Aviation
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Aviation Dipankar Banerjee (Defence Research and Development Organisation, India)
Aviation accounts for about 3% of the current global energy consumption of 15 terawatts (TW).1–3 The global annual growth of energy use in the aviation sector is likely to be around 2.15% and will exceed that in other transportation sectors, although land transport will continue to consume the largest amounts of fuel. Figure 1 displays the historical improvements in energy efficiency in the aviation sector.4 Fuel use is determined by both operational and technological factors.5–7 The former includes the passenger load factor, ground efficiencies, taxi procedures, take-off and landing paths and circuitry (actual distance traveled versus a great-circle distance), and changes in the mixture of old and new aircraft and propulsion systems with time. Technology factors, focusing on materials issues, are described in greater detail herein.
matrix composites that are significantly superior in specific strength, modulus, and fatigue resistance. Fighters such as the F22 and the Eurofighter use up to 70% composite materials by weight (Figure 2), and commercial aircraft such as the Boeing 787 use nearly 50%.8 The Airbus A380 design is more conservative in materials usage, but still employs an aluminum alloy– carbon fiber/polymer matrix composite sandwich configuration extensively for primary structures.9 The structural efficiencies of airframes could be improved through increased sophistication in the manufacturing of polymer matrix composites. Automated textile weaving processes that precisely control fiber spacing, directionality, dimensionality, and volume fraction can be utilized to allow designs that provide local rather than global responses to loads. Co-curing and co-bonding processes together with localized joining through electron beam or irradiation curing will eliminate metallic fasteners and rivets, thus providing increased structural integrity in addition to a reduction in weight. The temperature capabilities of polymer matrix composites need to be enhanced from their current limits of about 525 K, through molecular engineering or perhaps the use of matrix and fiber surfaces modified with carbon nanotubes, enabling further replacement of metallic parts in hotter sections of aircraft at temperatures higher than 600 K. A key challenge in this task will lie in ensuring that the toughness (about 0.04 design compression strain) and environmental resistance do not degrade with increasing temperature capabilities. Increases in fuel efficiency have, of course, been derived from aerodynamics. The challenge has always been to resolve the conflicting demands of wing design to reduce induced drag (arising from wing tip vortices) in the low-speed regime to parasitic (form, skin friction, and interference components) and supersonic wave drag effects that increase exponentially with speed. Concepts that seek to maintain laminar flow over the wing profile6 and a variety of wing profiles and geometries that
Technology
The Breguet range equation (E
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