As one of the first speakers at this Symposium, with no particular axe to grind and no panacea to offer, I think my most useful contribution will be to provide some sort of backcloth for later contributors. I therefore propose to discuss the relative effects of some of the factors affecting the design efficiency and operating costs of short-range aircraft so as to try to arrive at some impression of what are the more important things to concentrate on. This has been done before at various times, but I think it is worth doing again as a starting point for this discussion. The views expressed are my own and not necessarily those of RAE or MoA.

I shall be talking mainly in terms of generalised long-term effects, and the factors and exchange rates quoted will be the overall effects on an aircraft still in the design stage, assuming that it is re-optimised if necessary as each factor is varied. Without implying any preference one way or the other, I will assume a conventional wing-plus-body design with jet or fan engines; other contributors will be dealing with the possibilities of all-wing layouts and with the question of propellers versus jets for short ranges. I assume that we are thinking in terms of stage lengths of the order of 250-500 miles, and the costs and exchange rates will be quoted for this sort of range; so far as relative sensitivities are concerned the precise value is not very important once one is in this bracket (as compared with 1000-1500 miles, for instance).

Cheap and short range is a contradiction in terms if one is talking about cost per mile. Fig. 1 is from “American Aviation” for December 1964; it shows cost and revenue of US domestic operations in 1964. Over the average trip of 680 miles there was a margin of about 10 per cent of revenue over cost. At 200 miles, however, there was a deficit of 30 per cent. If the average 10 per cent margin were to be maintained at present fare levels, cost would have to be reduced by 35 per cent—no mean task.

The reasons for relatively high costs on short sectors are well known. Block speed is low; frequent stops consume much time on the ground and so utilisation of aircraft and crews is low; the outcome is that the output in seat miles per annum, and hence the revenue earning ability, is reduced. Landing fees and Station costs are spread over a smaller revenue.

The continued expansion of air transport is bound up with its possibility of producing ever lower fares. Thus the future of both sides of industry depends on the success in this field. This paper notes some of the difficulties seen from the manufacturer's side in this rather inexact science. It is essentially a personal view not associated with any one Company's views, but based on some years of experience in the industry. It answers no questions, but is aimed rather at provoking discussions on some of the important issues, particularly those which tend to be taken for granted.

It should be stated also at the outset that this paper is obviously affected by the current beleaguered state of the British airframe industry. There is nothing in it, however, which does not apply to any nation's airframe industry and it is not intended as criticism of the UK one. It is certainly not the intention to add to the volume of anti-British comment which is so valuable to our competition.

The aim of this paper is to show how design improvements may lead to a reduction in direct operating cost, pence per passenger mile. In all the comparisons made it is assumed that equal standards of equipment, accommodation, powerplant efficiency, and so forth, apply and that equal skill and standards apply in manufacturing; differences therefore are due to design features. The paper is in two main sections:

(1) A Satellite's eye-view of the whole design problem of the cheap short-range transport aeroplane.

(2) A more detailed description of two specific examples which illustrate the conclusions drawn from the general survey.

The first part is historically fiction but technically fact; the second part (despite the temptation to interchange the above two nouns and adjectives) is, I claim, fact both historically and technically.

I have departed from the historical sequence of events for the first part because we have now realised that it is possible to present in a comprehensive general argument the rather confused mass of data, ideas, techniques, inspirations and false trails that, in the course of time, led us to an enthusiasm for the all-wing Aerobus.

It is surely of the greatest importance that those engaged on the development of Civil Aircraft should give attention to all aspects of the economic operation of air transport and consider indirect operating costs and revenue, as well as the direct costs. This is no easy field of study and one may be accused of asking questions rather than providing answers. However, no discussion of short-haul transport can be complete without the fullest consideration of all aspects of airline cost.

Although the airframe, engine and accessory manufacturing industries are primarily concerned with the provision of vehicles, systems and equipment for Civil operators, they are also closely concerned with the utilisation of equipment and with the scale and direction of the developments of air transport in the future. We therefore subject to continuous study all areas of potential air transport growth and, of these, the short-haul domain is now of special concern.

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.

— A great deal of publicity has been given in recent years to the problems caused by microbiological attack on aviation fuels, although there had been considerable experience of the subject before the first serious problems arose in aviation. Intensive studies of the nature of the attack have shown that although limited use of biocides has been successful, the best control is by the elimination of stagnant water from the fuel supply system and the aircraft fuel system.

There seems to be a disturbing rate of increase in new scientific and technical terms. The purpose of these notes is to stimulate a discussion of this trend.

When inventing or introducing new terms the following points should be borne in mind: (1) is a new word necessary or desirable, (2) is it apt and well-constructed?

