The effect of trailing-edge extension flaps on propeller characteristics

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Material Information

Title:
The effect of trailing-edge extension flaps on propeller characteristics
Alternate Title:
NACA wartime reports
Physical Description:
8, 9 p. : ; 28 cm.
Language:
English
Creator:
Crigler, John L
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 )
Lift (Aerodynamics)   ( lcsh )
Aeronautics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: An analysis was made to determine the effect on propeller performance of extension flaps added to the trailing edge of a propeller blade. A method of calculating the changes in the ideal angle of attack, the angle of zero lift, and the design lift coefficient of a propeller blade section having a trailing-edge extension flap was utilized to calculate the performance of a six-blade dual-rotating propeller with extension flaps varying up to 40 percent chord. The method was used to determine the angle that the flap extension must make with the chord in order to obtain a particular load distribution. Although the analysis in this report was made for a wind-tunnel propeller designed to operate at low advance-diameter ration, the method is directly applicable to any propeller section under any operating condition.
Statement of Responsibility:
by John L. Crigler.
General Note:
"Report no. L-165."
General Note:
"Originally issued January 1945 as Advance Confidential Report L5A11."
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 - 003594725
oclc - 71000620
System ID:
AA00009368:00001


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Full Text
)ACA 4~


ACR No. L5A11


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WAIRTllIME REPORT
ORIGINALLY ISSUED
January 1945 as
Advance Confidential Report LAll

THE EFFECT OF TRAILING-EDIE EXTENSION FLAPS
ON PROPELLER CHARACTERISTICS
By John L. Crigler

Langley Memorial Aeronautical Laboratory
Langley Field, Va.


r'.: Cii-:


NACA:


WASHINGTON
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.


L 165


DOCUMENTS DEPARTMENT



































Digitized by the Internet Archive
in 2011 with funding from
University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation



























http://www.archive.org/details/effectoftrailing00lang









:iAOA ACR Ho. L5All


NATIONALL ADVISORY C IE FOR A7? .'I~..A..UTICS


ADVArC:- CO.:VI-i'IAL REPORT


THE F,:'' OF TTIAILI7NG-EDGE ::, i...LIOT FLAPS

ON PROPELLTERi C: .....'TERISTICS

By John L. Crigler





An analysis iwas made to determine the effect on
propeller performance of extension fl-)i. afled to the
trailincg edge of a propeller blade. A method of calcu-
lating the changes in the ideal angle of attack, thL
angle of zero lift, and the desi,-r lift coefficient of
a propeller blade section having a trailing-a-.: e e:xten-
sion flap was utilized to calculate the performance of a
six-blade dual-rotating propeller with extension flaps
vt-iing up to L0 percent chord. The method w-as used to
determine the angle that the flap extension nmst make
with the chord in order to obtain a particular loa:
distribution. Although the analysis in this report was
im'e for a wi~rnd-'tunnel propeller designed to o,'P:rate at
low aivance-diameter ratio, the method is directly appli-
cable to any propeller section under any operat.in.~
condition.


:iT.DTJDUCTIO!


Inasmuch as the production of a propeller of a
given design is an expensive manufacturing procedure,
it is expedient to make each existing design useful for
as many applications as possible. For this reason,
several choices of diameter have been available with a
given blade design. This flexibility of design has
recently been increased by providing a procedure for
adding an extension along the blade. iihe selection
of the width of extension permits a choice of riopeller
solidity for a given blade design and diameter. The
addition of the trsil -in-edge extension changes the
section airfoil characteristics by an amount dependent


CO'T'ID T iTAL


CONFIJIDE'ITiAL









2 CCrTFI 1Z:TIAL NACA ACR o. L5Al1


on the length and angle of extension. Some choice
in the airfoil characteristics is therefore permitted
when the extension flan is added to the trailing
edge. Reference 1 presents a method of analyzing the
change in airfoil section characteristics accom'r.piyin.
ch;ng-s in extension length and angle, and the present
report applies the method of reference 1 to the calcula-
tion of Tro-eller characteristics.

