The Aeodynaics o

1 D-Ak 4 2 AGARD-AG-295 The Aeodynaics o3, -DADVSOR GRU FO-AROP CE REEAC & DEVLOPENSEPj 14 ii 01 AGARD-AG-295 NORTH ATLANTIC TREATY ORGANIZATIONADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT(ORGANISATION DU TRAITE DE L'ATLANTIQUE NORD)AGARD ograph AERODYNAMICS OF of EngineeringThe UniversityLeicester LEI 7 RHUnited KingdomEdited Gilbert RoadCambridge CB4 3 PDUnited KingdomThis AGARD ograph has been produced at the request of the Fluid Dynamics Panel of __ ,. l ..____ -~ ..__h -I1| I- " -"" X ..THE MISSION OF AGARDThe m:sion of AGARD is to bring together the leading personalities of the NATO nations in the fields of science andtechnology relating to aerospace for the following purpose,:-Exchanging of scientific and technical information;-Continuously stimulating advances in the aerospace sciences relevant to strengthening the common defence posture;-Improving the co-operation anmong member nations in aerospace research and development;-Providing scientific and technical advice and assistance to the Military Committee in the field of aerospace researchand development (with particular regard to its military application);-Rendering scientific and technical assistance, as requested, to other NATO bodies and to member nations inconnection with research and development problems in the aerospace field.

2 -Providing assistance to member nations for the purpose of increasing their scientific and technical potential;-Recommending effective ways for the member nations tu use their research and development capabilities for thecommon benefit of the NATO highest authority within AGARD is the National Delegates Board conststing of officially appointed seniorrepresentatives from each member nation. The mission of AGARD is carried out through the Panels which are composed ofexperts appointed by the National Delegates, the Consultant and Exchange Programme and the Aerospace ApplicationsStudies Programme. The results of AGARD work are reported to the member nations and the NATO Authorities throughthe AGARD series of publications of which this is in AGARD activities is by invitation only arid is normally limited to citizens of the NATO content of this publication has been reproduceddirectly from material supplied by AGARD or the July 1987-Copyright 0 AGARD 1987 All Rights Reserved.

3 , , ,,,. ISBN 92-835-0422-4ig __ I_Printed bySpecialised PriLinSer mited40 Chkiell Lane, Loughkon, Essex IGIO 3 ZiiiPREFACEIn the aftermath of the 1939-45 war, as a more scientific approach began to supplement cut-and-try as a basis for thedesign of parachutes, first established a iound aerodynamic foundation for his subject in his book, 'Parachutes'.R61es which were being fulfilled by the parachutes which he described in it were firstly man-carrying for both life-saving andmilitary applications; secondly weapon and store dropping; and thirdly deceleration of aircraft. Looking back over the 35years that have elapsed since this publication, although their form has been greatly expanded, all of these are still essentialtasks for parachutes to fulfil. However, additional ones also are now required. For example, crews of spacecraft as well asaircraft make encapsulated descents using parachutes as essential parts or their total escape systems and in addition to dragproduction contemporary parachutes may also need to demonstrate siaificant lift-producing abilities or the capability of"rotation at chosen spin rates during their descent.

4 Not ony have parachuf s been used on a number of occasions to assist re-entry into the earth's atmosphere, they have also been employed in landing issential instruments on to other planets as wellas on to the planet have also had to find their place within the much wider classification of aerodynamic decelerators, in which theyshare a primarily decelerative task with balloons and various metallic non-inflatable devices. In his glossary in 1951, Browndefined a parachute as an umbrella-shaped device to produce drag, commonly used to reduce the rate of descent of a fallingbody'. A more precise and limiting definition is now customary. Within this broader classification of aerodynamicdecelerators parachutes are now considered to be that class of drag-producing bodies whose essential characteristics includetheir flexibility, their inflated shape being dependent on the flow field which surrounds greater precision in definition epitomises changes taking place in many engineering fields, not only in that ofparachute aerodynamics.

5 With the availability in most design offices of powerful mainframe computers and in manysituations of relatively inexpensive mini- and micro-computers, new possibilities exist for engineers to establish the relevantbasic relationships and to develop their subsequent solutions. For these task to be performed adequately, basic principlesmust be appreciated and agreed sign conventions is to meet all these kinds of need that' The Aerodynamics of Parachutes' has been written. In the subject of parachuteaerodynamics this AGARD ograph is envisaged as a direct descendant of Brown's 'Parachutes', for it has the same emphasis,that of selecting 'the principal aerodynamic characteristics of parachutes and the various known factors which affect thesecharacteristics'. It takes into account not only many of the subsequent publications which have been summarised in the 1963and 1978 United States Air Force Parachute Design Guides, but also the proceedings of the American Institute ofAeronautics and Astronautics Aerodynamic Decelerator Copferences which have been held every two and a half years, theHelmut Decelerator Systems Engineering Short Courses which took place in 1983, 1985 and 1987 and'TheParachute Recovery System Design Manual', which will shortly be used by the United States Naval Weapons has been anticipated that its main readers will be recent engineering graduates entering research establishments,parachute companies or related industries.

