Reduction of high-speed impulsive noise by blade planform modification of a model helicopter rotor

AVRADCOM

NASA

TechnicalRepart 82-E6

Technical Memorandum 84 5 5 3

Reduction of High-speed Impulsive

Noise by Blade Planform Modification

of a Model Helicopter Rotor

Ihvid A. Gmner and Danny R. H a d

structures Luhmrory A VRA DCOM Re .earcb and Technology Iplsmtories Lung&y Research Center Hampton. Virgnia National AWOMUtkS a d Space Administratton &htHkmdf@chlBk8l fnf0nMtbn- U s e of trade names or names of manufacturers i n this report does n o t constitute an o f f i c i a l endorsement of such products or manufacturers, e i t h e r expressed or implied, by the National Aeronautics and Space Administration.

SUMMARY A n experiment has been performeci to i n v e s t i q a t e t h e r e d u c t i o 2 of hiqh-speed impulsive noise by usinq an advauced main rotor system f o r the UH-1H h e l i c o p t e r . I?e advanced rotor system had a tapered hlade planform conpared with a r e c t a n q u l a r plan- for the s a n d a r d rotor system. mdels D f both t h e advanced main rotor system form the UH-1H stardard main rotor s y s t e a were tested a t 1/4 scale i n t h e I a n q l e y 4- and hy 7-Meter Tunnel (fcrmerly the Ianqley V/STOL Tunnel) usinq t h e q e n e r a l rotor model system ( G R C S ) . Tests were conducted throuqhout t h e UH-1H v e l o c i t y ranqe (80 to 110 knots) " ' o r which t h i s type of n o i s e is of concern. The t u n n e l - a s operated i n the cptional open-throat conficmration, with a c o u s t i c a l t r e s t m e n t a p p l i e d t o t h e c e i i i n q and floor t o improve t!!e a c o u s t i c c h a r a c t e r i s t i c s of t h e test chamber. In- plane a c o u s t i c measurements of t h e high-speed impulsive noise demonstrated t h a t t h e advanced rotor system on t h e UH-1H h e l i c o p t e r re&ced +_he hiqh-s-d impulsive noise by up t o 20 dB, with a reduction i n overall sound p r e s s u r e level of up to 6 dB.

INTRODUCTION Aerodynamically qenerated n o i s e from a h e l i c o p t e r can be broken down i n t o sev- e r a l cateqories n o t t o t a l l y independent of each o t h e r . Of most o n c e r n i s impulsive noise, or blade s l a p , because of its relative loudness (refs. 1 to 3). Impulsive noise, as reported i n reference 4, can be uenerated i n t h e followinq tun ways: ( 1 ) hiuh-speed impulsive (HSI) n a i s e due t o shock-wave formation and c o l l a p s e on t h e advancinq blade t i p ; and ( 2 ) blade-vortex i n t e r a c t i o n ( A V I ) i m p u k r v e n a i s e due to the impulsive chanqe i n hlade loadinq durinc; blade- and t r a i l i n q - v o r t e x i n t e r a c t i o n which occurs i n l o w - p a r e r des-endinq f l i q h t or maneuvers. This paper is concerned only with HSI noise.

Two d i f f e r e n t t h e o r i e s have been developed t o account f o r t h e qeneration of HSI noise. One theory ( r e f . 5 ) correlates c o r q r e s s i b i l i t y e f f e c t s :-elated t o hiqh rotor b l a d e - t i p Epeeds and observed blanc-tip shock-wave formations with observed HSI noise (ref. 6) models t h e HSI noise production b y pressure-time h i s t o r i e s . Another theory t h e pressure d i s t u r b a n c e of t!e f l u i d medium caused by t h e motion of ;'-he blade (rotor blade thickness e f f e c t ) . Both t h e o r i e s p r e d i c t t h a t t h e H S I n o i s e h a s t h e d i s t i n c t i v e c h a r a c t e r i s t i c of beinq d i r e c t i o n a l towards the forward resion of f l i q h t w i t h the peak p r e s s u r e i n t h e plane of t h e r o t o r . Because h e l i c o p t e r s q e n e r a l l y operate a t l o w a i t i t u d e e , m o s t surroundinq land s u r f a c e areas (except those immediately under t h e h e l i c o p t e r ) are s u b j e c t e d to t h i s in-plane HSI noise. I f t h e a i r c ; a f t is cperatinq i n a combat zone and t h e element of s u r p r i s e is d e s i r e d , any reduction of t h i s iiSI noise would reduce t h e a u r a l d e t e c t a b i l i t y of t h e a i r c r a f t .

Since t h e o r i q i n a l d e s i r n , t h e qross weiqht of t h e various :nodels of t h e UH-1H h e l i c o p t e r has increased s u b s t a n t i a l l y . "%is increase i n qross weiqht h a s necessi- t a t e d a correspondinq i n c r e a s e i n rotor t h r u s t capability. A new blade desiqn has been developed for which performance and HSI-noise p r e d i c t i o n r o u t i n e s i n d i c a t e d improvements over the standard blade ( r e f s . 7 and 8 ) . me planform cf t h i s desiqn is tapered, and the t h i c k n e s s is reduced a t t h e t i p compared with t h e c u r r e n t U H - 1 H

rotor blade desiqn. me reductioi? of bla,?e-tip thickness was expected t o reduce $?SI

noise. ?he noise reduction p o t e n t i a l of the new blade desiqn is t h e r e f o r e i n v e s t r - gated experimentally i n t h i s study. ?he experimental r e s u l t s are presented tc corn- pare t h e HSI n o i s e produced by a l j 4 - s c a l e d e 1 of t h e UH-1H v i t h advanced rotor blades with t h a t produced by a 1/4-scale d e 1 with s t a n d a r d rator blades.

first harmonic of lateral c y c l i c blade p i t c h , deq A1 rotor coning angle, f i x e d a t 2.75O f i r s t harmo!iic of l o n g i t u d i n a l f lappinq, deq first harmonic of l o n g i t u d i n a l c y c l i c b l a d e p i t c h , deq B1 f i , s t harmcnic of lateral f l a p p i n g , deq blS %tor torque rotor torque c o e f f i c i e n t , cQ 3 2 p a (PR) Rotor t h r u s t r o t o r t h r u s t c c e f f i c i e n t ,

cr

pltR2(QR) s t a n d a r d rotor system b l a d e chord, 0.1334 m C D rotor draq, dynes F F!

frequency, ‘i rotor l i f t , dynes F , + QR advancing-blade-tip Mach number, Local Speed of sound‘ MT peak neqative impulse p r e s s u r e , dynes/cm pP R rotor r a d i u s , 1.829 m rotor b l a d e - t i p speed, rn/sec vT free-stream v e l o c i t y , knots v m c o o r d i n a t e s for microphone l o c a t i o n s in tunnel, m X I Y I Z anqle of a t t a c k of rotor s h a f t , deg a r o t o r tip-path-plane anqle of a t t a c k , referenced t o tunnel qeometric a TPP c e n t e r l i n e , deg r o t o r d e s c e n t anqle, t a n ” (D/L) Y 9 r o t o r c o l l e c t i v e c o n t r o l anqle, deq C v advance ratio, Vm,WT P local free-stream d e r s i t y , kg/m T r e f e r e n c e impulse width 0 rotor angular r o t a t i o n a l v e l o c i t y , rpm Abbreviations : ARS advanced rotor s y s tern BY1 b lade-vor tex i n t e r a c t i o n HS I high-speed impulsive OASPL overall sound pressure level, d B (re 0.0002 dynes/cmL) r p m r e v o l u t i o n s per minute SPL sound p r e s s u r e level, dB (re 0.0002 dynes/cm ) SRS standard rotor system HELICOPTER MODEL, TEST FACILITY, AND INSTRUMENTATION Helicopter Mode1 This test w a s conducted i n t h e Langley 4- by 7-Meter Tunnel (formerly hie Langley V/STOL Tunnel) using t h e g e n e r a l r o t o r m o d e l system (GRHS) as d e s c r i b e d i n 9. me l/cl-scale model of t h e UH-1H f u s e l a g e w a s desiqned t o e n c l o s e t h e r e f e r e n c e basic m o d e l , transmission, and c o n t r o l s f o r t h e rotor system. A sketch of t h e h e l i - c o p t e r model is shown i n fiqure 1. Two six-component strain-gaqe balances w e r e used for this test, one supporting t h e f u s e l a g e s h e l l and one supporting the rotor system i n c l u d i n g t h e a c t u a t o r s , electric d r i v e motor, and transmission. Aerodynamic perfor- mance measurements presented h e r e i n were obtained from t h e rotor balance and refer- enced t o t h e s h a f t axis system. (.See ref. 7 . ) Tim d i f f e r e n t rotor systems were t e s t e d i n t h i s test, each mcunted on t h e same geometrically scaled version of t h e UH-1H rotor hub. C X l e rotor system used the s t a n - dard, or b a s e l i n e , rotor blades, which were geometrically and dynamically scaled models of the c u r r e n t UH-1H rotor blades. m i s system is h e r e a f t e r referred t o as the standard rotor system (SRS). These blades were rmde of a f i b e r g l a s s / K e v l a r l com- posite having a graphite/epoxy composite s t r u c t u r a l t c r q u e box. lhe aerodynamic contours were formed by means of an e x t e r n a l fiberqlass/epoxy s h e l l with a Nomex honeycomb c o r e i n t h e t r a i l i n g edge. Ihe o t h e r rotor system t e s t e d incorporated a t o t a l l y d i f f e r e n t blade planfarm and is r e f e r r e d t o as t h e advanced rotor system (ARS). lhese advanced rotor blades had a wider r o o t chora compared with t h e standard rotor blades, with a 3 t o 1 taper r a t i o beginning a t the 50 percent radius. Advanced Registered trade name of E. I. du Pont d e Nemours 6 Co., Inc.

