Springer Biographies Ludwig Prandtl A Life for Fluid Mechanics and Aeronautical Research MICHAEL ECKERT Springer Biographies More information about this series at http://www.springer.com/series/13617 Michael Eckert Ludwig Prandtl A Life for Fluid Mechanics and Aeronautical Research Translated by David A. Tigwell 123 Michael Eckert Deutsches Museum Munich,Bayern, Germany ISSN 2365-0613 ISSN 2365-0621 (electronic) SpringerBiographies ISBN978-3-030-05662-9 ISBN978-3-030-05663-6 (eBook) https://doi.org/10.1007/978-3-030-05663-6 LibraryofCongressControlNumber:2018966436 TranslationfromtheGermanlanguageedition:LudwigPrandtl:StrömungsforscherundWessenschafts- managerbyMichaelEckert,©Springer-VerlagBerlin,Heidelberg2017.AllRightsReserved. ©SpringerNatureSwitzerlandAG2019 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictionalclaimsinpublishedmapsandinstitutionalaffiliations. ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSwitzerlandAG Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Preface to the English Edition Forthecommunityofaeronauticalengineersandfluiddynamicists,LudwigPrandtl is a celebrity—not only in Germany. Yet the story of his life has found little attentionasthesubjectofscientificbiography.TheresponsetotheGermanedition shows that this neglect was undeserved. PartofthedelayedinterestinPrandtl’slifeisrelatedtowhathasbeennamedin German “Vergangenheitsbewältigung”, mastering the past. In earlier accounts, Prandtl’sscientificmeritsoutshonehisperformanceinthepoliticalarena.Exposing his less laudable activities as an advisor for Göring’s Air Ministry still evokes mixedfeelingsamongstsomeofhisGermanadmirers.Similarsensitivitiesmaybe observed in the case of other German scientists whose Nazi past prevents their unobstructed reverence. Prandtl’s political performance is all the more noteworthy because he described himself as “non-political”. To unearth evidence for this apparent contradiction has been one of the major challenges for Prandtl’s biography. Ofcourse,theportrayalofpoliticalactivitiesisnotmeanttodetractfrommerits in other areas. Prandtl’s international reputation as a pioneer of aeronautical research and fluid mechanics is beyond dispute. In this regard, it is of particular interest to observe the juxtaposition of science and technology which pervades Prandtl’s professional life—from his affiliation with aeronautics to his nomination for the Nobel Prize. As this dichotomy is shaped by national traditions and con- ventionsindifferentways,Prandtl’scharacterisationas“scientificengineer”should be interpreted by readers of this English edition as a peculiar German feature. Finally,IwouldliketoextendmythanksfromtheprefacetotheGermanedition to the translator, David Alan Tigwell, and Andreas Dillmann from the DLR for providingthefinancialsupport.Itisapleasuretoacknowledgethecloseinterestof Prandtl’s scientific heirs at Göttingen in this biography. Munich, Germany Michael Eckert November 2018 v Preface to the German Edition LudwigPrandtl(1875–1953),asthe“fatherofmodernaerodynamics”,isrespected by a worldwide community of aeronautical engineers. His scientific achievements arenotsimplylimitedtothefieldofaircraftaerodynamics,butalsoencompassthe entire spectrum of fluid mechanics. Ludwig Prandtl, ein Führer in der Strömungslehrewasthetitleofabookpublishedtocelebratehis125thbirthday,in whichleadingresearchersinthefieldoffluidmechanicshonouredtheworkoftheir master.1 The title made reference to Prandtl’s legendary “Führer durch die Strömungslehre” (Essentials of Fluid Mechanics), which has been repeatedly published, in many editions, and which, even today, still counts amongst the standard works on fluid mechanics.2 Prandtl was highly respected by his contemporaries. It was his model student Theodore von Kármán who gave him the name of “father of aerodynamics“.3 Nomenclaturesuchasthe“Prandtlnumber”,“Prandtl’sboundarylayer”,“Prandtl’s mixing length” and other specialist terms associated with his name serve as a reminder,eventoday,ofhow,throughhisscientificendeavours,hehasleftalasting mark on various branches of science. However, until now, there has not been a biography that has fulfilled the requirements of a modern history of science and technology, but also provided a summary of Prandtl’s life and work which is accessible to non-experts, as well. ThisdoesnotmeanthatPrandtl’sachievementshavedisappearedintoobscurity. His daughter has written a “Lebensbild” (biographical sketch) which provides a portrait ofPrandtlasaprivateperson andfather,drawing on numerous documents passeddownfromthefamily.4Therearealsohistoricalaccountsavailablefromthe Aerodynamische Versuchsanstalt (Aerodynamic Research Establishment) and the Kaiser-Wilhelm-Institut für Strömungsforschung (Kaiser Wilheim Institute for 1Meier(2000). 