Introduction to Aircraft Design JO H N P. FIELD IN G College of Aeronautics, Cran®eld University
p u b l i s h e d b y t h e p r e s s s y n d i c at e o f t h e u n i v e r s i t y o f c a m b r i d g e The Pitt Building, Trumpington Street, Cambridge CB2 1RP, United Kingdom cambridge university press The Edinburgh Building, Cambridge CB2 2RU, UK www.cup.cam.ac.uk 40 West 20th Street, New York, NY 10011-4211, USA www.cup.org 10 Stamford Road, Oakleigh, Melbourne 3166, Australia Ruiz de AlarcoÂn 13, 28014 Madrid, Spain # Cambridge University Press 1999 This book is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 1999 Printed in the United Kingdom at the University Press, Cambridge Typeset in TIMES [KT] A catalogue record for this book is available from the British Library Library of Congress Cataloguing in Publication data Fielding, John, P. 1945± Introduction to aircraft design / John P. Fielding. p. cm. ± (Cambridge aerospace series : 11) ISBN 0 521 44319 9 (hc.) 1. Airplanes±Design and construction. I. Title. II. Series. TL671.2.F46 1999 629.134'1±dc21 98-39489 CIP ISBN 0 521 44319 9 hardback ISBN 0 521 65722 9 paperback
Introduction 1.1 Why another aircraft design book? 1.2 Topics 1.3 The design process
Why should we design a new aircraft? 2.1 Market surveys 2.2 Operator-derived speci®cations 2.3 Speci®cation for a close air support aircraft 2.4 Airline speci®cation for a 150-seat airliner
7 7 11 12 13
Why is it that shape? ± Civil aircraft 3.1 Background 3.2 Civil aircraft types
19 19 24
Why is it that shape? ± Other types 4.1 Military aircraft types 4.2 Rotorcraft and V/STOL aircraft
37 37 50
What's under the skin? ± Structure and propulsion 5.1 General 5.2 The structure 5.3 Propulsion ± the primary power system
55 55 55 63
What's under the skin? ± Airframe systems 6.1 Secondary power systems 6.2 The fuel system 6.3 Furnishings 6.4 Safety installations 6.5 Landing gear installations
73 73 80 82 83 84
1 1 2 2
What's under the skin? ± Avionics, ¯ight control and weapon systems 7.1 Avionic systems 7.2 Flight control systems 7.3 Weapon systems Why do aircraft cost so much? 8.1 General 8.2 Acquisition costs (the costs of buying or acquiring the aircraft) 8.3 Civil aircraft operating costs 8.4 Military aircraft life-cycle costs 8.5 The costs of reliability and maintainability What help can I get? ± Bibliography and computer-aided design 9.1 Aircraft design bibliography 9.2 Relevant data sheets 9.3 Computer design tools 9.4 The integration of computer tools as part of concurrent engineering 9.5 Classic computer-aided design systems
89 89 96 100 109 109 109 115 116 118 129 129 131 135 140 141
The shape of things to come ± Should the project continue? 10.1 Introduction 10.2 Conceptual design de®nition 10.3 Comparison and choice 10.4 Simple decision-making techniques 10.5 Example of a conceptual aircraft design de®nition description ± The Cran®eld A±90 10.6 Progress of the A±90 project beyond the conceptual design stage
149 149 149 150 151 153
What can go wrong? ± Some lessons from past aircraft projects, and a glimpse into the future 11.1 Introduction 11.2 Aircraft that suffered from requirements that were too restrictive, too ambitious or were changed during development 11.3 Projects that were overtaken by events 11.4 A step too far or too soon? 11.5 Some challenging future projects 11.6 Conclusions
167 171 174 177
Appendix A ± Useful aircraft design data A1 Introduction
Contents A2 US/UK nomenclature A3 UK and US/SI conversion tables and airspeed charts A4 Aircraft leading data tables A5 Power plant data A6 Aerodynamic data A7 Structures and materials data A8 Landing gear data A9 Aircraft interior data A10 Aircraft weapons Appendix B ± A±90 parametric study. Example ± the A-90 500-seat airliner B1 Introduction B2 Landing ®eld distance B3 Take-off ®eld length B4 Second segment climb B5 Missed approach B6 Cruise performance B7 Ceiling with one engine inoperative B8 Arrival at the match point
ix 179 180 183 196 213 220 222 223 238 243 243 243 245 246 247 248 252 253
Appendix C ± The prediction of aircraft reliability and maintainability targets C1 Introduction C2 Commercial aircraft dispatch reliability prediction
255 255 255
Why another aircraft design book?
