Although weight engineers do not create new aircraft designs, they deliver essential contributions to new aircraft programs and the development of derivative versions. Weight prediction must be accurate because this is the basis of decisions on the feasibility of the project before the costly detailed design stage is entered. This chapter gives an overview of early Class II weight prediction for a complete civil airplane and describes how a typical initial wing and engine sizing is carried out. Design‐sensitive empty weight components and relationships for the installed thrust and the fuel load are derived. Closed form solutions are found for the empty airframe, power plant, fuel and maximum take‐off weight, enabling the computation of response surfaces.
The quasi‐analytical unconstrained optimization is demonstrated for a medium‐range Mach 0.80 airliner with a twin‐aisle cabin for 180–210 seats. Primary selection variables are initial cruise altitude and wing loading at take‐off. The cruise lift to drag ratio, thrust to weight ratio, mission fuel fraction and gross weight are computed. Partial optimizers are obtained for the fuel weight fraction, power plant plus fuel weight fraction, take‐off gross weight and energy efficiency. The results prove that different objective functions result in widely different 'best designs'. Effects of design constraints are treated in the next chapter.
Theory of Optimum Weight
Advanced Aircraft Design ; 229-259
21.06.2013
31 pages
Aufsatz/Kapitel (Buch)
Elektronische Ressource
Englisch
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