'K?vlar: Registered t r a d e name of E . I. du Pont de Nemorirs 6 i CO., Inc.

2Nomex:

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-10 R - I I .OS R _I____ -I ”--- 1.73 R Fiqure 1.- Sketch of GH-1H h e l i c o p t e r model tested.

r o t o r c r a f t a i r f o i l s ( r e f . 10) w e r e used, with t h i c k n e s s ratios ranging from 1 2 per- c e n t inboard t o 8 percent a t t h e t i p * Construction w a s similar to t h a t of t h e s t a n - dard r o t o r blades with t h e exception of a Styrofoam3/balsa t r a i l i n q - e d q e core. A s k e t c h of t h e t w o d i f f e r e n t rotor blade desiqns t e s t e d is shown i n f i g u r e 2 ; their dimensional c h a r a c t e r i s t i c s are presented i n table I.

The model has a teeterinq-type rotor hub. C o l l e c t i v e and c y c l i c p i t c h e s on the b l a ;es were c o n t r o l l e d by a swash p l a t e driven by remotely c o n t r o l l e d actuators and w e r e measured d i r e c t l y a t t h e rotor hub. Rotor-system t e e t e r i n q measurements were made a t t h e t e e t e r i n q a x i s . A 67-kW electric motor o p e r a t i n q throuqh a t r a n s m i s s i o n drove t h e r o t o r . An o p t i c a l encoder provided both rotational-s:peed measurement and azimuthal indexinq of t h e rotor system.

3Styrofoam: Reqistered t r a d e name of nOw Chemical Co.

T

i

Advanced Made

Fiqure 2.- Geometric comparison of s t a n l s r d and advanced rotor b l z d e s .

TABLE I . - ROTOR CHARACTERISTICS Airfoil s e c t i c n :

Standard blade .......................................................... NACA 0012

Advanced blade ....................................... RC(3)-12, RC(3)-10, RC(3)-08

Radius, m ..................................................................... 1.829

Blade chord:

Standard blade, m .......................................................... 0 . 1 3 3 4

Advanced blade, m ................................................ 0.0560 to 0.1681

Twist:

Standard blade, d e s ......................................................... -10.9

Advanced blade, deg ...................................................... -14.0

Planform s o l i d i t y :

Standard blade ........................................................... 0.04642

Advanced blade ............................................................ 9.04863

e n t r a n c e to t h e test chamher are 4.42 m hiqh by 6.63 m wide. 'Ihe c e i l i n g h o i q h t i n t h e open-throat c o n f i g u r a t i o n w a s approximately 7.50 F above the test chamber floor.

The model was supported i n t h e wind-tumel test s e c t i o n by a unique t h r e e - j o i n t s t i n q which allowed p i t c h and yaw c o n t r o l to *4S0 about a f i x e d p o i n t on the model. This t h r e e - j o i n t s t i n g w a s mounted on a node1 support system which allowed h e i g h t c o n t r o l as w e l l as l i m i t e d a d d i t i o n a l p i t c h and yaw c o n t r o l .

I n o r d e r t o o b t a i n realistic f r e e - f i e l d noise measurements i n this f a c i l i t y , a c o u s t i c treatment w a s i n s t a l l e d on t h e tunnel f l o o r and c e i l i n g . F i b e r g l a s s - f i l l e d aluminum panels 12.7 c m t h i c k w e r e i n s t a l l e d on t h e f l o o r d i r e c t l y under and forward of t h e model (see f i g s . 3 and 4) f o r a s e m i r i g i d f l o o r t o f a c i l i t a t e periodic main- tenance and modifications t o t h e model. Open-cell polyurethane f o a m 10.2 c m t h i c k w a s i n s t a l l e d on t h e floor d i r e c t l y ahead of t h e aluminum panels and overhead on t h e s u r f a c e of the raised ceiling. (See fig. 5 ) . An e v a l u a t i o n of t h e e f f e c t i v e n e s s of this c e i l i n g and floor treatment is reported i n r e f e r e n c e 11.

Instrumentation fie a c o u s t i c t r a n s d u c e r s used f o r t h i s i n v e s t i q a t i o n were 1 .27-cm-diameter con- denser microphones f i t t e d w i t h standard nose cones. Five f a r - f i e l d microphones were positioned upstream of the model and t h r e e near-field oicrophones were a t t a c h e d d i r e c t l y t o the model fuselage. (See f i g s . 3 t o 5 . ) A s k e t c h of t h e model i n s t a l l e d i n the tunnel with f l o o r treatment and microphone l o c a t i o n s is presented i n f i q - u r e 5. Near-field microphones 1 , 2, and 3 and f a r - f i e l d microphones 6, 7, and R were strategically mounted on a n i upstream of t h e model t o d e t e c t s p e c i f i c types of n o i s e o t h e r than HSI noise. Far-field microphones 4 and 5 were mounted upstream of t h e model RS f a r as p o s s i b l e from t h e rotor ( l . l O R ) b u t s t i l l i n t h e f r e e - f i e l d environ- m e n t of the f a c i l i t y . T?wse microphones were i n t h e r o t o r tip-path plane, where H S I noise has been shown t o be maximum ( r e f . 1 2 ) . These in-plane microphones were mounted approxinately 33O t o t h e r i q h t and t o the l e f t of t h e t u n n e l c e n t e r l i n e as measured from t h e rotor hub, so t h a t t h e support f a i r i n g wake was o u t s i d e t h e r o t o r disk. Only d a t a from microphones 4 and 5 a r e presented i n t h i s paper. Based on t h e coordinate system presented i n f i g u r e 5, microphone 4 was 1 x a t e d a t x = -3.27 m, y = 2.16 m, and z = -0.17 m, and microphone 5 was l o c a t e d a t x = -3.28 m, y = -2.23 m, and z = -0.17 m. The o r i g i n of t h i s c o o r d i n a t e system was a p o i n t i n space located a t t h e roto1 huh when t h e model was a t a f u s e l a g e angle of a t t a c k of Oo. S i g n a l s from each microphone were f e d through an a m p l i f i e r / a t t e n u a t o r i n t o a 14-channel, frequency-modulated (FM) tape recorder o p e r a t i n q a t a tape speed of 76.2 cm/sec. Blade azimuth and time code were recorded simultaneously w i t h t h e microphone data.

OPERATING PROCEDURES AND D A T A REDUCTION Operating Procedures High-speed impulsive noise has been shown t o propagate towards t h e forward reqion of f l i q h t , with t h e peak p r e s s u r e i n t h e plane of t h e rotor. Therefore, it was a p p r o p r i a t e t o position t h e microphones i n t h e plane of t h e rotor. The procedure used t o e s t a b l i s h each f l i q h t c o n d i t i o n a t a f i x e d r o t o r r o t a t i o n a l v e l o c i t y (1300 rpm) was to o p e r a t e t h e tunnel and t h e model a t t h e d e s i r e d simulation condi- t i o n and determine t h e rotor tip-path-plane angle of a t t a c k After s h u t t i n g aTPP.

t h e tunnel down, t h e microphones were manually moved t o be d i r e c t l y i n the plana of the r o t o r . The tunnel and t h e model were then brought back t o t h e proper

ORIGINAL PAGE 1 s

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t ( a ) Side view.

