rill

_._ NASA Technical Memorandum 81228 ' ' USAAVRADCOM TR 80-A-8¢

Comparisonof CalculatedandMeasuredBladeLoadson aFull-ScaleTiltingProprotorin a WindTunnel

Wayne Johnson

(N&SA-T_-t_1228) CO_PAR_.30N OF CALCUL&TED Nt;J-31360A_ID _&S[JRED BLADk LOAD5 ON A FULL-SCALE

TLLTLIIG PROPROTUI_ £N A _IL_D TUNNEL (;.'IASA)

22 p l{C AO2/I{F AO I CSCL 0 lC Utm£_-_G3/05 2_b_)8

_:_ September 1980 (."_x rip. "_0"_

: " t"- \x___'

_.' UnitedStatesArmy . ._" AviationResearch

_ NationalAeronauticsand andDevelopment i -_' " Space Aclm_n_strat_on Command

1980022880

https://ntrs.nasa.gov/search.jsp?R=19800022880 2020-03-17T10:18:34+00:00Z

_, NASA Technical Memorandum 81228 USAAVRADCOM TR 80-A-3

Comparisonof Calculatedand' MeasuredBladeLoadson a

Full-ScaleTiltingProprotorin a WindTunnelWayne Johnson, Aeromechanics Laboratory

AVRADCOM Research and Technology LaboratoriesAmes Research Center Moffett Field, California

Nabonal Aeronauhc ; and Unites States ArmySpace Admmk_;Ir,,;, n Awat_onResearch and UAmes Research Center DevelopmentCommandMoffett Field Cahforrb_a94035 St Louis,Missouri63166

1980022880-002

NOX_NCLATU_E

A rotor disk area, _r_ 2

%" bla'_.emean chow], I_rR/N

Cfc pitch llnk load coefficient

Cmx blade beamwise bending moment coefficient

Cruz bla_e chordwlse benr!ing moment coefficient

CT rotor thrust coefficient

F pitch link loadc

;I blade beamwise bending momentx

M blade chordwise bending momentz

N number of blades

r blade radial coordinate

R rotor radius

T rotor thrust (shaft axes)

V tunnel air speed

_.p nacelle angle of attack| 90° for helicopter configurationand 0 for airplane configuration (axial flow)

air density

_- rotor solidity (total blade area divided by rotor disk area)

_'_ rotor rotational speed

-iii-

1980022880-003

CCMPARISON C_ CALC[_ATED AND t,YEASU_ED BLADE ILADS

ON A ?L_LL-SCALE TILTING _.CPRCT('_.IN A WIND TUN}_L

Wayne Johnson

Ames _esearch Center

and

Aeromechanics L_bora tory

AVRAI_CM Research and Technolog_ La_ratories

ABSTRACT

The loads measured in a wim_ tunnel on a full-scale tilting proprotor

are compared with calculated results. The data consists primarily of

oscillatory beamwise bemling moments at 354 radial station, oscillatory

spindle chord bending moments, and oscillatory pitch link. loa_s. The

measured and calculated results as a function of thrust are compare_

over a range of nacelle angles from 0 to 750, and a range of speeds from

_0 to IR5 knots.

|

1980022880-004

INTRO uUCTION

A full-scale, glmballed proprotor was tested in the Ames 40- by

80-ft Wind Tunnel during 1970. _ese tests provided data on the performance,

blade loads, and aeroelastic stability characteristics of the rotor system

(ref. 1). It is the purpose of the present paper to compare the neasl_re_

rotor blade loads _;Ith calculated results obtalnecl using the rotorcraft

analysis described in reference 2. The objective is to provide the

background required for the use of that analysis in the design, eval_mtion,

and testing of tilting proprotors.

WIND TUNNEL TEST

The principal parameters describing the rotor are given in Table i.

A complete description of the rotor geometric, structural, inertial, a_

aerodynamic characteristics is given in references 3 and 4.

The bide loads data are given in reference I. Data are available

as a function of rotor thrust for pylon angles from 0 to 75°, and speeds

from 80 to 185 knots. _e critical loads for this rotor were identified

as the oscillatory beamwise bending moment at the .35R radial sta'tion;

the oscillatory spindle chord bending moment; and the oscillatory pitch

link force. The oscillatory load is one-half the difference between the

maximum and minimum load values occurring in a roto revolution. The

beamwise bending moment was measured relative to the blade principal axes

(rotated by the local blade pitch angle relative to the shaft axes).

