Composite main rotor blade of PZL-Sokol helicopter

El..EVEl!ITII EUROPEAN ROT<mCIJA<"'' ron.tnq

COM!'OS!rE MAIN ROXOR lll.ADE OF PZL-iJOlWL I!EIJ:COP:rER

•rranaportation

Equil'!""nt Fact~ry •PZt...tlw!DNIK•

llw:ldnik;' Pol.e.ndo'

september

io-n;

1985 London>

Engla'nit·•

ETrata of remarked errors in paper No 46o

r·---,---r---,---·

l

J!!2_2£ ...

!!!:t;_!r2~--~

Th i

I

Sh

ld

b

f

?age }below : above

I

era s

1

ou e

t---~---r---~---~---·

:46-7 : : 11

tHI.

of pylon

J ••

of blade

l46-8 ; : li

l

/see Fig. 2/ : /see Fig. 3/

146-8 1 1 13 1 ••• was close to .t •• was close to 4x

no-: 46-11

l

2 :

f-

AT DECENT •••

1

..

AT DESCENT

ClD}1P081~E MATti H.C.TDR BLADE OF FZL-SOKDL HELICD~""TEH

Stanislnv Knr.t1.l'i.ski) H~sc"l, Eng:~·

Chie£ Design E:~gir.em.•

'1'X'1Hl31Jort.a"tion Equip-.&C>nt Fac1.;ory 0PZL,..gw1::inika S"Widnikj Poland~

:tnt.rodu.ction to thto. -pa:pcl." inclu:les: sumr., intN""flzting aventr, from til~ history of compcui-te rotor blades .in PZlr~widnik.., The .follQwing chapte:t'B ino2uiie the blade cross section ;:rl':nJ,~tw-a 1 blade geometry1 nr:d its mass aod st!:r.frw.ss distribu't;iorm.,a. Reson,cance dingrani.S) on>? of them 'VJlth pylon .t.lexibillt:.y iHcludedg are glven ~ Surveys. oi: ertattc, dynnm.ic; .fatigue and we:1t!~er egein.g te.sta; the :te.sta on u tied-down heJJ.co-ptcr) and. the flig:h·t tests ar\:! alao discunst~d. .here:.

Unique dyn..n:mio phenomenon

ot

low tors:tonal. stiffrma;j bhd.s:e stall. flutter and 11'J1on res~J.= .nanc.e £l.1'l,} discussed in the FLIGHT TESTS chapte:::.r,..'

R Ji1, JIR ~

"'

Nm

a

i!'s

p GIO

lliy

l!.'I" <&

'

t lt.b r

!l.

NOTATION'

rotor raditt'SG meters

$0 rotor ongula.r speed.;

radiqoo l}?l" second .,... rotor tip npdedi mate:rll

· per seC(Illd

- blade chord

.. blndc rnd.ial coordinate~

meters

... Newton per meter := 1 kg

x

~eter

2

7 aeconi2

"" zecond

tlirnoru:d.on.:.tezs blade radiua 0 a'i:; ·Pt'~ center oi' tho rotor itr.d 1 -..0 at the tip

·o'u per IJl..':l.ill rotor .r-evolu ...

tion.

..,. tor..sioHr'll atif1Dess fJ.f

blade section N ;z m2

- bend~ng-stiffnoss oi blade

section in chordwise plana

N X m2

~ oonding stJ.fi'Mss o:t blade section in flirtwise plana; N " m2

~ blade azauth

'f

n

.£.

t;

0 ~

-.han the !>lad,~ is 'abwe tl1e he llcopter tall boom and

increases in

too

direction of rotation, degrees ""' time;, seconds

~ flapping ""E;lD of th~ blade positive for blade axis up>

degrees

~ legg;lng engla of tl1e bledb positive far bJ.l!de C!X:i.s _lag0 degrees

~ blade a:l.rfoU pl.tol:Wlg 1>0-~nt eoatt1o5~~t

46 ~ 1

l! _t

""'helicopter airspeed.)

km/h

·- blade tab deflection angle

positive i'or traili.'1g edge up9 dt'~grees

- bl<.Mh root torsional moct::-r:t /fent.heri:o.g :moment ... pitch link J.oad x the arm relati-.:re to pitching a:t:..iz/ 11 !1m

=

b1nde sBction torsional moment .at F u: 0..,595 ₉ Um

"" pitch housing CendiP..g mon:ent approx:toately in tho plene of rotation, Nm

= pitch housing ben.ding momertt 2PlJI"'1CtL!J.ltaJy in the thrust

p.J.a,.'1e ft Nm

rotor sna:rt b!i!nd.lng morr:.ents in rotational coo1Uinate system; suitably Oo6 ID DP~

Oo2 m dclim .from tho plar.n

ot

rotat:lon.; Nm

S!·1J.II:r'"" 3rd harmonic component of Wld

N ~ rotor r~pom@

... nomL'lal rotor r •'P~tn,.. ... blade natural frequency 0

cycles vq;r minute

m.in

=

minute

OAT ~ outside a:l.r temperature in

rught; "c

H ""' :rllghi.! altitude, m.c-tel'i3 '"" 1-'..-elicoytor talroof'f maas.,

1-'.;5n

IlttllODUt-TIOII

The history o:t FZIPIIwiardk compo-site rotor blades ba!gan

.t:n

1959o In 1960 tl1e main :rotol:' bleden tol' ·Che

SM~ t@.tlziii ~l:l?oU~Elr wrc dsaigood

Almost at tha same tim<l; compo~

site msin rotor blades for tho Mi•1 helicopter were dflaignad·o!> They were based on tho room tempa>:atura curing tccbnolollY .;. Some of those blade seta had :flown up to 400 houn,..•

Composite main and toil rotor blades for the Mi-.2 helicopter were designed in i 966o Their tccbnolo/lY

was

based on two stage; high tam= perature our:l.ng1 preliminllrily in

6o

0

_{c;· and}

then in

150°c.

