Document
I I
i " : NASA TECHNICAL NASA TMX-62,423
_ ' MEMORANDUM
D " i ° _&, ' / y o;
"_ : ; ' CORRELATION OF LOW SPEED WIND TUNNEL AND FLIG H T TEST ]
• DATA FO R V / STOL AIRCRAFT ' i
/: _i (
Woodrow L. Cook and David H. Hickey
_I" Ames Research C enter
.... Moffett Field, Calif. 94035
_ r - , " , s ,
: , . April 1975 --
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_= : ; ( N_ Sk-TM-X-62 4 231 CO R RELATI O N OF LO W SP E ED N 75-2 3 55 7
i! W I N D TUNP E L AND FLIGHT TE ST D & TA FO R ¥ / $ TO L
A I _ C _ k F T (N _ SA) 1 :3 p HC $3.25 CSCL 0 1C
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i' I I I I I t 0 _ , : 1 . _ N o . 2 . Govmsnw _ Acmm l on No . 3 . Rm:tplm . ' s C.,m l o l No .
, _" TM X -62, 4_ 3
"_ _' CORRELATION OF LOWSPEED WIND TUNNELAND FLIGHT TEST
_,_ DATA FOR V / STOL AIRCRAFT s. _ O _i m t_ C o d.
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_ ,. : . ,. The ava i lab i l it y o f wind t unnel t es t da t a £ or. correla ti on purpo s es o f t he same V / STOL a i rcra ft t es t ed i n f l i gh t i s very l i m it ed. Th i s i s due i n a large ,; par t t o size l i mi t a ti ons o f wind t unnels and the number o f wind t unnels ava i l- able f or t es ti ng o f f ull-scale a ir cra ft .
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,., , , The NASA Ames Research Center has tested two research ai rcraf t -- t he
XV-5B f an- l n- _ r l ng a i rcraf t and t he YOV-10 RCF ro t a t ing cylinder f l ap
_ ' _ a i rcraf t -- i n the Ames 40- by 80-Foot W i nd Tunnel. The t es t s were conduc t ed
/ ii: spec i fically t o provide for correlation bet ween wind t unnel and in-fllgh t
i. _ . aerodynami cs and noise t es t da t a. Correlation be t ween aerodyn ami c and noise • ._ . da t a are presen t ed and t es ti n g t echn i que s t ha t are rela t ed t o t h _ accuracy of t he da t a, or t ha t m i gh t affec t t he correla ti ons, are discussed.
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': l g ol ;" CORREL A T I ON OF LO W SPEED WI NDTUNNEL ANDFL I GH TT ES T D AT A FO R V / STOLAIRCRA F T _ b y W ood r ow L . C o o k an d D a vid H . H t cke y A mesRe s e a rch C e nt er , NASA Moffett Field ,C alifornia 94035 S UI O IARY Th e availability o f windtunnel tes tdata for co r rela tio n pu r po ses of t he same V / S T O La i r cr af t tes t ed in flightIs very li m it ed . Th(s I s d u e in a l a r gepar t to s i z elimi ta tions of wi n d tunnels and t h e nu mbe r of wi nd tunnels available for t es ting of full - scame alrcraf_.
S ince theA GA _ Dmee tingat R o me in Ig 6 6the N A S AAm e s Re s earch Center M s test e dtw o addition a l research air c raft - the XV - S B fan - ln- w lng aircrafta n d the YOV - IOR C F (ro t a ting cylinderflap)aircraft - in the _ me s 4 0- by 8 0- Foo tWln dT unn e l. Th e t e sts we re conduct e d s pe c'_flcally to p r o vide for correlati o n b e t we en wind tunnel e nd In-fllght a e r od yn am ic s and noise te s tda , . Co1 " relatlon b e tw e en aero d yn am ic and noise dataare ! p r esen t ed and test ing techniques t ha t a re re lated to th e accur a c y of th e d a ta, or t ha t m i gh t affec t th e corre l at i on s , a re di scuss ed .
: NO M ENC LA TURE i AL area of V / STOL liftin g ele mnt , n( _ DL = / 4) P Nd B ;er ce t ved n o i s e level ( PNL), dB A H mo m en tu m a rea of a ircr af t ° _ - h ' t / 4 q d y na mi c p r e s sure A T w ind tunnel c r o ss -sec ti o n a r e a S v , l ng ar ea a accele r at i on, g T fa n o r propelle r t h ru s t b w t ng span V ve l oc it y b t tunnel width v re lat t ve Jet veloci ty , V _l- V CO d r ag coeff i c i e nt , O / qs WF aircraft weight C L liftcoeffici e nt, Uqs o angl e of att a ck , dng O aircraft drag _ / fan l ou verv e ctorangle , deg OL di am eterof lifting e l eme nt , fan s or prop e ll e rs y aircraftflightpathangl e, de 9 L IIft 6 e el e vatordeflectlon ND aircraftno s edoo m 6f flapdeflection NU aircraftn o s e up u aircraft angle to hori z on , deg n nu m b e r of fan s or prop e llers SP L soundpre ss urel e vel Su b scr i p ts a a e ro dynamic , 0 no r mal • elevat o r R re l a ti ve t o free st r ea m v e locity F fl i gh tair c r a f t T ri n dtun ne l f fla ps V fan l ouv e r J J et X horizo nt al M momentum 1. INTRO OU C TI O N At th e R ome A G A RDF lightM e chenlcs P an e lM ee tingIn S e pt e m b e r Ig65,a p a pe r ( r ef .I) m s pres e nt e d r epo rting th e correlation o f win d tunn e la e rodynamic testdatawlth flightt e stdata for sev e ral V / S T O L a;r- craft. Fou rof theaircraft wer e t e st e dbothin th e _ e s 4 0- by 8 0 - _ootWln dTu nn e land in flig h t. M o re r e c e ntly, additional specific datahav e beenobtain e din flightt e stsof th e XV - SB fan-ln-wing aircraft { F i g .I) and theYOV-IORC F ( r o t a ting cylind e rflap)S T O L aircraft ( Fig. 2 ). Th e specific a e rodynamic dat a t es t po intssl m latlng lev e lflightand d e cel e rating, desc e nding flightc o nditions f o r the tw o aircraft w e re als oo btain ed In the 4 0- by 8 0 - foot wi n d tunn e lov e r th e low sp e e d range for c o rrelation with similar flight t e stp o ints. T hl s ap p r o ach r e duc e dth e int e rp o lation of the dataand th e relianc e on p ara me tri c in fo r m ati o n for correlation pu rpo s e s.M e a s ur eme nts havealso be e nn_d e of the nois e ch a ract e ristics of th e XV- 5B and YOV-IOR CF aircraftan d correlated wlth n o lsedata me asur e di n th e wln d tunn e lat th e sa mef lightconditions o f sp eed ,attitude, po we r,and fan lo u v e rs e ttings or prop e ll e r pitch se ttings.