The spindle chord moment was measured just inboard of the blade pitch

bearing and outboard of the spindle/yoke junction, relative to the rotor

shaft axes. The data will be presented here in terms of coefficients,

defined as follows:

C H M

_..m. : :

-2-

1980022880-005

Table i. Proprotor Parameters

Wotor type Gimballe(!, stiff-inplane

Number of blades, N 3

Radius, R 3._I m

Solidity, _- 0.089

Lock number, _ 3.67

Pitch/flap coupling, _3 -15°

Swashplate phase angle, _s 15°

Precone, _p 2.5°

Tip airfoil NACA (!_-208 (a _--0.3)

Root airfoil NACA 69$-035 (a = 0.3)

-3-

1980022880-006

Cfc Fc Fc

•" 2 _zR3

_ T

q-.

where I!is the bending moment (with subscript x for the beamw' _ monent

and subscript z for the chordwlse moment), Fc is the pitch llnk load, and

T is the rotor thrust (in shaft axes). The rotor was trimmed using

longitudinal cyclic control so that the longlt_linal flapping relative to

the shaft was zero. The lateral cyclic control was zero. For nacelle

tilt angles of OCp = 0 and 5° the longitudinal cyclic was zero as well.

ANALYTICAL MODEL

The analysis used to calculate the rotor loads is described in

detail in reference 2. The following degrees of freedom were use0 to

define the blade motion: glmbal pitch and roll| 3 coupled flap-lag

bending modes per blade| rigid pitch mode for each blade| and I elmstlc

torsion mode per blade. Little influence on the blade loads was found

using 2 to 6 bending modes or 0 to 2 elastic torsion modes. Ten harmonics

of the motion were calculated for each degree of freedom. A blade rigid

pitch frequency of 36 Hz was used, based on reference I. Higher values

of the control system stiffness would decrease the calculated control loads.

Static, two-dimenslonal airfoil characteristics were used, with

a correction for yawed-flow effects and a tlp-loss factor (see ref. 2).

The calculated inflow varied linearly over the rotor disk. The mean induce_

velocity was calculated from momentum theory with the ideal value multiplied

by a factor of Kf = 2.0 (see ref. 2) to account for nonldeal induce_

power loasses, which are expected to be large for this rotor due to its

high twist and small number of blades (values of _f = 1.2 to 1.5 would

be typical of conventional helicopter rotors at these advance ratios).

-4-

1980022880-007

In the calculations the rotor was trimmed to a specified thrust

and to zero longitudinal flapping angle by adjusting the collective

pitch and longitudinal cyclic pitch controls. For pylon angles of _p --

0 and 5° the cyclic control was zero and only the thrust was trimmec_.

RESULTS Ahq_DISCUSSION

The measured and calculated oscillatory bending moments as a

function of blade radial station are compared in figures 1 and 2. The

moments for r/R < 0.1 are relative to the shaft axes, while the moments

for r/R > 0.I are relative to the local blade principal axes. The

correlation is Generally good, although the predicted beamwise bending

moment (Crux)is somewhat low at r/R = 0.i6.

The measured and calculated oscillatory loads as a function of

thrust are compared in figures 3 to 5 for the beamwise bending moment

at 0,33R (Crux), in figures 6 and 7 for the spindle chord bending moment

(Cruz),and in figures 8 to l0 for the pitch link load (Cfc). The loads

are presented (a) for three speeds at a nacelle angle of 75° in figures

3, 6, and 81 (b) for four nacelle angles at i_O knots in figure_ L_,7,

and 9; and (c) for two nacelle angles at 177-i85 knots in figures 5 and

10. The rotor rotational speed was 565 rpm for nacelle angles from 15°

to 75° ,ancl 458 r_m for nacelle angles of 0 and 5°.

The oscillatory beamwise bending moments are predicte_ well in

figure 3, although the loads increase somewhat faster than pr_icte_ at

the highest thrust. The predicte_ loads at 140 knots (fig. 4) are high

for _p = 60° and low for _(p - 15°! the slope with thrust is predicted"

well for all four nacelle angles. The predicted loads are low for Np --

0 (fig. 5), but the magnitude of the loads is small in airplane configuration.

The oscillatory spindle chord bending moments are predicted well

in figure 6, except for the results at 140 knots and high thrust. That

the measured loads at 140 knots are lower than the loads at 120 knots is

--_--

1980022880-008

unexpected however, an_ suggests that the data is as likely t_ be _n error

as the _nalysis for these points. The predlcte3 load__ are low for _i'-

15° 7).

%_neoscillatory pitch llnk loa_!sare unc_erpre icte-'by _b(_J.