Polinh certification for these blades

was

obtained in 1968; after complotioq

ot

the tull stand;

ground;

and fligbt tests prog>:am; IDYl then; five sets o:r these blades were assigne_d ..• £or operation under Aviation Au• thorit!es supervision;,·

So i'ar;

we

have an almost :Cit•

teen..years~long e>.parience with tho above bl.aa~s. At present; several. years after manufacturing; some sats

ot

these blades are still in opera. :·: · tion on a f'cw ?21,-Kania helleopters-o1

Parale lly e: a few typos

ot

large

9

3; 6e c.nd 8 n:oters diamcte:rf' indu-strial r.:'~tor blades \'J0ro deslgned

and roanufact.vred on the basis

ot

room temperature technology• After almost twenty years o:t their oper-a-tion, no serious problems arose? apart from leading edge and blade paint erosion';>'

On the ba.'31s o:t the experiences mentioned above f in the p;re liminary stages o£ the PZL-Sokol helicopter development it was decided to deSign

and d~velop comriDsite

rotor

blades. with low torsional stil.fru.lss; with no fibre layers angled at 45° to the blade axis<l

The rink of development

ot

the low torsional stiffness blades

was

undertaken on the basis of earl.ier difficulties in obtain:l.ng high to~

:aionnl Btiffness o£ a composite structure; elast.ic in its natura; and also because

ot

'the qualitative expectation that such a atruct'Ul"S design may improve the hellcoptor parfonuanc.e•o'

Obviously, the involvlllOnt ot composite materials such aa glase

fibre and :tabrios in tho design of

tho

blade necessitated the in-house staticQ f'atigu.ag and environmental tests& which were r-equired for

cer-tii1oationp• as 'roll, aa evaluation

of solar boating etfaot; natural moisture absorbtion etc• The light-ning tests a.."'<> almost complatcd by

nowo•

A short aU!'Vey of static; tat1-gne0 and natural ageing tests made for PZL-Sokol blade qualification

is

presented here·• The unique phe• nomonon·o£ stall flutter with pylon

resonance presence, which appeared in preliminat".f stages of the l'ZL~

Sokol. tlight testa; is diecu,aed in a more detailed

way.-BL\DE DESCRIPTION

The main rotor of the l'ZL~okol

helicopter consists

o!

four

blad~5

with a :t.'ully ttri::icu:tated hubo The bnsi.c airfoil o£ th0 blade

has 440 lllJil nominal C)lOrd I,!AC.\ 230Mt

with 16 to 9 par cent thickness :from root to tip~~ Lin.c!ar twist along the blade length i.e 10°39'·••

The blade consists of s, D-front

apal .. !io1 :l:fte.rbody :;kins stabilized by

a honeycomb core made o:f glass :f'ab-riot)' and a trailing edge stripoj>~ In the outboard aNa of the blado ~ the trailing edge skine are stretched out of. the nominal chord in ordar to forill 5 per cent trai2ing edge

tabse~ Fig~1

1 presents a typical Cl.*Ot:S section of the blade&' Fig,/ 2 pre• aents blade g<~OI!l'!!tries in particu-lar variants of' design~~ '1'he key structural components of the spar are sprtnulsely o~iented glass fib~~

res and glass .fabrics in an epoxy mat:rix.i The fibr-es are wrapped around a two-hole :taatenerg so

that

they form a loop joint o:f the two~ longitUdinally oriented; ottachm&nt

bolts~ No tor~lon p~a with 45° fibre oriDntation are used.,'

In the outlloard area of the blade a leading nose block provid.aa the necessary section balance &lid ~

tationol incri;ia~· The honeycomb co~

e:r:te.l'ld!J .fi'\>!11 the trailing edga of: the spar to the unidirectional blade

·trailing edga member to support tht~

ski:i"lo' The skin consi:Jta o:t thrao plica nade of glass fabric with 0°$

90° £lbreo orientation.

Electrical heater mats w!tb. the supply wir~s for the deicing syate~

are also glued to the blade leading edge sur.t:ace a

The deformable trim tab o.f. tho blade is rJade of duralumino'

Pig~ 3 presents blade

masat

cen-ter o:t gravity g and elont.:ic eenter"S

d:l.stributionn.

Fig,. 4 pl:'Csents f'la~risev chord.-'ilrise 9 ar'..d torsi.:mal stii':t"nesz dis ... ·tributions o

t:

t.'he blade o

Figs, 5 and 6 present diagrams o! natuw:.l blade :frequencies-.,' The diagram in Fig, 6 includes the in-tlueuce of pylon flexibility •

ULTIHATE AND PROOF TFSTS AND OTHER MEASURFilENTS

The static test

progrnm

consists of the follo'tring tests:

1$ Static tension tests of the blade .... ultimate .strength factor equal

4·o' Th1s load factor incJ:lldes; beside the basic safety tactoP. equal 211 an extra safety factor

equal 1 ,33 •. tradi ti~nal.ly ap.o roved for composites in PZL $ S't-Tidnik$1

2~ Blade ultisste bending teats for

the 11_{stop dumpu case of flapping}

hinge;:.

3o' Root eud ultisste hending test in tlstwise and chordwise direc•

tions

/with tension/; and ulti-mate toraion tests /with tension/>' 4·.' Ultissto torsion tests of the

~~Thole blade·o' It should be streseed

here that the test resulted in blade failure at torsional moment equal 3670 Nm applied at

r

= O·o'9 and blade tip torslonal detlsc-·l.;ion equal to 146°·a'

5, Tenaion free ultinn te heudir>_g tests in chordwise direction in

order to determ.l.ns the !;'<lot <ll!d

•)

,·-·~·"· att~(3Mttellt fs-t.J.(htg~li ·ani.!

buci_-·

ling etroagt.h' of the bl.oc\m t~-. ling Ctdge ~

6.; :Slade tip proof loadi.ng in

!lop-wise awl chor.dwise direction. .... 7-Q' Determination of bend tng

stiff...-nesu in both planes and tors io-nal stiff'ness .

