Design of a class i remotely piloted aircraft for maritime surveillance

AIR FORCE ACADEMY Design o a Class I Remo ely Pilo ed Ai c a o Ma i ime Su eillance Pe o mance, Ae odynamics and S abili y Vasco Hen ique Reis F anco ALFAL/ENGAER 138080-L Thesis o ob ain he Mas e o Science Deg ee in Mili a y and Ae onau ical Sciences - Ae onau ical Enginee ing Examina ion Commi ee Chai pe son: MGEN/ENGAER 076441-J Paulo Manuel Veloso Gonc¸al es Gue a Supe iso : MAJ/ENGAER 129905-A Lu´ ıs Filipe da Sil a F´ elix Co-Supe iso : CAP/ENGAER 131603-G Jo˜ ao V´ ı o Aguia Viei a Cae ano Membe o he Commi ee: Dou o F ede ico Jos´ e P a a Ren e Reis A onso Sin a, May 2018 “O igno an e a i ma, o s´ abio du ida, o sensa o e le e.” A is ´ o eles iii Dedicado ` a Inˆ es, am´ ılia e amigos. Ag adecimen os Gos a ia de ende ec¸a o os de g a id˜ ao a um conjun o de pessoas cuja in e enc¸ ˜ ao e aux´ ılio p es ado se e es i am da maio impo ˆ ancia na ealizac¸ ˜ ao do p esen e a- balho. P imei amen e, ao Majo , Engenhei o Ae on´ au ico, Lu´ ıs F´ elix e ao Capi ˜ ao, Engen- hei o Ae on´ au ico, Jo˜ ao Cae ano, ag adec¸o a p opos a do ema e o ien ac¸ ˜ ao p o i- denciada ao longo da ealizac¸ ˜ ao do abalho. A o ma cons an e e semp e p esen e como, desde o in´ ıcio, incen i a am e acompanha am a e oluc¸ ˜ ao do p ojec o, o e e- cendo eedback e suges ˜ oes pe inen es em odas as suas e apas, e elou-se ulc al pa a o cump imen o dos objec i os incialmen e p opos os. Di ijo um g ande ob igado e um o e ab ac¸o ao meu cama ada, aluno da espe- cialidade de Engenha ia Ae on´ au ica, Jo˜ ao Co eia, que me acompanhou ao longo do caminho, nomeadamen e na ase concep ual do p ojec o, na qual oi necess´ a ia uma o e coope ac¸ ˜ ao e uni˜ ao de es o c¸os de modo a le ´ a-lo a bom po o. Ao Tenen e, Engenhei o Ae on´ au ico, Rica do Ve ´ ıssimo, demons o a minha p o- unda g a id˜ ao pelo aux´ ılio p o idenciado em ma ´ e ia de mecˆ anica de luidos com- pu acional, a a ´ es da u ilizac¸ ˜ ao do p og ama come cial S a -CCM+. Apesa de n˜ ao es a , em momen o algum, ligado ao p esen e p ojec o e como al es e n˜ ao se da sua esponsabilidade, semp e demons ou uma p on id˜ ao e p edisposic¸ ˜ ao pa a aju- da emendas. Po e acul ado o seu p ´ op io abalho inal de mes ado Bes P ac- ice Guidelines in CFD Ex e nal Ae odynamics: Applied o Unmanned Ae ial Vehicles a C uise Condi ions e escla ecido mui as d´ u idas, equen emen e em ho as menos opo unas, ´ e me ecedo de oda a minha es ima e g a id˜ ao. Ag adec¸o amb´ em ao Tenen e, Engenhei o Ele o ´ ecnico, Diogo Sil a po ga an- i , mui as ezes o a do seu ho ´ a io de se ic¸o, a p on a u ilizac¸ ˜ ao de equipamen o in o m´ a ico indispens´ a el ` a consecuc¸ ˜ ao do p ojec o. Ao Majo , T´ ecnico de Manu enc¸ ˜ ao de Ma e ial A´ e eo, Au ´ elio San os, e ao Sa gen o- Ajudan e, Ope ado Rada is a de De ec¸ ˜ ao, Paulo Mendes, memb os do Cen o de In es igac¸ ˜ ao da Academia da Fo c¸a A´ e ea, ag adec¸o a disponibilidade demons ada pa a, em ´ a ias ocasi˜ oes, comigo euni em e deba e em o p ojec o. Sem os e e idos con ibu os, es e abalho n˜ ao e ia sido poss´ ı el. ii Resumo ´ E obje i o da p esen e disse ac¸ ˜ ao o p oje o de um e´ ıculo a´ e eo n˜ ao ipulado de classe I, pa a igilˆ ancia ma ´ ı ima, moni o izac¸ ˜ ao de poluic¸ ˜ ao a mos ´ e ica e apoio a miss˜ oes de busca e sal amen o. O seu desen ol imen o engloba a o alidade do p oje o concep ual e pa e do p elimina , com oco nas ´ a eas de ae odinˆ amica, es- abilidade de oo, design ex e io e desempenho em oo. Os equisi os de miss˜ ao baseiam-se nas especi icac¸ ˜ oes da Agˆ encia Eu opeia de Segu anc¸a Ma ´ ı ima. A abo dagem ao p oje o concep ual segue uma me odologia in ui i a a a ´ es da qual a ae ona e ´ e concebida passo a passo, de o ma i e a i a, u ilizando olhas de c´ alculo. Inicia-se com a elabo ac¸ ˜ ao e consequen e selecc¸ ˜ ao de ´ a ios poss´ ı eis con- cei os de e´ ıculos a´ e eos, baseados nos esul ados de uma p ´ e ia pesquisa de me - cado. Segue-se uma es ima i a inicial do peso m´ aximo ` a descolagem, dimensiona- men o da asa p incipal, uselagem, es abilizado ho izon al e e ical, e ca ac e izac¸ ˜ ao do sis ema p opulso . Ap´ os uma an´ alise e inada da dis ibuic¸ ˜ ao de peso, ´ e au e ida a es abilidade es ´ a ica e dinˆ amica da ae ona e, incluindo o dimensionamen o das su- pe ´ ıcies de con olo, e analisa-se o desempenho em oo da mesma. Es a abo dagem baseia-se em dados emp´ ı icos ecolhidos de ´ a ias on es bibliog ´ a icas e simulac¸ ˜ oes compu acionais e e uadas a a ´ es do p og ama XFLR5. Na ase p elimina , ´ e emp egue o p og ama S a -CCM+, e amen a de mecˆ anica de luidos compu acional, num es udo pa am´ e ico da geome ia da asa p incipal com is a ` a maximizac¸ ˜ ao da au onomia em oo. Adicionalmen e, ou os componen es s˜ ao analisados e o p oje o ´ e e inado. Como p odu o da disse ac¸ ˜ ao, ´ e ap esen ada uma ae ona e concep ual capaz de cump i os equisi os de miss˜ ao impos os. Do es udo pa am´ e ico conclui-se que os bene ´ ıcios ae odinˆ amicos n˜ ao compensam os p eju´ ızos es u u ais e de manu a u a. Pala as-cha e: Ve´ ıculo A´ e eo N˜ ao T ipulado, Vigilˆ ancia Ma ´ ı ima, P oje o Ae o- n´ au ico, Desempenho, Ae odinˆ amica, Mecˆ anica de Fluidos Compu acional. ix Lis o Figu es 1 Ai c a de elopmen p ocess. Adap ed om [12]. . . . . . . . . . . . . . 9 2 Bounda y laye de elopmen o e a la pla e. Adap ed om [20]. . . . . 15 3 Rep esen a ion o elemen al panels and ho seshoe o ices o a ypical wing plan o m in he Vo ex La ice Me hod. Adap ed om [31]. . . . . . 20 4 Examples o s uc u ed meshes: (a) non-uni o m ca esian, (b) body- i ed C, (c) mul i-block. Adap ed om [37]. . . . . . . . . . . . . . . . . . 29 5 Examples o uns uc u ed meshes: (a) iangula , (b) hexahed al, (c) hyb id. Adap ed om [37]. . . . . . . . . . . . . . . . . . . . . . . . . . . 30 6 Wing sys em con igu a ions. Adap ed om [2]. . . . . . . . . . . . . . . 32 7 (a) Pushe (adap ed om [4]) and (b) ac o (adap ed om [46]) a ange- men s...................................... 35 8 Examples o ail a angemen s. Adap ed om [2]. . . . . . . . . . . . . . 36 9 (a) MiniFalcon (adap ed om [48]), (b) Nasnas MK1 (adap ed om [47]), (c) AR5 (adap ed om[49]) and (d) An ex X03 (adap ed om [7]). . . . . 39 10 Ske ches o se e al ai c a concep s: (a) Con igu a ion 1, (b) Con igu- a ion 2, (c) Con igu a ion 3, (d) Con igu a ion 4, (e) Con igu a ion 5, ( ) Con igu a ion6................................. 41 11 AHPhie a chy. ................................ 44 12 Missionp o ile. ................................ 46 13 Maximum ake-o weigh s aspec a io. . . . . . . . . . . . . . . . . . 48 14 Rep esen a ion o a segmen o he design space and iden i ica ion o he design poin . Range, endu ance and glide a io lines a e no ep esen ed. 50 15 SG6042 ai oil. Adap ed om [58]. . . . . . . . . . . . . . . . . . . . . . 53 16 Schema ic o ailing-edge plain and slo ed laps. Adap ed om [10]. . . 56 17 Fuselage o al d ag s ineness a io. . . . . . . . . . . . . . . . . . . . . 59 18 NACA 0009 ai oi. Adap ed om [52]. . . . . . . . . . . . . . . . . . . . 61 19 Maximum ake-o weigh and espec i e subg oups. Uni s in kg. . . . . 66 20 Th us (a) and powe (b) equi ed s c uise eloci y. . . . . . . . . . . . 74 21 Climb a e (a) and sink a e (b) s c uise eloci y. . . . . . . . . . . . . . 74 22 (a) Take-o and (b) landing b eakdown schema ic. Adap ed om [11]. . 77 23 P ojec ed iew................................. 78 x ii 24 F on iew. .................................. 79 25 Top iew. ................................... 79 26 La e al-p ojec ed iew. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 27 De ail o he 2D mesh su ounding he SG6042 ai oil. . . . . . . . . . . 86 28 (a) Li coe icien s angle o a ack and (b) d ag coe icien s li coe - icien cu es o he expe imen al da a and bo h compu a ional simula- ions a Reynolds numbe s o 1×106and 5×105.............. 88 29 P essu e coe icien dis ibu ion o e he SG6042 ai oil wi h AoA=0◦and Re = 1 ×106. ................................. 88 30 Con igu a ions A (a) and B (b). C and D ha e he same plan o m shape bu di e en wis angles, ha d o no ice, hence no ep esen ed. Only hal spanisdisplayed. ............................ 92 31 (a) Li coe icien s angle o a ack and (b) d ag coe icien s li coe i- cien cu es o bo h S a -CCM+ and XFLR5 simula ions o con igu a ion A. Re = 1 ×106. ............................... 93 32 Rec angula (a) and ape ed (b) plan o ms o each panel o he e ical s abilize . Only hal span is ep esen ed. . . . . . . . . . . . . . . . . . . 96 x iii Lis o Tables 1 Design p oposal adap ed om EMSA and p o ided by he AFARC. . . . 4 2 Ma ke esea ch esul s. . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3 E alua ion o he gene a ed concep s acco ding o he AHP. . . . . . . . 45 4 Payload, a ionics and p opulsion sys em weigh s. . . . . . . . . . . . . 46 5 Fuelweigh ac ions.............................. 47 6 Maximum wing loading (N/m2) allowed o each ligh condi ion o e- qui emen .................................... 50 7 Wing loading (N/m2) and powe - o-weigh a io (W/N) o simila ai c a s. 51 8 Compa ison be ween wing loading and powe - o-weigh a io alues o he di e en app oaches employed. Uni s as in able 7. . . . . . . . . . . 51 9 Wing geome ic pa ame e s. Fo mulas aken om [10]. . . . . . . . . . 52 10 Pe o mance esul s o he op six bes ai oils. . . . . . . . . . . . . . . 54 11 Pe o mance cha ac e is ics o di e en ailing-edge de ices. . . . . . . 57 12 Pe o mance esul s o NACA ai oils conside ed o he ail design. . . . 60 13 UAV Engines’s AR741 speci ica ions. . . . . . . . . . . . . . . . . . . . . 64 14 S uc u al weigh de e mined by c ewd ai c a [10] and RPA [2] s a is ical app oaches. Uni s a e in kg. . . . . . . . . . . . . . . . . . . . . . . . . . 66 15 Longi udinal oscilla o y modes and hei espec i e na u al equencies, ωn, and damping ac o s, ξ. ......................... 72 16 La e al-di ec ional oscilla o y modes and hei espec i e na u al equen- cies, damping ac o s, ime cons an s, τ, and ime o double he ampli- ude, 2. .................................... 72 17 S all speed a di e en ligh condi ions. . . . . . . . . . . . . . . . . . . 73 18 Ra e o climb a di e en ligh condi ions. Fligh speed, V, and he a io o ligh and s all speed, V/Vs, a e ep esen ed o compa ison pu poses. 75 19 Glide a io and sink a e a di e en ligh condi ions. Fligh speed, V, and ligh and s all speed a io, V/Vs, a e ep esen ed o compa ison pu poses.................................... 75 20 Take-o dis ance unde di e en condi ions. All dis ances in me e s. . . 77 21 Landing dis ance unde di e en condi ions. All dis ances in me e s. . . 77 22 Summa y o he ai c a ’s main cha ac e is ics. . . . . . . . . . . . . . . 80 xix 23 Bes p ac ice guidelines conce ning he physics model. . . . . . . . . . 82 24 Compa ison be ween expe imen al and compu a ional esul s o Re = 5×105. De ia ion o he la e om he o me is exp essed as a pe cen - age.Anglesindeg ees. ........................... 87 25 Compa ison be ween expe imen al and compu a ional esul s o Re = 5×105. De ia ion o he la e om he o me is exp essed as a pe cen - age.Anglesindeg ees. ........................... 87 26 Wing con igu a ions subjec o CFD analysis. Twis angle in deg ees. . . 92 27 S a -CCM+ esul s o all ou wing con igu a ions a an angle o a ack o 4◦. ....................................... 94 28 Pe o mance o a ious wing a angemen s. . . . . . . . . . . . . . . . . 95 xx Lis o Abb e ia ions 2D Two-Dimensional 3D Th ee-Dimensional AFARC Ai Fo ce Academy Resea ch Cen e AHP Analy ic Hie a chy P ocess AIS Au oma ic Iden i ica ion Sys em AMSL Abo e Mean Sea Le el AoA Angle o A ack BSL Baseline CAD Compu e -Aided Design CFD Compu a ional Fluid Dynamics CG Cen e o G a i y CPU Cen al P ocessing Uni DDD Dull, Di y and Dange ous DNS Di ec Nume ical Simula ion DP Design P oposal EEZ Exclusi e Economic Zone EMSA Eu opean Ma i ime Sa e y Agency EO Elec o-Op ic EU Eu opean Union FDM Fini e Di e ence Me hod FEM Fini e Elemen Me hod FVM Fini e Volume Me hod GPS Global Posi ioning Sys em GR Glide Ra io IR In a ed ISR In elligence, Su eillance and Reconnaissance HP Ho sepowe LEBU La ge Eddy B eak-Up LES La ge Eddy Simula ion xxi LEVM Linea Eddy Viscosi y Models LLT Li ing Line Theo y LOS Line-o -Sigh LRN Low Reynolds Numbe LSB Lamina Sepa a ion Bubble MAV Mic o Ai Vehicle MSL Mean Sea Le el MTOW Maximum Take-O Weigh NATO No h A lan ic T ea y O ganiza ion NLEVM Non-Linea Eddy Viscosi y Models NP Neu al Poin OCH Onboa d Compu a ion Ha dwa e PAF Po uguese Ai Fo ce PBM Pa s-Based Meshing PM 3D Panel Me hod RANS Reynolds A e aged Na ie -S okes RBM Regions-Based Meshing RDI Resea ch, De elopmen and Inno a ion ROC Ra e o Climb RPA Remo ely Pilo ed Ai c a RPAS Remo ely Pilo ed Ai c a Sys ems RSTM Reynolds S ess T anspo Models SAR Sea ch and Rescue SIR Sink Ra e SR Syn he ic Ape u e Rada Sa Com Sa elli e Communica ions SCM Second Closu e Models SST Shea -S ess T anspo STOL Sho Take-O and Landing TS Tollmien-Schlich ing TSB T ansi ional Sepa a ion Bubble TVR Tu bulen Viscosi y Ra io xxii UA Unmanned Ai c a UAS Unmanned Ai c a Sys ems US Uni ed S a es VLM Vo ex La ice Me hod xxiii Lis o Symbols G eek Symbols αAngle o A ack α0LZe o-Li Angle o A ack αsS all Angle o A ack α im T im Angle o A ack βSideslip Angle δBounda y Laye Thickness δ Flap De lec ion Angle Dissipa ion o Tu bulen Ene gy ηpP opelle E iciency θWing Twis λTape Ra io ΛLE Leading Edge Sweep Angle Λ /c Maximum Thickness Line Sweep Angle µDynamic Viscosi y µ Rolling F ic ion Coe icien µ Dynamic Tu bulen Viscosi y νKinema ic (molecula ) iscosi y ξDamping Fac o ρDensi y τTime Cons an ωSpeci ic Tu bulence Ene gy Dissipa ion Ra e ωnNa u al F equency xx ehicle, g ound s a ion, da a links and emaining in e aces. Unmanned ai c a (UA) o emo ely pilo ed ai c a (RPA) e e s o he ai bo ne pla o m alone [2]. Fo consis ency, he nomencla u e employed h oughou he ex is RPAS and RPA. In i s 2017 ma ke p o ile and o ecas , Teal G oup Co po a ion es ima es ha RPAS p oduc ion will inc ease om cu en wo ldwide p oduc ion o 4.2 billion dolla s annu- ally o 10.3 billion dolla s by 2026. Addi ionally, mili a y RPAS esea ch spending is p edic ed o con empla e 26 billion dolla s o e he same pe iod, making his he mos dynamic g ow h sec o o he wo ld ae ospace indus y [3]. Such me eo ic ise o unmanned a ia ion is closely associa ed wi h he ad an ages i o e s in pe o ming ce ain asks and missions when compa ed o manned ai c a , pa icula ly he ones ca ego ized as dull,di y and dange ous (DDD). The i s a e cha ac e ized by long ligh pe iods wi h li le s imula ion, p omo ing loss o human con- cen a ion and, he e o e, mission e ec i eness. Tasks pe o med in nuclea , chemi- cal, biological o adiological con amina ed a eas, haza dous o he human body, a e conside ed di y. Missions conduc ed o e hos ile e i o ies o unde h ea ening con- di ions, placing human li es unde ha m’s way, a e ypically de ined as dange ous. Fu he mo e, co e missions, whe e i is o i al impo ance no o ale a pa icula en i y o one’s p esence, esea ch endea ou s, whe e minimizing cos s and haza ds is pa amoun and en i onmen ally c i ical asks, whe e low le els o emission and noise a e desi able, add o he lis o missions, o mili a y and ci il na u e, whe e employmen o RPAS p o ides nume ous bene i s o e hei manned coun e pa s. A lis which is comple ed wi h he economic a gumen since om design and p oduc ion o ope a ion and main enance, he cos s associa ed wi h RPAS a e usually lowe [4]. Ha ing p o en hei alue in bo h mili a y and ci il con ex s o e coun less si ua- ions, RPAS a e a mus in any c edible a med o ce. As such, he Po uguese Ai Fo ce (PAF), in he con ex o accomplishing s ic ly mili a y na ional missions, o he missions o public in e es and in e na ional commi men s as a membe o he No h A lan ic T ea y O ganiza ion (NATO) and he Eu opean Union (EU), ecognizes he bene ical impac s o inse ing hese sys ems in i s ope a ional appa a us [5]. The con ex o In elligence, Su eillance and Reconnaissance (ISR) ope a ions, undamen al o he pe o mance o any mili a ized o ce and pa excellence he ap- plica ion con ex o RPAS, may be conside ed a key ope a ional domain, in which he 2 es ablishmen o a na ional RPAS capaci y may p o ide signi ican ope a ional bene i s by enhancing he lexibili y o he cu en appa a us [6]. Conside ing he dimension and con ex o he PAF, wo di e en , ye complemen a y, app oaches o he inco po a ion o RPAS a e sugges ed: one is h ough esea ch, de elopmen and inno a ion (RDI) p og ams, he o he ia acquisi ion o comple e, p o en sys ems [5]. RDI in he ield o unmanned a ia ion is conduc ed a he Ai Fo ce Academy Re- sea ch Cen e (AFARC). Since 1996 se e al p ojec s ha e been di ec ed, con ibu ing o he de elopmen o RPAS echnology and c ea ion o sys ems capable o demon- s a ing such echnology [7]. In 2009, he PITVANT p ojec spu ed he execu ion o ope a ional and echnological ac i i ies. In he wake o i s success, he AFARC be- gan pa icipa ing in se e al o he RPAS ela ed p ojec s supo ed by ex e nal inancing sou ces, namely he PERSEUS and SUNNY p ojec s, in he con ex o ma i ime su eil- lance, and he SEAGULL p ojec , in he domain o ma i ime si ua ional awa eness. By 2012, a ious class I pla o ms (maximum ake-o weigh , MTOW, unde 150 kg) had been designed, p oduced and es ed, exceeding a o al o 250 cumula i e ligh hou s [8]. 