Flight control systems : practical issues in design and implementation

407 Pages·2000·6.227 MB·English

by  Roger Pratt, Institution of Electrical Engineers., American Institute of Aeronautics and Astronautics

THGILF
LORTNOC
S M , , E T S Y S
practical" seussi n" I
ngised dna
noitatnemelpmi
detidE yb
Roger W. Pratt
The Institution of Electrical Engineers
Copublished by:
The Institution of Electrical Engineers,
Michael Faraday House,
Six Hills Way, Stevenage,
Herts. SG1 2AY, United Kingdom
and
The American Institute of Aeronautics and Astronautics
1801 Alexander Bell Drive
Suite 500
Reston
VA 20191-4344
USA
© 2000 Editorial selection and presentation: The Institution of Electrical Engineers
For copyright ownership details see final page of each chapter.
This publication is copyright under the Berne Convention and the Universal Copyright
Convention. All rights reserved. Apart from any fair dealing for the purposes of
research or private study, or criticism or review, as permitted under the Copyright,
Designs and Patents Act, 1988, this publication may be reproduced, stored or
transmitted, in any forms or by any means, only with the prior permission in writing
of the Institution of Electrical Engineers (lEE) or in the case of reprographic
reproduction in accordance with the terms of licences issued by the Copyright
Licensing Agency or Copyright Clearance Centre Inc. Inquiries concerning
reproduction outside those terms should be sent to the lEE at the address above.
While the authors and the publishers believe that the information and guidance given
in this work are correct, all parties must rely upon their own skill and judgment when
making use of them. Neither the authors nor the publishers assume any liability to
anyone for any loss or damage caused by any error or omission in the work, whether
such error or omission is the result of negligence or any other cause. Any and all
such liability is disclaimed.
The moral right of the authors to be identified as authors of this work has been
asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
British Library Cataloguing in Publication Data
A CIP catalogue record for this book
is available from the British Library
ISBN 0 85296 766 7
Printed in England by TJ International, Padstow, Cornwall
To Gill, Joanne, Ian and Sara
Contributors
B.D. Caldwell C. Fielding
Aerodynamics (W310C) Aerodynamics (W427D)
British Aerospace British Aerospace
Warton Aerodrome Warton Aerodrome
Preston PR4 lAX Preston PR4 lAX
UK UK
°V.M Cook
J. Hodgkinson
Flight Test and Dynamics Group
7022 Starstone Drive
College of Aeronautics
Rancho Palos Verdes, CA 90275
Cranfield University
USA
Cranfield, Bedfordshire MK43 0AL
UK
R.A. Hyde
L.F. Faleiro Cambridge Control Ltd
Control Design Engineering Matrix House
Institute for Robotics and Cowley Park
Mechatronics Cambridge CB4 0HH
German Aerospace Center UK
DLR Oberpfaffenhofen
Postfach 1116
R. Luckner
82234 Wessling
DaimlerChrysler Aerospace Airbus
Germany
GmbH
Flight Mechanics
R,D. Felton
Flight Guidance and Control
14 Cromwell Court
PO Box 95 01 09
Eynesbury
D-21111 Hamburg
St Neots, Cambs. PE19 2NZ
Germany
UK
J. Fenton D.G. Mitchell
Smiths Industries Aerospace Hoh Aeronautics Inc.
Bishops Cleeve Vista Verde Center 217
Cheltenham, Glos. 2075 Palos Verdes Drive North
GL52 4SF Lomita, CA 90717
UK USA
xiv Contributors
R.W. Pratt T,D. Smith
Formerly: Flight Test (W27K)
Department of Aeronautical and British Aerospace
Automotive Engineering Warton Aerodrome
Loughborough University Preston PR4 lAX
Loughborough UK
UK
R. Taylor
Now with:
Ricardo MTC Ltd.
Ricardo MTC Ltd.
Midlands Technical Centre
Midlands Technical Centre
Southam Road
Southam Road
Radford Semele
Radford Semele
Leamington Spa
Leamington Spa
Warwicks CV31 1FQ
Warwicks CV31 1FQ
UK
UK
S.P. Ravenscroft
Flight Systems (W354C)
British Aerospace
Warton Aerodrome
Preston PR4 lAX
UK
Preface
If you belong to the school of thought that says 'give me a model and I'll give
you a controller' then this book is not for you. If, however, you believe that
using linear-control design methodologies to develop flight control laws
requires a fuller understanding of the dynamics of the plant (aircraft), the
problems associated with implementation and the need to satisfy the
requirements of a highly trained human operator (pilot) then the chapters in
this book should help you to develop that understanding. In essence, much of
this book is a message to the academic researcher which says: 'If your work is
to be useful to practising engineers in industry, then you need to understand,
or at least appreciate, the issues dealt with in this book'. Additionally, young
engineers who are beginning their careers in the aerospace industry should
find it useful to have a coverage of the key aspects of flight control in a single
volume
The authors were chosen because of their depth of experience and mix of
backgrounds, which I believe are reflected in their individual contributions.