.-So Date:r.'llti.natio~ of blade tip de-fieution under own weicht; 9"'' Determ:inatlon of elnstic centers

location in trvicnl cross aec-tlona

or.

the blade~

iO~<' Determination of mass and center

ot

gravity distribution in typi-cal cross sectionB of the blnde and blade dynamic axis location

~ cuttL~ the blsde into seg-ments and W.11!)ropriate measttro-ments and c:alculo.tions ,·

DYNAMIC Tl!STS

Dynamic tests consisted in laadlng the blade root end into vibra:tiou with a dynamic sholmr- J.n order to de-ta.rn:dna the .firstJ seconu.~t and third flspJlso natural frequencies and mode- shapes; and thr2 first and second torsional natural :frequencies and mode shapes 6>'

The test cor..zisted in vibrating

the blade sinusoidally and vmying ti'te frequencies. until the blaC:e natural .frequencies were foundo

Measurements o:£ the .first tor ... aional natural :!'requency of the blades on an unoperating helicop-ter in order•to consider the influ-ence

ot

control system stiffness and blades coupling through the awa.sh plate were carried out inde-peudently,

T~ lowest .results. received were as follows:

- 3.1 P tor isolsted blade torsion vibration tests

•o3-,'6 P for blade torsion vibration test on an unoperatiag helicopter /It seems that these meespremanta

In t'wl course o:f tOO Mi•1 and · Hi-2 h&lioopte:!"& prototype bledes .. !fP-ve lopment"; tOO coupon :fatigua taeta """"' collductad 1n order to . build Wlfnler•s and !la1gll'a diagrams

which are not inclUded in current literatt1l'<>·o' On tllis basis tOO fa• tigua testa tol' the PZL...Sokol h&ll~

copter hledes were o~nduoted on 12

ihl!l'll'ltitfl•

a;f

Ji'l">t<>~pe bllld<>s

onl¥··'

Two

blade sectiono and root seg• ments involving root,retsntion .fitting were eY..amined'o' ·For ea.clt of these two blade secti-ons two se-g ... mento for each b<'llding plom were

~steda Identical tests mre car- .

l:'ied out up to 50 x 1 o6 cycles on each load level•'

There were three J.~a.d levels~ with tezmiJ.-2 oont-r.!:t:ugal

-tol"Ce··

Eaoh subsequent lovel of bending leads dii:fered from the preceeding one by

50 per cont at conctant tensile force.

In the course of :further testa the nUhlber of each type of blade segments is planned to- be increased to t, -a- 6., It provt!!d impossible to do.JT.:age the· blade spar in the course o:f: t1:m abO'"JC testa-.·

A .fe\'r blade segments that passed

t~ above -tests ur~erweut some extra fatigue. tests ("!; the tenwe:rature ot

80°C, and such tests with: a"l opera-ting deicing system. /Thin system

o~erated at 'limited electrical power

supply/...' An appropriate temperatUl"e' in the test c!Jnmller was kept by lamps

radi~:ting beat at: both up,PCl" and lo ... wer. skillS of the blade segme-nts·J

WEATHr:R1NG TESTS

!n order to check th& .fntl.uenee: o:l? 11 long-lasting exposition to tll:ia weaCher conditions upon the glass-epoxy composite strength; a

lot

of

small samples- we-re produce-di and subjected te- static:~: terufit:lni com.,.

pra~N.fon• and bend;litg ts:>tso: Th& tezrt.n: o£ ~iC-"ttlar

zets ot

SaJnllli>a

11\9~ carried

out :ttf:er

2 .. 3

ye:tm~ of tOOm king G"'l)<!Sod to '""'~

t00>·1ng; Considerable <laet'l!ase 1n tll$ stl.'!ngth was nota<! in O!l!le o:t the t1llP

pa1ntad salnlllos .' Ill cu& of the samplols paints<'! ~lth an epoXy paint thin do~

·crease

was

oonsiderably amallero The

gNataot decrease and

scatter

ci:t: strength wall rwealold by samples subw

jecf:ed to OOml;tr<!as:!.on mats •

Fiw Mi-2 h&llcopter com,Podta blo.d~s 'l!ll:<'ll aloo exposed to "a"too~ l'ing,;

These

blades """" subjeci:od

to

sti:t::tmss maru~uremants and ultiui!!t& tiJir.s:!.cn testa each th:cae yeara O!

natural ageinft~ The

msts o:> swan

sa!llPlo.s were hold up to 10 year.li o£ natural ngeing;· and whoJ.e bl!ldos lllP ·to 15 years'!~-Tho mea:zurements of stii':l:mss and ultili!il't<> taooion t0sts o:t: aged blades

aitsr

15 years of M$ tura.l egei.J:J8 revealed satisfaototy statio .str£!ngthl and sop th~y v-;erc-approved :fOP. oporation tor such a

period of" tima.,'

1'h2 conclusions drtu·f.'3. .from the above tests trore uCiJ.ized iu 0.esig-ning the PZL-Solwl bl2,des 9 which ar-e made o:r al.I!.tost tm same mat.e.Lialc.,.

ThcGe tests nre beLDg carried out

by Warsaw Institute of Techl:to1orry;. and are alm>Jst completed by now .. '

All these testo gave basis :tot'

approving the blades .for te-sts on a tied""'Ciowri helico-p't:t:l"'"P and then :tOl"'

flight tests; with a zuggestion of' vpe:ra.t;ion on a ~rFA-IL SAFEif pri.ncip!h'a'

TIED~DO!IN HELICOPTER TESTS Those- ta.sts be-ga11 t1ith th~ measu:t"€1-ments of loads in

the

ehosen bla~e svc-tionsg rD-tor hubV rotor shaftu and, smwh plote - at !Ull 1'>\JW'Z of col.;, "' lective arlli <:-Jelic pitch

am

m1:1in ro-to:t· Z"o'PonloJ> :P:I:utter margin. had been. chetclr..ed earlier by 3- ptil'l"'" e-ant

d'if5P'laee-ment of the blode dymrllic llJl:is in di~

""'ction to the trailing edge; H had heeD. dono by placing appropriate

wights on the blade ·tra!line edge at 0'¢17 -> 0~75 of the blud$ rndiu.s.<

Thm~ different typo!s of blade

ga:rwJtr#stl t~~el'l! teatad,.' /See F1g·.1

2/ ~- '£hey c"~i:f'.fered in tipa and lo,.. cation of trailing tab.s,.