1.2 Mo i a ion Wi h an Exclusi e Economic Zone (EEZ) o 1.656.181 km2, e i o ial sea o 50.960 km2 and inland wa e s comp ising 13.419 km2, Po ugal possesses a as ma i ime a ea, a ound 18.7 imes he na ional land e i o y, o e which so e eign y and ju isdic ion a e exe cised. In addi ion, es ablished by in e na ional commi men s, a Sea ch And Rescue (SAR) ma i ime a ea o 5.792.740 km2, oughly 63 imes he na ional e i o y a ea, is assigned o he Po uguese Republic. The s a egic impo ance o he wide e i o ial wa e s is ein o ced by he ac ha 60% o all po uguese in e na ional ade, 70% o na ional impo s and 53% o he EU in e na ional ade lows h ough hem. A b oad lis o h ea s o he ma i ime en i onmen jeopa dize he exe cise o na ional so e eign y, ha ing nega i e impac s on global and na ional s abili y, he mos ele an being e o ism, pi acy, p oli e a ion o weapons, na co a ic, human a icking, illegal immig a ion, deg ada ion o ma i ime esou ces and sea pollu ion [9]. I is, he e o e, no su p ise ha mos o he RDI p ojec s in which he AFARC is in ol ed a e ela ed wi h he ma i ime en i onmen and ha e he common objec i e o 3 ope a ionalizing RPAS echnology, keeping in mind i s in eg a ion wi h he ope a ional appa a us o he Ai Fo ce esponsible o ma i ime su eillance and SAR missions [8]. Conside ing he AFARC need o pu sue his line o in es iga ion and es ing o pla - o ms and echnology wi h possible applicabili y in ope a ional con ex s, a design p o- posal o a class I ehicle has been issued, mo i a ing he p esen disse a ion. Mis- sion and pe o mance equi emen s a e se in o de o comply wi h a call om he Eu opean Ma i ime Sa e y Agency (EMSA) o an RPA capable o pe o ming ma i ime su eillance, SAR and pollu ion moni o ing. Table 1: Design p oposal adap ed om EMSA and p o ided by he AFARC. Ope a ional Requi emen Desc ip ion Obse a ions MTOW <150 kg Full se o senso s. Endu ance 8 hou s Longe endu ance abo e 8 hou s is a key ad an age o he sys em Range 300 km Fligh ceiling 15 000 Abo e mean sea le el Take-o and landing Con en ional G a el/Non-p epa ed Take-o dis ance 150 m G ound oll and o a ion Landing dis ance 150 m F ee- oll and b aking Maximum ake-o al i ude 10 000 Abo e mean sea le el C uise speed 90 k s Full se o senso s Maximum speed 120 k s Maximum s all speed 55 k s C uise con igu a ion Maximum s all speed 45 k s Landing con igu a ion Minimum glide a io 10 Minimum climb a e 750 /min A MTOW Engine ype In e nal combus ion Fuel injec ed Syn he ic ape u e ada Ai pollu ion moni o Payload AIS ecei e Dis ess senso Pilo Cam Gimble EO, IR and lase Au opilo T ansponde Sa elli e communica ions A ionics Powe supply Onboa d compu a ion Se o-ac ua o s Da alink 4 1.3 Objec i es The pu pose o he cu en disse a ion is o design a class I RPA, wi h special incidence on ae odynamics, s abili y, ex e io design and ligh pe o mance, capable o mee ing he a o emen ioned equi emen s and being manu ac u ed wi h he a ailable esou ces a he AFARC. Due o empo al cons ain s and a ailable esou ces, a ully de ailed and comple e design is no a ainable in he scope o he cu en academic endea ou . As such, he main objec i e is o pe o m concep ual design in i s en i e y and ini ia e p elimina y design. The au ho cla i ies he objec i e by di iding i in o se e al goals: •S a e-o - he-A : –Re iew o undamen al concep s conce ning he design p ocess, ligh pe - o mance, ae odynamics and he compu a ional app oach o design; –Assessmen o con empo a y RPA design bes p ac ices and ma ke e- sea ch; •Concep ual Design: –RPA concep gene a ion, selec ion and ini ial sizing; –De e mina ion o he concep ual ai c a ’s cha ac e is ics wi h special em- phasis on ae odynamics, s abili y and pe o mance; •P elimina y Design: –Es ablishmen o a compu a ional luid dynamics (CFD) me hodology appli- cable o he cu en design; –Pa ame ic s udy o he main wing o maximum endu ance by means o he e e ed CFD model; 5 1.4 Me hod The design p ocess ough o s a wi h a e iew o he cu en s a e-o - he-a ai c a con igu a ions o he pa icula se o equi emen s ha ha e o be me . This includes unde s anding he indus y bes p ac ices and aking a look a he ae ospace ma ke in o de o iden i y exis ing ai c a ha possess pe o mance and ope a ional cha ac- e is ics similia o he ones desi ed, gi ing he in en o g ea e insigh in o he speci ic challenge. Due o i s emb yonic na u e, concep ual design makes use o his o ical ends and empi ical da a, based on ai c a simila i y, o es ima e ce ain design pa ame e s. A wide eposi o y o li e a y wo ks on his subjec is a ailable. Some o he mos no o ious in academia a e he wo ks by Thomas Co ke [10] and Daniel Rayme [11]. Speci ically w i en o RPA design a e he ex s by au ho s Jay Gundlach [2] and Reg Aus in [4]. I is he au ho ’s decision o ollow Co ke’s sp eadshee app oach o concep ual design, complemen ed wi h in o ma ion om Rayme and Gundlach’s ex s, in o de o augmen i s eliabili y. Supplemen ing he e e ed me hod, XFLR5 6.33 low analysis a e conduc ed in o de o p o ide addi ional esul s and he e o e enhance he ini ial sp eadshee es- ima es, pa icula ly in he ields o ae odynamics and s abili y, he main ocus o he cu en ex . XFLR5 is a compu a ional ool, based on XFOIL, Li ing Line Theo y (LLT), Vo ex La ice Me hod (VLM) and Panel Me hod (PM), ha is equen ly used in he ae ospace communi y as an auxilia y design ool. I p o ides as calcula ions wi h a ine balance be ween p ecision and compu a ional equi emen s [29]. As he design ma u es and en e s he p elimina y phase, a mo e compu a ionally demanding, complex and eliable ool, such as S a -CCM+ .8.04, is used. This CFD so wa e is an ex emely powe ul design ins umen , able o supply he designe wi h de ailed cha ac e iza ion o he low o e he ai c a ’s componen s, cap u ing he as majo i y o low phenomena [28]. I assumes pa icula ele ance when e ining and de ailing he RPA design. 6 1.5 Layou The p esen disse a ion is s uc u ed in he ollowing way: chap e 1 comp ises an his o ical and si ua ional backg ound o RPAS, ollowed by a mo i a ion o he p ojec unde de elopmen , inden i ica ion o i s objec i es, a b ie desc ip ion o he me hods used in achie ing he la e and an ou line o he ull documen . Chap e 2 ad esses a se o undamen al concep s ega ding he design p ocess, ligh pe o mance and ae odynamics, ollowed by a de ailed discussion on he heo- e ical basis o he compu a ional app oach, i s po en iali ies and limi a ions. I also desc ibes he s a e-o - he-a o RPA design, culmina ing in a ma ke esea ch epo . In chap e 3 an ex ensi e deba e o e concep ual design is pe o med, om he ea ly concep gene a ion p ocess o he inal ligh pe o mance calcula ion. The line o hough in building up he ai plane is p ope ly explained as well as he employmen o sp eadshee s and complemen ing XFLR5 simula ions. P elimina y design is ini ia ed in chap e 4 as CFD ools en e he design en i on- men . Es ablishmen o a obus , applicable CFD me hodology is conduc ed, in acco - dance wi h he communi y bes p ac ices. Once de ined, he CFD model is used in a pa ame ic s udy o he main wing o maximum endu ance. A gene al o e iew o he p ojec is done in chap e 5, as well as an a ay o pe - inen conclusions. Finishing he disse a ion, ecommenda ions o u u e wo ks and u he de elopmen s necessa y o accomplish he ul ima e goal o p oducing a class I RPA a e d awn. 7 2 Fundamen al Concep s & S a e-o - he-A 2.1 The Design P ocess 2.1.1 Design Me hod Design is de ined as “ he p ocess o planning he physical cha ac e is ics and cons uc- ion me hods o a p oduc ” [12]. In he p ocess o in en ing a p oduc , design is he mos impo an phase, whe e he indi idual esponsible o i – he designe – a emp s o mee a se o es ablished equi emen s while making he bes use o esou ces and p ojec ing an e icien cons uc ion p ocess. Based on he scien i ic me hod, he design p ocess can be in e p e ed as a g oup o i e s eps, s a ing om he p oblem de ini ion, ollowed by da a collec ion, c ea ion o design concep s, analysis o hei pe o mance and, ul ima ely, decision making which is based on he esul s ob ained. This is a highly i e a i e p ocedu e since he esul s will o en ail o mee he objec i es, o cing he designe o e u n o he ini ial s eps and pe o m sui able changes. Re inemen is also a sou ce o i e a ion and is pe o med in o de o make he bes possible design, i.e., one ha is op imized o i s ull po en ial and enables he c ea ion o a ue supe io p oduc . I is equen , howe e , o de e mine ha one o he o iginal equi emen s is un easonable o wo o hem con lic wi h each o he . In his si ua ion, a ede ini ion o he cus ome ’s demands is conduc ed [12]. Acco ding o Nicolai [13], he design p ocess equi es h ee main ac ions: syn hesis, analysis and decision making. The i s is cha ac e ized by a ela i ely uns uc u ed, o en in ui i e c ea i e hinking whils he emaining wo a e ma ked by hei highly s uc u ed and me hodical hinking. In o de o succeed, designe s mus mas e bo h ypes o hough p ocesses which is a challenging ask due o hei sha p dissimila i y. 2.1.2 Ai c a Design An ai c a design is ini ia ed because cus ome s such as ai lines, co po a ions, p i a e pilo s, go e nmen agencies o mili a y se ices, ha e needs. These a e usually spec- i ied as one o mo e design missions ha he ai c a mus be able o accomplish and a se o cons ain s o pe o mance equi emen s ha ha e o be me and a e o mally 8 desc ibed in a design p oposal (DP). The mos impo an equi emen s o mee – de- sign d i e s – ha e he s onges in luence on he con igu a ion and cha ac e is ics o he ai c a and mus be clea ly iden i ied [12]. The p ocess is b oken in o h ee majo phases: concep ual, p elimina y and de ailed design. Figu e 1: Ai c a de elopmen p ocess. Adap ed om [12]. Concep ual design answe s he basic ques ions o con igu a ion a angemen , size, weigh and pe o mance. I in ol es es ima ion o weigh s, choice o ae odynamic cha - ac e is ics ha bes sui he mission speci ica ions, o al d ag p edic ions, powe plan sizing, de e mina ion o he bes ai ame o accommoda e he payload and main com- ponen s, loca ion o p inciple weigh g oups, es ima es o s a ic s abili y beha iou , siz- ing o con ol su aces and p edic ions o ligh pe o mance [10]. All his is done in a e y luid p ocess whe e new ideas and p oblems a e cons an ly eme ging as he de- sign ma u es and is u he in es iga ed in inc easing de ail [11]. Con inuous i e a ion compels he designe o keep a keen eye on he in luence o mino changes on he gene al pic u e and keep he design upda ed. Once a concep ual ai c a , capable o ul illing he mission equi emen s, is designed, one may mo e on o nex phase. When he majo changes a e o e , p elimina y design begins. In his phase, mi- no e isions may happen bu he con igu a ion a angemen is expec ed o be ixed and emain cons an . Specialis s in a eas such as ae odynamics, p opulsion, s uc- 9 u es and s abili y and con ol will design, analyse and es speci ic componen s o he ai plane [11]. A ine uning o he concep ual design is made h ough compu a ional simula ions and wind unnel es s ha allow o he p edic ion o in ica e aspec s such as he s uc u al and ae odynamic in e ac ion be ween he wing, uselage and ail su - aces. A mo e de ailed analysis o ae odynamic loads and componen weigh s is also pe o med, leading o a e inemen in he s uc u al design [10]. A he comple ion o his phase, he design is ozen and a comp ehensi e de ini ion o he comple e sys em wi h i s in e aces is elabo a ed. The de ailed design phase comp ises he design o he ac ual pieces o be ab i- ca ed and a plan o he ai plane manu ac u ing p ocess, s a ing wi h he smalles and simples subassemblies and building up o he inal assembly. Compu e -aided design (CAD) ools a e ex emely use ul a p o iding ealis ic h ee-dimensional (3D) iews o he in e io layou . A his poin , es ing e o in ensi ies as majo i ems and s uc u al componen s a e buil and es ed. A de ailed s uc u al design o he ai c a , con aining e e y de ail needed o i s cons uc ion, is he inal ou pu o his phase [10], [11]. Typically, a e conclusion o de ailed design, a p o o ype is p oduced and ligh es - ing ini ia es [10]. The need o subsequen modi ica ions may a ise due o laws iden- i ied du ing his pe iod. Once es ing is success ully accomplished and ai wo hiness and ce i ica ion issues a e deal wi h, he ai c a en e s ope a ion. While in se ice, se e al imp o emen s migh be conduc ed, leading o new e sions o he p oduc . All changes pe o med since he ini ial manu ac u e a e conside ed pa o he design p ocess [4]. An ai plane design b ings di e en a eas o ae ospace enginee ing oge he , such as ae odynamics, p opulsion, s uc u al mechanics, s abili y and con ol. Each o hese a eas is pa amoun and in ol es pa ame e s ha go e n he size, shape, weigh and pe o mance o he ai c a . Ideally, a designe seeks o op imize all hese aspec s, howe e , such is p ac ically impossible since op imizing one cha ac e is ic usually de- g ades o he s. Fo his eason, comp omise is o en he na u e o ai c a design, i.e., ob aining a balance be ween he di e en aspec s o he o al pe o mance while a - emp ing o op imize one o mo e, based on clea ly iden i ied mission equi emen s, is he objec i e [10]. Gene ally, he pa ame e which exe s he bigges in luence on he design o a RPA 10 is he payload. I s size, mass and elec ical powe equi emen s a e c ucial in de e - mining he layou , dimensions and MTOW o he ai c a . O he pa ame e s can be jus as impo an as he payload, namely endu ance, ange, speed ange and launch and eco e y speci ica ions [4]. 2.1.3 Concep ual Design App oach The i s ask o he designe is o ead and ully comp ehend he design p oposal. This implies unde s anding h ee dis inc ideas: he mo i a ion o he design, i.e., he ai c a ’s pu pose o mission, he echnology eadiness o new echnology o inco - po a ion in o he design, and he speci ic se o design equi emen s ha comp ises pe o mance pa ame e s (e.g., ange, ake-o and landing dis ances and speed e- qui emen s), bu also a as se o ci il o mili a y design speci ica ions which mus be me (e.g., s all speed and s uc u al design limi s) [10], [11]. Concep ual design usually s a s wi h a ious concep ual ske chs o di e en con ig- u a ions. Such d awings include he app oxima e wing and ail geome ies, he uselage shape and he loca ions o majo componen s such as engines, payload compa men , landing gea and uel anks. They a e used o p edic ae odynamics and weigh ac- ions by compa ison o his o ical da a and, in u n, p oduce ini ial es ima es o he equi ed o al and uel weigh . This i s -o de sizing is complemen ed by ac ual ae o- dynamics, weigh s, p opulsion and s abili y in o ma ion, leading o a de ailed sizing calcula ion. The pe o mance capabili ies o he design a e calcula ed and compa ed o he equi emen s. Re inemen ollows in o de o ob ain be e es ima es o di e - en pa ame e s which lead o e isions in a ious a eas o design. The e ined esul s equen ly demand changes in he design layou . A e some i e a ions, he e ised concep ual ai c a is expec ed o mee he ull equi emen s and con iden ly ansi o he p elimina y design phase [11]. Co ke [10] sugges s an in ui i e and me hodic app oach o he p ocess o concep- ual design which consis s in b eaking i down in o 14 s eps and de eloping i in a s ep-by-s ep ashion. This s a egy ocus on he implemen a ion o sp eadshee s o i - e a i e and epe i i e calcula ions. Using hese, he e ec o di e en inpu pa ame e s may be easily in es iga ed and op imums can be sough . Re e ence ai c a a e used in o de o check a ious design elemen s and de e mine i hey de ia e oo a om 11 len skin- ic ion and delaying ansi ion in o de o ex end he lamina po ion o he low. Thei desc ip ion is ou side he scope o he p esen ex , howe e , he au ho poin s ou he wide use o de ices like ible s and la ge eddy b eak-up de ices (LEBUs) in he educ ion o u bulen skin- ic ion. Shaping he ai oil and educing su ace oughness a e he mos simple measu es employed in lamina low con ol [23]. As equa ion 6 sugges s, inc easing bo h Oswald e iciency ac o and aspec a io leads o a educ ion in induced d ag. Aspec a io canno be excessi ely inc eased as i leads o s uc u al and weigh penal ies. Hence, a comp omise be ween ae o- dynamic and s uc u al pe o mance mus be es ablished [23]. The Oswald e iciency ac o accoun s o he de ia ion o he ac ual li dis ibu ion om he ideal ellip ic one, he e o e, he key concep is o app oxima e he li dis ibu ion o ha o an ellip ic. This is ypically accomplished by ape ing o wis ing he wing [11]. An al e na i e and widely employed echnique o educing induced d ag is he de- elopmen o wing- ip de ices such as endpla es and wingle s. This solu ion ocuses on educing he e ec s o wing- ip o ices, which a e he main sou ce o induced d ag [23]. 