1316 Book reviews / Automatica 39 (2003) 1313–1321

time-delay systems, IDP for singular control problem. Eachchapter begins with logic behind the method and follows bynumerical examples. The list of computer programs is givenin Appendices. In summary, this book is a well organizedand clearly written introduction to IDP. The strongest featureof this book is numerical examples illustrating the use andlimitations of IPD algorithms.

Jerawan ChudoungDepartment of General Engineering;

University of Illinois at Urbana-Champaign;104 South Mathews Avenue; 117 Transportation

Building; Urbana; Il 61801; USAE-mail address: jerawan armstrong@yahoo.com

doi:10.1016/S0005-1098(03)00079-7

References

Bellman, R. (1957). Dynamic programming. Princeton, NJ: PrincetonUniversity Press.

Bellman, R. (1971). Introduction to mathematical theory of controlprocesses, vol. 2. New York: Academic Press.

About the reviewerJerawan Chudoung received the Ph.D. degree in Mathematics fromVirginia Polytechnic Institute and State University (Virginia Tech),Blacksburg, VA, in May 2000. From June 2000 to April 2002, shewas a Post-Doctoral Research Fellow at University of Illinois atUrbana-Champaign. Dr. Chudoung is currently self-employed. Her re-search interests include hybrid systems and control, nonlinear controlsystems, and complex systems modeling. She has published papers inrefereed professional journals and conferences. Dr. Chudoung is a mem-ber of American Mathematical Society (AMS), Society for Industrialand Applied Mathematics (SIAM), and IEEE.

Advances in aircraft ight controlMark B. Tischler, Taylor & Francies, London, 1996,ISBN 0-7484-0479-1

1. Introduction

This book is a compilation of papers on various practicalaspects of aircraft Kight control design. An all-encompassingarray of aircraft types is presented, with the common themeof meeting suitable performance requirements through thedesign of the Kight control system. The papers are all writ-ten by experienced practitioners performing and implement-ing designs. Many of the papers were originally assembledas part of a 1994 special issue on aircraft Kight control(Tischler, 1994) that were updated and supplemented withothers from an AGARD meeting (AGARD, 1994).The aircraft Kight control problem itself is historically acomplex one of great interest. Its interdisciplinary nature hasmade it one of the more challenging control problems overthe years. The primary Kight control design challenge is toachieve good performance in terms of response to the pilotdespite large variations and uncertainty of the dynamics ofthe aircraft over its vast operational envelope. The accom-plishment of Kying qualities requirements continues to bean issue, and is a fundamental thesis of this book. Each ofthe chapters details exactly how performance requirementsare translated into desirable aircraft responses through thedesign of the Kight control system.

2. The book

After a short section on aircraft Kying qualities andsystem identi<cation, the book considers three separate<elds of Kight control: rotorcraft and V/STOL (verti-cal/short takeoH and landing) aircraft, transport aircraft, andhigh-performance, <ghter aircraft. Each of the articles in thebook is complete by itself, and none depend on previous

chapters, although a good understanding of aircraft Kyingqualities is important to appreciate the technical details inthe subsequent chapters.

2.1. Part one: speci5cations and validation models

Chapter 1, “Handling-qualities speci<cation—a func-tional requirement for the Kight control system,” describesthe use of handling qualities as the functional requirementsto guide the development of the Kight control system. Ratherthan a summary of the Kying qualities speci<cations them-selves, this chapter guides the reader through the processof selecting appropriate quantitative requirements for par-ticular missions. Practical considerations beyond technicalreasons are emphasized. Response types and mission typeelements, elements that consist of Kying qualities tasks, arediscussed for <xed and rotary wing aircraft. Finally, a sum-mary of quantitative criteria such as short-term pitch re-sponse requirements are given.The authors lament that these Kying qualities requirements

are often not used in practice, which leads to problems inKight testing that could have been avoided. In particular,pilot-induced oscillations, or PIO, a condition in which smalltime delays in the response of the aircraft cause the pilot toovercompensate until an out-of-control condition occurs, hashappened on several cited occasions because of this. Whileall of the technical content of the chapter remains highlyrelevant today, the authors describe the outdated US militarystandard speci<cation, which has since been replaced bya military handbook and is no longer strictly required formilitary aircraft programs.Chapter 2, “System identi<cation methods for air-

craft Kight control development and validation,” reviewsfrequency-domain system identi<cation methods for Kightcontrol system development with emphasis on rotor-craft. The chapter is mainly a description of how theCIFER (Comprehensive Identi<cation from FrequencyResponses) analysis facility is used throughout diHer-

Book reviews / Automatica 39 (2003) 1313–1321 1317

ent phases of Kight control system development at AmesResearch Center. Details of system identi<cation tech-niques are omitted in lieu of a description of the typesof transfer function and state space models that result,and a description of how these models and responsedatabases are used in speci<cation formulation, design,simulation, Kight control system development, and Kighttesting.

