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![Page 1: TECHNICAL NOTE - NASA · TECHNICAL NOTE D-995 NASA TN D-995 AERODYNAMIC LOADS ON AN ISOLATED SHROUDED-PROPELLER CONFIGURATION FOR ANGLES OF ATTACK FROM -10° TO 110° By Kalman J](https://reader030.vdocuments.us/reader030/viewer/2022040523/5e84e2be62d17d5e877582f8/html5/thumbnails/1.jpg)
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TECHNICAL NOTE
D-995
NASA TN D-995
AERODYNAMIC LOADS ON AN
ISOLATED SHROUDED-PROPELLER CONFIGURATION
FOR ANGLES OF ATTACK FROM -10 ° TO 110 °
By Kalman J. Grunwald and Kenneth W. Goodson
Langley Research Center
Langley Air Force Base, Va.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON January 1962
https://ntrs.nasa.gov/search.jsp?R=19620000022 2020-04-01T18:51:08+00:00Z
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IX
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
TECHNICAL NOTE D-995
L
i
1
T
AERODYNAMIC LOADS ON AN
ISOLATED SHROUDED-PROPELLER CONFIGURATION
FOR ANGLES OF ATTACK FROM -lO ° TO llO °
By Kalman J. Grunwald and Kenneth W. Goodson
SUMMARY
An investigation of the division of loads between the propeller
and the shroud of a shrouded-propeller configuration was conducted in
the 17-foot test section of the Langley 300-MPH 7- by lO-foot tunnel.
This investigation covered an angle-of-attack range from -i0 ° to ii0 °
and a range of advance ratios (0 to 0.595) typical of the transition
speed range of a tilt-duct VTOL aircraft.
For the configurations with fixed blade angle (24 ° at the three-
quarter radius), the normal force and pitching moment developed by the
propeller and spinner were only a relatively small part of the overall
normal force and pitching moment of either a stalled or an unstalled
shroud. The ratio of the thrust of the propeller and spinner to total
thrust was found to vary from about 0.4 in hovering to about 0.7 at the
highest advance ratio of the tests, 0.595, with the shroud at zero angle
of attack.
INTRODUCTION
The ducted- or shrouded-propeller configuration has been proposed
as one means of attaining VTOL flight. At the present time information
is available on the aerodynamic performance of wing-tip-mounted tiltable
shrouded-propeller configurations. (For example, see refs. 1 to 3.)
Information on the division of loads between the shroud and the propeller
is useful in analyzing aerodynamic performance _id structural require-
ments. Because of the scarcity of such information, the present program
has been conducted to obtain experimental data on the division of loads
for an isolated shrouded-propeller configuration.
The basic shrouded propeller of this investigation was previously
used (mounted on a wing tip) in the investigation reported in reference i.
The shroud had 5/16 the dimensions of the shrouded-propeller configuration
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2
of reference 2 but the propeller design was different. The results inreference i showedthat, because of the low Reynolds numbersof the tests,the stalling characteristics of the smaller shroud differed from thoseof the larger shroud of reference 2. Therefore the basic configurationwas modified by the addition of shroud leading-edge fairings to alleviatethis shortcoming. Inasmuch as the range of Reynolds numbersof the pres-ent tests is the sameas that in reference l, both the basic model andthe modified model (which incorporated the smaller of the leading-edgefairings used in ref. l) were employed in the present investigation.The models were tested through an angle-of-attack range from -lO° to ll0 °.The advance ratio was varied from 0 to 0. 595. The propeller-blade angleat the three-quarter radius was held constant at 24°. Tests were con-ducted in the 17-foot test section of the Langley 300-MPH7- by 10-foottunnel (ref. 4).
Presented herein, for both the basic and modified configurations,are measuredforce and momentcoefficients of the shroud without a pro-pellet, the shroud with a windmilllng propeller, and the shroud with athrusting propeller. Included in the last category are measurementsofforce and momentcoefficients of the propeller and spinner operatingwithin the shroud.