At tha beg inning val?i"-"t A bla"' den were Lestod-., These bl.fi4eJS caused a heG\'Y vihratl.on. o£ a tied-do-w

001.tooptsr~ which could be decr'?.HWIZ!d l1y i:':hang:Jng the- helicopter hu.rden

i:a. orrlor to dPtune jJ; from. the mairA £.mque .. 1csr transmitted through the bu'b, ;L.e, 4 Po' Gor>.z:tderablP- inr~Jre­

aR& in vibration wa.<; :1otlc.ed~

par-tic\.tlsrly at hjg}l collpctivc: and cycl.ic p11;ch, a~1d ~rt dccreas5.ng the m..1.in rotor I'".c',P .. m.

A simil!ar phonoruenou~ but con~

JSiderabl:V uJDl"e inte;n.se₀ waa obset"Ved

on u full scale tr:msrnls::don r.ea't ::rtand,'

In spite o:f' an alarming beho.viour o:r a tiJ}d...Q.o"t<;n helicopter$ ;Lt. 'WaS decided to tes:t t.hQ blF .... dcs ;tn fligh.'l;;·o~

:r·t

was as.s.uood hern.; that the charao-tB:ric:tics

ot

t'11c pylon "" rotor sys ...

i::0'1l .i.s diffsrent in. flight than whtm

tied Llow.o. or on· a t.ra.nsmlssion sta.mh1 /;Jee chapter. concern:lng tests in

n{gnc/•

The endurance tied...Uown teats:- wre oattied ottt for ·10oo hrs ,· Each l.r.div1~

dual test lasted for 200 hrs, The

teats al'l> to be continlM>d up to 1500 hrsfJ- total.-.

Dur~ng the :t.ir.st 150 hrs·o'

ot

a tied...Q.O".m helicopter testa small. but esscntiul changes in blade construe,.. tion wero lle:l.ng tested., '1'ha variant C bludea

underwent

the tests atter first 200 hm o:t tr:-stingo.1

'Test load

measurements

in pa~tioular operatic~

ru.l sta(l()s

ot

200

hrs·,•

test """"'

~

out

ilt!:er the first

100

hrs•,'

of helicopter oPQration aXld then

bo foi'l> Blld e!ter -.ach 200 hm •'

peri0\1~'

A short maiden flight at limited zpo!ed was po!r;fol:'lJ!lld

on

thll halloopw.

ter Yb!eh wu to be used for tied"" dctru tosts; with tabluss blades; tapered at the

tips;

Piloting and handl.l.ng of the holico)iltor waa gc-ll<ll'<>lly good; but; fr<>m titue to t.ioo (,' some short. wa\l""es of vi bra ... ticn were observed in the tuselag,J even in h~ver: The meaaure~nts of

nu~a.n loada in the collective con ... trol nystem. roVthtkd too h.tgh valt!og·.,.' It was then decide'! that tho Vad.~nt A blad<2s; Fig.,.; 2f arc· to ~ tested on th~ :first flight. prototype he llcoptc.·!'·$' The variant A blades had 9 per cent tabs at Z:: :Q "0~29 e- 0.-7t and angles o.t def ....

leoti-en h 'l' m 15° + 4° UP'>'lUrd to the nominal aii~.foil chords .. ·

Fil•:Jt flights with the variHnt A blades revealed too high a hc:J.l~.~

copter vibl~ation; high hub ar;d controL Ejatom loads within the airspeed ra:ngt? .from 30 to 120 krn/h~

and UU.<Jafe Wl.luos at the a:trsp-2eda ovc::.• 120 kmjh·.,' Shortening the tab.a lrc:J 9 to 5 ~r cent resulted ln considerable improvement:, but did not soJve the whole pro'bleu-.· Tharc: ware- nlr:o certain difficulties .tn

b:k1.de tmcld.n.g.;

Th{! l'eCOrtta

ot

blade to:t•sional moments T₁

o:t

X:

~ 0~59:) and. fea-thering moment T₀ versu .. .:; blade azii:!Plth are shown in Fir;s$ 7 and 8

~or hover and level flight at V ~ 80

km/h•'

1\. hypothesis had been put

for-warn

that the oel:f....,Y..Citing vibra-tion !frovokcd by self-control o:f hydraulic booot~rs groro gear box body vibratl.on; way bo reeponziblu for theao probl('H'!ls~' In order to solve them~ the range of hydraulic

botJstors insehsivity 'had been ,in-a t)~asad..,' It appeared;· however' that

the problem rernnir..ed tmsolved •· Tba pilot had again hat! SOllllil probluw.ll Jn controlling the aallooptor; oven in hover-.. ·

Tbe situat:ton

was

critical ... tli..t?re ho.d OOen a he-licopte-r; but tl!ere ware no possibility to .fly it.

were rather depressed and cre:;rtfal,. leno Variou.rn hypotheses \'mre baing put :f'ol'Will'd. CheckL'lg them did not gl:;e any s'l-t:i.a:factory explanation of the Ifuenooonon.,

Nevertheless :it

was

s\l.I'C that there is some self-excited vibra-tion on tho helicopter,. The question. remained: by 'l'lha~ chmmaJ. and ..,.;t...ere

from the anergy 1z transmitted to the helicopter.systems· supporting l:ts vibration?

In this critical momen:t, the chie.f designer put for.·1ard a see..; mingly incredible hypotheol.st at very lovr .forward speeds 1 and

some-times in hover,. there appeal"S a · strong stall flutter phenomenon on the rotor blades .. This conclunion had been drasm from t.h.e records of blo.do to\"Bioual moments lJ.•_{1 and} T

0

-Figs., 7 and 87 "Vrhere the notation 3

dcnotos suspected complete cycle of rJ.orucnt stall. 'Xhe records of tor-sion3.l moments T₁ a·t ;(': = 0$595$ in

Figs. 7a and 8~, show an un.sta.ble behaviour of the outboard blade p~rt

oud it could 00 suspected that seve-ral stJll cycles exist there.

