Wind-tunnel tests of a dual-rotating propeller having one component locked or windmilling

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Material Information

Title:
Wind-tunnel tests of a dual-rotating propeller having one component locked or windmilling
Alternate Title:
NACA wartime reports
Physical Description:
6, 20 p. : ill. ; 28 cm.
Language:
English
Creator:
Bartlett, Walter A
Langley Aeronautical Laboratory
United States -- National Advisory Committee for Aeronautics
Publisher:
Langley Memorial Aeronautical Laboratory
Place of Publication:
Langley Field, VA
Publication Date:

Subjects

Subjects / Keywords:
Propellers, Aerial   ( lcsh )
Aeronautics   ( lcsh )
Genre:
federal government publication   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: The effect on the propulsive efficiency of locking or windmilling one propeller of a six-blade dual-rotating-propeller installation was determined in the Langley propeller-research tunnel. Tests were made of both pusher and tractor configurations, with the unpowered propeller both leading and following the powered propeller, which was set at a blade angle of 40°. The maximum propulsive efficiency of the powered propeller in combination with the locked or windmilling propeller was, in all cases, lower than that of the powered propeller operating alone. The locked propeller gave greater maximum propulsive efficiencies when used as a contravane to remove rotational energy from the slipstream than when used as a means for imparting initial twist to the air. The windmilling propeller, however, was equally efficient both leading and following the driven propeller. In the tractor installation, smallest losses in maximum propulsive efficiency were obtained when the unpowered following propeller was locked at a blade angle of 90° and when the unpowered leading propeller was allowed to windmill at a blade angle of 45°. In the pusher installation, equal losses in maximum propulsive efficiency were obtained when the unpowered following propeller was either locked at 90° or windmilling at 55°, but the unpowered leading propeller gave smallest losses when windmilling at 55°.
Statement of Responsibility:
by Walter A. Bartlett, Jr.
General Note:
"Report no. L-214."
General Note:
"Originally issued January 1945 as Advance Restricted Report L5A13a."
General Note:
"Report date January 1945."
General Note:
"NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were previously held under a security status but are now unclassified. Some of these reports were not technically edited. All have been reproduced without change in order to expedite general distribution."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003594003
oclc - 70901264
System ID:
AA00009364:00001


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MAck-


By Walter A. Bartlett, Jr.


Langley Memorial Aeronautical Laboratory
Langley Field, Va.


WASHINGTON


I.NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of
advance research results to an authorized group requiring them for the war effort. They were pre-
viously held under a security status but are now unclassified. Some of these reports were not tech-
nically edited. All have been reproduced without change in order to expedite general distribution.


1 1,


DOCUMENTS DEPARTMENT


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WARTIllME REPORT
ORIGINALLY ISSUED
January 1945 as
Advance Restricted Report L5Al3a

WIID-TUNMEL TESTS OF A IJAL-ROTATIfG PROPELLER HAVING
OHE CCMPODN LOCKED OR WIlMILLING


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NACA ARR No. L5A15a

NATIONAL ADVISORY CO:.TMITTEE FOR AERONAUTICS


ADVANCE RESTRICTED REPORT


,WDID-TUNNEL TESTS OF A DUAL-ROTATING PROPELLER HAVING

O:;F COMPONENT LOCKED OR iWIND:.TLLrNG

By Walter A. Bartlett, Jr.


S T 'ARY


The effect on the oronulsive efficiency of locking
or windmilling one nroneller of a six-blade duel-rotating-
oropeller installation was deternnned in the Langley
rroreller-research tunnel. mests were made of ooth
pusher and tractor configurations, with the unpowered
nrooeller both leading and rollow.rn the roa'red orn-
neller, which was set at a blade angle of 0.

The maximun propulsive efficiency of the powered
propeller in combination with the locked or windmilling
propeller was, in all cases, lower than that of the
Dowered propeller operating alone.

The locked propeller gave greater maximum propulsive
efficiencies when used as a contravane to remove rnta-
ttonal energy from the slipstrean than when used as a
means for ii-.rarting initial twist to the air. The
windmilling nroneller, however, was equally efficient
both leading and following the driven propeller.