Additionally, in a number of cases the chapters were reviewed by senior
managers who have spent their entire careers in the aerospace industry.
Hopefully, the experience which lies behind the individual contributions will
encourage a new generation of engineers, mathematicians and scientists to
become involved in this exciting branch of engineering--flight control
systems.
In the late seventies and eighties very few texts were produced on flight
control. Then in the nineties a number of books appeared. For readers who
are new to flight control it might be useful to attempt to assign a place for this
text in the total grouping. Fundamentals of the subject with varying degrees
of emphasis on aircraft dynamics and flight control are covered by a number
of texts 1-7. All of these texts should be of use to undergraduate students
in the final year or years of their courses, as well as to postgraduate students
who are in the process of strengthening their knowledge of fundamental
concepts before immersing themselves in their specific topic. The texts by
McLean 4 and Stevens and Lewis 7 will extend the reader's knowledge
into the realms of research work. The contribution edited by Tischler 8 is
significantly different from the other texts in that experienced practitioners,
some of whom have contributed to this book, give a strong account of the
state of the art, for rotorcraft, combat aircraft and fixed-wing transport
xvi Preface
aircraft. Our text is seen as bridging the gap between the work on
fundamental principles and Tischler's excellent collection of research
reviews.
The aim of this text is to build on the fundamentals of flight dynamics and
flight control as described in References 1-7 and embellish these principles
by assigning their relevance to the development of flight control systems in
the aircraft industry. The first seven chapters cover most of the key areas
within the discipline of flight control systems with explicit reference to recent
development programmes written by engineers who were closely involved in
the work. The last two chapters look at just two of the multitude of modern
control methods which have been the subject of research studies. The text is
largely restricted to military and civil fixed-wing aircraft. Only the constraint
of space has prevented equivalent material for rotorcraft and missiles from
being included.
The book comprises nine chapters:
Chapter 1 'Industrial considerations for flight control', Chris Fielding and
Robert Luckner: the authors set the scene for the whole book by explaining
the industry's perspective on flight control systems, giving a comprehensive
overview of the subject with more detailed discussions of some particular
topics being given in later chapters. The authors have carried through their
chapter the parallel themes of military combat aircraft and civil aircraft, an
interesting feature which strongly reflects their backgrounds.
The Chapter begins by examining the general objectives of flight control
and the role of the flight control system (FCS). This is followed by the
operational requirements for both types of aircraft and a discussion of the
benefits of fly-by-wire (FBW) in the pilot-vehicle system. The systems issues are
explored, as are reliability and integrity, the twin versus--verification and
validation. The Chapter is rounded off by a discussion of the state-of-the-art
and a look at some exciting future developments.
Chapter 2 'Aircraft modelling', Mike Cook: the author summarises from his
own text 3 the main elements of axis systems and the equations of motion
for the longitudinal and lateral dynamics of fixed-wing aircraft. Aircraft-
response transfer functions and state-space representations are then
developed from the equations of motion. Any reader who requires a fuller
treatment than can be given within the confines of this book is strongly
recommended to refer to Mike's own text.
Chapter 3 'Actuation systems', Steven Ravenscroft: since the advent of
powered control surfaces without manual reversion, in the era of the
Lightning, actuation systems have assumed great importance. The sig-
nificance of actuation systems has been further enhanced by the drive to
develop highly agile combat aircraft in which a safety-critical flight control
system is required to stabilise the unstable open-loop dynamics of the aircraft.
This comprehensive chapter begins with an overview of primary and
secondary control surfaces and their operation and leads on to a discussion
of performance criteria and modelling. The latter sections discuss more
Preface xvii
advanced topics: nonlinear frequency response, saturation analysis, jump
resonance and failure transients.
Chapter 4 'Handling qualities', John Hodgkinson and Dave Mitchell: uses
the response transfer functions developed in Chapter 2 and examines the
response of the aircraft from the pilot's viewpoint. The subjectivity which is
inherent in the assessment of handling qualities has, inevitably, given rise to
a number of metrics and these are discussed in relation to the dynamic modes
for the longitudinal and the lateral motion. This leads on to stability and
control augmentation systems and a discussion of some control design
concepts. Clearly, a chapter on handling qualities has to include a discussion
of pilot-induced oscillations (PIOs). This topic is given a thorough and up-to-
date treatment which reflects the very recent research carried out in the
United States.
Chapter 5 'Automatic flight control system design considerations', John
Fenton: this chapter gives a clear and practical breakdown of the tasks which
are necessary in the management of the development programme for a
complex flight control system. The conciseness of the chapter stems from the
detailed breakdown of the main areas, the development programme
requirements definition and verification, system design considerations and
AFCS architecture, into detailed subtasks.
