Peter G. Hamel Editor Translated by Ravindra V. Jategaonkar In-Flight Simulators and Fly-by-Wire/Light Demonstrators A Historical Account of International Aeronautical Research In-Flight Simulators and Fly-by-Wire/Light Demonstrators Peter G. Hamel Editor In-Flight Simulators and Fly-by-Wire/Light Demonstrators A Historical Account of International Aeronautical Research Translated by Ravindra V. Jategaonkar 123 Editor PeterG.Hamel Director (Retired) DLRGerman Aerospace Center Institute of Flight Systems Braunschweig Germany e-mail: [email protected] [email protected] Translated by Ravindra V.Jategaonkar SeniorScientist (Retired) DLRGerman Aerospace Center Institute of Flight Systems Braunschweig Germany e-mail:[email protected] Thisbook canbeindexed,referenced, andcitedas follows: In-Flight Simulators and Fly-by-Wire/Light Demonstrators: A Historical Account of International Aeronautical Research, Edited by Peter G. Hamel, Translated by Ravindra V. Jategaonkar, and published bySpringer, March2017. Revised, extendedandtranslated from the originalbookin German: “Fliegende Simulatoren und Technologieträger: Braunschweiger Luftfahrtforschung im internationalen Umfeld“, edited by Peter G. Hamel and published by Appelhaus Verlag, Braunschweig, 2014, ISBN 978-3-944939-06-3. ISBN978-3-319-53996-6 ISBN978-3-319-53997-3 (eBook) DOI 10.1007/978-3-319-53997-3 LibraryofCongressControlNumber:2017933443 ©SpringerInternationalPublishingAG2017 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartofthematerialis concerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation,broadcasting,reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation,computersoftware,orbysimilarordissimilarmethodologynowknownorhereafterdeveloped. Theuseofgeneraldescriptivenames,registerednames,trademarks,servicemarks,etc.inthispublicationdoesnot imply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevantprotectivelawsand regulationsandthereforefreeforgeneraluse. Thepublisher,theauthorsandtheeditorsaresafetoassumethattheadviceandinformationinthisbookarebelieved tobetrueandaccurateatthedateofpublication.Neitherthepublishernortheauthorsortheeditorsgiveawarranty, expressorimplied,withrespecttothematerialcontainedhereinorforanyerrorsoromissionsthatmayhavebeen made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Printedonacid-freepaper ThisSpringerimprintispublishedbySpringerNature TheregisteredcompanyisSpringerInternationalPublishingAG Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Be more attentive to new ideas from the research world George S. Schairer, Former Vice President Research, Boeing (1989) Foreword to the English Edition For the first 40 years of aviation, most of the failures of the earliest attempts at powered, fixed-wing flight were associated with inadequate understanding of dynamic stability and control. Although Lanchester, Bryan, and Williams had already developed the theory of aircraft dynamics by the early 1900s, their work still had found negligible use for design purposes by aslate asthe mid 1940s. However, WWII brought demands formaneuverability so that aircraft dynamic stability and control has been a focus of attention ever since. Itwasthroughtheresearchandthetechnologydemonstratorsthatareexcellentlyreviewed, chronicled,anddocumentedinthisbookthattheaviationindustrygainedanunderstandingof aircraft stability and control. With that knowledge, aircraft designers have been freed forevermorefromtheconstraintsoftheclassicalconceptionofstabilityandcontrolassociated with fixed stabilizing fins and manually movable surfaces for control. Fly-by-Wire artificial stability systems give the designer the flexibility to design an aircraft solely from the per- spective of performance and ignore the classical stability requirements. The genesis of the development of artificial stability was in the pioneering work that was done primarily in the United States and in Germany (often in collaboration). IntheUS,theearlybasicstudieswereconductedinthe40sand50sbyNASAandbythe Flight Research Department of the Cornell Aeronautical Laboratory (CAL, now called Cal- span) with totally different objectives.Thescientists atNASAwereseekingways toimprove