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A Z V ._4A B Y 0¥ _J.._7._ S S- R C'I_ ) M___K_RCK AT ![ASA - ,I__NCL E Y J o hn F. W a rd arJd Robe.-_ J . _us_o u Aerospa c e E_Ine e r . _i Tre n ch _._ _-qlght Me c ha n ics a n d Tecb_l ol og j D i vlsl e n : N . _ S A Langle y Res ea zca Center _ _" _ 5 _.3 _ _ a_"pllt n d e o f b l ade first b_r r .onlc flap p i_ " _ _r 4 _l e w ith re,pa c t to _f_% f t _xis, r _di_s res e arch InYestlgatl o us c o n_u . _ted at the NASA 7 blade !_ck n,_._.ber z La n gle y :_esea r ch Ce n ter - These Inve_tlga_ions 4 include first; an explorato_-q_ fllght-te_ pz'ogra= 3 bl_e cyclic pitch az Litud£, radlans ..... inK a thr_e-bIRde hID_le . _ ro_or installed - { on an H-I_ __eLiCOl.ter; mm_,, second, the _ud-tar m el 90 b l ade collective oir, eh a r _le , r_i_s _estln g of an a e _elas_'-ai! y scaled rese arc h model . ? o_. a .hin_eless-rotor hel!copte_ ___ si_ralated for- el blade twi_ _. , tad!ann -_ ws_-_ Speeds up to _0 _ wl_h full - s c a_e _.eynolds [ n u mber a n d Mach member sL_,-la_ion. T _e third a re a of eff u r_ deals w ith the a n a lyt i c al t reat m en t of )' In _low rat i o . the hl n ge l es s rotor. This work _ s d o ne t o d efine t he fumdam_at -1 r ea sons bahia9 th e res u lts obtai n e d _ r o tor t . i. _ _- gu ed __a_lo i n t h e e x pel_m en ta l in vest,_at x ens.
'__s blad e first bending mode , ncnretating , The flight-r e.a t-progra m re s ' .%11_s lllu_trate na t u r a l f r e q uency, c_m th_ in;roved -^_t-'_-I _er and damping cha c acter- "st'_c_ of the . hi, g al en ,-rotor sy&t_ a n d th _- _ rotor _o'_at!on&_, speed, inf l uence of the increased _ue u _erabilit7 on the rotor st_- i ctura ! l o ad s. _ r<-_Its of the dy n amic fl_, n o rm al o_erating rotor _tations: -_pc_d, model wln a -tuD m _ el in v es_i._ / _ti o n incD*d e a _ rpm of the e ffect _n s_ruct u r_! loa_ s and d)_s a .mlcs of " redeci ; 4{ rotor blade eho_ ! __ze stiffens tO the-- introduc tion !ev_l o f the blade fla;wi_ s t i ffn e s_ _ _ / _# The r_ - n e wed interes t in utilizing hin_ e l e ss No t ati o n ro t or s on th e helicopter st em s from _ he p o t e ntial .' _lv ant a g e_ that may be . chi evc d In tbr ee p rincipal • A i bl_e l o r_ituilr_ ' , cy c lic p ! tc h am p litude , area s. First, b e cau s e of c antilever action of * h e rad_ns hingeles r blade system, large s lr c raft control m oments are transferred directly from the rotor mo rotc z c oning ar 4 _le, r_di m ns int o t h _. fus e lage a s a stron g source of a lrcr a / ' _ _It c hlng a u d ro lling m_ment. _hi_ resu l ts in t B l b_ade la te ral cyclic 9it c h amulltude_ o rder -o f-m a gnltude I m pr o vements in the co v tr o l- " - la b i_ _t_ and f]_vln g qu alities o f the h e li c opter.
r_lans The s econd area of imp r oveme n t stems from the blade _ c tual r ig / d offset, no n di m e n siozal op portun i ty t o ach ieve _u bs t_nt i a l re duc tion i n rot or h u b dra_ . __"_ s d _ redu c ti o n co _- - _ a b o ut I mass _r__rt c,f ine 1 __a of _.iade about as a result of the aerodynamic _xeanness that may fla_plng h'_ng e , s_ug-ft 2 be schl e ved b y the elimin a tion of flappi_. g and lagging hinges, in-plane u lade dampers, _nd asso- K pylon suppor_ spra_ m Iffness, ib / _n, elat e d hardw_rm in the vicinity o f the r o t o r hu'D.
• This reduction in co mplexity leads to a third ar _ a _ effective s;rl_ st if F ,e s s , A r t ual lag of improve m e n t, w hi_ i s a su_ bs t a zti al _ d' _,ct io _ hi nge , I n - ! b / radls m in ma c han lca] _Inte n_nc e .
M total hub m o m ent, ft-lb The log_.cal qu e stion t b _t ar i ses is: If the hlnge l ess system l oo k s _ ,o pr e ss i ng now, why _ s MA longitudinal hub moment, ft-lb its dev e lopmen_ been postpo ne d f o r s o ] . o _? As po inted o ut in refer e n c e I, s ome light ca_ b e saed on t hls question b y co n si der in g a b i t o f h i _ tory MB la t e r al hu b m o me n t, ft -l b c o n n e cted w ith an e arl ie r non s rt i cu la t e d or b in g e- les s system . I v 1 939, ian_ ie y f l ight te_te_ a Mti p rot o r advanc i ng t i p )_c h n u_er n on artlcu la ted, st i ff b l aded "rigid" r o t o r (_f. 2 ). O n e of the conclus i o n s resulting fr om q air c raf_ pltc h in_ velo c ity, zadis m s / sec this i nvestig a ti on w as t hat flexibil i ty sh o u1_ b e i n trod uc ed i n to t he system. I t is b el i eved th a _ V velocity along fll g ht p_$h, m F n mo s t and perhap s a l l past fail u r es with "r i g i d" Vsi m simulated I_ ll- scsle velo c ity alo n g f l l@ht rotor system s in volv ed attempts a t p reve n ting, path, mph L-3983 i instead ¢ ,f incor p or a ti n g_ flexibility. T_day's aircr a ft'z flY % 'k / qualities. This instrumentation hlnge_e_ - _ rotor designs do not atte_ to avoid included as.Debility for measurement of alr-raft fl e xibility bat, rather, veryir4 a m u unts of flex / - center-of-gravity lln_ar acceler a tions; a._rcraf_ bil l ty are used _a s means c.f alleviating hi gh angular-vel o cities in roll , pitch a nd )_w; and ztres. _ levels i n the ro_oz sysLem, pil o t's contr o l p ositions.