Chapter 6 'Ground and flight testing a digital flight control system', Terry
Smith: discusses the techniques which have been employed by the UK's major
aircraft manufacturer, British Aerospace, as it has progressed with the
development of fly-by-wire combat aircraft. The chapter gives an excellent
description of the need to progress a test programme in a way which
minimises both risk and cost, from the philosophy, tools and techniques of
flight testing through the elements of simulator and rig testing, ground
testing and, of course, flight testing.
Chapter 7 'Aeroservoelasticity', Brian Caldwell, Roger Pratt, Richard Taylor
and Richard Felton: discusses how a safety-critical flight control system can be
affected by the elastic behaviour of the aircraft structure, namely the
phenomenon of aeroservoelasticity or structural coupling. As with the
previous chapter, the material draws on the experience gained at British
Aerospace with a series of aircraft in which the open stability has been
reduced to the point of severe instability in order to enhance manoeuvrability.
The contributions from Richard Taylor and Richard Felton are based on the
results of research programmes which were carried out at the Universities of
Loughborough and Lancaster, respectively.
Chapter 8 'Eigenstructure assignment', Lester Faleiro and Roger Pratt:
represents one contribution to the work done under the GARTEUR Action
Group on robust flight control in which a group of universities, research
establishments and aircraft companies contributed under Jan Terlouw's
(NLR) excellent stewardship. Eigenstructure assignment was chosen in this
case because it appeared to offer a more visible methodology than other
modern control techniques. The case study (RCAM) was based on a flight
xviii ~aferP
profile for a civil aircraft which consisted of a base leg and a two-stage final
approach. The chapter is intended as an honest assessment of eigenstructure
assignment in this type of application.
Chapter 9 'An ~0H loop-shaping design for the VAAC Harrier', Rick Hyde:
describes one of the most exciting research programmes which has been
carried out in the field of modern control engineering applied to flight
control. ~0H designs were evaluated extensively by piloted simulation and on
the VAAC Harrier at DERA Bedford where the controller was in competition
with designs from British Aerospace and Smiths Industries. The early work
benefited enormously from the rapport between Rick and the RAF's test pilot,
Bj6rn Singer.
A step-by-step guide is given to the linear loop-shaping design process with
a clear description of the use of the knowledge of the aircraft's dynamics. This
is followed by the work on implementation and flight testing which explains
the approach that was taken to gain-schedule controllers, deal with antiwind-
up as well as describe the impressive results achieved during flight testing.
I would like to thank George Irwin, co-editor for the series, for inviting me
'to write or edit a text of flight control': certainly, there have been moments
when I have regretted yielding to George's Celtic persuasion. However, over
twenty or so years I have benefited greatly from my association with the
control community in the UK and, more recently, this has been equally true
of my association with the guidance, navigation and control activities within
the AIAA in the United States and GARTEUR in Europe. My contribution to
this book can be viewed as a partial repayment of a very large debt. Obviously,
an edited text is the product of a team of authors. I have been extremely
fortunate to be able to assemble a very strong team, but more than that, they
have been great people to work with. Although, inevitably, experienced
people have many calls on their time and from time to time this has caused
the usual problems, everyone has come through and I have greatly
appreciated their support and friendship throughout the preparation of the
text. Additionally, I would like to thank the people who have volunteered to
review individual chapters. Tony Lambregts (FAA) and Mike Walker (British
Aerospace) are two people who are known to me, others have been
acknowledged by individual authors.
The process of publishing an edited text with several contributors is a
demanding task. I have been extremely fortunate to work with Jonathan
Simpson, then the IEE's commissioning editor for the project. Jonathan's
quietly efficient style impressed me greatly and on many, many occasions I
have been extremely grateful for his support and guidance. I would also like
to thank Robin Mellors-Bourne, Director of Publishing, who managed the
project in addition to his normal duties during a very difficult period and
Sarah Daniels, Book Production Editor, who joined the project at a late stage
and injected some much needed energy and enthusiasm.
Finally, I would like to express my thanks to Penny Pilkington whose
support and commitment I have greatly appreciated throughout this project.
Preface xix
Penny has acted as the focal point for communications and retyped
contributions and patiently, well mostly patiently, endured the seemingly
endless edits.
References
1 BABISTER, A.W.: 'Aircraft-dynamic stability and response' (Pergamon Press,
1980)
2 BLAKELOCK, J.H.: 'Automatic-control of aircraft and missiles' (Wiley, 1991, 2nd
edn.)
3 COOK, :.V.M 'Flight dynamics: principles' (Arnold, 1997)
4 ETKINS, B, and REID, L.D.: 'Dynamics of flight: stability and control' (Wiley,
1996, 3rd edn.)
5 MCLEAN, :.D 'Automatic-flight control systems' (Prentice-Hall, 1990)
6 NELSON, R.C.: 'Flight stability and automatic control' (McGraw-Hill, 1998, 2nd
edn.)
7 STEVENS, B.L., and LEWIS, EL.: 'Aircraft control and simulation' (Wiley, 1992)
8 TISCHLER, M.B. (Ed): 'Advances in aircraft flight control' (Taylor & Francis,
1996)