- , '. ' ;; f't 4t .... DEC 23 1946 ,i!. ACB Bo. L5All I l-: " I .... NATIONAL ADVISORY COMMITTEE FOR AERONAunCS .;/If , , , ORIGINALLY ISSlED JIIDUIL17 .. MftDCe CoD:r14e:D1i1al Bqort L5UJ. Maori&! AeroDautlcaJ. La'borato17 T.e-nglQ' l'1e14, Va• ... '. " .... - • WASHNGTON NACA LIERARY I ANGLEY MEMOr-IAL LABORATORY LaDIlef P1eJd, V.. NACA WARTIME REPORTS are reprints of papers origiDally issued to provide rapid d.1str1buUon of advance research results to an authorized group requ1r1ng them for the war effort. They were pre- viously held under a security status but are now unclaB8:l:f1ed. Some of these reports were not tech- mcally edited. All have been reproduced without change in order to aped.1te general. distrlbuUon. L - 165 1 ... - -- - •
Transcript
~-, '. '
;; f't4t .... ~
DEC 23 1946,i!. ACB Bo. L5All
I l-: "
~' e"~
I
.... NATIONAL ADVISORY COMMITTEE FOR AERONAunCS.;/If, , ,
NACA WARTIME REPORTS are reprints of papers origiDally issued to provide rapid d.1str1buUon ofadvance research results to an authorized group requ1r1ng them for the war effort. They were previously held under a security status but are now unclaB8:l:f1ed. Some of these reports were not techmcally edited. All have been reproduced without change in order to aped.1te general. distrlbuUon.
L - 165
1... - -- -
•
L:
Imllllllnllnll~13 1178 01403 3923
---- . --- .-._---- -~
NACA ACR No. L5All
NATIONAL ADVISORY COMMIT~~E FOR AERONAUTICS
AnV!NCE COJ.(FlDENTIAL REPORT
THE EFFECT OF TRAILING-EDGE EXTENSION FLAPS
ON PROPELLSR CHARACTERISTICS
B~ John L. Crigler
An analysis was made to determine the effect onpropeller performance of extension flaps added to thetrailing edge of a pro~eller blade. A method of calculating the C!lwgaR :1n the ideal anE:;le of s.ttacY.:. theanele of zero lif"-, and the design lift coefi'lcient ofa prop~ller blade section having a trsillne-enge extension flap was util~zed to calculat~ the verformance of asix-bla.de d11aJ.-rotating propeller wtth e::~tension flapsvarying up to ~_O pcr-c enb chor-d , The, me bhod w&.~ used. todetermine thF.l angle tha.t the flap extons ion I::rU,S t makewi~! the chord in order to obtain a particular loaddi~tributlon. AlthOUgh the analysis in this report wasm~.:~t'l for e. wind-tunnel propeller de aLgned to operate atlow alvUDce-diamoter ratio, th~ mothod is directly applicable to any propeller section un~er any operatinscondition.
INTRODUCTION
Inasmuch as the production of a propeller of agiven design is an expensive manufacturing procedure,it 1s expedient to make each existins des1gn useful foras many applications as possible. For this reason,several choices of diameter have been available with agiven blade design. This £lexibility of design hasrecently been increased by providing a procedure foradding an extension along the blade. The seleotionof the width of extension pormits a choice of propellersolidity fo~ a given blade design and diamete~. T.headdition of the trailing-edge extension changes thesection airfoil characteristics by an amount dependent
2 NACA ACR NO. L5AM
on the length and angh of extension. Some choloeIn the airfoil charaote~lstics Is therefore permitted -when the extension flap is added to the trailingedge. Reference 1 presents a method of analyzing thechange In airfoil section charaoterlstics accompanyingchanges in extension length and angle, and the presentreport applies the methcd of referenoe 1 to tbm calcula-tion of propeller characteristics.
The calculations givm heretn were made for a six- “blade dual-rotatln propeller for values of advance-diameter ratio (V~nD) that are encountered in theoperat?.onof a propeller used to drive a wind tunnel.The same methods are applicable, however, to propellersfor any operating condfl.tion.Preliminary calculationswere first made on the propeller with the originalblades in order to study the distribution of loadingalong the blade fdr a power coefficient Cp = C.31 atan advance-diameter ratio V/nD = 0.33. Pbr this valueof v/ilD, the inboard sections of the propeller werefound to stall before the outboard sections and,furthermore, the whole proneller wss found to stallbefore a power coefficient of 0.31 was absorbed. Inorder to make the design suitable for these operatingconditions, it was necessary to increase the solidityof the original propeller. Trailing-edge extenslenflaps were used for this purpose and were attached insuch a manaer as to change the angle of’zero lift alongthe blade to increase the load on the outer sections.Inasmuch as the effect of such extension flaps isapplicable to both tunnel and aircraft propellers, themethod given herein for use in tunnel-propeller designmay also be used Zn determining the effect of trailing-edge extension flaps on propeller sections for aircraftapplications.