Most of the recent resear ch a n d devel o p ment Co'.tr ol and ..esDonse of t_-_ _ hi."_eless r e %or pri:l_ip!e has been carried o u t hy L o ckheed A l rcz_ft Cot @ oration, Bail While the docu m entation of the sircra ? t_s chosen %he hingeless-re ;or helicopter as its entry p a rticul a r program , _he aircraft cent-el a nd i nto the helicopte r f_eld . , is in','olv, ! . '.m the r esponse wil l be discussed flrs1_ in order to dev e l o pment of wh a t _s Intended to be a u op t '_zed d_scribe the gener a / behavior of the r esp o nse t-_ o p erati on a l aircraft of th_s type (see ref. 3)- p i lot contr o l a nd in order to for m a basi s for _he Bell's work o n t_e hin_ele_s roto £ (ref. _) has l_te r _Isc,,ssl o n of the s t ructural l o ads associated _ m vol_ed the use of a n u mber o f experimental rotor " - _-t.% the a ir c r a ft's r espor._e.
systems insta l led c n e z lst! n _ hellco!_ers to pro- vide research information. _easured re_-_Onse.- The faverab!e flying qual- i_!es c'_ _he hln g el e ss rotor be , : _._ _ult e obvious Beca,a&e of it_ pot e nti al for c ontributing te early in the flight p_gr a m. A s a m ple illustra- _h_- so l uti o n o f s om e existi n g llzlt a t t o ns of t h e tl o n o f the i m p r o v ed c h a r a cter i stics i_ . p e ese n _ed articulated rotor system an d the nee d for _:- - 'c_- i n figure _. This fig u re, taken fr o m :_ference 6, sta n d i n g t h e _eandame n t_ - i a dv - nta_s ad d res_ric - shows a t_e hist o ry o f t h e a i r c r a ft's ang ul ar ti o ns o f t h e hi_-_c i _ss &vst_, _ 1 3A - __m n g!ey bms v _ locl ty in p i tc h pro d u ce d by a l o n g i tudin a l co n - _,_n-dc: 5a _ _: n a re_ e n r e h p rog r a m i n volv i ng both trol step _ n put. The r e_n_e of the hinge l ess- fli_ht and w ' .__i . . t u nnel t-_vest_ - _ticnz. - "_ c pr o g- r o tor h_iico p %er _uOW_ o y _ne solid line is very res_ zf t_l_ - : e*_ has _en _ po rted In r efer- rapid when c o ml _ re d to the response of aD - - rLizu- e m c e e i, 5, 6 , ann 7 . _-e present p ape r w il l re,m- lated rotor a s i n dicated b y t h e dashe d line.
m a r lze t.he re_nll.a to date an d p.-c_ent s om e. of the ge n - -rc! stz - a c tu r a l an_ dyn a m ic c b_.-acter i _.i c s of Ya le improvement in a i rc raft respons e is f a r the b l n_eless-rotor syst._ m as dete rm i n ed from th - m o r e s i gr l fic an _ th_n c a n be in d icated in f i g- flight and wind-t u nnel inv._stigat l ons, g_r e 3( a ). As pointed o , ,. %n referen c e 6, the ti m e l a g of the hinge! a s s syste m , d u e _o a r a mp ___* i_ u t in control, plus the time constant (the time required to reach 6 5 p er ce nt c_' the stead_'-state I n o1-_e, to begin ex p loratory fllght-test value) I b of the o rder o 2 t w o-tenths of a seco n d.
work wlth a hin_eless-r o tor system, N A SA l_ / rch a sed Because of the "tlgh%" respOnse of the hingelesa f r om Eell Hallcopter Comp a ny s dupl i cate of s u , sys t em, the zilot rece£ves early an l clear evidence exl e t izg set of experiment a l h ln _eless-_9__-v co_- of , _ h. _ angular velocity dev e loped by the contr o l w_nents (see ref. 4). Thes e roto r a n d centrex motion. In contrast, the sample a_ l oalated rotor syste m c o m ponents were installed on an Ar , ,_ r_£p o nse i_ _ach th a t the pilot mu_ wait over s u pplie d _-I3 G helicopt e r s u nd a fl'[,IAu-te s t pr o - i serond before the resulting steady-sta_,. _ngular gr a m wa s ce r rled o u t at i , ' _ m gl e y. T e e % e at a .' r- v el o city i: rea c hed.
c raft is s_e w _ i n figure i. _q!Is aircra f t we . not i n tende d t o _ ' e a n o p t l m um d es i gn b u t was an a vail - T h e _eas ur ed co,,tro _ i*_#e r and damping (in a ble exper L m e%:tal vehi c le which offered a n o p po_- pi t ch ) of the hin_e_ c ss system is plo _* " i i n fig- tu_ i ty to c c _dt ' e t a _'elimi_ ar y investig a t ion of ure _(b J ralat_v_ to the h a nd din z -qunlities b_ u nd- t h e hluge l e ss - ro te r c o nc ept, ar i e s o f r "h_ren c e 8. The hi,_e l e.,s rotor H -1 2 C ,_ u lly . _-_ts the mini m l_ req u ire De n • s v - nd, in f a ct, Du r i n g the p r o g r a m , da t a wer e o b t a ine d fo r po_ u sses con t r o l power a nd damp i ng values an v a r i o us f l ight co n dition s throug ho ut the forward- o_d e r o f mag n itud e grca_e r th a n conventlonsl arti c - s pee_ r s .T_e. I n a d li tl o n to level-flig h t c o n d i- tl a ted l_+zl_. P r evious in vest i g a tion s by N A SA to ti o n s dat a were obt a i n ed i n a ut or o t a tio n , ve_i ca / _qt_ o l lsh min i m u m desir a ble contr ol and re s ponse dem e snes, "+.e e p turns in le v el an d a u t o _o,._t(v _ ch_ra c ter l st ic s (:_f. 9 ) c overe d o nly i h e b o rl _m f l ight, toP, sneers, and _lope take o ffs a.z_ c or_er of figure } (b) sh own a s the line d and l a n d ing, 6 , do tt-d a re as . The cal culate_ co ntrol powe r en d da m pi,'g of the H -13 G hingele_s r o tor is also pl o t- Tnst_, u, ent a tton ted in fi_are 3(b). _s l_ , tnt was calculat e d, using th, _ methods o f :- eferen 'e lO_ ass u ming no Since the princi p al inn o vation _n the h i n 6e- control washout . Actually, the H-l_G contr o l less system is the abi l ity to transfer large sy s tem had a n o nll a ear washout o f contr o l input m o ments f r o m th e rotor system into the hub and which was a fucction of pylon deflection .
r o tor shaft, attention was f o cused on the m e asure- meet o f the structural loa d s in th i s a_ea. Another exampl_ of the im p rove d flying qu a il- Details of the huh s s sembly are sh o wn i n figure 2. ties of th_ s hingeless _'_t o r is reflected in the •he blade root, hub_ rotor shaft and contr o l link- fact that with no artifici a ± c+abilizatio n devices ages were the p ri_a_y components selecte d f o r nor a tail s u r face on t he fuselage, the test s ra l n-gage instr u ment a tion. Fli_ht-tes_ instru- rot o r-fuselage Combin a ti o n was stable througnout mentation a l_o included measureme n t of the the speed range. T he response o f the helicopter to a pull-and-hold m aneuver at 79 m ph is shown ill presentation is used in figure 5(b) for rotor fi_,re h for two differ e nt spra_ mount stlff n esses, pitch angular velocity damp i ng moment and damping (The sprag moun+s r _straln the lower axtremes of cross-coupl_ng moment.