2.3 XFLR5 Due o hei semi-empi ical na u e, concep ual design es ima es, pa icula ly in he ields o ae odynamics and s abili y, may bene i om being complemen ed wi h in o - ma ion ob ained om compu a ional analyses pe o med by simple nume ical ools wi h easonable eliabili y. XFLR5 p esen s i sel as one o such ools, o e ing he possibil- i y o conduc ing ae odynamic and s abili y s udies o simple 2D and 3D geome ies a subsonic condi ions wi h an adequa e ade-o be ween accu acy and compu a ional and empo al e o s. Al hough limi ed in scope, i is widely employed h oughou he ae ospace communi y as an auxilia y design ool [28], [29]. The XFOIL code is he ounda ion o XFLR5 2D analyses whe eas i s 3D simula ions a e based on LLT, VLM and PM. In he con ex o he p esen wo k, due o so wa e cons ain s and s anda diza ion o all li ing su aces analyses, i is he au ho ’s decision o pe o m only VLM simula ions. 18 2.3.1 XFOIL Ini ially w i en by Ma k D ela in 1986, XFOIL has since hen unde gone se e al up- g ades and enhancemen s, gi ing i he s a us o a mode n, in e ac i e p og am o he design and analysis o subsonic isola ed ai oils [29]. I s heo e ical model is mainly cha ac e ized by an in iscid linea - o ici y s eam unc ion o mula ion which inco po- a es iscous displacemen e ec s, he e o e coupling in iscid and iscous low. The ai oil ou line and wake ajec o y a e disc e ized in o la panels. Knowledge o he geome y o he p oblem, i.e., o all ai oil and wake panel nodes, oge he wi h he imposi ion o a cons an alue o he s eam unc ion a any ai oil node and a Ku a condi ion a he ai oil ailing edge, yields a linea sys em o equa ions o all node alues. Speci ying an angle o a ack (AoA) p o ides an in iscid solu ion. The iscous o mula ion employs di e en se s o bounda y laye go e ning equa- ions, depending on whe he he low egime is lamina o u bulen . These equa ions a e disc e ized using wo-poin cen al di e ences wi h hei undamen al a iables de- ined o be loca ed a he panel nodes. By coupling he esul ing sys em o equa ions wi h he in iscid o mula ion, a iscous solu ion is ob ained. The iscous/in iscid solu ion scheme is a dis inguishing ea u e o he XFOIL me hod, allowing he solu ion algo i hm o p ope ly handle he e y s ong and nonlinea cou- pling be ween he iscous, ansi ion and in iscid o mula ions ha a e excep ionally impo an a ansi ional sepa a ion bubbles, cap u ing he complex physics o such phenomena. The abili y o ep esen all impo an physical mechanisms ha a ec ai - oil pe o mance ( iz., ins abili y, sepa a ion, bubble losses) while demanding modes compu a ional equi emen s, a es s he ele ance o he p esen compu a ional model o ini ial concep ual ai c a design [30]. Be o e mo ing on o he VLM, a ema k on ansi ion c i e ia is in o de . XFLR5 uses he eNme hod o p edic bounda y laye ansi ion. Based on linea s abili y heo y, i is ega ded as a eliable me hod o he p edic ion o lamina o u bulen ansi ion o wo-dimensional lows, wi h ele an applica ion in he s udy and design o ai oils [33]. A ange o N alues de ines he ansi ion egion. Da a ob ained om la pla e expe imen s se s his ange as 7.8-10 [33]. In he speci ic case o lows o e ai oils, he ansi ion egion is in p ac ice a ansi ion poin de ined by an ampli ica ion ac o o 9, acco ding o expe imen al da a [34]. In ac , he alue N= 9 is conside ed uni e sally 19 alid o ai oil applica ions [33]. 2.3.2 Vo ex La ice Me hod The VLM is a nume ical me hod widely employed in he s udy o 3D li ing geome ies. I s o mula ion is based on he heo e ical model o a sys em o o ices ha impa he su ounding ai a mo ion simila o he ac ual low o e a wing and sus ain a o ce equi alen o he wing li known o be gene a ed. Such sys em – o ex ing – is di ided in o h ee main pa s: he s a ing o ex, he ailing o ex sys em and he bound o ex sys em. The s a ing o ex, howe e , soon alls behind and he pai o ailing o ices s e ches e ec i ely o in ini y as s eady ligh p oceeds, esul ing in a ho seshoe o ex, a h ee-sided o ex made up by he bound and ailing o ices [26]. The wing is ep esen ed as a su ace disc e ized in a ini e numbe o apezoidal panels. By associa ing a ho seshoe o ex o each panel, a g id o ho seshoe o - ices is supe imposed on he wing, app oxima ing he con inuous dis ibu ion o bound o ici y o e i s su ace. This si ua ion is illus a ed in igu e 3. Figu e 3: Rep esen a ion o elemen al panels and ho seshoe o ices o a ypical wing plan o m in he Vo ex La ice Me hod. Adap ed om [31]. The eloci y induced by a o ex ilamen a a con ol poin o a gi en panel is gi en 20 by he law o Bio and Sa a . Fo a ho seshoe o ex, he e ec o each segmen is calcula ed sepa a ely and added o he emainde . The o al induced eloci y a he e e ed poin is ob ained by conside ing he e ec o all o ices supe imposed on he wing. A sys em o linea equa ions, one o each panel, is hus c ea ed. Knowledge o he wing geome y, combined wi h he bounda y condi ion ha he low is angen o he wing a any poin , p o ides a solu ion o he linea sys em o equa ions, yielding he induced eloci ies a each con ol poin . Consequen ly, he p essu e di e encial be ween he uppe and lowe wing su aces is de e mined. When in eg a ed, i yields he o al o ces and momen s ac ing upon he wing [31]. An al e na i e o mula ion o he VLM, p esen in XFLR5 6.33, is one whe e he o ex sys em is modeled as a o ex ing ins ead o a ho seshoe o ex. In his si u- a ion, a g id o ing o ices is supe imposed on he wing and he induced eloci y a a con ol poin depends on he con ibu ions o all ou segmen s, i.e., bound o ex, ailing o ices and s a ing o ex. The emainde o he o mula ion is iden ical [32]. The o ex la ice me hod o e s he abili y o e alua e a as ange o li ing su ace geome ies, including wings wi h sweep, dihed al and low aspec a ios. Con igu a ions wi h mul iple su aces can be analysed simul aneously, ully cap u ing all in e ac ions such as he downwash e ec o he main wing on he a ail. In addi ion, VLM is able o p edic no jus li and d ag dis ibu ions bu also ae odynamic de i a i es o i al impo ance o s abili y and con ol analysis, making i a sui able me hod o concep ual design so wa e implemen a ion [2]. 2.4 Compu a ional Fluid Dynamics P ope unde s anding o ae odynamic phenomena is manda o y when aiming a c ed- ible and success ul ai c a designs. The go e ning luid dynamics equa ions ha cha ac e ize such phenomena a e app oached in h ee di e en , ye complemen a y, ways: heo y, expe imen and compu a ional luid dynamics. By 1995, due o ad ances in s o age and speed capaci y o mode n digi al compu e s, CFD h ee-dimensional low ield solu ions we e al eady plen i ul and becoming inc easingly p e alen in he ae ospace indus y, pe o ming a s ong ole as ai c a design ools [35]. The u n o he cen u y consolida ed his idea, making CFD he indus ial s anda d ool o sol - ing luid low enginee ing p oblems and he e o e cons i u ing a eliable ins umen o 21 ai c a design and ae odynamic analysis [36]. The ollowing discussion on CFD in ends o highligh basic concep s and summa ize he cu en ae ospace communi y bes p ac ices o ex e nal ae odynamics applica- ions, adop ed in he S a -CCM+ analysis conduc ed du ing p elimina y design. In he con ex o he p esen disse a ion, CFD is me ely used as a design ool and does no ep esen i s co e subjec . The e o e, an ex ensi e e iew o i s concep s and s a e-o - he-a is no in he scope o his wo k. The au ho ’s pu pose is simply o p o ide insigh in o wha is done and why i is done in such way ega ding he p elimina y design CFD analysis. 2.4.1 App oxima ion Models CFD ans o ms a physical con inuum and i s in eg al/di e en ial go e ning luid dy- namics equa ions in o a disc e ized compu a ional domain go e ned by a sys em o algeb aic equa ions. Th ee me hods exis o engage he e e ed disc e iza ion: he Fi- ni e Di e ence Me hod (FDM), Fini e Elemen Me hod (FEM) and Fini e Volume Me hod (FVM). The i s , despi e i s adi ional and e e en ial aspec s, is limi ed in scope o s uc u ed g ids. The second, highly dominan in he wo ld o s uc u al mechanics, is seldomly employed in CFD. The hi d, FVM, is by a he mos widely applied me hod in CFD (including he analysis so wa e S a -CCM+). Cha ac e ized by i s gene ali y, concep ual simplici y and ela i e ease o applica ion o bo h s uc u ed and uns uc- u ed g ids, i is sus ained by a la ge ex en o li e a y wo ks [37]. Hence, he ollowing discussion is de o ed o he Fini e Volume Me hod. The basic equa ions o luid mechanics, known as he sys em o Na ie -S okes equa ions, exp ess he conse a ion o he undamen al quan i ies – mass, momen um and ene gy – h ough a sys em o i e ully coupled ime-dependen pa ial di e en ial and nonlinea equa ions ha a e inhe en ly and in ica ely complex. A consequence o he nonlinea i y o he low equa ions is he appea ance o u bulence, a spon a- neous ins abili y o he low, esponsible o he s a is ical beha iou o all low quan- i ies. These can be in e p e ed as luc ua ions supe imposed on mean o a e aged alues ha can o en a ain 10% o he o me , al hough low egions such as sepa a- ion zones may achie e conside ably highe le els o u bulen luc ua ions. Due o hei s a is ical na u e, u bulen lows canno be desc ibed in a de e minis ic 22 way. None heless, he u bulen luc ua ions can be compu ed nume ically, allowing a nume ical desc ip ion o u bulen lows by he di ec nume ical simula ion (DNS) ap- p oach. I s objec i e is o simula e on compu e he whole ange o u bulen s a is ical luc ua ions a all ele an physical scales. Clea ly, such is a o midable ask, demad- ing ex emely high pe o mance o compu e esou ces which is ou o each, in he o eseeable u u e, o indus ial applica ions, a leas in accep able compu e cen al p ocessing uni (CPU) imes. The enginee ing solu ion o his p oblem is he employmen o app oxima ion mod- els ha educe he complexi y o u bulen lows, ye s ill accoun o i s e ec s. Two amilies o models a e p esen ly a ailable. The i s – La ge Eddy Simula ion (LES) – is he highes app oxima ion, compu ing di ec ly he u bulen luc ua ions in space and ime (simila o DNS). Howe e , his is only accomplished abo e a ce ain leng h scale, named he subg id scale, below which u bulence is modeled by semi-empi ical laws. The second highes app oxima ion model – Reynolds A e aged Na ie -S okes (RANS) – is cu en ly he mos widely applied in he CFD communi y and he ocus o he cu - en discussion. In his app oach, u bulence is a e aged ou , in ime, o e he en i e spec um o u bulen luc ua ions, equi ing empi ical o semi-empi ical in o ma ion on he u bulence s uc u e and i s ela ion o he a e aged low [37]. Any a iable can be w i en as he sum o a ime-a e aged alue (s eady lows) o an ensemble-a e aged alue (uns eady lows) and a luc ua ion abou ha alue. By o mula ing he go e ning equa ions in e ms o he a e aged low ield quan i ies, he RANS model elimina es all u bulence luc ua ions. Howe e , inspec ion o he a e - aged momen um equa ion ( o incomp essible low and no body o ces), equa ion 7 [38], un eals a e m ha canno be ep esen ed uniquely in e ms o he mean quan i- ies. ∂(ρ¯ui) ∂ +∂ ∂xj (ρ¯ui¯uj+ρu0 iu0 j) = −∂¯p ∂xi +∂ ∂xjµ∂¯ui ∂xj +∂¯uj ∂xi (7) The e m ρu0 iu0 j, dubbed he Reynolds s ess enso , p e en s he sys em o equa- ions om being a closed sys em, i.e., he numbe o a iables exceeds he numbe o equa ions, since he ela ions be ween hese and he mean low quan i ies a e un- known. In o de o close he sys em, an app oxima ion – u bulence model – which p esc ibes he Reynolds s ess enso in e ms o he mean quan i ies has o be used 23 [38]. Following he RANS concep , all u bulence is modeled and he compu a ional e o is placed on de e mining he mean low quan i ies, disca ding any a emp o esol e u bulen s uc u es in ime and space. This signi ican ly educed complexi y o u bu- len low simula ion associa ed wi h he RANS model allows i , i selec ed and applied p ope ly, o p o ide a e y in e es ing balance be ween compu a ional esou ces and accu acy equi ed o mos indus ial applica ions. Ne e heless, one should always keep in mind ha he RANS model is an app oxima ion o eali y and has o b idge many o de s o magni ude in compu ing powe , wi h he consequence o no always p oducing esul s wi h a na ow e o ma gin [39]. 2.4.2 Tu bulence Models Th ee main amilies o u bulence models exis : Linea Eddy Viscosi y Models (LEVM), Reynolds S ess T anspo Models (RSTM) (o Second Closu e Models (SCM)) and Non-Linea Eddy Viscosi y Models (NLEVM). The i s da es back o 1877 when Joseph Boussinesq in oduced he concep o an eddy iscosi y o dynamic u bulen iscosi y, µ , which ela es he Reynolds s esses o he a e aged eloci y g adien s. When ca e ully applied, LEVM p o ides easonably good esul s o many lows. RSTM o SCM we e ini ially de ised in he 1950’s by Julius Ro a who laid he ounda ion o u bulence models ha disca ded he u bulen iscosi y concep by in- oducing a model o he di e en ial equa ion go e ning he e olu ion o he Reynolds s ess enso , allowing a di ec de e mina ion o he u bulen s esses by sol ing a anspo equa ion o each s ess componen . Fo 3D lows, se en equa ions ha e o be sol ed, six coupled equa ions o each Reynolds s ess enso componen and one o he u bulen leng h scale. RSTM p o ides ad an ages such as na u ally accoun ing o non-local and his o y low e ec s, making he e e ed model sui able o compu ing complica ing e ec s such as s eamline cu a u e o igid body o a ion. Howe e , he la ge numbe o equa ions and complexi y in ol ed inc eases he compu a ional e o and balances he o me bene i s [40]. NLEVM has a heo e ical ounda ion simila o LEVM, algeb aically ela ing he u - bulen s esses o he a e aged eloci y g adien s. The di e ence lies in he use o 24 highe o de quad a ic and cubic e ms ea u ing addi ional coe icien s. Al hough no s ongly es ablished as i s linea coun e pa , NLEVM is compu a ionally e icien and may p o ide g ea e accu acy in p edic ing u bulen low phenomena [36]. LEVM is he dominan app oach in indus ial CFD applica ions, he e o e, special emphasis is pu in e iewing i s o mula ions. These come in he o m o ze o-equa ion (algeb aic), one-equa ion o wo-equa ion models, which a e dis inguished by how hey de e mine he eloci y scale, qs, and leng h scale, Ls, ha cha ac e ize u bulence. The ze o-equa ion model, o mixing-leng h model, is he simples . The eloci y and leng h scales a e ela ed o he local low p ope ies ia algeb aic equa ions whe e Ls is a p esc ibed unc ion o he coo dina es and qsis di ec ly p opo ional o Lsand o he local eloci y g adien s. Howe e , accu a e p esc ip ion o Lsis only possible o simple lows, lea ing sepa a ed o highly h ee-dimensional lows ou o he model’s ange o applicabili y. The e o e, he ze o-equa ion model is limi ed o ela i ely simple lows and i s employmen in RANS applica ions is discou aged [38]. One-equa ion models a e an imp o emen o e he o me . By using an addi ional di e en ial anspo equa ion ha ela es qswi h he kine ic ene gy o he u bulen luc ua ions, k, low his o y is aken in o accoun , imp o ing he model’s ma hema ical desc ip ion o he u bulen s esses and, consequen ly, i s abili y o p edic he p op- e ies o u bulen lows. The leng h scale p esc ip ion ollows he same app oach as in he algeb aic model, wi h he same limi a ions. One-equa ion models a e he leas popula and success ul wi h he Spala -Allma as being, pe haps, he mos no o ious. These models a e conside ed incomple e due o he need o a u bulen leng h scale speci ica ion which equi es p io knowledge o he low, o he han ini ial and bounda y condi ions, in o de o ob ain a solu ion. Two-equa ion models a e he mos widely employed in CFD indus ial applica ions, making use o wo di e en ial anspo equa ions o de e mine he eloci y and leng h scales. The o me ly e e ed equa ion o kde e mines qsand an addi ional equa ion is in oduced in o de o compu e Ls. These a e comple e models since hey do no equi e p io knowledge o any low de ails in o de o ob ain a solu ion. The equa ion used in compu ing he leng h scale de ines he pa icula wo-equa ion model [40]. Ini ially de eloped by Pe e Chou in 1945 and made amous by Jones and Launde in hei 1972 pape , he k−model uses a di e en ial anspo equa ion ha ela es 25 he dissipa ion a e o u bulence ene gy, , o he leng h scale Ls[40]. The mos popula o all wo-equa ion models, i adequa ely p edic s nea -wall and ee-shea - low phenomena and success ully accoun s o low Reynolds numbe ea u es o u bulence, accu a elly p edic ing eci cula ing and bounda y laye lows wi h low sensi i i y o ee s eam alues. Howe e , due o limi a ions in he modeling o he low in nea -wall egions, such as he e ec o s eep p ope y a ia ion, he model becomes inadequa e in he p esence o ad e se p essu e g adien s, and ypically misses o unde p edic s low sepa a ion [41], a handicap in he simula ion o ai oil and wing lows. The second mos popula wo-equa ion model was p oposed by And ey Kolmog o in 1942 and con inuously imp o ed o e he cou se o he yea s, i s mos no o ious o mula ion elabo a ed by Da id Wilcox. The k−ωmodel ela es he dissipa ion a e o u bulence ene gy in uni olume and ime, i.e., he speci ic u bulence ene gy dis- sipa ion a e, ω, o he leng h scale Ls ia a di e en ial anspo equa ion [40]. By pe o ming excep ionally well close o walls in bounda y laye lows, pa icula ly unde ad e se p essu e g adien s, he k−ωmodel elimina es some o he k−model’s sho comings. Howe e , de ailed in es iga ions [42] concluded ha he magni ude o he eddy iscosi y can be changed by mo e han 100% i di e en ees eam alues o ωa e speci ied, e ealing a s ong sensi i i y o he model o ees eam alues, a non-exis en handicap o he p e ious one [43]. The me i o combining he bes o bo h wo lds belongs o Flo ian Men e , who, in 1993, p oposed he Baseline (BSL) and Shea -S ess T anspo (SST) models. The BSL model is iden ical o Wilcox’s k−ωmodel in he inne hal o he bounda y laye and g adually changes o he s anda d k−model owa ds he bounda y laye edge, keeping he p ope ies and excellen pe o mance o he o me close o walls and he la e ’s low sensi i i y o ees eam alues. The SST model is an imp o emen o e he BSL. I pe o ms in a simila ashion wi h he addi ional capaci y o accoun o he anspo o he p incipal u bulen shea s ess in ad e se p essu e g adien bound- a y laye s, based on he assump ion ha he p incipal shea s ess is p opo ional o he u bulen kine ic ene gy. Bo h models we e es ed o a la ge numbe o meaning- ul low ields o ae odynamic applica ions and p o ided esul s in ag eemen wi h he accu a e modeling o nea -wall low and no ees eam dependence, wi h he SST ex- celling i s p edecesso by showing be e ag eemen wi h expe imen al da a o ad e se 26 p essu e g adien bounda y laye lows [43]. 