1'00 hypot.he3is was confirmed by _T1

wavo~orm, Fig .. ec$' where evident calm-n.::ss o£ the wo.vcfoX'!1~₁₁ au.:l a smaller amplitude a:ro observed·., Handling of the helicopter in descent, .fl~1;:;m the

very

beginning o:f the flight tests;

\'las suf.ficicmtly good and vibrati<?n \'IUS kept at a low level·$

It is t1orth to mention that the suspected moment stall spikes in the

fe.o.thering moment records /T

r/

ap~

pt"!arcd as cycles o.f tors.ional :ros-!JOT.Ze •::e 11 wlthin the basic 1 P

wave-formf Fig,. sa ..

Aiter receiving the above mentioMd results, tho work was conccntre.ted upon the bJnde., At tbe same tiiDn tl:t..e solution :for 'the pylon resonanco 1froblem was soug'ht. Among other things ~t o. pendulum vibration absor-ber, mounted on a hub head; :for tlre 3rd excitation i'requenc--y in the ro-tation pbne was '?onstructer.'Ll'

Sunpocting "chat the main Te.Json !or the stall flwtter was the

irn-proper characteristits of tho air-foil aerodynamio momant coefficient at

r

ru 0!')75

*'

11(!0; and the decroase

in CLmaX o:f tha airfoil at

r

=

0.29

~ 0,695 in result of tns trailing edge tabs defl.ected uxrwardfl:t ~

,. the tabs at

r

= 0,29 .- 0,695 ware removed, and 7.tJ;lor cent c chord tabs in the chord tJlane at

P

= Oo 75 i- 1(,0 11-erc illt:roducud o

The taos· f'ol'il'lhd extensions o! ·the catalogue_ airfoil chords except for one tah-segruent a t ; c o.S67 7 Oa925 deflected 8° upvm.rds .. In re-sul.t of these yllLU"..ges

p

variant B blndc

f!/20-metry was received,, Figa

2.,-With this blade variant installed the helicoptet' e.X'rived at: the t{SSt1med

for the test airspeod of 200 lm:/h, revealing considerably lov:er vib:t.•a.,•: -tion.,

r·t

becaoo cleo.r tf.!St tha -tra:I .... ling edge tabs·constitute an irJporn. tsmt :factor~ l'ihich influences tho

love~ o;f hBlicoptcr vibration .. T11.iil blade cottld c.l!;l(; be Gaslly tr.sJ.::Y..able,.. An experimental flight wao also per ....

formed.(,' with all the above mentioned tubs detl.ccted 4° upvrards - the level. of vibration increased conside~ably

again; so tho tab angles 11ere cortverbf ted to the former ones~

Hcvsver; because of tho high J11Ltan load On the Si'!BSh plater it \1(:1;5 de""' cidcd to try t.he variant C bladas /Fig~ 2/;; with tupe:rod tips 9 and

si-miliarly arrange.i tabs f but~ 5 v~r

cent c long-.

Since a set of bJ.ades, V&"!:"</ simi,... liar to variant c, was prepared L"l the ~6antime$ it was decided to ~4r­

fo:rm Gxperimental f:..ights \ii·th ·tben~ blades~· These blades were denoted a.s variant effie

This set o:f bladeS had 7 ..-5 per cent c tabs a1 .... :a.nged identically e.s variant Bi- hut had no tab at

r

=-0.,.925 t- 1

·"o"

To more detune the fuselage from the main excitation fraquoncy 4P9

'th;: ·top oi' ·thtl wain rotor -e1ta:ft·;\ The lmlioo'pter in th16

Uf£':1; ui~h tbil variant bladS!s ilk>'t&llzd; <'<~&Ciled 260 !r:El/h m;rll\rum

l@V¥JJ. _apo~d$' The recorda of eelr!!obld

mt-dB t""oior- are presented in

9i

<10,, .arrti 1:h 'T!wy shaw

th&t tha- e!wr:aoteri$tic stall mp:Lkk?z appea:t' u~l:: \1 u .2.60 .at. 20-'taw tip speed IL H ~ Zl2.5 m/s /F~.;

Ha/;

tlw.d confirm: t~ ymBence of pylon :t'0ZJ0llance vi th ::Jrd ilamon:to exci-tntW:r- :fnq_ooncy in chordwitlc p'l€ne

11 b/e ond with 9th har;JIDniO ezoitation freqtle:ncy in .tla.j?w.tse

plane~ /fligs' 1ic/4 /See a1Bo Figc' 6/',' I t !lllll'!'t !Je also noted t!Jet tlw 3rd hat'turmic of shaft: bending morr<0nt c:ons.tck:rahly in<:::t"eases; together· with t:he zop--oarnnce of ob.aractor.tg-tio stall. spilroa on T

0 plottir'ij.

rt can be seen in Figs.' 10d nnd 11d• wh0:re it i.s alnlost doubledo'

Sl,mili&:rly i it lla)!FOOO wit.h tlw :tlapp1ng ungles; Figa~ 10£' and 11!,;1

F1_g;~~ 12. presents :feattwrir:g mo~ 7il!JUts '1'₀

tor

VO:I'iant C'fl. bledea with all th%1 5 pe1 ... cent taba de!leoted 4° up.., weight flf: 6100 kf!,s/ It

w,ay

be observed that t'hidtJe charac~rist1c

"pilros "~'"""" at 'I s 22.0 l!m/h, and

rr;tol'

tip SlJ'led ib fl. .; 200

!IJ/a>

/li'ils•'

12a/ ~ and they disau1p(!ar wi:th rotot' tip speed incn:-ease to Qt Ra 221 m/s& /IN,g. 12.b/. Tl121, aPll'l!U' again with the ll~licopter all't:llJ'led increase up '.to V rn 260 km/h Jli'ig;, 1'2.e{.