th e rotor pylon which is essentially pivoted near t_ aircraft ce '. ter oi' gravity.) The time history Referr i ng to figure 9, it can be seen that it of the normal acceleration is s e en to be concave would requJ re approximately 15-percent offset for _ow n war d within 2 se c on d s for t h e har d s p rag t h e articulated system t o a c hiev e tn_ c ontro l- a n d mounts and w i thin slightly o ver 2 sec o nds f o r the da m p ing-mcment c a pability o f the hi r _=le _ _c system s oft sprag mounts. A sh o rt-p e r i od oscillat' on with a zer o offset. If eo u - ! vaiue_ o f _,ifset a r e t app e a rs _o " o e 5iightiy more prono un ced for the used for bo_h ayzt=ms, _he h i ngei _ _ss rut_,r pru v id=_ i har d sp r ag mounts than for t h e so_t sprag mounts, gre _ - _t_ c _ub mOm e nt capa b ility ov e r th e rang e of believ ed to b e a t le a st part_ ,// _ - due to the giv e n offset hi n g e d rot o r design, _h e s i mpl e i Th e sta bl e re sp o ns e t o a pul l- a nd- h old r_u e ,__._ c r is p ractic a l offs e t values. I n oth e l wor d s , f o r any | res u l ts of a n e ffect i ve spring consta n t between removal of the hinge, chang i ng the bla d e funda- + . he _ w as_pl a te and the pilot' s c ontr o l. Th e m e nt a l mode from the p endulum mo d e to the canti- elastic r e str a ints at ; he lower en d of the rJtor moma_t capa b il i ty . This i s equiva l ent to supp?ying i fl e xib i li ' cy in th e rotor mast c o upl e d w i th tb_ lever first be nd ing mod e results in an i n cr e as e in mast r e s,A l t i . _ the control syst e m having at . e ffec -- an additional l O t o 15 p e rc e nt of effective offset tire s p rl n @ be,_w e en th e c o ntr o l input an d sh e to the c rib _ hal hing e d r o t o r . This i ncreased swas h ul a t , _ . Mil le r has in di cated t h e improve d momen_ c a p a b ility is ac c omp l ished with t he lik e ly res p o n _c c haracter i stics the o reti c ally ob'c ai nable prosp_ -c t of a d ecrease in hub d rag and complexity.
b y th e use of "rigi d r o to rs ," or fla p pi n g o ff se t (ref. 11) or the u se of spring an d dampe r s i n the The influen c e of bla_e eti_u_Lu_l stiffness c o ntrol system (ref. 1 2 ). The combi n ati o n of a on the e_ntrol moment and d am ping cap a bili_ :y of h i n geless rot o r (resulting in an effective offset the hlngeleos syst e m is i l lustrated in f igures 6(a) o f app roximat e l _ " 1 2 per c e n t) a nd t he e ff ec tive an d 6( b ), respect r _ely . The varlatic _ _o f r c tor spri n g in the c on trol s ystem h s _, in thi s case, h u b n cn d lman s i o na l lo r_itu d inal c cntro l momont per res u lte d _m a helicopter with angle-of-atta c k eta- ra d lan of blade lateral cyclic pit c h and the r o tor bil i ty. T h e effect of a cha n ge i n the sprag hub d amping mome n t p e r unit pitch angul a r velocity stiff n ess (or " the cout_l-system spr i ng) has modi- are presente d (left-han d p lot in fi_. b( a ) a n d fied the stability char a cteri s tics. 6(b)) as functions of rotor bla d e nonrot a ting first-mo d e z 'lapwis e b e nding-fre q uency r u ti c _ Calculated control s ued da_i n 6 moments.- It a_ i s / _ . Curve s are pr e se n t ed for thr_e value s of iz f_ l , _ '-ntly stated that _he control-moment an d bl a de Lock number (_blch _epresents blade dens i ty) .
d a m pi n _-m_ n ent capabil i ty of the hlr_less r o tor These calculatio n s were based uD on the use of an may b e achieved with an a r tl_n L lat_:_ rot o r with eq u ivale n t o ffset hing e b lad e with s pring restr a int sufficient flapping hinge offset. It may b e of at the hinge, which g a ve the cantilever'first Interest to note in passing theft theoretical bending mode natural frequency an d approximate mode exami n atio n s ho _ _ there is no m_ch thi n g as an shape (ref . i 0) . The cr o ss coup l ing, o r r ol ling e q uivale n t flapping-hinge o ff s et wh i ch represents moments , d ue to bla d e lateral cyclic pitch input a l l characteristics of a hin_eless bla d e. A corn- a n d pit_:hi_ velocity are s h o wn in the rig h t-ha n d pertso n o f the hub m o ments of the hing e less and plot o f £:gur_a 6 (a) and 6(b), r e s pe c ti v ely .
articulate d systems is shown in f_gure 5 a s a f_ain the momant_ sac sh:_ n as a function of ol a de fu nc tion o f bla d e offset . In figure 5(a) acom- ronrotating first-ben d ing-m o de frequenzy ratio.
_arison o f the hub total c o ntrol mo m e nt per radian o f blade cyclic pitch is p resented as a A successful hingeleas rotor can be expecte d function of actual bla_e offset _ for a fixed t o have a frequency rati o of 0.2 or less, which is blade _aius an d a conventio n al bla d e stiff=hess, ap p roximately that o f the first cantilever ben d ing I n calculating the hub m ome n ts for th_ hinge l ess mo d e of curre n z articulated rotor blade d esigns .
rot o r the simpl i fied metho d s p rese n te d in refer- _l l g h e r _ a l u es of _ I s / _ re su l t i n high bending ence lO were used. T_is method utilizes an e qu ivalent "virtual offs e t" hinged bla_ wXth a stresses at the blade root becaus _ . of lack of the spring at the hi n ge which gives the approximate centrifu_._ t l relief on a ve_ stiff blade. Also as cant ile v e r b l a d e r l r st fla pwise be n ding mo de s ha p e in d icated l _ _Igure 6 t here w e a ld b e exces si ve s_ud n a t u ra l fre q uency. I n o rde r to c la rify th e cro_s cou p lir_ oi hub moments . The cro s s cou p ling ter m inol ogy use d in this pa p er _t is pointed out a ss o ciate d with bla d e lateral cy c lic p itch in p ut that the h u b moments i n figure 5 are compared o n ca n b e eliminated by p r op er mecha n ical p h asin g of the bas i s of "actual" rigi d off s et (the o ff s et of c ont ro l i n put; however, the r ed uction of the cross t >e bl a de fla ppi ng hing e in t h e case of t he attic - c o up l ing of angular v elocity dam p ing p re se n ts a u l a_e d b l ade or the point of a ttac h ment of the more diffi_ : it problem.
cantl_ e ver bl,de in the ca s e o f the hingeless s y s t em; The f t , f o re, once an a ct ual of f set wa s Th e si m p l est _I n ge le .s bla d e de si g n a p pro a ch as sig ne d to t h e cant il e ver b l _ d _ , an equi va len t w o ul d b e to provide a flexi b l e b l a d e w i +_ h t h e h i n ge d sytte_ wit h ad d iti o n al " vi r t ual " off se t l owe s t va lue of _ i s / _ w hich w ould prov i d e g e n - and s p r i n g ,_str aln t co uld be det e rm i ned . It has erous con tr ol pow er aud da m pi ng c a pab ili ty wi t h bee n a s sumed that the effectiv_ thr u st vector minimum cross coupling . The bla d e l l apwi s e flex_ - t il t o f t h e h / L_e_ess and articulated rot:,rs is of bility w i ll allow for th e centri, _ nga! relief of _ e cond or d er, _Ins co n stan t , a n d i s . roxi - la rg e a e ro d y n amic f l apw is e ben din g mo m en ts, th e r e b , r mately e qu a l for b _t_ ty p es (ref . i0 ). _ _e sa . _e minimizi n g the blade flap w ise b e nding s tr e s se s .
_f _ S _ actural _ ads m l Dd , t o o, t hat t he order of i mp o r+ _ ne e i m pl i e d in f i g u re 7 for the s ever a l co m pon e nt s doer n ot Th e g ener a l a ppr o ach i n t he i nv estig at io n w a s r e pre s en t t he ov er a ll r es ult s o f t h is st_:d y.
