On the application of light weight materials to improve aircraft fuel burn - reduce weight or improve aerodynamic efficiency?

TLDR: In this paper, an analysis of the relationship between changes in aircraft weight and changes in the energy to revenue work ratio (ETRW) is presented, which, for a given aircraft on a given route, correspond to changes in trip fuel burn.

Abstract: An analysis, based upon exact relations and previously published approximate relations, is presented. It describes the connection between changes in aircraft weight and changes in the energy to revenue work ratio (ETRW), which, for a given aircraft on a given route, correspond to changes in trip fuel burn. This is used to establish the link between weight saving and fuel burn improvement at both the total aircraft and the component levels. The analysis is then extended to address the impact of trading weight savings anywhere on the aircraft for increased wing aspect ratio, whilst the aircraft total weight remains the same. It is shown that, for flights in excess of about 350 km, if saving fuel is the objective and provided that all the aerodynamic design and airworthiness requirements can be met, it is better to trade weight saving for increased aspect ratio. In general, the ratio of fuel burn reductions for traded to non-traded weight varies with aircraft size, design range, distance flown and payload carried, with the maximum values, for typical operational payloads, ranging from 2·8, for the smaller aircraft, to 2·2 for the largest aircraft, with medium haul operations deriving the largest benefit. It is estimated that, over the past 50 years, about 10% of the operational empty weight has been traded for increased aspect ratio, giving close to a 20% improvement in ETRW. Finally, estimates are produced for the impact of weight reduction and traded weight reduction on the fuel burn for the current global fleet.