III Designing UAVs
The Process of Design
As has already been pointed out, the whole purpose of design is to achieve a set of goals while meeting various constraints, usually in an iterative process proceeding through the various stages of design described earlier. The goals in unmanned air vehicle (UAV) design are related to mission and payload while the constraints are those associated with the various ways aircraft can go wrong. In this part of the book, we set out in more detail how designers can use analysis to achieve good designs, that is, those that flexibly achieve the mission goals and avoid the common forms of failure that all aircraft are subject to.
A typical aircraft design project will go through the stages illustrated in Figure 8.1. For a very low cost, or student, fixed-wing UAV project, the aircraft is generally defined by perhaps 10 parameters at the conceptual stage, several tens of parameters at the preliminary design stage, and hundreds of parameters at the detailed design stage. There is an exponential growth in the information content. This is one of the reasons why design has to be carried out in a systematic manner to ensure that reliable decisions are made before moving onto the next stage in the design process. A detailed description of the overall design-stage logic is given in Appendix A.
Having decided on the goals and constraints and selected the toolsets to be used, we start with concept design based around constraint analysis, spreadsheets, and simple sketches before moving on to physics-based analysis applied to computer-aided design (CAD) geometries using computational fluid dynamics (CFD) and structural finite element analysis (FEA). We then describe lab-based experimental work before concluding this part with a chapter on detailed design.