In the tractor installation, smallest losses in
maximum propulsive efficiency were obtained when the
unpowered following propeller was locked at a blade
angle of 900 and when the unpowered leading propeller
was allowed to windmill at a blade angle of [50. In
the pusher installation, equal losses in maximum pro-
pulsive efficiency were obtained when the unnowered
following proneller.was either locked at 900 or wind-
milling at 550, but the unpowered leading propeller
gave smallest losses when windmilling at 550.








IACA ARR N'o. L5A13a


INTRODUCTION


In the event of engine failuie in multiengine
airplanes fitted with single-rotating propellers, the
unpowered propeller is usually feathered in order to
reduce the drag. For a dual-rotating propeller, it
was desired to determine whether the feathered position
is the optimum setting for the blades of an unpowered
component. Tests of a six-blade dual-rotating propeller
have therefore been conducted in the Langley propeller-
research tunnel to determine the effect of a windmilling
or locked component upon the aerodynamic characteristics
of the complete propeller installation.

Tests of the propeller in both pusher and tractor
configurations were conducted with the unpowered component
both leading and following the powered component. The
blade angle of the powered propeller was held at 400
and the blade angle of the unpowered propeller varied
from 250 to 100. This variation depended upon whether
the installation was tractor or pusher and whether the
unpowered component was winndmilling or locked.

Because of the limitations in tunnel airspeed
(100 mph) and propeller rotational speed (450 rpm),
the Reynolds number and the propeller tip speed were
appreciably lower than those normally encountered in
flight. The maximum Reynolds number at the 0.75-radius
station was of the order of 1 000,000, and the highest
tip speed was approximately 240 feet per second.
Reference 1 indicates that the effects of Reynolds
number and tip speed are not critical within the range
of the tests.


APPARATUS


The test setup was that used in previous propeller
tests in the Langley propeller-research tunnel and is
described in reference 2. Outline dimensions of the
streamline nacelle are presented in figure 1, and
photographs of the setup with a dual-rotating propeller
installed as a tractor and as a pusher propeller are
given in figure 2. The propeller blades used were the
Hamilton Standard 5155-6 6right-hand) and 5156-6 (left-
hand). The geometric characteristics of the blade are









?JACA APR i'o. L5tl'a


given in figure 3. The front (right-hand) propeller
disk was separated from the rear (left-hand) propeller
disk by approximately 10 inches.


RESULTS ANID DISCUSSION


The results are presented in tne form of dimen-
sionless coefficients, which are defined as follows:

CT thrust coefficient
(pn2D

Cp power coefficient nD
(pn3D5
V/nD propeller advance ratio

S propulsive efficiency -
Cp nD
where

T actual thrust of Dowered propeller minus drag of
unpowered propeller and slipstream drag of
nacelle, pounds

P power absorbed by propeller, foot-pounds per
second

V airspeed, feet per second

n propeller rotational speed, rps

D propeller diameter, feet

p mass density of air, slugs per cubic foot

Also,

R propeller radius, feet

p blade angle at O.75R, degrees
Subscripts:

F, R front and rear propellers, respectively








'ACA ARR Uo. L5A15a


The results obtained for the various combinations
of a powered component with a locked or windmilling
component are compared with the characteristics of
three-blade single-rotating propellers. The aero-
dynamic characteristics of the three-blade tractor
or pusher propeller operating in either the front
or the rear hub are presented in figure 4. Test
points included in figure !(a) indicate the experi-
mental accuracy of the tests. The increase of
approximately 1 percent in maximum propulsive efficiency
when the three-blade propeller was operating in the
rear hub over the efficiency when the propeller was
operating in the front hub is within the experimental
accuracy of the tests and hence cannot be ascribed to
difference in shank losses.

