NASA research on viscous drag reduction

NASA Technic a l M emor a ndum 84518

t NASARESEARCH ON

I VISCOUS DRAG REDUCTION -_

NASA-T M -84518 19820025468

RICHARD H, PETERSEN

AND

DAL V, MADDALON

AUGUST 1982

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LANGLEY RESEAR, ' : . H ]I.:r,JTER LIBRARY, NASA HA,_._PIOhl, VIRGINIA

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National Aeronautics and

Space Administration

L a ngley ResearchCenter

Hampton, Virginia23665

N AS A R E S EA R CH O N VI S COU S D RAG R EDU C TIO N R . H. P eter s en and Dal V . M a ddalon N ational Aeronauti c s and Sp ace Ad minist r at i on Lan g l e y R e se a r c h C e nt e r Ham p ton, Vir g inia Abstract Current NASA resea r ch po i nts to w a r d excitin g S up e r 80 , and th e A- 3 10). Fo r all such aircra f t, oppo r tuniti e s fo r lar g e redu c tions in viscous ho we ver , th e present stat e -of-th e -art is fo r d ra g. R e s e a r ch is und erw a y on n a t u r a l l a m i n a r ai rpl a ne des igns b a s e d on t u rb ul en t f l o w wit h f low, la m inar fl o w con t ro l b y suc t ion , and the att e ndant pena l t y f o r viscous d r ag.

t u r bulen t d ra g reduction. P r eli m in a ry r esu lt s sugges t t ha t a signi f icant a m ount o f n a t u r a l Viscous d r ag re pr esents ap pr oxi m a t e ly ha lf o f l a mina r f low can b e achiev e d on small, s tr aight- th e to t a l d r ag and f u el bu r n f o r a l ong- r ange w ing a i rpl an e s . On l a r ge r , s w e p t- w in g a irc r a ft , co mm e rc ia l t r a ns p o rt ai r c r a f t and r esults in la m in a r f low con t rol b y dis tr ibu t e d suc t ion i s about a t h ird o f its di r e ct o p e r a t ing cost.

e x p ec t ed t o r e su lt in significan t fuel savi n gs. A c hi e ving a ll - l a m ina r f lo w on suc h an ai r c r a f t The a r ea ove r which lamina r f lo w con t r ol I s w ou l d r e duc e viscous d r ag b y nea rly 9 0 % , f uel applied de pe n ds o n tr adeo ff s invo l vi n g s t ructu r al b u r n e d al m os t 4 5% , an d direct ope r ating cost co m p l exi ty , m aintenance, a n d cos t. S e v er a l a bout 27 %.

met hods o f reduci n g tu r bule nt s k in fr iction by alte ri n g t h e t urb ulence s tr ucture i tsel f ha v e Mil i tar y t r ans por t ai r c r a f t w oul d show the sho wn p ro mi s e i n ex p lorator y testi ng . T his sa m e dra g and f u el re ductions t but less r elati v e pa p er re vi ews the status o f these t echnolo g ies cost sa v i ng s. Fo r m ilitar y aircr a f t, lamina r and i nd icates the bene f its o f app lyin g them to f lo w o ffe rs the ad v anta ge o f tr e mendous increases f utur e aircra f t, in rang e a nd pa y load capabilit y (I).

Introduction NASA res p on d ed t o the i ncreas e d f uel p r i ces b y g i v i ng m uch m or e emphasis to research w hich F r om 1 96 0 t o 1 972, j et fue l p rices p a id b y i mp roved ai r cr af t f uel consu mp tion ch a rac t eris - U.S. a i rl i nes w ere n ear ly cons t ant at about 1 0¢ tics. Pa y o f fs f rom such res e arch we re identi fi e d p er g allo n . A f ter the Arab oi l embar g o o f 1 973 , in reference s 2 and 3 . T hrou g h the Aircra f t ho we ver, domest i c f uel prices increased b y o ve r E ne r gy E ff icie n c y (A CE E) Pro gra m, NASA f ocused a n order o f magnitude to th e p rese n t le v el o f a i rcra f t f uel conse rv at i on technolo gy de ve lo p m en t abou t $1.O 5 ( f i g . 1). Du r in g this ti me , t he in the d isci p lin e s ci en ces o f a e rod yn amics , annu a l U.S. airlin e f u e l bill rose f rom 1 billion s t ructures, mate r ials, controls, and p ropuls i on( 4 ) do l lars to over 11 billio n dollars. T h e p ercent - - an d much wa s acco mp lished wit h this pro g ram.

of a irli n e direct o p e r ating cost du e to f ue l Ho we ve r , it is e x p ect e d that fuel prices w i l l i ncreased f rom 2 4% t o a s t a gg erin g 6 0 % a nd conti n ue to increas e in the f uture and there is ine v ita b l y f a res - - on avera g e - - rose. T h e stil l a lot that c an be don e . W e there f or e p lan i mp act o f these cos t i n creases has be en s igni f l- to b u il d on our pre v ious effo rt s in thes e basic ca n t. Maj or cha ng es occurred in th e k i n d o f dlsclpl l nes. T his pa p er w ill co v er NASA research airline ser v ice o ff er e d. M or e seats w e r e a d de d in j u s t one area, that of v isco u s d r a g reduction.

to airc r a f t, fare in ce n tives wer e g i v e n to H e re , p articula rly , cu r r e nt eff orts indicate i n cr e ase ai r pla n e us e , desi g n ra nge wa s bet ter exci t in g possibiliti e s f o r l a r ge dra g reduct i ons matche d to route s tr ucture, a n d dr a g clea n u p b ecause of technolo g ical ad v ances in , f or exa m p le, o p erations w er e p e r f o r med w herev e r p ossible, new m a t er i a l s, f a br icatio n techn i qu e s, sta b il i t y A maj or im p r o v e men t i n fu e l ef f icienc y re su l te d theo ry , a n d airfoil a n d w in g desi g n m ethodolo gy .

w ith t raf f ic Increasin g f rom 162 b i l l ion S pe ci f ic a r e as o f r e se ar ch to b e addressed are p a ss eng er miles per y ea r in 197 3 to 254 bill i o n nat u ral, la m inar f lo w , suction - co n trolled l a minar passe ng er miles per y ear In 1 9 80 w hile f u e l burned flo w , and turbule n t s ki n fr i ct i on reduction.

in m o v ing this tra ff ic w as re d uc e d fro m a b out This pa p er re v ie w s the status o f these technolo- 10.7 m i ll i o n g a llons annu a lly to only 10.2 g les , how the y mi gh t be i n t egr ate d i n t o air c ra f t , m i ll i on gallons, y i eld i ng a 65% i mprovement in the and the potent i al benefi t s that mi ght be passenger m il es obtained per gallon of fuel used. realized.