'_ t o sa m p l e a ll p r a c t ical f l ig ht c o n diti on s i n a n e ff or t to i d e nt i f y t h ose c o n diti ons w hic h re qui r ed D u ri n g the t e s t p rogra m , s tr u ct u r a l l oa d s m o st i_te an d d et ai l ed st ud y o f lo ad s a nd were monit o r e d c a ref ull y as t h e fl i 6h t en vel o p e d _ e s. _1c s truc t ural lo ad s da _ a obtain e d w a s ex pand e d in o r der to as s u re s a f e t y o _ f l ig_.
d u r in g the fl ig ht p rog r a m pro d u ce d a n u mb e r o f As t h e prog r a m pr og r esse d , it be c a me appare n t t ha t in teres t i n g re sul ts . Pr io r t o t h e f l ig ht progra m : b y u t i li z ing t h e im pr o ve d ma n e u ver c apa b i li t y o f it was a n ticipat e d t ha t t h e s tress le ve l s in a t h e h i_ ele ss - roto r sys t em hi g h s ru c t tu' a l l o a ds n u mb e r of stru ctural co m p o nen ts m ig ht b e hig h and we r e induc e d. I n _ne ral 3 t h e hi gh i oad ings w ere c ou ld pe r h _s li mit t h e n u mb er o f f l igh t c o ndi- n u t o f a crit ic al natur e_ and t h e _ _ _ er e a s_ in l o ad ti o n s inv e stl ga te d. Fo r th e most pa rt , t h e s e high l e vel w ith s e ver it y o f t h e m a n e u v er 1 'as ce r tai nl y stre s s cond itio n s d i d n o t ma t e ria l ize or cou ld b e no t un e x p e c te d , e s p eci a lly wit h reg ard t o r ot or a v o ide d wit h pr op er p ilot tech n iq u e , sh a ft a nd b l a d e fla p wlse bendln g m o me n ts . H o w - ever, the structural loa d ing of m o st eo n c e r_ Grou n d uper atlon.- With t he airc r a ft r e s ting t u r n ed cu t t o be t h e " in -pl a ne " or c h or dw ise o n t h e g r o und the ro t o r- s ha f t stress le ve l s w ere b e ndin g mome n ts i nd uc ed in the roh o r b l a de s. T he stro n g ly de p e n aen t o n pil o tin g tec hniq u e . The s_ n p l lt u d e o f t h e roto r bla d e-c h ord wis e c y clic hln ge l es s r o to r s ha ve the c a pab i l i t y f o r pr o du cing ben d i n g mo m e n t _ . s v er y s e n sitiv e to m an e uv e rs i n rely hi g h ro ll i n g a Ld p 1tc h i ng = nt s ( e ve n wi th w hich hig h ai r c r a f t e n @ u l a r ve l o cit ies were z e ro co lle L_c i ve pit c h _ as a re sult o f v e r y s m all d ev elop ed . In s o me ins t an c e_ th e a m pl itud e o f cycli c stick diepl a ceae n ts. _ h ere f ore , d u r _ t h i. _ ! oe . di n6 ex pa nded well b eyond t h e structura l g ro u n _ r u _- up a nd lift - off_ e x t_ care h ad t o b e fat i g u e l i m i t , du ri n g l_ i tc h an d roll ma n _ uve r s e x erc i se d b y th e p i l ot to k e ep t he c y c l ic stic k th at were wel l wit h i n t h e cap a bi l ity of t he nir- ce nt ere d . I t was n ec es s ar y for t he pi l ot to craft. The b u il d u p of cyclic chor d wis e b e _ d in g a nt ici pa t e th e c y clic t ri m p ositien du ring the m u m_ n t wit h ang ul a r v e locity occurre d in pitch en d tr an s it i on f ro m the g zo und to airbo rn e con d itio n , ro l l m -n e u v e rs t hro u g h o u t +, h e spe ed ra n g e. T his : In thi s c a m e it w as diffic ul t t o avoi d h ig h r ot o r - is i llu st rated lu f ig u res 8 a nd 9 w h ere s a m pl e s h aft c y c l ic s tre s s e s, t i m e histories o f th e bla de cyc l ic c h or dw ise !
b_ d ing mom en ts ar e p rese nt e d for a h overi n g D U _ s l o p e l a n di n gs a nd ta_-offs t h e sit u- _euver an d a mane u ver at a f o rward speed of a_io n was s_m ilsr to the lev el gro u nd co nd itio n 8 0 m p h. The s a m pl e l o ad s meas ur e m e n ts pr es e nte d b Ut, i n a dd itio n , i t was n ecessary for t h e p _lo t in f i gure 8 (re f . 6 ) are fo r a h ov e ring mane u ve r to arrive a t a level -at titude h ov e r co nd itio n, w h er e in the p ilot e x ecuted a lon_itu d inal co n trol Thi s add e d t o the dif f icnA lt y of a voi d i n g h ig h ste p di spla c e m e n t - _ . _ r e cov e ry . Dur i n g t he per i o d rotor st re ss le v e l s. Howe ve r , i t w as d e t e r mi n ed of m s _ n _m a n _ . r v_ l oc i ty, t h e bUil du p of t he that t h e b e st techni qu e was to ap p ly a l most f u 3 1 cyclic c h or_-_ l s e b e n _ng mo m en t s r eac h e s a m_xi m um col l ec_ive co n tro l first t o re d', c_ ,t _ gear of plu_ an d mi nu s 30 000 i n ch-pou nd s, whic h i s reacti on on t he ground p rior t o br i n gi n g t he ai r - a _J#e t he str u ct u r al fa ti g ue limi t of t h e bla Je .
cr a ft to a le vel a%tit u de wit h c y c l ic co n tro l . It sh_ald be p ointe d out t_at a large portio n o f T h e re ve rse co n t rol se q uence was u se d in sl o pe t h e s tea d y or _c an c ho rd w is e be ndin g mom e nt l enti l, s . I n ad diti on to p _l o t t e c hn i que , there ( a.. r_ro_ _m a t e l_ 2O, 00 C i n ch - p ound s) for this rot or ar e a n _ber o f a_, t la ble ap p roache s to w a r d th e cl ads is due t o t h e _la d e en ter- o f-_ravity axis re d ucti on of t h is s tr e ss p roblem, b ut it wi)D being n oncoi n el den t with I A e nev. tr o l a xis of t h e re qu ire spe cific d esig n a tt ent io n, bla d e .
