This paper reviews some of the options for limiting emissions from aircraft engine exhausts. Its main purpose however, is, to investigate the possibility of a Government-airline partnership and to this end, the issues are reviewed along with a summary of the possible approaches that have been identified to date.

The technical features of the data acquisition system used in Blue Streak flight trials are summarised briefly. The results obtained from this system, and the design modifications to which they have led, are then discussed under the heading of performance, control, structure and environment and propulsion and pressurisation.

A survey is made of the effects on aircraft of the main atmospheric factors and of the way they are dealt with, in design and operation, at the present time. Possible developments in the pattern of the relationships of aircraft to the atmospheric environment are discussed, in the light of expected advances like operational VTOL, and orbital-type flight, reliable weather forecasting, and effective turbulence avoidance and gust alleviation systems. These developments should all be conducive to safer and more comfortable flight. Marked further benefits would accrue from weather control in the vicinity of airfields, of which there are some prospects, improvement in en-route operation through weather control appears less probable, and the prospects of smoothing turbulence ahead of the aircraft are speculated on.

Frederick Handley Page was, in every sense, a well-rounded man. His interests were wide—from ancient history to science fiction. They ranged through all branches of aeronautics into astronautics. And he was not afraid to show enthusiasm, tempered with a certain—proper—cynical optimism.

In the 25 years during which I knew him (from 1937 to his death, at the age of 77, in 1962) I found increasingly that one of the endearing characteristics of HP was that he maintained an exceptionally close and imaginative interest in the four main aspects of aviation in which he had been involved from his pioneering days:

• Aircraft manufacture

• Aircraft operation

• Aerodrome provisions, and

• Air education

All of these subjects are just as relevant today.

With drastic increases in oil prices fresh in our memories, with a world recession in full swing, and with two Middle-East countries at war, this is not an auspicious time to speak about the future of civil aviation. But I am following an excellent precedent. In 1940, in circumstances of unrelieved gloom, Dr. Roxbee Cox, now Lord Kings Norton, addressed this Society on ‘Looking Forward’. His lecture was a message of confidence in the long term future of civil aviation, fully justified by later events. Though the energy threat is barely comparable with the state of affairs in 1940, its potential is very serious.

I am wholly confident that aviation can once again rise to the occasion. But this by itself is a small part of a big picture. We need to be satisfied that the world will cope sufficiently well with the energy situation that our future way of life will not be so impoverished that flying becomes an unjustifiable luxury.

In the coming century, the impact of air travel on the environment will become an increasingly powerful influence on aircraft design. Unless the impact per passenger kilometre can be reduced substantially relative to today’s levels, environmental factors will increasingly limit the expansion of air travel and the social benefit that it brings. This essay considers the three main impacts, noise, air pollution around airports and influence on climate change. Of the three, impact on climate change is taken to have the greatest long-term importance and is discussed at the greatest length. It is argued that, of the three main contributors to climate change from aircraft – CO2 emissions, NOX emissions and the creation of persistent contrails – it is the last two which are the most promising targets. Ways of reducing the impacts of these two are discussed and it is noted that, in each case, the best environmental result is likely to entail some increase in CO2 emissions. It follows that regulatory or economic measures to reduce impact on climate should be framed so as to do just that. Measures framed purely in terms of CO2 emissions are likely to be counter-productive. Nevertheless, the design of aircraft to reduce fuel burn and hence CO2 emission remains a key long-term objective; the essay considers the potential offered by new technology and new design concepts in this arena.

Aircraft noise disturbs a significant number of people who live close to airports. It is tolerated due to the economic and social benefits those aircraft bring to society as a whole. However, the levels that are tolerated from individual aircraft must reduce, to compensate for increases in numbers of aircraft movements and the desire for an ever-improving environment for all of society's members. The issue is how to achieve that reduction without destroying social and economic benefits of air travel.

The subject of the quiet helicopter is receiving increasing attention throughout the world because it is now established that a helicopter can be made quiet. Quietening is also needed as more helicopters are being used over cities and residential areas. To date, little attention has been paid to helicopter quietening because the emphasis has been on achieving maximum payload and other performance. Now that the basic helicopter design has been established, refinements for quietening are becoming practical. The comparison is much like the evolution of the automobile and the truck in the city. Initially these vehicles were noisy. As their number increased and their design evolved, mufflers and sound-deadening materials were skilfully applied to reduce their noise to more acceptable levels for each type vehicle.