Further i mprove m en t s, however, depend pr i mar i ly , on vehicle and sys t em te c hnology advances. Dis cussion A i rl i nes res p onded b y placing orders for an e n t i re ly n e w gen e r a t i o n of fu e l -e ff icl e n t j et Background . _ transpor t s, t he. 767 and 757 . The 767 begins F i gure 2 displays the fue l eff ic ien c y that ; ; s c heduled servl c e th i s year and the 757 enters might b e attained on a 1 990 te c hnology le v el , servi c e in early 1983 . In addi t ion, many new four-engine, long- r ange transpor t airplane. T his " f u el -e ffl c l e n t models of existing ai rc r a f t we r e ref e ren c e a i rc r a ft is f a bri c at e d o f c ompo s i te (or will be) in t roduced (i.e., L-lOl l -500, DC-9 materials, utilizes super c ritl c a l airfoil technolo gy, h as an aspe c t ratio 12 w in g_ a nd acti v el y re s earching t h ese p o tential ba rr iers to uses an a c tive control system featuring relaxed laminar flo w flight.

static stability. It is deslgned to carry about 5 00 passengers and 43 ,0OO pounds of cargo to a Natural Laminar Flow ra ng e o f about 5000 n.mi. A ircra f t character is- a n dNatura /d la m inars _l_Ww (N LF) In w i n t unn e l as b oth i n fl i gh t (6 ) tic s are su mm ar i zed in Tab l e 1. The result i ng ( 7 ) ach i eved over 35 years sea t - m ile s p er gallon (smg) a t c ru i se i s about ago under very l i m i te d c ond i t i ons on c e rt a i n 11 2 , al m o s t double t he 60 smg possible w it h a i rfo i ls. W i nd tunnel tests yielded t rans i tion c urren t long-range a i r c raft. Als o shown i n Reynolds nu mb ers as h i gh as 14 m i ll i on(7) for f i gure 2 i s the perfor m ance poss i ble wi t h the natural l a mi nar flow, under essen ti ally ideal 1990 a ir pla n e i f l a min ar f l ow coul d b e at t ai n e d co nd i tions of w ing smo oth n es s , t w o - d im e ns i onal o v er al l of th e aircraf t' s surfaces. Such an f low ( n o cr o ss - f l o w disturb an ces), fav o r a ble a l l -l a mi nar ai r pla n e wo uld a chieve 2 25 s mg , a pr e ssure gra d i ent, a nd ve r y l ow tu nn e l t urbu l e n ce 275% i n creas e o v er the base airc r aft ' s perf orm - le v e l . H o w e v er, exte n si v e re g io n s o f n atura l a n te and a 10 0 % i n cr ea se o v e r the 1990 a dv an ced la m inar f l ow w e r e ne ver a chie v ed o n gen e r al tech n o l og y ai rp l an e, a v iatio n o r tran s po rt a irplan e s In routi ne oper ati on s bec a use o f the pra ctica l c on st r ai n ts Attai n me n t o f la m inar bou n dar y l a y er f low in of l ar ge Reyn olds numb e rs, hi g h s peed, an d rou g h da y- to - da y airp l a n e operati ons w ith th e r e s ult i ng w i ng f i n ishes. Th e w i ng size and the swe ep a ngl e reducti o n in s k i n fricti on has long bee n th e ass o ci a ted w ith a mod er n tr an sp o rt air p la n e m a y dre am of the ae rod y nam i clst. To app reciate th e p reclud e ex te n siv e u s e of NL F o n such a ircraft po tential p rob l e m s associated w ith this v e ry i n the f o r eseeable f uture. G en era l aviation di ff icul t tas k, co n sider the ph y sic al par a meters b usi n ess an d c omm ut e r a irc r a f t , h ow e v er , ar e much w hich af f e ct la mi nar f lo w . Fi g ure 3 l ists the s m a ll er and usu ally fr ee o f c omp le x l ea d i ng- ed g e m o s t im p o r tant. Mo s t fu n d amen tal , o f c o u rs e , i s fl a p s. Fur t he r, ge ner a l av i a ti on aircr af t the R e yn o l ds number at w hich l a m i n ar f lo w b e co me s t yp lcall y fl y at low er s p eeds a n d do not require turbu l e n t, the de g r ee of w i ng s w ee p use d, a n d the the l ar g e w i ng s w eep a n gl es w hich ca n i n tr o duce air f oi l g eo me tr y . If v e lo cit y and al titu de a re c ross-flow i ns t ab i l iti es and s pan-w i s e c on t am i - c on st ant , the larger the a i rplane -- the higher nat i on. Achiev i ng NLF on such a i rcraft is the Reynolds numbe r , and the m ore diff i cult i t is therefore greatly s i mpl i f i ed . Furthermore, to keep flow lam i nar over a s i gnif i cant par t of compos i te materials have already been i ntrodu c ed i ts chord. If the alrplane i s also des i gned for i nto general av i at i on a i r c raft on a lim i ted basis.

high speed, we i ght considerations usually Such mater i als offer surfaces wh i ch ar e very d i ctate tha t the wing have a s i gnif ic an t degree smooth and wh ic h may eventually offer low of swee p -- thus g r eatly compl ic ating the bas i c m anufa ct uring c osts. These air c raf t are pro mi sing task of preventing trans i t i on. Sweep i ntrodu c es cand i da t es for NLF appl i cat i ons.

cross-flow boundary layer d i s t urbances that may a mp l i fy, i ntera c t w i th T ollm i en-Schl i cht i ng Recen t development of im proved NLF a i rfo i ls at waves, and c ause trans i t i on. Airfo i l geometry Langley has led to a new look at NLF t echnology ( 8 ) .

de t erm i nes the extent of the favorable pressure Elements of the NASA N LF fl i g h t program(9) are grad i en t and suct i on requ i rements needed to help i llustra t ed i n f i gure 4. During 19 8 1 and early stab i l i ze boundary layer fluc t uations. I deally, 1982, test flights were made on the follow i ng new l amin a r flow wing d e sign s should a c hieve d r ag air c raf t: T-34 C (mo d if ie d), V ari-Ez e , Long-Eze, divergen c e Math numbers a t tainable w i th turbulent a biplane ra c er, Skyro c ket II, Beech Sierra , sup e rcrl t l c al wlng technology. A t the pr e s e nt C essna P-210, and a Learj et . For most airplanes, time, howev e r, little i nformation is available transition was detected by use of sublimating for appli c atlon to pra c ti c al transonic laminar c hemi c als su c h as naphthalene , dipheny], flow air c raft wings. NASA is comm i tted to a c enaphtene, and fluorene. These c hemicals providing s u ch fundament a l data. evaporate as a fun c t i on of lo c al sh e ar stress and heat transfer thus providing a visual New air c raft stru c tures su c h as graphlte-epoxy indi c ation of laminar flow breakdown.

c omposite mater i als offer the promise of airfoils of nearly perfe c t shape, toleran c e , and smoothness Natural ]aminar flow flight tests on two at reasonabl e c ost. When su c h stru c tures are c anard c onfiguratlon s (Vari-Eze and Long-Eze) fabri c a t ed or undergo deformation under load, showed large ef f e c ts on a i rplane performanc e and surfa c e d e viations must b e kept small to)prevent stability and c ontrol when laminar flow was lost.

the o cc urren c e of lo c a] pressure waves (5 whi c h Wind tunnel tests with simulated rain on one c an c ause trans i tion. Leading-edge roughness c anard airplane (Var i -Eze) c onfirmed lo s s of c aused by con t aminants su c h a s insects, dirt, laminar flow due to ra i n. Future flight tests on erosion, or forelgn obje c t damage must be minim i zed smooth airplanes capable of supporting laminar or turbulen c e wlll result. Su c tion systems used flow should therefore in c lude fixed transition t o s t abllize a i rplan e boundary layers t yp lc ally t es ti ng as well as fr e e t ransi t ion te s t s . Finally, have very flne surfa c e openings that must be easy tests on one c onf i guratlon (Skyrocket II) showed to c l e an and repair while also resistant to extensive laminar flow in the propell e r sl i pstream.

c logging and c orro s ion. Nois e from the propulsion sys t em c an amplify bo u nda r y l ayer dis t urban c es Max i mum t ransi t ion Reynolds number observed " and c au s e prematur e transltlon. Finally, was about II m l ]lion (fig. 5), an expe c ted result atmospheric c ond i tions c an profoundly influen c e to resear c hers familiar w i th the early work on the performan c e of a fleet of a i r c raft designed smooth wlngs(7) but nonetheless a dramat ic for low vls c ous drag -- sin c e these air c raft s urprise to those who h ad always a s sumed turbulent would operate throughout the world at a variety flow (based on exper i en c e with rough aluminum of altl t udes and weather c ondition s . NASA is now wings). The signifi c ance of this work is that it d em o n s t r a t es that NLF c an i nd eed be ob t a ine d in e nabl e d by th e v e ry larg e re duc t ion i n s k in fligh t on mod e rn produ ct lon quali t y air c raft f ric tion drag . LFC, the r efore, c an pr ov i de wings, for th e c ase of low Reynolds number, m ajor benefi t s in re d u c ed fuel use, lower smooth wing, lo w cros s-f low d isturba n ces, to a oper a ting costs , a nd i n creased range -- a s .

chord location o f about 3 0 -50% in a f avorab l e shown in NASA - sponsore d indu s tr y stu d ies(! 5 -17 ) pressure g radient.