T he correlation of n o isemeasur eme nt s m ad e with a J- a S e ngin e m ount e don a F- f06aircraft duringlow altitudefl) o ver s wlth th e sa me J- 85 engin e mo u ntedon a mo deland te s tedIn th e A mes 40- by 8 D-foot Wind T unnelar e alsoreported.
2. COM P ARISONS O F AERO O V N / _ I IC OAT A T abl e I sho ws s ome of th e charact e ristic f e atures of th e XV - S B_ , YOV-IORCF aircraft, rep o rt e dIn ref s .2, 3 and 4. T lp turbin e drivenl.l - pressure - ratio fansw e r e utili z edin th e XV-S B wing s with each f an pr o viding ap p roxi mat e ly _0 0 Ib (10gO k g) of thrust. T h e YOV-IORC F aircraftwa s op e rat e dIn landing approach up t o llftcoeffici e nts - f abo u t 4. 3 . Th e trailing edg e flaps had fo u r 12-in.(0.305 m) diameter rotating cyli nd e rs mou nt e d at th e fo_ m rd e dgeof th e fla , s and dri v e nby h yd raulic t u rbines at th e e nd of e ac h of the fo u rcylindersections at spe e d sof 750 0 RPM. In ge n e ral , th e XV - SBapproaches w e r e flownat n , .
r _ 'i 19-2 tt y ,m.TO• an d st a rte d at about B O k nots,decelerating to ho v er conditions and v ertical landing. T he YOV-. I O . : RO F a i r c raf t a pproaches were a t c onst ant s p ee d f o r a r a nge o f _ pe e d s fr om 5 5 t o 7 5 k n o ts wi t h a p p r oach + angl es v a ryi ng f ro m 3° t o ab out B°.
_. I LV - 5B V / $T OL Fa n-In-Wine A ircra f l;: T he XV - 5_ aircraft was muu n ted i n the 40- by _fJ-footwi n d t u nn_ .l i n tne c o n v en t i o n a l m a n n er wl th a t a i l st ru t s upp o rt as shown in Fig. 3 . Win d tunnel me as urements were made of s.pe- : .'. c l f i c f l i g ht test p o ints fo r ste ad y, level fl i g ht, 1 g cond itions, a nd fo r d ece l e ra t i ng flight at I0° des ce nt _ ' : . angle , The r esults o f t he win d t un n el te s t s, c om p ared to f l tg h t te st re s u l t s f o r s evera l level f l tg h t ;ndi - c a te d alr s p ee d con d itions, ar e sh o wn in Fig. 4 , where aircraft p o wer , a n gle o f attack, a n d l ouver angle were _ " set a t the s a me v a lues a s du ring f l ight t e st. L u ngi tudln al c o ntr ol w a s t he n s e t t o t h e nece_s , Jry u u s i t iLm it, f or t rlmme d m o m en t co ndi t i ons i n th e wind tu nn e l re s ulting in a measure d t o ta l l ift a nd d rag of t h e aircraft.
. _od cor r elat i on of s t ick po s iti o n for t r im conditio n s was _bt a in e d. Th e re sul t s a ls o indi c ate that the l lft In t i lewind tunne l f o r t h e lo wer speeds, 3 0 to 70 knots, wa s within I p erce n t of the f l ight v al u es o f wei gh t. Ho w eve r, a t 85 k no ts the win d tunnel l ift wa_ mea s ure d a t a v a lu e 4. 7 percent gre&ter tha n that i! obta i ned fr om the fl l ght test r esults , per h a ps p a r tl a ll y d u e t o a kno w n p r o b l e m with on e o f the l ift r e cur- ,: d l ng s y s te ms. Th l s d i sc r ep a n c y i s equ i v a len t to a d i f f e re n ce I n a n gle o f a t t a c k o f 1. 2 ° a nd I s within t he , _' accurac y ex pec t ed fr om r e f. 1 . The r esul t I s no t su r p ri s i n g bec ause the a e r od y n ami c llf t is a r e l ati ve l y :::. mall porti o n o f the tot al l i ft value ( 5 % a t 3 0 kn ot s and 36 % at 8 6 k no t s); t hus t h e ll ft i s r e l atively . i nsensit i ve t o e rr o r s I n a ngle o f a tta ck . Th e s am e may be s a i d f o r long it ud ina l c on tr ol , beca u se e v e n a t / " 85 k n ot s a maj o r po rti on o f the 1ong ltudl n a l c o ntr ol is p ro v i d e d by the re a cti on c on tro l s.