L161
7
SYMBOLS
b
C
CL
Cm
CQ
CT
CX
D
FX
h
L
propeller-blade section chord, ft
duct chord, 0.859 ft
lift coefficient, L/qS
pitching-moment coefficient, M/qSc
torque coefficient, Q/pn2D 5
thrust coefficient, Tp/pn2D 4
longitudlnal-force coefficient, Fx/qS
propeller diameter, 1.25 ft
longitudinal force, lb
propeller blade-section thickness, ft
lift, lb
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L16
1
7
M
Mp
n
N
Np
q
Q
r
R
S
T
To
Tp
V
x
8.79
n
P
total pitching moment, ft-lb
propeller pitching moment, ft-lb
propeller rotational speed, rps
total normal force, ib
propeller normal force, Ib
dynamic pressure, 21--pV2
motor shaft torque, ft-lb
radius to propeller blade element, ft
propeller-tip radius, ft
projected shroud area, (Shroud chord) X (Exit diameter),
i. 21 sq ft
total thrust, ib
hovering thrust, 49 lb
propeller thrust (including spinner forces), ib
free-stream velocity, ft/sec
transfer distance from propeller-moment reference point to
duct-moment reference point, 0.129 ft
angle of attack, deg
blade-sectlon angle, deg
blade angle at three-quarter radius
net efficiency, TV/2_Qn
density, slugs/cu ft
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4
MODELS AND APPARATUS
Photographs of the basic symmetrical model are shown in figure i.
A side-view sketch giving the principal dimensions and showing the major
features of the model support system is presented in figure 2. Basic
shroud coordinates are given in table I. The leading-edge fairing
employed to adjust the shroud-stalling characteristics of the model is
outlined in figure 3. Because of its purpose, no great attention is
given to details of the fairing.
The three-blade propeller was constructed of plastic reinforced with
glass fiber over a balsa-wood core. Geometric characteristics of the
propeller blade are given in figure 4. Blade sections consisted of
NACA 6412 airfoil sections. The blade-angle setting at the three-quarter
radius was 24 ° . The shrouded propeller had a tip clearance of 0.04 inch
and a root clearance of 0. i0 inch.
The model was supported in the tunnel by a shielded sting-support
system attached at the rear of the motor nacelle as indicated in fig-
ure 2. Total forces and moments were measured with a three-component
straln-gage balance located at the foot of the strut. Forces and moments
of the combined propeller and spinner were measured with strain-gage
beams mounted within the motor nacelle. The thrust of the combined pro-
peller and spinner Tp was measured as shaft tension without corrections
for pressure differences within the nacelle. Such corrections in the
present case are believed to be very small.
L
i
6i
7
TESTS
Measurements of the forces and moments of the shrouds with the pro-
peller removed and with a windmilling propeller were made at a tunnel
speed of i00 feet per second. Powered tests, with a constant propeller
rotational speed of 8,000 rpm, were made at the various tunnel speeds
required to cover the desired range of advance ratio V/nD. At each
selected advance ratio, the angle of attack was varied over a range which
would include anticipated conditions of steady level flight, climb, and
descent for tilt-duct VTOL configurations. Measurement of the thrust
defined herein as hovering thrust To was made at _ = 900; in view of
the large ratio of the volume of the surrounding enclosure to the volume
of flow through the shroud, the effect of the surrounding enclosure on
the measured hovering thrust is believed to be extremely small.
Since power-off tests were made at a wind speed of i00 feet per
second, the Reynolds number based on shroud chord was 550,000. For the
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power-on tests, the Reynolds numbervaried from 0 at V/nD = 0 to 550,000at V/nD = 0.595 (the maximum V/nD of the tests).
DATAREDUCTION
The results are referred to the system of wind axes shownin fig-ure 5. locations of the shroud pitching-moment axis and propellerpitching-moment axis are given in figure 2.
The free-stream dynamic pressure was used in nondimensionalizingthe data for the power-off conditions and the data in the relativelyhigh-speed flight regime. However, in the transition speed range, coef-ficients based on the free-stream velocity would approach infinite valuesnear hovering flight; to avoid this problem, transition speed-range datahave been nondimensionalized by dividing by the static thrust in hovering.
RESULTSAND DISCUSSION
The basic data for the shroud configuration with the lip modifica-
tion are presented in figures 6 and 7. Figures 8 and 9 contain the
basic data for the unmodified configuration. Fi_Ires 6 and 8, which
contain the data for the highest speed condition tested, show the results
for conditions of power off with propellers off, power off with pro-
pellers windmilling, and power on with propellers operating at
V/riD = 0.595.
Power-Off Characteristics
In the plots of figures 6 and 8 for lift coefficient as a function
of longitudinal force coefficient, it can be observed that the maximum
lift coefficient of the shroud with a windmilling propeller is greater
than that of the shroud with the propeller removed. This higher lift
is attributed to the action of the propeller in redistributing flow
energy through the duct, to the lift component of the propeller, and to
a delay of flow separation within the duct due to the turbulent action
of the propeller-blade wake on the duct boundary layer; and of course
there may be other causes. Redistribution of flow energy in the duct
arises from the action of the propeller in removing energy from regions
of high velocity and adding energy to regions of low velocity in the
duct.