The technical validit y o f a l amlnar f l o w W e plan to extend t hese studies b y m e a s urin g contro l (L F C) s y stem has been demonstrated in transit i on location s on a NLF g l ove in s tal l ed both wind tunne l s a n d f light, the mos t notab l e on the T -34 aircra f t wing usin g thin f i lm g age s examp l e being the X - 2 1 re s earch program con d ucted to correlate the t r ansi t ion result s with the betwe e n 196 2 and 1965 (18 - 2 3 ). This ef f ort was chemica l tests. A s tud y o f sev e ra l di ff e r ent terminate d b ecau s e th e Air Fo r ce had more urgent typ e s o f porous l eading edges (p e r f orat ed prio r ities an d l ack ed an aircra f t program that ti t anium and co m po s ite s ) which can both we t and requi r e d thi s technolo gy . F urthe r , at that tim e , de - ice th e air f oi l s ur f ace wil l al s o b e done in f uel w a s r ea di ly a vailab l e and o f low co s t. In t h e L ang l e y Research Center L ow Turbu l ence 1965 , the ma in technical problem was th e P ressure Tunnel and the L a ng le y 4- by 7-M eter di ff icu l t y in achieving and maintaining ver y T unnel . The la t te r te s t s will de termine I f s m oo th su r fa c es bet w e e n m et al j oints a n d gaps .

na t ural la mi nar flo w can be retalned after Today, ne w mater i als and fabr ic a ti on t e c hniques inse ct s imp a ct the w e t m odel surfa c e , an m ake th i s c ons i dera b ly eas i er . Many te c hn ic al im portant c onsidera ti on s i n c e residue result i ng p ro b le m s w ere resolved du ri ng t he X-21 tes t s .

fro m bug im pa c t w it h an a i r c raft's lead i ng edge After several years of d i l i gent effo rt, lam i nar c an c ause an effe c t i ve roughness w h ic h t r ip s the flo w w as repeatedly a c h i eved over almos t all of boundary layer and i n iti a te s a " w edge" of the i ntended lam i nar upper wi ng area(24 ) t o t urbulen t flow. Fu t ure i nvest i gation of p r o p eller Reynolds numbers of about 20 m i llion. Lam i nar sl ip str e a m effe ct s a r e planned, as are s t ud i es flow w as also a c h i eved on a non- r out i ne bas i s t o to deter mi ne the pra ctic al u p per Reynolds nu m ber Reynolds nu mb ers as h ig h as 47 m i ll lon. The m a i n l i m it for a c h i ev i ng lam l nar flo w on m odern p roble m i n re t a i n i ng la mi nar flo w was t he produ ct lon quali t y wings. Stud i es of pass i ve i n c rease d importan c e of surfa c e r oughness a t these surfa c e coa t ings to pro t e c t NLF lead i ng ed g es h i gher Reynolds numbers. T he span wi se c ontam i - are also planned , nat i on problem w as i den ti f i ed and largely resolved ; the solut i on be i ng to su c k t he leadlng In add iti on, an i ni ti al fl i ght i nvest i ga ti on edge and / o r m i n imi ze the lead i ng edge rad i us .

of the effe ct of s w ee p on natural laminar flo w Unresolved at the t im e t he X-21 w as c an c elled has been re c en t ly a cc ompl l shed wi th a "glove" w as the e c onom ic feas i bil i ty of an LFC syste m a i rfo i l m oun t ed on a var i a b le-s w ee p F-111 i n c lud i ng unkno w ns such as syste m rel i abil it y, alrpiane(lO ) . Resul t s i ndi c a t e that extensive m a i n t enan c e requ i re m ents, and c os t . NASA's r eg io n s of na t ural lam i nar flo w c annot be effor t s i n resolv i ng t hese un c ertain ti e s began ob t aine d for lead i ng-edge wing s w eeps g r eater i n 1976. We have studied the aero d yna mic s, t h a n ap p roxl m a te ly 16 degree s. L i near boundary- mater i als, stru c tures, systems, and o p erat i onal layer s t abll it y theory i s c urren t ly being appl i ed proble m s asso ci ated w i th a lam i nar flo w c on t rol t o thes e da t a i n orde r to quant i fy the effe c t on syste m . Re c en t progress has been i mpress i ve.

posi ti on of transl tl on of the i ntera cti on bet w een c ro s s-flo w i n st abll lti es due to s w ee p and Stab i l i ty c odes have been developed(25&26 ) , Toll m eln- Sc hl ic h tl ng i nstabil i t i es . Quant i f i ca- c o m pared to exper i men t s(26), and found to t lon of t hi s In t era ct ion effe ct i s the key t o a c curately pred ic t boundary layer flu c tuat i on natural laminar flo w wi ng des i gn and must be gro w th. An advanced LFC a i rfo i l i n c or p ora ti ng ba s ed on exper i mental data. Plans are be i ng the latest super c r i ti c al te c hnology has been made to obta i n t he required add i t l onal data . des l gned (26) and i s no w be i ng tested i n the Langley 8-Foo t Transon ic Pressure T unnel Lam inar Flow Control (f i g. 7). T he a i rfo i l des i gn p ressure d i str i bu- Na t ural la mi nar flo w m ay not be pract i cal on t i on per mit s a drag d i vergen c e Ma c h numbe r m odern lon g -range transports ex c e p t for l imi ted c omparable to tha t obta i ned w i t h t he latest ap p li c at i ons su c h as the outboa r d wi ng region su p er c r i tl c al tu r bulen t a ir fo i ls. S i gn i f ic ant and lo w Reynolds number ta i l reg i ons. To reg i ons of super c r i t ic al flo w wi ll ex is t on the a c h i eve extenslve reg i ons of la mi nar flo w on up p er and lo w er su r fa c es. The lea d ing edge has tr anspor t a i r c raf t chara c ter i zed by large s i ze, a small nose rad i us wh ic h helps to stab i l i ze Reynolds numbe r , and wi ng s w eep , a su c t i on syste m boundary laye r c ross-flo w d i sturban c es and r edu c e Is required to re m ove a small part of t he a i rfo i i's the amoun t of su cti on n eeded . The m odel ( f i g . 8) boundary layer . Par ti al boundary layer removal has a 7 . 07-foot c hord, 23 degrees s w ee p , a s t ablllzes (redu c es di sturban c e gro w th rate to th i ckness rat i o of 13%, a des i gn po l nt ch ord an a cc ep t able level) the boundary layer and keeps Reynolds number of 20 mi ll io n , an d a p red ic t ed It l a mlnar (fig. 6 ) . T he LFC con c ept is llft c o e ff icie nt of 0.55 at th e d e sign H a ch appli c able to all a i rplane surfa c es , but w ork to number of 0.755 (normal to the lead i ng edge ) .

date has generally been l i m i t e d to studies of A flap extends over the rear w ard 10 . 9% of t he wings. V i rtually all ava i lable reports on LF C c hord (for pressure d i str i but i on c on t rol at off- c an be found in referen c es 11-14. An LF C syste m des i gn co nd i t i ons) . Span w ise su c tion sl o ts range requires a p erforated or slotted surfa c e , i nternal from 0 . O025 to 0.006 in. in w i d t h, and are du c ting to su c k alr from diffe r ent se c tions of spa c ed 0 . 12 to 1.7 In. apart. Slots c over nearly the airfoil, and a c ompressor to expel1 the air. all of the upper surfa c e and about 85% of the S u c tion p ow er req uir ement s a r e s m all c o m pa r ed to l ower su r fa c e, and c an be i nd iv id u a ll y the redu c ti o ns obtained in propulsive power c ontrolled.