250 to 300 N for all cases (figs. _ to I0), inclu_!in6 the noninal!'j

axial flow condition of _p = 0 (fig. 10). _e source of the v._-^:1_'t_:r:__

pitch li_._loads for %_ = 0 is not known, but it appears to be extant

for all ol_ratlng conditions. It is also note,_that for °0 knot: (_iC. _)

the increase in pitch llnk loa_!at high thrust (pres_z-_ably,lueto _t_.ll)

is not predlcted.

The rotor power is predicted well for _p = 0 to 60° (airplane

and, tiltrotor configu_tions), but is overpredicted at _(p _-75O. An

Im_ucel power loss less than t_t pre_!icted is .notproh%ble (at _ _:onf]rne"

by nonunifo_ inflow calculations), so the profile power is bein{_over-

prellcted. Thlz can be attrlbuted to deficiencies in the stall non,el

since the In_x)ard portion of thl_ highly twisted rotor bla'e is s%alle

at _p = 75° even for moderate thr_t.

CONCLUDING R_A_KS

?ne blade be_!ing momen+_ an@ pitch link loac!sneas_me_: on ;_

full-scale proprotor in a wlncl tunnel _%ve _en cozpare,_ w_th ca]c,;i-te_

results. _ne correlation is generally good for the oscillatory ben'%ng

monents. _e oscillatory pitch li_k loads are u:w]erpreZicte_ifor all costs,

Includi_ the nominally axial flow condition of _p = 0. _se_ _ on this

correlation, the analysis can be reliably used in the Cesign an,' eval,_%tion

of tlltir_ proprotoz_.

Improvln_ %he prediction of the proprotor bla_e and contro] loa_s

will require consideration of the details of the flow flel_. Speclflc;_ll>,

:!ynamic stall and nonuniform inflow may be expected to influence the

loads. However, it is difficult to investigate the influence of the

--6--

1980022880-009

<_.etailer_characteristics of the rotor ae_odynanics ultho.:t corre._pcn_'iaLl7

detailed measurements (at least the time histories of the lo_s), in

a_!dltion, current dynamic stall and nonuniform inflow zo_el_, which are

;Allenpirical to some extent, were not c_evelope,,_for the aerodyn::n_u

environment that ch_%racter_zes the tilting proprotor. Hence _t r+aybe

anticipated that further development of these r_todelzwill be req_,Src-:be['_,re

they provi_+e any significant improvement in the loa_s predictive zaT_bi]'_1,7

for proprotors.

-7-

1980022880-010

REFERBNC_S

1. Bell Helicopter Company, "Advancement oi Proprotor Technology --

Wind Tunnel Test Re_ult_," NASA _ t14363, September t971

2. Johnson, Waynet "A Comprehensive Analytical _iodel of Rotorcraft

Aerodynamics and Dynamics," NASA _._I_1182, J1.neIn:_0

3. Bell Helicopter Company, "Ar]vancementof Proprotor Technology --

Design Stu(_ySummary," NASA C.R11&6_2, September YOK_

t_. Joh_on, Wayne, "Ar_lytical tlodelingRequirements for Tilting

Proprotor Aircraft Dynamics," NASA TN D-8013, July Io7_

1980022880-011

..d

•016 J" TEST THEORY

[3" • Cmxlo

• D Cmz/O.012

E .008 •

0 r/R 1.0

Ftg_'e 1. Csctlla_ory "oea_wtse _endtng noment o._,a functLon

Or r_(qlS"A1 S_P_t4LO II _Or al_I) " 7500 ._.m 5_ _ _Jn,

V - 120 kno_s, ar_ C_/v" - 0.102 (fla_e_ s_bols&re mee_suz'ementJon spinc_!e).

-9-

1980022880-012

.016 [" TEST THEORY

0 Cmx/°

.012 0 • Cmzh

E .008 O

O

.004

I I

0 r/R 1.0

Figure 2. Csclllatory chordwise ber_Ing reorientan _ function

of ra_ial _tatton fo_ e_p - 7:5° , ._A-- 56.5 rpm,

V = ]20 knots, an(_CT/v" - 0.102 (flagge_ symbo!_are measurements on spittle).

-10-

1980022880-013

.O02

I I I I I I

0 .02 .04 .06 .08 .10 .12

CTlo

Figure 3. C,scillatory beamwise bending moment at 0.35R as

function of thrust for _ = 7.5° and _= 565 zpr..