(b) Top view.

Figure 5 . - R e l a t i v e p o s i t i o n of components in a c o u s t i c test of UH-1H h - ? &copter model.

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f l i g h t condition and approximately 20 sec of information from t h e microphones waa recorded o n tape. A rotor l i f t c o e f f i c i e n t of 0.0031 (defined as rotor l i f t non- dimensionalieed by the product of rotor disk ai'ea, hover blade-tip-speed squared, and l o c a l free-stream d e n s i t y ) was maintained throughout the HSI-noise p o r t i o n of the a c o u s t i c test. A t each simulated forward-fliqht speed desired, estimates of f l i g h t - scaled rotor-shaft angle and l a t e r a l flapping were used to set the d e 1 c o n d i t i o n s i n the wind tunnel. Rotor c y c l i c and c o l l e c t i v e pitch c o n t r o l s were a d j u s t e d t o obtain these values and to t r i m the r o t o r t h r u s t vector t o balance the drag of t h e fuselage. For each data p o i n t taken, corresponding model and t u n e 1 information were recorded simultaneously w i t h the a c o u s t i c information u s i n g the tunnel data a c q u i s i - t i o n system. The f u l l aerodynamic-performance characteristics for the speed range of !80 t o 110 knots) are l i s t e d i n table 11, and t h e s i g n convention used for concern these parameters is presented i n f i g u r e 6. A t each tunnel speed tested, backgrc .nd noise measurements were made w i t h the blades off and the r o t o r hub t u r n i n g a t the proper test conditions.

TABLE 11.- ROTOR OPERATING CONDITIONS [See f i g . 6 for a x i s c o n v e n t i o n ] I :andarc rotor system

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167 2152 8 0 . 5 -3.76 -1.69 5 . 2 1 - 2 . 4 1 0.27 0.166 0 .OO31 0 .@0010 168 2155 8 5 . 5 -3.74 -1.81 5.34 -2.36 .0031 .00010 169 2158 9 0 . 1 -3.89 -2.05 5 . 4 0 -2.26 . 0 0 3 1 .00011 170 2162 9 5 . 0 -3.87 -2.1C 5 . 5 2 -2.24 -196 .0031 .r)OOll 171 2164 100.6 -3.85 -2.25 5 . 6 5 -2 -20 .0031 .GOO1 1 171 2165 100.3 -3.84 -2.22 5.66 -2.20 .09 .207 .0031 .00011 172 2169 1 0 5 . 5 -3.82 -2.30 5 . 7 7 -2.18 .11 -218 ,0032 .00012 173 2172 110.6 -3.81 -2.53 5 . 9 3 -2.05 .13 .229 .0031 .00012

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1 Ivancec rotor system

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202 2603 80.0 -3.79 -1.78 7.44 0.55 1 . 8 9 -1.54 -0.51 0.166 0.0032 -3.19 0.00009 203 2607 8 5 . 1 -3.77 -1 e94 7.50 -3 e 1 6 .92 1 . 7 0 -1 -60 - . 3 5 .176 .0032 1 .OOOc)It 205 2614 9 0 . 0 -3.76 -2.10 7.60 -2.93 1 . 1 2 1 . 5 4 -1.48 -e51 a186 e0332 .00009 206 2618 9 5 . 1 -3.87 -2.12 7.73 -2.86 1 . 2 4 1 . 6 3 - 1 -45 a 0 1 e197 e0032 I .00009 207 2620 100.0 -3.85 -2.36 7.92 -2.78 1 . 7 5 1 . 3 6

-1.48 -03 .207 .0032 1 .00010

1 e 7 5 207 2621 1 0 0 . 1 -3.85 -2.33 7.92 -2.78 1 . 4 0 -1 -49 e19 .207 ,0032 .@OO t 3 209 2628 1 0 6 . 0 -3.87 -2.92 8.33 -2.64 2 . 7 7 -83 -1.47 -1.08

.219 .0032 1 .00011

210 2633 110.2 -3.83 -2.64 8 . 3 6 - 2 . 4 9 2 . 6 0 1 e07 -1 -38

-a21 ,228 e0032 I .00011

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Before and after the tests, "pink" and "white" noise s i q n a l s were recorded to v e r i f y t h a t the complete a c o u s t i c system (exc1udit.q the microphones) hcd a f l a t fre- quency response over the ranqe of i n t e r e s t (30 t o 8000 Hz). A l l microphones were c a l i b r a t e d w i t h a 1 2 4 4 8 pistonphone a t 250 Hz before and a f t e r each s e r i e s of tests.

L a T i p - p a t h p l Hub p l a n e No- f e a t h e r I1 Figure 6 . - Sign convention for aerodynamic performance characteristics.

Data Ebsduction Correction8 f o r jet-boundary and blockage e f f e c t s were handled on-line to e n s u r e proper h e l i c o p t e r model o p e r a t i n g conditions. 'Ihe c o r r e c t i o n s wore computed i n g r e a t e r detail o f f - l i n e f o r cvmplete aerodynamic-performance data reduction. The method of applying these c o r r e c t i o n s is described i n r e f e r e n c e 13.

Bach a c o u s t i c record was d i g i t i z e a t a rate of approximately 22 118 samples per second. The data were then processed through a low-pass filter o f 10 000 Hz t o pre- vent a l i a s i n g . A once-per-revolution e l e c t r o n i c p u l s e generated by the optical encoder w i t h i n the rodel w a s used as a t r i g g e r Pbr precise d i g i t i r a t i o n so #at 1024 samples were obtained during each revolution. f i e timedomain data prebented i n this paper were obtained by ensemble averaging 40 rotor re-rolutions for a l l t u n n e l speeds

e x c e p t 110 h o t s , which was averaged u s i n g 6 rotor revolutions. mi8 cnsemble

averaging was done t o enhance periodic-noise components. 'Itrese a c o u s t i c data uere a l s o analyzed using a fast-Fourier-transform technique w i t h a %oxcar windowit-7' f u n c t i o n for maximum r e s o l u t i o n ( r e f . 14). 'Ihe bandwidth of these data was 21.65 Hz, with a blade-passage frequency of 43.3 Hz. Eighty degrees of freedom were o b t a i n e d by averaging 40 spectral c a l c u l a t i o n s of 1 revolution. Based on t h e chi-square dis- t r i b u t i o n of the variance for 80-percent confidence, the d i g i t a l - a n a l y s i s process y i e l d e d a v a r i a b i l i t y of 20 percent i n the spectral-power estimates.

DISCUSSION OF RESULTS Data R e p e a t a b i l i t y In order t o confirm t h a t the data presented i n t h i s paper are r e p r e s e n t a t i v e samples of t h e overall data collected d u r i n g t h i s test, a data r e p e a t a b i l i t y conpari- son for VoD 100 knots is presented i n f i g u r e 7. Figures 7 ( a ) , 7(c), 7(e), and 7 ( g ) ahow comparisons of random ' - r e v o l u t i o n samples, whereas f i g u r e s 7 ( b ) , 7 ( d ) , 7 , f ) , and 7 ( h ) p r e s e n t comparisons of the periodic-noise s o u r c e s a s a 40-revolution average. The two d i f f e r e n t sets of d a t a which are compared throughout f i g u r e 7 were obtained as two separate data p o i n t s taken back t o back without changing any model or t u n n e l parameters .

As expected, t h e randownoise comparisons of t h e one-revolution-sample p l o t s are n o t i d e n t i c a l , although they a r e very similar. me n e g a t i v e HSI-noise s p i k e s show very good r e p e a t a b i l i t y whon they are n o t contaminated by background n o i s e (which is n o t related to rotor n o i s e ) .

The periodic-noise comparisons cf the 40-revolution-average p l o t s show very good comparisons of the noise level generated by the rotor b u t n o t r e l a t e d t o the H S I - n o i s e waveform, whereas comparisons of the negative HSI-noise s p i k e a r e n e a r l y iden- tical. Even €or the case of t h o ARS a t aicrophone 5 (fig. 7 ( h ) ) , i n which no HSI- n o i s e s p i k e is e v i d e n t and the vertical scale spans only 200 dynes/cm2, a remarkably good comparison waa obtained. This i n d i c a t e s r e p e a t a b l e p e r i o d i c n o i s e e x i s t s o t h e r t h a n t h a t due t o HSI noise.

(a) Standard rotor system; 1-revolution sample from microphone 4.

...

. - * .