Th e t un n el w all has b ee n fai r ed w i t h a line r d ia m ete r and structu r a l co nf i g u r at i o n a r e s i mi l a r that produce s an in f i n ite s we pt -w in g fl o w over to that o f the pre v ious ly d i scussed w i n d - tu nn el the m odel s urf a ce( 27 ). E xtens iv e fl o w qual i t y mode l . T he D A C s y ste m uses a K rue g er flap as im pr o v eme n t mo d ifi cat i o ns to the tun nel p le n u m b o th a hi g h - li f t de v ice a n d a bu g sh i e l d. T he cha m be r i n clude the a dditio n o f a h on e y c om b fl a p has a built - i n s p ra y n o zzle for w ash i n g and scree n a n d f i v e w ire m esh screens that reduc e de ici ng . T his l im its LF C to the u pper surface th e tunne l t u rbu le n c e le ve l t o appr ox ima t e l y of th e airfo i l (which a ccoun t s fo r nea rly two - .05 % . A two -w a l l cho k e betwee n the mo d el a nd thirds of the w in g dr ag ). Suction s y st em s f or d i ff us er pr ev ents d i f fu s er no i s e f r om pro pag ati ng both gl oves a re lo c a ted e n tirel y a he a d o f the upstream and trip ping the m o del bou n d a r y l ay er, w i ng box. T he suct i on s y stem was no t extended T e sts wi ll d e te rm i ne the ef fe ct o f fl o w qua l it y , i n to the wing b ox ar e a t o keep c o st a nd c o m ple xit y o p ti m u m suct i on a r ran g em e nt , unit R e yno lds number , l o w. Howe ver, the p rimar y pr ob l ems w lth a LFC fl ap an gl e , an g l e o f a tt a c k , an d rou g hne ss , s y s tem o ccu r in th e lea di ng ed ge r e g ion.

I n iti al te st r e sul t s on t h is model w er e ob t a i ned earlier this y ea r . Fl i g h t t es t i ng w i l l beg i n i n 1 983 w i t h i n iti a l re su lt s a v a il a b l e a b o ut l a te su mmer 1 98 3. T h e W he n the tests on th e slot t e d m o de l a re ob j ec t i v e is t o d e m o n strate the e ff ecti v e n ess co m p l e t e i n e a r ly 198 3, th e u pp er su rfa ce o f o f le ad i ng-e d ge L FC s y ste m s i n m ai n tai n i ng the m od e l w il l be r ep l a c e d w ith a p e rf o ra t e d l am i na r f l ow u nde r co n di t i o ns of v a ry i ng we ather( 34 ), tita n iu m sur f ac e ( f i g . 9 ) fabr ic at ed by t h e g e ogr aph i ca l l o c at ion , an d alt i tude -- to p rov ide D ou gl a s Airc r a ft C o mpany ( D AC). T h e po rou s th e o pe ratio n al da ta ne e de d f or f ir m ana l y sis of de si gn i n cor po rate s el ect r o n beam d r i l led hole s th e e x t re m es e n cou n t ered in a ctu a l a ir l i ne se rv ice w ith dia m eters o f a p pro xi m a t e ly .002 5 i n . a t ( f i g . 11). T wo hu n dred hours o f f li g ht tests a re th e s k i n sur f ac e and t w ic e tha t a t th e b a c k p l ann e d . Such dat a w ill pr o v ide a si g nifica nt of t h e .0 25 in. t hic k s k i n . Ho le s a r e s pa c e d par t o f th e e s sen ti al i n f o r ma tio n about LF C fl i g h t a b o u t .02 5 i n . ap art. A f i be r gla s " hat " s ys te m s th a t cou ld n ot be o bt a ined duri ng the st ru ctu r e s u ppor t s th e porous skin and blocks X-2I f l ights.

abo u t one - t hird o f the suctio n hole s . T h e m o d el c an ther e f o r e be m ore a ccur ately T o dat e , the N ASA LF C p ro g r am g i v es p rom ise de scrib e d a s a por ous "s tri p" s uctio n des i gn , t h a t th e la t e st st ruc t ur a l and m a t eri a l techn o lo gy E a ch po r o us stri p is app roxi m a t el y 1 i n . w id e may b e us ed t o b uild L F C struc t ures u t ilizi ng (ch ordwl se), I n fu t ur e t e s ts i n the 8-F o o t de s ign an d p ro d ucti on t e ch n iques app lic ab le to Tu nn e l, we ex pe ct t o r epl ac e the s e an d other m od ern a ir plane pr oducti on l i ne s. F l i g h t q u al it y parts of t he model so t ha t w e c an c onduc t t e s t s proto t ype hardware has been buil t . Un c er t a i nt ies of n a tur a l l a minar flow conf i gur a t ions, hybr i d reg a rding LFC applica ti on to a t ran s port aircraft laminar flow airfoils, diff e rent nose shapes, wing which r e volve around the l ong -ti me LFC a nd surf a c e roughness. Other w i nd- t unne l t es t s questions of re a l - wor l d reliability, m a i n t enance , to be c ondu ct ed during 198 3 in the Langley 4- by and cos t will be largely answered by t he LEFT 7-Me t er Tunnel will de t erm i ne the h i gh-l i f t fl i ght tests conducted under operatlonal a irl i ne characte r istics a nd re q uire men ts of LFC c on di t ions.

a i rfo il s ( 26 ).

Ap p licati o n of a l am inar fl o w contr o l s y s t e m Und er N ASA cont ra cts, new structural to t he wi n g and tail of a 1990 t ra n s por t a ir plane co ncep ts sui tab l e fo r actu a l ai rcra f t wi n gs would dramatica l ly i mprove t h e se at mil es obtained have been designed, built, and tested. A per gallon of fuel used. Figure 12 shows an slot t ed skin(28) has been developed by the improvement of 25% to 140 smg. Thes e calculat i ons Lockheed-Georgia Company (GELAC) and the same assume either a slotted or porous suction surfa c e has been accomplished with porous skin (29) by (or a combln a tlon of the two) us e d ov e r a ppro x l- the Doug l as Aircraft Company. Perforated skins mately 75% of the wing and tai l area. Such a c an now be rout i nely fabr i cated with a wavine s s system would result in obta i ning about one-quarter (due to the "hat" substructure described of the benefit possible w l th the a l l- l aminar earlier) of l ess than O.OOi in. Superp l astlc- airplane.

-formed diffus i on-bonded titanium fabrication processes have b e en app l ied to both slotted No effort has yet been made to adapt an LFC and porous sk l n surfa c es (30"32). system to an aircraft fuselage. Laminar i zatlon is especia l ly difficult here sin c e al l the The culmination of the current NASA lam i nar boundary-layer stab il ization problems encountered flow control program will c ome with the flight on the wing are present plus very hlgh Reynolds t e s t ing of l e a ding-edge flight test (LEFT) numbers ; roughness associated w i th the l ocat i on ar t l c ies in l ate 1982 and 198 3 . This program of the cockpit, doors, and hatches ; and the involve s LFC gloves mounted on the l eading edges compli c ated flow i n the wing-fuselage junct i on.

o f an e xt e nsive l y mod i fied JetStar aircraft Prov i ding hope for an e ventua l solution, howev e r, (f i g. lO). Very smooth suction surfaces are are wlnd-tunnel tests on a R e i c hardt body of integrated with a d u cting system in a manner revo l ution which have shown the feas i b i lity of s uch th a t c leaning and repair are eas i ly using an LFC system t o ma i n t ain laminar flow t o - a cc ompl i shed. The left glove is a slotted GELAC a Reynolds number of at least 58 milllon(35-37).

c o nflgur a tlon(28). Surfa c e s lo ts are used not Perhaps at ]east partial fuselage laminariz a tion o n ly for su c tion but also for washing and dei c ing, will eventually be possible. If 75% of the Laminar flow i s att a ined on both the upper and fuselage area c ould be laminarized on the 1990 lower s u rf ac e s; the des i gn does not utilize a airplane, fuel effi ci en c y in c rease s to about leading-edge flap. The right glove i s the porous 189 smg (fig. 12). Su c h a large payoff c ertainly co n fig u r at io n( 33) d eveloped by DAC ; s uct ion hole r e present s a temp ti ng targe t for f uture v is cous dr a g redu c tion.