In the period since the inception of civil jet transport, during which a dramatic increase in travel and commerce by air has taken place, the research and development directed towards the containment and reduction of aircraft noise has spread across a steadily broadening front. The noise of the simple jet engines which propelled the first civil transport aircraft was almost entirely due to the high exhaust jet velocities that were used to obtain thrust from comparatively small mass flows. This is illustrated in Fig. 1(a), where it is seen that noise from other sources, such as the compressor and turbine, is comparatively insignificant. Thus aero engine noise research in the late fifties and early sixties was concentrated mainly on the prediction of jet noise and the development of noise-reducing propelling nozzles. It was not until bypass engines began to appear, with higher propulsive efficiencies resulting from lower exhaust jet velocities and higher mass flows, that the noise of their larger compressors drew attention to the turbomachinery as an additional source requiring investigation.

At the Symposium in April last year the Society met to consider how design and operation of quiet aircraft related to the often conflicting economic and environmental pressures. The prospects for quieter aircraft and engines were discussed from many technical points of view. The message emerging from the discussion was that, compared to the improvements made in the past 10 years, and which would be available now at the cost of replacing existing noisy, older generation installations, further reductions in noise at source would be very much harder to win. Moreover, they would be made against a steeply-rising trend of overall detriment to performance and direct operating cost.

So far as the possibilities are concerned for further reductions in the noise of subsonic propulsion engines, if we are to have more than modest, evolutionary improvements in levels, there will need to be radical changes affecting engine design, such as a definite move towards lower jet velocities.

The helicopter has the ability to operate from small spaces. Its ability to hover and fly slowly efficiently allows it to perform tasks such as surveillance and rescue even in an urban environment. It is however its ability to provide a form of transport into urban communities where surface transport is restricted by the number of routes and/or congestion, as well as to smaller but less readily reached locations that attracts much attention. The development of cost effective helicopters, as well as commercial helicopters with a larger payload indicate that the world is entering another phase in VTOL travel. It is therefore natural that one should consider the environmental factors in such operations.

Normally when I am speaking I have to balance both sides of the argument to make sure that everybody has a fair crack at the whip, and make sure that both points of view are put. Today I do not. It has been made abundantly clear to me they wish me to speak straight on an environmental point of view with particular reference to the noise problems. I will do so with the greatest of pleasure. We have a document here which has good and bad points, from the environmental point of view I would like to state the good, because there are some in this document. Firstly, we know where we are going and we know what we have got to argue about. We know where the Government wants to go in the size and use of our airports and from the Gatwick point of view this is something we have wanted for a long time. Secondly, major developments at the airports in future may be subjected to some form of local authority control, an argument the local authority has been making for a long time.

The advent of the high altitude supersonic aircraft has brought in its train a whole host of complex control problems. As far as the engine manufacture is concerned, these are perhaps best indicated in the diagrammatic layout shown in Fig. 1

It is not my intention however, to go into the question of multiplicity of controls and their proper co-ordination, nor will I venture into the abstruse province of stability. I should like instead to concentrate on the fuel system itself, i.e. the supply and control of fuel to the main engine combustion chamber.

The effects of aviation on the environment are becoming increasingly important. The world's airlines already have thousands of aircraft serving the passenger and freight markets and the market demand is still increasing. Unless steps are taken to address the problems created by aircraft noise and emissions, the future progress of the air transport industry will be inhibited.

The seriousness of the topic and the factual nature of the Technology Sub Group report are the reasons why this special issue of The Aeronautical Journal is being devoted to “Greener by Design”. Although the report has been carefully read by a number of people outside the Sub Group, it has not been refereed in the normal way (though a number of minor numerical changes have been made to the tables and text of the original report, partly to correct errors and partly for internal consistency). The reports from the other two Sub Groups, covering operations and market-based options, together with the Summary for Policymakers of the Technology Sub Group, will be issued shortly in a single volume but will not necessarily be published in The Aeronautical Journal.