" i l - ; s<- : w - I 'I- - a;,.- (b) Standard rotor system; 40-revolution averaqe from microphone 4.

Fiqure 7.- Data repeatahility comparison €or V , = 100 knots.

PAGE is

ORlGlN AL QUALm OF POOR (c) Advancod rotor System; I-revolution sample from microphone 4.

a- x- 'X- I . - _ ~ i .

(d) Advanced r o t x system; 40-revolution average from microphone 4.

Figure 7.- Continued.

A S*r ; - 2 I u

i' ----- z''

; . i .. . .. . . . . .. . ... -- . __ _ _ -. - . - . ... . - - . -. . . __

-I) . = . ? .' . m -* r.a=

(e 1 Standard rotor system; 1 -revolution sample from microphone 5.

(f) Standard rotor system; 40-revolution average from microphone 5 .

Figure 7.- Continued.

ORIGINAL PAGE I S

OF POOR QUALlW i $ ?

.................................................

. z 53 l 3 L .

*I . . C T e * r.. ulr w .

( 9 ) Wvanced rotor system; 1-revolution sample from microphone 5.

' 4 'SI I . * .

L1.l

:: - .%--

' \ - - - - - . % : I L.

!t r ...............................................

x '. I, '- .I*. .>1 * , ,*. .hub.* i*.) Advanced rotor system; 40-revolution average from microphone 5 .

Figure 7 . - Concluded.

1 s *e data p r e s e n t e d i n f i g u r e 7 shar camparisens that provide a high leva1 of confidence i n t h e overall data q u a l i t y obtained d u r i n g the HSI-noise portion of this w i n d - tunnel test.

I n t e r p r e t a t i o n of Basic Data 'Ihe most direct method f o r comparing a c o u s t i c data is through a n analysis of acoustic p r e s s u r e t i r e h i s t o r i e s . Such a comparison is i l l u s t r a t e d i n f i g u r e 8(a) f o r a forward v e l o c i t y of 80 knots. In this f i g u r e , a large, negative, almost sym- m e t r i c a l l y t r i a n g u l a r p r e s s u r e pulse d a d n a t e s t h e waveform character i n the SRS data. mis l a r g e , negative pressure p u l s e has been shom i n r e f e r e n c e 10 to be typ ical of HSI noise. A mch 'Jammer, smaller amglitude, positive p r e s s u r e Mse precedes the l a r g e , negative pressure p u l s e and has been shown i n reference 9 to be attributable to blade-vorter i n t e r a c t i o n s . The width of this positive pressure pulse indicates that its energy c o n t e n t was c e n t e r e d around 1700 Rz (model scale), whereas t h e width of the large, negative p r e s s u r e pulse i n d i c a t e s a n energy c o n t e n t c e n t e r e d around 700 Hz (model scale). Since t h e frequency c o n t e n t of these pressure pulses v a r i e s as the i n v e r s e of their period ( w i d t h ) , a narrow impulse c o n t a i n s more energy a t h i g h e r frequencies than one which is broader; thus, a narrow impulse possesses the p o t e n t i a l for a greater annoyance factor to t h e human ear. Por this paper, the term .inpulsiveness" is used as a measure of the width of these p r e s s u r e pulses.

Important i n t h e a n a l y s i s of most n o i s e sources is a d e t e r r i n a t i o n of radiated energy Versus frequency content. Although n o t t h e only rethod for a n a l y z i n g impulsive-noise smrces, a spectral e s t i m a t i o n of t h e c h a r a c t e r i s t i c waveform does i n d i c a t e in what frequency band the n o i s e is predominant. por t h i s reason, the c h a r a c t e r i s t i c waveform of the SRS i n f i g u r e 8(a) has been transformed i n t o t h e fre- quency domain i n figure 8(b). Frequencies up to 8000 tlz are shown. nbst of the energy i n the large, negative p r e s s u r e p u l s e ( t y p i c a l of HSI n o i s e ) is c o n t a i n e d i n the low-frequency harmonics up t o approximately 1000 Hz (nodel scale) (ref. 8).

S i m i l a r l y , most of the energy from BVI noise is c o n t a i n e d i n t h e 1000- t o 2000-Hz frequency range (model scale). In the lower frequency range, t h e f i r s t peak i n the p l o t t e d data r e p r e s e n t s the fundamental blade-passage frequency of approximately 43.3 HE. The following peaks r e p r e s e n t the harmonics of the fundamental blade- passage frequency. Because t h i s paper is concerned p r i m a r i l y w i t h a comparison of high-speed impulsive noise, t h e lower frequency harmonics up to approximately 1000 tle are of most concern.

Acoustical Perf ormanee Important observations made on both the SRS and t h e ARS are d i s c u s s e d i n this section. Also, important observations made on the d i f f e r e n c e s between t h e SRS and

me e n t i r e data set o b t a i n e d from t h i s experiment is

the ARS are d i s c u s s e d here.

included i n the appendix.

E

a 4 rl i a s

s

s

Lc U Q -4% -r4 i c yc U

iii

ro Y Analysis of the pressure-time h i s t o r i e s from microphone 4 f o r the S shaws that t h e amplitude of t h e HSI-noise pressure s p i k e i n c r e a s e d from 870 dynes/c? a t = 0.828 t o 1930 dynes/ca2 a t = 0.866 ( f i g . 9 ) . A n i n c r e a s e i n impulsiveness B e c r e a s i n g p u l s e width) to t h i s i n c r e a s e i n noise-spike amplitude w i t h i n c r e a s i n g MT can also be seen i n f i g u r e 9. As measured a t t h e r e f e r e n c e p r e s s u r e 0 dynes/cml, t h i s noise-spike d u r a t i o n encumpasses a b o u t 0.00194 sec a t of t h e p u l a e decreased t o a d u r a t i o n of a b o u t

% = 0.835, whereas a t % = 0.859

0.00125 sec.

0 Pp for SRS 0 T f o r SRS 0 Pp f o r ARS A T f o r ARS

-

2 O W r .OM0

-

-

la00 .m36

-

-

1600 .0032

-

-

1400 .ma

-

-

cv 1200 .W24 O 6 - 4

. n U u

-

-

.W20 t loo0 r

-

-

.0016 an Mo -0

-

600- .0012

-

-

400 .o008

- -

.OW4 0 1 0 Figure 9.- Peak negative impulse p r e s s u r e and reference impulse width v a r i a t i o n as f u n c t i o n s of advancing-blade-tip Mach number from laicrophone 4.

Analysis of t h e pressure-time h i s t o r i e s from microphone 4 f o r the ARS shows t h a t the amplitude of the HSI-noise p r e s s u r e s p i k e increased from 225 dynes/cm2 a t

PIT = 0.818 to 630 dynes/crn a t ?+ = 0.858 ( f i g . 9). 'Ihe impulsiveness of t h e s e

HSI-noise s p i k e s follows t h e same t r e n d s for the ARS as was seen for t h e SRS. A n increase i n impulsiveness corresponding t o t h i s i n c r e a s e i n noise-spike amplitude with i n c r e a s i n g can be seen f o r the ARS i n f i g u r e 9. Again, as measured a t t h e

+

r e f e r e n c e pressure of 0 dynes/cm2, t h e noise-spike d u r a t i o n decreases from 0.00333 sec a t $ = 0.816 t o 0.00230 sec a t % = 0.858. Figure 9 a l s o shows t h a t , f o r a given forward-flight speed, the two r o t o r systems operated a t s l i g h t l y d i f f e r - e n t r o t o r advancing-blade-tip Mach numbers, even though t h e rotor rpm's were iden- tical. 'Ihese ?+ d i f f e r e n c e s were due t o changes i n humidity, which a f f e c t t h e speed of sound.

dRMlNAL PAGE 13

OF POOR QUALITY Coaparisons of the pressuretime histories obtained from microphone 4 for both the SRS and ARS show that the ARS reduced the amplitude of the HSX-noise presaure V , = 110

spike by 74 percent at V- - 80 knots (fig. 8(a) 1 and by 68 percent a t

knot8 ( f i g . 10) 0 N -400-

> -5oo-

Q C $ -600- a L -700- m

: -800-

n -900- VI - 1 o o o - - -1100

-

- 1 2 0 0

-

-1300 -1400- -1500- - -1600 I

LLl I I I I I I I I I I I I I I I I I I 1 1 I I I I I I I I 1

L L L L l I d 35 45 55 65 75 Time. fraction of one rotor rtvnlutioo Figure 1 0 . - Comparison of pressure-time histories for microphone 4 at V, = 110 knots.