Hybr id Laminar Flow Control Turbu le nt drag r e d ucti on approa ch e s g e nerally As the parameters affe ct ing boundary-layer involve some type of nonplanar local geome t ry(39).

transi t ion and th e c riteria for ma i n t aining More than t e n approa c h e s are now under s t udy, bu t laminar flow were gradually i dent i f i ed and the present dis c uss i on is conf i ne d t o two me t hod s unders t ood, con c ep t s were developed for using which have ind ic ated posslble net drag redu c t i ons .

suction in the l e ad i ng-edge reglon of the Drag redu cti ons observed to date ha v e been measured airfo i l to mainta i n laminar flow far downs t ream at relat i vely low Reynolds nu m ber and speed, in a o f the s u ctio n sur f ace. Thi s v ar iati on of a bo u ndary la y er th a t w as artificiall y tri pp ed , and L FC s y stem has rece n tl y bee n re f erred t o as a o n l y i n a wi n d tunne l .

hyb r id la m in a r f low contro l s y s tem ( H LFC) .

Su c tion i s used i n the lead i ng-edge reg i on to In the f i rst approa c h, c alled "r i blets ''(40) control the g r owth of cross-flow ins t ab i l i t i es the boundary layer stru c tur e near the su r fa c e i s i ntroduced by sweep af t er whi c h the pressure a l tered by us i ng small flow-aligned g r ooves on d i stribut i on i s "tai l ored" to control the the wall. So m e of the conf i gurat i ons tes t ed a r e Toll mie n-S ch llc ht lng d ist ur b an ce growt h o v er s hown i n f i g u r e 15. R i bl et hei gh t s t yp i cally th e w i ngbo x. A H L FC w i ng wo uld h ave a su per- rang ed f r om .0 25- .0 50 c m . a n d sp ac i n g v aried fr om c r itica l pressur e pro f i l e perh ap s si m i lar t o . 0 2 5 - . IO O c m . R e yn o l ds n u m ber is t y p i call y ab o ut tha t o f fi g ure 1 3. Pressure d ist ri butio n s o n 2 m illio n . The saw to o th g eo m etr y p r o v id ed a 10% the su r face s of a H LFC air f oil w ould b e fa v o rab l e n et re du c t i on i n dr ag, the mo st fa v or a b l e r l blet ov er a la rg e r e g i on rath e r th an ha v e t he ne arl y result o bt a i n ed. In an a ctua l appl icat ion, the co n s tan t pro f i l e as s o ci a t ed w ith t he w i ngb ox g ro ov es c o u ld b e man u fa ctured b y extrus ion r e g i on o f an a d v a n ce d L FC w i ng . m o l d lng a thi n , lo w de n sit y f il m wi th the requi r ed g eo m e t r y ; a dhes iv es w ould be used to app l y the T h e h y bri d approa ch may p r o vid e mor e e x t e n si v e non- lo a d c ar r y i ng fi lm to t he su rf ace. R ib l et lamin a r f lo w tha n po s s ib l e w ith NL F o n s w e pt w ei g ht es t i ma tes ap p l ied to a 7 4 7 class f usela g e w i ng s , bu t l ess than th at expec t ed w ith re a so n ab l e i n dic at e a p e nal t y of ab out 700 p ou n ds, w hich i n ch ordw i se e x ten ts of L F C . Exte n si ve chor dw ise the mo s t favora b l e case c o u l d resu l t i n a n a irpla ne suctio n, ho wev er, i mpos es p e nal ties i n we i g ht dr ag reducti on of a bo ut 2- 1 / 2 % .

and sy s t e m s c omp l ex i ty, e s p ecia lly i n t h e re g io n of the wlngbox where fuel is stor e d. HLFC, T he se c ond approa ch (41) involv e s al te ra t ion of t herefore, Is a c ompromise between drag redu c tion the large scales in the ou t er par t of t he t urbu- and s y st em s impli cit y t ha t requires evalua t ion, lent boundary layer by inserting a low-drag devi c e wi t hin the boundary layer. In effe c t, t he boundary A preliminary s t udy of t he hybrid c oncept layer is "aged," a phenomena equivalen t t o an appli e d t o a tr a ns p ort wing wa s ac c omplish e d by incr e ase in Reynolds n u mb e r. T h e ba s i c approa ch the Boeing Company(38) with NASA sponsorship is ind ic ated in figure 16. The vortex from the and i ndi c ates sign i fi c ant po t ential. Laminar large-eddy breakup devi c e is used to d i minish the flow may o cc ur to approximately 30-60% chord boundary layer turbulen c e stru c ture . Early resul t s depend i ng on fl i ght altitude, wing surfa c e, and indi c ate that this very simple dev ic e c an severely spanwise lo c atlon. Expe c ted gains for th i s alter the outer turbulence s c a l es and provide a c on c ep t as applied to a transport-size air c raft net drag redu c tion, at least for the lim i ted wing would In c rease the smg of the 1990 transport s t udies completed to date where Reynolds number airplane by about 12% to about 125 smg, with at the device lo c ation is typi c ally about 2 mill i on compar a t i vely li t tle c hange in th e basic des i gn and abou t 4 mi l lion w h er e drag redu cti on s a re of the aircraf t (fig . 14). measured . At present, it is not known to what Reynolds number the effect may persis t . Effi c ien t The hybr i d con c ept i s far slmplier t han a full me t hods of mounting such a drag reduction device laminar flow control sys t em, and should therefore are not yet developed .

be more reliable . Given these very sizable advantages -- in addition to t he relative ease Early wind tunnel resear c h indi c a t es tha t both with wh ic h such a sys t em could be applied to a of these me c hanisms may a cc omp l ish a ne t t urbulent produ ct ion alr c raft at reasonable c o st , I t Is drag redu c tion. However, the spe c ific pro c esses likely t hat a hybrid sys t em will be the first involved are not well unders t ood. The la c k of appli c ation of laminar flow control to a commer ci al theory to fully explain su c h ph e nomena t oge th er aircraft wing. For the same reasons, such a wl t h the absen c e of a sign i fi c ant amount of data system may also be considered i n the fu t ure for w i th which to optimize t hese de v ices mean t ha t use on a transport aircraft's ta i l and fuselage, future progr e ss will be heavily dependen t on the extent and quality of our experimental results.

Turbul ent Skin Friction Reduction Confirmat i on of any drag r e du cti on w i ll of Th e d i s c uss i on t hus far ha s cons i dered atta i n- ment of lam i nar flow, g e nerally on wings. Ano t h e r c ourse, awai t flight t es t ex periments. If th es e po t ential benefits c ould be applie d to t h e fuselage poss i ble a p pr o a c h to vis c ous drag redu c t i on is to of the 1990 airplane wit h laminar flow cont r ol on reduce sk i n fr icti on drag. T his conc e p t may hol d the wing and t ail, however, a fur th er 7% improvemen t promi s e for t he fuselage where Reynolds numbers t o 149 smg may be possible (fig. 17) are very hlgh and a c hieving LFC is difficult.