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Power-0nCharacteristics
The basic data obtained through the angle-of-attack and advance-ratio ranges of the tests are presented in figures 7 and 9 for the modi-fied and unmodified configurations, respectively. As mentioned earlier,the low Reynolds numbersof the tests gave rise to a region of stalledoperation in the case of the unmodified shroud. Tuft studies madeduringthe tests gave evidence that the stall was due to flow separation fromthe shroud lip; the occurrence of stall wa_ marked by a distinct changein the character of the noise emitted by the model. In figure 9 thestall is marked by rapid reductions in the lift and pitching-momentcurves and by sharp increases in thrust and torque. For the modifiedconfiguration (fig. 7) the rapid changes do not occur. Up to the pointof llp stall, the characteristics for the unmodified configuration arepractically the sameas those for the modified configuration.
L161
7
Division of Loads
The primary purpose of this investigation was to determine the
division of aerodynamic loads between the shroud and the propeller.
The results in figure 7(c) (modified configuration) and figure 9(c)
(unmodified configuration) show that the propeller contribution to the
overall normal force and pitching moment of either configuration is
relatively small. Relative magnitudes are shown more directly in fig-
ures l0 and ll. Although stalled operation (fig. 9(c)) causes appreciable
changes in propeller normal-force and pitchlng-moment characteristics,
these quantities remain small in comparison with the overall values.
The ratio of propeller thrust to total thrust as a function of angle
of attack for a number of advance ratios is shown in both configurations
in figure 12. In hovering (V/nD = 0), the propeller carries approximately
40 percent of the total thrust. At the highest V/nD value of the tests,
0.595, the propeller carries about 70 percent when _ is near 0 °.
For the unstalled operation, figure 12(a), the ratio of propeller
thrust to total thrust generally decreases as _ increases at a constant
value of V/nD. Beyond the stall, on the other hand, the ratio increases
as _ increases (fig. 12(b)). This increase in thrust ratio is due
primarily to a reduction in shroud thrust caused by the lip stall
(fig. 9(c)), and is due partly to an increase in propeller thrust which
is also caused by the lip stall (fig. 9(b) or 9(c)).
In figure 13, the propulsive efficiency and thrust ratio obtained
for the modified configuration at _ = 0° and V/nD = 0.595 are shown,
together with curves obtained from reference 5 (a sharp-radius inlet
configuration). From the position of the propulsive-efficlency point
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of the present configuration in relation to the efficiency curves ofthe reference configuration, it can be judged that peak efficiency wasnot reached with the present configuration; it occurs at a value ofV/nD higher than 0.595. For the reference configuration the thrustratio lies in the neighborhood of 0.9 at V/nD = 0.595, and the resultfor the present investigation is 0.7. Someof this difference is dueto the difference in the ratio of shroud-exit diameter to propellerdiameter for the two configurations.
SUMMARYOFRESULTS
For the shrouded-propeller configuration of the present investiga-tion the normal force and pitching momentdeveloped by the propeller andspinner are a relatively small part of the overall normal force andpitching momentof either a stalled or an unstalled shroud; therefore,the duct is the primary source of pitching momentand normal force loads.
The ratio of the thrust of the propeller and the spinner to thetotal thrust varies from about 0.4 in hovering to about 0.7 at the high-est advance ratio of the tests, 0.595, with the shroud at zero angle ofattack. For the unstalled operation this thrust ratio in generaldecreases as angle of attack increases at constant advance ratio. Beyondthe stall and at constant advance ratio, on the other hand, the thrustratio increases when the angle of attack increases.
Langley Research Center,National Aeronautics and Space Administration,
Langley Air Force Base, Va., September28, 1961.
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8
REFERENCF_
i. Goodson, Kenneth W., and Grunwald, Kalman J.: Aerodynamic Character-
istics of a Powered Semispan Tilting-Shrouded-Propeller VTOL Model
in Hovering and Transition Flight. NASA TN D-981, 1962.
2. Yaggy, Paul F., and Mort, Kenneth W.: A Wind-Tunnel Investigation of
a 4-Foot-Diameter Ducted Fan Mounted on the Tip of a Semispan Wing.
NASA TN D-776, 1961.
3. Tapscott, Robert J., and Kelley, Henry L.: A Flight Study of the
Conversion Maneuver of a Tilt-Duct VTOL Aircraft. NASA TN D-372,
1960.
