The Impact of Customer Requirements
Perhaps more useful still is the knowledge of the shape of the feasible region itself; this may give us a good sense of which of the design requirements is likely to have the strongest impact on subsequent design decisions. Is our wing area driven by the stall constraint and all other constraints are likely to be met comfortably? Or is the wing area driven by a strict rate-of-turn constraint and other constraints play no significant role? What type of high lift system is likely to be needed (a very weighty, as it were, concept design decision)?
At the beginning of this chapter we underlined the importance of a dialogue between the customer and the engineer as part of the process of drawing up a design brief. This conversation can be informed by the constraint diagram. At this stage the customer may not have a thorough understanding of the importance of certain numbers in the initial design brief they had drawn up. For example, they may have specified a “dirty configuration” approach speed based on little more than an educated guess, but they may be prepared to relax this requirement when told that, say, a 2 knot compromise may save them 10% on the wing area (as well as on the overall cost!) or even mean the difference between a plain flap and a sophisticated (and hugely expensive) multislotted flap system.