| Flight lo ad ss . -The _a - f li g h t struct u r a l load s The o sci lla to r y f l a pwl se b en ding mo me n t I" e h qoun t e re d are _ z _ l _ e r ed in two cat e g o ri es - i n creases d uri n g t h e recovery ma ne uv e r, bu t d oes i_ f i r st, those m e as u re d in leve l flight an d , second, not sLow t he d egr ee o f s en sitivity to the m aneu ver i t he l o ads m e as u r ed i n m aneu v e ring flight, ex h i b ite d b y the c hord wise b e nd ing m_me n t . The : f lap w ls e b e ndi _ m o m en ts are m ea sure d _r o m t he I : Th e le v el -f ! _ h l , s trmct u ra l l o ad s i n p r i _ non ro t at in g d _ T _ p l o ad co nd iti on ; th . , the i _ r oto r c o m pon e n ts ar e s u m_iz ed in fi gure 7- m ean fl ap wise m_ e nt i n flight is a i _j. . ._. e ly a ' A l thou g h + . b e test r o tor wa s f abricat e d from s t a nd - zero st e a 'j mome n t _ n ditio n. _ a r d ar ti culate_ com p o n e n _. s ' , xce p _ f or t h e hub I _" i t sa lf J, the m ea s u r ed l oa ds exper i en c ed i n l ev el The ro t _ti n _ m ast m_se n ts d ur ln _ ' , _ t i al f l ig h t tA_ rOU g h o u t t he s pe ed ra n ge w e r e no t abo v e p orti on of t h e ma neuve r d o n o t bu il d u _ t o t he t h e de sign " f ati g ue li m i t" for t h ese com p o n e n ts , a ppl ic at io n of a co n t r o l mome n t beca u se _ ne ini- _ at i_ l imit" i s d e f ined a s the c yc lic lo ad t ial con t ro l mome nt cancels a m_e n t due t o s o ma anl _t ud e whic h _Itlts I r a fatig u e lif e e qu a l mi n or cen t e r -of-g ra vity of fset . Ro w e ver : d u r i n g to 108 c ycl e s . Al_ ou _ h _he pi t c a l i nk load s the reco ve ry_ _ re t he c ontrol mom e nt an d t h e a ppe a r to be the la r g e s t i n mag n i tude i n fig u r e 7, o f fs e t cent er - of -g ra vity m_u t ad _ l _ th e c y clic th e y we re n o t censi d e red to he unum _ all y h ig h . m a st mome n ts r e a c h a ma x _ _ urin g ma x im u m a n @ u - d ur ln _ t ran si t io n w ere on th e o r d e r of _ 8 0 l _U nd s t ha t carefu l de sig n c on sid e r a tic_ wil l h e re q ui r ed !
wit h a ze ro m e a n lo a d . Yt is i_ por _ to _ear i n t_ pr ovi de l arg e al l ow a b l e ce n t e r- o f-gr a v i ty tr a v e l in conjunct i on with _ ii ma n euver capabili t y.
T he max i m u m co n ti n uo us cyclic _itc h iank l o ad s f a r acce l eratl o _. X t a pp ear_ from t his resu l t i The si tuat i o n at a i orw ard sp ee d of 8 0 m ph i n of t he fi rs t - an d s econ d-p h a se t es tz n g wi l l b e a i. _ t u r n is sh ow n in 2 1_ .r e 9. A g al u t h e choz d - pu b li s h e d in r efe renc e 1 3 .
w i se be ndi p_ m om e n t s h ows t h e,l ar g e bu il d up _it h an g u la r v _ loc i ty , i n t h is c a m, t o a n am p li t ude o f A c o nsid er a b l e nu m b er o f dy n am i c c o n fi_tr a- 39, 000 in c h - p o und _, and ag_iu a_ o v e t he str uc t u r a l t i on s h a v e b ee n t es t ed d u r in g t he _r o gr a m .
_ fa t i g u e l i m it . C o n ti nuous o pera t i o n at th is loa _ R e s e arch in fo rma t ion o f g e ne r al i n t e rest r e s_ itln g l eve l wo u ld re sul t in a i O- h ou r fat i g ue l i fe f o r f ro m t h e p r o gram in c lu de s c om pl et e _tr uc t u r al l oa d t h i s rotor blade. In c on tr a _ t o t he lo a_ meas- an d aer o dy n ami c data for t h e various rot o _ c cn fig- ! u rcd in h ov e ring and m axi_ t m f o r wa r d-spe e d m lneuv e r u r a t io n s. R o t o rs t e st e d i nclud e d t ho se w it h c o ndi t i o n s are t h e loa d s meas u re d d u r in g the m a n e u tw i tted an d un t wi sted blad e s ; 3 - , _ - , an d 6 - bla d e ver s p e rfor m ed in au t o rotat i o n s tart in g a t 5( mph. r o t o r s ; a nd var i ati o n s in b l a d e f l ap wls e and c h ord - T _ is cas e i s sho wn in f i g ure i0 an d t h er e is a wise stif fn es s and st i ff n es s dis t r ib u tio n. Ea c h c _ap l ete la ck o f b uildup in ch o rdwis e b e nd l n _- of t h es e co nf i g ur atio ns w as t e s t e d t h r ou g h a m o men t a m p l i t u de dur i ng t h e m a n e u v e r, _-v e n t h oug_ for_ r d -s p ee d an d loa d - fa c t o r g r a ng e s i mu la t i ng an ang u lar velocity of 0 .4 red / see w as obta in ed, h e lico p ter, u n loade d rotor, an d co m poun d heli- copter operation.
Thi s larg e ch a n g e i n c h or d l o ad ma n e u ver s en - s i t i vity w i t h f li g h t co n ditio n pr e se n t ed a very Mod e l and Inztr u mentatlon in t e re s t i ng sit uat icn wh i ca req uire d a n u nder- s * a din g of the fu nd a m e n ta l f a ctors inv o l ved . To A s c hemati c o f the mo del an_. . s uppo rt s y s t em u nd e r st a n d t h is p ot en tia l p rob l mm a re a a n a n a_i - is show n i n fig u r e 11 . The mo d e l rotor i s i0 fe e t cal treat m e n t was und ertake n . The oretica l ana l y s is i n di am e t e r an d t h e f us e l ag e i s sup p orted o n a of the oceil l atory ch: _wise ben d ing m ome n ts d u ring soft spr in g mou n ting a bove the tunnel bala n ce m a n euv e r co n dit ion s wa s p erformed u s i n g an e q u i v a - s y stem . In the 16- Foot T ra n soT . ic D ycam i cs Tunn e l l e ut o ffset fla pp inf, hl n g_ rotor wit h s p ri n g _ speci al slx-com p o nen t stral n- gage b alance w a s re s trai n t. T h e res u lts of this a n alysis i nd icat ed u sed " i n st e ad of th e normal tun n el s ting balanc e that fo r a give_ co n figur a ti on th e bl a de o scil l a- arran s ement. Ir th e l_ull -S cale -T u nne l _e s tlng t h e to r y cho rd wis e b e n_ .. ing m o ment b u i ldu p dur ing t u n nel ba la nce s y stem was u se d. 90 - horsepo w er ma neu ve r s is pr i maril y d ep en d en t u po n c hord w i s e elec t r ic mo t or dr i ve sy st e m was in sta l le d wi th i n stiff n ess, collective p itc h , b ] _ .e f l app i ng, an d t he _e l a se o f t h e mo d e l an d th e mo del wa s coni n g de formati on , restra in e d in ya w t o p rovi de the rotoz amtitor q u e mo m ent. _ae m o de l wa s e ssentially "flow n " i n the M e ffi - K_ + - + + 2 ( i ) pit c h, cyc l ic p itc h , an d mo del attit,,de co n tro l 3 i npu t s u e re ma de .
Th erefore, in t hi s a u torotA_t i o n wit h low collec t i v e In addi t ion to t h e s ix-c _mpo n e n tb alanc e da ta pi tc h a nd re duc e d f la p pi ng, t he osc illa _ o ry m om en t availa b l e, t h e mod e l w as f ull y i n str u me nte d to du _i n 6 t he maneu v e r would be p r ed ict e d to b e su b- o b t a i n s tr u u _ u _ " loads , v i brat i o n , a nd c o n tro l s ta n tiall y r educed a s w a s t h e ac t u a l c a s e i r Po si t ion d ata. h is in stru_ en t a tlo n Incl M d e d t he figur e I0. foll owing .