Aircraft design is a complex and fascinating business and many books have been written about it. The very complexity and dynamic nature of the subject means that no one book can do it justice. This book, therefore, will primarily act as an introduction to the whole ®eld of aircraft design leading towards the subjects summarized in Fig. 1.1. It will not attempt to duplicate material found in existing design books, but will give information about the whole aircraft design environment together with descriptions of aircraft and component design. It also presents otherwise unpublished data and design methods that are suitable for aircraft conceptual, preliminary and detail design activities.
Fig. 1.1 Aircraft design data sources.
The following chapters are arranged as a series of questions about aircraft design, the answers to which give largely descriptive overviews of all aspects of aircraft design. This will provide an introduction into the con¯icting requirements of aircraft design specialists in a design team, with a view to improving understanding, and the integration of a sound overall design. The book is divided into chapters which answer a number of signi®cant design questions. The question `why design a new aircraft?' is answered in Chapter 2 which shows the derivation of aircraft requirements for civil and military aircraft from market surveys, and gives examples of operator-derived speci®cations. Chapters 3 and 4 answer the question `why is it that shape?' with an initial discussion of aircraft wing and tail shapes, followed by descriptions of the con®gurations of a wide range of civil and military aircraft types. The question `what's under the skin?' is answered in Chapters 5, 6 and 7, which deal with structures and propulsion, airframe systems, avionics, ¯ight controls and weapons, respectively. These chapters describe the interiors of aircraft, ranging from structures to weapon systems via airframe systems, avionic systems and landing gears. In Chapter 8 the crucial areas of acquisition and operating costs are discussed and some prediction methods are described and the importance of good reliability and maintainability are stressed in order to answer the question, `why do aircraft cost so much.' The answer to the question `what help can I get?' is provided in Chapter 9 which contains a bibliography of the most important current aircraft design books. It is followed by a description of some of the computer design analysis and computer-aided design (CAD) tools that are available. A summary of relevant data sheets is also given. Chapter 10 draws together the information produced at the end of the conceptual stage and leads on to the preliminary and detail design stages in order to explain `what happens next'. The question `what can go wrong' is answered in Chapter 11 in which many unsuccessful or partially successful projects are examined and conclusions drawn from them. The aircraft designer is bedeviled by lack of design data. Appendix A pulls together information that is not generally available, and includes simple aerodynamic and structural design formulae. It also provides a US/British translation list for aeronautical terms. Appendix B presents a parametric study design example which describes the author's parametric study of a 500-seat transport aircraft. Appendix C considers reliability and maintainability targets by discussing targets for civil and military aircraft and describing a method to be used for the prediction of dispatch reliability.
The design process
There are a number of generally accepted stages in the design, development, manufacture and operation of aircraft, each with associated design methods and data requirements. These are shown schematically in Fig. 1.2, which also shows how the modern practice of concurrent engineering has reduced the overall timescale from conception to service. Figure 1.3 gives some idea of how a designer's prejudice may affect his or her design to the detriment of others. It is an exaggeration, but not much of an exaggeration!!
1.3 The design process
Fig. 1.2 Comparison of traditional and concurrent design approaches.
Fig. 1.3 Different specialist's views of an ideal aircraft.
The most crucial stage of any design process is to arrive at the correct set of requirements for the aircraft. These are summarized in design speci®cations for the particular aircraft type. Typical examples of design speci®cations are shown in Chapter 2. They are augmented by a large number of airworthiness requirements for civil aircraft or Defence Standards for military aircraft. These are distillations of decades of successful (and unsuccessful!) design, manufacturing and operational experience. Fig. 1.4, adapted from Haberland et al. , shows a very helpful illustration of what may happen after the issue of the design speci®cations, and illustrates the iterative design process that is not apparent in the simpli®ed illustration in Fig. 1.2. A converging iterative spiral of design stages, ending in the detail design, and ultimately manufacture and operation of the aircraft can be seen in Fig. 1.4. It is a truism that 99% of the decisions which affect aircraft success are made on 1% of the facts available during the conceptual design phase. Very coarse methods have to be used which are then re®ned by progressively more accurate methods as the design evolves. This is true if the spiral is convergent, but there are occasions where the spiral is divergent and the design must be abandoned, and started again, unless signi®cant modi®cations are made to the design. Figure 1.5 shows the author's usual design procedure for conceptual design and the start of preliminary design process.
Fig. 1.4 The design spiral.
1.3 The design process
Fig. 1.5 Major stages in an airliner initial design process.