Early explora t ory work has suggested that a ne t Concludinq Remarks drag redu cti on (after a cc oun t ing for t he drag of the devi c e) may be possible. T hese g ai ns are Grea t promise exis t s for redu c ing vis c ou s drag at t ained by al t ering the s c ale of t urbulen c e near in t he near fu t ure. E xperimen t al resul t s, bo t h t he wall and in the outer par t of the boundary in wind t unnels an d fligh t , indi c a t e tha t su c h layer. Possible advan t ages in redu c ing turbulen t drag (ver s us LFC) i n c lude redu c ed opera t ional t echnology is rapidly being advanced from t he resear c h stage t o that of pra ct i c al appl ic a t ion.

sensitivi t y an d t herefore in c reased reliabili t y.

As now envisioned , the NASA program in viscous 9 Hol m es, B. J.; and 0bara, C . J.: Observations drag reduction is summarized in f igure 18. NASA and Implications o f Natural L aminar Flow on i s c ontinui n g wind tunnel and flight t e sts on Pr a ctical A irp lane Surf aces . I CAS-8 2-511, gene r al av iat ion a i rc r a f t to p r ovi d e the da t a August 1982.

base neede d t o give in d u str y the con f i d ence requ ir ed to exploit natural laminar flo w t ec hno l - l OMo nt oya, L . C.; St e er s , L. L .; C h r ist op he r , ogy. For t r an s po r t a pplica t io n s, s ome form of D.; and Truji ll o, B.: F-I l l TACT N at u r a l L a mina r l aminar f lo w c on tr ol s y st em will p r obably be Flow Glove Fli g ht Re s ul t s. NASA Co nf erence nece s s a ry. A si zea bl e b a se of fund am en t a l Publica t ion 2208, Sep t em b er 19 8 1.

r ese a rch data on a tr a n s onic LFC wing is n ow be in g acc um u l at ed in gr ou nd-b a sed te s ts, llBushne l l, D . M.; and T u t tle, M. H . : S urv ey P r e li min a ry st r uctura l des i gns of bot h s l otted a nd Bibliog r a p hy on Att ai nment of L a m i na r F l ow and p o r o u s s uction w i ngs h a ve been accomplished. C o ntr o l i n Air Us i ng P r essure Grad i ent a nd Actual operation of a LFC airfoi l in F l ight w l l l Suct i on - Vo l u m e I. NASA RP-10 3 5, Septembe r 1979.

b e gin i n 198 3 . Turbulent sk i n frict i on r edu c tlon

is now In an exp lora to r y r e s ea r ch s tage wlth on l y ] 2Bushnell, D. M .; and Turtle, M. H.: Survey a s m a ll a mount of expePiment al g r ound-based da ta a nd B i bliogr a phy on Att ai nment of Laminar Flow ava i l a ble. Co ntr o l i n Air Using Pressure G r ad i ent and Suction - Vo l ume II . NASA RP- 1 0 3 5, J u l y 1 979.

T a ken togethe r , the re s ults o bt ai ne d to d a te Confident ia l.

are ve r y encou r a ging a nd offe r hope for a futu r e improvement i n the perform a nce of m ost types of 13 j obe, C. E.: A Bib li og r aphy of AFFDL / FXM air c raft. S u ch impro v ement is likely to take the Reports on L aminar Flow Control. AFFDL-RM- 7 6- 2 6- form of large increases in the speed and fuel FXM, U.S. Air Force, March 1976.

efficiency of general avi a tion aircraft, in the fuel efficiency of transp o rt aircraft, and in a 14Tutt l e, M. H.; and Maddalon, D. V.: Lami n ar dramatic advance in the range and pay l oad Flow Control 1 9 76-1 9 82; A Selected, Annotated capability of m ilitary aircraft(42 ) . Bibliography. NASA TM-84496, 1982.

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16Sturgeon, R. F.; et al: Evaluation of 2Nagel, A. L.; Aff o rd, W. J., Jr., and Laminar Flow Control System Concepts fo r Subsonic Du g an, J . F., J r.: Future Long-Range Transports - Commercial T r ansport Aircraft-Sun_ n ary. NASA Pro s pects f o r Impr o ved Fuel E ffi c ien c y. NASA CR-15 9 254, September 1980.

TM X-72659, February 1975. } 7pearce, W. E.: Progress at Doug l as on 3Maddalon, D. V.; and Wagner, R. D.: Energy Lam i nar Flow Control App l ied to Com m ercial and Econ o mic Tr a de 0ffs for Advanced Technology Transp o rt Aircraft. NASI- 1 6 2 34, Dou g las Aircraft Subsonic Aircraft. NASA TM X-72833,April 1976. Co. Presented at NASA-Dryden Flight Research Center, September 1981.

4povinelIi, F. P.; Klineberg, J. M.; and Kramer, J. J.: I mproving Aircraft Energy IBAntonatos, P. P . : Laminar Flow Control - EFf i ciency. Astronautics and Aeronautics (A I AA), Concepts and Applications . Astronautics a n d Vo l . 14, No. 2, February 1976. Aeronautics, J uly 1966.

5pfennlnger, W.; Reed, H. L.; and Dagenhart, 1 9 Nenni, J. P.; and G1uyas, G. L.: Aerodynamic J.R.: Design Considerations of Advanced Design and Analysis on an LFC Surface. Astronautics Supercrlt i cal Low Drag Suction A i rfoils. and Aer o nautics, J uly 1966 , Viscous Flow Drag Reduc t ion, Vat. 72, Progress i n A s tronautics a n d A e ron au tics, 1980 . 20White, R. C.; S udd er th , R . W. ; a n d Whe ldan , 6Smith ' W.G. : L ami n ar F lo w Contro l on t h e X - 2l .

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7Braslow, A. L.; and Visconti, F. : Investiga- 22Chup r un, J.; and Cahill, J. F.: L FC on tion of Boundary- L ayer Reynolds Number for Large Logistics Aircraft. Astronautics and T r an siti on on a n NACA 65 ( 215)-I14 Airfoil in the Aero na utics, J uly 1 9 66.

Langley T wo-Dimension a l Low-Turbulence Pressure Tunnel. NACA T N 1704, July 1948. 23Anon: Final Report on LFC Air c r a ft Design Data L a minar Flow Cont r ol Demo n str a tion Pr o g r am.

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2 4 L eo na r d , R. W.; a nd W a gner, R. D . : A i rfr ame 38 Bo e ing C o mm ercial Airplane Compan y : H yb r i d Technolo g y f o r En e r gy E ffi cient Tr a n sp ort Laminar Flo w Control S tudy F i nal Technical R eport .

A i rc ra f t . Pre s en te d at th e SA E 1 976 A e r o sp ac e NA S A CR- 1 6593 0 , 198 2 .

E ng ineeri ng a nd M a n ufacturi ng M eetin g , San Die g o , C a l i f o r nia. Novemb e r 2 9 - D ece mb e r 2, 39 He fn e r , J . N.; W e in stein, L. M . ; a n d Bush n e ll, 19 7 6. D.M . : Lar ge- Edd y Br ea k u p Scheme f or Turbu l ent 25E l _H ad y V i sco us Dra g Re du c ti on. V i sc o us Fl ow Dra g , N. M.: Hady-l, A For t r a n P r ogr a m Reduc t ion, Vol. 72, Progre s s i n As tr onaut i cs for t he Compres si b l e S t abi li ty Analysis of Three- and Aeron a u t ics, 19 8 0.

Dimens i ona l Bounda r y Layers. NASA CR-3467, Sep t ember 1 98 1 . 4OWa l sh, M. J.: Drag C ha r a ct er i st i cs of V-G r oove a nd Transve r se C urv at u r e R ib le ts .