This RSI-noise spike is n o t only reduced i n amplitude but is also less impulsive, as it h a s a wider waveform compared w i t h the sR6 n o i s e spike. (See a180 fig. 9.) How- ever8 t h e c o n t r ' h t i o n s to HSI noise for both the SRS and the ARS are i n the band of 0 to 1600 Hz f o r a l l V , t e s t e d . mere also appear t o be =re blade-vortex i n t e r a c - t i o n s t a k i n g place w i t h the ARS than w i t h the SRS, a t least for a free-stream veloc- i t y of 110 knots (fig. 10).

A comparison of the narrav-band spectrum p l o t s f o r the SRS and the Ms as mea- sured a t microphone 4 (see the appendix) shaws a s u b s t a n t i a l decrease i n sound pres- s u r e level (SPL) i n the ARS d a t a for frequencies up to 1000 Ht. A t frequencies above 1000 Ht, t h e ARS spL e i t h e r r e r a i n s unchanged or, i n most cases8 a c t u a l l y increalres s l i g h t l y campared with the SRS. fiese r e s u l t s can be seen c l e a r l y i n f i g u r e 11, which p r e s e n t s t h e SPL d i f f e r e n c e (6sPL) between the SRS data and the ARS data a8 a f u n c t i o n of frequency F and free-stream velocity. In this f i g u r s , a positive ASPL i n d i c a t e s t h a t the ARS reduced the SPL, whereas a negative BPL i n d i c a t e s that the ARS a c t u a l l y increased the SPL.

10.0 0.0 - -

1 -yv -

V , = 110 knots 0.0 0.0 AS&,

1 1 \\I V ' " V - w v " V , . 1W knots

d0 0.0 0 .o 0.0 0.0 t -10.0

i

a . 0 L ' r 1 ' * ' * ' ' a a * * * * I ' ' ' ' I I * * . ' ' * ' ' "

0 l m o 2 a Q ) m o w Q ) s Q l o ~ ~ ~ F , nz Figure 11.- Difference i n sound pressure level due t o advanced r o t o r syatem from microphone 4.

ORIGINAL PAGE I$ OF POOR QUALITY Figure 11 shows t h a t for frequencies between 3 and 1000 b, where HSI noiae i a predominant, t h e ARS reduced the nraximun SPL by 15 to 20 dE compared with t h e SRS.

‘Ihe 15-dB reduction occurred a t V , - 90 knots, whereas t h e maximum 20-dB reduction

occurred a t V - 105 and 110 knots. Fbr f r e q u e n c i e s g r e a t e r than 1000 Hz, t h e ARS = 80 increases the 8PL by a n average of about 1 dB a t t h e lower forward e p d s ( V to 90 k n o t s ) to an average of a b o u t 4 dB a t t h e higher forward speeds ( V , = $5 t o 110 k n o t s ) .

Before beginning a d i s c u s s i o n of the d a t a collected from microphone 5, a few words about t h e q u a l i t y of t h e s e d a t a are a p p r o p r i a t e . Figure 12 p r e s e n t s the f . M I ( a ) Standard r o t o r system a t Vs = 80 knots.

-

U Y -- m.0 (s 10.0

I;‘

0.0 (b) Standard r o t o r a y r t e n a t VoD - 110 k n o t r .

Figure 12.- Narrow-band mpectrun increment above background noire from microphone 5.

-

y0.u - l o . 0

-

m.0

-10.0 -20.0 j lmo m gm YDm Sam (ym m rn

F. HI ( c ) Advanced r o t o r system a t V , = 80 knots.

-

w-0 - lo.0 - 20.0 ID L 10.0 - YI 0.0 -10.0 1 ,

-20.0 : . I m m m o y m o S a m ( y m m ( D Q I

F . HI (d) Advanced rotor system a t V , = 110 knots.

Figure 12.- Concluded.

narraw-bcaad spectrum increment above background n o i s e for microphone 5 data f o r v = 80 and 110 knots. The v e r t i c a l scale of f i g u r e 12 represents the d i f f e r e n c e i n SFL between the t o t a l system n o i s e and t h e background n o i s e , w i t h a positive ASspL i n d i c a t i n g the SPL above background noise. This f i g u r e s h m t h a t for tbe fre-

quency range of concern ( 0 to 1000 Hz) , t h e SRS data are 6 to 18 dB above the back-

ground n o i s e a t V - 80 k n o t s (fig. 1 2 ( a ) ) and 4 t o 12 dB above background n o i s e a t V p = 110 k n o t s These i :vel8 are s u f f i c i e n t l y above background-noise (frq. 1 2 ( b ) ) .

levels t o c o n s i d e r t h e SRS data n o t c o n t m i n a t e d by background noise. I n c o n t r a s t t o the SRS data, the ARS data a t Vm = 83 knots ( f i g . 1 2 ( c ) ) and a t v = 110 k n o t s ( f i g . 12(d) ) are only 2 to 5 d B above t h e background n o i r e a t f r e q u e g c i e s of 0 t o 1000 He, t h u s leaving doubt as to the v a l i d i t y of t h e s e ARS data. Nevertheless, f i g u r e 12 shows t h a t while t h e SRS d a t a are w e l l above t h e background-noise levels between 0 and 1000 Hz, the ARS is so q u i e t t h a t its n o i s e d a t a are down nbar the l e v e l s of t h e background noise.

Analysis of t h e pressure-time histories from microphone 5 f o r the SRS shows t h ~ t the a u p l i t u d e of the HSI-noise p r e s s u r e s p i k e i n c r e a s e d from a minimum of

360 dynes/cm2 a t va. = 80 knots (fig. 1 3 ( a I 1 t o a maximum of 420 dynes/cm2 a t

V - 100 k n o t s ( f i g . 1 3 ( b j ) . The impulsiveness of t h i s spike a l s o changed vary l f t t l e w i t h i n c r e a s u g free-stream v e l o c i t y , i n d i c a t i n g t h a t n e i t h e r t h e amplitude nor the impulsiveness of t h i s spike is a function of forward speed (as measured i n t h i s microphone p o s i t i o n ) .

The d u r a t i o n of this HSI-noise s p i k e is approximately

0.0329 sec tnroughout t h e range compared with 0.00185 sec a t % = 0.828 and

0.00125 sac a t 9 = 0.866 or microphone 4 data ( f i g . 9). In add:t;on, t%..cz

appears to be no B V I noise p r e s e n t i n t h e s e data as there w a s i- + * e data of microphone 4.

Analysis of the pressure-time histories from microphone 5 for the il i g . 13) reveals that no HSI-noise spikes or BVI-noise s p i k e s appear anywhere i n data a t any forward speed. The pressure-amplitude range of t h e s e d a t a is small and r a r e l y exceeds f l O O dynes/cm2, i n d i c a t i n g that there is r e l a t i v e l y l i t t l e energy content.

A comparison of t h e narrow-band spectrum p l o t s f o r t h e SRS and the ARS as mea- sured a t microphone 5 (see the appendix and f i g . 14 f o r increment p r e s e n t a t i o n ) shows a s u b s t a n t i a l SPL decrease i n the ARS data a t the lower frequencies, whereas the SPL is unchanged o r i n c r e a s e s a t the higher frequencies. Between 0 and 1000 112, which is t h e range i n which H S I noise is predominant, a decrease i n SPL of as much as 15 dB is seen with the ARS a t the lower free-stream v e l o c i t y of 80 knots, whereas a t t h e high- est free-stream v e l o c i t y of 110 knots, this SPL decrease is reduced t o a maximum of 9 dB. This decrease i n SPL reduction with i n c r e a s i n g free-stream v e l o c i t y i s n o t due t o an i n c r e a s e i n the ARS SPL or a decrease i n the SRS SPL; it is due to t u n n e l back- ground-noise contamination of t h e ARS data. A t the lowest free-stream velocitv of 80 knots, f i g u r e 1 2 ( c ) shows that the tunnel background n o i s e is contaminating ;he ARS data a t the lower frequencies, whereas f i g u r e s 1 2 ( b ) and 1 2 ( d ) show that a t Vap = 110 knots both the SRS and t h e ARS data are t o t a l l y contaminated a t a l l fre- quencies. This contamination by background n o i s e does n o t e x i s t f o r t h e data e x c e p t a t one or two d j s c r e t e frequencies a t obtained w i t h microphone 4,

Vap - 80 knots. (See t h e appendix.)

Figure 15 shows a comparison of the o v e r a l l sound presswe l e v e l (OASPL) i n d e c i b e l s for t h e SRS and the ARS as a f u n c t i o n of advancing-blade-tip mch number.