6 In its preparation some appreciation on the part of the reader of basic mechanics,elementary fluid mechanics and the principles of computing has been from KarI-Friedrich Doherr and my own research associates, too many other individuals have contributed theircomponents, criticisms and suggestions for me to mention their names individually. I can only hope that they will recognisetheir invaluable contributions in the publication which has resulted from all of our CockrellLeicester- 1987Au lendemain de la guerre de 1939-45, aiors qu'un dimarche plus scientifique commenqait A completer les mithodesempiriques du genre "on dicoupe et on essaie" comme base de la conception des parachutes, fut ie premier Ailaborer une theorie arodynamique saine pour cc qui faisait I'objet de son livre 'Les parachutes". Les fonctions remplies parles matiriels qu'il y d&crivait itaient d'abord r'emport des hommes dans ie double but de la sauvegarde de la vie humainc ctdes applications militaires, en de"xAivme lieu le largage d'armes et d'approvisionnements, en troisiime et dernier lieu lad~ des avions i I'atterrissage.

7 Si on itudie Its 35 annies qui se sont icoulces depuis cette publication, tous cesemplois sont encore essentiellement ceux que ron attribue aux parachutes mime si leur aspect extirieur s'est beaucoupdiversifii. Neanmoins il en but maintenant quelques modles Par exemple, les 6quipages des deI'espace comme ceux des avions font des descentes enferme dans des capsales dquipies de parachutes qui constituent lapartie essentiele de l'ensemble de leur systime d'cvacuation; et en plus de [a production d'engins basis sur la train e, il pe ;aussi &ae demand6 aux parachutes modernes de posseder des qualitis de portance ou d'aptitude i tourner sur eux-mbnes iune vitesse donnde au cours de leer descente. Des parachutes ont eti utilisds non setlement en de nombreuses occasionspour faciliter la rentrde danrs 'atmosphere terrestre, mais aussi comme instruments essentiels d'atterrisage, qu'il s'ag, se de seposer sur notre globe ou sur d'autre a Egalement fallu leur trouver un crdneau dans la classe beaucoup plus vaste de ddcil-ratenrs airodynamiqucs ou ilsremplissent, concurrement avec les ballons et divers disposiifs metalfiqtjes non gonflabkls, unc tiche qui consistetMowessentiellenient A assurer un freinage.]

8 Dans son glossaire do 195 1, Brown a d~fini le parachute comme "un dispositif enformc dc parapluie, fournissant une trainie. utilis commniunment pour diminuer la vitesse de deacente d'un corps quitoinbe". La difinition courante actuelic eat plus prdcise et plus limitative. Au sein de la cattdgorie tri~s vaste des dt~cleirateursadrodynamiques, lea parachutes sont gindrateurs do trainee dont une des caractdristiques essenitielles est Ia souplea-sed'emploi, car une fois gonflis, lour fornme d~pend dc l'coulcrnent de r'air autour deux,Cotte meilleure pr~cision dana [a difinition risume bien l'volution qui *s't faite dana beaucoup de secteurs derindustric, et pas sculement dana l'aMrodynamiquc des parachutes. Grice A Ia pre~sence de puissants ordinateurs centrauxdans la plupart des bureaux dditude et, dana beaucoup dc caa. It Iutilisation de mini- et de micro-ordinateurs relativementpeut coOteux, lea ing~dniurs disposent de posaibilitds nouvelles pour Etablir lea foninules de base voulues et ddvellopper leasolutions qui en ddcoulent en vuc de la conception.]

9 Pour quc ces tiches puissent 6trc exdcutdes efficacement. il faut biencerner lea principes de base et appliquer lea conventions de symbolique pour satisfaire tous ces besoina que louvrage "Afrodynamique des parachutes" a &t6 6crit. Danas le domaine dontil port le titre, cet "AGARD ographe eat considdre comme Ia suite directe du livre "Les parachutes" de Brown, car il insistesur le maine themne: 'lea principales caractiristiques des parachutes et lea divers facteurs connus qui les affectent". 11 dientcompte, non seulement du grand nonibre de publications postdrieutes qui ont dti! redpertorides et rdsumdes dans lea "Guidesde conception des parachutes" de l'arniee de l'air anidricaine de 1963 h 1978, mais fgalcment des comptes rendus de dibatsdes confirences de l'Institut arndricain d'Adronautique et dAstronautique ("Amierican Institute of Aeronautics andlAstronautics") sur Ia d~ciltation adrodynamique qui se sont tenues tous les deux ana or demi, des coura techniques abrdgdsde Helmut sur la technique des systimes de dical~ration qu'il a doennis en 1983, 1985 et 1987.

10 Et du "Manuel deconception d'un projet de r~cupdration par parachute" qui sera prochainoment publiE par Ic Centre des arniements navalsamidricain ("US. Naval Weapons Center").On a prdvu que lea principaux lecteurs de cot ouvrage sertient lea inginieurs traichement dipl6mds qui sont sur leapoint d'entrer lea eitablissenients de recherche, lea sociE~t~s do fabrication de parachutes ou lea industries qui lour sontassociies. Pour priparer sa pr~sentation, on a supposE que Ie lecteur posseddait quelques connaissancea de mdcaniquefonedamentalle, des notion& Eldmentaires de mdcanique des fluides et des principes de l' dehors de Karl-Friedrich Doherr et de mes propres associes en mati&re de recherche, lea autres personnes qui ontapport6 la contribution de leura connaissances, de leurs critiques et de ]cuts suggestions sont trops nombreuses pour quc jepuisse lea citer toutes individuellement.