2.4.3 T ansi ion Models A conside able segmen o indus ial lows is cha ac e ized by Reynolds numbe s ang- ing om 104 o 106, whe e he egime o bounda y laye lows is no comple ely u bu- len , a he consis ing o an ini ial, o en signi ican , lamina po ion. T ansi ion om lamina o u bulen has a hea y in luence on low p ope ies, namely, a subs an ial in- c ease in skin ic ion, which is conside ably highe in he u bulen egime. In addi ion, unde ad e se p essu e g adien s, lamina sepa a ion bubbles wi h u bulen ea ach- men may appea [39]. The e o e, knowledge o he loca ion and ex en o ansi ion is ele an in he s udy o indus ial lows and in he design and pe o mance o ae ospace de ices, pa icula ly when he e ec s o wall shea s ess and bounda y laye sepa a- ion a e o in e es . Th ee main concep s exis o ansi ion modeling: applica ion o low Reynolds num- be u bulence models, he eNme hod and expe imen al co ela ions. The i s me hod’s abili y o p edic ansi ion is a he coinciden al since i is mainly based on ep oducing he iscous sublaye beha iou ins ead o ac ually p edic ing ansi ion om lamina o u bulen low. Using low Reynolds numbe u bulence mod- els wi hou any coupling o an in e mi ency equa ion o en p o es o be an un eliable me hod o p edic ing ansi ion. Fu he mo e, hese models can only be applied o by- pass ansi ion which excludes hem om being employed in many ae odynamic lows. The eNme hod is conside ed semi-empi ical. I is mos ly used in 2D p oblems, namely o isola ed ai oils, whe e i has been shown o p oduce e y good ansi ion p edic ions compa ed o wind unnel measu emen s. Howe e , o gene al ae ospace applica ions, a se o ba ie s p e en s i s usage. Since i is based on linea s abili y heo y, i canno p edic ansi ion due o non-linea e ec s such as high ees eam u bulence o su ace oughness. Mo eo e , ypical indus ial Na ie -S okes solu ions a e no accu a e enough o e alua e he s abili y equa ions, c ea ing he need o couple hese solu ions o accu a e bounda y laye codes. On op o i , he need o ack he g ow h o he dis u bance ampli ude a io along he s eamline esul s in a conside able issue o 3D lows whe e he s eamline di ec ion is no aligned wi h he g id, jeopa diz- ing he use o his me hod o h ee-dimensional lows. In ligh o hese conside a ions, 27 he con en ional one in e ms o ae odyamic e iciency and pe o mance. Howe e , he analysis equi ed o op imize he con igu a ion o bes pe o mance demands ex- cessi e ime and complexi y which, o a simple RPA con igu a ion, is no jus i ied. Addi ionally, he inc ease in weigh , manu ac u ing cos s and suppo abili y impac s, coupled wi h a highe di icul y in s abili y and con ol analysis and he lack o design expe ience, p e en s his con igu a ion om being widely adop ed [2], [11]. Las ly, he lying-wing con igu a ion has a single wing ha ac s simul aneously as a li ing and imming su ace. I is cha ac e ized by i s simplici y since he manu ac u ing, anspo a ion and main enance e o s a e conside ably educed ela i e o he emain- ing con igu a ions, due o i s ewe componen s. I also o e s ad an agens o s eal h missions and p o ides a ligh e ai c a . Fo ange missions, due o he d ag educ ion caused by he exis ence o ewe pa s which leads o highe li - o-d ag a ios, he ly- ing wing becomes a good op ion. Howe e , he same canno be said o endu ance missions, whe e he educed li ing capaci y, caused by upwa d ele on de lec ion and im necessi ies, p o ides a lowe endu ance pa ame e ela i e o he con en ional con igu a ion [2]. Fu he mo e, as in he case o a cana d a angemen , i possesses a educed e ec i e ail-a m and is he mos di icul con igu a ion o s abilize, e en by compu e [4], [11]. The wing e ical loca ion wi h espec o he uselage can be classi ied as high, mid o low. Wi hou going in o de ail, he ollowing ema ks a e conside ed. High wings ypically p o ide adequa e g ound clea ance, which allows placemen o he uselage close o he g ound, bene icial om a weigh pe spec i e. Howe e , i may p o e p oblema ic when conside ing ex e nal payload in eg a ion. High wings also a ou s abili y in de imen o maneu e abili y. Low wings p o ide g ea e maneu e abili y a he cos o g ound clea ance. F equen ly, a dihed al angle is se in o de o augmen s abili y and p o ide g ea e clea ance. The mid wing a angemen gene ally p o ides he lowes d ag and is a comp omise be ween he o me wo [11]. 2.5.2 P opulsion In eg a ion The p opulsion sys em design is cons ained due o he design p oposal equi emen s ha demand in eg a ion o an in e nal combus ion, uel injec ed engine. Thus, elec ic p opulsion is immedia ely cas aside. Je engines and u bop ops a e also no con- 34 side ed as possible solu ions gi en he ac ha hei ypical and e icien employmen is ou side he scope o he eques ed ope a ion condi ions [4]. Hence, i comes down o an a gumen conce ning ecip oca ing-p opelle engines and wo possible a ange- men s: pushe o ac o [2]. (a) (b) Figu e 7: (a) Pushe (adap ed om [4]) and (b) ac o (adap ed om [46]) a ange- men s. Mos RPAs equipped wi h ecip oca ing-p opelle engines use pushe ins alla ions, la gely due o bene icial payload in eg a ion op ions. Pushe con igu a ions clea he on o he ai c a o he ins alla ion o he payload, p o iding an unobs uc u ed iew o wa d [4]. In addi ion, i p o ec s he payload om engine exhaus and leaked luids, sou ces o con amina ion. A ac o con igu a ion does exac ly he opposi e. Addi ional ad an ages a e he inc ease in ae odynamic pe o mance due o he low en ainmen which causes he d ag o he body ahead o he p opelle o be educed, and also pi ch and yaw s abilizing e ec s. The downside is he educed p opelle e iciency and noise inc ease, bo h caused by he wake gene a ed by he body ahead o he p opelle [2]. Con e sely, he ac o con igu a ion, seldomly seen in RPAs, bene i s om ha ing clean ai low o he p opelle which esul s in highe p opelle e iciency and educed le els o noise compa ed o i s pushe coun e pa . Also wo hy o conside a ion is he impac ha he p opulsion sys em con igu a ion has on he ai c a weigh dis ibu ion. Due o longi udinal s abili y equi emen s, he ai c a cen e o g a i y should be lo- ca ed ahead o he neu al poin . In o de o accomplish his, he ai c a usually has mo e weigh in he on han in he ea which is in acco dance wi h using a ac o con- igu a ion. The pushe engine is gene ally loca ed in he ea o in he cen al sec ions o he ai c a which migh be challenging om a s abili y pe spec i e [2]. 35 2.5.3 Fuselage Con igu a ion The uselage con igu a ion is in ica ely connec ed o he ail con igu a ion and he p opulsion sys em loca ion. In o de o be e ec i e, he ail needs o be placed a a conside able dis ance om he wing o p o ide a p ope momen a m. The ubiqui ous a angemen o a con en ional wing con igu a ion wi h a pushe engine has wo ways o mee ing his equi emen . One is o place he engine in he ea o he ai c a , c ea ing a single con inuous uselage ha ac s as a ail a achmen . This app oach has he disad an age o placing a hea y weigh a a he CG. A minimum weigh in he nose is needed o coun e he engine momen and a oid s abili y p oblems. The o he is o place he engine in a cen al sec ion o he ai c a , close o he CG, and make use o booms o p o ide o ail momen a m. Single and win booms a e bo h alid op ions wi h he la e being, by a , he mos adop ed. T ac o a angemen s ypically yield single uselages as he placemen o he engine a he on o he ai plane mi iga es s abili y issues [2]. 2.5.4 Tail Con igu a ion When i comes o he ail con igu a ion, he designe is aced wi h nume ous possibili- ies, some o which can be seen in igu e 8. Figu e 8: Examples o ail a angemen s. Adap ed om [2]. As depic ed in igu e 8, he e a e wo main g oups o ail con igu a ions: single- a achmen poin and win boom ails. This obse a ion con i ms he in ica e connec- ion be ween ail and uselage con igu a ion, p e iously s a ed. An exhaus i e discus- sion on he p os and cons o he many possible ail con igu a ions is no in he scope o 36 he p esen wo k. Howe e , a ew ema ks mus be made abou he mos p edominan a angemen s. Con en ional ails p o ide su icien s abili y and con ol a he lowes ail weigh and s and as he da um agains which o he con igu a ions a e compa ed [10]. T- ails allow o smalle e ical s abilize s due o end-pla e e ec s and smalle ho izon al ones due o hei clea ance om he main wing wake. The downside is he weigh inc ease caused by he s eng hening o he e ical ail in o de o suppo he ho izon al one. The c uci o m ail is a comp omise be ween he o me wo wi hou he end-pla e e ec bene i [11]. Ad an ages o he H- ail a e he posi ioning o he e ical s abilize s in undis u bed ai and educ ion o he ho izon al s abilize size due o end-pla e e ec s gene a ed by bo h e ical ails. Again, he need o s eng hen one su ace inc eases he o e all weigh abo e he con en ional ail’s e e ence [10]. V- ails educe he su ace a ea and he numbe o su aces which esul s in a ail d ag dec ease, pa icula ly in e e ence d ag. Con ol-ac ua ion is mo e complex due o he mixing o udde and ele a o in he same su ace which is p one o p oduce ad e se yaw- oll. The in e ed V- ail a oids he la e . Howe e , i causes di icul ies in p o iding adequa e g ound clea ance [11]. Wi h some mino di e ences, he o me conside a ions a e alid o he win boom ails. These a e ypically hea ie han a con en ional (single) uselage cons uc ion [11]. In he case o in e ed-V ails, g ound clea ance is no longe an issue and he end-pla e e ec s o he e ical s abilize s on he ho izon al su ace can be conside ed o he con en ional a angemen . 2.6 Ma ke Resea ch Pe haps he bes way o conclude he cu en chap e , he ma ke esea ch ac s as he ideal ansi ion om he s a e-o - he-a discussion o he design p ocess i sel , p o id- ing insigh in o possible ai c a con igu a ions and pe inen design aspec s. Fi s o all, he mission equi emen s and pe o mance speci ica ions gi en in he design p o- posal ha e o be clea ly unde s ood. Only hen is he designe in posi ion o sea ch he ae ospace ma ke in o de o ind RPAs wi h simila pe o mance capabili ies, such as endu ance, c uise speed and MTOW, ha may be used as e e ence ai c a h oughou he p ojec . 37 Bo h in e na ional and na ional, mili a y and ci il a eas o he RPA ma ke a e anal- ysed. Shepa d’s Unmanned Vehicles Handbook 2008 [47] o e s an ex ensi e compi- la ion o exis ing RPAs and is he e o e he main sou ce o in o ma ion. Addi ionally, special a en ion is aken wi h inno a i e and en ep eneu ial na ional companies such as Teke e , Ha pia Tech and UAVision as well as wi h u he ai c a ope a ed by he PAF. The esea ch esul s comp ise a o al o 10 pe inen ai planes ha exhibi ce ain pe o mance pa ame e s in line wi h he design p oposal: AAI Co po a ion’s Shadow 200 (RQ-7B) and RQ-2 Pionee , Innocon’s MiniFalcon, ATE Vul u e, Elbi Sys ems’s He mes 180, Soko ZI B4, Tunisia Ae o Technologies’s Nasnas MK1, L-3 BAI Ae osys- ems’s Viking 100, Teke e ’s AR5 Li e Ray E olu ion and PAF An ex-X03. The lis is na owed down o he bes ou ai c a , depic ed in igu e 9, whose cha - ac e is ics and pe o mance bes ma ch he ones co e ed. Thei speci ica ions a e shown in able 2, in acco dance wi h da a ei he p o ided by he espec i e manu ac- u e s, iz. [48], [49] and [7], o by he UV Handbook [47]. Table 2: Ma ke esea ch esul s. Fea u es Goal MiniFalcon Nasnas MK1 AR5 An ex X03 MTOW (kg) <150 150 125 150 150 Endu ance (h) >8<15 >14 8-12 >15 Range (km) 300 <200 - - - C uise Speed (k s) 90 - - 75 - Max. Speed (k s) 120 120 70 -70 Ceiling ( ) 15000 <18000 16000 -15000 As a i s commen , i is no iceable ha none o he selec ed ai c a is able o ully ma ch he design a ge s, highligh ing he challenging and inno a i e aspec o he cu en p ojec . Inspec ion o he ma ke esea ch’s bes anked RPAs e eals common design ea- u es be ween hem. As a s a ing poin , a con en ional wing con igu a ion wi h a main wing and a ail is always obse ed, lea ing ou amous con igu a ions such as cana ds and lying wings. The main wing is ypically ec angula , al hough a ew exhibi ape . P opulsion is p o ided by pushe -p opelle sys ems wi h in e nal combus ion en- gines. The p opulsion sys em placemen is mos ly a he ai c a ’s cen al sec ions, close o he CG. The AR5 and He mes 180 a e he only excep ions as hey ha e he 38 (a) (b) (c) (d) Figu e 9: (a) MiniFalcon (adap ed om [48]), (b) Nasnas MK1 (adap ed om [47]), (c) AR5 (adap ed om[49]) and (d) An ex X03 (adap ed om [7]). p opulsion sys em placed a he ea . The la e op ion esul s in a con igu a ion which is simila o many con en ional manned ai c a , wi h a single con inuous uselage whe e he ail di ec ly a aches. Howe e , mos con igu a ions do no esemble his one, spe- cially i he p opulsion sys em is ins alled nea he CG, and make use o ail booms ins ead. A single boom such as in he MiniFalcon may be used, al hough win booms such as he ones in Nasnas MK1 and An ex X03 a e mo e equen ly designed. H and con en ional ails a e p edominan , accoun ing o 70% o he lis ed ai c a . The excep ions a e in e ed V ails used by bo h MiniFalcon and Shadow 200 (RQ- 7B) and he Vul u e’s T ail. Figu e 9 also illus a es he icycle dominance ega ding landing gea con igu a ions, pa en in he emaining ai c a as well, wi h he Vul u e being he only excep ion. The ma ke esea ch demons a es he expec ed p e alence o he win boom pushe con igu a ion. 60% o he RPAs iden i ied ha e such a design and, o hese, app oxi- ma ely 83% ha e H o con en ional ails, e idencing he success ul combina ion o win boom pushe and H/con en ional ail design. The second mos equen design is he 39 one using a single boom o place he ail a some dis ance om he main wing, whe he he boom is loca ed abo e (MiniFalcon,He mes 180) o below (Vul u e) he uselage cen e line. I comp ises 30% o he selec ed RPAs. Teke e ’s AR5 s ands ou as he only aic a wi h a single con inuous uselage. The success ul RPA designs and espec i e ea u es showcased in he cu en sec- ion should no be pe cei ed as manda o y, a he as ecommended. The win boom pushe design displayed by he majo i y o cases analysed, o any o he con igu a ion shown, a e no he only alid choices, only op ions ha ha e so a p o en success ul. O he al e na i es may p esen hemsel es as alid design op ions. Indeed, inno a ion is o en a e y impo an c i e ia in de ining a pa icula design, al hough o en accom- panied by an associa ed isk. In he wo ds o Jay Gundlach [2], “I is a adeo be ween he in luences o “nobody e e go i ed o buying a con en ional win boom pushe ” and a “me oo” design”. 