: . In F I g . 5 t he wind t unnel and f l ight t e s t data for the XV-SB I n d e ce le r a ting, descending flight at y - -I0% ar e c o m pa red . C o mpari son s a re sho w n f o r l o n gitu d i nalcon tr ol st i ck pos iti on, norm al a nd ax ia l : a ccel er a ti on f o r t he a ir c raft h a v ln g t h e same power c on diti on s, f a n ex i t lou v e r a ng l e s , a nd a ng l e o f at t ack.
: . For th e se da te the a ir c r a ft a x i s wa s a p pro x imately p ara ll e l t o the f l ight path and the aero d y n a mic l ift : coef fi c i ent w as a b out 0 . 5 . A s imi l ar c o m pa rison i s s h o wn in F ig. 6 with t he a ircraft a x i s ap p r ox im a t el y C h o r lzon ta l du rin g d ec ele r a t ln g app r o a ches a t y = - 10°. T h e a e r ody nami c 1 1f t coe ff i cient wa s a bo u t l .2 f o r " . l _ lel a t te r appro a ch c o n d i t i on . Goo d co rrel a tion is sho wn f o r stic k positi on a nd no r mal a c c el er a tl on wit h _ =: _ the aircr a f t de c k pa r a llel t o th e f l ig h t p a th ; ho we ve r, t h e a x i a l d ec el er a ti on v a lues me a sure d i n t he wi nd _ . t un n el a r e 0.05 t o 0 .I g l ess , ( the gre a ter differences occ u rring a t hi gh er fo rwar d spee ds ) th an t h o se o bt a i n ed I n fli gh t te st f o r the s a me p o wer and louver angle con d iti o n s . S o m e o f thls d ifference may be due : to the inabili t y t o de t e rmin e s tr u t inter f erence effects w h ich woul d ha ve a l arg e r e ffect o n t h e a e rodynamic i dr a g a t th e h l gh f o rw a rd ve loc ities. T he wi n d tun n e l su pport struts were directl y i n fr on t of th e XV-S B la nd in g ge a r a nd , hence, c_ ]d h av e re d uced the gear d rag a n d acc o u n te d f o r p a rt of the d ece l erati o n value : ' d iff e r ences . Better corre_dtlon was obtained with t he a ircraft dec k pa rall e l t o t h e flight p a th an d with l o wer aer o dyn a mic llft c o efficient than with the aircraft deck hori zo ntal during the de s cending flig h t tests.
N o rm a l a nd h o riz o ntal deceler a ti o n v a lues measured in the wind tunnel differed by as much as 0.15 g from the : .. fl ig ht test r es u l t s f o r t h e l a tter c o n d ition.
= ° " " At th e lo wer tra ns ition speed range, the differences between the acce l eratlon values measured in the wi nd tu nn e l a n d f l ig ht tests are equ J valunt t o l ess tha n 2 ° l ouver deflectinn ang l e for comparab l e dece l er- _ . at i on v a l u es; J-85 en gi n e sp ee ds must be 0.5 percent a n d 2.0 perce n t l e s s f o r com p a rable n o rmal a cceler a tion " " v a lues in the wi n d t unnel for d ec k parall el and d e c k horizontal apprrJach c on d iti on s, r esp ectively. H o wev e r, at fo rw a r d veloc ltle s a bo v e 55 k n o ts, where the d ifferences in acce l eration are g r e a ter, t h e louv er a ngl e s ": , . i n th e wi nd t u nn el m us t be 9 o a nd 7 _ more ve rtical to o btain c omparable d eceleratio n val u es; J-85 e ngi n e sp ee ds m ust be 2 pe rcen t a nd 8 percent less for comparable nor , ha l acceleration va l u_.sf o r the deck paral l el and d eck h o rl zontal a p pr o ach c ond i t ions, respectively.
Y OV-IO RCF STOL Rese a rch Aircraft: T he YOV- ] O aircraf t mounted i n the Ames 40- by 8 0-F oo : Wind T unnel on tw o sep ar a te m oun ti n g sys tems i s s hown in Figs. 7 and B. T h e mounting s y stem s hown i n F : g. l was u sed pri or ' t o th e f l ig ht t est . p rimarily fo r fu n ctiona l check ou t, u nder air l o a d, of s uc h sy s ter+_ as the rot a ting _ : c y l ind er fl a ps, m od i f ied p r op e ller , and i nterconnect sys tems with the Lycoming T - 5 3 ,-n gl n es. T h e st r ut Sy st em sho w n in Fig. 8 wa s us ed s pecifi c a lly for the flight and wi nd t u nne l tes t d a t . z c o rrel a t ion.
/ ' As s h o wn In F l g . 7 , t h e t a ll str u t i_ moun t ed on the l o wer surface o f the hori zo nt a l t a i l , fairl y cl o se to the qu a rt e r -chord po i n t, a n d c ould h a ve cause d an a dv erse d isturbance in t h e flow f ield on the l ifting ' s l de o f t he t a ll w h ere high negative pressure gr a d ients exist. The ho ri zon tal tal l eleva to r settiP_ re qu ire- me nts fo r trl m are s h o w n in F ig. g for b ot h t he f li gh t r e su lt _ a n d t h e tests wi+h t he air c r a f t mo u n t ed o n Jl (_k_- , . the t wo st r ut s y s te ms. As sho wn, the win d t unn e l te s t da t a taken wi t h th e s tru t in te rferenc e e ffects o n t he h o r izo nt al t a il sho w s l ar g e d ifferences in elevator require m ents f o r l ongi t u d i n a l trim an d in sta t ic stabil- ; I t y c o m p a re d t o fli ght test res ult s; on the other hand, _ l evato r requir e ments f o r lo nqit u d lna ] t r im an d : S ta tic s ta bil i t y us ing t he no n in te r f erence str u t loca t ion s h ow c lo; . ecor r e l ation wi th flig h t t est results.
