I have for several years past been a strong proponent of the helicopter—by which I mean an aircraft in which the means of lift, propulsion and manoeuvre are all combined in one system, the rotor.

It always seemed to me that, despite its ungainly appearance, there was a lot more to come if the benefits of new materials and new aerodynamics could be properly taken. I was reinforced in this view by the appearance of almost all the devices from compound helicopters through convertible aircraft to fan lift VTOL types with delta wings, which were supposed to outdo the helicopter. Of them all only one even looks like an aeroplane.

But that there are limits to the helicopter is undeniable and I now find myself in the position where I can see, or believe I can see, almost the whole extent of helicopter improvement. So what, if anything, is to follow has become a frequent question. Will the new helicopter be such, given the peculiar nature of the tasks which it must perform, that nothing better is wanted, particularly by society which has for years wilted under the pressures of aeronautical progress?

The commercial need to standardise aircraft power supplies has resulted in virtually all modern aircraft (with the possible exception of certain light aircraft) being equipped with a 115/200 volt, three phase, 400 Hz ac primary power system. This is invariably supplemented by 28 volt dc and 26 volt single phase 400 Hz ac secondary systems. If this is the case why is there so much controversy concerning power supplies for avionics and why is there criticism of present day power systems whose performance is so superior to that achieved only two decades ago?

There are two basic reasons for the present situation.

Firstly, development of sophisticated avionic systems has resulted in increased susceptibility to certain aspects of the power supplies and this, coupled with the ever increasing application of avionics for the basic control and safety of the aircraft, has highlighted interface problems with power supplies.

Most civil and military aircraft developed over the past 10 to 15 years have relied upon increasingly complex avionic systems. Some units in this category have been developed to improve the presentation of information to the crew or to decrease their workloads; others have come to play a vital role in automatic flight control (such as fly-by-wire), so that it may not be possible to fly the aircraft without them (and indeed, in the case of ccv the aircraft may even be unstable without them); others again have been developed to give the crew better communication with each other and the outside world, and more detailed information from the radar system and its display. Figure 1 lists a breakdown of systems in a typical modern military aircraft in each of these categories: information and display, control, communications and radar.

Rolls-Royce develops engines for both commercial and military purposes. The majority of the military business is through the Procurement Executive branch of the Ministry of Defence. It is not the purpose of this paper to describe the cost estimating and control of contracts with HMG, but to discuss our procedures for commercial engines.

Expressing a programme in figures of £'s sterling is a convenient way of aggregating many dis-similar resources.

Although this paper is intended to contribute to the symposium a view on the subject from within a major equipment supplier to the aerospace industry, the views expressed, whilst based on experience gained from working within the Aviation Division of Smiths Industries at Cheltenham are my own, and do not necessarily represent those of the Company.

'Avionics’ is used in the title for brevity, although if one accepts the definition of avionics as being the application of electronics to airborne systems and equipment, it does not strictly cover the whole range of products with which Smiths Industries Aviation Division at Cheltenham is concerned. However, since electronics form the major part of Head Up Displays and Flight Control Systems, and an increasing proportion of Flight Deck Instruments and Components, it is the most convenient generic term.

Box-shaped containers when carried by cable harness from helicopters are known to have complicated motions, in many degrees of freedom and with varying degrees of stability. The resulting motions are caused by the complex aerodynamics of, for example, unsteady movements of the containers. These motions create, and are in turn sustained by, complex aerodynamic flows and forces.

Steady forward motion of the container results in separation bubbles initiating from the container leading edges. Sometimes the separating stream surfaces will re-attach to the container surface at some station downstream from the leading edges. In other cases, no reattachment occurs and the container is considered to be in the ‘wake’ of the forward facing surface.

Unsteadiness in the fluid motion, when induced most importantly, for example, by the pitching of the container, can significantly alter the criteria governing the formation of the separating stream surface and its re-attachment.