The calculations given herein were male for a six-
blade dual-rotating prcreller for values of advance-
diameter ratio (V/nD) that are encountered in the
operation of a pro'reller used to drive a wind tunnel.
The same methods are applicable, however, to propellers
for any operating condition. Preliminary calculations
were first made on the propeller with the original
blades in order to study the distribution of loading
along the blade for a --ower coefficient Cp = 0.51 at
an advance-diameter ratio V/nD = 0.33. For this value
of V/nD, the inboard sections of the propeller were
found to stall before the outboard sections and,
furthermore, the whole propeller was found to stall
before a power coefficient of 0.51 was absorbed. In
order to make the design suitable for these operating
conditions, it was necessary to increase the solidity
of the original pr:-eller. Trallin;-ed e extension
flaps were used for this purpose and were attached in
such a manner as to change the a:,-le of zero lift along
the blade to increase the load on the outer sections.
Inasmuch as the effect of such extension flaps is
applicable to both tunnel and aircraft propellers, the
method given herein for use in tunnel-propeller design
may also be used in determining the effect of trail:ng-
edge extension flans on propeller sections for aircraft
applications.

The method used to calculate the changes in the
ideal angle of attack, the design lift coefficient,
and t*--- angle of zero lift resulting from a flat sheet
attached to the trailing edge of an airfoil section is
outlined in reference 1. This method was used to
calculate the lift as a function of angle of attack for
the sections of a six-blade dual-rotating nropeller
having Curtiss blades 856- and 337-172-13 with trailing-
c. ce extension flaps. The calculate: thrust- and
torque-distribution curves for the oropeller with a
40-rercent-chord trailing-edl: flap are presented for
two ooeratin7 conditions.


CO IFI:-7 "TIAL









NACA ACR :-o. L5Al CONFIDENTIAL 3




b chord of rro-eller blade element

CL section lift coefficient T7 (

CLD section design lift coefficient; lift coefficient
at ideal angle of attack

Cp power coefficient (P/pn3D5)

C torque coefficient (Q/pnr25)

C thrst coeffi -'ent T/on2D4)

D pro. --ller c ae ter

d- element 'orque coefficient f- n- I
dx "\ pknD/
dC /ddx
-- element thrust coefficient d ---2D
dx 2D

h tilckness of ,roreller blade element

L lift of blade section

M Mach number

n propeller rotational se:d-

p -eometric pitch of propeller

P input power to propeller

Q torque of propeller

r radius to any blade element

R tic radius

T thrust of propeller


CONFIDENTIAL









4 CC'TDi''AL NACA CAC .:o. D CT11


V airspeed

x radial location of blede element (r/R)

a angle of attack

aL angle of zero lift
-o
aI ideal angle of attack

3 propeller blade angle at 0.75 radius

e propeller blade angle at radius r

p mass density of air

Subscripts*


P front propeller

R rear propeller

0.7 at 0.7 ra'dus

._ :-T.L"STS


The propeller analyzed is a six-blade dual-rotating
propeller with Curti5s blades (56-1C2-15 (front, right
hand) and 357-1C2-15 (rear, left hand). Blade-form curves
for the propeller are given in figure 1. The propeller
conditions analyzed vary fror- a value of Cp = 0.51
at V/nD = 0.55 to a value of Cp = 0.095 at V/nD = 0.26.
Preliminary calculations showed that the propeller with the
original blades would stall at an ad- ance-diameter ratio
of 0.55 before absorbing a power coefficient of 0.51. In
order to use the available propeller for this condition,"'
it was necessary to increase the oropeller solidity by the
use of extension flaps attached to the trailing edre.
.. pension flaps cause a change in the angle of zero lift,
which results in an effective change in the prcp.ller
pitch distribution. It was necessary, therefore, to
calculate the lift of the sections as a function of angle
of attack for use on the propeller. The method of


Cr TIDE- IAL








NACA ACR No. L5All


reference 1 was used to calculate the change in lift
characteristics caused by extension flaps, and the results
show the angle that will be required between the extension
flap and the chord line of the original airfoil to
produce zero change in pitch distribution for several
sections along the blade.