40 3 Concep ual Design 3.1 Concep Gene a ion & Selec ion 3.1.1 Concep Gene a ion Concep gene a ion is whe e he enginee ’s c ea i i y s eps in o he ame. As demon- s a ed in 2.6, he e is no ideal con igu a ion, a he a b oad panoply o success ul solu ions. Keeping in mind he mission equi emen s speci ied in he DP, he au ho , in collabo a ion wi h he emainde o he design eam a he AFARC, de eloped a se ies o ini ial ai c a concep s ( igu e 10). Payload in eg a ion and endu ance maximiza ion a e conside ed he design d i e s, and he e o e exe he s onges in luence on he ehicle con igu a ion. None heless, ae odynamic pe o mance, s abili y and con ol, weigh impac s, s uc u al complexi y, manu ac u ing easibili y and associa ed cos s a e also key pa ame e s o be e alua ed, gi en hei majo impac on he inal p oduc . (a) (b) (c) (d) (e) ( ) Figu e 10: Ske ches o se e al ai c a concep s: (a) Con igu a ion 1, (b) Con igu a ion 2, (c) Con igu a ion 3, (d) Con igu a ion 4, (e) Con igu a ion 5, ( ) Con igu a ion 6. All six concep s a e de ined by a con en ional wing con igu a ion. This is jus i ied 41 by he deba e on he opic in 2.5.1. Due o poo pe o mance in endu ance missions, di icul ies ela ed o s abili y and con ol and lack o design/ope a ional expe ience in dealing wi h lying-wings, hese a e cas aside. The same goes o bo h andem and h ee-su ace con igu a ions, whe e an e en ual supe io ae odynamic pe o mance is o e shadowed by an excessi e inc ease in weigh and design/ope a ional complexi y. The a gumen is be ween he con en ional and cana d a angemen s, whe e consis- ency h oughou he li e a u e, ega ding ae odynamic pe o mance, ails o exis . Ne - e heless, conside ing he in e io s abili y and con ol pe o mance o he cana d, as well as he associa ed lack o expe ience, he designe chooses a con en ional wing sys em. Fu he mo e, i mus be s a ed ha he AFARC has signi ican expe ience in he manu ac u e and ope a ion o he la e , which ac s in i s a ou . Since s abili y is a mo e impo an han maneu e abili y, aking in o accoun he mission equi emen s, a high wing concep is conside ed. Ano he common ea u e be ween all six concep s is he pushe -p opelle a ange- men . Such is s ongly based on payload in eg a ion conside a ions. Ma i ime su eil- lance is he p ima y mission, he e o e payload o wa d ield o ega d is o c ucial impo ance. In addi ion, a oiding payload con amina ion due o engine exhaus and leaked luids is also o key impo ance since i may jeopa dize he da a collec ed by he op ical sys ems (gimble) and he ai pollu ion moni o ing equipmen . Concep s 1 and 2 a e he ypical win-boom pushe con igu a ions. Wi h he p opul- sion sys em close o he CG, hey mi iga e e en ual s abili y p oblems. The di e ence be ween hem is he ail a angemen , in e ed-V and T- ail, espec i ely. P os and cons o bo h ha e been discussed in 2.5.4. Concep 3 esembles he MiniFalcon. No as widely adop ed as he p e ious wo, i also b ings he p opulsion sys em close he CG and makes use o a single boom o p o ide ail momen a m. Howe e , s uc u al p oblems may a ise om he boom connec ion o he uselage, pa icula ly excessi e o sion and shea s esses caused by he weigh o he boom- ail. Agg a a ing he si ua ion is he ac ha he uel anks a e loca ed a he sec ion o he e e ed connec ion. I should also be no ed ha concep 3 is pe cei ed as di icul o manu ac u e. Concep s 4, 5 and 6 all aim a inno a ion wi h a single uselage placing he engine a he ea . Such a angemen is ypically ligh e han a win-boom and may e en 42 p o ide be e ae odynamic pe o mance due o i s ineness a io ( o be discussed a la e s ages o he design). The downside is he weigh dis ibu ion di icul y o placing a hea y componen a he ea o he ehicle, penalizing s abili y and con ol. The di e ence be ween hese h ee concep s is he ail con igu a ion, H- ail, in e ed-V ail and T- ail, espec i ely. Again, hei p os and cons ha e al eady been deba ed (2.5.4). Due o he expe ience acqui ed in ecen yea s in RPA ligh ope a ions, AFARC membe s o he design eam sugges ed ha i would be posi i e o keep he ho izon al s abilize ou o he wake o he p opelle low. This is because changing he engine egime changes he low gene a ed by he p opelle . I he ele a o is in he wake o such low, a need a ises o con inuously changing ele a o de lec ion o answe he engine egime a ia ions and keep he ai c a immed. To a ce ain ex en , all concep s a emp o comply wi h he o me sugges ion, wi h concep s 4, 5 and 6 p o iding he bes solu ion as he p opelle is ins alled a o he ail. 3.1.2 Concep Selec ion Selec ing a pa icula concep om a gi en se o possibili ies is no an easy ask. A such an emb yonic s age o design, i is ha d o quan i y he in luence o se e al design pa ame e s on he o e all ai c a pe o mance and classi y he gene a ed concep s acco dingly. In an a emp o ci cum en such hind ance, he decision-making me hod – Analy ic Hie a chy P ocess (AHP) – p oposed by Thomas Saa y [50] is adop ed. The AHP is a heo y o measu emen h ough pai wise compa isons and elies on he judgemen s o expe s (design eam) o de i e p io i y scales ha measu e in angibles in ela i e e ms. Compa isons a e made using a scale o absolu e judgemen s ha ep esen s how much mo e one elemen (ai c a concep ) domina es ano he wi h e- spec o a gi en a ibu e (compa ison pa ame e ) [50]. The AHP app oach has been alida ed and p o en success ul in ai c a concep ual design [51]. Figu e 11 ep esen s he es ablished hie a chy in ligh o which all six gene a ed con igu a ions a e assessed. This hie a chy is de ined by he au ho in collabo a ion wi h he design eam and comp ises ou main a eas: ope a ion, cons uc ion, main e- nance and inno a ion. As he pu pose o he RPA is o ly and accomplish a designa ed mission, ope a ion is conside ed he mos impo an a ea and, acco dingly, is gi en he highe weigh . Since he cu en p ojec is cons ained by he need o manu ac u e 43 ained u n while he ligh equi emen s include climb g adien , climb angle and c uise speed. Fo each si ua ion P/W is plo ed agains W/S. The design poin is ound by ollowing wo s eps: i s , one de e mines he c i ical ligh condi ion/ equi emen which gi es he minimum wing loading. Calcula ed alues a e shown in able 6. Subsequen ly, he c i ical condi ion o he powe - o-weigh a io is de e mined. This co esponds o i s maximum alue a he minimum wing loading. Iden i ica ion o he design poin p o ides knowledge o he maximum possible W/S o ligh ope a ions and he co esponding minimum possible P/W. This si ua ion is illus a ed in igu e 14. Table 6: Maximum wing loading (N/m2) allowed o each ligh condi ion o equi emen . Requi emen W/S S all Speed 583 Range 837 Endu ance 1450 Maximum Ceiling 670 Glide Ra io 1112 Landing 450 Figu e 14: Rep esen a ion o a segmen o he design space and iden i ica ion o he design poin . Range, endu ance and glide a io lines a e no ep esen ed. 50 Table 7: Wing loading (N/m2) and powe - o-weigh a io (W/N) o simila ai c a s. Ai c a W/S P/W Pionee 653 10 MiniFalcon 534 19 Nasnas MK1 537 15 Shadow 200 557 17 He mes 180 637 15 Viking 100 354 18 Vul u e 404 19 B4 544 13 An ex X03 350 19 AR5 684 – A e age 540.5 17 Conce ning he ai c a simila i y app oach, all RPAs ound in he ma ke esea ch a e aken in o accoun and he co esponding W/S and P/W alues compila ed. An a e age alue is calcula ed o bo h pa ame e s. Table 7 displays he esul s. I is el- e an o e e ha he wing loading alues a e no p esc ibed by he ab ican s, o cing he au ho o make an es ima e based on he ai c a weigh and wing dimensions. Na - u ally, such p edic ion is p one o e o s due o he lack o p ecision in es ima ing some dimensions. P/W is aken di ec ly om each ai c a da ashee . A e comple ing bo h app oaches, he desi ed pa ame e s a e compa ed. As able 8 illus a es, he esul s ob ained using he i s me hod a e mo e conse a i e, gi ing a lowe wing loading and a highe powe - o-weigh a io. Conside ing ha a wo s case scena io app oach allows o a sa e design, hese a e he selec ed alues. Table 8: Compa ison be ween wing loading and powe - o-weigh a io alues o he di e en app oaches employed. Uni s as in able 7. Design app oach W/S P/W Fligh pe o mance 450 18 Ai c a simila i y 540.5 17 Ha ing W/S de e mined and knowing WTO om p e ious es ima es, calcula ion o he main wing e e ence a ea yields S= 3.27 m2. Simila ly, ha ing de e mined P/W and WTO, he minimum powe o ligh ope a ions is ound o be P= 35.7HP (ho se powe ). 51 3.4 Wing Design 3.4.1 Plan o m De ini ion & Fligh Regime Cha ac e iza ion Fligh egime is cha ac e ized by bo h Mach and Reynolds numbe s. A c uise condi- ions, Mach numbe is 0.14 which, acco ding o he discussion in 2.2.2, is in he ange o incomp essible lows. The Reynolds numbe needs in o ma ion on he wing mean ae odynamic cho d, demanding a i s ske ch o he wing plan o m geome y. This is done by adding he ape a io, λ, and leading-edge sweep angle, ΛLE, o he known alues o wing a ea, S, and aspec a io, AR. Consequen ly, he wing span, b, oo , c , ip, c and mean ae odynamic, ¯c, cho ds a e de e mined. A his poin , λis se o uni y o simplici y and ΛLE o ze o acco ding o his o ic ends based on he c uise Mach numbe [11]. Table 9 shows he esul s. Table 9: Wing geome ic pa ame e s. Fo mulas aken om [10]. Pa ame e Fo mula Value (m) b b = (S·AR)1/26.26 c c = 2b/[AR(1 + λ)] 0.522 c c =λ·c 0.522 ¯c¯c= 2c (1 + λ+λ2)/[3(1 + λ)] 0.522 Wi h a cha ac e is ic leng h de e mined, he Reynolds numbe ha de ines c uise ligh is compu ed as app oxima ely 1.3×106, ou side he low Reynolds numbe ange acco ding o he discussion in 2.2.2. 3.4.2 Ai oil Selec ion The ai oil is he ounda ion o he wing, he p ima y sou ce o i s ae odynamic cha ac- e is ics. I s shape is selec ed based on wo c i e ia [10]: ha i p oduces he design CLin le el ligh and ha he ange o CL alues om he s a o he end o c uise gene a es he minimum possible d ag. In le el ligh , he equi ed li equals he weigh o he ai c a which leads o he ollowing exp ession o he li coe icien [10]: CL=2W ρV 2S(11) Du ing c uise, as he ai c a bu ns uel, i s weigh dec eases. I al i ude and eloci y emain cons an , his leads o a educ ion in CL. Ha ing knowledge o he uel mass 52 ac ions, he designe is able o de e mine he ai c a weigh a he s a and a he end o c uise and, consequen ly, he co esponding li coe icien s. The espec i e alues a e CLs a = 0.42 and CLend = 0.352. Thei mean alue yields CLdesign = 0.386. Two op ions p esen hemsel es: ei he a new, cus om ai oil is designed o one is selec ed om a ailable sou ces. The i s op ion equi es conside able ime and le el o in es men ha he p esen p ojec canno a o d. The second one is qui e as e and cheape and also enables he choice o a sui able ai oil gi en he as and ich a ailable da abase [2]. The e o e, ha ing in conside a ion he p e iously calcula ed pa ame e s (Reynolds numbe and CLdesign ), maximiza ion o he endu ance pa ame e , C3/2 L/CD, and o he impo an ac o s such as s all beha iou , hickness- o-cho d a io, ( /c), and maximum li coe icien , CLmax , an exhaus i e esea ch is conduc ed in o de o ind he bes ai oil. Re e ences [52] and [53] p o ide an ex ensi e in en o y o exis ing ai oils. O e 200 comp ising D ela, Da id F ase , Del Uni e si y, Epple , Wo mann, NACA, Selig, Selig-Dono an, Selig-Gigue e, amongs o he s a e analysed. All analysis a e conduc ed using he so wa e XFLR5 6.33. Viscous low wi h M= 0.14 and Re = 1.3×106is simula ed o e an ai oil disc e ized in 300 (maximum) panels using he eN ansi ion c i e ia wi h Nc i = 9 o e an angle o a ack ange a ying om -10◦ o 20◦. The selec ion p ocess is na owed down o six ai oils ha a e compa ed o pe o mance pu poses. Ha ing he wing geome y de ined, i s 3D cha ac e is ics, based on each ai oil, a e de e mined and ep esen ed in able 10. Na u ally hese, and no hei 2D coun e pa s, ac as decision c i e ia. As able 10 illus a es, he e is no ideal ai oil. Bes ae odynamic pe o mance o c uise condi ions occu s o a gi en ai oil whils bes s all beha iou and maximum li coe icien a e a ained wi h a di e en one. The key objec i e o maximizing he endu ance pa ame e ac s as a ieb eake , deciding in a ou o he SG6042 ai oil, depic ed in igu e 15. Figu e 15: SG6042 ai oil. Adap ed om [58]. The 3D li coe icien is de i ed om heo y and gi en as [10]: 53 Table 10: Pe o mance esul s o he op six bes ai oils. Pa ame e NACA 25112 W. FX63-147 SG6042 SG6043 S1210 S4180 Two-dimensional cha ac e is ics Clmax 1.49 2.02 1.73 1.88 2.21 1.82 Clα(/◦)0.113 0.117 0.097 0.103 0.113 0.112 α0l(◦)-1.2 -7.7 -5 -7.3 -6.8 -4 Cd00.0082 0.011 0.009 0.02 0.07 0.0095 Cdmin 0.0056 0.0065 0.005 0.0055 0.008 0.0055 ClminD 0.1-0.3 0.6-1.0 0.4-0.8 0.7-1.1 0.6-1.2 0.4-1.0 ( /c)max 0.12 0.13 0.1 0.1 0.12 0.098 αs all(◦)15 16.4 16.5 16.5 13.5 15.5 Cl00.12 0.95 0.55 0.79 1.12 0.47 Th ee-dimensional cha ac e is ics α im(◦)2.8 -3.8 -0.85 -3.1 -2.7 0.1 αs all(◦)12.9 10.8 11.2 11.1 14.1 13.3 CD0.011 0.011 0.0096 0.011 0.012 0.011 CLmax 1.34 1.82 1.51 1.69 1.98 1.64 CL/CD35.1 33.6 36.7 36.1 32.6 36.2 C3/2 L/CD21.8 20.9 22.8 22.4 20.3 22.5 CLα =2πAR 2 + q4+(AR.p1−(M. cos(ΛLE)))2(1 + an2(Λ /c) 1−(M. cos(ΛLE)2) (12) Λ /c ep esen s he sweep angle o he wing maximum hickness line. I yields CLα = 0.093/◦. Due o he linea a ia ion o he li coe icien wi h angle o a ack, he la e , o c uise condi ions, is gi en as [10]: α im =CLdesign −CLα=0 CLα (13) CLα=0 is he li coe icien a ze o angle o a ack, de e mined ha ing knowledge o he ai oil ze o-li angle o a ack, α0L=−5◦, and he e e ed linea a ia ion. The ou pu is α im =−0.85◦, wi h CLα=0 = 0.466. To p o ide complemen a y da a, he wing is subjec o an XFLR5 iscous low anal- ysis, a Re = 1.3×106, using he VLM. Nume ical calcula ions p o ide CLα= 0.087/◦, α0L=−4.7◦,CLα=0 = 0.410 and αs all = 13◦. The esul ing angle o a ack o c uise is α im =−0.27◦. Due o hei highe eliabili y, compu a ional esul s a e used h oughou he p ojec . 54 3.4.3 Wing D ag Es ima ion The wing d ag, di ided in o pa asi ic and induced d ag, is he i s componen o he ai c a o al d ag o be de e mined. A wo-dimensional pa asi ic d ag coe icien , Cd0, has al eady been de e mined du ing he ai oil selec ion p ocess. Howe e , due o h ee-dimensional e ec s such as low dis u bances caused by he wing a achmen s o he uselage and su ace impe ec ions like hinge gaps a mo able su aces, he h ee-dimensional coe icien is ac ually la ge han he es ima ed Cd0. The 3D pa asi e d ag coe icien can be compu ed in he ollowing manne [10]: CD0=C ·F·Q·Swe S(14) In he o me equa ion, C is he iscous d ag coe icien , F he o m ac o , Q he in e e ence ac o and Swe he wing we ed a ea. In o de o es ima e C , a his s age o design, one assumes he heo e ically well unde s ood low o e a la pla e wi h he same Reynolds numbe [11]. Since ansi ion is expec ed o occu , con ibu ions o bo h lamina and u bulen po ions o he low a e conside ed. A ansi ion Reynolds numbe o 1×106is assumed [10]. The o m ac o es ima es he o m d ag con ibu ion, pa icula ly due o low sepa a ions. I depends hea ily on he maximum hickness- o-cho d a io o he ai oil and also on i s loca ion, sweep angle a i s line and Mach numbe [11]. The in e e ence ac o p edic s he inc ease in pa asi ic d ag caused by uselage and wing a achmen s in e e ence e ec s. High wings ha e Q= 1 [10]. The induced d ag coe icien , CDi, accoun s o he d ag gene a ed due o li and co esponds o he second e m o equa ion 6. Fo c uise condi ions, equa ion 14 yields CD0= 0.004 and he second e m o equa- ion 6 p o ides CDi= 0.0056. The wing o al d ag coe icien comes as CD= 0.0096. The esul ing d ag o ce is app oxima ely 32 N. In compa ison, XFLR5 calcula ions p o ide CD= 0.010, which esul s in a d ag o ce a ound 35 N. Keeping in mind he wo s case scena io app oach o design and he mo e conse a i e na u e o nume ical esul s, hese p e ail o e he semi-empi ical ones. 55 3.5 Enhanced Li Design Typically, he enhanced li design is conduc ed in la e s ages o he concep ual de- sign, in o de o achie e desi ed alues o CLmax , usually o mee ake-o and landing dis ance equi emen s [10]. I is he au ho ’s decision o conduc such an analysis a his poin o ob ain be e es ima es o he ac ual alues o CLmax . This a iable is im- po an in he design poin selec ion and, he e o e, ha ing a be e es ima e allows a mo e accu a e p edic ion o he wing loading and powe - o-weigh a io, educing he chances o ha ing o i e a e he en i e p ocess a la e s ages. The goal o he enhanced li design is o achie e a gi en alue o CLmax ha sa is- ies ake-o and landing dis ance equi emen s. In o de o do so, wo echniques can be employed: passi e and ac i e li enhancemen . The la e is usually he subjec o STOL (sho ake-o and landing) and ul a-STOL ai c a designs [10] and is no jus i- ied o he p esen case. Passi e enhancemen comp ises he use o aling-edge and leading-edge de ices. The use o bo h inc eases he numbe o pa s o manu ac u e along wi h he wing weigh and such may no be necessa y. As a s a ing poin , only ailing-edge de ices a e con empla ed. T ailing-edge laps ac o inc ease he cambe o he ai oil sec ion, which shi s α0L, p oducing a highe li coe icien a a gi en angle o a ack. The mos common ypes o ailing-edge laps a e plain, slo ed, spli and owle laps [10]. Fo he sake o manu ac u e simplici y, only plain and single slo ed laps a e conside ed o analysis. Figu e 16: Schema ic o ailing-edge plain and slo ed laps. Adap ed om [10]. As shown in igu e 16, a plain lap is me ely a de lec ion o he ailing-edge o he ai oil sec ion whils a slo ed lap is a plain lap wi h he addi ion o a slo a he hinge poin o allow high p essu e ai om he lowe side o he ai oil o pass o e he uppe su ace, delaying bounda y laye sepa a ion [10]. 56 The sp eadshee app oach equi es h ee inpu a iables and in o ma ion on he ype o lap desi ed in o de o p oduce i s ou pu . The inpu a iables a e he a io o he plan o m a ea o he wing ha ing he lap span o he o al wing plan o m a ea, SWF/SW, he lap de lec ion angle, δ , and he a io o he lap cho d o he wing cho d, c /c. The ou pu a iables a e he maximum li coe icien p oduced by he wing, CLmax , and he inc ease in pa asi ic d ag due o lap de lec ion, ∆CD0. Table 11: Pe o mance cha ac e is ics o di e en ailing-edge de ices. Flap Type CLmax ∆CD0 Plain 2.45 0.058 Slo ed 2.61 0.018 The esul s shown in able 11 a e ob ained wi h SWF/SW= 0.54,δ = 30◦and c /c = 0.3. The plan o m a ea a io is limi ed by he need o lea e enough oom o he aile ons, he de lec ion angle a emp s o maximize he li coe icien wi hou gene a ing oo much d ag and he cho d a io is based on his o ic ends [10]. The single slo ed lap p o ides mo e li and less pa asi ic d ag han i s plain coun e pa , making i he bes choice ega ding ae odynamic pe o mance. The use o laps causes he s all angle o dec ease. The sp eadshee app oach p o ides a s all angle o αs= 11.2◦ o he wing wi h a clean con igu a ion. Wi h he laps de lec ed, i dec eases o αs= 9.4◦. 