The rapid rate at which the world's oil reserves are being used up, and the lack as yet of convenient substitute fuels at a competitive cost level, are leading to an increased emphasis on fuel economy in the design and operation of aircraft. This paper outlines technological advances that will contribute to the reduction of fuel consumption and attempts to give a broad indication of the overall improvements that may be achievable in relation to current technology. Since a companion paper is concerned specifically with work in the United States aimed at such objectives, attention is concentrated mainly on advances being made in the United Kingdom.

In the past, it has been generally accepted internationally that in order to land aircraft in runway visual ranges below 400 metres—ICAO Category 3 conditions—a fail operational automatic landing system is required. The Trident aircraft with its triplex system is of course an example of this philosophy. However, the overall system requirements for such operations were specified nearly a decade ago and considerable advances have been made since then on such aspects as understanding fog characteristics, avionic system design, visual aids and of course, airline experience of all-weather operations. Consequently, there is now a world-wide interest in trying to ease the system requirements without jeopardising safety, for example, by considering the use of less complex fail-passive autopilots. If feasible, this would allow existing suitably equipped aircraft to operate to lower minima and hopefully, widen the spectrum of aircraft capable of being equipped, with overall benefits in terms of increased regularity and hence revenue.

The helicopter industry has been experiencing a dramatic conversion from a market which was almost completely dominated by the military, to one in which the civil customer is playing an ever increasing role. As part of this change there is an increasing demand for vehicles whose interior noise levels are substantially lower than those of their predecessors.

One of the most significant recent events in the area of helicopter noise has been an impending regulatory action, rather than a technological breakthrough. This action is the development of helicopter noise standards which are currently being considered simultaneously by the International Congress of Aeronautical Organisation's (ICAO) and by the Federal Aviation Administration (FAA) in the United States. Up to the present time the specification of external noise limits, if any, were either made by individual customers, based on a particular need, or by the designer and manufacturer who might try to forecast how noisy the aircraft could be and still meet market requirements. It is highly probable that the effect of the new standards will be to require future helicopters to be substantially quieter than many of the current models.

In Ref. 1, an exact theoretical analysis is given for the buckling of sandwich columns in compression. The theory is able to predict both overall buckling and face wrinkling and the present paper extends this work by suggesting a design procedure for obtaining least column weight for a given end load and column length. It is shown how a family of optimum design curves can be obtained for given material properties, which encompass all of the geometrical parameters excepting column width. For a given end load, least weight is obtained with least width, but the limiting factor then becomes one of overall instability in the transverse direction of the column. The columns are not optimum in the sense that the buckling and compressive failure loads are made to occur at the same time. Generally speaking, it is not possible to design to this condition for given core and face plate materials and there is found to be a large margin of safety between the buckling stresses and the ultimate failure stresses.

It has long been suspected that the inner portion of any turbulent boundary layer velocity profile obeys a so-called law of the wall which takes the form:

where u is the boundary layer velocity at a distance y from the wall, uτ is the friction velocity given by √(τw/ρ) in which τw is the wall shearing stress and ρ is the fluid density, v is the kinematic viscosity and A and B are constants.