The OASPL is used here because it gives a s t r o n g i n d i c a t i o n of ' & e energy c o n t e n t of the lower frequencies, which is the area of concern of t h i s paper. A l s o p l o t t e d i n f i g u r e 15 is t h e OASPL for frequencies up t o 1000 Hz only. If the H S I n o i s e is s t r o n g , t h e s e two curveb should f a l l n e a r l y on top of each crher. As the H S I n o i s e decreasee, t h e OASPL curve f o r 0 t o 1000 Hz should tend t o drop below the OASPL curve f o r a l l frequencies. mis f i g u r e s h a m t h a t f o r t h e SRS, which has a s t r o n g H S I - two OASPL curves noise c o n t e n t , the f a l l n e a r l y on t o p of each other. P o r t h e Am, however, which has less HSI noise, the OASPL curve f o r 8 to 1000 Hz does tend t o d r o p s l i y h t l y belaw the OASPL curve for a l l frequencies a t a l l advancing-biade-tip Mach numberu. In f i g u r e 15(a) (microphone 41, the OASPL f o r the AM has been reduced by 7 dB a t t h e lower b l a d e - t i p Mach numbers and by 5 dB a t t h e h i g h e r b i a d e - t i p Mach numbers. In f a c t , t h e ARS generates l e s a n o i s e a t 110 knots ( = 0.858) than t h e

SRS a t 80 knot8 (% - 0.828). The tunnel background n o i s e is ? a,To shown i n f i g -

ure 1 5 ( a ) and is 8 t o 10 dB lower than the ARS data. It appears the tunnel c - -I VI r 2 - -----I=- 4

c E '

I f

8 "

d o 9 =-=------c-

L .

d-d-

4 f >*

II 90 .O 2 0 .O 10 -0 0 .o 0 .o 0 .o ASPL , dB 0-0 V , = 95 knots 0 -0 0 -0 0.0 I -10.0 -20 .o ,', .

Figure 14.- Difference i n sound presm'. 1 - . advanced

rotor system from microk 0 SRS; all frequencies 0 SRS; 0 t o lo00 H t 0 ARS; all frequencies A ARS; 0 t o loo0 Hr 125 r Tunnel

100 I I I I I I 1 I 1

.50 .81 .82 .83 .84 -85 .86 -87 .88 (a) Microphone 4.

125 F

noise

loo I I 1 1 I I I I I

.80 .81 .S2 .83 .84 .85 .& .87 .88 MT (b) Microphone 5 .

Figure 15.- Overall sound pressure level generated by standard and advanced rotor systems.

backqrmnd n o i s e could p o s s i b l y be pushing up the value of the ARS OASPL a t the higher blade-tip Mach numbers. figure 1S(b) shows a plot of t h e OASPL i n decibels for microphone 5 as a f u n c t i o n of the a d v a n c i n p b l a d e - t i p Mach number. T h i s plot 8hous the ARS OASPL to be reduced by 6 dB a t the lawar Nach numbers and by o n l y 2 dB a t t h e h i g h e r Mach numbers -red with the SRS data.

A n experimental i n v e s t i g a t i o n was conducted i n t h e Langley 4- by 7-lleter Tunnel to determine the high-speed ispulsive-noise c h a r a c t e r i s t i c s of a new advanced main rotor system for t h e UH-lR helicopter. A 1/4-scale d e l of the UH-lH fuselage was fitted to the g e n e r a l rotor model system (GRUS) of the Langley Research Center. TWo d i f f e r e n t dynamically scaled rotor systems were tested, each mounted on t h e same q e o w t r i c a l l y scaled vexsian of t h e OH-1H h e l i c o p t e r hub. The f i r s t rotor system tested used the Standard, or b a s e l i n e , rotor blades which e r e g e o m e t r i c a l l y and d y n a n i c a l l y scaled to thc c u r r e n t UR-lH rotor blades. An advanced set of rotor blades with higher Mist, advanLud airfoil s e c t i o n s , c o n s i d e r a b l e taper, and dynamic c h a r a c t e r i s t i c s similar to t h e s t a n d a r d system was also tested. Acoustic data were taken w i t h upstream microphones l o c a t e d i n the rotor tip-path plane.

Ihe r e s u l t s of t h i s i n v e s t i g a t i o n can be summarized ds follows: 1. lhe experiaen’al procedures and data r e d u c t i o n methods used i n the p r e s e n t i n v e s t i g a t i o n y i e l d h i g h l y repeatable a c o u s t i c data.

2. Over t h e o p e r a t i n g range i n v e s t i g a t e d , t h e dominant hiqh-speed impulsive- noise component w a s reduced by as much as 20 dB by t h e advanced rotor system. The maximum o v e r a l l n o i s e reduction was 6 dB.

3. me peak negative impulsive p r e s s u r e w a s reduced by a s nuch as 74 p e r c e n t by the advanced rotor system.

4. Based on measurements made upstream of the advancinq rotor blade, the overall noise generated by t h e advanced rotor system a t 110 k n o t s w a s less than that gen- erated by t h e s t a n d a r d rotor system a t 80 knots.

5. Data f o r t h e advanced rotor system from t h e microphone upstream of t h e r e t r e a t i n g rotor blade contained no d i s t i n c t high-speed impulsive-noise waveforms of

any kind a t any forward speed. me high-speed impulsive n o i s e measured a t t h i s

microphone f o r t h e s t a n d a r d rotor system showed a much weaker dependence on forward speed compared with the measurement made upstream of t h e advancing rotor blade.

Lanqley Research Center National Aeronautics and Space W m i n i a t r a t i o n Hampton, VA 23665 November 3, 1982 APPEWDIX COIBLETE HSI-WISE ACOUSTIC DATA SET A l l pressure-time h i s t o r y data contained h e r e i n i n c o r p o r a t e similar plotting formats. The vertical a x i s p r e s e n t s t h e acoustic p r e s s u r e amplitude w i t h a n absolute scale reasured i n dynes per centimeter squared. Por r e s o l u t i o n purposes, t h e vertical-scale f a c t o r varies with forward velocity. The h o r i z o n t a l a x i s preser a time and is sham as a f r a c t i o n of one rotor revolution; only one-half of one rotor revolution is shorn. Fbr ease of conparison, SRS and ARS noise d a t a are p l o t t e d on t o p of each other, with a solid l i n e r e p r e s e n t i n g t h e SRS data and a dashed l i n e representing the ARS data.

S p e c t r a l analyses of t h e data from t h e pressure-time h i s t o r i e s are p r e s e n t e d as narrow-band frequency p l o t s . A l l narrow-band plots have i d e n t i c a l p l o t t i n g formats.

The v e r t i c a l a x i s p r e s e n t s the sound pressure level (SPL) i n decibels. The h o r i - z o n t a l a x i s p r e s e n t s t h e frequency F i n h e r t z from 0 to 8000 B z . Fbr c l a r i t y , SRS and ARS spectral c h a r a c t e r i s t i c s are p l o t t e d s e p a r a t e l y . Spectral c h a r a c t e r i s t i c s of the tunnel background noise are a l s o presented f o r maximum and minimu forward veloc- i t y only.

The complete data set obtained d u r i n g t h e hiqh-speed impulsive-noise p o r t i o n of t h i s i n v e s t i g a t i o n is presented as follows: Figure E f f e c t of r o t o r system on noise s i g n a t u r e generated by h e l i c o p t e r model a t V = 80 knots: Comparison of pressure-time h i s t o r i e s f o r microphone 4 ...................... A l ( a ) Narrow-band spectrum for standard r o t o r system f o r microphone 4 ............. A 1 (b)

Narrow-band s~;ect-run for advanced rotor system for microphone 4 ............. A l ( c )

Comparison of pressure-time h i s t o r i e s for microphone 5 ...................... A l ( d )

Narrw-band spectrum for standard rotor system for microphone 5 ............. A l ( e )

Narrow-band spectrum f o r advanced rotor system f o r microphone 5 ............. A1 ( f

E f f e c t of r o t o r system on noise s i g n a t u r e generated by h e l c i o p t e r model a t V = 85 knots: Comparison of pressure-time h i s t o r i e s f o r microphone 4 ...................... =(a) Narrow-band spectrum f o r standard r o t o r system for microphone 4 ............. A Z ( b )

Narrow-band spectrum for advanced rotor system f o r microphone 4 ............. M ( c )

Comparison of pressure-time h i s t o r i e s f o r microphone 5 ...................... A2(d)