3.6 Fuselage Sizing The uselage mus house he payload, p opulsion sys em, uel s o age, a ionics and he emaining ixed equipmen . When sizing he uselage, he main goal o he ai c a designe is o gua an ee p ope dimensions in e ms o heigh , wid h and leng h ha p o ide he in e nal olume necessa y o he e e ed accommoda ions while keeping i s pa asi ic d ag o a minimum [2]. In o de o make he bes use o he a ailable olume, minimize emp y spaces, and keep a simple concep , he uselage c oss-sec ion is concei ed as ec angula wi h ounded co ne s. I s dimensions a y along he uselage leng h since di e en s a ions accommoda e equipmen wi h di e en olume equi emen s. Bo h wid h and heigh ex end om 0.3 o 0.4 m. 57 Ha ing wid h and heigh ixed by in e nal olume cons ain s, de e mina ion o he uselage leng h ollows. The ineness a io, d/l, is de ined as he a io o he uselage maximum diame e o i s leng h [10]. In compliance wi h he o me de ini ion, consid- e ing a ci cula c oss-sec ion wi h he same a ea as he ec angula one, an equi alen diame e is calcula ed a each c oss-sec ion. The highes alue is aken as he use- lage maximum diame e , Dmax = 0.45 m. Fo subsonic condi ions, he uselage o al d ag coe icien is minimized by a ineness a io o app oxima ely 0.3 [10], esul ing in a o al leng h o L= 1.5m. Wi h he uselage geome y comple ely de ined, he designe is in posi ion o es i- ma ing he d ag i gene a es, de e mining ano he componen o he ai c a d ag build- up. In his case, since he e is no li p oduced, only pa asi ic d ag is gene a ed [10]: D0=q·Swe ·C ·F·Q(15) In he p e ious equa ion, q ep esen s he dynamic p essu e and Swe he uselage we ed a ea. Again he ic ion coe icien comes om la pla e s udies and depends on whe he he low is lamina o u bulen . The o m ac o accoun s o o m d ag and depends solely on he ineness a io. The in e e ence ac o is, in mos cases, negligible when conside ing he uselage and a alue o Q= 1 is assumed [10]. In o de o es ima e he o al d ag, he uselage is di ided in o Nsegmen s o con- s an leng h. Fo each, he we ed a ea and ic ion coe icien a e calcula ed and he segmen d ag is ound. One should no e ha he Reynolds numbe used in de e min- ing C is he local Reynolds o each segmen , whe e he cha ac e is ic leng h is he segmen posi ion om he s a o he uselage. The o al d ag is ob ained by summing up all segmen con ibu ions. [10]. A his poin , gi en he sho leng h p oduced by he heo e ical op imum ineness a io, a pa ame ic s udy is conduc ed in o de o in es iga e how he uselage o al d ag a ies wi h d/l. One can obse e by means o igu e 17 ha he ineness a io o bes ae odynamic pe o mance is si ua ed in he ange 0.15–0.25, lowe han he expec ed 0.3. Mo i a ed by he o me and by he need o inc ease he uselage leng h (1.5 m is pe cei ed as oo sho o p ope ly ha bou all componen s and p o ide adequa e ail momen a m), he ineness a io is changed o 0.15, yielding a o al leng h o 3 m. The co esponding 58 uselage d ag is app oxima ely 16.7 N (CD0= 0.005). Figu e 17: Fuselage o al d ag s ineness a io. 3.7 Tail Design 3.7.1 Ho izon al Tail Sizing Ini ial sizing o he ho izon al ail is based on empi ical da a h ough he use o a coe i- cien ha co ela es ea u es o di e en ai c a ele an o he ail design. I is de ined as [10]: CHT =SHT ·lHT ¯cw·S(16) SHT ep esen s he ho izon al ail plan o m a ea, lHT he dis ance be ween he qua e -cho d loca ions o he mean ae odynamic cho ds o he main wing and ho i- zon al s abilize , and ¯cw he main wing mean ae odynamic cho d. Due o he lack o empi ical da a and his o ic ends on RPA design, he e is no in- o ma ion on ail coe icien s a ailable in he li e a u e. The e o e, an app oxima ion has o be made based on ai c a simila i y. Wi h his in mind, he ho izon al ail coe icien is aken om he homebuil ai c a ca ego y, yielding CHT = 0.5[11]. In o de o mee he coe icien equi emen , he designe can adjus he ail su ace a ea o i s loca ion. Inc easing he su ace a ea esul s in a weigh and we ed a ea in- c ease, bo h undesi able. Co ke [10] sugges s ixing lHT and, consequen ly, calcula ing SHT . In compliance wi h his, and conside ing he uselage leng h and he es ima ed 59 Table 14: S uc u al weigh de e mined by c ewd ai c a [10] and RPA [2] s a is ical app oaches. Uni s a e in kg. S uc u al componen Co ke [10] Gundlach [2] Wing 18.9 18.5 Fuselage 12.1 – Tail 4.8 2.8 Landing gea 15.7 9 S uc u al Weigh 51.6 30.3 and en ing. The unins alled engine and gene a o weigh s a e known. The emaining a e es ima ed ia empi ical ela ions [2]. The ixed equipmen weigh con ains he ins umen a ion, communica ions, wi ing, ligh con ol sys em, elec ical sys em, en i onmen al con ol sys em, auxilia y powe uni and also he pain weigh . The ins umen a ion subg oup consis s o he au opilo , ai da a sys em, GPS an enna, ine ial na iga ion sys em and he onboa d compu a- ion p ocesso s. The la e and he au opilo a e known, he emainde a e aken om s a is ical es ima es [2]. The communica ions subg oup comp ises he da a link equip- men , he line-o -sigh (LOS) communica ion equipmen and he Sa Com, all o which a e known weigh s. The ligh con ol sys em, auxilia y powe uni and elec ical sys- em (composed by he ba e ies and he ene gy con e e box) a e also known. Wi ing, en i onmen al con ol sys em and pain weigh s a e es ima ed om his o ic da a [2]. The sum o all hese weigh s is mul iplied by an ins alla ion ac o , yielding he ins alled ixed equipmen weigh . The weigh o all payload elemen s has been iden i ied in sec ion 3.2. The uel weigh es ima e is e ined in o de o accoun o he oil weigh [2]. Figu e 19: Maximum ake-o weigh and espec i e subg oups. Uni s in kg. 66 The e ined weigh analysis esul s in a ake-o g oss weigh o 152.4 kg, abo e he maximum allowable MTOW o class I RPA. Since se e al wo s case scena ios we e assumed in he weigh build-up p ocess and some o he empi ical ela ions used end o o e p edic he weigh , i is plausible ha he ac ual MTOW is unde 150 kg. Howe e , an accu a e es ima e can only be pe o med a he p elimina y design le el. 3.10 S a ic S abili y S a ic s abili y exis s i , gi en a dis u bance o an equilib ium s a e o ligh , he o ces c ea ed by he dis u bance ac in o de o es o e he ai c a o i s o iginal s a e o mo ion. I is o key impo ance ha he ai c a is s a ically s able in ligh o any o he h ee di ec ions o mo ion: longi udinal (pi ch), la e al ( oll) and di ec ional (yaw) [10]. 3.10.1 S a ic Ma gin The s a ic ma gin is de ined by equa ion 22, whe e xnp is he longi udinal posi ion o he ai c a neu al poin (NP) and xcg he longi udinal posi ion o he ai c a cen e o g a i y. Fo s abili y, he s a ic ma gin has o be posi i e which means ha he CG mus o be o wa d o he NP [10]. SM =xnp −xcg ¯cw (22) The e ined weigh analysis allows an ini ial p edic ion o weigh dis ibu ion along he ai c a leng h. As he engine is ins alled in he ea o he ai c a , he ixed equip- men and payload ough o be placed, i possible, in he on in o de o balance he weigh . Since he uel anks should be si ua ed nea he CG in o de o minimize i s a ia ion as uel is bu ned, an ai c a CG wi hou conside ing he uel sys em is i s ly compu ed. Subsequen ly, wo sepa a e uel anks a e placed o wa d and a o he o me ly de e mined CG, a he same dis ance, in o de o keep i s posi ion cons an . The neu al poin is de ined as he CG loca ion ha p o ides no change in pi ching momen as angle o a ack is a ied. A semi-empi ical es ima e is pe o med, accoun - ing o wing, uselage, ail and engine con ibu ions [11]. Acco ding o he design eam’s ope a ional expe ience, he s a ic ma gin should be in he ange 15%-30%. Compliance wi h his ecommenda ion p o ed di icul and 67 could only be achie ed a e an exhaus i e i e a i e p ocess, in which he loca ion o se e al componen s was cons an ly adjus ed. The designe se led o a s a ic ma gin o oughly 20%, ob ained wi h CG and NP loca ions o 1.48 m and 1.58 m, espec i ely. Howe e , compliance wi h s a ic ma gin ecommenda ions was achie ed a he cos o ail e ec i eness. In o de o mo e he NP away om he CG, he main wing had o be placed a o i s ini ial posi ion, esu ing in a dec ease in ail momen a m om he ini ial 1.44 m o 1.19 m. Due o his educ ion, bo h ho izon al and e ical ail coe icien s d opped o 0.41 and 0.033, espec i ely. Fu he in es iga ion on his opic led he o he conclusion ha , o an H- ail design, he ho izon al ail coe icien can be educed by 5% [10], esul ing in an ini ial equi emen o CHT = 0.475. Ne e heless, bo h ac ual ho izon al and e ical ail coe icien s a e below he ecommended alues o 0.475 and 0.04, espec i ely. This does no necessa ily ep esen a design handicap since hese alues a e aken om he homebuil ai c a ca ego y (simply he one ha e idences g ea e simila i y wi h RPAs) as a e e ence o he ail ini ial sizing. Fu u e calcula ions p o e ha he ac ual ail coe icien s a e adequa e. 3.10.2 S abili y De i a i es The s abili y de i a i es measu e he ai c a ’s eponse o a changing pi ch, oll o yaw angle condi ion. The longi udinal, la e al and di ec ional s abili y equi emen s, in e ms o hei de i a i es, a e gi en as [10]: CMα=dCM dα <0 ; CLβ=dCL dβ <0 ; Cnβ=dCn dβ >0(23) In he p e ious se o equa ions, CM,CLand Cn ep esen , espec i ely, he pi ching momen , olling momen and yawing momen coe icien s o he ai c a and αand β he ai c a angle o a ack and sideslip angle. All de i a i es a e compu ed om semi-empi ical ela ions ha ake in o accoun he con ibu ion o di e en ai c a componen s [11]. CMαis de e mined di ec ly om he symme ic o he p oduc be ween he s a ic ma gin and he main wing li coe icien , conside ing con ibu ions om he main wing, uselage, ho izon al ail and engine. Cnβ depends on he main wing, uselage and e ical ail. As o CLβ, bo h he main wing and e ical s abilize s exe a conside able in luence. Calcula ions demons a e ha CMα=−1.05,Cnβ= 0.08 and CLβ=−0.04. An 68 app op ia e ange o alues o he i s wo de i a es is −1.5< CMα<−0.16 and 0.08 < Cnβ<0.28 [10]. CLβshould ha e a magni ude abou hal ha o Cnβa subsonic speeds [11]. As expec ed, he longi udinal and la e al de i a i es a e nega i e and he di ec ional de i a i e posi i e, wi h hei magni udes in he expec ed ange o alues. Hence, a a concep ual le el, he ai c a is conside ed o ha e adequa e s a ic s abili y cha ac e is ics. 3.10.3 Tail Fo ce & T im D ag In o de o keep he ai c a balanced, he ho izon al ail mus gene a e li [10]. Knowing he o al weigh and CG loca ion du ing c uise, as well as he loca ion o he main wing and ho izon al s abilize ’s ae odynamic cen e , an ini ial es ima e o he esul ing ail o ce is compu ed as app oxima ely -61 N (downwa ds). In sec ion 3.4 i is s a ed ha o le el ligh he li gene a ed by he main wing mus compensa e he ai c a weigh . Howe e , as he p esen sec ion illus a es, in o de o keep he ai plane immed, he wing li mus compensa e bo h he ai c a weigh and nega i e li p oduced by he ho izon al ail [10]. An i e a ion is he e o e equi ed in o de o upda e CLdesign . Since he ho izon al ail gene a es li , i will also gene a e li induced d ag – im d ag – ha mus be accoun ed o . This d ag componen is de ined as [10]: D im =L2 HT q·SHT ·π·ARHT ·eHT (24) LHT ep esen s he ho izon al ail li , ARHT he ho izon al ail aspec a io and eHT i s Oswald e iciency ac o , es ima ed as app oxima ely 0.8 [11]. Fo c uise condi ions, D im = 0.6N. As a ule o humb, he im d ag should be less han 10% o he ai plane o al d ag [10]. In he cu en case i is oughly 0.7%, p o ing ha he s a ic ma gin does no ha e a nega i e impac on pe o mance. The im d ag has o be included in he d ag build-up, leading o a new alue o he ai c a o al d ag a c uise condi ions. I e a ing, he o al d ag comes as 83 N and he equi ed powe o c uise as 12.9 HP. 69 3.10.4 Con ol Su aces Sizing Ini ial sizing o he p ima y con ol su aces – aile ons, ele a o and udde – is deal wi h in he p esen sec ion. In o de o keep a cohe en , linea wing s uc u e, he aile on cho d is se o equal he lap cho d, i.e., 30% o he wing cho d. Acco ding o his o ical guidelines, his ough o co espond o a a io o o al aile on span and wing span in he ange 0.3-0.37 [11]. Knowing ha 6.4% o he wing span is in eg a ed on he uselage and 54% is occupied by he laps, he emaining 39.6% is le a ailable o he aile ons. Consequen ly, hese a e designed o ex end along 36% o he wing span, mee ing he empi ical ecommenda ions and lea ing a sa e y ma gin o 3.6%. Acco ding o Rayme ’s semi-empi ical o mulas [11], o he e e ed pa ame e s, an aile on de lec ion o 30◦ esul s in a oll a e o app oxima ely 22.4 ◦/s. Ele a o s and udde s gene ally begin a he side o he uselage and ex end o abou 90-100% o he ail span and 25-50% o he ail cho d [11]. In lack o a me hodic app oach o ele a o sizing, he design eam conside s a wo s case scena io co e- sponding o s all, in o de o design his con ol su ace. When lying a s all speed, he ho izon al ail needs o gene a e a li coe icien a ound -0.39 o im he ai plane. XFLR5 simula ions show ha , o an ele a o ex ending om he uselage o he ip o he ail, wi h 30% o he ail cho d and a de lec ion o 30◦, he necessa y li coe icien is a ainable. Thus, an ini ial p edic ion o his con ol su ace design is accomplished. The udde is ypically sized in o de o p o ide di ec ional con ol capable o holding a ze o sideslip angle based on a wo s case condi ion consis ing o one o wo scena - ios: an asymme ical powe condi ion caused by ha ing one engine ou o landing and ake-o in a c oss-wind o 0.2VT O and β= 11.5◦[10]. Since he RPA unde design is equipped wi h a single engine, he i s scena io is inapplicable. Conside ing he landing and ake-o in c oss-wind si ua ion, a udde wi h oughly 30% o he e ical s abilize a ea and a de lec ion o 20◦should be able o p o ide p ope di ec ional con- ol [10]. This condi ion yields a necessa y con ol su ace a ea o 0.085 m2 ha can be achie ed wi h he udde ex ending along he en i e span o he ail and up o 30% o i s cho d. 70 3.11 Dynamic S abili y A e assu ing ha he ai c a is s a ically s able in all h ee di ec ions o mo ion, he ollowing design s ep deals wi h gua an eeing dynamic s abili y. Dynamic s abili y ad esses he way he ai plane e u ns o he equilib ium s a e a e being dis u bed, conside ing es o ing and damping o ces, as well as mass dis ibu ion. I he dynamic mo ions o he ai c a allow a e u n o he o iginal ligh s a e, he ai c a is said o be dynamically s able. I no , and he esul is an o e sho o he o iginal s a e, causing he ai plane o oscilla e wi h inc easing ampli ude, e en ually losing con ol, i is said o be dynamically uns able [11]. Dynamic s abili y analysis is complex and demands a compu a ional app oach in o de o ob ain accu a e esul s [11]. Es ima ion o an ai c a ’s dynamic mo ions a a concep ual design le el is no exac ly s aigh o wa d conside ing he lack o in o ma ion in concep ual design e e ence ex books ( iz. [2], [10] and [11]). In o de o bypass his obs acle, he au ho ga he s in o ma ion om e e ences [54], [55] and [56], and adds a new s ep o he sp eadshee app oach, in which dynamic s abili y cha ac e is ics a e assessed. The gene al idea lies in sol ing he equa ions o mo ion and de e mining he oscil- la o y modes. The e e ed equa ions a e go e ned by pi ch, yaw and oll o a ions as well as e ical, la e al and longi udinal eloci ies. Taking in o accoun he ai plane sym- me y, i is possible o sepa a e he longi udinal sys em o equa ions om he la e al- di ec ional one, esul ing in wo sepa a e sys ems o equa ions ha cha ac e ize bo h longi udinal and la e al-di ec ional mo ions [11], [54]. To sol e bo h sys ems, he ollowing sequence mus be obse ed. De e mina ion o longi udinal and la e al-di ec ional dimensionless de i a i es, using semi-empi ical ela ions [54], is he s a ing s ep. Calcula ion o he dimensional de i a i es ollows. Ha ing hese de e mined, along wi h in o ma ion on he ai c a ’s momen s o ine ia, compu ed in acco dance wi h [11], he longi udinal and la e al-di ec ional ma ices a e illed [54]. Sol ing o he eingen alues, one ob ains he oscilla o y modes o each sys em o equa ions, ep esen ed in ables 15 and 16. A dynamic mode is said o be s able i he eal pa o i s eigen alue is nega i e. Bo h longi udinal modes a e s able and wo o he la e al-di ec ional as well, he du ch oll and oll modes. The spi al mode is uns able, ye , such ins abili y does no necessa ily 71 Table 15: Longi udinal oscilla o y modes and hei espec i e na u al equencies, ωn, and damping ac o s, ξ. Oscilla o y Mode (a±bi)a b ωn( ad/s) ξ Phugoid -0.0073 0.3606 0.3607 0.0202 Sho Pe iod -2.1047 4.6152 5.0725 0.4149 Table 16: La e al-di ec ional oscilla o y modes and hei espec i e na u al equencies, damping ac o s, ime cons an s, τ, and ime o double he ampli ude, 2. Oscilla o y Mode (a±bi)a b ωn( ad/s) ξ τ 2(s) Du ch Roll -0.3437 3.1724 3.19 0.1077 – – Roll -11.788 0 – – 0.0848 – Spi al 0.0433 0 – – – 15.98 pose a p oblem as he ime o double he ampli ude o mo ion may be long enough o pe o m he p ope co ec ions [11]. Flying quali ies can be assessed by aking in o conside a ion he ai c a class and he ligh phase ca ego