The loads measured in a wind tunnel on a full-scale tilting proprotor are compared with calculated results. The data consists primarily of oscillatory beamwise bending moments at 35% radial station, oscillatory spindle chord bending moments, and oscillatory pitch link loads. The measured and calculated results as a function of thrust are compared over a range of nacelle angles from 0 to 75 deg, and a range of speeds from 80 to 185 knots

Johnson, W.

English

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_._ NASA Technical Memorandum 81228 ' ' USAAVRADCOM TR 80-A-8
¢
Comparisonof Calculatedand
MeasuredBladeLoadson a
Full-ScaleTiltingProprotor
in a WindTunnel
Wayne Johnson
(N&SA-T_-t_1228) CO_PAR_.30N OF CALCUL&TED Nt;J-31360
A_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 2020-03-21T17:37:49+00:00Z
_, NASA Technical Memorandum 81228 USAAVRADCOM TR 80-A-3
Comparisonof Calculatedand
' MeasuredBladeLoadson a
Full-ScaleTiltingProprotor
in a WindTunnel
Wayne Johnson, Aeromechanics Laboratory
AVRADCOM Research and Technology Laboratories
Ames Research Center Moffett Field, California
Nabonal Aeronauhc ; and Unites States Army
Space 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 moment
x
M blade chordwise bending moment
z
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 configuration
and 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 I
0 .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 I
0 .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
0
I
.012 / /
.008
%/
.004
I I I I I I
0 .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 l
0 .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 knots
Z_ 140
[] 120
O 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 (Zp
0 ----- is
A .... 30
0 75
.020 -
0 0
o _ o
E] O
.016
.012-
.008 A ..- .., ... --" ""
.004 _--------'--" - "--"
- , .i _ , .. t .... J
0 .02 .04 .06 .08 .I0
CT/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 .08
CT/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-8
4 Title and Subt,tle 5. Report Date
COMPARISON 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-8318
iO. Work Unit No.
9" PecformtngOrganization Nan,, and Address 505-42-21
Ames Research Center and Aeromechanics Laboratory _I ContractorGrantNo
AVKADCOMResearch and Technology Laboratories
Moffe,-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 and
14. Sponsorm9 Agency Code
U. S. Army Aviation Research and Development Command
St. Louis_ Missouri 63166
15. Supplementary Notes
,i ,....
16 Abstract
The loads measured in a wind tunnel on a full-scale tilting
proprotor are compared with calculated results. The data consists
primarily of oscillatory beamwise bending moments at 35% radia station,
oscillatory spindle chord bending moments, and oscillatory pitch llnk
loads. 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 of
speeds 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


Comparison of calculated and measured blade loads on a full-scale tilting proprotor in a wind tunnel

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