Test results obtained with one component of the
dual-rotating propeller operating and the other
component locked either following or leading the
operating component are presented in figure 5. These
data, when compared with those in figure 4, show that
the drag of the locked propeller at all blade angles
tested more than offset any increase in thrust due to
contravane action. The addition of the 900 locked
propeller following or leading the driven tractor
propeller lowered the maximum propulsive efficiency
of the three-blade propeller 5 and 8 percent, respectively;
and the addition of the 900 locked propeller following
or leading the powered pusher propeller lowered the
maximum propulsive efficiency and 6 percent,
respectively. The data show that smaller efficiency
losses resulted when the locked propeller was installed
as a contravane to remove the rotational energy from the
slipstream than when used as a means for imparting
initial twist to the air.

For both tractor and pusher configurations,
when the unpowered propeller was allowed to windmill
either following or leading the nowered propeller,
the maximum propulsive efficiency was found to be
essentially independent of the location of the wind-
milling component for blade-angle settings from 400
to 550. (See fig. 6.) The maximum propulsive efficiency
of the tractor installation with the windmilling com-
ponent following or leading the driven component was
lower than that of the reference propeller by 6 percent
and 7 percent, respectively; corresponding differences
for the pusher installation were of the order of









NACA ATR No. LAl3Sa


4 percent. Very little friction opposed the windmilling
propeller, and results indicated that the value of
V/nD at which the propeller windnilled was independent
of the rotational speed of the driven propeller, the
forward or rearward location of the windmilling
component in either the tractor or the. pusher instal-
lation, and the operation with oi' without the driven
propeller.

Aerodynamic characteristics are oresanted in
figure 7 for the three-blade propeller operating alone
and in optimum combination with the locked or wind-
milling component,both following and leading the
driven component. For the tractor installation, with
the unpowered propeller following the driven propeller,
the beneficial contravane action of che rear propeller
was greatest w-en locked at 000. When the unpovered
propeller led the powered proneller, the maximum
efficiency was greatest for the combination with the
windmilling proneller set at a blade angle of $50. For
the pusher installation, with the unpowered propeller
following the powered propeller, the maximum rropulsive
efficiencies of the combinations with the locked nro-
peller at a blade angle of 900 and with the windmilling
propeller at a blade angle of 550 were of the order
of JO percent. "then the unpowered propeller led the
driven propeller, highest efficiencies were obtained
with the windmilling component dt a blade angle of 550.


SUMMARY OF rESULTS


Wind-tunnel tests of a six-blade dual-rotating-
propeller installation with the operating propeller
set at a blade angle of 400 and with the inoperative
propeller locked or windmilling indicated the following
conclusions:

1. In all cases, the maximum propulsive efficiency
with the locked or windmilling component was lower than
that obtained with the three-blade propeller operating
alone.

2. The locked propeller was most efficient when
used as a contravane to remove rotational energy from
the slipstream.









NACA ARR No. L5A13a


5. For blade-angle settings from 400 to 550, the
windmilling propeller was almost equally efficient
both following and leading the powered propeller.

4. In the tractcr-oropeller installation, smallest
losses in maximum efficiency were obtained when the
inoperative following nroreller was locked at a blade
ang.le of 0 and when the Inoperative leading propeller
was allowed to windmill at a blade angle of 450.

5. In the pusher-propeller installation, equal
losses in maximum propulsive efficiency were obtained
with the following propeller locked at a blade angle
of 900 or windmilling at a blade angle of 550, but the
inoperative leading nroneller gave smallest losses when
windmilling at 550*


Langley Memorial Aeronautical Laboratory
National Advisory Committee for Aeronautics
Langley Field, Va.




REFERENCES


1. Biermann, David, and Gray, '.'. H.: Wind-Tunnel Tests
of Eight-Blade Single- and Dual-Rotating Pro-
pellers in tle t'ractor Position. IIACA ARR,
i.ov. 1941.

2. Bierman-n, David, and Hartman, Edwin P.: Wind-
kTunnel mests of Pour- and Six-Blade Single-
and Dual-Lotat'ng Tractor Propellers. HACA
Ren. Io. 77, 19 2.







NACA ARR No. L5A13a


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