The computer can be used in many ways to assist in the project and design stages of aircraft development. As would be expected it was used first to assist in the more unwieldy calculations of the design stage. Massive calculation sequences which previously involved much tedious labour, or were effectively beyond the capacity of a design office to perform, suddenly became a few hours work for one or two technicians. Project analysis, being concerned with an earlier stage of development where calculations are simpler and more approximate, tended to remain largely unaffected. However, it became clear that the very simplicity of the preliminary project calculations would, at least in principle, allow the entire project analysis phase to be computerised, so allowing many parametric variations to be done in a short time with minimum effort. The natural follow-on to this was the optimising project analysis program of which examples now exist. With such programs one is able to predict an optimum configuration to meet a given requirement, given only the basic data to define the scope of the calculation.

Subsonic jet transport has been with us now for about a quarter of a century. There are young people starting their careers today who have never known a sky without jet noise and the V-wing silhouette of a passenger carrying aircraft. Indeed, it must seem to them as permanent a feature of our world as the steam train between the world wars was to people such as myself; the big difference is, as I hope to show, that air transport has not yet reached a development plateau.

Aviation has always been a dynamic industry, with a rapidly expanding technology and opportunity which has now taken it beyond the atmosphere, into space and onto the planets. The spectacular steps have not been taken in the first place for the benefit of commercial transport operations—although there have often been consequential advantages. Advances were pursued because they were thought necessary for the maintenance of effective armed forces and the provision of efficient weapons.

Active Control Technology (ACT) is not a new subject; it has been utilised in engineering circles for over a century in various guises, the first application of any significance being the steam engine governor. The history of the subject is accordingly long and is well referenced, and we shall depart from the time-honoured rigmarole of providing a detailed survey of early developments by directing our audience instead to Ref. 1 where such a survey may be found. In similar mildly unconventional vein, we note that this platform, and many others like it in this country and elsewhere, has been used many times by eminent individuals to expound their own idiosyncratic views as to how ACT should be defined in its constituent functions and how, in turn, these might possibly be applied without much in the way of reference to what has been done or to the many practical limitations. While our own views presented here will also be idiosyncratic, we shall attempt to relate what we say to that which has been achieved in actual applications and, based on these achievements, to what might follow in the foreseeable future.

I consider it a great honour, and most appropriate that the first function to be performed by a Chairman of the Flight Simulation Group, the youngest group of the Royal Aeronautical Society, is to present this paper to the Section which represents the interests of the younger members of the Society. I bring the best wishes of the Group to the Graduates and Students Section and I hope that this paper will stimulate an interest in the subject of flight simulation. The established members of the simulator fraternity who are present this evening will at least forgive me, and some, I hope, may agree with me, when I suggest that simulation is one of those areas of aeronautical engineering where a young and fresh approach to the problems encountered is likely to pay dividends.

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?

Increasing mechanisation and population densities in our society, coupled with higher standards of living and education, have in recent years resulted in a growing concern about pollution and its effects on the environment. The era of sporadic individual complaints to government is being rapidly superseded by one where strategic concerted action by irate citizens’ interest groups is becoming commonplace. As a result, governments are becoming increasingly involved with the problem of environmental pollution; in Canada, for example, the Environmental Protection Service of the Department of Fisheries and the Environment for fiscal year 1976–77 had a staff of approximately 800 and a total budget of $22 million.

The primary effects of aviation on society are cited fairly regularly by both the aviation community and its critics. Papers already presented at this conference and others have reviewed the direct benefits to commerce, economic development, and world trade, and the unfavourable aspects of energy usage and environmental disruption.

There are also some secondary effects which in the long term may prove even more significant. The characteristic influences of improved transportation systems in general are magnified in the case of air transportation because of its greater scope and pace. The growth of a major transportation system eventually transforms almost every facet of society—the distribution of population within and among countries, the evolution of cities, the development of remote areas, the birth of new industries, the advent of multi-national corporations, the location and structure of governments, the interchange of social philosophies, and even the spread of disease. Increased mobility has accelerated the civil rights movements and the pressures for independence throughout the world. The full schedules of sporting events made possible by air transportation create an outlet for national rivalries on a relatively peaceful basis.

Much of the data published on the subject of cost prediction for aircraft has dealt with empirical methods of estimating the total engineering hours of design and development. Less seems to have been written by or for the practising estimator, concerned not only with the total estimate at the initial stages of the project but also with its continuous refinement to full go-ahead, on to certification and later still to variants. In this paper the authors describe some of the methods they use, the historical background against which the methods have evolved and discuss some of the problems which are met.

There can be no question that manoeuvrability is one of the principal requirements for a combat aircraft, and achieving the necessary amount of usable lift is never an easy design task. The lift generated by the wings ceases to be usable when it is accompanied by unacceptable levels of buffet or degraded handling or loss of control. Practically all combat aircraft have to penetrate some way into this region where things begin to go wrong, and the problem we are concerned with in the Royal Aircraft Establishment is to see how certain we can be, before the first flight of a new design, that the so-called buffet boundary will allow the specified manoeuvrability to be achieved. One line of attack is to take an existing aircraft, record and analyse its behaviour in these limiting conditions, and see whether design and test methods are good enough to predict what we find in flight.

If the term ‘angle of incidence’, so frequently used in aeronautical discussions, could be confined to a single definite meaning, viz., the angle at which aeroplane and wind actually meet, much error and confusion would be averted. But many of the best writers use this term loosely and inexactly, with the result that their calculations and explanations of phenomena are thereby often rendered of little value, and students are misled.