Certain assumptions regarding the airfoil character-
istics of the propeller were necessary in order to make
the calculations, _Yperimental data are usually used In
analyzing propeller performance. Inasmuch as the Curtiss
blades 836- and 857-1C2-13 are of NACA 16-series airfoil
section, the section lift characteristics (fig. 2) for
the original propeller were obtained by extrapolating
the experimental data of reference 2. The design lift
coefficients and the operating ;:ch numbers for several
sections along the blade for the limiting condition
of operation are shown in figure 2. The calculations
for the sections with extension flaps were made on the
assumption that the addition of flaus did not cirnrig:
the slope of the lift curve for a given section.
Inasmuch as no experimental data were available
for the airfoil sections with extension flaps, it was
necessary to use theoretical calculation in analyzing
the performance of propellers with these sections.
The calculated and experimental values of anc for
the original sections are not in perfect agreement.
Since experimental data were used for the original
sections, the differences between the calculated
values for the original and the extended airfoil section
characteristics were applied to these experimental
data. The corrected values were then used in calculating
the performance of the propeller with extension flaps.


RESULTS AND DISCUSSION


Conlaitations were made to determine the effect of
the trailing-edge extension on the lift characteristics
of an airfoil as a function of angle of attack. Curves
showing the results of some of these computations are
presented in figures 3 to 6. The calculated angle of
zero lift ao, the ideal angle of attack aI,
and aI a2 (on which the design lift coefficient
depends) are given for the propeller section at the


COTTF'ID ,'iIAL


C i ri 7 NTD 'IAL








NACA ACR No. L5All


0.45 radius in fig'ire 3. The calculated angles are
measured from a straight line joining the extremities
of the mean camber line of the extended airfoil section
but are plotted against the angle between the extension
flap and the straight line joining the extremities of
the mean camber line of the original airfoil section,
as was done in reference 1. The effects of a
10-nercent extension, a 20-percent extension, and a
40-percent extension are compared.

In the use of this information for propeller
calculations, it is more convenient to refer the
calculated angles to the line joining the extremities
of the mean camber line of the ori '.:al airfoil section.
The angular difference al between the two reference
lines is given by the following formula:
extension n length'
tension length sin (Angle of extension)
tan-la1 = ---
1 (tExtension length
1+ ( Chtension cos (Angle of extension)
Chord

The results for the 0.45 radius plotted in figure 3 are
reolotted in figure 1b4ut in figure 1 the calculated
angles are measured from the chord line of the original
airfoil section. The calculated and extrapolated
experimental values of ao and aT ao for the
original section (without flap) are shown in figure 4.
T1:- r-oints on the curves also show the calculated
angles at which the extension flap :nust be set to the
chord line of the original section to give the same value
of Co or aI a;o for the extended section as for
the original section. If the values of aLo for the
sections with the extension flan are the same as for
the original sections, the pitch distribution is
unch.Lr!;- 1. Since aT for the ori--in~ l section
(16 series) is zero, "the crossing of the aI curves
with the zero ordinate gives the angle of extension
for an unchanged aI. Figure 5 shows similar curves
for a 20-percent-chord extension flap and for a
40-nercent-chord extension flap at the 0.95 radius.
In figure 6 the curves at several radii are coinmared
for the 20-rercent-chord extension. From curves of
this t-T-, any desired change in the pitch distribution
of a propeller may be made by properly settin- the
extension-flan angles.


CO;- 'T ;' I"AL


*CONFIDENTIAL








"AACA ACR io. L5All


Since the inboard sections of the original propeller
stalled much earlier than the outboard sections for
low V/nD operation, it was decided to change the
angles of zero lift of the blade sections in order
to shift more of the load toward the tip. This change
in the angle of zero lift is obtained by setting the
flap extension at the proper angle to the chord line.
The angles of zero lift of the blade sections were
changed by the amount shown by the solid line in
figure 7. This curve may be shifted up or down, as
is shown by the dashed lines in figure 7, with no
change in the load distribution; the only ch.,n-s
resulting are in the design lift coefficients and a
constant shift in the angles of zero lift of the
sections. In :na,:in" the propeller performance calcu-
lations, however, a shift in the angles of zero lift
results in a change in the 'ropeller Ditch setting for
constant Cp and V/nD. Thl only change in CT and r
will result from the small effect of the change in the
drag of the airfoil sections.

Examination of the results (see figs. 4 to 6)
shows that a 20-nercent-chord extension to the Curtiss 856-
or 357-1C2-15 blade should be set about 7.20 to the
chord line at all blade sections to give the various
angles of zero lift that would be obtained by
adding Aao, (solid line in fig. 7) to ao of the
original section. A 40-oeicent-chord extension should
be set about 6.40 at all blade sections. The angles
of zero lift for the sections at all radii given in
fig'-ire 2 were increased by the amount shown by the solid
line in figure 7 for making the calculations of the
propeller performance with the extension flap.