The paper reviews the development of amphibious hovercraft and considers the noise emission levels of current types of in-service craft. A brief reference is also made to side wall hovercraft and hover barges.

An outline of suggested methods for quantitative measurement of noise level and format is given, should legislation be deemed necessary at some future date.

Finally recommendations are made for further research and development programmes aimed at achieving significant improvement in the next generation of hovercraft.

This paper describes the current status of knowledge regarding the impact of aviation on the atmosphere. The growth of the aviation industry is likely to continue in the future and at present there are significant concerns that this will adversely affect climate and local air quality in the vicinity of airports. Indeed, it is possible that air quality may become a constraint to increased capacity of some large hub airports. Currently the radiative forcing impact from aircraft emissions, other than CO2, are not accounted for in the International Civil Aviation Organization emission trading scheme proposals. Taking only this approach, emissions trading could, in theory, increase the radiative forcing, rather than decrease it. The study of improved ‘environmentally friendly’ flight is still in its infancy, however any proposed and actual new developments, in terms of technology and operational practice, should include an environmental assessment.

The demand for aerial spraying is determined by agricultural needs and timing. The degree to which an aerially applied compound is effective is governed by many factors, which exercise their influence both at the time the compound is applied and for some time before and after this event. The impact of the weather and its interaction with other factors may be felt at all stages of relevance to an aerial spraying operation—these stages, which are of course also relevant to ground based spraying operations, may be categorised as follows:

• (i) The long term pre-spraying environment (measured on a time scale of days or weeks).

• (ii) The immediate pre-spraying environment (measured on a time scale of hours).

• (iii) Conditions at the time of spraying.

• (iv) The immediate post-spraying environment.

• (v) The long term post-spraying environment.

The Paper describes a metal and composite recurrent cost model of a large civil aircraft wing structure for a multidisciplinary design, analysis and optimisation (MDO) environment. The work was part of a recent European MDO project (BE95-2056) which investigated methods for the integration of structures, aerodynamics, dynamics and manufacturing cost at the preliminary design stage.

The paper discusses the cost modelling approach, which is based on parametric and process cost model methods, and the integration of the cost models into an MDO process. Results for the cost models are shown.

A framework has been successfully developed which allows the incorporation of manufacturing cost models into an MDO environment. It allows a designer to evaluate cost changes with respect to specific design changes such as rib pitch, stringer pitch, wing area and wing sweep.

Three subjects have been selected for discussion in this paper, each of which has a major influence on aircraft design and operating economics. These subjects are airfield performance, noise and aircraft utilisation.

For an aircraft to have good operating economics it must be able to operate with a high load factor over a large percentage of the routes on which it is to be used. The permissible take-off or landing weight, and hence the payload, can be limited by any one of many airworthiness requirements. These include take-off distance and climb, landing distance and climb, and obstacle clearance in the vicinity of the airport.

This paper relates to a recent project in which the aim was to devise a procedure that could be used to identify the linearised transfer functions of the longitudinal motion of the solar powered airship Lotte from flight test data.

Using a non-linear mathematical model of the Airship, a linearised state space model was derived numerically and this was used to derive the response transfer functions, which formed the theoretical results. A test procedure was then developed to identify the transfer functions experimentally from frequency response data obtained in simulated flight tests. Initially, the linearised model was used and the test procedure was refined until a suitable level of coherence between the experimental and theoretical results was observed. The test procedure was then applied to simulated flight test data from the non-linear model, and finally sensor noise was added in order to represent actual flight test conditions as closely as possible. Unfortunately, the results were inaccurate and in some cases, they were unacceptable. When the test procedure was applied to the non-linear model, significant errors were seen in all the results. The addition of sensor noise led to heavily distorted results and a further degradation of the resulting transfer function estimates.

It was concluded that meaningful results could not be achieved unless frequency response data with a higher resolution could be obtained and the effects of sensor noise could be reduced. Presently, no test procedure has been developed that would be of any use in a practical situation. However, a number of ways of possibly improving the test procedure or otherwise improving the quality of the results were conceived near the end of the project. It is therefore the purpose of this paper to account for the shortcomings that were encountered in the project and to introduce briefly the unexplored remedies, in the hope that these may be of some benefit to future identification studies.