If a plane be held stationary in a horizontal wind (Fig. 1), the angle of incidence A C D will be equal to the angle with the horizon. But if the wind have an upward trend, the angle of incidence will be increased to A C D2. A calculation based on the assumption that A C D still remained the true angle would, of course, be seriously in error.

It is an historical fact that the Rotol Airscrew Co was formed in the late 1930s specifically to manufacture variable pitch propellers. It would not be unnatural, therefore, to think that the development, in 1975, of a propeller for a crop spraying aircraft would be a routine matter for a company with nearly 40 years experience in the business. To some extent it was, but in other ways it proved to be an interesting and exciting challenge. Perhaps this was partly due to the fact that it was a new type and new types of aircraft or engine or major accessories are something special these days. But the main reason was that some fairly radical changes in design philosophy to those which the Company was accustomed were employed and these provided the major source of development activity.

The problems involving vibration which affect helicopters can be divided into two major categories:

• (a)Forced vibration effects

• (b)Aeroelastic and aeromechanical instabilities.

Forced vibration effects are subdivided into two categories.

• (i)Effects due primarily to aerodynamic forcing; and

• (ii)Effects due primarily to mechanical forcing.

Forced vibration effects have important repercussions in the area of:

• (i)Crew comfort and efficiency

• (ii)Fatigue strength of dynamic components and the airframe

• (iii)Reliability of electronic equipment.

The most important forcing effect is aerodynamic in origin, and this will be considered first.

My first comment is about the term ‘third level'—I believe it to be bad. I think it does the operators concerned an injustice. I think it inappropriate because, as we all know, almost anything with the word ‘third’ applied to it is widely accepted as being sub-standard. In some cases, as in the bad old days of third-class railway travel in the UK, it was virtually an admission that the standard offered was poor.

For these reasons the term is quite misleading in the aviation context, for third-level operators are in fact actively engaged in raising the standards of air transport in the regional areas. In doing this they are following the trend in aviation generally. The introduction of jets over intercontinental routes was inevitably followed by their use over major domestic networks. Today we are witnessing their increasing adoption in regional air transport, one of the principal reasons being that passengers accustomed to top class amenities on intercontinental flights are not happy about anything much less comfortable or less speedy when they leave the big jet at ths major international airport; they have come to expect comparable standards from the feederline or regional service by which they are to complete the journey.

It is my privilege to speak to you tonight on some aspect of the work of testing experimental aircraft, and in order to present my subject to you in as lucid a manner as possible, I am going to ask you to consider that we actually have a machine before us waiting for its first test.

We must assume that the cockpit arrangements have been approved before this, for so much has to be done that can only rightly be done as the machine is being built. The seat and rudder positions must be comfortable, windscreening good, view ample, engine controls handy, flying controls accessible, smooth and firm, petrol flow satisfactory and necessary instruments must be clearly visible. The first thing to be done is to weigh and balance the machine. From this we learn the total weight—the designer learns whether he has been clever or not—and then we chase that elusive spot the e.g. The wing position and tail setting have been designed with the e.g. in an assumed position, and if one weighing shows it to be seriously out, then before the machine can be flown it should be ballasted to bring it to the required balance. The flying controls should be carefully tested by the pilot. It is not sufficient to waggle the joystick and watch the ailerons and «levators move; very careful attention must be given to see that they move the right way.

By way of introduction, I suggest you consider for a moment of four aircraft as dissimilar as a small general aviation aircraft, a large transport such as the Airbus, a glider and finally a fighter aircraft such as the Tornado. As regards handling in the air of these widely differing flying machines, their most significant common quality is perhaps that they can all be flown by a human pilot.

In the definition of the desirable handling qualities of these aircraft, one might—in complete innocence—expect to find a description of such desirable qualities in terms of the behaviour, capabilities and limitations of the human pilot, which one would, of course, expect to be independent of class or category of aircraft.

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.

Aircraft lift and drag characteristics can be measured in flight by subtracting the components of engine net thrust along and perpendicular to airspeed from the corresponding components of the total aerodynamic force R.

In steady straight flight the flight path angle can easily be measured and consequently the components of R when aircraft weight is known. Measurements in steady-straight conditions, however, are time consuming and furthermore the resulting accuracies are limited due to unavoidable deviations from the nominal straight flight condition.

It is understandable for fundamental cycle efficiency reasons that the technology level claimed by manufacturers in the development of gas turbines has tended to be judged by the declared maximum TET, but this is not any longer an adequate criterion. A better criterion would be the maximum TET at which it is possible to operate a turbine for a given value of the net turbine shaft efficiency after allowing for all the cooling losses without a penalty in the operating life of the turbine in service.

Figure 1 shows how the specific fuel consumption of turbofan engines varies with turbine entry temperature and overall pressure ratio for different levels of polytropic efficiency of all the components of −2%, +2%, +4% relative to datum. The importance of obtaining the highest possible component efficiencies rather than by further increasing TET and overall pressure ratio (which increase engine complexity and cost), is clearly brought out.

The possibilities for technical progress in every aspect of aviation during the first half of this century have indeed appeared as a limitless horizon. Increasingly since that period, as we have moved outward toward the technical horizons, the course has become rougher, and we find ourselves in the foothills with a high and formidable range of mountains looming into view before us.

These figurative mountains are representative of the increasing interface deterrent which we are encountering at the edge of the aviation systems’ advancing fronts. These deterrents include socio-environmental and political impacts, economic factors, and the need, in many cases, for redirection and/or equivalent progress in non-aviation technical systems which interface with aviation development. Specific areas are increasing costs for R & D, increased fuel costs, environmental effects of new aircraft and air transport ground systems, changing requirements and demands of the public, increasing liability exposure, increasing regulatory constraints and conflicts, etc.