T he f l i gh t t est d at a i n dicate elevator requirements tdr trim that fall between uncorrected win d tunnel data "_ " and wind tu nnel d at a incorp o rati n g c onv en ti on a l win d tu nn e l w all cor r e ct ions .
' / Th e lift, d r ag a nd an g l e o f a tt ac k base d on , _-,,- - yfur given c o n d itions o f stea d y fli ght a nd prt ) pel- '_
:':" ._
_L let"th r us t a re sh o w n in Fig. lO i o r f l ight test and wind t un nP l r esults. Goo d correlation is shown with the non i n t e rf e re n ce struts; a l th o ug h not shown, go_d co r relatio n was also obt a ined with the tail s trut n_unted • .' , a t the horl z on ta l tai l f o r a ll p a r am e ters e x ce p t the previ ou sly dis c ussed lon gitu d l n a l c_ nt r ol an d s t a t ic = : _ 1ong lt u dln a l st a b lllty . In t r o ducln 9 c o n v entiuna) tunne l wa il co rrec tinn appears to o v e r c l )r re c fth - da t a , : wh e n it i s com p a re d wlth f l ight t e st r e su lt s. ( : f ) r r e l ,) t lnn betw e en f light a n d wind tun n e l test data fn r llft c o e fficient an d angle of attack was qui t e good when an_le of attack was de te rmined fro_taircraft a t t i- ; r ude, e (m ea su r ed wi t h a n Attltu de / Hea di n_ Ref e r e nce S y stem ) a nd c a lcu la t e d f lig h t p a th a ng l e , .+. ( T h is tech n i qu e was a lso us ed f o r t h e XV - SB an d the d ata in ref. 1 .) H o wever, as s ; , o wnin r ig. 11 , t he a n g le of a t tack, _, mea s ured by the v a ne o n t he nc ,' ,e bomb, was approximately 6 _ hl_ler tha n t he ang l e d e te rmined by the e -y me t h od ; th e d iffer en ce was d ue i,,the high upwash e f fects , o n the v a ne at thes e hlg h l i f t coef f i- c ien t s. T h e an gl e o f atta ck v ane w,ls l ot, t ie d 7 . 1 1 (hr, r d len gt hs forwar d o f th e wing 1 _adl n _ edqe a n d 0. 4 7 ....... ch o rd leng t hs b elo w the wi n g cho r d p l an e.
Wind Tunnel Test Par am et e rs f (, rV_ / S TO L: Win d i, nne i s_ z in , j i , ara,,,eters fo r t:sting V / S T OL oir v r ,_ft nr ' ; m od e ls ,_). 12, we r e s u gg est e d " In--r a f t 1 h , r u n a, : , _ e l _r , l t e d f l i g ht co n O it ' ,ons+ T he XV- fB an , )YOV -I O _ Irc ra f t , , . _ ..'. . -L L. : ", . , - . , _ , + , . ,+ / 19- _ : . : w ere s i zed w ith i n the test p a r ame t e r s s ho w n i n the f i gur e . Th e si z e of th e ai r c r aft, span to t un ne l w i dth, o, the l i fting el eme nt, a r e a. an d t h e mom_ ; n tu ma r e a pa r am e t ers , app e a r to be r ea ,; r ) n ab l e b a se d o . t he c or r e la t ion results for lev e l fli g ht t est cond i t i o n, , _.,f th e :; _ t Y P e ' , o f V / 5] Ot ,_ t rcr a ft i n t he 40 - by 8(J- toot wtnJ tu n n e l.
• Alt hough the me o su r e m e n ts n _ d u for d(; c elerat l ng, des . . ndi r , q f l i g h t were l es_ ,oncl u sive, i t appear ; t ha t i f a ll fa cto r s ( su c h a s strut i nt e r fe r e nc e dr '_geffe( . L s ) ( , _u l d t , o ac,ura te ly d c r r , u nted f o r, f,,i,'l y , 1 ( , od pr(_d tc- , t l o n of f l i ght pa th d e sc en t a n g l e, p o wer requ i r emen t , d e c elerati o n, an d vect o ri n g re qu ire m ent could by n _ d e , fr o m wl nd tunnel t e st r esu lt s w l t h m od e l s s i z e d wi t hin t h e par ameters outl i n e d in ref. I.
- 3. COM PAR I SO N OF A C OUS TIC MEAbUREMFNTS v B ec ause o f a f o rw a rd spe e d e ffect on the ge n eration of t h e no ise, c or re l atiun of n o ls u dd t _ f r om / s t a ti c te s t s tand with fl lg ht tes t d a t a i s o ften p oo r . F i g. 13 i llus trates s o m e of t h e p o ss i b l e f or wurd ve l o cit y eff e ct s . Alt h o ugh so me acoustic research can be c a rried on In flight, t he environment is r e l a ti vel y ,i'i' un c o ntr oll ed, da ta samples are nec e ss a r i ly sh ort , an d the t estin g is e xpe nsi ve . Fu rt h erm or e, d la c _ o s t lc 'H , , studies o f t he e ffec t of v e lo c i ty on th e no is e so urc e a r e e x t remely d i f fi cult . Fo r t he se rea sons , Ames has ° con c e n tr a t ed o n develop i n g t ec h ni ques f o r me a suring no ise in the 4 0- by 8 0-f o ot wi nd tun nel . O f cou rse, ,:, ' th e fl ne l proo f o f thes e t ec hn i qu e s Is a c om p ari so n o f no i se m easur eme nt s m a de in the wind tunn e l with t h ose me asu red i n f l igh t . This s ec t io n o f t; , c, - =perwi ll brief l y d e s cribe t he t ech n i qu e u s e d for mea s uring no is e i n a wi nd t unn el, a nd will t he n pre s en t c o mp a rison s o f n o ise d a t a obt a i n e d in win d tunne l te s t s wlth those ob tai n e d i n f l i g h t t est s f o r bo th fa n -p o were d an d jet-p o were d f l ig ht of the XV- S B aircr a ft, a nd the YOV- I O i n a wi nd tu nn el m a y b e c ont ami n ated by t h e reverberant s o un d fiel d an d the backgr o und n o ise. These prob- lam s a re d isc u s s e d inde p en d ent l yalth o ugh sol u ti on s f o r one p r o b l em ma y allevi a te the other.