theflyingqualitiesofaparticularexistingaircraftwithacontrolproblem.Meanwhile,CAL’s objective was to develop methods for measuring and describing the dynamic stability and control characteristics of any aircraft in flight. Both paths led to the invention of variable stability aircraft that could be used in the early stages of design of automatic control for stabilityaugmentation.ThisbookdescribesthemultipleprojectsinUSfrom1947untiltoday that produced a progression of theoretical and experimental advances in aircraft dynamic stability and control. InGermany,significantcontributionstounderstandingdynamicstabilityandcontrolbegan even earlier than did the work in the US, but there too, as with NASA, the initial work was largely concerned with correcting an existing control problem. Since WWII, important con- tributions have come mostly from the Institute of Flight Mechanics of DFVLR (since 1999 Institute of Flight Systems of the German Aerospace Center—DLR) in Braunschweig. That Institute,undertheleadershipofitsDirector,Dr.PeterG.Hamel,hasestablishedaworldwide reputation for its expertise in all the fields related to flying-qualities investigations and, in particular, the development and highly innovative use of their in-flight simulators of both fixed-wing and rotary-wing aircraft, and their novel applications of Fly-by-Wire and Fly-by-Light.Althoughautopilotfunctionswithlimitedstabilizationwerealreadyavailableon aircraft with mechanical flight control systems, stability augmentation and variable stability aircraft would not have been possible without Fly-by-Wire. Peter and his Institute are also to be credited with their pioneering work in the adaptation of the concepts of system identifi- cation to flight vehicles. Aircraft system identification is a way to build the accurate mathematical model of an aircraftthatisessentialtodesigningaugmentedstabilityandautomaticcontrolforthataircraft. vii viii ForewordtotheEnglishEdition An ever-increasing number of modern civilian and military aircraft is inherently aerody- namically unstable. However, thestability augmentationand automated controlthat arebasic to all current aircraft designs ensures the comfort and safety of your flight. Peter and his collaborators at the DLR Institute of Flight Systems achieved important advancements in the multiple technologies of stability augmentation and in-flight simulation decades before they were thought of anywhere else. These achievements have been particu- larlynotedandpraisedbytwowell-knownexpertsinthefield,MalAbzugandGeneLarrabee, in their 2002 book titled, “Airplane Stability and Control: A history of the technologies that made aviation possible”. Peterandtheco-authorsofthisbookhavemadeanoteworthycontributiontothehistoryof aviation.Thebookistheconsequenceofanenormousefforttocoverthecompletespectrumof internationalcontributionsintheevolutionofartificialstability,variablestabilityaircraft,and in-flightsimulation.ItalsoaddressesthedevelopmentofthetechnologiesofFly-by-Wireand Fly-by-Light that made these developments possible. While this book presents an exhaustive account of variable stability and Fly-by-Wire research and demonstrations worldwide, it emphasizestheworkinGermanyand,inparticular,atDLR’sInstituteofFlightSystems.The prominenceofdescriptionsofrelatedactivitiesinGermanyisunderstandableandappropriate considering that much of the pioneering work was done there and that this is the first time it has been so well documented. The extensive efforts in Germany that go back over 100 years and,inparticular,theachievementsattheInstituteofFlightMechanicscontributedprofoundly to the development of stability and control augmentation and the use of in-flight simulation. I can personally attest to the scope and value of contributions to the current state of under- standing aircraft dynamic stability and control made by Peter and his Institute. I have known Peter G. Hamel for over 40 years and I have had the pleasure of collaborating with him in several projects related to the topics of this book. Through my personal knowledge, I can vouch, without hesitation that he is eminently well qualified to chronicle and evaluate the worldwide developments of these capabilities that have