1. The Air Travel Greener by Design Technology
Sub-Group see the next decade as a period over which research,
technology demonstration and design study will be crucially important
to achieving the objectives of the Greener by Design Associated
Foresight programme. The following, not in any particular order,
are considered priority areas:
2. Atmospheric Effects of Aircraft Emissions.
There are important programmes in Europe, the USA and Japan but
there is much more that needs to be done. CAEP has defined five-year
goals in a number of specific research fields but continued research
beyond then is likely to be needed. Quantitative understanding
in this field, particularly of the significance of NOx and contrails
and their dependence on flight altitude, latitude, climate and
season, is the key to framing aircraft design concepts and requirements
to minimise impact on climate change.
3. Aero Engine Combustion. Research is needed
both to develop engine combustion systems with reduced Nox emissions
and to improve understanding of the fundamental processes of Nox
generation at high temperatures and pressures. Advanced combustor
development is a particularly high priority, given the number
of conventional turbofan engines that are in service, or will
enter service in the coming decades. Nevertheless, the investigation
of the ICR engine cycle should also be taken to the point where
its practicability can be assessed and its potential to reduce
Nox emission evaluated. For both conventional and ICR systems,
research which holds out real promise needs to be followed by
4. Natural and Hybrid Laminar Flow Control.
For short and medium range aircraft, up to 150-200 seats, the
potential of natural laminar flow design merits further study,
despite the disappointing conclusions of (26). Hybrid laminar
flow control has far wider ranging potential, however, and merits
further study both to develop and validate aerodynamic design
principles and to develop and demonstrate the necessary manufacturing
and systems technology. The goal should be to bring this technology
to the state where it can be incorporated into chosen production
aircraft in order to obtain an adequate base of experience of
operation and maintenance of the system in airline service. Wind
tunnel testing of hybrid laminar flow designs will present novel
technical problems relating to aerodynamic scaling which should
also be addressed.
5. Blended Wing-Body. The current studies
of the blended wing-body configuration should be carried forward
to the point where all key issues have been addressed on paper
or by experiment and the more critical issues earmarked for further
investigation. These are likely to include stability and control,
aerodynamic and structural optimisation, powerplant integration
and acceptability to passengers. Ride quality control may be a
key issue. In the longer term, the studies should be extended
to cover the aerodynamic and engineering aspects of applying hybrid
laminar flow control to the outboard wing and other appropriate
surfaces and to the re-optimisation of the configuration with
6. Laminar Flying Wing. A new aerodynamic
and engineering study of the all laminar flying wing should be
undertaken in order to re-assess its potential in the light of
technical advances since the concept was first proposed.
7. Alternative Fuels. Current research into
the hydrogen fuelled aircraft concept should be carried forward
to provide a basis for assessing the practicalities of converting
to hydrogen fuel for civil aircraft in the event of the fuel becoming
generally available at an environmentally acceptable cost. Research
into the feasibility of carbon-neutral fuels derived from biomass
should also be pursued.
8. Multi-Sector Long Distance Travel. A
total system study should be made of the concept of undertaking
long distance travel in sectors not exceeding some defined maximum
(in Appendix A4 a provisional figure of 7,500 km is suggested).
The study should cover engineering, operational, infrastructure,
safety, market, economic and overall environmental issues.
9. Design for Minimum Impact on Climate
Change. A study should be made of aircraft and engine design concepts
aimed specifically at minimising impact on climate change rather
than fuel burn. Possibilities might include aircraft optimised
to cruise at lower altitudes, with less efficient engines having
higher exhaust temperatures and lower Nox emissions. Further progress
in the atmospheric sciences is needed before such a study can
reach definitive conclusions, but it is not too soon to begin
to formulate the key questions and build a framework for weighing
the balance between commercial and environmental goals, the latter
including noise and local air quality as well as impact on climate
change. Such a study is likely to help shape future research priorities.
For example, any conclusion that it would be beneficial to design
for lower cruise altitude, which implies higher wing loading,
would highlight the need for research to develop more capable
and lighter high lift systems, possibly using some of the novel
flow control technology which is now emerging.
10. Associated Research. In parallel with
the above, environmentally related research areas, mainstream
research in aircraft and engine aerodynamics, structures, materials,
systems and noise must continue. All are capable of contributing
to future reductions in the effect of air travel on climate change
and to improvements in the airport environment.