_ o. R C F a i rcr af t . R esu l ts o f a j o in t p r o gr a m with Lewis Re s earch C en t e r a re a ls o p resente d . N o ise measurements T h e wi nd tu n n e l is semlreverberant in tha t the s o und energy flows out of the test section f ro_,the ' _ u pst.-eam an d do w n s tr e a m e n d . T he res ul tant pr op agati o n o f noise i n t h e te st s e cti o n is s h o w n i n Fi g. 14 as _ the cha nge i n s ou nd p re ssu re l evel as a function of distance. In the free fiel d , the so u nd pres su re ] * ve l _," d r ops 6 dB pe r doubltng o f d i st a n ce . I n th e test sec t ion , ho we ve r, t he no i se a p pr oa c h e s a c ons tant va, u e i ' " a t so m e d i st a nce fr o m t he sou rc e be c a u s e t he re v erb e ra t io n sign a l i s add ed to the d irec t s igna l . Th e fina l : : level and d ista n c e from th e s ou rce is d epe nd ent on th e freq u e n c y a s s ho w n in t he fig u re, a nd a lso o n th e , : . , dire c tion. To obta in fr e e f i e l d m e as u reme n t s in this e nvir o nment, it is n eces sa r y t o s u b tract t h e re ve r- _ ., b e rant fiel d stre n gt h from the m ea su remen t .
Th e reverber a nt _ield strength is determined by a calibration pr o cedure w h ich is illustrate d in Fig. 15.
" _' The c h a r act eri st ics of ' a sou rce, dep icte d b y t h e louds p e a ke r i n t h e f ig u re, a re me a su re d in a n a n ec ho i c ch a mb e r, o r ou tsi d e, to d etermine t h e free fiel d characteristics. T he s o urce I s t he n place d i n : he win d _ : '_;_ ;: t u nnel te s t s ec t i on , w h ere its characteristics are again m e a s u red. Th e in crement b e t wee n t hes e two m e a su re- ' m en t s is t he s tr ength of t h e re v erberant fiel d . T his i n crement i s s ub tra c te d fr o m t he win d t un ne l d ata on , : _: a I / 3 octave b a nd ba s is. Fo r c o mpact n o ise s o urces, a sp ea ke r can u su a ll y b e u s ed i n t he d e te rmin a t i o n o f th e re v erber a ti o n correction; however, for extended sour c e s , such as s upers on ic jets, the corre c tion can _ " b _ st be determ i ned by de ri v i ng the c o rre c ti o ns us i n g t h e actual s ou rce t o be m ea su re d . Th e w ind tu nn e l , _- o; i', st ru ts , a nd m i cr o ph o ne ,w) un tsa l l c o ntribute ba, zk groundnoise, w h ich fo r s i m pl e measurements m u st be l ess --ii" t h a n th e no i se fr o m th e sou rce bei ng st udi e d . F o r no sig n ificant backgr ou n d n o i se c o n tr ib u ti o n, 1 0 d B '. se p a r at io n is re q uir ed, whl l e d a t a with gre a te r than 3 d B separation c a n be c o rrec t ed. A 11 d ata us e d in ' : th i s p a p er wer e suf ficie n tly ab o v (; t h e background n oise l e v e l o f t he wind tun n e l t o extract th e d a t a. Where , the ba ckg r o u nd level i s t o o high f o r co nventional m ea su rements, a ph ased micr o p hon e a r ray ( re f . 5 ) ca n be o ' : us ed t O ext rac t t he noi se b ei n g mea su red fr o m th e ba ck gr ou nd no ise . Wi n d t unn e l d ata u _e d In the follo wing _' c o m p ar isons wa s c o rre ct e d f o r reverberations as prevl o us|y d e s cribe d . In a d di t i o n, some of th e d a t a in the _ ; F - f06 J et nol s.e com p aris o n w e re c o rrected for background a n d near-flel d e ffe c ts. T he ef f ec t of meas u rements : i n t h e ne a r f iel d was obt a ined b y s u btrac t ing a n o ise i n crem e nt f r o m the d at a t h at were de riv e d f ro m a tom* ;i_ par t s o n o f n e a r-fi eld and far-field d ata from t he static tes t s tand.
o! Fl i gh t te s t d ata have been c o rrec t e d f or g r ound re f le c tions and, where necessar y , the d op pler shift.
. _i, The tre a t _ nt for di ffe r en t m ea su ring d i s tances v aries wi th the particular tes t a nd i s desc r ibe d in e ac h : case.