The method used to calculate the changes in theideal angle of attaok, the design lift coeff~cient,and the angle of zero lift resulting from a flat sheetattached to the trailing edge of an airfoil section isoutlined in reference 1. This method was used tocalculate the lift as a function of angle of attack forthe sections of a six-blade dual-rotating nropellerhaving Curtiss blades 836- and d3T-lc2-13 with trailing-odge extension flaps. The calculated thrust- andtorque-distribution curves for the propeller with a@=percent-chord trailing-edge flap are presented fortwo operating conditions.
\ NACA ACR No. L5A11 1~) 3
SB!BOLS
chord of propeller blade element
section llft coefficient
()*..
section design lift coefficient; lift coefficientat Ideal angle of attack
power coefficient fp/pn3~5)
torqre ?oefflc~ent (Q!W2D5)
(L)d dxelerl.ert:orqu9 coef’f~ci9nt
\Pn2D5
*
()
element thrust coe.fflclent -pndd+
thlclmess of nroneller b?.ad.eelement
lift of blade section
Mach number
propeller rotational spead
geometric pitch of propeller
input Dower to propeller
torque of proneller
radius to any blade element
tip radius
thrust of propeller
4
v
x
a
al0
‘I
Pe
P
airspeed-. .
radial location of blade element
angle of attack
angle of zero lift
ideal angle of attaak
?WCA ACR i~O..L~ll
(r,&)
propeller blade ar.gleat 0.75 radius .
propeller blade anglo at radius r
mass density of air
Subscripts
~ front propeller
R rear propeller
0.7 at 0.7 raldiua
The propeller analyzed is a six-blede dual-rotatingf’36-1c2-15 (front, rightpropeller with Curtiss blades ~
hand) and 8~~-lc2-13 (rear, left hand). Blade-form curvesfor the propeller are given In fi~9 1. “me propellercond~.tionsanalyzed vary fro~L a v&lU~ of Cp = ().31
at V/nD = 0.33 to a value of Cp = 0.095 at v,41D= 0.26.Preliminary calculations showed l%at the propeller with theori~inal blades would stall at an advance-diameter ratioof 0.33 before absorbing a power coefficient of 0.31. Inorder to use the available propeller for this condition,;+it was necessary to increase the propeller solidity by theuse of extension flaps attach.edto the trailing edge.Extension flaps cause a change in the angle of zero lift,which results in an effective c-nangein the propellerpitch distribution. It was necessary, therefore, tocalculate the lift of the sections as a function of angleof attack for use on tb.epropeller. The method of
. .—— , ,- -, .,-. , ,,, mm — ,, ,
.
reference 1 was used to calculate the change In liftoharaoteristlcs caused by extension flaps, and the resultsshow the angle that w1ll be required between the extensionflap and the ohord line of the original airfoil toproduce zero change in pitch distribution for severalsections along the blade.
Certain assumptions regarding the atrfoil character-istics of the propeller were necessary In order to makethe calculations. Experimental data are usually used inanalyzing propeller performance. Ihasmuch as the Curtissblades 836- and 83Y-1c2-13 are of NACA 16-series airfoilsection, the section lift characteristics (fig. 2) forthe original propeller were obtained by extrapolatingtk experimental data of reference 2. “The design llftcoefficients and the operating Mach numbers for severalsections along tb blade for the limitlng conditionof operation are shown in figure 2. The calculationsfor the sections with extension flaps were made on theassumption that the addition of flaps did not changethe slope of the lift curve for a given section.Inasmuch as no experimental data were availablefor the airfoil sections with extension flaps, it wasnecessary to use theoretical calculation In analyzingthe performance of propellers with these sections.The calculated and experimental values of ato for
the original sections are not in perfect agreement.Since experimental data were used for the originalsections, the differences between the calculatedvalues for the original and the extended airfotl sectioncharacteristics were applied to these experimentaldata. The corrected values were then used in calculatingthe perfommnce of the propeller with extension flaps.
RESULTS AND DISCUSSION
Computations were made to determine the effect ofthe trailing-edge extension on the lift characteristicsof an airfoil as a function of angle of attack. Curvesshowing the results of some of these computations are
. presented In figures 3 to 6. The calculated ahgle ofzero lift azo, the ideal angle of attack aI,and aI - azA (on which the design lift coefficient
depends) are”given for the propeller section at the
6 NACA ACR Ho. L5.111
0.45 radius in figure 3. The calculated angles aremeasured from a straight line joining the extremitiesof the mean camber line of the extended airfoil seotlonbut are plotted against the angle between the extensionflap and the strai@t line joining the extremities of’the mean camber line of the original airfoil section,as was done in reference 1. The effects of a10-percent extension, a 20-percent extension, and a4.O-percentextension are compared.