2.2. Part two: rotorcraft and V/STOL

The next section consists of four chapters describ-ing Kight control for somewhat unusual classes: rotor-craft and vertical/short takeoH and landing (V/STOL)aircraft. These aircraft are, for the most part, unique tothe military, and, not surprisingly, the four chapters inthis section each describe a diHerent aspect of militaryaircraft.Chapter 3, “A high bandwidth control system for

the helicopter in-Kight simulator ATTHeS—modelling,performance and applications,” discusses the AdvancedTechnology Testing Helicopter System (ATTHeS) at DLRin Germany. In particular, the chapter details the explicitmodel-following control system, including the model struc-ture and parameters for the feedforward and feedbackportions of the control law. There are links to system iden-ti<cation in the previous chapter, but the identi<cation hereis based on time-domain models, rather than frequency do-main. The ATTHeS is used for handling qualities researchand helicopter in-Kight simulation.Chapter 4, “Advanced Kight control research and devel-

opment at Boeing Helicopters,” overviews the V-22 Ospreylessons learned and how they apply to the RAH-66Comanche helicopter. Rather than technical detail, thechapter begins with a description of the history of Boeinghelicopter programs. The focus is on the successes ratherthan on lessons learned, with emphasis on control lawsand control hardware. Much of the chapter focuses onhow various features are integrated into the vehicle man-agement system. The style is very high level, with blockdiagrams and broad descriptions in lieu of particular de-tails. The control law design process focuses on corpo-rate processes, omitting technical details such as controland analysis techniques, but giving the reader a thor-ough understanding of the steps the Boeing team goesthrough.Chapter 5, “Application of nonlinear inverse methods

to the control of powered-lift aircraft over the low-speedenvelope,” is the <rst of two chapters dedicated to V/STOLaircraft. In this chapter, nonlinear inverse methods appliedto powered lift aircraft are described. An important conceptin modern Kight control is presented: the use of nonlinearinversion-based control laws. The primary idea is that anon-board model and a model of desired dynamics are used toimpart desired dynamics to the closed loop aircraft. One of

the primary challenges in low-speed Kight of V/STOL air-craft is that the dynamics change dramatically during transi-tion between Kight modes, and using dynamic inversion theKight control law design can be done eHectively over widelyvarying dynamics. One interesting note is that lift and dragcharacteristics of the test aircraft were found to vary10–20% between Kight test and wind tunnel data, yet therewas no degradation in control system performance, attestingto the robustness of this architecture.Chapter 6, “Flight control and handling research with the

VAAC Harrier aircraft,” focuses on what will be requiredof STOVL aircraft that replace the Harrier. Several con<g-urations and control designs developed and tested throughpiloted Kight test are described. The array of con<gurationsshows the complexity of the STOVL Kight control prob-lem. Control laws range from open loop control laws toclassically designed single-loop-at-a-time laws to multivari-able feedback designed using H∞. The lowest-complexityfeedback controller was able to provide a considerablereduction in pilot workload, with the largest reduction inpilot workload caused by eliminating all conscious modechanging.

2.3. Part three: transport aircraft

Chapter 7, “The design and development of Kying quali-ties for the C-17 military transport airplane,” details Kyingqualities for the US Air Force’s most recent transport air-craft, the C-17. There is a general description of the air-craft, especially the cockpit, heads-up-display or HUD, and29 aerodynamic surfaces comprising the mechanical Kightcontrols. A description of the Ky-by-wire control hardwareas well as block diagrams of the control laws are given. Thedesign process for the control laws, including a discussionof the Kying qualities requirements used, and a good sum-mary of the process from requirements de<nition to pilotedsimulation to Kight test is given.Chapter 8, “Fly-by-wire for commercial aircraft: the Air-

bus experience,” gives an overview of the Kight control lawcharacteristics and constraints for the Ky-by-wire Kight con-trol systems developed for Airbus aircraft. Constraints suchas sensor failures, actuator rate and position limits, passen-ger comfort, and human factors are discussed in terms ofthe control law structure and gain scheduling. Details aregiven for the A320 and A340 aircraft, including predecessoraircraft programs. These descriptions emphasize the impor-tance of piloted simulation in the aircraft design and devel-opment process. In particular, this simulation has the abilityto both improve the safety and reduce the sale of Kighttesting program, greatly reducing cost. Finally, the Kightcerti<cation process is adapted to take account of bene<tsof the Ky-by-wire design.Chapter 9, “Practical control law design for aircraft us-

ing multivariable techniques,” gives an overview of thehistory of multivariable Kight control. Two design exam-