Narrow-band spectrum f o r standard rotor system for microphone 5 ............. =(e)

Narrow-band spectrum f o r advanced r o t o r system f o r microphone 5 ............. A2(f 1 E f f e c t of r o t o r system on noise s i g n a t u r e generated by h e l i c o p t e r model a t V = 90 knots: aD Comparison of pressure-time h i s t o r i e s f o r microphone 4 ...................... A3(a) Narrow-band spectrum f o r standard r o t o r s y s t e v far microphone 4 ............. A3(b)

Narraw-band spectrum f o r advanced rotor system for microphone 4 ............. A3(c 1

Comparison of pressure-time h i s t o r i e s f o r microphone 5 ...................... A3(d) Narrow-band spectrum for s t a n d a r 3 r o t o r system for microphone 5 ............. A3(e)

spectrum for advanced r o t o r system f o r microphone 5 ............. A3(f)

Narrow-barld Figure Effect of rotor system on noise s i g n a t u r e generated by h e l i c o p t e r model a t V = 95 knots: s

4 ...................... A4(a)

Oomparison of pressure-time h i s t o r i e s f o r microphone

Narrow-band spectrla for standard rotor system for microphone 4 ............. A4(b)

spectrum f o r advanced rotor system f o r microphone 4 ............. M(c)

Narrav-band Comparison of pressure-time h i s t o r i e s for microphone 5 ...................... A4(d)

Natrar-band spectrum for standard rotor system for microphone 5 ............. A4(e)

for microphone 5 ............. A4(f)

Narrow-band spectru f o r advanced rotor system, Effect of rotor system cn noise s i g n a t u r e *aerated by h e l i c o p t e r model a t VE) = 100 knots: Comparison of pressure-time h i s t o r i e s f o r microphone 4 ...................... A5(a) Narrow-bani! spctrma f o r standard r o t o r system f o r microphone 4 ............. rsdfb)

Narraw-bi1.d spectrum for advanced rotor system f o r microphone 4 ............ A!5(c)

Comparison of pressure-time h i s t o r i e s for microphone 5 ...................... AS(d)

Narraw-bad spectrum f o r standard rotor system f o r microphone 5 ............. =(e)

Narrow-band spectrum for advanced rotor system f o r microphone 5 ............. AS(f)

Effect of rotor system on n o i s e s i g n a t u r e generated by h e l i c o p t e r model a t V = 105 knots: OD Comparison of pressure-time h i s t o r i e s for microphone 4

...................... A 6 ( a )

Narrow-band spectrum f o r standard rGtor system f o r microphone 4 ............. A 6 ( b )

Narrow-band spectrum for advanced rotor system f o r microphone 4 ............. A6(c)

Comparison of pressure-time h i s t o r i e s f o r microphone 5 ...................... A 6 ( d )

Narraw-band spectrum f o r standard rotor system f o r microphone 5 ............. A6(e)

Narrow-band spectrum for advanced r o t o r system f o r microphone 5 ............. A6(f)

E f f e c t of rotor system on noise s i g n a t u r e generated by h e l i c o p t e r model a t V = 110 knots: QI Comparison of pressure-time h i s t o r i e s f o r microphone 4 ...................... A7(a)

Narrow-band spectrum f o r standard rotor system f o r microphone 4 ............. A7(b)

Narrow-band spectruu for advanced rotor system for microphone 4 ............. A7(c)

Comparison of pressure-time h i s t o r i e s for rnicrophone 5 ...................... A7(d)

Narrow-band spectrum f o r standard rotor system f o r microphone 5 ............. A7(e)

Narrow-band spectrum f o r advanced rotor system f o r microphone 5 ............. A7(f)

APPENDIX ( a ) Comparison of pressure-time h i s t o r i e s for microphone 4.

Figure A1.- Effect of rotor system on n o i s e s i g n a t u r e generated by VoD = 80 knots.

h e l i c o p t e r model a t APPENDIX ORIGINAL PAGE E3 OF POOR QUALITY 115.0 105.0 m 95 0 0 m .) 85 .O .A a 75 .O v) 65 .O 55 .O

0 loo0 2ooo 3Ooo wlo 5ooo 6oOo

F , Hz (b) Narrow-band spectrum for standard rotor system for microphone 4.

F. Hz ( c ) Narrow-band spectrum for advanced rotor system for microphone 4.

Figure A I .- Continued.

APPENDIX SRS; % = 0.828 --- -c ARS;

5 = 0.818

( d ) Oomparison of pressure-time histories for microphone 5 .

Figure A1 .- Continued.

APPENDIX 115.0 105.0 c n 3 5 . 0 U .) S . 0 A & v) 75 .o 6s -0

ss .o

0 loo0 2Ooo 3Ooo yo00 so00 6Ooo 7001) F, Hz (e) Narrow-band spectrum for standard rotor system for microphone 5.

¶15.0 105.0 95 .O 85 -0 75 -0 6s -0 55.0 F , Hz (f) Narrow-band spectrum for advanced rotor system f o r microphone 5.

Figure A1 .- Concluded.

APPENDIX SRS; NT = 0.835

--- - - ARS; pt 0.825

1 0 0 -100 N -200 E

5 -300

u' m

E -400

a U C 1 -500 -600 -700 -800 -900 -1000 -1100 ( a ) Comparison of pressure-time h i s t o r i e s for microphone 4.

Fiqure A2.- Effect of rotor system on n o i s e s i g n a t u r e generated by h e l i c o p t e r model a t V , = 05 knots.

APPENDIX ORIGINAL PAGE tS

OF POOR QUALITY

ii5.0 105.0 -J Q 75 .O v) 6s .O

ss .O

F , Hz

(b) Narrow-band spectrum €or standard rotor system for microphone 4, F, HZ ( c ) Narrow-bad spectrum €or advanced rotor system for microphone 4.

Figure A2.- Continued.

APPENDIX

SRS; 5 = 0.835

------- ARS; 3 0.825

I I I I I I ~ I I I I I I I I I ~ I I I I I I I I I ~ I I I I I I I I ~ ~ 25 3 5 .45 55 65 .-I2 Time, fraction of one rotor revolution ( d ) Comparison of pressure-time h i s t o r i e s for microphone 5.

Figure A2.- Continued.

APPENDIX 115 0 0 € 105 a 0 95 -0 m 'FI .I 85 .O -I 0 Y , 75 -0 6s .O 55 -0 F, Hz (e) Narrow-band spectrum for standard rotor system microphone 5.

F, Hz ( f ) Narrow-band spectrum for advanced rotor system for microphone 5 .

Figure A 2 . - Concluded.

APPENDIX ORIGINAL PAGE 1 s

I)F POOR QUALIW

-

SRS; 9 - 0.839

A

-------ARS; #r * 0.829

I1 E Y ‘ I1

> -200-

I I -3oG- -600 I : J a -700-

--

-800 - -900

-

-lo00

-

-1100 - -1200 -1300 - I

I l l l l l l l l l l l j l j l l l / I l l l l l l j l l l l l l l j l l l ! l l l l l l

.25 .35 .15 .55 .65 .75 Time, fraction of one rotor revolution ( a ) Comparison of pressure-time h i s t o r i e s for microphone 4.

Figure A 3 . - Effect of rotor system on noise signature generated by helicopter model a t V , = 90 knots.

APPENDIX 116.0 F 106.0 m 9s .O L 8s.O -1 Q 75.0 v) F, Hz (b) Narrow-band spectrum €or standard rotor system for microphone 4.

F , Hz ( c ) Narrow-bend E-ctrum for advanced rotor system microphone 4.

Figure A3.- Continued.

APPENDIX --E; I+ = 0.839

-----ARs; y = 0.829

i 100

-1

I I I ~ I

~ I I I I I I I I , I I I I , I I I I , I I I I , I I I I I I I I , I I I I I I I I I , .35 .45 .55 '65 .75 h e . fraction of one rotor revolution ( d ) Qmparison of pressure-time h i s t o r i e s for microphone 5.

Figure A 3 . - Continued.

APPENDIX 115-0 105 .o F, Hz (e) Narraw-band spectrum for standard rotor system f o r dcrophone 5.

m F, Hz i f ) Narrow-band spectrum for advanced rotor system for microphone 5.

Figure A3 .- Concluded

i APPENDIX

SRS; % = 0.849

------ ARS; 5 = 0.837

I i I Y '

I '

I I Time. fr~cCon of one rotor revdution ( a ) Comparison of pressure-time histories for microphone 4.