y. The o me is class I (small, ligh ai planes) and he la e is ca ego y B o C, whe he he ligh phase is a non e minal one wi h g adual maneu e s o a e minal one wi h p ecise ligh pa h con ol, espec i ely [55]. Acco ding o lying quali ies c i e ia [56], he sho pe iod, du ch oll and oll modes a e e alua ed as le el 1. This means ha he lying quali ies associa ed wi h each mode a e adequa e o he mission ligh phase. The phugoid and spi al modes demons a e lying quali ies o le el 2, i.e., he mission ligh phase can be accomplished a he cos o an inc ease in pilo wo kload and/o deg ada ion in mission e ec i eness. Due o he lack o in o ma ion conce ning RPAs, he e e ed c i e ia is based on mili a y speci ica ions o pilo ed ai planes and is employed me ely o p o ide a e e ence o he concep ual ai plane’s lying quali ies. 3.12 Pe o mance 3.12.1 S all Speed & C uise Veloci y Op imiza ion S all speed is de ined as [10]: Vs=s2W ρSCLmax (25) 72 Mission equi emen s demand a maximum s all speed o 55 k s a c uise condi ions, wi h a clean con igu a ion, and a maximum o 45 k s a ake-o and landing condi ions, wi h he laps deployed. Table 17 demons a es how bo h equi emen s a e me . Table 17: S all speed a di e en ligh condi ions. Fligh Condi ion Con igu a ion Vs(k s) C uise Clean 45 C uise Flaps 35 Take-o (MSL) Flaps 33 Take-o (10000 ) Flaps 38 Landing (MSL) Flaps 31 Landing (10000 ) Flaps 36 Pe o mance in s eady le el ligh is assessed by endu ance and ange. Acco ding o he B egue equa ions, o p opelle -powe ed ai c a , he o me can be maximized by maximizing he endu ance pa ame e , C3/2 L/CD, which is done by lying a he eloc- i y o minimum powe . Maximiza ion o ange equi es maximiza ion o he li - o-d ag a io, L/D, accomplished by c uising a he eloci y o minimum h us . Bo h eloc- i ies can be de e mined analy ically assuming ha he ze o-li d ag is cons an wi h eloci y, and d ag due o li ollows he pa abolic app oxima ion in which Kis cons an wi h eloci y. These assump ions a e accep able only in he case o ai planes wi h high aspec a io wings lying a low Mach numbe s [11]. Indeed, such is he case o he cu en design. None heless, in o de o augmen he le el o con idence in he esul s, a g aphical analysis is pe o med, as ecommended [11], in which he ac ual h us and powe equi ed a e plo ed agains he eloci y. In p ac ice, o p ope ly de e mine he eloci ies ha maximize endu ance and ange, engine pe o mance has o be conside ed. Howe e , due o lack o in o ma ion con- ce ning he la e , he au ho is unable o pe o m an accu a e assessmen . The ollow- ing esul s a e, he e o e, based on he a o emen ioned heo e ical pos ula es. Looking up a igu e 20, he eloci ies o minimum h us and powe can be iden i- ied as app oxima ely 76 k s and 56 k s espec i ely. Bo h cu es poin o he ac ha he speci ied c uise speed o 90 k s is a om op imizing pe o mance, sugges ing he pe inence o a e ision and possible ede ini ion o he mission equi emen s. A e due conside a ion and discussion o he opic wi h he design eam, a c uise speed o 70 k s was speci ied. Such decision is based on a comp omise be ween 73 (a) (b) Figu e 20: Th us (a) and powe (b) equi ed s c uise eloci y. app oxima ing he c uise eloci y o he endu ance op imiza ion speed (56 k s) and no de ia ing oo a om he ini ial equi emen (90 k s). An addi ional bene i is he ac ha he selec ed eloci y is close o he ange op imiza ion speed (76 k s). Na u ally, such a undamen al change in he mission equi emen s demands a new i e a ion o he whole design p ocess. 3.12.2 S eady Climbing, Gliding and Le el Tu ning Fligh Analy ical op imiza ion o eloci y o a e o climb (ROC) can be cumbe some. G aph- ical analysis is mo e eliable and ega ded as he mos accu a e me hod [11]. In igu e 21, a e o climb is plo ed agains eloci y, using ac ual h us and d ag da a (c uise condi ions), and de e mined by iden i ying he peak o he cu e. Table 18 shows he bes a e o climb in h ee di e en si ua ions: a c uise, ake-o a MSL condi ions and ake-o a 10000 . Addi ionally, he a e o climb a ained wi h he c uise speed o 70 k s and ake-o speed is also p esen ed. (a) (b) Figu e 21: Climb a e (a) and sink a e (b) s c uise eloci y. 74 Table 18: Ra e o climb a di e en ligh condi ions. Fligh speed, V, and he a io o ligh and s all speed, V/Vs, a e ep esen ed o compa ison pu poses. Fligh Condi ion ROC (k s) V(k s) V/Vs(%) Bes ROC a c uise 11.4 56 24 ROC a c uise speed 11.1 76 56 Bes ROC a MSL 11.8 52 58 ROC a MSL & VT O 11.6 36 10 Bes ROC a 10000 11.3 60 58 ROC a 10000 & VT O 10.7 36 10 Acco ding o Co ke [10], o mili a y ai c a , a minimum climb speed o 1.2Vsmus be obse ed. Table 18 demons a es ha he op imimum eloci ies mee his equi e- men o e e y condi ion conside ed. I can also be seen ha , o he e e ed condi- ions, he a e o climb does no change signi ican ly. The design p oposal speci ies a minimum climb a e o 750 /min (7.4 k s) a MTOW, and as able 18 clea ly illus a es, he a e o climb is conside ably abo e he equi ed minimum in any ligh condi ion. In igu e 21(a), he poin o angency o he s aigh line om he o igin ep esen s he eloci y o bes climb angle – 22 k s. Such si ua ion is imp ac ical due o he ex emely low eloci y equi ed, signi ican ly below he s all speed. In gliding ligh , he h us is se o ze o and he mo ion o he ai plane is de e mined by he glide a io (GR), i.e., he a io be ween ho izon al dis ance a elled and al i ude los which is equal o he li - o-d ag a io. Hence, maximizing his pa ame e implies lying a he eloci y o minimum d ag. An addi ional impo an pa ame e is he sink a e (SIR), i.e., he e ical componen o eloci y which de e mines how much ime he ai plane can emain in he ai . The bes sink a e is achie ed when lying a he eloci y o minimum powe [11]. Table 19: Glide a io and sink a e a di e en ligh condi ions. Fligh speed, V, and ligh and s all speed a io, V/Vs, a e ep esen ed o compa ison pu poses. Pa ame e GR SIR (k s) V(k s) V/Vs Bes Glide Ra io 19 4 76 69 Bes Sink Ra e 16.6 3.4 56 24 C uise a 70 k s 18.9 3.7 70 56 Table 19 displays he g aphical esul s o h ee di e en si ua ions. As illus a ed, bes glide a io occu s a c uise speed, which minimizes d ag and he e o e maximizes 75 The ai oil unde s udy is he SG6042. I s coo dina es a e manipula ed a he ailing edge in o de o ob ain a ini e (segmen ) ins ead o an in ini e ailing edge (poin ) o p o ide inc eased g id quali y and nume ical s abili y o u u e simula ions. In o de o simula e he low o e he ai oil, a con ol olume has o be c ea ed. Fo a 2D analysis, his is de ined as a squa e wi h he objec o in e es , he ai oil, placed a he cen e . The a - ield dis ance, measu ed om he ai oil, should be oughly 60 imes he ai oil cho d in o de o p ope ly simula e he ees eam, undis u bed low [28]. Fo an ai oil ha ing ¯c= 0.522 m, hal he side o he squa e will be app oxima ely 32 m (60×0.522). The physics model should be able o accu a ely p edic he low ield cha ac e is ics and phenomena in he domain o in e es , speci ically nea he ai oil. I is di ided in o se e al submodels ha de ine speci ic aspec s o he low physics: space, ime, ma e ial, low, equa ion o s a e, iscous egime, u bulence model, ansi ion model and wall ea men , all de ined in acco dance wi h [28]. Table 23: Bes p ac ice guidelines conce ning he physics model. Pa ame e Space Time Ma e ial Bes p ac ice Two-dimensional S eady Gas (ai ) Pa ame e Flow Equa ion o s a e Viscous egime Bes p ac ice Seg ega ed Cons an densi y Tu bulen Pa ame e Tu bulence model T ansi ion model Wall ea men Bes p ac ice RANS wi h k-ωSST γ−ReθLow y+ In compliance wi h an ai oil analysis, wo-dimensional space is modeled. In o de o sol e he s eady-s a e go e ning equa ions, a s eady model is selec ed. Since he ai c a mo es in he a mosphe e, he ma e ial is gas (ai ) and i s p ope ies, namely, densi y, ρ, and dynamic iscosi y, µ, co espond o c uise al i ude condi ions. Seg ega ed low is modeled because o i s incomp essible na u e (M= 0.11 <0.3). The seg ega ed low model, in opposi ion o he coupled low model, is ad an ageous in e ms o compu a ional esou ces since i sol es he low go e ning equa ions in a seg ega ed, uncoupled manne , i.e., sequen ially, one equa ion a e he o he , linking hem by means o a co ec ion equa ion. Also linked o he incomp essible beha iou o he low is he equa ion o s a e model – cons an densi y. This model is used o compu e he densi y and i s de i a i es wi h espec o p essu e and empe a u e. A cons an densi y model assumes ha his a iable is in a ian h oughou he en i e 82 domain [57]. Gi en he Reynolds numbe o 1×106 ha cha ac e izes he low, bounda y laye ansi ion is expec ed o occu , i.e., he ini ial po ion o he low o e he ai oil is lamina up o he ansi ion egion whe e i begins o de elop as u bulen . To model his si u- a ion, one de ines he iscous egime as u bulen and selec s app op ia e u bulence and ansi ion models. The ecommended u bulence model is he Reynolds-A e aged Na ie -S okes (RANS) wi h he k-ωSST model. As discussed in 2.4.2, i demons a es excellen pe o mance nea walls in bounda y laye lows, namely unde he in luence o in ense ad e se p essu e g adien s, p o iding accu a e p edic ions o low sepa a ion phenomena while keeping he sensi i i y o ees eam/inle condi ions o a minimum. The γ−Reθ ansi ion model is selec ed. Acco ding o he in es iga ion pe o med in 2.4.3, his is a co ela ion-based model coupled wi h he k-ωSST model ha o e s e y good ansi ion p edic ion capabili ies and is pe ec ly compa ible wi h uns uc u ed CFD codes and ae onau ical low applica ions. I possesses an impo an pa ame e ha mus be de ined by he use : he ees eam edge. De ini ion o his pa ame e is ecommended o be a ound ou imes he es ima ed maximum bounda y laye hick- ness, δ[28]. To comple e he physics model, a low y+wall ea men model is selec ed. This one is sui able o low Reynolds numbe u bulence models, as is he case, and assumes ha he iscous sublaye is co ec ly esol ed, which in u n equi es a ine mesh nea he wall. P ope de ini ion o bounda y condi ions is o key impo ance in assu ing ha he inal solu ion con e ges and accu a ely ep esen s he eal low ield phenomena. The upwind (inle ) and la e al bounda ies o he con ol olume mus be de ined as eloc- i y inle s and he downwind (ou le ) bounda y as a p essu e ou le . This equi es he eloci y o be de ined in e ms o i s componen s ela i e o a e e ence axis so ha , in p ac ice, he eloci y is no mal o he upwind bounda y (inle ) and angen o he la e al bounda ies. The eloci y magni ude co esponds o he ai c a c uise speed. Two ex emely impo an pa ame e s ha a e imposed as bounda y condi ions a e he u bulence in ensi y, Tu, and he u bulen iscosi y a io (TVR), bo h p esc ibed a he inle and as ambien u bulence. Values ange om 0.001-0.01 o he o me and 1-10 o he la e [28]. Ini ial condi ions speci y he ini ial ield da a o he simula ion. Values o eloci y, 83 u bulence in ensi y, u bulen iscosi y a io and p essu e a he ou le should mee he bounda y condi ions alues so ha he simula ion migh each he inal con e ged solu ion as e and educe compu a ional e o s. Howe e , o s eady-s a e simula ions, he inal con e ged solu ion i sel is independen o he ini ial condi ions [57]. Pe haps he mos c i ical aspec in he es ablishmen o a solid CFD me hodology o a pa icula applica ion is he mesh se ing. Fo he sake o cla i y, he ollowing discussion is spli in o h ee opics: meshe s, de aul con ols and cus om con ols. S a -CCM+ o e s wo meshing s a egies o uns uc u ed meshing: Pa s-Based Meshing (PBM) and Region-Based Meshing (RBM). Fo be e con ol and au oma ion, since i de aches he meshing om he physics and p o ides a lexible and epea able meshing pipeline [57], he i s s a egy is adop ed. The mesh models (meshe s) used a e he immed cell and p ism laye meshe s. The o me o e s a obus and e icien me hod o gene a ing a high quali y g id in which cells a e p edominan ly hexahed al wi h minimal skewness, e inemen is based on su ace mesh sizing and use -de ined con ols, and he mesh is aligned wi h a use speci ied coo dina e sys em [57]. The la e c ea es o hogonal p isma ic cells nex o wall su aces o bounda ies, equi ed o p ope ly sol e he go e ning equa ions and he e o e cap u e he low p ope ies inside he bounda y laye egion. The p ism laye meshe s e ching unc ion, esponsible o p o iding he o mula used in gene a ing he cell laye hickness dis ibu ion, is a hype bolic angen . The co esponding s e ching mode is wall hickness. This mode se s he hickness o he laye adjacen o he wall bounda y as he s a ing poin o he p ism laye gene a ion. Addi ional pa ame e s o in e es a e he minimum hickness pe cen age and laye educ ion pe cen age ha a e se o 0.01 and 0, espec i ely, he la e o con o mal p isms in all laye s [28]. De aul con ols a e he main, gene ic mesh p ope ies. The base size is ecom- mended o be 10% o he ai oil cho d [28]. Due o compu a ional memo y and p o- cessing cons ain s, he designe has o limi he base size o a maximum o 20% o he cho d. Howe e , alues o CLand CDob ained wi h he coa se mesh di e -0.008% and -0.028%, espec i ely, om he ones ob ained wi h he ine mesh, concluding ha he e e ed limi a ion does no ha e a nega i e impac on he inal esul s. The basic su ace cu a u e anges om 36 o 54. Cell size anges om a minimum o 25% o he ailing edge hickness o a maximum o 100% o he cho d. A minimum ace quali y o 84 0.2 is demanded. Su ace g ow h a e anges om 1.05 o 1.3 while olume ic g ow h a es a e se o e y slow. The p ism laye a ound he ai oil is cha ac e ized by ha ing 32 laye s, a nea wall hickness ( i s cell heigh ), y1, and a o al heigh se ing, δ, gi en by [28]: y1=y+ a ge ·µ ρ·Uτ ;Uτ=√0.029 ·Re−0.2·V2(26) δ≈0.37 ·Re−0.2·l(27) In he p e ious se o equa ions, y+ a ge ep esen s he a ge wall y+, p e e ably in he o de o 0.25, V he mean ees eam eloci y and l he componen e e ence leng h (ai oil cho d). The p ism laye o al heigh se ing co esponds o he bounda y laye hickness es ima e. Cus om con ols a e manda o y on e e y li ing su ace and ecommended in he ou e bounda ies. Mesh e inemen close o he ai oil is equi ed in o de o p ope ly cap u e he low beha iou and sol e he go e ning equa ions. This is done by gene - a ing a nea ield su ounding he ai oil, in which cell size ma ches he ecommended 10% o he cho d, and a su ace con ol a ound he ai oil whe e he e e ed pa ame e is se o 12.5% o he base size. Fu he e inemen s a he leading and ailing edges a e pe o med, se ing he cell size o 3.125% o he base size. In addi ion, su ace cu a u e on he ai oil should be inc eased o 76. In o de o cap u e he ai oil wake, a e inemen o 50% o he base size is done up o app oxima ely 10 cho ds downs eam o he li ing su ace. Cus om con ols on he ou e bounda ies a e gene a ed wi h he pu pose o a oiding an unecessa y inc ease in compu a ional e o by limi ing he cell size o a minimum o 100% o he cho d [28]. The inal s ep in es ablishing a CFD me hodology ad esses he solu ion moni o ing. As he so wa e sol e s a emp o esol e he low in he con ol olume, speci ic pa- ame e s o in e es a e de e mined: hese consis o he ai oil li and d ag coe icien s, Cland Cd, espec i ely. Such pa ame e s a e he ul ima e goal o he CFD simula ions. Residuals a e au oma ically calcula ed and plo ed o all anspo ed quan i ies, allow- ing he use o moni o hei e olu ion as he simula ion p og esses. A simila se o moni o s o Cland Cdshould also be c ea ed o he same pu poses. The con e - 85 Figu e 27: De ail o he 2D mesh su ounding he SG6042 ai oil. gence c i e ia is ecommended o be he s abiliza ion o esiduals and pa ame e s o in e es [28]. 