INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL

Int. J. Robust Nonlinear Control 8, 1307—1308 (1998)

BOOK REVIEW

ADVANCES IN AIRCRAFT FLIGHT CONTROL, Editedby M. B. Tischler, Taylor & Francis Ltd, London,U.K., 1996

Advances in Aircraft Flight Control, edited byMark B. Tischler and published by Taylor & Fran-cis, is a valuable addition to the recent literature inthe field with an uncommon perspective. The focusand organization of the book distinguishes it fromclassic texts such as Etkin’s Dynamics of Flight orAircraft Dynamics and Automatic Control byMcRuer, Ashkenas and Graham. Instead of theexposition of principles presented in these earliertexts, the Tischler book provides something ofa ‘case study’ approach. The majority of the bookis devoted to reviews of the flight control systemdesign for a number of specific aircraft. Thesechapters typically review an aircraft’s mission, theflight control and handling qualities requirements,the application of design methodologies and tools,simulation programs, and flight test. The problemsand surprises that arose in the programs, and theirresolution, are inevitably among the most valuableand interesting sections in the book. Anothernotable recent book, Airplane Stability and Controlby Abzug and Larrabee, also addresses the dynam-ics and flight control of specific aircraft but froma distinctly historical perspective. The Tischlerbook, however, is clearly focused on the currentstate of the art in flight control design—at leastwithin the decade-long time frames of modern air-craft program evolution.

The book covers a range of aircraft typesin three categories: Rotocraft and V/STOL, Trans-port Aircraft, and High-performance Aircraft.Consistent with a focus on advanced flight control,more conventional types such as commuter andgeneral aviation aircraft are not addressed. Em-phasis is given instead to the most important re-cent advances in aircraft flight control includingrelaxed static stability airframes with high author-ity, multiple-redundant digital fly-by-wire control.Some new aircraft types of current interest, such asvery high altitude aircraft and UCAV are not in-cluded, but the book can certainly be read withprofit by those looking to unconventional mannedaircraft of the future. The book takes a interna-tional view as well with examples not only from the

( 1998 John Wiley & Sons, Ltd.

US, but also from Europe/NATO and Israel aswell. The only obvious omissions are aircraft fromthe former Soviet Union, but this is probably rea-sonable given an emphasis on issues such as digitalfly-by-wire development over, say, aerodynamicdesign. Each of the aircraft example chapters areindependent, generally written by key participantsin the programs discussed. No direct comparisonsor summaries are made across the example air-craft, but there is enough comparable material toallow the reader to readily compare problems andapproaches.

Flight control system design practice for realaircraft is the unifying theme of the book. Thisprovides a valuable view of the arena where con-trol theory meets the real world and a useful con-trast to the unbridled theorizing that fills manytechnical journals. Examination of the case studiesin the book emphasies that real world flight con-trol design remains a complex, iterative processthat requires a detailed understanding of the dy-namics of the specific aircraft and a conceptualunderstanding of the flying qualities requirements.Clear differences in focus and emphasis are seenbetween the concerns of those who design actualflight control systems and the currently prominentresearch areas in control theory. Many of the de-signs were done using classical methods—withseveral groups noting the deeper physical insightavailable as a key reason. There is little indicationthat the advancement of aircraft flight control isbeing significantly impeded by limitations in multi-variable control theory. On the other hand, theinability to predict subtle flying qualities problemshas much more impact on the design process.Modern approaches to multi-variable robustnessanalysis do appear to provide utility in preliminarydesign. But the more important effort is the refine-ment of the aircraft dynamics model using nearreal time system identification as an integral partof the flight test effort (e.g., the X-29).

Two cross-cutting themes, flying qualities andsystem identification from flight test data, appearand reappear through the design cases. Overviewsof these topics are thus appropriately presented inthe first two chapters of the book. The first chapterentitled Handling-qualities specification—a func-tional requirement for the flight control system

reviews the current approaches to relating flyingqualities requirements to the flight control designprocess. Emphasis is given to MIL-STD-1797A asthe most detailed (fixed wing) specification avail-able. The evoluton of the specification in recentyears to accommodate highly augmented fly-by-wire aircraft that may have unconventionaldynamics is emphasized. Recent efforts to develop‘mission-oriented’ specifications are reviewed as well.

The second of the two overview chapters, en-titled System identification methods for aircraftflight control development and validation, reviewsthe modern use of system identification techniquesin flight control design. Frequency domainmethods are emphasized and their convenient con-nection with frequency domain flying quality met-rics are noted. An example of extension of thisactivity to practical extraction of MIMO singularvalue robustness measures in flight test is seen inthe chapter on the X-29 program.

While there is no explicit summary of the casestudy implications, recurring flight control designproblems may be clearly seen. Sensor problems,often related to redundancy management, arenoted in a number of designs. Examples includeproblems with the angle-of-attack (AOA) and air-speed measurement in high AOA aircraft such asX-29. The book does not address redundancymanagement practice specifically, but it does pro-vide a practical survey of current practices. Sim-ilarly detailed design practice for other hardwarecomponents such as actuators and computers arenot explicitly addressed, but there is considerableinformation on current practice in the context ofoverall system design. In general, the book focuseson the overall control system and its interactionwith the aircraft dynamics and handling qualities.Thus while the aerodynamic considerations in

control surface design is not addressed broadly orin depth, the book provides a useful look at howmultiple, redundant control surfaces are beingintegrated in modern aircraft designs (e.g. the LaviElevons Separation Logic). This view reveals howsubtle differences in aircraft characteristics orchanges in the airframe configuration can requirecomplex changes in control surface mechanization.Examples of the influence of aeroelasticity on con-trol include specific cases of aeroservoelastic prob-lems dealt with on aircraft such as the V-22 Osprey.

The role of simulation, in particular, pilot-in-the-loop simulation on the ground and in inflightsimulators is seen in many of the case studies.Examples of recognized limitations of simulators,such as difficulty in predicting stick gains (e.g. C-17roll control), are presented.

The next decade, following the unprecedenteddefense cutbacks of the early 1990s, should indi-cate if aircraft flight control will continue to evolvesignificantly or approach a plateau, as has sub-sonic transport aerodynamic configuration. As-suming there will be something new and significantto come in flight control, a sequel to this book(prior to the editor’s retirement party) will cer-tainly be appropriate in the future. In the mean-time, any practicing aircraft or flight controldesigner would be well advised to slide Etkin andMcRuer, Ashkenas and Graham respectively tothe left on the shelf (about 1)25 in) and slide ina copy of Tischler’s Advances in Aircrat FlightControl.

TOM MYERS

Systems Technology, Inc.13766 S. Hawthorne Blvd.

Hawthorne, CA 90250-7083,U.S.A.

1308 BOOK REVIEW

( 1998 John Wiley & Sons, Ltd. Int. J. Robust Nonlinear Control 8, 1307—1308 (1998)