The history of the Agena space vehicle starts in the years immediately following the Second World War, when the Rand Corporation under a contract with the U.S. Air Force examined the potential applications of satellites, recognising their technical feasibility as an additional bonus from an inter-continental ballistic missile development programme. The U.S. Air Force kept this concept alive throughout the development phase of the ICBM programme; the Lockheed Aircraft Corporation actually received its first contract, for detailed engineering studies, in 1955. The Agena space vehicle has grown from these beginnings and is now the vehicle selected for a large variety of U.S. space projects. Most of these are satellites, but they include a few space probes and moon explorers.

A summary is given of some of the more important experimental results relating to the noise radiated from a cold subsonic turbulent jet. These are then related to the predictions of Lighthill's general theory of aerodynamic noise.

For types of structure where safety standards cannot be preserved by reliance on inspection, a permissible “safe life” has to be determined by relating the loads experienced by the aircraft in service to the fatigue performance of the structure, with due allowance for scatter in fatigue strength and in the frequency with which loads are encountered. This paper gives a working method for estimating the “safe life”—at which the risk of fatigue failure is negligible—of the wing structure of a transport aircraft, where the flight loads giving rise to fatigue are overwhelmingly due to atmospheric turbulence but where allowance has also to be made for “ground-to-air” loads.

The increasing importance of agricultural aviation can best be judged by a table setting out the area treated in the U.S.A., U.S.S.R., U.K. and other countries, which was compiled from recent publications. Fig. 1 shows how important a sector of aviation agricultural aviation has become.

Like other aircraft operations, agricultural aviation is not particularly profitable. Therefore a certain amount of work has gone into economic studies and into development work on methods for improving the service rendered to agriculture in order to improve the economy of aircraft operation.

The process of atomisation is of primary importance in several branches of engineering, such as in the combustion of liquid fuels, in the chemical industry, in operations involving drying, evaporation, absorption, and so on, in fire-fighting and the production and dissipation of fogs and in agriculture.

In agriculture, the spraying of small drops is employed in the dissemination of insecticides, herbicides, etc., for the purpose of crop protection, and the spraying of large drops is used for overhead irrigation.

Since the advent of the atomiser, a hundred years ago, the engineer has been in advance of theory in his practice of atomisation. For lack of fundamental data he has had to rely upon laborious hit and miss experiments to obtain a design suitable to a particular requirement. Thus the atomiser has been a fruitful avenue for the inventor. Its small size and apparent simplicity has, however, deceived many into the belief that the problem is simple. Research over the last thirty years has proved this to be anything but true, and even now our knowledge is still extremely limited.

What is the normal practice of a reasonably good farmer in the matter of fertiliser application to both arable and grass crops? First, there is such a wide disparity between the practice of a good farmer and the rest that it can only be hoped that all will soon be brought up to the good standard. A recent survey showed that about 50 per cent of temporary grass and 70 per cent of permanent grassland in England and Wales still receive no nitrogen fertiliser.

Normal application to both temporary and permanent grassland (for light and medium soils) is three to five cwt. of a compound (12: 12: 18) plus two applications of nitrogen, or expressed as straight fertilisers:

When one considers future developments in Agricultural Aviation there are two questions which need explaining from the past and present and they are difficult to reconcile with one another. One is “Why did not agricultural aviation come into fairly general use 40 years ago in, say, 1920?” The other is “Why has it begun to come into general use now?”

The first paper read at the 1876 meeting was by D. S. Brown, his fifth paper to the Society, entitled “ The Advantages of employing power for aerial propulsion in an intermittent manner, and on the soaring of birds.”

Brown was silent on the advantages of intermittent application of power for flight, and was not much impressed by Sir George Cayley's ideas about birds soaring in upward currents of air reflected from cliffs, hills, and so on. But he spoke with obvious knowledge of the effects of increased size on a weight-strength ratio in the light of the cube/square law.

James Armour, whose paper, “ Wings for Men,” filled fifty pages of small type in the 1873 Annual Report, presented a further paper on the subject, read this time by Brearey in the absence of the author, entitled “ Air Compression under Wingplanes.” James Armour was a good engineer, and had to confess that though he argued on general principles about the supporting forces of an aeroplane in full flight, there were many unknown parameters.

The Rayleigh-Ritz method for approximate solution of equilibrium or stability problems in elasticity is based on the theorem of the minimum of the total potential. Hence the assumed displacements have to satisfy only the geometrical boundary conditions of the problem in order to be admissible. The displacements are expressed as a series of suitable chosen functions, called co-ordinate functions, multiplied by parameters which are determined by the minimisation procedure of the method. Except for the essential requirement that these co-ordinate functions have to satisfy the geometrical boundary conditions of the problem, no general rule for their choice can be given, and experience and physical considerations have to be relied upon.

Static pressure in a moving fluid is usually measured by means of a static hole either in a probe or on the wall of a duct. Such a hole creates a disturbance in the flow and thus has some error associated with it. The determination of the magnitude of this error has been attempted by several investigators and the procedure adopted in each case has been as follows :

The pressure in a region of sensibly constant static pressure was registered using holes of various diameter and a curve of pressure versus hole size plotted. The true static pressure was then obtained by extrapolating this curve to zero hole size, and the errors for the various holes were found. This procedure involves the assumption that, as the hole size tends to zero, the pressure registered tends to the true value. It is usually argued that this must be so because the disturbance caused by the static hole is progressively reduced as the hole size is reduced. Obviously, the validity, or otherwise, of the argument is of fundamental importance in the estimation of static hole error, and a somewhat more rigorous justification of the use of the extrapolation procedure is attempted in what follows.

In the technical note in the August JOURNAL by Morgan and Saunders the values given in the last column of Table I on p. 572 are actually the square roots of the open area ratio.