26M a ddalon, D. V. (Editor): Laminar F l ow Vi s cous Flow Drag Re d uction, Vol. 72, P r ogres s Contro l - 1 98 1 Research a nd Technology S t udie s . in As t ronau ti c s and Ae r onau ti c s , 1 980.

NASA CP- 22 18, Marc h 19 8 2. 4 1 27Newman ' Corke, T. C.; Nagib, H. M.; a n d Gue z ennec, P. A.; Anderson, E. C.; and Y.G.: A New View on Origin, Role a nd Manlpu la - Pe t erson, J. B., Jr.: Numerica l Design of t he t ion of Large Scales in Tu r bulen t Boun da ry Con t oure d W i n d - T unnel L iner for t he NASA Swept- Layers. NA S A C R-165861, Fe br uary 1982.

Wing LFC Te st . AIAA 82-0568, Mar c h 1982.

42jobe, C. E.; Kulf a n, R. M.; a n d V acha l, 28Anon: Laminar flow Con t rol. Lockheed- J.D.: Appli c a t ion of La min a r F low Con t rol t o Georgia Company (NASI-162 19 and NASI-16235). Large Subsonic Mili t ary T ranspor t Airplanes.

Presented a t NASA-Dryden Fligh t Resear c h AIAA Paper No. 78-95, Janua r y 1978.

Cen t er, Sep t ember 198 1 .

29Anderson, C. B. : Lamin a r F low Con t rol Wing Surface S t ruc t ure Developmen t Prog r am. (NAS I - 16234, Douglas Aircr a f t Co.) Presen t ed a t NASA- Dryden Fligh t Rese a rch Cen t e r , Sep t ember 1981.

3OMcQuilk l n, F. T . : S t udy of t he Applic a tion of Superpla st l ca lly Forme d and Diffus i on Bonded (SPF / DB) Titan i um Struc t ure to L aminar Flow Con t rol (LFC) Wing De s ign. NASA CR-158979, December 1978.

31Wilson, V. E.: Des i gn S t udies of Laminar F low Con t rol (LFC) Wing Concep t s Us i ng Super- pl a st i c Fo r ming a n d Diffus i on Bondi n g (SPF / DB).

NASA CR-159220, May 1 980.

" 3 2 Do u gl a s Aircr a f t Comp an y: Lami n ar Flow Con tr ol SPF / DB Feasibil it y Demons t r at ion. NASA C R -165818, 1981.

33McNay, D.; and Allen, J.: L aminar Flow Control L e a ding Edge Glove Flight Test Article Development. (NASI-16220, Dougl as Aircraf t Co.)

Presen t ed at NASA-Dryden Fl i ght Research Cen t er, Sep t ember 1981.

34Nas t rom, G. D.; Holdem a n, J. D.; and Davis, R.E.: Cloud En c oun t er and Par t icle Number Densi t y Variabilities from GASP Da t a. AIAA Paper No. 81-0308R, January 1981.

35Gross, L . W.; and Pfenninger, W. : Experi- ment a l and T heore t ic a l Inves t ig at ion of a Reich a rd t Body of Revolution Wi t h Low Drag Suc t ion in t he NASA Ames 1 2 -Foo t Pressure Wind T unnel. Nor t hrop Report NOR 6 3 -46, B L C-148, 1963.

36Gross, L.W.: Inves t iga t ion of a Reichardt Body of Revolution With Low Dr a g Suc t ion in the Noralr 7 x I 0 Foo t Wind Tunnel. Northrop Repor t B L C-143, NOR 62-126, 196 2 .

37G r oss, L .W.: Inves ti gation of a L amin a r Suc ti on Relch a r dt Body of Revolution in t he Ordnance R ese a r c h Labor at ory 4-Foo t W at er Tunnel.

Nor t hrop Repor t BLC-167, NOR 65-311, 1965.

TABLE I - AIRCRAFT CHARACTERISTICS SU MMA RY Take o f f Oper a tin g S eat Miles Gross E mp t y Lift / D r a g G allon We i g ht, W ei g ht , at at Ibs. lbs. M id -C r uise M id -C ruise 1 97 0 Technology 8 3 9 ,000 3 99 O 00 1 7 .2 6 0 A d vanced Techno l o gy* 603 , 0 0 0 2 9 8 00 0 20. 1 1 12 Hy brid LF C* 5 8 0 , 000 2 9 2 00 0 22.0 1 2 5 LF C W in g / T a i l * 557 ,0 00 285 0 0 0 2 4.4 14 0 LFC Wing / Tail + R edu c ed T urbu l en t Skin Fri ct ion* 547,000 282 000 2 5.9 149 LFC Wing / Tail / Fuse l age* 51 1, OOO 272 000 31.7 18 9 All-Lamin a r Air c raf t * 490,000 2 66 O00 36.7 2 2 5 Payloa d = 490 pass e nge r s and 43000 p o unds c argo Des i gn Range = 4800 n . ml.

Engines = 4 *1990 Te c hnology (AR = 12)

II0 -

I00 - ..

90-

80-

70-

60-

FUEL PRICE , 50-

CENTS PER

GALLON

o

30-

10-

0 I I I I I I I I

1973 1974 1975 1976 1977 1978 1.979 1980 1981 1982

YEAR

FIGURE 1 - DOMESTIC U.S. AIRLINE JETFUEL PRICE H!STORY

250 -

200 _LL-I A M! NARAIRPLANE

SEAT MILES

PERGALLON150

I00 _-- _x_1990

ADVANCED TECHNOLOGY

5O

_- 1970 FOUR ENGINE WIDE-BODY

0 I I I I I

0 I 2 3 4 5x10 3

RANGE, NM

FIGURE 2 -ADVANCED TECHNOLOGY FUEL CONSERVATION POTENTIAL

M UFACTURING QUALITY

o WAV I NES S. SMOOTHNES S

Q JOINTS (STEPS, GAPS}

SUr:T ION SYSTEf\r1

o SURFACE 0 ENINGS

o SUCTION DfSTRI Burl 0 t

STRUCTUR

o SIZE

':'-- ------=~fO f SE

o SURFACE DEFORMATION

o ENGJi ES

UNDER LOAD

SUCTION PUMPS

....

....

FLIGHT CONDITIONS

/

o VELOCITY

LE. \Dl G EDGE COND ITI ON

o ALTITUDE

° INSECTS. DIRT

o ICE CRYSTALS

,0 EROSiON

<crRl\IN

FtGURE 3 - F 'TORS, FFE .11 I

LONG-EZE

SKYROCKET .

I N-FLI GHT TRANS ITION .....

T -34 C!GLOVE

FllllTACT

FIGURE 4 - NATURAL LAW;INAR FLOW FLIGHT EXPERIMENTS

SOLIDSYMBOL = METAL

OPEN SYMBOL = COMPOSITE

.8 -

LEAR 28 / 2 9

. 6 -

MACH

NUMBER

.4-

yBIPLANE RACER

/ _MOONEY Z31

LONG-EZE _Of SKYROCKET II

L _

• 2 (_ _ _CESSNA P210

VARI-EZE

"BEECH 24R

0 , I i I , I I I , I I I

2 4 6 8 ]0 ]2x]06

TRANSITION REYNOLDS NUMBER

FIGURE .5- NATURAL LAMINAR FLOW TRANSITION REYNOLDS NUMBER IN FLIGHT FOR

EIGHT GENERAL AVIATION AIRCRAFT

TURBULENT BOUNDARYLAYER

_'_ CONVENTiON_

U_

LAMINAR BOUNDARY LAYER

FIGURE 6 - LAMINAR FLOW CONTROL CONCEPT USINGSUCTION

q i

t ' '

FI6URE7 - ADVANCED LA / V INARFLOW

P Q" ''P

_,:_ , _, , OL / :IRFOILiiq LANGLEY 8 FOOT TUNNEL

"15

BOX S

BEA M - X PLICE-- , X

-_-4 1 ,-_ : _ , I T I ' t ! _ _ ' ' i""

_ CHOR D= 7.07FT. _I

I

FLAP

PANEL-BOX BEAM

ATTACHMENTS

MODEL DES IGNPO!NT

M = 0.82,M z --0.755

Rc = 20x 106

c = 7 . 07',A = 23 °

( V ck = ]3 .