1318 Book reviews / Automatica 39 (2003) 1313–1321

ples are given for transport aircraft, one of which is inservice on Boeing 767’s today, and one example is givenfor a tactical <ghter aircraft. On the Boeing 767, LQRis used to eliminate a limit cycle in the lateral motion.There is quite a bit of technical detail in these sections thatgive the reader an excellent introduction into the basics ofKight control law design, complementing some of the otherchapters that focus more on the control hardware, aircraftprograms, and processes used to translate requirementsinto Kight-worthy systems. Even though the control designtechniques are multivariable LQG, there is a great dealof frequency domain that provides insight into the designelements.The design example for a post-stall, highly maneuverable

<ghter aircraft of the type that was thought to replace the<ghters developed in the 1970s and 1980s is given next.Much work was done in the <elds of unsteady aerody-namics and nonlinear Kight control to support this type ofaircraft, but other considerations ultimately displaced thisconcept with that of low-observable, ‘stealth’ <ghter air-craft as the successors to the current Keet. The introductionof thrust vectoring control and the gain scheduling ofhigh-order multivariable controllers are highlighted. Thrustvectoring has remained as a practical method of addingcontrol power for modern <ghters, while the acceptance ofnonlinear dynamic inversion control laws solved the prob-lem of gain scheduling by dependence of on-board modelsrather than interpolated point designs. This chapter is anice lead-in to the high-performance aircraft of the nextsection.

2.4. Part four: high-performance aircraft

Chapter 10, “Lavi Kight control system,” and Chapter11, “Digital autopilot design for combat aircraft in Ale-nia,” describe Kight control system development in Israeland Italy. The <rst chapter gives a description of the Lavi<ghter aircraft, including details and technical data on con-<guration of the aircraft. The digital Kight control system isdescribed, with design philosophy underscored by the Ky-ing qualities requirements and how requirements were trans-lated into a feasible design. Flight test responses and Kyingqualities are presented. In the second chapter, digital Kightcontrol systems and autopilots of the Alenia company aregiven. The company has been involved in the developmentof Kight control systems and autopilots for three <ghter air-craft: the Tornado, AMX, and EF2000; the functionality, de-sign, implementation, and Kight test are described for the lasttwo.Chapter 12, “Development and Kight experience of the

control laws and the aeroservoelastic solution in the Ex-perimental Aircraft Programme (EAP),” and Chapter 13,“X-29 Kight control system: lessons learned,” provide someinsight into the design of technology demonstrator aircraft.This type of aircraft consists of a single or small number

of vehicles developed to demonstrate advanced technolo-gies. Con<dence and experience gained is used to transi-tion these technologies onto production aircraft. In the <rstchapter, the EAP, which Kew in the UK from 1986 to 1991was to demonstrate technologies relevant to future com-bat <ghters. The main focus of the Kight control systemwas the ability to control an unstable aircraft at high an-gles of attack with carefree handling. The control law de-sign method is described in detail. Classical feedback con-trol was used, with detailed block diagrams and descriptionsproviding the reader with great insight into the successfulachievement of Kying qualities. The program was extremelysuccessful, primarily due to the high quality modelling ofthe aircraft. It is interesting to note that remarkably littleadjustment to the model was required as a result of Kighttesting.In the next chapter, the US-developed pair of X-29’s is

described. As with the EAP, this aircraft was produced todemonstrate technologies for highly maneuverable <ghters.The X-29 has an unusual forward-swept wing design forimproved handling at high angles of attack. Two separatedesigns on the two aircraft, one for the low angle of attackKight and one for high angle of attack Kight, are given. In the<rst case, the main diAculty of the design was meeting thegain and phase margins, which were ultimately relaxed in the<nal design. There is a good description of both single-loopand multivariable stability margins, and how control lawswere modi<ed to meet bare minimummargins. In the secondcase, the focus is on the envelope expansion. The contrastbetween this chapter and the previous one is interesting, inthe diHerence in diAculty in designing robust Kight controlsystems for the diHerent aircraft.Chapter 14, “Practical aspects of the design of an inte-

grated Kight and propulsion control system,” and Chapter15, “Control law design and Kight test results of the ex-perimental aircraft X-31A,” describe two experimentalaircraft: the STOL Maneuver Technology Demonstrator,which is a modi<ed F-15B, and the X-31A aircraft. Theprimary technology considered for the STOL/MTD wasthe integration of the two-dimensional thrust vectoringand reversing exhaust nozzles into an all-new digital in-tegrated Kight and propulsion system. This chapter docu-ments the development of two competing control designs:a classically designed one and an multivariable one. Lit-tle technical detail is given, but it is interesting to see thecomparison of the two competing designs. As expected,for traditional Kight modes, the multivariable design of-fers no bene<t, and when there are multiple eHectors orcomplex requirements, the multivariable technique waspreferred. One interesting note is the unexpected syner-gism between the two parallel design eHorts; the classicaldesign bene<ted from the knowledge of achievable per-formance from the multivariable design while the multi-variable design was able to be reduced in complexity withknowledge of performance achievable from the classicaldesign.

