“Design for Customer”
Nicolai  introduced a meaningful term, Design for Mankind, which should be the goal for all designs, not exclusive to the aerospace industry. This book focuses on specific issues of engineering design and operation by suggesting the Design for Customer, as explained in this section.
Using a holistic approach as a tool to address simultaneously the sixteen “Design for…” considerations in trade-off studies, the author suggests a Design for Customer index to measure the merits of a product . This applies to pricing of the variants in a family of derivatives but also can include the pricing structure of competition aircraft. The expression of Design for Customer is not substantiated by a large database; it may require fine-tuning for better accuracy. However, it conveys the idea that there is a need for such an index to compare the merits of any aircraft within a class. It suggests a pricing policy to arrive at the most satisfying product line that offers the best value with the widest sales coverage.
Using an empirical formula, a set of standard parameters can be established for the baseline aircraft in the class (i. e., payload range). To remain within the linear range of variation, the family-variant parameters and competition aircraft should not differ by more than about ±15%. The baseline standard parameters of interest are denoted by an asterisk as in the DOC* in U. S. dollars per seat per nautical mile, the Unit Cost* in millions of U. S. dollars, and the delivery time t* in years (from the placement of an order). To evaluate variant designs, they must be compared to the baseline design. DOC levels out well before it reaches the design range.
A baseline aircraft is designed to have the best L/D ratio at midcruise weight (i. e., the LRC condition). Normally, the L/D characteristic is relatively flat and the family derivative designs have an L/D ratio close to the maximum design value of the baseline aircraft. The Breguet range equation indicates that the range is proportional to the square root of the W/S. A shortened variant with a lower payload and range has a lower W/S with a derated engine. This aircraft has more wing than what is required and has a better takeoff performance but a slightly degraded range performance. Conversely, the extended version has more payload; weight control may have to be traded with range capability. The takeoff mass invariably increases, requiring uprated engines, especially to make up the takeoff performance due to a higher W/S (i. e., undersized wing).
This formulation is inline for comparison, satisfying the customer’s operational requirements for the product usefulness in terms of unit cost, operational cost, and timing to meet the demand. From this definition, an increase in the product value is achieved through improved performance (better), lower cost (cheaper), and less time (faster delivery). The DFM/A methodology contributes directly to lower cost, improves quality, and reduces manufacturing cycle time, thereby increasing the product value.
The higher the value, the better it is for a customer to use a product family incorporating a wide range of design considerations to satisfy operational requirements at the optimal ownership cost and purpose. In the absence of standard LCC data, the DOC is used. In this context, the following section introduces a design for customer index to compare the values of other aircraft in the class.