飞机设计导论(第八章)

1、Introduction to Aircraft Design,Chapter 8 Why do aircraft cost so much?,8.1 General,This chapter discusses the costs of buying and operating civil and military aircraft. The former costs are termed acquisition costs for both classes of aircraft, whilst the latter are termed operating cost for civil

2、a/c and life-cycle costs for military a/c. The costs associated with aircraft reliability and maintenance are significant contributors to operating and LCCs.,2020/6/25,2,隐身技术,8.2 Acquisition costs,The reasons for high aircraft acquisition costs: high performance requirements, safety consideration, q

3、uality control, tooling requirements, labor-intensive production(Fig. 8.1), high overheads, large financial investment, interest cost(Fig 8.2), short production runs. The advent of integrated computer aided design and manufacture systems has gone some way to reducing the above problems, particularly

4、 in reducing development times and improving initial build quality.,2020/6/25,3,隐身技术,8.2.2 Acquisition cost prediction methods,The two main approaches to cost prediction are termed top-down and bottom-up. The former is used during the conceptual or preliminary design stages, whilst the latter is uti

5、lized during the detailed design and development phases. There is little published information about the bottom-up approach.,2020/6/25,4,隐身技术,8.2.2 Acquisition cost prediction methods,There are several top-down approaches, but all use statistical data from as wide a range as possible of existing air

6、craft. Some use data for complete aircraft, as shown in Fig. 8.3. Much of the published work has its origins in work by the Rand Corporation. Statistical data are gathered and analyzed to predict costs of both development and production costs.,2020/6/25,5,隐身技术,8.2.3 Typical acquisition costs,Fig. 8.

7、4 shows civil aircraft costs, based on published data. Fig. 8.5 shows calculated and quoted prices of combat aircraft, based on work performed by a Crandfield student, Spencer Woodford, which is to be published in his PhD thesis.,2020/6/25,6,隐身技术,8.3 Civil aircraft operating costs,Transport aircraft

8、 costs are sub-divided into what are termed indirect and direct costs. The indirect operating costs (IOC) are those associated with running an airline, rather than those directly concerned with operating aircraft. Such coats cover such things as central administration, sales and publicity, airport c

9、osts and passenger service. The accommodation for passengers delayed by an aircraft failure would be taken as indirectly.,2020/6/25,7,隐身技术,8.3.2 Direct operating costs,Direct operating costs (DOC) do vary with aircraft type and trip length. Fig. 8.6 shows a pie-chart with recent data of DOC elements

10、 for Boeing 747-400. Ownership costs cover the cost of depreciating the aircraft acquisition costs over a reasonable aircraft life. Airframe and engine spares may also be included in this figure.,2020/6/25,8,隐身技术,8.3.2 Direct operating costs,Some ways in which it was hoped that advances in aircraft

11、design could improve DOC for new aircraft in the same performance category as the 747-400 are provided in a reference book. The projected savings are shown in Table 8.1. These are very challenging targets and it remains to be seen if they are achieved by the target date of 2015.,2020/6/25,9,隐身技术,8.4

12、 Military aircraft life-cycle costs,The life-cycle costs of a military aircraft are analogous to the sum of both indirect and direct operating costs of civil transports. There is a surprising number of self-explanatory cost elements as shown in Fig. 8.7. Table 8.2 shows a summary of the various elem

13、ents of Royal Air Force Expenditure during the mid-1980s. Table 8.3 gives a breakdown of the total life-cycle costs for a military aircraft.,2020/6/25,10,隐身技术,8.5 The costs of reliability and maintainability,The most dramatic form of unreliability is an aircraft crash with loss of life. It is imposs

14、ible to quantify the value of a human life although some attempts have been made to put cash values on lives. The next item of unreliability cost is that of delays and cancellations. Fig. 8.8 shows the proportions of causes of delay. Fig 8.9 shows a typical breakdown of the system causing technical

15、delays. The 3rd major cost of unreliability is fault diagnosis, removal and repair or replacement of faulty components.,2020/6/25,11,隐身技术,8.5.2 Military aircraft unreliability costs,Aircraft crashes are again costly in terms of life and material costs. Fig. 8.10 shows the possible maintenance cost s

16、avings that were predicted for 385 Tornado aircraft relative to the F-4 Phantom, over a 10 year period. Fig. 8.11 shows 1987 figures for failure rates against aircraft empty weight. The latter is a measure of the complexity of the aircraft.,2020/6/25,12,隐身技术,8.5.2 Military aircraft unreliability cos

17、ts,Figure 8.12 shows trends in specific reliability over a 25-year period. Specific reliability is defined as the number of failure per flying hour per unit of aircraft mass. F-22A are to double the sortie rate of the F-15, and do so with half the maintenance personnel required and twice the mean ti

18、me between failures (MTBF).,2020/6/25,13,隐身技术,8.5.3 Factors affecting maintenance costs,The magnitude of maintenance costs has already been mentioned, and is closely linked to the unreliability of the aircraft. An aircraft with low operation costs will need to have high reliability. Fig. 8.16 shows

19、an overall plan for maintainability (ease of maintenance). Not all of these features are within the control of the designer, but must be aware of them.,2020/6/25,14,隐身技术,8.5.3 Factors affecting maintenance costs,Fig. 8.17 shows a modular aircraft engine. This design means that engines can be dissembled in situ (on site) and modules rather than engines can be changed and refurbished (整修). Fig. 8.18 shows some examples of good maintainability features. Fig. 8