As n ot ed above, t he amp li t ud e of t he b lade Bl a d e flap w ls e be n di n g m oment s ch o rdwl se be nd ing mome n t is p ro p ort i o nal t o b lad e Bla d e ch o rd wls_ ben ding moment s c ho r d wise structural s t if f nes s K_ , a nd t h is Bla de t o rs i o n Bl ad e p itc h p osit i o n o ff e r s a means of al l evlat in _ the ch o rd l oad se n- P i t ch llnk l o e ds s lt iv ity t o m ane u ver s b y re duc ing t h e h laS , e ch ord - S w a shplat _ p osit i on wi se st i ffnes s. A d e m cns tr atl o n o f t h _ f easib i li ty Roto r s_ u _f_t o r_,!o n o f re du c i ng b l ad e st ruc t u rs_l l oads B y l .e, l uc e d B o d y a c celer a t io ns (3 c o m p o ne nts) ,:h ordwi se s t if f n e ss wil l be in c lud ed in t he f o l - l o w ing d is cu ssio n o f h l n geless-r o t o r d _ mml c m cd e l B o d y p itch and ro ll m_ en t wi n d - tu rmel test results . B ody a n g l e of att ac k D_namic Model Inves_l_atibn The b al a n c e dat a were r e co rded on pun c h cards and s imul ta n e o u s l y all mo d e l i n str u m en tatio n o u t pu t • As p art o f t he hln ge le ss-ro t or res e arc h p r o - w a s r e c o r de d on an osci llo gr a p h o r mag neti c t ape . , _ gram, L a n gl e y h as t a ke n pa rt in a coo p erative R e su l ts _ , _ e ffort i n volvi n g U. . _. Arm_- T R ECO M , L ock h eed Ai r c raf t, an d NASA _ Tb Js pr og r a m _ as i n vo l v ed t he Ph as e I. - S e v e n roto r co_A f ig u ratio n s w e r e _ d re ign , co n Ltr u _io n , an d wi n d - t vnn e l tes t ing of t e ste d in t ------ _ L a n g le y 30 -F oo t by 60-.F oo t F ull- s ! / _sca le h l n ge l e s s - rotor h e l ico p te r mo_ el , S cal e Ttua nel . Th e se te sts cov ered a sim ul at ed " ' whic h was a eroel astic all y s c aled. Th e p ro gr a m ha s spe ed ra n _ e fr o m h o v e rin_ to 1 2 0 m i le s per hou r '_ _roc e ed ed in t hree p has es. The fi r st - phase and lo ad f a ct or s up to 2 . _.
t e sti n g w as do n , " , i n L a n gley 3 0-Fo ot by 6 0- Foot , F u ll -S cal e Tunn el an d t h e seco n d_ a nd t h lr d-ph as e % pho togra ph of the mo del i n _+ . allatio n i n t h e testing was d o n e i n th_ L a n g le y 1 6 - Foot T ranso n ic tu nnel te s t s ec t i on is s h ow n i n fi_ 12. Th e D y n amics T u nnel. The _uitial resu l t s an d e n a l ysis r o t o r co n figurat i on s t e ste d w ere a ll 3 b l aded an d ,_ 2 _ 2 th e b lad es we r e o f w i de ch o r d givi n g a rotor solid - Whil e t h e _ ss u l t s p r es e nLe d in part ( a ) of i t y o f 0.1 2 . T_e t es t i_ in t he Full-Scale Tunne ? f igures 13 , 14 , _n d i_ au_ f o r 1 g f liEb t , t he wa s d one to st u d y a var i ety of rot o r d y n amic co n- e ffects of var ia tions _ ',l oa d fact o r w ere i n v e st i - fig u ratio ns at lo w a nd mo d erate f orwar d sp e e d s ga t ed a nd t he re s u_t_ are pre 3e n t ed i n p a_ . (b ) of pr i or to te s ti_ s el e c te d co n fi@_r a t i _'s a t hi g h figures 133 1 4j a n d i _. . _ Ind i c ated i n f lg - for wa r d spee d i n th e T ra n so n i c D y n e m ics Tunn e l. u r e 15 (b ) , la rge r e d ___ ". J__ _ . _ b lad e c h or d wi s e T h e m o de l w a s properly scaled in all resp e cts cycl i c l oa u l n_ wer e _-iu o _t a i n e d wit h t he i n tro- e xce p t M as h n u mbe r an d Rey n o l ds n u mbe r for t h e d u ctio n of c h ordwi ' _e fle_. : i l ity ph as e I te_ti_g .
P h ase II .- _ollo w i n g co m p l etio r >f t he mod e l Scme of t h e highlight_ of t h e str u ctur_l loa d s tests in the F all- S '_ a le T u un e l at e l mu lat e d f orw a r d re sults ar_ s how n i n figure_ 1 3, 1 4, a n d 1 5. In sp ee d s up t o 1 20 mp h , t he m o d e l ws_ '; este d i_ t he part (_ . ) o f each figure _a r ;es are s h oal for th r ee L s_ey l_ -F oot Transonic Dy n amie_ T_u_ue i . In rotcr co n figu r ati o ns in i g trimme d f l ig h t c ond i- th e se t e st s t h e mo d e ! was reba l _ s t ed a _d + - es t edi n tions . One configur a tio n repres e nts conventio n al Fre on at a d e nsity of 0.0 0 8 s l w_ p e r c u bic f oo t b l a d e d esign with a b lad e cantilevere d from t h e an d co, l ets d y n amic and aerobe, n a mic scalim_ was rotor hub which had a very high ch o r d wise stif f ness achieved i r _clu d i n g M a ch n _mhe_ a n d Rey n o l ds n umber rel a tive to its f l a p wlse stiff n ess. Th e seco nd simi l it ud e . . Th e m o d el is sh c _ n i n sta ll ed i n t he conf i _,ratio n was th e sa m e b l a d e wit h a re d uced T r an so n ic D yn a m ic s T u n nel i _ •_ .g u r_1 6 . Th e basic c h or_ w is e s_iI Tn e s s at _ he root a c hi eve d by usin g co nfi g u ratio n tested w a s th u _- blade r o to r wit h a f l exib le dr a_ li nk. Th e s tiff ness o f t h e d rag matched root sti ffn ess. A_ro_c a nd s t ructural li n k was s u c h th at t he static d ef le c t ion o f t he lo a d d ata were obtai n ed w l _ h simulate d forwar d bla de tip und er a ti p loa d was e q u al i n b ot h t he sp e eds from 60 to 2_0 m ph a nd ti p M ac h n um b er u p to fla p wis e r . n _c h or d wi s e d irection . Th e thi rd c o n - 0. 91 . H e l ico p ter, u _ l o a _e d rotor, _ n d com p o u nd fi@_r a tio n wa s a bla d e i n w hi c h t he chordwl s e h e l ico p ter m o d es o f o p era t io n were aam pl e_. Ch ord- st -' uctural st i ff n e s s alo n g the en tire b l a d e was wi se c y clic l oa d d ata obtal u e d a r e _h u w n i n fig - e qu a l to t h e f l a p wise bl a d e stiff n ess, u re 1 7 . Th is fig u re a l oo i n c l uS e s t h e corre- s p o nd t m6 d a t a obtained I n t h e Full - S ca le Tunn e l Th e variatio n i n o s cil la tory b l a d e torsio n al (fig . 15) for com p ariso n pu r p ose s. A b e n eficial l oad throug h o u t the sA_ed ra n g e is s h ow n in f iE- i nfl ue n c e of bl a d e twist is also in d icate d i n t h is u re 13(a ) . T h e correspo n di n g variatio n in the fi 6 ure. T his be n e f icial i n flue n ce of b la d e twist ' , mag n itu d e of cyc li c fla p wis e b en di n g m o me n t is o n c ho rdwi se cy c lic l oa d was a ls o n ot e d at t he s h ow n i n f ig u re l _(a) . In this ca s e t h e f irst higher for wa rd s p ee d r u ns du _ng the F u ll - S ca l e harmo n ic co n te n t of the fla p wise mome n t was s u b- T u n n el t e sts o f twisted an d u n twisted conve n tio n a l Ject to some inaccur a cy at t h e hi g her speeds due bla de s.
to th e m odel b eing slight l y out of trim .