-ii-

1980022880-014

TEST THEORY _p

.010 - A 30

[] 60

0 75

.008

.11112-

, I I I I I0 .02 .04 .06 .08 .10

CT/O

Figure 4. Oscillatory beamwise bending moment at 0.35_ as a

function of thrust for _'4= 565 rpm and V _ 120 knots,

-12-

1980022880-015

TEST THEORY _p V, knots

[] - 5 177

O 0 185

.008

.0O6

x [3 r.-1E.O04

u Q

_--o"_ o.11112

I I I I0 .02 .04 .06 .08

CT/O

Figure 5. Oscillatory beamwise bending moment at 0.35] as a

function of thrust for /l = _58 rpm and V = 177-185 knots.

-13-

1980022880-016

TEST THEORY knots

.020 /_ 140

[_ ----. l 120

0 ------- 80

.016 0

0I

.012 / /

.008

%/.004

I I I I I I0 .02 .04 .06 .08 .10 .12

CT/O

Figure 6. Oscillatory spindle chord bending moment as _.

function of thrust for C_p --.75° and -_.--565 r?r_.

-14-

1980022880-017

TEST THEORY O_p

.020 <_ 15_ 30

60

0 75.016

.o12- o oil/°_ 0

•_- o y/ / '

I I I I l0 .02 .04 .06 .08 .10

CT/O

Fi6nAre7. Oscillatory spindle chord bending moment as a

function of thrust for /_4= 565 rpm and V = 140 knots.

-15-

!

1980022880-018

TEST THEORY knotsZ_ 140

[] 120O 80

.020 - Z_ A

A L_[]

.016 _ 0

.o12 __/ o,,- o

.008 0

.004

I I I , I A I

0 .02 .04 .06 .08 .I0 .12

CT/O

__ig_e _. tscillatory pitch llnk loa4 as a function of t."r'.s:

for _F = 750 and._4 = 565 rpm.

-16-

1980022880-019

TEST THEORY (Zp0 ----- isA .... 30

0 75.020 -

0 0

o _ oE] O

.016

.012-

.008 A ..- .., ... --" ""

.004 _--------'--" - "--"

- , .i _ , .. t .... J

0 .02 .04 .06 .08 .I0CT/O

Figure 9. Oscillatory pitch link load as a functioa o£ thrust

for _'_= 565 rpm and V = 140 knots.

. -17-

i

1980022880-020

TEST THEORY (_p V, knots

[] 5 177

0 0 185.012

.008

-- []

u __..EL O O

.004 -

I I I •

0 .02 .04 .06 .08CT/o

Figure tO. Cscillatory pitch llnk load as a function of thrust

for _ = 458 rpm and V = 177-185 knots.

-18-

1980022880-021

I R,por, No NAsA TM-81228 2 Government Access,onNo' 3. Rec,p,en't'sC_t,l_ No

USAAVRADCOM TR-80-A-84 Title and Subt,tle 5. Report DateCOMPARISON OF CALCULATED AND MEASURED BLADE LOADS

ON A FULL-SCALE TILTING PROPROTOR IN A WIND TUNNEL 6 Perform,ng Or_mn,za't,o.Code

7. Author(s) 8. Performing Or_mzabon Report No

Wayne Johnson A-8318iO. Work Unit No.

9" PecformtngOrganization Nan,, and Address 505-42-21

Ames Research Center and Aeromechanics Laboratory _I ContractorGrantNoAVKADCOMResearch and Technology LaboratoriesMoffe,-t Field, California 94035

13. Typ_ of'Repo_ and Period Covered

12. Sponsoring Agency Name and Address National Aeronautics and Technical Memorandum

Space Administration, Washington, D. C. 20546 and14. Sponsorm9 Agency Code

U. S. Army Aviation Research and Development CommandSt. Louis_ Missouri 63166

15. Supplementary Notes

,i ,....16 Abstract

The loads measured in a wind tunnel on a full-scale tiltingproprotor are compared with calculated results. The data consistsprimarily of oscillatory beamwise bending moments at 35% radia station,

oscillatory spindle chord bending moments, and oscillatory pitch llnkloads. The measured and calculated results as a function of thrust are

compared over a range of nacelle angles from 0 to 75°, and a range ofspeeds from 80 to 185 knots.

17. K_ Wor_ (Su_t_ _ Author(t)) 18. Dittributi_ Statement

Rotor loads Unlimited

Tilting proprotor

STAR Category - 05

19. SOcmtty Oemif. (of this report) _. SIcwity CkNlif. (of _| II_ll) ;1. No. of PaCes 22. _ice*

Unclassified Unclassified 22 $4.00

"For Mle by t_ Nltlonel T_hmc_! Infliction _I_, Sl_i_fkNd, Vi_m0# 22161

1980022880-022