Figure A4.- Effect of rotor system on noise signature generated by V- = 95 knots.

helicopter model a t 4 2 APPENDIX 1 1 5 . 0 105 .o m 35 .O U L A 85 .O Q.

v) 7 s . O L 65.0 55 .O F, Hz (b) Narrow-band spectrum for standard rotor system for microphone 4.

1 1 5 . 0 E 1 0 5 . 0 95 0 0 8s.O 7s .O F 65.0

ss .O

F, Hz (c) Narrow-band spectrum for advanced rotor system for microphone 4.

Figure A4 .- Continued.

APPENDIX ( d ) Oomparison of pressure-time h i s t o r i e s for microphone 5.

Figure A4.- Continued.

APPENDIX f, Hz (e) Narrow?-band spectrun for standard rotor system for microphone 5.

F, HZ ( f ) Narrow-band spectrum for advanced rotor system for microphone 5 .

Figure A4.- Concluded.

APPEFtDIX

m

- 1 M -200 N -300

i

2 -10

C

; -500

d L -600

p -700

a -800 fl -900 -1OOO -1100 -1200 -1300 -1400 -1500 -1600 -1700 1 1 1 1 1 1 1 1 1 I IU I 1 1 1 1 I I I I I I I 1 1 1 1 1 1 1 I 1 I I I 1 1 I 1 1 J I 1 1 I I 1 1 1 25 .35 .45 .55 .65 .75 Time. froction of one rotor revdution (a) Comparison of p r e s s u r e - t i n e h i s t o r i e s for microphone 4.

Figure AS.- E f f e c t of r o t o r system on n o i s e s i q n a t u r e qenerated by h e l i c o p t e r model a t V , = 100 k n o t s .

ORfGtNAL PAGE !ti: OF POOR QUALITY F, Hz (b) Narrow-band spectrum for standard rotor system for microphone 4.

F, Hz (e) Narrow-band spectrum for advanced rotor system €or microphone 4.

Figure AS.- Continued, APPmDIX ( d ) Comparison of pressure-time h i s t o r i e s for microphone 5.

Figure A5.- Continued.

APPRNDIX 110.0 c F, H2 (e) Narrow-hand spectrum €or standard rotor system for microphone 5, F, Hz ( f ) Narrow-band spectrum for advanced rotor system for microphone 5 .

Figure AS.- Concluded.

APPENDIX I' I " I I I

-

* -800 U C - J -900 v1 - -1000 -1100- - -1200 - - 1 300 - - 1 420 -1500- - -1600

-

-1700 - 1 8 0 0 , I I I I I I I I ~ I I I I I I I I I ~ , I I I I I I I I ~ I I I I I I I ~ I ~ ~ I I I I I I I I I J 25 .35 .45 55 .65 15 Time, fraction of one rotor revolution ( a ) Comparison of pressure-time histories f o r microphone 4 .

Figure A6.- Effect of rotor system on noise signature generated by helicopter model a t V , = 105 knots.

APPENDIX

ORIGINAL PAGE: fS

OF POOR QUALln 115.0 105.0

3 56.0

.)

A 85.0 a .

v) 75 e 0 65 -0

ss .O

F, Hz (b) Narrow-band sp@ctrum for standard rotor system for microphone 4.

F, Hz Narrow-band spectrum for advanced rotor system for microphone 4.

Figure A6.- Continued.

APPENDIX (d J Comparison of pressure-time histories for microphone 5 .

Figure A6.- Continued.

5 2

1000 rn 2 m %ooo so00 6ooo 7000 8Mlo

F, Hz (e) Uarrow-band spectrum for standard rotor system for microphone 5.

110.0 lllo.0 % 90 -0 .)

J 80 .o

Q Y , 70 *O 60 -0 50.0 F, tit ( f ) Narrowband spectrum for advanced rotor system for microphone 5 , Figure A6*- Concluded.

APPENDIX

X Q t- n

SRS; 5 ' 0 . 8 6 6

------ ARS; 5 = 0.858

Ith

; I A I I I I I I I I I lime. froctlon of one rotor revolution ( a ) Comparison of pressure-time histories for microphone 4.

Figure A7.- Effect of rotor system on noise siqnature generated by helicopter model a t V , = 110 knots.

120 -0 110-0 100.0 .

90 -0 A v) 80 -0 70 .O 60 .O F, Hz (kl Narrow-band spectrum for standard rotor system for r.icrophone 4.

F, Hz (cl Narrow-band spectrum for advanced rotor system for microphone 4.

Figure A 7 .- Continued.

APPENDIX ( d ) Comparison of pressure-time histories for microphone 5 .

Figure A 7 .- Continued.

APPRNDIX 110.0 100 .o m V 9 .O ., A M .O Q m

M .o

60 .O 50 .O f. Hz (e) Narraw-band spectrum for standard rotor system for microphone 5.

110.0 r m -0 Tunnel background noise

0 loo0 m 3ooo 5003

f. Hz ( f ) Narrow-band spectrum for advanced rotor syscem for microphone 5 .

Figure A7.- Concluded.

1 . towson, n. V.; and Ollerhead, J. B . : Studies of Flelicopter R o t o r Noise.

USAAVWBS Tech. Rep. 68-60, 6 . S . Army, Jan. 1969.

2. Langenbucher, V.: Noise Phenomena W i t h Rtlicopter Rotors and Possibilities of Noise Reduction. ESA -244, Peb. 1976.

3. Powell, Clemans A.; and UcCurdy, David A.: E f f e c t s of R e p e t i t i o n Rate and Impulsiveness of Simulated Helicopter Rotor Noise on Annoyance. NASA -1969, 1982.

4. Hoad, Danny €?@bert: H e l i c o p t e r Blade-Slap Noise V a r i a t i o n W i t h Tip Vortex Modi- f i c a t i o n . I4.S. Thesis, The George Washington University, 1979.

5 , V a u s e , C. R.; Schmitz, F. H . ; and Boxwell, D. A.: High-speed Fielicopter Impul- sive mise. P r e p r i n t NO. 1004, Proceedings of the 32nd Annual National V/STOL F o n m , American Helicopter SOC., Inc., Uay 1976.

6. Farassat. F.: Theory o f Noise Generation From Moving Bodies With a n A p p l i c a t i o n to Helicopter Rotors. NASA TR R-451, 1975.

7. Berry, John D . : Performance T e s t i n g of a -in Rotor System for a U t i l i t y Heli- copter a t 1/4 Scale. NASA -83274, AVRADCM TR 82-B-3, 1982.

8. H o a d , Danny R.; and Conner, David A.: Acoustic Performance Evaluation of a n Advanced UWl Helicopter !lain Rotor System. P r e p r i n t 81-58, Proceedings of the 37th Annual Forum, American Helicopter SOC., May 1981.

9. Wilson, John C.: A General R o t o r We1 System for Wind-Tunnel I n v e s t i g a t i o n s .

J. Aircr., vol. 14, no. 7, J u l y 1977, pp. 639-643.

10. Bingham, Gene J.; Noonan, Kevin W.; and Jones, Henry E . : Fbesults o f a n I n v e s t i - of Several N e w Rotorcraft A i r f o i l s as Related to Airfoil Requirements g a t i o n Advanced lkchnology A i r f o i l Research, Volume 11, NASA CP-2046, 1979, pp. 109-119.

1 1 . Theobald, M . A.: Evaluation of the ?caustic Measurement C a p a b i l i t y of the NASA Langley V/STOL Wind Tunnel open %st Section W i t h A c o u s t i c a l l y Absorbent Ul- i n g and Floor Treatments. Rep. No. 3820 ( C o n t r a c t NAS1-14611-181, B o l t b - r a n e k and Newman Inc., May 1978.

12. Schmitz, F. H.; and Boxwell, D. A.: I n - P l i g h t Far-Field Measurement o f Helicop- ter Impulsive Noise. P r e p r i n t No. 1062, Proceedings of t h e 32nd Annual N a t i o n a l V/STOL Ebrum, American Helicopter S o c i e t y , Inc., May 1976.

1 3 . Heyson, Harry H . : U s e of Superposition i n D i g i t a l Computers 'Ib Obtain Wind- Tunnel I n t e r f e r e n c e Factors for A r b i t r a r y Configurations, With P a r t i c u l a r Ref- e r e n c e t o V/STOL Models. NASA TR R-302, 1969.

14. Singleton, Richard C . : (3n Computing t h e Fast F o u r i e r Transform. Commun. Am, vol. 10, no. 10, 1967, pp. 647-654.