D u e to the fact t h at the rotor ha d been F rom t h e stard_o i nt of structural lo ads, the de sign ed to e n a ble w i d e variatio n s in d y n amic char - m o s t sign_ _ fi c ant res u l t o f _ h e ph ase I t e _ti n g is act e ristics, a mec h a n ica l co n figuration , resu l ted _ h o wn in ,fig u r e l_(a ) w hi c h s h o w s t h e e m pli tu d e o f whic_ was aerody n a_ic all y un s ui t ab le an d i n sc_ e cyclic chor d wis e m o n _ n t a t t h e b l a d e root for co n f i g u ratio ns h a d exc e s si ve str u ctural d a m p i n g; i & "l i@kt ov e r the si m u lated s p e e d ra n ge. As t h erefore t he d ata for t h e p hase II t e sti n g w e re in d icated in t he figure there is a large incre a se n ot re p re s eutat i ve of an optimi ze d d esign. There- i n cho r d wi_ cy cl ic l oa d wit h incre as ing s p e e d for f o re, " _hethird ph as e of t e sti n g was u nd erta ken to t h e c o n ve n tio n a l b l a d e (t hat is, f o r a bl a d e wi t h o b tain refi n e d d y n a m ic a nd a e rody n a m ic i n formatio n . high e h or d wise stif r _¢z, a nd l ow f lapw i se stiff- a t more extreme co nd itions.
ne ss ). _e chordwi s e s tres s l o . _ i s re a c h e d on the co n v en tio n _lbla d e w er e excessive for _cn+i nuo us P hase I l l . - In t h e t hird pha s e , w h ich w a s o_e ra t i o n . B y us i_ a fl ex i b l e dra g lln k at _ h c rec e nt l y co m pl et ed _ t he mo d e l was a _ ain te s te d i n blad e root to re d u c e t h e b lad e chordwis e _tiff n e s s t he T ra n so n ic D y n a m i cs Tunn e l. T he blad e and rotor to ma t c h t h e f l a p w l s e st iffn es s a lar ge re du ctio n hu b d es i gn was o p t i m ized f o r l o w d rag an d t h e i n c h or_wise cyc l ic l o ad i n g w a s obt ain e d over the b l a d es were o f mor e co n ve n ti_ n al a s p ect r a tio a nd e n t i re s peed range . A n eve n gre a ter re du ct i o n i n t h e b lad e flapw ise an d c h ordw l se s tiff ne ss were t_-_ _ ! = - _ f ._ w aa ac h ieve d by matc h ing t he c h or d wi se a p p r o ximat e ly matche d alo n g t h e e n tire b lade .
s ti f f n ess t o t h e f l a p wise s t iff n ess a l o n g t he _oto r s wit h 3, _, an d 6 bla d es wer e teste d wit h ent i re bla de. H ere agai n t he L ntro d uct i o n o f r otor soli d iti e s of 0. 0 6 , 0 . 0 8 , an d 0.-2 , res p ec- f l. - .x lbi l ity h as l e d to l oad re du ctio n an d t hi s tive l y. T h e _- and ) _bla de mo d e l co_figur at io n s m et h c 4 o f r edu ci n g c h ordwis e l o ad ing s h ows p ro_ . se a re s h own i n fig u r e s 1 8 a n _ 1 9. Th e f o u r-b l a_e of off er i n g t he solut io n t o t h e p r ob le _ of hig h m o d e l was c c _sl de re d a s th e b asic t e st c o n figura- ' , cy c l ic c h o rd wi_ e m_me n ts ex pe rie n ce d in th e f l ight- tlon. As in t h e p re_ I c u _ t e sts, s t ruct u ral load s tes t ma n e u ver_ me n ti on e_ in t h e f i r st p art of this a nd pe r forma n ce d at a were obtai n e d fo_" a rang e of p a p er ( f igs. 8 s nd 9 ). As indic a te d i n e_u a - l oa d factors a nd forwar d spee d s in the helico p te : ti on ( 1) and demo nst r',ted i n the wi nd -t unnel -t es t and un loaded ro t o r mode of Ope rat . _ _ n . The fo l- res ult s the b lade c . _r d wi s e s t iff ness K_ is a l owin_ i lsti_ ; re p resents t he max i m u _ oper a ti n _ co n ditio n s reac hed in +_,_ - _ . _ i _e_e d roto r co nf ign- prim a ry factor in d ete rm i ni ng the mag u it u d e of th e ra t io n for t he 4-blade r otor co n fig u r a tio n .
c_ordwls e cyc l ic l oa d ing_ hioGeless-rct or dynamic m o d e l.
co ncludin_ R e marks t h is ty p e I . t e ntat i vely bel_g plann e d using th e .... I n general; the fl i ght-re s earch a nd win d- _ __ t u n n e l ir_vestlg a ti o ns c a rrle d out to date on the hingele'_b-rotor principle have been very _ncour- _n - " normal s l m_"mte d helicopter aging an d h , ve J'_dicated d e finite promise of op e rat i ng rotor s p eed J m pr ) vements h_ be obtained by proper application of ,.h_ princi p l e . The hingeless-rotor sy s te m will The data obtained in the third phase of t, a doubted ) j Lc ;ubJect, in some degree, to many of testing are currently being redu c ,i an d analyzed, the probl-_= ?need ; . vthe various articulated rotor from the _,rellmlnary r e su l ts nt . tedas the te;[ There'are m a ny wayr, o _n to c ope w ith these prob- i and are ho be re p orte d in the P _tur_; however, systems in addition _o some problems of its own.
. procee d e d , the " o p t i m i z e d" rotor d _s i gn wi+ h t h e l ens wit h p r oper dPsign att en tlc_ based u p o n s u f - i r_ chord w lse _tiff ne ss bla d es s_ _s c o nsi d e rable ficient r es earch i_formatlon . Therefore, resea r c h i or o m i s e f r om _he standpoint of s_ruct_ira l J , _a d s, investigations to __.pletel . _ define the a d vantages _ibra_lc_ a r.d_erfgrm an ee. Thi s i s not in t_ded and l i m i t a ti o n s cf t h e pr i nc ipl e , and solut i on s _o t o i mply th a t ¢ _I pr o b l em s hav e b e e n sa t l =f a . o - p r oblem ar e as should proceed i n an orderly m an ner.
l_ l lysolve d , b ut r a i l s_ t h at t h e h i _eless rotor has bee n successfully o pe r a_ea a_ c_nditions w hic h R eferen . , es _ere m o r e e xtrem e i n regar d t o combine. '. _ . - .m_c prep: s urea n d Mach number than any kno w n te s ts in 1. G u stafso n , _. B . , Powered-Lift Re search at the p ast. __engleyFiel d. Presente d a t the R o yal Aerona , tical Soc iety R o torcr a ft Sectio n Additional observations - One of the ar e as M eeting, i_zdon_ England , De c ember 7, 1 9 62.