become essential to aviation. This book will be of interest not only to novices, but also to practicing scientists and engineersandtothoseinterestedinaviationhistory.Thiscomprehensivehistoricalaccountis devoid of mathematical equations and deep theoretical discussions, but it is full of tales of innovativeexperimentsandcreativethinking,amusinganecdotes,andfascinatingphotosthatI have no doubt the readers will enjoy. So, my advice to the hesitant reader is, if you are interestedingainingreliableknowledgeabouttheorigins,theinnovators,andtheevolutionof stability augmentation, variable stability aircraft, and in-flight simulators as well as of Fly-by-Wire/Light this is the book for you. Mountain View, CA, USA Irving C. Statler September 2016 Principal Engineer, Flight Research Department Cornell Aeronautical Laboratory, 1946–1970 Director, U.S. Army Aviation Aeromechanics Laboratory, 1970–1985 Director, NATO Advisory Group for Aerospace R&D, 1985–1988 Research Scientist, Human Factors Research Division NASA Ames Research Center, 1988–2008 Foreword to the German Edition A beautiful definition of performance is: “A impersonates B, while C observes”. Applied to the in-flight simulation, a highly sophisticated modified aircraft “impersonates” in real flight anothervehicleinthesenseofa“flyingactor”,while scientistsandengineers“observe”,that is, analyze the outcome offlight to make decisions. One shouldbeabit careful whileusing theterm “supremediscipline”,nomatter inwhich area,becausetherebyyouimplicitlydegradeallotherdisciplinesinthesamefield,orinother wordsassignthemalowerimportance.Inthepresentcase,however,itseemsjustifiedtospeak of in-flight simulation possibly as a “supreme discipline” in aircraft construction, as it encompasses all other disciplines such as aerodynamics, flight mechanics, construction, structures,aircraftsystems,andaeroelasticity.Inordertogetanin-flightsimulatoroperational in the air, best experts in all these fields have to work together, as one encounters the boundaries of physical sciences and engineering techniques, which have to be fathomed and extendedinthismostchallengingtask.Thiswastrueinthepastwithfewertoolsavailableto developaircraftsuchasthetechnologydemonstratorVFW614ATTAS,justliketodaywhen the demands on the prediction accuracy have increased with the availability of better numerical and experimental tools. ItgoestothecreditofPeterG.Hamelasaninitiatorandeditorofthisbook,supportedby manywhowereinvolvedthenaswellaseventoday,tohavelookedbackandreappraisedthe technicalhistoryofin-flightsimulation.Forhiscontributionsinthisfield,hewashonoredwith themostprestigiousaward“Ludwig-Prandtl-Ring”oftheGermanSocietyforAeronauticsand Astronautics. Prandtlwas theone who has provideda scientific basis to flight science, which was still in the infant stages during the early twentieth century, through his work on the boundary layer theory and the construction of wind tunnels. Almost a century after Prandtl’s fundamental work, the author looks back at the history of in-flight simulation and illustrates thereby the rapid development offlight physics. ThishasalongtraditioninGermany.Inabroadsense,theworkofthefirstflightscientist OttoLilienthalmaybeinterpretedinafigurativesenseascontributionstoin-flightsimulation. Hewantedtoreplicatetheflightofbirdswithhisgliders.LaterthetheoreticalworkbyLudwig Prandtl appeared, the aircraft profile and the flying wing by Hugo Junkers, the jet engine by HansJoachimPabstvonOhain,andthesweptwingbyAdolfBusemann,justtonameafew. Thisbookshowsimpressivelyhowtheeffortsofscientistsandengineersinthiscountryhave contributed not only with technical achievements to the success of aeronautics, but also established over a long period a highly successful unified community of research, education, development, production and operations. Only such a close cooperation in a fertile network guarantees a technically and socially valuable future in the days to come. Aircrafthavechangedonlyalittleinrecentyears.However,thereisnowanurgentneedfor fundamentally new aircraft to meet the growing demands for better cost effectiveness, envi- ronmental sustainability, and passenger comfort. These new devices need different properties