Book reviews / Automatica 39 (2003) 1313–1321 1319

The goal for the X-31A aircraft was to allow maneuveringto 70 degrees angle of attack, that is, to be able to maneuverbeyond when wing stall occurs and aerodynamic eHectorsare of no use. The structure of the control laws, the deter-mination of the feedback gains though an LQR design, andthe accounting of nonlinear eHects are described. Quite afew Kight test results are presented in terms of the achievedKying qualities. As in a few of the previous chapters, it isinteresting to note that no signi<cant control law structurechanges were made during Kight tests. It is also interesting tonote that aerodynamic model updates just before <rst Kighthad minimal impact because of the optimal control approachused.

3. Conclusions

This book should be of interest to anyone involved withany level of development of Kight control systems. Thereare several chapters that provide good basic introductionsto the Kight control system itself, both in its form and inits function. Several other chapters provide rich technicaldetail to enable the control engineer to learn from the com-bined experience of many of the developers that have pre-ceded them. Although this is probably not a suitable book

doi:10.1016/S0005-1098(03)00102-X

for course-work of any kind, it is a valuable reference thatbelongs in the library of any Kight control engineer.

Andrew SparksAir Force Research Laboratory;

Air Vehicles Directorate;AFRL/VACA; 2210 Eighth StreetWright Patterson Air Force Base;

OH 45433-7521; USAE-mail address: andrew.sparks@wpafb.af.mil

References

Tischler, M. B. (Guest Editor) (1994). International Journal of Control,59 (1) (Special Issue: Aircraft Flight Control).

AGARD, 1994. Proceedings of the AGARD @ight mechanics panelsymposium on active control technology: Applications and lessonslearned, AGARD-CP-560, Turin, Italy, May 9–13, 1994.

About the reviewerAndrew Sparks received his Bachelor of Science and Master of Sciencedegrees in Mechanical Engineering from the Massachusetts Institute ofTechnology in 1986 and 1988, respectively, and his Ph.D. in AerospaceEngineering from the University of Michigan in 1995. Since 1988 he hasbeen with the Air Force Research Laboratory (formerly Flight DynamicsLaboratory and Wright Laboratory) at Wright Patterson Air Force Basenear Dayton, Ohio, the birthplace of aviation. His research interests includerobust, decentralized, and cooperative decision and control systems formanned and unmanned aircraft.

Control of complex systems K. AstrUom, P. Albertos,M. Blamke, A. Isidori, W. Schaufelberger and R. Sanz;Springer, London, 2001, ISBN: 1-85233-324-3.

This edited book is a fruit of the 5-year COSY project,among leading European researchers, on topics related tocomplex dynamic systems. I enjoy very much reading thisbook because it covers a wide range of important issuesin Automatic Control, with a good balance between theoryand application. I highly recommend this book to scientists,researchers, educators, and research-oriented practicing en-gineers. Some materials can even be borrowed to teach anupper-level graduate course in systems and control.The book starts with a nice introductory chapter dis-

cussing in general terms research challenges and opportu-nities in complex systems. K. AstrUom, the author of thischapter, <rst reviews some traditional and modern examplesof complex engineering systems, and the role of feedbackin investigating these systems. Then, he quickly brings thereader to a good number of fascinating research problemscurrently facing the systems and control researchers andengineers. Chapter 1 ends with a brief discussion of the sub-sequent chapters addressing these problems, authored bydiHerent European researchers who have been involved inthe COSY program. Some supplementary references in com-plex systems can be found in Holland (1998) and Murray

(2002), where it is clearly spelled out how the <eld of anal-ysis and control of complex systems crosses various disci-plines of engineering and sciences.Chapter 2 describes a new object-oriented modeling

language, named as Modelica. As shown in detail by theauthors, this object-oriented approach of modeling has manyadvantages over the traditional approaches from physics anddata, and is particularly suitable for describing complex sys-tems in multi domain. The focus of this chapter has been ondiHerential–algebraic equations with discrete-event features.More remains to be accomplished in this area.Chapters 3 and 4 report on recent developments in non-

linear control. The interested reader should read these twochapters together with other key references (Isidori, 1999;Jiang, Teel, & Praly, 1994; Kokotovi�c & Arcak, 2001;Sontag, 2000) to gain a big picture on Sontag’s input-to-statestability (ISS) theory, nonlinear ISS small-gain theorems,and other tools for constructive nonlinear control design andapplications.Physical systems are strongly nonlinear and well

structured. The authors of Chapter 3 demonstrate how thepassivity concept can be systematically exploited for con-trolling physical systems and some classes of nonlinearsystems written in the general form of ordinary diHer-ential equations. A good review of the past literature inpassivity-based approaches is given along with other re-