Comparison of N o is e -Data XV - SB A ircraft: N o ise was _a_ured i n the win d t u nne I a r l d in f l lght fo r t h e X V- IB f Jy_n g i n b ot h the fa n Z - - p o w e - r-_ -a_j - e- t=powe r ed f ligh t n _ d es . F i lght n o ise d ata we r e c o rrec t e_ to the mic r o- p h o ne d i s tance f o r th e wind tunne ] noise m e asuremen t s. F_,_s. 1 6 through 18 show spectra from a in d tunnel an d flight for the XV-5B in the fan-powered m{_Jeat a n airspe e d of l O Wn()t s . In Fig . 16 t he microphone was far _" " a he a d of t he aircraft. T h e sp e ctra ag r ee within ' _ d l Ja c ross t h e sp ec trum and ov era ll s o u n d pr e ssure lev e l a gr e es within 1 . 7 d B. Th e n_I. _ a use of th i ,, d i , ,t'ep,| n c ] I, ; d _ 'd _ disLre I)d nLyat the fan f u_ , lamental t r a m P, Th e micr o ph o ne f o r the data In Fig . 1 7 is als o ahead u f the _irura f t, Just f orwar d of the n r _se. Again, the " spec t ra ag r ee wit h in . 3 d B, b u t the ov era l l sou n d pressur e level is within 0 . 7 dB. T he data i n rig. 1 8 are fr o m a micr o phone behind the aircraft. In thi_,_ase. the spectra are in g o o d a _ J ree_en tt ( ) 16D0 Hz ; h owever ° the fan t o ne in t h e win d tun n el was 5 d_ hiqh u r than In fllqht, and the wlnd t u nnel mPa_ , ur_._en t _ a t hl q h fre- qu enc y were conslstent l v above the f I iqh t {_e a sur_ , e .t . In assessing the shape ,_ f the % -,e_tr,] ,_ndc_.,q_r_n_ l w lt h the oth er tw o mlcroph_)nep n _itto_s , i t a p $_ edr _pr o bab]e t hat the f li q ht measure me n t s -, f blade pa', ' ,in 9 f r e- q ue n c y , ¢ , P L , are in err o r rat h er t h an t he wind tt_nne ] _ u ast_re_ents. In any , ; ase,the wfnd tunnel _,_is_' , '_e , _s- uromen t _ give a g o o d rep r esentati{,n of t h e f l i ght meac, J r e.._n t ' ; for th e X V-S [ _i n fan-pow e r ed f l fq h t ' : Figu re I g s h o ws the n o i s e spe_tt ' a f ,Jrth e W V-SB i n ) et -pow e red f l igh t . Thes e d a t a w_re rep o rted in ref. 6 . In t his _ase, t he no i se was predominantly broadban d in na t ure . T h e ,,pe ct ra s h_)w r ; auree within ' : d B , w hi ch wa s a lso the a c cura cy ,f the s p ectra fo r a ll o f the r_ea su rl n qpositi o ns. I n term . , ot _ w e r aIl ; sou nd pres s ur e l e v e l a nd p er cei ve d n (, i se l e v el the wi nd tu n n e l an d f li qht meas u r e m e nt s agr ee d wi th in 1 d B.
, Compa r iso n of N o i s e Dab_ - YOV- I O R , ! Aircraft: [)u r lnqthe wi n d tun n el tests o n t he YOV -I O P [ . Fai r c r af t , w a - s - _-e_-u_ 6 _ ] -an_- t !lien co _P_ r 6 ( l w - _t__ I _ q - ] _t t, , ' , t_ , . F i ,|u r e_ ' ( } s hr ,wsnoise sp ect ra fr_. nth e w_nc lt unnel , an d flight te st f o r a mi_ ' rnp h n ned l r e E tly _nder th e huge , , f t h . - a_r( : raft. Th e data have been ,_ , r rt '_ t e d t (_- t h e m ic r o p ho ne d_tance of lg ft (f.H _) the di,, t a n , ( , r_ f th e w i_d f u , m nl c . _ ( , ) _ . ur e m e nts f u r the,, (,r i arise , ' .
The sp e c t ra agr ee v e r y well , bo th for t h(, hid , i(, p ,_,,cln_ f r eq . _n , y (._,,l,_ r ,ents an d the b r. ad ban,_( , _:, r ,( ) nt - n ls .
. , . , I 1g-4 Ther e d o es ap pe a r to be a p r obl e m a t 1 0 ,000 H z th a t ma y be caus e _ b y e xc es sive line lengt h for t h e fl i ght te s t measur e ment s etup. A s s ho _ in r e f o 6, t hi s good agree ten t was typic a l f or al l mi cro p hone loc a t i on s .
The over all F A R- 3 6 take o ff and la nd i n g no ise l ev e| s for the YOV- l O R C F air cr a ft a r e ver y to w. IJ urinq tak e off, 3. 6 n a ut i c al mil e s from start o f gr ound r o ll , t h e n(_t_e lev e l was ] e s_ th d n 83 P NdI _a nd d u r i nq l a nding a pproach, w i t h a desc e nt a ngl e o f 8° , th e no tse dir e c tly b e ne a th t he ai rcr a f t at d i_ La il ( e o f ) n a, J _ ttc a l m i l e f rom touchd ow n was a bou t 88 P NdB. Th is i s p a rti ally du e to t h e st ee p gr a d i ent $1 0L pe rt ( ) rma nc e c a pabil it y of t he ai rcr a ft, but tn la rge par t i s due to t he lo w t i p s pe ed of t h e reduced d ia me t er p r ope ll e rs.
Exhaust Suppressor M e a su re me n ts J-85 Engine: Although no t d ire c tly r e lated t o V / STOL, a compar ison o f wi nd t u nnel a nd f li ght measu r e men t s of n oise of e xhaust sup p re s sor s prov i d e s fu rt he r i nf o rmat i r)n o n th e q u, . , .ti( , , , of whether ground- ha s ed f a cil i t i es c a n b e used to ev a l u a t e fli ght no i se s ig n a tures, Fo r _nm_ , t l m _ ,o [e w i , _ Rese a rch ha s studied th e effec t iveness of mi xer-supp r essor e _ h a us t nozzles i n f li gh t u sin g t h e F - I O _ , as th e test b ed (Fig. 2 1 )° A nac e ll e wit h a J -85 j et eng in e a nd approp ri a t e supp r esso r ha r dwa r e w a s mounted und er - ne a th t he wi n g . The a i rc ra ft w as then f l o w n ove r a noise t e st _ a n ge a t 3 0 0 f t a l tit u de wi th t he p ri m a r y power p l ant th r ott l ed back a s much as poss i b l e.