In 0.ach case tho stall a-pil",.os ~

11'!!!1:'6<1> tlw helicopter, v~bmt1on lJl.. on;aJJr::d.-&1 _{Vi& can say}

_that

_{tho: mre}

,i,ataMe· apik!)fiiJ' the mo:t'EI intense th.e hlllioopt.er vibratio.nf;o1 _{Neve~las£.~.p'}

tlw gene® opinion of tlll pilot;· oo w?l.l -as th-~ me~.Stt'l:'emont :recot'd.s ·bake~

flit

IIR '" 220 ro/Sl' ''"'""' ratlw:r podt:l:V<lb' ColllPL!ri&on of tho r&t§Ults of nigl:ti;

tosts. ot

var~ts !l and C~lllades sllowo:A 'blwt the swept back tl!.paw.d tip g!veB higher ro:san loarla 0.n

control

systamo· both in co:UeH.rl;in alld cycll.o pit®&'

mcreas5eng the lllean anti perticularl{f first hel1ll(Jnl.o

ot

tlla f@atll~X'ing

V1011Wll:1.:ci

if-<mJ.--1.r.ll1t c bla.do ncrnmtitut.es ~tne .final con:f'igurB'l:i!ln e;f PZL....Sokol ~in rotor blade; Tho 5 par cent tabn at

r

~ .04"l55 .lj< 'htl fom exb&n ..

tions o%. upper .and iowr sld.ns of' the bl.gd;z. u±td colnaide with the

oht,Jn'f.$ o:l nominal air.foil.'(l ~ eXC\?pt

at

r

<:1 o¢-f151 i?' 0;.:925,1 wham tl'i..e tab

ma~:nt is

dQf1eoted 4°

upwardA. ~d~ ditio1JH'l 9 ]JOI' cent o tab at 'r =

01b695 q. 0-~:>4152 is mudo of duralumin

and jJ3 used £or tMl"l"'>'Jd_ynaroic blade

iaiacking"'

· A:Cter introduct:.to.n cr.f th~ ubove blarl.esp md a hub mountvrt.;. Sa1.omon

i;y.pt;J& pendul1nn vibl"ation absorber fer 3tt'i. ha::wonic .fruqmm.cy in the rot:ation plane~ the helicopter rnacl'J.ed th& level speed mrer· 260 lnll/ht with

£.\

R

=

220 m/s.

It al'J?>Ol"'d that at .12 R ~ 21 0 m/a ·the hollcopt-ec IDo.y 112ach tJm o.ir-speed

at

240 km/b@' cmdt at fit R =

200 rn/s

tao

lrnl/h ,the level o:£ ~ibrution rGrnaining lowa

It """ l'ww1ct

out

that i:t

.ib

R i£1 not inOI'eB-£Hsd above tiu:wo vsluca :tt

leads to incrunsad

vib~~ton

and

cha-raotcri3tic spi~es in !oatharillg :mtJment :t'OC::Oxds: T

0;- and increo.se o!

"""'"" plate al:ternate JUO!l!ellts ; es~

Jli'Oi&:U;,r ll'ngi~udinal; in cyclic oontr':'l; lihich; as a 'Whole 1 may be 'treated as tl:ll'! evidence :for stall

tlutter~1

Tl-w recorda o! feathering moroortt J:or• final con:f&j!umtion of tho he:ll<oo>>tor with variaut c bli>des aru shotm in Fig¢ 13-.1 _{Figs' 1ft. presents}

the ch811gos l.n svaoh plate control. loads ve!:'!lte• he:Ucoptcr a.ixslJ'lOd.'

!fox- economic:al. reasonst in :result iiJt.ilt :fllght ·tests ;• it """ doclt!ed to

pruso"""e the possiblJ:> range o! Jl R m

200 "' 22.0 m/8$' >tnl.eh !led been rulOU!'0d e!U'li<lr

1J:r

appropriate doaign o:i: the !X>Wt9:r:!'ltmt a:JEctro'"ll:jrdraullo :tui>l ccntZ"')l system;:,!

A:Uwa!Jlz rotor t:l.p SlJ'leds verntm hellco)ll;e>' &irspe•d and dell!lity alti~

1d The main reason fo~ the negative dynamic phenomena on the l'Z!PSol<lll helicopter in

the

preliminary

stage

o! :flight testa was the staU fiutJ:er o! the main rotor blades

0

which a!""

poared at very. low airapeedaf

and on a tied"'(].own hellcopterp· as 'tWll

as

on. a natural.transmisaion test standj)1 _at high collective ruaior cyclic pitoh;,1

The second but not less important reason \'i'M that the so ... onlled pylon resonance frequancy 'i'ms close to no-minal main rotor rop~1n-· ueur.tngu the prob,em Uf elimination o! pylon re• sonance only woUld be a passiVe m~ thoo;· which would <Improve naither the

blade operation nor the helicopter

~rformonce;.· It also '\'!Ould not au£ ... :ficir::m-:1.y decrea.s€:: the hub and swash pL.l.i:O load!r,· An ac·Cive method of dru.ling with the problem \'1M to ;re ...

move ·tho .Ertall :flutter·,,' It decreased the loads on t.hc hub and SivMh plate;; the helicopter vibration; and 5..m"" proved its perforroru1co-.:. Neverthelesa;· with no hub mounted vibration absor..., bert it would be difficult to talk about a good helicopter,.

2o It ::!.i3 particularly iiDporta.ut

tor

the blade t·Tith loH torsional stif ... fncss to appropriately select the aerodynamic characteristics o:f the airfoils f especially s.~

.. ·

3 .. St:cpt back tapcre?- tip appeared. to be lc.ss e:tfec·tive than tapered tip in

the PZL-Soh.ol. blade configuration .. It t•Io.s responsible .for the increase of mean and 1st harmonic feathering

mo-ments-.. Ho1·revor1 a positive f'oatu_~ oi

thls tip should also be mentioned here - it increases ·the blade J?~ndulum

flutter margln ..

Lv., Upvani d(-:!.flection of the air-.foil trnili11G edge tnbs. in tM PZL...sokol. bhde config;trrotivn. decroaac-s the atall flutter mnrgin1 increases tho hub and

control system loads; and helicopter vibration(!

