experimental results are available.

The general problem of a finite plate containing a circular hole was examined by Sekiya who selected various combinations of the general solutions of the biharmonic equation in polar co-ordinates such that the boundary conditions on the hole were satisfied exactly. The boundary conditions on the sides of the plate were satisfied approximately by collocation. The same approach has recently been suggested by Waters for the particular case of a stress-free hole.

In the course of a recent meeting of the Performance Data Sheets Committee of the Royal Aeronautical Society to discuss thrust measurement in flight, it was pointed out that it is easy to apply the equations of motion incorrectly to the case of an aircraft which is losing mass due to fuel consumption. The rate of change of aircraft momentum is obviously affected by the loss of mass and so, at first sight, it may appear that the margin of thrust over drag required to achieve a given acceleration and /or rate of climb at any particular instant would be affected also. In fact this is not the case. To clarify this point, this account of the momentum and energy balances of an aircraft with an air-breathing engine has been prepared at the suggestion of the Performance Committee.