T he same nace ll e, wit h t he J -85 engine, a nd s ome o f t he s a me m ixe r -supp r essor nozz l e s we v . , tes t ed i n th e 4 0- b y 80-foot wind tunne l ( v ef. 7). The n a ce ll e w a s moun t ed under t he w i ng o f a 3 / 4 sc a l e mude l o f th e F- l S (Fig. 22) to s im u l a t e th e i nsta ll a ti on effects. I n o r de r t o ma x im ize s i gna l - t o-no ise r a ti o f o r the qu i e t e r supp r essors, the m ic r ophones we r e a t a 13-f t (3.96 m ) s i de li ne dis ta nce f rom t he j e t . T he effect of me a su e t ng in the nea r fie l d was co rr ecte d by a n a moun t determined i n outdoo r s t a tic tests. Th e w ind tu nne l .d a ta wa s ext r a pol ated to a 300-ft ( 91 .S m ) sidel i ne fo r t h e compa ri so n. In these cas e s, spectr a f r om t he f li gh t data wer e not a lway s av a ilab l e, so the c om pa r ison i s of p e rc e i v ed noi se l ev el .
F igure 23 shows t he re sul t s fo r a conic al ejector nozzle. W ind t unnel and f lt _ht t es t d a t a a g ree _th tn ± 2 dE except fo r t he rear -most angle. Figu r e 24 shows r esu lt s f o r a 104 tube nozzle whe r e t he w in d t un n e l e nd fl i ght test da ta ag re e wi thin ± 1 dE . F t nally, figu re 25 sho w s da ta fo r t he 104 t ube nozzle w it h an a cous t tc shroud w hich sho w s ag re e me n t w i t hin ± 2 dE . I t sho u ld be noted that t he d a t a f o r 1 04 tube no z zle with out supp re ssors w a s not ava il ab le a t some an g les fro m t he w tnd tunnel te s t s be ca use the b a ck- g roun d no i se l eve l w a s t oo h t gh. Thus t he backg r oun d no i se level of t he factlt t y c an se r iousl y li mit t he data obtai n ed. Use o f a phased m icropho n e arr a y desc ri bed i n re f. 5 wou l d have sol ve d t h i s p r oblem.
4. CONCLUD I NG RE MA RKS Fu r the r c o rr e la t i ons be t we en w ind tunne l and fli gh t t e st d a ta fo r a t r c ra t t ha ve te nded t o c o nfirm t h e mo de l -to- w ind tunn el size rati os sugges t ed in r ef. 1 for V / S T OL te s t ing wit h sma ll wall c orre c t ion s . A s was em ph a s i z e d in ref. I, t hese li m it s a pp ly o nl y for le v e l , u nacc e lerated flight at s p eed s a b o v e 30 k n ots.
Indications are that for descending / dec e lerating flig h t of - ,= - I0 ° and O.2go t h e data will be useiul , but norm a l a nd axi a l a ccelerations m ay be in error.
Correlation of noise me a sured in the wind tunnel with that measured in flight was generally good , indicatin g th a t large wind t u nnels can be u s ed to m a k e meaningful noise m easurements at forw a rd speed.
ACKNOW LEDGE MENTS : The authors wish to thank tho s e st a ff memb e rs of the Large Scale Aerodyna m ics Branrh Re s e a rch Aircr a ft Projects Office, and the Flight and Sy s tem : Research Branch at the NAS A Ames Research Center who conducted the necessary te s ts and assisted in collecting the data presented in t h is paper.
REFERENCES I. Hi ckey, D a vid H. an d Coo k , Wo o drow L. : CJ _parison of Wi n _ Tunnel and Fli g ht T est Aerodynamic D a t a in t h e Tr a nsition Flight Speed R a nge fo r Fi_e V / STOL Aircraft. AGARD Rep o rt 520, 1965 (Al_o available in Conference on V / STO L and STOL Aircraft, NASA SP I16 , 19 6 6).
2 . G e Nes, Ron a ld M. and Hynes , Ch a rles S.: F actors Affecting H a ndling Qu a lities of a lift-F a n AircraFt Du ring Steep Termlr m l Area App r oaches. Presented at the )7th Annual National V / STOL Foru_ r :fthe American Helicopter Society. _y Ig71.
3 . Cichy , D. R. ; H a rris, J. W. and Mackay , J. K. : Flight Tests of a Rotating Cylin d er F lap o , , )_rth A_rlcan Y O V I0 Aircraft. NASA C R 21 3 5, Nov em b e r 1972.
4 . Wei be r g , J. A. ; Glullanettl, D. ; G_b u cci , B. an d I t .hiS , R. L .: T akeo*f and L an c l l n 9 P erfor_nc_ a rid N o i s e Measurement s of a Deflected Slip s t r eam STOL Ai r plane with Interconnected PropelIer_ an_ w , _t a _I r .'J C y linder Flaps. NASA T NX 6 2 , 320, CJece_ber197 ) .
S . S o der ma n , Paul T. a nd Nob e l, Step h en C. : A Directional Mi c r o p ho ne A rr a y for A¢oustIL _tudies tf Win_ Tu nnel Nodel s . AIAA Paper 7 4 -6 4 0, JuI_, I@74.
6. Ate n c io, _doI Ph , Jr. and C.._der ma n, Pa_l ? .: Co_,par_sonof Aircr a ft Noi s e Me a s u red :r r ll) h t T e_t an_J in th e _ SA A m e s 4 0- by _O - F o ot Wind T unr, el. AI_.APaper )3-I0 4 7, CKtob e r 1 973.