4. Kuhn, Richard E., and Hayes, William C., Jr.: Wind-Tunnel Investiga-
tion of Longitudinal Aerodynamic Characteristics of Three Propeller-
Driven VTOL Configurations in the Transition Speed Range, Including
Effects of Ground Proximity. NASA TN D-55, 1960.
5- Grose, Ronald M.: Wind Tunnel Tests of Shrouded Propellers at Mach
Numbers From 0 to 0.60. WADC Tech. Rep. 58-604, ASTIA Doc.
No. AD-205464, U.S. Air Force, Dec. 1958.
L
i
6
i
7
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9
TABLE I .- DUCT COORDINATES
kO
Yi
V =
X_
in.
0
•o78•125
•188
•25o•312.438.625
.938i.25oi.562i.8752.1882. 500
2.812
Straight line
t5. 375
5.9386.25o6.562
6.8757.188
7.5oo7.812
8.125
8.4388.750
9. 375
i0. 312
Yi,
in.
0.875
.663
.589513
4634o6
357263
163
i00
•050• 019•006
0
0
0
0
0
0
0
0
Straight line
.)50
YO_
in.
0. 875
1.144
l, 206
1. 256
1. 287
i. 325
i. 375
i .457
1.506
i.556i, 587
1.613i •625
1.637
i. 644
i .644
i. 644
1.644
i. 644
i. 644
i .644
1.625
i. 600
I. 575
1-537
]_.5OOi. 463
1.425
i. 375
I. 3511.281
1.163
.981
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lO
,-I
LrXI
0LD
r--
1I--
o
t_Oo
4-_0
!
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_D
Figure 1.- Concluded. L-60-_43
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12
Shroud pitching-moment reference
3.5
15.5 -_
'rPitch I
axis
I
I
1690
,I
Strutshield
Strut
t-
t--
i-
Tunnelfloor
Balance
Figure 2.- Sketch of model and model support system. Dimensions are ininches.
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13
_D
J
o
0
.-4
!
I
,,p
o
b_
A
!
°r..,I
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14
_3
_ooqqb
_o°_
6ap "B" a/ 6uo
O/q,O!/O./ _a/ au.m!p -o4 - p./oq.3
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I'-
-,'4
_3
o,-4
,--tt_O
-.o
I1)R
Q)
0
0
m
11)
-0°,-.IffJ0
°r-t
o
©ul
o
-o
!
°r..,l
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16
cL
36
32
28
2.4
20
1.G
/.2
.8
.4
0
/>
/
/
//
0 Propeller off
m Pro oeller windmilling
0 Propeller rotational speed -
BOO0 rpm ,V/nD =.595
_"___ \
i
-.41.G 12 B .4 0 - .4 -8 - 12
Cx
Figure 6.- Aerodynamic characteristics of the modified-llp configuration
in the power-off and low-power condition.
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2X
17
r__D
CL
/6
,8
Cm
0
-8
Cx
2.4
/.6
.8
0
-,8
-,8
0
.8
-15-20
z,J"
0
r'l
<>
iPropeller off
Propeller windmilling
Propeller rotationol speed
80C r V/nO =.595
<
/I/
/
//
/Y
//
s//
0 20 40 60 80
a ,deg
im
!II
/00 /2O
Figure 6.- Concluded.
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18
l
14
12
.2
0 _
V/nD
D 0n .0320 O90
.164
.187
298
.506
_, 401
0 .595
_6
-4
-2
0
2
I_ I [ i I
I0 20 30 40 50 60 70 80 90 I00 IlO 120
a, de 9
(a) Lift, longitudinal force, and pitching moment (modified-lip
configuration).
Figure 7 .1 Effect of advance ratio and angle of attack on the aerodynamic
characteristics of the modlfied-lip configuration.
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19
.024
i i
i [J, i ] - ;
[ J _ __
,-i_o,-i
co
.020--
.0/2
i......
V/nD
n 0o .032<> .090_, .164o .187
_. .298306
v .401
o .595
.004
C T
]
]0
2O
./6
L ,l 12:
08 i i:'! ---II i--i
! t
it
i
i
i[ i
J
r -: i
t.,0 I0 20 30 40 50 60 70 80 90 I00 1I0 120
a, deg
(b) Propeller thrust and torque coefficients (modified-lip configuration).
Figure 7.- Continued.
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20 ""
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21
32
0 Propeller off
n Propeller windmiHing
(> Propeller rotational speed
8000 rpm , V/nD :.595
CL
0
\
I
-Z2
Figure 8.- Aerodynamic characteristics of the original-lip configuration
in the power-off and low-power condition.
