Aircraft Costing Methodology: Rapid-Cost Model

This section presents a rapid-cost modeling methodology [2] specifically aimed to the coursework needs of DFM/A considerations during the conceptual design phase of commercial transport aircraft. This is why Chapter 15 suggests the layout of the structural concept and the use of CAD. The basic structural philosophy is to address

Table 16.4. Life cycle cost (military aircraft)

Production In-service Disposal

A (Baseline: existing design)

B (New Design: to estimate)

Tsls lb

9,220

14,000

Engine dry weight (lb)

1,625

2,470

Engine-face diameter (inches)

49

50.6

Nacelle weight (lb)

536

860

Nacelle maximum diameter (inches)

56

60

Nose-cowl length (inches)

35

29

DFM/A considerations as early as possible to provide a sense of manufacturing cost reductions through trade-off studies. Many publications suggest empirical relations to predict aircraft cost based on various types of aircraft weights, performance capa­bilities, and other details. Empirical relations use coefficients and indices with some degree of success; however, without the actual industrial-cost details, it is difficult to fine-tune the DFM/A gains. A methodology must have input based on real data in order for gains to be obtained through the application of the fundamentals of modern manufacturing philosophy.

The rapid-cost model is based on parametric methods in which cost drivers are identified. In the nacelle example, eleven drivers are involved. From a known base­line cost, the rapid-cost model demonstrates a fast and relatively accurate predic­tion and identifies areas that contribute to cost. A normal market situation with­out any unpredictable trends (i. e., global issues) is assumed for the methodology. The methodology is based on a generic turbofan nacelle, which typically represents the investigative areas associated with other aircraft components and makes use of industrial data. Figure 16.3 shows the generic nacelle components: (1) nose cowl, (2) fan cowl, (3) core cowl with thrust reverser, and (4) aft cowl. The method does not reflect practices by any organization and does not guarantee accuracy; it is intended only to provide exposure to the complexities involved in costing.

The example of the rapid-cost methodology concentrates cost modeling of the nose cowl structural elements of two generic nacelles – Nacelle A and Nacelle B – in the same aircraft and engine family. The methodology uses indices and factors, which is why two nacelles are used. Nacelle A is an existing product and is used for the baseline design. All cost data for Nacelle A are known, from which the indices are generated. Nacelle B has a higher standard of specification and a new design, in which the indices are adjusted and then used to predict cost. The two nacelles are compared in Table 16.5. All figures are in FPS, as obtained from the industry.

Table 16.6. Manufacturing cost components

Cost of materials (raw and finished product)

Cost of parts manufacture

Cost of parts assembly to finish the product

Cost of support (e. g., rework/concessions/quality)

Amortization of nonrecurring costs

Miscellaneous costs (other direct costs, contingencies)

For dissimilar components, a similar methodology can still be applied with extensive data analyses to establish the appropriate indices.

Although the aerodynamic mould lines of both nacelles are similar, their struc­tural design philosophy – hence, the subassembly (i. e., tooling concept) – differs. With commonality in the design family, the study presents a focused comparative study of the two geometrically similar nose cowls in a complex multidisciplinary interaction that affects cost. The total manufacturing cost of the finished product is the sum of the items listed in Table 16.6; the cost of manufacture is not the selling price.

Generic nacelles typically represent the investigative areas associated with the design and manufacture of other aircraft components (e. g., the wing and fuselage). The rapid-cost-model methodology presented herein can be applied to all other air­craft components, with their appropriate cost drivers, to establish the cost of a com­plete aircraft. Industrial shop-floor data are required to estimate the cost in dollars. All data are normalized to keep proprietary information commercial in confidence.

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