7. Be ul ke, M. R.; Clapper, W. S.; _cCann, E. O. and t% eoE_i, A. M .. A r c.r_r ' J _Pe_r J Ff(_.t ' , _t urJ _e_.
J e t Nois e F rom S e ver a l Suppres s or No z z les in th_ NAr_A / _S ¢0 - by P _;-Fc__t gir_JT_nr,_l ' t_ , ACP - )1 4 7 4; .
Ig74.
• . _ , ..
i I ]
. : 1 9-5 .- , : T a ble 1. - R e se a rch Aircraft Ch a r,cter t sttcs :_ CHARACTER ! SI' I CS X V -5B VOV- I 0 RCF Gross weight, lb 12,100 11,700
(kg) 155 001 1 53 20)
Mtng a re a , ft_ 260 . 3 244 ; ( m2 ) 124.17) (22.67) M tng span , ft 29.8 34.0 ;: (m) (9 . 071 (10.36) .,! , ; Fan or propellor diame t er, ft 5.16 / 3.0" 9.4 2 ! (m) (1.574) / (0.915) ( 2 .87) , " T / W ratio, untnst a lled 1.251total ) 0.45 _ Fan pressure ratio 1.1 - ' / : Ro tA ting cylinder, RP W HP 7 500 / 30 _ ; diamete r , f t 1.0
: .. (m) 10.305)
_i App roa ch velocit y , knot s 100 + 0 57.0 Decel era t l n9 _ :'- _ , Appro a ch CL V / STOL 4.3 _ " App r oach y, de9 -10 t o -20 -3 to -8 Stdeltne Noise Level, PNdB ? 1500 f t 1152.5 m)) Ta keo f f 113 99 :" Landt n9 11 2 93 :; : i _ ltng F a n / No se F a n Diameters / , ".',,'.
/ , z FI g. 1 )V- SB f a n- l n - w ln g ai rc r af t Fi g . 2 Y OV- I O RC f A ircraf t in f |i q ht t e s t in fllght t e s t . , , .. . ,, , '° .... _ , '_ .. i . . ll :" ; /"i' . 'IF.? !_' . ' : _,i'_ ' _ - ,' "i,I_:: . _\ ''_ ' " " q c, _, o _ v , ,_ )# . , ,, ,_ "" +,, ....... _ '+ + + _, '> + , : ",, t _':' ' " L ..... , _+_ " + , I I
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_ ' ) ¢ t I 19-7 , . - ; !
' ; 1 9- 8 :. o -3 0 L--. _ -J - ..- - - I - J • ! ! !I m j ! I I ! J T3 0 1 2 4 6 8 10 Ib 29 30 40 6 0 OI S TANCI: FROM SOURCE, ft Fi g. 14 Reve r be r a n t ft e l d meas u r ed t n the _12 o j _ , _ 40-b ¥ 80-foot tunnel f r o m an .; •
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g It / _,, o o . . S NA K E . I N F Re_ = _mt D S ee AK eR m T _ S T S E C : .ON _ _ ' / _ '_[ A mCHO m =o X. _y _r a_ mNT S o _ s Pt : " WALL _ OU _ 90 b O WtNO _ NNE 1 1_, _ IOL- ................ 1 ......
" , ' _J _ MIC _ 1 " 0 1000 10 000 " " 50 " -- _ MIC // , C , @'! I'_ F t g . 17 C o m p ari sonof no is e sp ectra in t he wi n d ' I I _ tunn e l and i n fl i ght for th e X V- S_ i n f an poweredfl i ght , V = 70 knots
• . , , ,. , _ , . ouNo
_ - / .1 . F i g. 15 Reverbe r ation cal i b r a ti on ,r 100 # # 110 _ ;_ 65 Y,*" 9 ( 0 WI N D TUN N I L 1 _ 1R _ 100' - - '" ' _ IN L1 lllt, d_l t 1 _ 8( , _, ' 80 ! . J _ _ -" u tO0 tO00 tO,O00 l O _ t O( R _ I n re) r .
, FR _ O UI NCY . He _ H _ Ot I_ NC _ _ I _ . : t : F i g . 16 Co m pa r is o n of n o i sespec t ra in t he win d F ig. 18 Co m paris o n of nois e spec t ra in th e wind '. t u nn e l and in fl i gh t fo r t heXV - SB i n fd n t u n nel an d in fl i g htf or t h e XV-St l i_ _ a.
: powered f l i gh t . V = 7 0 kno t s p o w e re dfl i g h t. V = 7 0 k n ot s J ,
t I
19-9 160 ....
V 1 00 kflol _ I W IND TUNNEL DISTAN C E) - - 198 1 2 0 ACOUSTIC AN G L E 1,, l(V 58
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_ -- MIC R O P HONE I OASPL PNdB l: 0 FLYOV E R 110 . 8 122 7 6 0 O WIND TUNNEL 100,0 121 6 40 ,- I ! J S O 100 1DO0 T O .DO 0 FR E QUENCY, H # F t 9. 19 Compar i son of no t se spe c tra t n the wt nd tunnel and t n f11ght for the XV-SB _ n J et powered fl lqh t , + ....................... . , ; +........ . + . • .................. _+ . .... + - ..+,+ ,. _+. . _+_+ " " + '-:++ "
. .: . 19 -1 0
I_ O _ oF1068 FLIGH T OiTA ' , _ • 40 BY O0 WINO TUNN(L O A T& ., 90 _ - VR , _m l l lc 11780 ft / ll¢| ACOUSTIC ANGUE RE ]q _ TO INLET. ci8 9 Ftg. 25 Compar i son o f w tnd t unnel data wit h fl t ght ,'; data for t he 104 tube nozzle wtth acoust i c shroud .!