thantheaircraftflyingtoday,andthesepropertiesmustbesimulatedinadvance,especiallyin flight.Hence,theneedforsimulationsandin-flightsimulatorsishigherthanever,andassuch this book is not only a historical reappraisal, but also represents a mandate for the future. ix x ForewordtotheGermanEdition Thebookyouholdinyourhandsshowsinanexcellentmannerthetechnicalfacetsandthe greateffortswhichareneededtosuccessfully“act”asaproblemsolverinaeronautics.Iwould like to take this opportunity to sincerely thank the editor, Peter G. Hamel, not only for his technicalexpertise,butalsoforhistenacityonthelongroadfromanideatorealizingthebook initsimpressivefinalform.Tothereaders,Iwishmuchenjoymentinreadingthebook,many insightsintotherichpast,ownperceptionsofthecurrentglobalstateoftheart,andinspiration derived thereby for the future. Cologne, Germany Rolf Henke August 2016 Member of the Executive Board German Aerospace Center (DLR) President, German Society for Aeronautics and Astronautics (DGLR) Foreword In-flightsimulationistheultimateapproachinappliedflightsciencestoassessmentandevaluation of aircraft and other aeronautical systems, as it represents the most intense fusion of flight mechanics,flightcontrol,flightsystemstechnology,andflighttesting.Itisaversatiletoolforflight researchandaircraftindustryalike.Startingwithstudiesoffutureconfigurationsuptothesimu- lation of atmospheric phenomena including system influences, dependencies, and even failure casescanbeaddressedwithin-flightsimulation,reachinghightechnologyreadinesslevels. But is this approach still the best way to tackle the current and future questions in aircraft flightresearchanddevelopment?Fromtheviewpointofaresearchinstitutionwithstronglinks toaircraftindustryandgovernmentalpartners,wecanstatetodaythatin-flightsimulationstill hasandmostprobablywilleverhaveanimportantroletoplayinaeronautics.Thereasonsfor this are many and I would like to mention just three of them. Firstly,newconfigurationsareabouttoenterthescenarioofmodernciviltransportaircraft with possibly radical new features with no proven databases to rely on. Early in-flight sim- ulations of potentially unstable configurations and, even more important, of the flight control systems will be an efficient, fast, and reliable way to establish the required confidence of engineers and management alike. Secondly, the segment of unmanned flying vehicles is the fastest growing area in modern aeronautics. Autonomously operating vehicles will enter the world’s airspace in the next decades.Mannedandunmannedin-flightsimulationwillbeoneofthemostpowerfultoolsto prove the maturity of new designs and, not to forget, new legal approaches to certification. Thirdly, international aeronautics industry starts to detach from national institutions and educationalsystems,leavingnationalauthoritieswiththetaskofmaintainingbasiccapabilities inaeronauticaldesignanddevelopment.Asthein-flightsimulationplaceshighestdemandson the key competencies of aircraft modeling, control, and integration, it is best suited to ensure maintaining the expertise in these areas. This is all the more true in the future with new systems having ever-increasing complexity and safety standards. The implementation of in-flight simulation will help us to understand that technical capabilities will not be sufficient tomakeaflightvehicledesignoptimalbuttheknowledgeonhowtodesignanddevelopwill beasimportantasthetechnicalskillsandincludesadeepunderstandingofthehumans,acting within the engineering, design, and decision processes. Therearemanygoodreasonstopursueinthefuturethisjewelofmodernflightsciences.It is apparent from this book that a symbiosis of scientific excellence at universities, research institutions, industry capabilities, and political focus is mandatory in this pursuit. It is highly appreciatedthattheauthorsofthisbookpresentthehighlights,achievements,andworldwide historicalevolutionofthisaspectofflightengineeringsciences.Thankstotheauthorsforthis brilliant and one of the most vivid compilations of aeronautic achievements that has been given to international scientific communities! Braunschweig, Germany Stefan Levedag November 2016 Director, Institute of Flight Systems German Aerospace Center xi