5 .. The PZL-Sokol. main rotor bladeV being a low tor!fional atif.ffl..oss bl!>.de has some features of tte

Aerocl&Jti-cally Confo:i:mablo Rotor Concept /ACRC/ bladeg- ns the airfoils pr~ssure centers are col'lGide-rably behind the olru.rtic . centerB'o1 _{/Se.e F'ig'o' 2/}

6o' In the development of

the

ACRC blode aJ.imination of the stall flutter pJ_w.., noil'l!?nUn may appear a seriotLS. pr,fblemp which; as it seeDJS~ has not bet.m dis~~

cussed so .faro

REFERE!lCES

1·ol Fo-'Oo'Cartag' et$'al·"·o Detel"min..<1.thm of airfoil and rotor blade dynamic eta.11

~sponse.g· Journal o:f the Amel"ican Helicopter society; Vo·i 18, Ho. 4; 1973<;

2~· Rn-It:::Blackt.;e-11; et al-,;$- Wind tv.m:;.cl evaluation

ot

.aeroelazticr1lly com~-·

:f'ox'I!lable rotors;· Journal orf' the J';.me'"'

rican Helicopter Socie·ty; Vol., 2.6; Uoeo 2Q 1981-.,/

.3"-:.' R,.:fl,.Stroub; et al·,.1_{;: Roto:r blaG.C tiD} shnpe effects on performanct? ond control loads ~rom full-scaln ~:T:!'.:rvl

tUD.llC'1 testing; Jour11al of Amnri.can Helicoptcu• SooiAty;' VoJ.~'- 2.lfv No·.,. 5~

1979o'

4o J·.,t·1.Hartin, et ul., t' An cxperintmtal analysis of dynamic stall on hn oz ... cill:lting ail•foil; Jourf!..al of th0 American Helicopter Society; Volo 195 No·,. 1; 1974-.,·

5·., R"R9Black"i:m1J.t et al· .. ·; The aeroeluo'"' tically coniormable P~otoi' Concept; Joul"''lal of ·the American Helicopter Society; Vol·9' 24j No., 4, 1979 .. Go F.:;J·.,Tarzanin, Jr .. ;: Prediction of

Control. Loads Due: to B1.t.rle Stall; Journal. of tho American Hc-L.copter Society; Vol. 17; llo. 2, 1972.

7·c'

'!'[.,'Johnson;' <::t al,,:;· On the LCJc-ha-nisn\ o:f dynamic stall.; Journal of the Aoori.can Helicopter .Soc.i.ety tl Vol·,; 17; No·e.; l~; 1972e

8·~- RnG-eoffray Ben.son:1 et al·,.T In.flu""' eilce of s.irfolls on otall .flutter· boundaries o:f articulated he licop+-: ter rotors .t JDurnal o:f tho Anmri~~

c-ru1 Heltcopter Society~ Vol,.' 'I S9

core

trailing

edqa:

tab

Figure 1. TlJpical

outboard section

of blade variant·

.,c''

geometry.

Tab

Blade's parametres:

~.

vqrtant:

A."

)

7

Radius

7,85m .. ·

Nominal chord O,'Hm

Tab

Airfoil

NACA

230M

~

vari.ant

.B".

)

ThicKness ratio:

7

_16.;.

9~

_from

_{root to tip.}

Twist 40"39,

•

₁₀

Tab

Tip

speed

wR=210-mfe.

i~

voris:mt,c•_.

-~

0.695

0,9.253

~--4---~---~*---~~~T

0,0 0,1036

t

UJ 0

ID

~

!5

:::!10

<(

~

5

0.29'!9

0,7526

1,0·

Figt..we2. Rotor blade

geometri~s.

_::L.-~Mfns

kqm

10

c.

a,

E ..

c

[mmJ

8

6

FEATERINC.

;:

ELASTIC CENTERS E.C.

Figure

3. Mass, centers of·gravitlj ·and elastic centera

di&tri buhons.

·~Cr:tlJo

1o·4

e~

16

3

£::k

[N

rr,

2]

(Nm")

,.50

40

30

l...______ff --

~'

~·

~~---~

.

20

10

TORoiONAL 5TIFFNE55 C.;:Jo - --~

1---r---~---~~---~

T

~

2

A

~

B

1D

F'IC:.Uri.E

4.

Fl.APWI&E AND CHORDW15E BENDING STI FFNE&S Af.lD r0R510f'JA1-STIFFNESS DtsTRIBIVTION5.

P/Nnam

10

B~-+--4---~-+~~~~

7~-~~~~~~¥-~

6

1---:1-::s,.e:::.+----f-Hhl-i~~l

p

FIGURE

5.

CALCULATED .BlADE FREC.UENCY DIAGRAM WITHOUT T>!E INFlUANCE OF PYLON FLEXIBILITY.

HUB .REACTIONLE5S MODES.

4·6 -10

FIC,URE 6.CALCULATED BLADE FREGUt--JC( DIAGP.AM WITH THE IN

FLU-ANCE OF PYLO~J FLEXIBILITY. HUB REACTION CYCLIC N\ODES.

·o-=-140±140Nm

Or---~~-=~--~~~----~~---~-l~

~

~

..

'E

~.

..,_,~':=1

+i

z

'

.FIGURE.

7.

RECORD!\ OF

TOR~!ONAL

N\OMENTS

OF

THE

BLADE

".4

AT

f

=

O,tl95

AND

To AT ROoT

₁ .

IN ONE Of' HOVERS. QR=210mjs.TOM ..

5410

kg

BLADES - VARIANT

A.

V"'80km/h

H=600m

~

o

t-+---¥-l---+-P~--+----,l..-,i--+----,r--~QR=212m/s

'X

!::

0

To=-134±316

Z

"l

Nm

9~---4·~+----+~~·~

~r---~-+---=~--hr---~-=---r---~-~

I

~~~~.

Nm

~~~~·hR~~t~-U~~b4~~A~A+-~~ru~~~~++4A~

'I(

~2

_I

Cf

00"

A0°

J~

~~---~-~--~·~~~----~~~----~~_;-~~T~

0

0,2

0,8

l:

1 Decent

0

_....

~ 0~--J~----+~--~--+-~~~

H=500m

V=90km/h

-f---1...-+---.f----41To=~a9:!:217

E

z

Nrn

~~--~~~.~-4~~~:=~--t~T=----~~-1~~1=~07149

1

Nm .

.

~---4~--~~~----~~--~--~~w

0.2

(44

0,6

0,8 '

t

1.0

FJOURE

8.

RECORDS OF TORSiONAL

.MOMENTS

OF

THE

BLAPE:

.

£.

AND

.Q.-

AT LEVEl- FLIGHI WITH V

=

00

l<.m{h

""-AT DECENT

WITH

V=90kmjh.