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22
Cm
.8
0
-.8
7
%
1
CL
Cx
40
2#
16
.8
0
-8
-.8
0
.8
16-20
0 Propeller off
o Propeller windm q0 Propeller rotal_i speed
8000 rpm , V/nD =.595
,<
!i
0 20 40 60
a, deq
80 lOO 120
Figure 8.- Concluded.
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23
2
6
BI0 10 20 30
y s//i ! I
I
40 50 60 70
a, de_
I
V/_D
o 0a 0450 /28
189
o 193268
o JOl371
o 595
i I
(a) Lift, longitudinal force, and pitching moment (original-lip
configuration).
Figure 9.- Effect of advance ratio and angle of attack on the aerodynamic
characteristics of the origlnal-lip configuration.
![Page 26: TECHNICAL NOTE - NASA · TECHNICAL NOTE D-995 NASA TN D-995 AERODYNAMIC LOADS ON AN ISOLATED SHROUDED-PROPELLER CONFIGURATION FOR ANGLES OF ATTACK FROM -10° TO 110° By Kalman J](https://reader030.vdocuments.us/reader030/viewer/2022040523/5e84e2be62d17d5e877582f8/html5/thumbnails/26.jpg)
o32 j I
02B I
024 I
!
P
==:.L_ ¸ • _Iz_
t ,. .........
I
Il
CO
J
.020, r
OI6_--
L
i
I
,OO4
0
.24
V/nD
[] 0r_ .0450 .128a .189o .193_. .268O .301
_7 .5710 595
C T
201
.16
.12.
O8
i
Ji
IIIi
!
o4 ! II
00 lO 20 50 40 50 60 70
a jdeg
8O 90 IO0 IlO 120
(b) Propeller thrust and torque coefficients (original-lip configuration).
kO
Figure 9-- Continued.
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2_
,.-4
!
o
o
o+_
+_
.
Co
_-_
_._
_o_
0
_._
o_v
0
o
o
o_D
o
f
![Page 28: TECHNICAL NOTE - NASA · TECHNICAL NOTE D-995 NASA TN D-995 AERODYNAMIC LOADS ON AN ISOLATED SHROUDED-PROPELLER CONFIGURATION FOR ANGLES OF ATTACK FROM -10° TO 110° By Kalman J](https://reader030.vdocuments.us/reader030/viewer/2022040523/5e84e2be62d17d5e877582f8/html5/thumbnails/28.jpg)
26
o o
+ _.
I
+
k_r_.
931oj /Ou././ON
I
d,o
o
o
,.-t
.00
4._
.0
o
og-i
,-4
o
o,--t,-t
0
ao,_o_ /o_,_ON
t-
e--
I
![Page 29: TECHNICAL NOTE - NASA · TECHNICAL NOTE D-995 NASA TN D-995 AERODYNAMIC LOADS ON AN ISOLATED SHROUDED-PROPELLER CONFIGURATION FOR ANGLES OF ATTACK FROM -10° TO 110° By Kalman J](https://reader030.vdocuments.us/reader030/viewer/2022040523/5e84e2be62d17d5e877582f8/html5/thumbnails/29.jpg)
27
b-
.0
!
J_
JuaLuOul _ulq31 i d
IUBUdO_ _U/_31/d
0 _.,-t •
o oo 4_
, _,--I -o
-o
,-4,-t
o o
0
•,4 __ 0_ m0 _o %
,--I
o !°r-I
o i1)
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28
v,,.p
0-- ' 0 .090
A /64
_.29B
v 4010 595
..... + --
.... +. _
70 80 90 I00
i
l
(a) Modified-lip configuration.
T
p---....7._--_. +-
.6 ..... _
-- I3 ..... _
i
12....
I .-
i
I _ _ --- _ ......
_--_- __ __
_- +--+ .... _ -____+_
I0 20 50 _ 60 -8_
a, deg
l
i
o 0o ,128
.18.9
_. ,268
.3 71
0 .595
(b) Original-lip configuration.
Figure IP._ Variation of the ratio of propeller thrust to total thrust
wlth angle of attack.
I
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29
8i
6
4
2
Reference 5
o Figure 12 (a)
TpT
0 19.75 =17 °
/f
LO If jJ
J
.8
.6
,4 j
_,75 =27°
/
.2
=
00 .2 4 .6 .8 10 12 14
V/nD
Figure 13.- Propulsive efficiency and ratio of propeller thrust to total
thrust for modified configuration and configuration tested in refer-
ence 5. _ = 0 °.
NASA-Langl.ey, 1962 L-1617