Today's high competitiveness in the airline industry urges for the development of evenmore efficient transport aircraft. In many cases lower operating costs are the key to survival.Although the introduction of emerging advanced technologies has shown improvements bothin safety levels and performance, with the associated reductions in costs, the search for moreeconomical aircraft must also take into consideration changes in current design practice. Thestudy of novel configurations is a contribution to this view.In this research project, advantage was taken from multidisciplinary synergism todesign and optimise conventional and three-surface configuration commercial aircraft, tosatisfy the same mission and operational requirements. An integrated conceptual designsynthesis approach was employed where typical aeronautical disciplines, as well their complexinter-relations, were taken intoaccount. All these considerations, together with both cruise andfield performance, and static stability and control requirements, resulted in different baselineconfigurations of the two concepts, although sharing the same fuselage and the sametechnology standard, but with different Maximum Take-off Weights (MTOW), lifting surfaces,turbo-fan engine sizes, and economics. After coupling the design synthesis program to agradient based numerical minimization routine, optimisation of these designs was performedfor minimum Direct Operating Costs (DOC) and minimum MTOW, and their performanceand economics were compared on an equal basis. Trade-off studies were conducted on allaircraft for 1000 through 3000 NM design mission ranges while keeping the same fuselagesize, lifting surface planform shapes and same static longitudinal stability margin (inherentlystable designs), as obtained for the respective datum designs (Range = 1250 NM).Thus, using the same comprehensive design tool, built on the same primaryassumptions, and using the same analytical methods and principles which include many reallife considerations, a systematic and conýistent study of both design concepts was conducted.The potential merits of a realistic three-surface transport design were clearly established, whencomparison was made with an equivalent mission conventional twin turbo-fan airliner. Withinthe usual limitations of any initial conceptual design study, it appears that the concept of thethree-lifting surface transport can effectively improve in terms of performance and directoperating costs, when compared to conventional aircraft designed for the same operationalenvironment and mission profiles, and may show a promising future.
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