We have followed with considerable interest the two recent technical notes that have appeared in the Journal on aquaplaning (Mr. Gadd, p. 189, March 1963 and Mr. Gray, p. 302, May 1963). May we take this opportunity of drawing to your attention some work on this topic which has been carried out in the Civil Engineering Department of the University of Melbourne in co-operation with the Department of Civil Aviation, Commonwealth of Australia?

Mr. Wilkinson's paper (July 1963 Journal, pp. 421-6) will doubtless be universally applauded by airline management. One can only hope that it receives equal attention from those responsible for the education of Graduate Engineers.

His point about economic training is basic. It is extraordinary how, as professions evolve, certain fundamentals appear to be lost. From the earliest days of Engineering, an Engineer was denned at “a man who could do for a penny what any fool can do for twopence.” I think if the point were raised with most Engineers they would all admit that economy is at the very root of the profession. Nevertheless, how true Mr. Wilkinson is when he points how that Engineers receive little or no formal economic training in their basic education.

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.

The Evaluation of buckling loads of columns presents a difficult problem whose rigorous solution may be very difficult particularly when the variation of moment of inertia or the axial load does not follow a simple law. Hence approximate methods such as the variational and numerical methods will have to be employed. An approximate method is suggested in this note which offers a convenient method for the calculation of buckling loads of bars with any type of end conditions.

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.

All too often, points dealing with some aspect or other of the thermodynamics of powerplants are made which are incomplete, ambiguous, erroneous, or a mixture of all three! The purpose of this note is to try to give a limited, but logical, theoretical analysis of one type of propulsion powerplant, namely the by-pass engine with the possibility of heat exchange between the by-pass air stream and the main gas stream before expansion through the propulsion nozzles. This is a problem to which the solution is not obvious, and which would probably present difficulties to the average student. Heat exchangers are perhaps more of hypothetical rather than practical interest at present, but it is important that a correct thermodynamic approach be made in every case. Nothing is less likely to be engineered than a Carnot engine, and the general line of argument should be of wider appeal than the particular example to which it is applied.