2Oertel(2008),Oertel(2010). 3vonKármánandEdson(1968,p.97). 4Vogel-Prandtl(2005). vii viii PrefacetotheGermanEdition FluidMechanics),inwhichPrandtlservedasdirectorduringhistimeinGöttingen.5 Prandtl acted locally as the founder of the Göttingen Aeronautical and Fluid Mechanics Research Facilities and nationally as an advisor to government min- istries and internationally as a representative of German research. For this reason, therefore, this biography is not concerned so much with a “forgotten pioneer” of fluid dynamics, but instead offers an account of the life of a researcher and rep- resentative of science who, at many levels, has had an ever-unfolding influence, right through to today. There is no ideal biographical approach to individuals such as Prandtl, who made technology and science their purpose in life butwho, beyond that, have also played a decisive role as experts in politics and industry. Their careers and pro- fessionalassociationsaretoodifferent.Soalsoaretheirpersonalidiosyncrasiesand their relationships within their families, to society and to politics which, in the course of time, give an orientation to the life of an individual and allow the biographer to subordinate the totality to a rigid schema. Despite the number of comprehensive biographies that are available and a wide discussion about the role of biography in science and technology,6 no methodology has been identified for best bridging the divide between “life” and “work”. All too easily, biographies of scientists split into chapters with generally understandable descriptions of the cir- cumstances surrounding the scientist’s life and those with technical scientific accounts that are difficult to follow. Finding a continuous account that integrates both the subject’s life and work is one of the most challenging tasks of scientific biography. Fortunately, in the case of Prandtl, there is a very extensive legacy of letters,manuscriptsandotherhistoricaldocumentation,sothatthebiographycould becreated,toalargeextent,fromauthenticsourcesthatoftenintegratehislifeand workinanaturalway.Therefore,aboveall,thematerialgleanedfromlettershasa great value from the methodological perspective. In his correspondence with politicalauthorities, it isapparentthat Prandtl’s science—fluidmechanics—played suchanimportantroleinrelationtowarandpeacethatpoliticaldevelopmentsmust also be an integral part of this biography. Figures such as Prandtl are always an inspiration for the close interdependence of science and politics. When considering the role of experts who offered their knowledge and expertise to the Nazi regime, “self-enforced conformity”, “self-mobilisation” and “collaborative relationships” are expressions which are frequently employed.7 Across disconnects in the political system—from the GermanEmpireviatheWeimarRepublicthroughtotheNSstate—therehasbeen, inthecourseofthetwentiethcentury“adeepandfar-reachingchangetakingplace regarding what politics and science are or could be”. This was the way in which a new social–historical study of science and politics addressed the interaction of the two spheres. “Even when one speaks of two fundamentally separate spheres and, forvariousreasons,acertainpracticalvaluecanbeclaimed,inthemeantime,they 5Rotta(1990a),Tollmien(1998). 6ShortlandandYeo(1996),FüsslandIttner(1998),Klein(2009). 7Mehrtens(1986),Mehrtens(1994),Trischler(1994). PrefacetotheGermanEdition ix havebecomesostronglyintertwinedthatonecannotgetbywithouttheother”.8At thesametime,scienceandpoliticsappearas“resourcesforoneanother”,9whereby the term “resources” must be understood not only in the economic sense. “The resources referred to here can be cognitive-conceptual, instrument-based- institutional, financial or also of a rhetorical nature”.10 This is readily apparent taking Prandtl as an example. Included in the category cognitive–conceptual resources are “epistemic techniques”,11 such as the boundary layer theory or the airfoiltheory,withwhichPrandtl’ssciencegainedaparticularinterestforpractical application and consequently for politics. The instrument-based institutional resources came to be used in the form of