4.1.2 Resul s & Valida ion The es case comp ises a se ies o simula ions, each co esponding o a gi en angle o a ack and Reynolds numbe . The angles o a ack ange om -2◦ o 18◦. Due o empo al cons ain s, only e en alues a e submi ed o analysis. Bo h Reynolds numbe s o 1×106and 5×105a e conside ed. The o me de ines c uise condi ions whils he la e co esponds o expe imen al wind unnel es s condi ions [58]. Due o i s simplici y and eliabili y o simple ae odynamic calcula ions, XFLR5 is employed in o de o p oduce addi ional esul s ha may c oss- alida e he ones ob- ained om CFD simula ions. Again, es cases o Re = 1 ×106and Re = 5 ×105a e un, wi h he same a ia ion in angle o a ack (-2◦ o 18◦). The ai oil is disc e ized in 300 panels and he eN ansi ion c i e ia wi h Nc i ic = 9 is applied. The expe imen al esul s, displayed o alida ion pu poses, co espond o wind un- nel es s conduc ed by he Depa men o Ae onau ical and As onau ical Enginee ing o he Uni e si y o Illinois a U bana-Champaign [58]. Un o una ely, hese es s we e conduc ed up o a maximum o Re = 5 ×105and he e o e do no con empla e a ange o Reynolds numbe s ha encompasses he design condi ions. The au ho could no ind a ailable li e a u e ha con empla ed expe imen al da a o he SG6042 ai oil sub- jec o a Reynolds numbe o in e es . Ne e heless, he CFD me hodology is pu o he es agains expe imen al da a o Re = 5 ×105. Tables 24, 25 and igu e 28 display a compa ison be ween nume ical and expe i- men al da a. Conside ing igu e 28, one may obse e how S a -CCM+ esul s desc ibe 86 Table 24: Compa ison be ween expe imen al and compu a ional esul s o Re = 5 × 105. De ia ion o he la e om he o me is exp essed as a pe cen age. Angles in deg ees. AoA Expe imen al XFLR5 S a -CCM+ ClCdCl%Cd%Cl%Cd% -2 0.30 0.0090 0.32 6.7 0.0083 -7.8 0.24 -20 0.0071 -21.1 0 0.51 0.0068 0.53 3.9 0.0065 -4.4 0.45 -11.8 0.0067 -1.5 2 0.72 0.0073 0.75 4.2 0.0064 -12.3 0.68 -5.6 0.0073 0 4 0.93 0.0090 0.94 1.1 0.0078 -13.3 0.90 -3.2 0.0084 -6.7 6 1.10 0.0126 1.11 0.9 0.0115 -8.7 1.09 -0.9 0.0108 -14.3 8 1.25 0.0170 1.26 0.8 0.0155 -8.8 1.25 0 0.0145 -14.7 10 1.38 0.0220 1.40 1.4 0.0202 -8.2 1.37 -0.7 0.0214 -2.7 12 1.46 0.0305 1.50 2.7 0.0272 -10.8 1.44 -1.4 0.0321 5.2 14 1.50 0.0430 1.56 3.4 0.0396 -7.9 1.49 -0.7 0.0442 2.6 16 1.49 – 1.56 4.7 0.0609 – 1.62 8.7 0.0728 – 18 1.45 – 1.52 4.8 0.0952 – 1.20 -17.2 0.1800 – Table 25: Compa ison be ween expe imen al and compu a ional esul s o Re = 5 × 105. De ia ion o he la e om he o me is exp essed as a pe cen age. Angles in deg ees. AoA Expe imen al XFLR5 S a -CCM+ Cl/CdC3/2 l/CdCl/Cd(%) C3/2 l/Cd(%) Cl/Cd(%) C3/2 l/Cd(%) -2 33.3 18.3 15.9 19.1 1.5 -9.5 0 75.0 53.6 8.7 10.8 -10.4 -15.9 2 98.6 83.7 18.9 21.3 -5.5 -8.2 4 103.3 99.7 16.7 17.2 3.7 2 6 87.3 91.6 10.5 11 15.6 15 8 73.5 82.2 10.6 10.9 17.3 17.3 10 62.7 73.7 10.5 11.3 2.1 1.7 12 47.9 57.8 15 16.8 -6.3 -6.9 14 34.9 42.7 12.9 15.2 -3.2 -3.4 he an icipa ed beha iou o bo h li and d ag cu es. In ac , i can be seen ha , in he linea po ion o he Cl−αcu e and in he egion o minimum d ag o he Cd−Cl g aph, nume ical and expe imen al esul s co ela e qui e a ou ably, wi h no immedi- a e dis inc ion be ween bo h Reynolds. This poin s ou o he possibili y o ex apola ing esul s, i.e., i he CFD me hodology is success ully alida ed o Re = 5 ×105, i is sa e o assume ha , a he leas o he e e ed po ions o bo h cu es, i is also alida ed o Re = 1 ×106. In es iga ion o able 24 shows ha S a -CCM+ p edic ions end o unde es ima e 87 (a) (b) Figu e 28: (a) Li coe icien s angle o a ack and (b) d ag coe icien s li coe i- cien cu es o he expe imen al da a and bo h compu a ional simula ions a Reynolds numbe s o 1×106and 5×105. li and d ag while XFLR5 ends o o e es ima e li and unde es ima e d ag. In design, conside ing ha a ce ain amoun o unce ain y is e e p esen , a conse a i e ap- p oach unde p edic s li and o e p edic s d ag, he e o e es ablishing a sa e y ma gin. I is also obse able ha S a -CCM+ d ag esul s co ela e mo e a ou ably wi h expe - imen al da a, while ega ding li XFLR5 shows be e ag eemen . When conside ing bo h coe icien s oge he , in he o m o li - o-d ag a io and endu ance pa ame e , S a -CCM+ ou pe o ms XFLR5, as demons a ed in able 25. Figu e 29: P essu e coe icien dis ibu ion o e he SG6042 ai oil wi h AoA=0◦and Re = 1 ×106. The p essu e dis ibu ion o e an ai oil cons i u es an impo an pa ame e in a CFD alida ion p ocedu e [28]. P essu e coe icien alues, o bo h uppe and lowe su - aces o he SG6042 ai oil, ob ained ia compu a ional simula ions using S a -CCM+ 88 and XFLR5, a e plo ed in igu e 29. The e is an e iden esemblance be ween he esul s ob ained wi h bo h ools, a simili ude ha allows c oss- alida ion o bo h esul s. The exis ence o lamina sepa a ion bubbles in he p essu e and suc ion su aces o he ai oil is ep esen ed by each cu e (s eep a ia ion nea c=0.4 m), i.e., as expec ed, bo h nume ical ools a e able o cap u e such phenomenon. CFD esul s an icipa e and delay he loca ion o he LSB in he suc ion and p essu e su aces, espec i ely. The a ou able pe o mance demons a ed in p edic ing he p essu e coe icien dis ibu ion a ound he ai oil ein o ces he alida ion o he CFD me hodology o he Reynolds numbe o in e es . In ligh o he o egoing esul s, he es ablished CFD me hodology is conside ed alida ed and may be applied in p elimina y design analyses. 4.1.3 Applica ion o 3D Flow The wo-dimensional me hodology o me ly de ined can be applied o h ee-dimensional lows, i compliance wi h he ollowing ema ks is me [28]. Fo h ee-dimensional lows, he con ol olume is de ined as an hexahed on and one o i s aces co esponds o he wing (ai c a ) symme y plane. This de ail poin s ou he simpli ica ion o simula ing he low o e only hal o he body due o i s symme y abou he longi udinal axis. The emaining aces co espond o he a - ield bounda ies (inle , ou le , op, bo om and la e al bounda ies) and mus dis ance 60 cho ds om he e e ence objec . The physics model is cha ac e ized by a h ee-dimensional space model o p ope ly simula e 3D low. The hexahed on ace con aining he wing oo sec ion is de ined as a symme y plane and he la e al a - ield bounda y as a eloci y inle , wi h he eloci y di ec ion angen o he su ace. Fu he e inemen s a e equi ed in o de o gene a e a p ope 3D mesh. A cus om su ace con ol a ound he wing ip, similia o he one c ea ed a ound he leading and ailing edges, should be se , as well as a cus om olume ic con ol downs eam o he wing ip, necessa y o cap u e o ices ha a e shed in hese loca ions. The olume ic con ol e inemen is conduc ed up o 8 cho ds downs eam o he body, speci ying a cell size o 25% o he base size in he y-z plane (pe pendicula o he ai c a longi udinal axis). 89 4.2 3D Analysis: Wing Con igu a ion Pa ame ic S udy A he p elimina y design le el, he main wing is he objec o mo e e ined and eliable ae odynamic CFD simula ions, conduc ed in o de o de e mine he bes combina ion o geome ic pa ame e s ha will, ul ima ely, de ine i s ex e nal con igu a ion. The main goal o his p ocess is o p o ide a wing geome y ha maximizes endu ance, keeping in mind he inc ease in ae odynamic pe o mance agains he inc ease in manu ac u e and s uc u al design e o . Acco ding o concep ual design p edic ions, o c uise a 70 k s, he main wing is, by a , he majo con ibu o o he ai c a o al d ag, being esponsible o mo e han hal o i (app oxima ely 60%). I is also es ima ed ha oughly 78% o he wing d ag is li -induced d ag. This means ha 47%, nea ly hal o he ai c a o al d ag, comes om he main wing induced d ag, a s a is ic which is in acco dance wi h he d ag discussion pe o med in 2.2.3. In ligh o he o egoing da a, he e e ed pa ame ic s udy is conduc ed in o de o dec ease he main wing li -induced d ag componen . 4.2.1 Con igu a ion Layou Acco ding o equa ion 6, he induced d ag coe icien is a unc ion o he li coe i- cien , CL, aspec a io, AR, and Oswald e iciency ac o e. Fo a gi en se o c uise condi ions, he li coe icien is de e mined by he need o coun e bo h he ai c a o al weigh and nega i e li p oduced by he ho izon al ail. The e o e, i canno be changed wi hou adjus ing he mission equi emen s, WT O o im condi ions. Fo he cu en analysis, CLis ega ded as a ixed alue. Inc easing aspec a io is, on he one hand, bene icial in e ms o ae odynamic pe o mance, as i educes bo h he amoun o li los due o 3D e ec s and induced d ag. On he o he hand, i inc eases he wing weigh , which consequen ly agg a a es s uc u al and manu ac u e complexi y. Mo eo e , high aspec a io wings a e mo e p one o ip s all and, o cons an wing a ea, p oduce sho e cho ds, educing he likelihood o ansi ion om lamina o u bulen low. In he e en o bounda y laye sepa a ion, his is a d awback, as he low will no be able o ea ach o he su ace. Conside ing he p os and cons o inc easing aspec a io, a comp omise o AR = 12 was achie ed a concep ual design. Fo he pu pose o he wing pa ame ic s udy, his 90 pa ame e is ega ded as immu able. Acco ding o li ing line heo y, he ellip ic spanwise li dis ibu ion, ob ained wi h an ellipse-shaped wing, gi es he minimum induced d ag. The Oswald e iciency ac o measu es he de ia ion o he ac ual li dis ibu ion om he ideal ellip ic. The e o e, inc easing e, i.e., b inging he li dis ibu ion close o an ellip ic one, imp o es he o e all ai plane ae odynamic pe o mance [11]. Tape a io, λ, and wis angle, θ, bo h a ec li dis ibu ion and so a e ega ded as he a iables o he pa ame ic s udy. The s a ing poin o he op imiza ion p ocess is he ec angula un wis ed wing, wi h an aspec a io o 12 and a plan o m a ea o 3.67m2, ske ched a he concep- ual design le el. The plan o m a ea is de e mined by wing loading equi emen s and, he e o e, is conside ed a ixed alue. De ined as he ip cho d o oo cho d a io, he ape a io is ypically employed in o de o app oxima e he li dis ibu ion o an ellip ic li dis ibu ion by means o delinea ing a apezoidal plan o m shape. Fo unswep wings, ape a ios abou 0.4- 0.5 minimize CDi[11]. Pa ame ic s udies conduc ed a a concep ual le el show ha o a gi en angle o a ack, he endu ance pa ame e is maximized by ha ing a ape a io in he scope o 0.4-0.6. The wing wis , θ, is a combina ion o geome ic and ae odynamic wis . In o de o a oid unecessa y design and manu ac u e complexi y, he op ion o inco po a ing ae o- dynamic wis is pu aside, keeping he ai oil sec ion cons an . The esul ing geome ic wis se es wo pu poses: o p e en ip s all and app oxima e he li dis ibu ion o an ellip ic one. Tape ing he wing causes a ip cho d educ ion which, in u n, educes he ip Reynolds numbe , inc easing he likelihood o low sepa a ion and s all. Applying wash-ou (placemen o he ip ai oil a a nega i e angle compa ed o he oo ai oil) educes he angle o a ack o he ai oil sec ions loca ed nea he wing ip, he e o e p e en ing ip s all. Wash-ou also eshapes he li dis ibu ion due o he angle o a - ack educ ion nea he ip. I is, howe e , o impo an no ice ha op imiza ion o he li dis ibu ion by wis ing he wing is only alid o a pa icula li coe icien and is qui e a di icul and complex ask o achie e such op imiza ion. As a s a ing poin , a wis angle o -3◦, as ecommended [11], is selec ed o he ip ai oil incidence. I a ies linea ly along he span. In con o mi y wi h he o egoing discussion, he ollowing wing con igu a ions a e 91 5 Conclusions & Recommenda ions 5.1 Conclusions The objec i e which he au ho se ou o accomplish was he design o a class I e- mo ely pilo ed ai c a , in ended o ma i ime su eillance, wi h special emphasis on ae odynamics, ligh s abili y, ex e io design and ligh pe o mance, based on a se o mission equi emen s and pe o mance speci ica ions p e iously de ined. As a longe endu ance abo e he equi ed minimum was conside ed a key ad an age o he sys- em, signi ican e o was expec ed in o de o maximize his pa ame e . The ehicle i sel was mean o be buil a he Ai Fo ce Academy Resea ch Cen e , making use o i s acili ies and esou ces. The e o e, cos and easibili y issues cons ained he design om he s a , guiding he designe owa ds a necessa ily simple, ye eliable, solu ion. In compliance wi h he p ojec demands, an ex ensi e li e a u e e iew o unda- men al concep s conce ning h ee majo a eas was pe o med. The i s co e ed he subjec s o design, pe o mance and ae odynamics. The ai c a design p ocess was desc ibed, ligh pe o mance pos ula es ega ding in e es a eas o he cu en de- sign we e p esen ed, ae odynamics o iscous lows was succin ly discussed and an o e iew o d ag componen s and i s educ ion echniques conduc ed. The second pa co e ed he undamen als o he compu a ional app oach o design, ocusing on XFOIL, o ex la ice me hod and compu a ional luid dynamics (CFD). Ul ima ely, he s a e-o - he-a o emo ely pilo ed ai c a s design was discussed, explo ing he bene- i s and d awbacks o di e en con igu a ions and culmina ing in a ma ke esea ch. Chap e 3 p o ided a de ailed desc ip ion o he ai c a ’s concep ual design. F om ea ly concep gene a ion, selec ion and ini ial sizing, ollowed by he design o he main wing, uselage, ail su aces and e ined weigh , s a ic and dynamic s abili y analysis, inishing wi h a pe o mance check, he i s o he h ee majo phases o ai c a design was ho oughly sc u inized. The sp eadshee app oach p oposed by Thomas Co ke [10] se ed as he p ima y design ool, guiding he au ho in a s ep-by-s ep me hod ha allowed an in ui i e and o de ly ai plane build-up. Whene e possible and app o- p ia e, ele an in o ma ion om o he li e a y sou ces, namely [2], [11], [14], and om XFLR5 calcula ions was added and inpu ed in o he sp eadshee s, complemen ing and enhancing he design. 98 By he end o chap e 3, concep ual design was comple ed and a lyable ai plane, capable o ul illing he mission equi emen s and pe o mance speci ica ions was p o- jec ed. The au ho poin s ou he ac ha no s uc u al analysis we e conduc ed as such was no in he scope o i s wo k, being assigned o a di e en designe . In chap e 4, p elimina y design was ini ia ed. Based on he bes p ac ice guide- lines [28], a solid me hodology o CFD analyses was es ablished and employed in h ee-dimensional simula ions o a ious ai c a componen s. The nucleus o p elim- ina y design was a pa ame ic s udy o he main wing o longe endu ance. Resul s demons a ed ha , om an ae odynamic poin o iew, he ape ed and wis ed wing p o ided he bes pe o mance. Howe e , since he ac ual inc ease in endu ance was no signi ican and such con igu a ion esul ed in a conside able inc ease in s uc u al and manu ac u e complexi y, he ec angula un wis ed wing p e ailed. Subsequen ly, he e ical s abilize was subjec o analysis in o de o de ine i s inal plan o m – un- wis ed ape ed su ace. The inal design e o g adually inco po a ed he main wing, ho izon al and e ical ail su aces in o one simula ion, accoun ing o downwash and endpla e e ec s and ixing he ho izon al s abilize ’s incidence angle o gua an ee im a c uise condi ions. The objec i es ini ially ou lined we e all success ully comple ed. Concep ual design is consumma ed and impo an s eps ha e been aken in he p osecu ion o p elimina y design, which is no ye inished. The au ho enhances he bene i s o being able o go beyond he ini ial goals and p o ide aluable in o ma ion o he emainde o he cu en p ojec . 5.2 Recommenda ions The wo k de eloped in he cou se o he p esen disse a ion ep esen s a no ewo hy s ep owa ds he comple e design and de elopmen o a class I emo ely pilo ed ai c a o he Po uguese Ai Fo ce. Howe e , impo an asks emain unaccomplished as empo al and equipmen esou ces a ailable we e limi ed. Al hough he main wing pa ame ic analysis ailed o p o ide conside able ae ody- namic ad an ages, he ai c a o al d ag can s ill be educed, and he key ad an age o a longe endu ance achie ed. Such may be accomplished wi h he in oduc ion o wing- ip de ices such as wingle s. CFD analyses ha e o be pe o med in o de o assess 99 he in luence o such de ices on he o e all ai c a d ag, and he e en ual ae odynamic bene i s o hei inco po a ion mus be balanced agains he d awbacks o inc easing weigh , s uc u al and manu ac u e complexi y. O he measu es such as he use o i- ble s and educ ion o he su ace oughness can also be employed o educe pa asi ic d ag and imp o e ae odynamic pe o mance. CFD analyses o he low o e he ehicle a c uise condi ions we e pe o med, in which he main wing, ho izon al and e ical s abilize s we e modeled, he e o e ep- esen ing he ai c a . The emaining componen s should be g adually inco po a ed in hese analyses in o de o p o ide a mo e ealis ic ep esen a ion o he ac ual ai - plane. The p esence o a uselage unde a speci ic sec ion o he wing esul s in an ac ual lowe li coe icien which in u n causes i s incidence angle o be highe han ex- pec ed. The same e ec occu s o he ho izon al ail. As such, including he uselage should be he nex mo e as i would allow o a mo e p ecise es ima e o he equi ed angle o incidence o he main wing and ho izon al ail. A e ha , he emaining com- ponen s such as landing gea s u s and wheels, p opelle and ex e nal payload should also be modeled. Pe o ming a ull-con igu a ion analysis is pa amoun as i p o ides insigh in o he low ield phenomena ha cha ac e izes c uise ligh and yields a mo e p ecise es ima e o he ai c a o al d ag, li and pi ching momen . Fu he mo e, he au ho sugges s using CFD as a ool o de e mine he ae ody- namic de i a i es o s abili y, conside ing all h ee di ec ions o mo ion, as well as o model he con ol su aces and enhanced li de ices (aile ons, ele a o , udde and laps) and de e mine he ae odynamic de i a i es o con ol. Ideally, CFD should be complemen ed wi h expe imen al wind unnel es s. How- e e , he au ho is awa e o he inhe en di icul ies o he la e in he Po uguese Ai Fo ce due o he lack o a ailable quali ied pe sonnel. I he o me ecommenda ions a e ollowed and he emainde o he design eam is able o p o ide an accu a e, compu a ional, ini e-elemen based, s uc u al analysis o he comple e ai c a , p elimina y design may be conside ed accomplished. De- ail design mus ollow, wi h he iden i ica ion o each and e e y componen and sub- componen o he ai c a , and he in eg a ion o all sys ems and subsys ems. The inal ou pu mus be a se ies o d awings de ailing he in e nal and ex e nal layou o he ai plane, which by hen can be assumed eady o manu ac u e. 100 Re e ences [1] BARNHART, Richa d K. [e al.] – In oduc ion o Unmanned Ai c a Sys ems. Boca Ra on: CRC P ess Taylo & F ancis G oup, 2012. ISBN 978-1-4398-3520-3 [2] GUNDLACH, Jay – Designing Unmanned Ai c a Sys ems: A Comp ehen- si e App oach. Res on: Ame ican Ins i u e o Ae onau ics and As onau ics, Inc., 2012. ISBN 978-1-60086-843-6 [3] CORNELL, Doug [e al.] – Wo ld Mili a y Unmanned Ae ial Sys ems: Ma ke P o ile and Fo ecas , Teal G oup Co po a ion [Online]. 2017. Up- da ed 08 No . 2017. [Acessed 25 Jan. 2018]. 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