(CL) ± = 0.55

FLAP CHORD= I0 . 9 %

FIGURE 8 - ADVANCED LA M INAR FLOW CONTROL AIRFOIL

.SUCTION SURFACE PANEL CONSTRUCTION

o o _ 1 SUC T 'ON1

0 . 0 25 IN

0 0 0 o o

OUTER

O . 0025" D RFACE PERFORATED

SURFACE

0.025IN. BOND

I TITANIUM '_

l ...... -__ LINE

!

FIBER GLASS SUBSTRUCTURE

,/

FIGU R E 9 - ELECTRON BEAM PE R FORATED TITANIUM

WINDTUNNEL MODEL PANELS

MODIRED JETSTAR

LOCKHEED

CONCEPT

DOUGLAS

CONCEPT

FIGURE 10-LFCLEADING EDGEFLIGHT TEST

S IMULA TED AI RLI NE SERV I CE HOME BASES

• GROUND AND FLI GHT

ACCEPTANCE

• SYSTEMS EVALUATION

AND PERFORMANCE

• SIMULATED AIRLINE

SERVICE (200 HOURS)

FI GURE 11 - LEAD I NG EDGE FLI GHT TEST PROGRAM

200 _ %'- LAMINAR FLOW CONTROL

SEAT MILES f (WING.TAILANDFUSELAGE)

GALLON

PER

_- %---LAMINAR FLOW CONTROL

(WlNGANDTAIL)

1" 3

100 _

'_ 1990 ADVANCED TECHNOLOGY

5O

0 , , I , ,_X10 3

0 I 2 3 4

RANGE, NM

FIGURE ]2 -LAMINARFLOW CONTROL FUEL CONSERVATION POTENTIAL

Cp

x / c

LAMINAR FLOW

, _J

SUCTION '"

IZl

SURFACE

FIGURE 13- HYBRID LAMINAR FLOW CONTROL WINGCONCEPT

SEAT MILES

PER GALLON 150 / -HYBRID LFC

€ ,

100 _--

m 1990ADVANCED TECHNOLOGY

5O

0 l I I I ,I 3

0 ] 2 3 4 5xi0

RANGE, NM

FIGURE 14- HYBRID LAMINAR FLOW CONTROL FUEL CONSERVATION POTENTIAL

"' R!BLET CONFIGURATIONS

FLOW (TRAN SVER SESECT ION)

TURBULENT

BOUNDA R Y / V_ _AyV

LAYE R

////// I Zl lZ/// - I// I I I I I /I lll I I I I I i

_ / x__ A _ _

N'q',,

_ / VVV_ _

Q FLOW

RI BLETS

F!GURE 1 5 - TUR BULENT DRAG REDUCTI ON- RI BLETS

TURBULENT

--~~FLOW

BOUNDARY

LAYER

SMOKE FLOW PAlTERN

HIGH DRAG-WITHOUT CONTROL

LOW DRAG-WITH CONTROL

FI GURE 16 - TUR BULENT DRAG REDUCTION LARGE-EDDY BREAK-UP DEVI CE

• _ q r

250-

TURBULENT DRAG REDUCTION ANDLFC

200-

1 5 0 _ .

SEAT MILES _--LAMINAR FLOW CONTROL (WING andTAIL)

PER GALLON _

I00

k_

m 1990 ADVANCED TECHNOLOGY

0 I I I I , J

0 I 2 !) 4 5 x 103

RANGE, NM

FIGURE 17- TURBULENT SKINFRICTION ANDLFCFUEL CONSERVATION POTENTIAL

_COMPLETE _ooo_ APP R OVED _ PROPOSED

FISCAL Y EAR

81 82 83 84 85 +

NATURAL LAMINAR FLOW

FLIGHT TRANSITION STUDIES _ _ _o o _

WIND TUNNEL TESTS II

F-111 SWEEP EXPERIMENTS / ANALYSI S __

LAMINAR FLOW CONTROL

S TAB I L IT Y CODES __

AIRFOIL DEVELOPMENT andTESTS __

INDUSTRY SYSTEMSTUDIES

STRUCTURAL CONCEPTS _ m

HYBRID SYSTEM STUDY andTESTS __,_

LEAD INGEDGE FLi GHT TEST _

VARIABLE SWEEP FLIGHT TEST

LAMINAR FLOW WINGFLIGHT RESEARCH

TURBULENT SKINFRICTION

EXPLORATORY WINDTUNNEL TESTS __ _'-'--_

FLIGHT TESTS I

FIGURE 18- NASA VISCOUS DRAG REDUCTION PROGRAM

I

1. Report No. 2. Government A cc es s ion No. 3 . Recipient ' s' Cat a log No.

NASATM- 84518

4 . Title a n d S ubtitle 5. Re po r t Dat e

A u,qu st 1 982

NASAResearch on Visc o us Drag Re d ucti o n s. Pe rfor m ing O r gani zation Co d e

534-01-1 3 -0 6

7 . Author(s) 8. P er f orming Organ i zation Report No .

Ri cha r d H. P e t e rs en a nd

Dal V. Maddalon io W o r k Uni tNo.

9. P e rf o r m i n g O rg an izati on N ame a n d Addre ss

NASALangley Research Center

Hampt o n, VA 2 3 665 11 Con tract o r G r an t N o , 13 . Ty _ o f R e po_ a n d P e r io d Cov e r_ 12 . Spo nso r ing A g e ncy Na m e an d A d d r e ss

Nati o nal Aer o na u tics and Space Administrati o n Technical Memorand u m

Washington,DC 20546 14. Spon s o r ingA_ncy Code

15. _pplem enta r y Not es Th is p ap e r w a s pr e s en t ed at t he 1 3 t h C ong r e ss o f t he I n t e r n ati on al C ounc il o f t he Aerona u tical Sciences (ICAS) / AIAA Aircraft Systems and T echnology Meeting at Seattle, Washington on August 22 to August 27, 1982.

16 . Abs t r a c t

Current NASAresearch p o ints t o ward exciting opp o rtunities for large reductions in

viscous drag. Research is underway on natural laminar flow, laminar flow control by

suction, and turbulent drag reduction. Preliminary results suggest that a significant

amount of natural lamin a r flow can be achieved on small, straight-w_mg airplanes. Qn

] arge r , swept-wing aircraft, laminar flow control by distributed suction is expected

to result in significant fuel savings. The area over which laminar flow control is

applied depends on tradeoffs involving structural complexity, maintenance, and cost.

Several methods of reducing turbulent skin friction by altering the turbulence

structure itself have shown promise in exploratory testing. This paper reviews the

status of these technologies and indicates the benefits of applying them to future

aircraft.

17. Key W o rd s ( Sug g _ te d by A utho r ( s) ) 1 8 . D istribution S tatement

Viscous Drag Reduction

Natural Laminar Flow

Laminar Flow Control UNCLASSIFIED- UNLIMITED

Turbulent Drag Reduction

PerforatedMaterials Subject CategoryO2

1 9. S_u rity O a ss if . (of t hi s re po rt) 2 0 . Security C la ssi f . ( of thi s _ ) 2 1 . No . o f P a _s 22 . D ice

UNCLASSIFIED UNCLASSIFIED 27 A03

,-30s F o rsaleby t he Na t ionalTechnical l n f orma t ionService, Springfield . Virgin i a 22161 J

I

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