wind tunnels and other experimental facilities.ResourcesofarhetoricalnaturearerepresentedbyPrandtl’ssubmissions andmemorandatospecificallytargetedpoliticians.Nonetheless,throughouthislife, Prandtl considered himself to be non-political. In 1946, he addressed a memoran- dumtotheBritishMilitaryAuthoritywiththeheading“Thoughtsofanon-political German on denazification”. This self-assessment was in line with that of a Nazi henchman who described Prandtl as being “completely uninterested” in politics. But, Prandtl’s contact with politics, from the “Deutsche Forschungsrat für Luftfahrt”(GermanResearchCouncilforAeronautics)inthelate1920sthroughto the“Forschungsführung”(ResearchExecutiveCommittee)underHermannGöring, duringtheSecondWorldWar,givesadifferentpicture.Theresourcesconcept,with which the diverse relationships with politics show up, reveals the incongruity between the self-assessment made by Prandtl as being a “non-political German” and his actual political role. However,Prandtlwasfirstandforemostascientistandengineer.Therefore,the biography must—if it is to remain generally understood—dispense with some things that experts would consider to be of value. Dispensing with mathematical deliberations is, in the case of applied mathematics and mechanics, as Prandtl’s scientific discipline was known from the 1920s, particularly agonising. In order to provide readers with a preparatory mathematical background (but not, however, necessarily expert knowledge in specific sub-specialities), whilst giving a better insight intoPrandtl’swayofthinking, atappropriate pointsinthetext,boxes have been inserted that contain background information which elucidate the subject matter discussed in the main text. In these boxes, the core of the relevant research work(e.g.thederivationofthelawofthewall,inthecaseofturbulentpipefriction) is exemplified. More comprehensive accounts can be found in the specialist literature. Withoutthehelpandassistanceofmanyindividualsandinstitutes,itwouldnot havebeenpossibletogainanoverviewandadequatelyrepresentPrandtl’slifeand work with all the diverse connections with science, technology and politics during 8Ash(2010,p.11). 9Ash(2002). 10Ash(2010,p.16). 11Pleaserefer toMoritz Epple’sexpansionoftheRheinbergerterm“epistemicthings”inEpple (2002b). x PrefacetotheGermanEdition theturbulent times inwhich helived.First and foremost,Iwouldlike tothank the DeutscheForschungsgemeinschaft(GermanResearchFoundation)forthefinancial support they have provided over the years and the Research Institute of the Deutsches Museum in Munich, which provided an ideal environment for research in the history of science and technology and which also made available the infrastructureoftheDeutschesMuseum—fromarchivesthroughtolibraryfacilities and departmental collections (in particular, those related to aviation). I would also like to thank, at this juncture, the numerous archives that allowed me to access relevant source material, above all, the archive of the Deutsche Zentrum für Luft- und Raumfahrt (German Aerospace Centre) in Göttingen and the Archiv zur Geschichte der Max-Planck-Gesellschaft (Historical Archive of the Max Planck Society) in Berlin. I would certainly not have been able to have written this biography if I had not had access to the letters exchanged with Prandtl. I owe a specialwordofthankstotheVogelfamily,whogavemeaccesstoPrandtl’sprivate collectionofmanuscripts,notesandmemorandaleftbehindafterhisdeath.Florian Schmaltz gave me access to several chapters of the rough version of his unpub- lished monograph about the Aerodynamische Versuchsanstalt (Aerodynamics Research Institute), in which he shed much light on the institutional context of Prandtl’s working. I also owe him a special word of thanks for his critical com- ments on the preliminary version of this biography. I would like to thank Cordula Tollmien for providing access to the collection of material she assembled in the 1980s for her article on the history of the Kaiser-Wilhelm-Institut für Strömungs- forschung during the time of National Socialism,12 also for the information about herfather,thepupilofPrandtl,WalterTollmien.Last,butnotleast,Iwouldliketo express my thanks to my colleagues at the Deutsches Museum, especially Silke Berdux, Ulf Hashagen, Jürgen Teichmann, Helmuth Trischler and Stefan Wolff who, for many years now, have accompanied my research about Ludwig Prandtl. Munich, Germany Michael Eckert December 2015 12Tollmien(1998).