Analyses of propeller performance for several pro-
pellers indicate that single-rotating propellers stall
at section lift coefficients of about 1.0 for most of
the blade and that the thin sections near the tip stall
at section lift coefficients of 0.8 to 0.9. The calcu-
lations presented herein show that these lift coeffi-
cients were realized for a pitch setting of 240 at the
0.7 radius for operation at V/nD = 0.35 and that a
40-percent-chord extension (40-percent increase in
solidity) is required to absorb the nower. Experimental
data on dual-rotating propellers, however, show that
the dual-rotating propeller can be operated without
stall at higher blade angles and at higher section lift
COCIFI", '"TIAL


CCI' I -PC IAL








.NACA ACR No. L5A11


coefficients than single-rotatinr; propellers. It is
quite possible, therefore, that tL.e O4-percernt-chord
flao extension to th3 tun-el rroneller that would be
required for a single-rotating -ropeller will not be
necessary to prevent stall for the l..miting condition
of oneratron with dual-rott ing propellers and that a
lower solidity may be used. -vertheless, in order to
obtain conservative result, tie calculations for the
tunnel rroneller have been made on the basis of a
.0-percent-ch.ord flan extension and the results for
two operating conc.itions are given.

Figure b shows the differential thrust and torque
curves plotted against x for operation at a V/nD
of 0.3J wLth the front-propeller blade angle set 24L and
the rear-oropelle- blade angle set 230 at the 0.7 radius.
The element 1Lft coefficients at several section radii
are shown in this '"in1re. *~ .ure 9 shows similar curves
for operation at V/nD 0.26 with the front-propeller
hlade a-gle set 120 -And the rear-oroneller blade angle
set 110 at the 0.7 radius.


CONC L"UDT.. RE1iARFS


The solidit- of a six-blade dual-rotating propeller
having Curtiss 356- and S57-1C2-15 blades has been
increased bC adding extension flans to the trailing edge.
The method of analyzin, the new blade-section character-
istics in this case was ar-l-ied to a particular or-neller
for oneratior at a ver lo.;a -dvance-diamete: ratio, but
the be!.od a a'plied to any propeller section under
any operating condition. The oitch distribution of the
D'irneller with flaps ma"- be held constant or, if desired,
may be varied for different design operating conditions
by properly setting the flap angle.


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


C ON Dl T l 1








HACA ACR il). L5A11


RE LrF' K.S

1. Theodorsen, Theodore, and Stickle, Geo2ge W.: Effect
of a Triail ir'-Edge Extension on the Characteristics
of a Propcller Section. HACA ACR No. L4121, 19-4.

2. Stack, John: Tests of Airfoils Designed to Delay the
Compressibility Burbcl. J CA TN No. 976, Dec. 1S-l).
(Reprint of ACR, Junm. 1-99.)


CONFfI: r.t' AL


CONFIDENTIAL







NACA ACR No. L5A11










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CONFIDENTIAL


Figure 1.- Blade-form curves for dual-rotating propeller having
Curtiss blades 836- and 837-1C2-15. Diameter, 15 feet 5 inches.


CONFIDENTIAL


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NACA ACR No. L5All


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CONFIDENTIAL


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Figure 2.- Lift characteristics for 16-series sections for original Curtiss propeller blades
836- and 837-102-13. Diameter, 13 feet 5 inches. Data extrapolated from reference 2.


CONFIDENTIAL


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NACA ACR No. L5A11 Fig. 3










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Figure 4,- Variation of aI aI, and ai aio with angle of extension
at x = 0.45. (Angles measured from chord of original airfoil.)


Fig. 4







NACA ACR No. L5A11


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Figure 5.- Variation of alo, ai, and aI ao
at x = 0.95. (Angles measured frum chord of


CONFIDENTIAL
with angle of extension
original airfoil.)


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NACA ACR No. L5AI1


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Figure 6.- Variation of Co, a"i and ai ato with angle of extension
for 20-percent-chord extension flap, (Angles measured from chord of
original airfoil.) CONFIDENTIAL
CONFIDENTIAL


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