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 benefits that it brings. The three main impacts are noise, air pollution around airports and changes to atmospheric composition and climate as a result of aircraft emissions at altitude. The lecture will review the work done within the Air Travel – greener by Design programme to assess the technological, design and operational possibilities for reducing these impacts. The main aeronautical disciplines all have something to contribute but it is in aerodynamics that the greatest opportunities appear to lie. If these opportunities are pursued, the aircraft in production in 2050 could be very different from those of 2005. It is for the aerodynamicists, supported by the structures and systems engineers and the materials scientists, to make the case for a radical leap.

We set a target for a ‘Silent’ aircraft to be imperceptible outside the airfield perimeter in an urban environment, and then address conceptual designs to meet this requirement. Avoiding some traditional aircraft noise sources requires a radical rethink about the configuration. An all-lifting design has many benefits, enabling a closer integration of airframe and engine than the traditional ‘tube and wing’. Low-noise design includes taking advantage of shielding of engine noise by the airframe; low-noise engines with large, low speed jets; an order of magnitude increase in absorption by liners; and operations for low-noise informing the design. Progress to date on the Silent Aircraft Initiative is presented, along with some conceptual aircraft and engine designs. The further work needed to develop these into viable future aircraft is discussed.

Currently, there is great emphasis, worldwide, on environmental issues. This will have an impact on civil aircraft design, manufacture and operation.

Since the advent of the jet engine and swept wing aircraft, the trends have naturally tended towards greater productivity through increasing speed and payload. The cruise speed of conventional civil aircraft is unlikely to increase beyond current levels. Further increases in productivity are achieved by increasing payloads. This has led towards larger aircraft with the capability for increased ranges. It is shown that designing aircraft for longer ranges increases fuel burn significantly.

A series of aircraft operational parameters have been analysed. Selected data and established trends for current and future aircraft are presented. The data has been interpreted into efficiency terms, relating payload, range, fuel consumed and a measure of unit costs. It is shown that ‘value’ (cost) and noise effective efficiencies decrease dramatically with increasing range.

Environmental and economic considerations, in the future, may well demand greater efficiency in preference to productivity. One solution for long-range services is to use short-range hops. Another is via air-to-air refuelling. This will be addressed, in more detail, in a future paper.

A variety of related questions is posed. Are the right priorities for future aircraft design being set now? New civil aircraft types could be ‘silent’, i.e. make much less noise than current types. They could be ‘green’, i.e. safeguard the environment. Is silent as important as Green? The crucial answer is that future aircraft design should focus on substantial reductions on climate change impact. The air quality targets proposed by the ‘Sustainable Aviation’ initiative appear very ambitious: they should be pursued only to the extent that they do not affect improved fuel efficiency and reduced climate-changing emissions. Good progress has already been made on the aircraft noise targets proposed by the ‘Sustainable Aviation’ initiative, but again they should be pursued only to the extent that they do not affect improved fuel efficiency and reduced climate-changing emissions. The financial case for designing to reduce aircraft noise in order to deliver novel financial benefits, e.g. increase airport flights at night and/or relocate airports, is weak.

The main objective of the paper is to evaluate the potential of reducing the environmental impact of civil subsonic aviation by using hydrogen fuel. The paper is divided into three parts of which this is Part I, where the background, prospects and Challenges of introducing an alternative fuel in aviation are outlined. In Part II the aero engine design when using hydrogen is covered, and in Part III the subjects of optimum cruising altitude and airport implications of introducing liquid hydrogen-fuelled aircraft are raised.

Looking at the prospect of alternative fuels, synthetic kerosene produced from biomass turns out to be feasible and offers environmental benefits in the short run, whereas hydrogen seems to be the more attractive alternative in the long run.

Powering aero engines and aircraft with hydrogen has been done successfully on a number of occasions in the past. Realising this technology change for a fleet of aircraft poses formidable challenges regarding technical development, energy requirement for producing hydrogen, handling, aircraft design and making liquid hydrogen economically compatible with kerosene.

The main objective of the paper is to evaluate the potential of reducing theenvironmental impact of civil subsonic aviation by using hydrogen fuel. Thepaper is divided into three parts of which this is Part II. In Part I thebackground, prospects and challenges of introducing an alternative fuel inaviation were outlined. In this paper, Part II, the aero engine design whenusing hydrogen is covered. The subjects of optimum cruising altitude and airportimplications of introducing liquid hydrogen-fuelled aircraft are raised in PartIII.

The study shows that burning hydrogen in an aero gas turbine seems to be feasiblefrom a technical point of view. If the priority is to lower the mission fuelconsumption, the results indicate that an engine employing increased combustoroutlet temperature, overall pressure ratio and by-pass ratio, seems to be themost attractive choice. The mission NOx emissions, on the other hand,seem to be reduced by using engines with a weak core and lowered by-passratio.

The main objective of the paper is to evaluate the potential of reducing theenvironmental impact of civil subsonic aviation by using hydrogen fuel. Thepaper is divided into three parts of which this is Part III. In Part I thebackground, prospects and challenges of introducing an alternative fuel inaviation were outlined. The aero engine design when using hydrogen was coveredin Part II. In this paper, Part III, the subjects of optimum cruising altitudeand airport implications of introducing liquid hydrogen-fuelled aircraft areraised.

For minimum global warming, the results of a preliminary analysis associated withlarge uncertainties suggest that cryoplanes should cruise at an altitude ofabout 2-3km below where conventional aircraft cruise today. Ignoring the costimplications, from an airport infrastructure point of view, it seems feasible tochange to hydrogen use. With respect to the availability of energy, it would bereasonable to change from kerosene to liquid hydrogen as fuel for all civilaviation refuelling in Sweden.

This paper looks at how the aerospace industry can achieve the Acare goal of greener manufacturing, maintenance and disposal. It looks further than merely reducing waste and eliminating hazardous materials and processes and suggests that the organisational structure of the industry will play an important role in facilitating a move towards such a goal. Greater co-operation or integration within the industry at all stages of the product life cycle chain is a fundamental requirement as individual companies run a risk of increasing the total environmental burdens if they concentrate solely on reducing their own impacts without considering the effect a change they make may have on other companies. The use of comprehensive environmental supply chain management systems and end of life plans can smooth the implementation of extended product responsibility and accelerate the benefits of greener manufacturing, maintenance and disposal.