wh i c h re qui res c ar e ful I m - , est . gati on i n _-ef e re n c e t o t le r ed u c ed c ho rdwise st i ff. ' es s bl a d e d e s i gn is 2 . Gu stafs o n, F . B . , Pli_ht Tests of the Wilford t h e groun d resonanc e p h enom e non, l_c t o the fa_t XOZ -i S e_ G _' opl _e . N A C A u np ub li shed paper, t h at t h e b l ade "i n- plane" fir s t b en d i n g m o de 19 _ i.
natural fce q uency fal±s below no rmal . _per a ting rot o r s p ,: ¢i, a coupl i ng of the in-p S _Aue bla d e 3. Statler, _ . H., Heppe; R. R . , an d C_z, E. S., o _ cilla t_ o n wi t h bod_ " _ i tch o r ro ll o sc i l l ation Res ults of the XH-_IA Rigid Rotor Research may occu:rd _ rin g r un-up or s hu tdo wn o f t h e r o t or. Hellcc_t._r Progra m . A m e ric rn H e licop ter Thi s pr d 0 1 em is t h e d yn amic e q uiva l e n t o f c l a s s i- So c ie ty Pro ce e d in gs o f t h e N i n etee n t h A n nu a l cal "grntbnd res ona nc e" ex- pe r i e n ced wi t h hin ge d Nat io na l For u m , Ma y i -_ , 19 6_, W as hi ngt o n, ro t o r sy s tem s. The s olu t io n IN t h e c a s e of t h e D.C. , p p . i19-1 3_ .
hinge d syst._m requir e d t h e ad ditio n of blade la g da m p ers a n d landing-gear d _mpers to stabilize the _'. Cre_ a p, W . L., _ _i d Rotor Develol_nent and cou p le d o scill a ti o ns of the _ , tor a n d bo d y . F light T ests . Presented at the IAS 30th Arn us 3 . M eeting, Ne w Y o r k , New York, An extens i ve t h e o retical analy si s o f the January 22 - 2_, 1 962 .
ground re so nance p henomen o n f o r the h i ngeless rot o r has been c arried o u t in reference 14. This _. G u stafs o n, F . B., Relieol_ter D esign an.d analysis'includedrotor aerody n amics; the result_ C a p ability Trends as Seen from a Re search of t hi s work, prese n ted in r e ference l_, in d icate V_. Presented at the !962 SAE Natio n al that the coupl ed v i bration mo d e can %_ stab i lized Aerospace Engineer i ng an d Man u facturing without ad d iti on of artificial damping. During M eeting, Los A n geles, Calif o rnia, the t h ir_ phas e of m od e l testing in th e T ransonic Octo_=_ 8_ !2 , 19 6 2 .
D To mmics _ m ne l , limited ground resona n ce testing w as cond u cte d in ai_.with the mode l bal l asted for 6. Huston, R o bert J ., a nd Tapsc o tt, Robert J . , t e sting in Freo n. 'Foisre s ult e d i n a dynamic sire- Th e Results of Some Wind Tunnel and Fli_nt ulat i o n wh e z e a er od y n s_mic force s were d l mins h ed Stu dies with Helicopter at NASA. Presented by a pp rox i mately 60 percent . U n der these co ndi - at New York Academy of Sc i e n ce s C on fe rence o r tion s , c a ses of _mstable "ground reson a nce" were V ertical Ta k e - 0ff an d Landing Aircraf% , New encountere d . I n or d er t o _ssure safe op e r a tion in Ne w Y o rk, New Y ork, December lO-12, 1 96 2.
the tu n ne l t he body p i tch a _d -_ l ! fre qu encies w er e adjusted to e l imi na te un stable resonance _h en 7. Campb ell , J . P . , Status of V /STO L Resear-h _" / _ operati n g i n air . Operati on st i l l i:,_ o lved an d Develop ment in the United States. Poe- pas si ng through a b o d_ pitc h fre q uen c y a t i _ _e n t e d at t h e N inth AI A A Ang l o-Am e rican rotor speed, which the o retica ll y re p r e _ont e d a Confere nc e, Boston, Massachusetts - Mo . _tr=a! .
3round resonant c o nditi o n. Subsequent ope_ . _ . tion Canad a , Oct ob er 17 - 22, 1 9 63 .
in Fre o n w a s carrie d out w ithout exper i encing unstable gr o und resonance. A th o rough study of 8 . A no n., M il i tar_ Sp ecificati o n - G e n , : rsl the ground r es o nance prob l em w . snot un d _.rt a ken Req u irements for H el ico p t'er F l ying ' anTG r oun_ during t h e tunn e l pro g ram t o d e t e r mine , e xp e ri- Ha nd l in _ Q u a l ities. ' _41 L -_H_ I A , _'q --- -- . -- m enta ll y, t h e r o le o f r o t or a ero d y n a mi cs, b l ade stiffness, and c on tr ol f eed b a ck ; how e_er, wo r k of i_ ._,_ •ena of High-Speed Rigid R otor Aircraft: Criteri_ for Control snd Re s ponse __ R _ > Cbaracteristic_ in Koverlv_ an_ Low S_eed _ . Armo r - THE COM T echnica l _. 9. Ta psc o t t , Ro b e rt j. , Hel ic opters and VTOL 1 3 . Hans on , T. F. j Inv eetigation of Elastic _ight.. Aer o space En g in ee ri ng , V o lume 19 : R e port 6 " _ubmitted_und e rcontract _ o _be r 6, Jane i_0. D A _ l _-l ' , . by L o ckheed - Califor n ia c om_e n y, ...._ 1 9 64 . ) i0. Yo u ns, Dr. M . I . , A Simpli fied _neo_ of i Ki n_eless Rotors with Application to Tandem 14. K an no, j. S., an d L un d gren, S., E__uatio n sof K e l i c opter_ss. Am e rica n H el i co ;t e r S oc ie t y Motion for the D_na mic A na l[sis of a Kov_ I nK P ro ce e d imgs of t h e E ig h t e e n t h . _nu a l N atio n al Rotor In clu d i n g G yro Cc n troL b_ e m. L ock h e ed F o b-Am,M a y 2-4, 19 623 Was h in g t o n, D .C., _ l ifor n i a Com p a n y, L R 17189, Jun_-1 9 6 1 .
p p . 3 8 -45. ( S u b mitt e d u nd er U . S . Army - TKECOM co ntract nA _ - 177 -TC- 82 8. ) ll. Mill er, R, H ., Hel $copter Control _n_ S ta bil- ity in H overi ng Flight. Jo u r n al Aero n a u tical i _. Ka nn o , J . S. . . a n d Lund gre n , S., lO-Foot RiGid S cie n c e s, A u g. 1 948, vol . i _, n o. 8, Rotor Model Basic Data and Results of Hoverin_ pp . 493 - 47 2. C Tclic Stabilit._ Anal_sls. LR 16997, J u ly 1 9 63 . (Subm i tted und er U .S. A rmy - T REC OM 1 2 . M i lle r, R . W. , A Method of Im_rovinE the co n tract DA _ / _- 1 77-T C- 82 8 . ) I nherent Stabilit_ of H ellcop ters. J o u r n al A e ronautical Sciences, June 1 9 30, vol. 17 , n o. 6, pp . _6 5 -37_.
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