B!.APE!:>- VARIANT

A.

TOM "' 5410

1<.9.

M.t'"

150:!:661

~--~---~----~-h~---~~-+----~--~---4

Nm

o"

360°

SMd'"245~5650

Nm

ot

....

A

-

,.

I'

...

..

I

_!{

a

_{:7 -}

,.

'

.0

.i

..;,

. .2

.3

.4

_..5

.6

13

.9

1,0

_'C

'

~r---~---·---a

I

y

b ' - - - H - , J - - - -

---i -

I

I

T

₀

=-32t211

---1--1

Nm

Mr=20.5!958

Nm

SMd=-265!349..5

\

Nm

~;J~-+.~r-~+~~~~-4~-~r~7r~~-~~fl-~

\/ 5Mu=304:!:1725

Nm

5Mdnr~:t2220Nm

Figure 10. Records

of rotor

system parametres at level fliqht-

·

with V

=

206

kmfh.

.

. · ·

TOM"'

5410 kq, H =

562

m , OAT:::: 26°C, QR= 217

m/s. .

.Blade:.- variant

c~

vvi th

onetab8"'upfarr

=-0,6617-0,~25

'

~

"

·_g_

.·

A

ts

n

I

_{. J}

_\,..To

.

I

\

/

• ' f\

'

\

.

{\

I

1\j

L

\J

' _'

J

J'v'

r

5

i/,

I

\

_':L

..

I

·l

•

!\

.A

.Q.

(\

2.~

t-

'{\

MY 1

'

.

/

0~

.,-)<

E

:zo

.

A

V'

_I

V\

v

n

3

''v

V\

v

_V\

-v

\

0

~

1:---1--fr---+----:-.--:-f~--.!1·1!-l!-..,..

X

E

0 f---1-=::-:r--IH+-''--'.1---HI--..-IH---+i K+f-\-f---"--4 z"'~"

v

-r

~

--v

I

----::--:;-11 ' •

-lll'\t"'447t497

1\lm

o.o

Y:

!P

1----.-+::;;;..

E

:z

...

8 '\

I

g.:l...

--..~!_

. .:..· __ _.

'

.6

.7

.2

/'") To=-160±2!"5.5·

1---1--.;.1

N m

I

\ s :

_{I t} v , 'J I

.8

•

.9

1.0

To=-156:!:286

Nm

Flc;;.UP.E

12.

RECORDS OF TORSIONAL MOMENT$

To

OF

TH.E

BLAD!:

WITH Dl FFERENT ROTOR. TIP· SPEEDS.

.

TOM"' 6100

kg

₁

H

=

650

m,

OAT= 25°C.

BLADES

-MODIFIED VARIANT C':ji.WITH.S

1o

C TABs,·

ALL DEFLECTED

4

°

up·

'

_.9:.

oo

Hover

""'

H=58m

XCII

f.,..

Z l

To=-74:!:80

(;!q

....

oo

:5600

_'Y

Nm

"'

A

"'

I

0

~2

.4-

.o

.B.

t

1.0

C\1

..,..

I

V=80km/h •

oo

-1

To==-84±163

...

·x

I

_Nrn

Et:'l

zT

2!;

J·

I

oo

360'

(J)-4>

₊

....

"'

A

~0

.2

.4

.6

.8

1:

1,0

--+c

J

To

_j-

\i

_V=227km/h

,,

- t - -

--~

r;

_-"o'j-<-

2'~4

I !

o-

..; -

?..

I

; .

N

n:

I

'

I j I

"i'

_i

- - - i

I

~,

I

360°

'

I

!

<pj

0"

I

~-

+

4>

I

₀

C'l

-'<:"

0

'<:"

)( 0

E

z

01

""

I

'+

q

-I

;;s

I Q

"'

+

4-.2

.6

,6

,l..

_...

_1:0

I

·-j

V:::265 km/h

To

_I

___J

To=-116:!:.24-1

I

'

I

Nm

....

...

.z

t+-

.13

FIGURE 13. RECORDS OF TORSIONAL MO!Y\ENTS

To

OF

THE

Bl-ADE

IN

HOVER

AND AT DIFFERENT

LE:VEL

AIR!:>PEEDS

TOM =6100

kg,

H= 440m

j0AT=2"C

1

QR"'

220 m/s

E>l..ADES ·- VARIANT C.

LONGITUDINAL

MOMENT

·Nm

:roo

!ll

_...

.

•

•

\J5TEADY

I

..

400

..

3 ~ 200

_ALTERNATE

100 0 Oo ₀

~

C>

...,

0 0 0

lA:'>

0

--kmjh

100 120 140 160

180

200

2ZO

240

260

Nm

_{LATERAL MOMENT}

200

ALTERNATE

100 4

-.

~

0

--A

...

"'

lAS

0 100 120

140

160

·lBO

200 220 240

-260

k.mfh

-100

-200

·500 -400

_STEADY

-500

~

·600

1000

COLLECTIVE LOAD

0

IA5

100

120

140

160

180

200

220

240

.260

km/h

-1000

-2000

STEADY

•

~

•

•

_"

•

"

~

-3000

N

FIGURE 14. SWASHPLATE LOADS VERSUS AIR5PEED

₁

TOM

,.6100

kg.

QR=220mjl>.BLADES-VARIANT C.

.

.

~

i;;

E

I· Ul

A

·::l ;.. ~ <(

~

,ifi

z

llJ

A

5000

4000

.3000

.woo

1000

1--I

I

"'

'

'\

-10J INDICA1 ED

"\

"

-"'

---TC

_f\11.

Fo6

oc

kq

-"'

... .s;>

"'

l\p

.. r

"'~'-" ~

R.,

~.--.

;y---~~- ~ ~

.

'~ ~-

_{I~ ~}

~--

;JJ

---f-~·-I -

i'-..

1'....1\

I

I

r-.._

f'\

0

.5000

1---1--l--1

100

200

INDICATED AIR,;PEED -

>~mft,

-

1----

-

1-:;oo

FIGURE 15. MA'/.fMi.JM ALLOWA.BL.E AID5PEED VS r.ENS!TY

ALTITUDE

AND

QR, BlADES-

VARIANT

C.