As regards (1) the usual justification is that science and engineering are developing so fast that in order to communicate new ideas and new concepts an increase in the vocabulary is essential. This, however, can be overdone. The very act of coining a new word implies a theoretical assessment, almost an acknowledgment of the fact that a concept or phenomenon, or particle has a well defined identity. The following, somewhat exaggerated examples, illustrate this point. It would have been most unfortunate if spectroscopists at the end of the last century had insisted on giving one and the same chemical element different names according to the wavelength of the light they emitted. I wonder whether the many names allocated to elementary particles today may not become an embarrassment should it turn out that they are in many cases just excited states of one and the same particle. Conversely, one must applaud the restraint of the nuclear physicists for not giving separate names to various radioactive isotopes. After all, as far as nuclear properties go, many isotopes (e.g.57Co, 58Co, 60Co) have very little in common. And, although we have a separate name for the heavy hydrogen isotope (deuterium), physicists and chemistsi have so far resisted the temptation to give the light isotope of helium (3He) a name and we are still spared “trelium”.

—The experience from several environmental trials on helicopters is reviewed to show how the life of main and tail rotor blades was reduced by erosion and how effective various modifications have been in protecting these blades. The compressors of the gas turbine power units were also affected by sand ingestion and intake filters were used on later trials to protect the engines. The engine erosion problem is discussed with reference to the position of the intake, the degree and type of filtration and the design of the compressor itself. The design features of the helicopter which affect its ability to operate in dust and salt-laden atmospheres are also considered, along with suggestions for further research and development.

In the Introduction to the second paper in this series (September 1965 IOURNAL), a simple flow diagram illustrates the relationship between demand and supply for aircraft and air transport which is shown in Fig. 1.

Manufacturers supply airlines with aircraft from which a fleet is built. The airlines are thus faced with problems of capital investment and procurement programmes, which were discussed under the heading of fixed costs in the second paper.

The discussion of problems of fleet effectiveness and optimal utilisation begun in the second paper, and elaborated in the third (October 1965 JOURNAL), is continued in Section A of the present one.

Attention is then switched in Section B to the demand for air transport. On the basis of demand for transport of passengers and freight, airlines must determine routes, allocate frequencies to these routes, and prepare time-tables.

The paper concludes the discussion of Operational Research applied to airlines by summarising the models used in the series in the light of the aims specified in the first paper (August .1965 JOURNAL).

On unswept wings, or wings with small amounts of sweep, the favourable pressure gradient round the leading edge, where the flow is rapidly accelerated away from the stagnation line, ensures a certain amount of laminar flow, provided the wing surface is sufficiently smooth. On highly swept wings, however, it has been found that turbulent flow can exist on the attachment line itself and there are therefore no naturally occurring regions of laminar flow. This trouble arises from the turbulence at the root of the wing, which sweeps along the attachment line. If the Reynolds number of this turbulent attachment line boundary layer is greater than some critical value, the whole attachment line boundary layer remains turbulent and the complete wing is contaminated. But if the Reynolds number is below the critical value, the turbulence decays along the leading edge and the boundary layer on the attachment line reverts back to the laminar state. This situation arises when the leading edge radius is small and the wing is only slightly swept. The attachment line boundary layer Reynolds number, Rθ, is given by the following equation:

—Measurements of pressure distribution and skin friction have been made on an 11% thick aerofoil in the presence of a variable base bleed flow. These tests show that the effects of bleed decay rapidly upstream of the base and are measurable only over the rear 40% of the chord. The integrated profile drag values also confirm that wake traverse measurements are subject to error in a strong vortex street.

In using the method of stage stacking to compute the off-design performance of multi-stage axial compressors, it has been observed that the limitation on performance at speeds above the design speed has been set by the stall and the choke points of the rear stages(1). Thus if the rear stages can absorb a wide range of mass flows between stalled conditions and choked conditions, a better performance could be obtained.

Compressor stages using low stagger blades will absorb a large range of mass flow between stalled and choked condition; but because of the high axial velocity involved in their use, they tend to be unsuitable for low pressure stages because of the high Mach number obtained. In the higher pressure stages the increased gas temperature will lower the Mach number for the same velocity and give more efficient operation.

The rate of change of the pitching moment coefficient upon an aerofoil with respect to the deflection of a flap control—a quantity denoted by m2—is of interest in its effect upon the torsional twisting of an aerofoil and hence upon the wing reversal phenomenon. The value of m2 is very susceptible both to small aerofoil profile modifications and to boundary layer conditions. As a result this quantity is not very amenable to attempts to correlate experimental values and this is particularly so for the small values of the control chord that are typical of control tabs.