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A method of estimating the load-bearing fuselage weight and wing weight of transport aircraft based on fundamental structural principles has been developed. This method of weight estimation represents a compromise between the rapid assessment of component weight using empirical methods based on actual weights of existing aircraft, and detailed, but time-consuming, analysis using the finite element method. The method was applied to eight existing subsonic transports for validation and correlation. Integration of the resulting computer program, PDCYL, has been made into the weights-calculating module of the AirCraft SYNThesis (ACSYNT) computer program. ACSYNT has traditionally used only empirical weight estimation methods; PDCYL adds to ACSYNT a rapid, accurate means of assessing the fuselage and wing weights of unconventional aircraft.

Structural optimization has seen remarkable progress in recent years, and is now recognized as a practical design tool. The ingredients of a structural optimization computer code include finite element analysis, sensitivity analysis, and optimization. Each of these are now available, but are seldom contained in a single computer code. Notably, sensitivity analysis must often be calculated as a post-processing operation to the finite element analysis. These various aspects of structural optimization are discussed, with emphasis on sensitivity calculations. Examples are given to demonstrate the present state of the art. It is argued that, while experts in the field can now create this capability by combining existing software, this is still a major task. Thus, it is most desirable that general-purpose, commercial software be created at the earliest possible date in order that this technology be used to its potential.