In recent years, increasing attention has been given in the aerospace industry to integration of aircraft design disciplines. This approach has been applied theoretically to sailplane design and to solar powered high altitude long endurance (HALE) aircraft design. More recently, it has been applied to the design of microwave powered aircraft. These studies describe attempts to arrive at integrated designs of one class of aircraft using then-existing state-of-the-art computer capabilities. No

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... empt was made in any of these cases, though, to use new programming techniques derived from Artificial Intelligence (AI) research to develop more flexible systems for the conceptual design of HALE aircraft. The purpose of this study was to investigate the feasibility of developing a general parametric sizing capability for micro-computers using integrated design methodology implementing an existing HALE methodology as a test case. The methodology described here incorporates some detailed calculations, many qualitative rules-of-thumb and constraints which are not easily quantified except by the accumulation of design experience. In this regard, the resultant software which will be developed in future efforts will be a knowledge-based system for the conceptual design of HALE aircraft. An alternative view of the computer has been around since Alan Turing's epoch-making work in the 1930's: the view of computing as manipulation of symbols, (which might include numbers among other things). The great beauty of Turing's work is in the intimate connection between the scientific definition of what a computer is (it's called a Turing Machine) and aspects of mathematics as a language that are among the most important scientific discoveries of this century (Kurt G6del's completeness and incompleteness theorems). What does any of this have to do with design or aircraft? After all, designers are notoriously,and admittedly, innocent of mathematicsl. However, designers, like everyone else, use a language of symbols to solve problems. The idea of a symbolic programming language for (aerospace) design, clearly delineated and with most of the main pieces present, is the primary innovation of the work described in this paper. The application, if not the development, of a programming language for design must be graphical since designers think graphically. A symbolic "design programming language" must provide the designer with the means to describe design concepts and manipulate them in a convenient, but disciplined, manner. Certainly, the language must provide the capability to describe (1) the air vehicle itself ("What it is"), (2) the functional decomposition ("What it does") and (3) various approximate theories, analyses and models which collectively describe "How it works". What does it mean to execute or "run" (the word "interpret", in its everyday sense, rather than in the specialized computing sense, is probably most accurate) computer programs written in such a language? Interpretation of a computer program involves defining contexts (environments) in which names (variables, attributes) are bound (assigned, set) to values (which may be numbers or other symbols)? Procedures, in which the named variables appear as parameters, are then evaluated in the environments. On the other hand, execution of an air vehicle design process involves exploring how alternative design ideas fit together by preparing engineering drawings and performing analyses. The process of making an engineering drawing is a decision-making process that results not only in the design specification, but in the designer's understanding of how the final concept works and why design decisions were made the way they were. It is this understanding that allows the designer to conscientiously "sign off" that the design is correct in the designer's professional opinion.