In the use of this information for propellercalculations, it is more convenient to refer thecalculated angles to the line joining the extremitiesof the mean camber line of the original airfoil section.The angular difference al between the two referencellnes is given by the following formula:
( )Extension lengthChord sin (Angle of extension)
tan-lal =1+
F )
tension len,gth
Chordcos (Angle of extension)
The results for the 0.45 radius plotted in figure 3 arereplotted in figure ~but in figure 4.the calculatedangles are measured from the chord line of the originalairfoil section. The calculated and extrapolatedexperimental values of =2o and aI - al. for theoriginal section (without flap) are shown in figure 4..The points on the curves also show the calculatedangles at which the extension flap must be set to thechord llne of the orighal section to give the same valueof al. or aI - =20 for the extended section as for
the original section. If the values of azo for the
sections with the extenston flap are the same as forthe orlglnal sections, the pitch distribution isunchanged. Since al for the original section(16 series) is zero, the crossing of the aI mrveswith the zero ordinate gives the angle of extensionfor an unchanged aI. Figure 5 shows similar curvesfor a 20-percent-chord extension flap and for a40-percent-chord extension flap at the 0.95 radius.In figure 6 the curvas at several radii are comparedfor the 20-percent-chord extension. From curves ofthis type, any desired changa in the pitch distributionof a propeller may be made by properly setttng theextension-flap angles.
1
NAC.4AC:fl~\;O. L5A11 ,~, 7
Since the inboard sections of the original propellerstalled much earlier than the outboard sections forlow v/’rlD operation, it was decided to c’nange the ..angles of zero lift of the blade sections in orderto shift more of the load toward the tip. This changein the angle of zero lift is obtained by setting theflap extension at the proper angle to the chord line.The angles of zero lift of the blade sections werechanged by the amount shown by the solid. line infigure 7. This curve may be shifted up or down, asis shown by the dashed lines in fiSure 7, with nochange in the load distribution; the only changesresulting are in the design lift coefficients and aconstant shift in the angles of zero lift of’ thesections. In making the nropeller performance calcu-lations, however, a shift in the angles of zero liftresults in a change in the ~ropeller Pitch setting forconstant Cp and V/nD. The only change in CT and rj
will result from the small effect of th,e change in thedrag of the airfoil sections.
~xamination of the results (see figs. 4. to 6)shows that a 20-nercent-chord extension to the Curtiss 836-or 337-1c2-13 blade should be set about 7.2° to thechord line at all blade sections to give the variousangles of zero lift that would be obtained byadding Aazo (solid line in fig. 7) to aLo of the
original section. A )+0-:percent-chord extension shouldbe set about 6.)+0at all blade sections. The anglesof zero lift for the sections at all radii given infigure 2 were increasedby the amount shown by the solidline in figure 7 for making the calculations of thepropeller performance with the extension flap.
Analyses of propeller performance for several pro-pellers indicate that single-rotating propellers stallat section lift coefficients of about 1.0 for most ofthe blade and that the thin sections near the tip stallat 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 2)+0 at the0.7 radius for operation at V\nD = 0.33 and that a,!+O-percent-chord extension (lO-percent increase insolidity) is required to absorb the power. Experimentaldata on dual-rotating propellers, however, show thatthe dual-rotating propeller can be operated withoutstall at higher blade angles and at higher section lift
,, ,,, , ,,,-,. ! !m. ! .! !-.. ! ,.. .. ..
8
coefficients than sin~le-rotati.ilg propellers. It isquite possible$ there~ore, that th’e ~0-percent-chordflap extension to the tunnel..propeller that would berequired for a single-rotating wropeller will not benecessary to prevent stall for “~he lii;litin~ conditionof operation with dual -~otatfi.ng propellers and. that alower solidity may be used. Nevertheless, in order toobtain conservative results, the calculations for thetunnel propeller have been .nade on the basis of a)+0-percent-ckord flap extension and the results fortwo operating con(;.itions are given.
Figure 8 s’hews the differential thrust and torquecurves plotted against x for Oneration at a V/nDof 0.35 with the .front-uropeller” blade angle set 2)+0 andthe rear-propeller k!.ade afi~le sat 23° at the 0.7 radius.The element lift coefficients at several section radiiare shown in this ~j.:y~~e . yj.:u~e ~ shows similar curvesfor o?>eration at V/nD = 0.26 wttb.the front-propellerblade aj;gle set 12° and the rear-propeller blade angleset 11° at the 0.7 radius.
The solidity of a six-blade dual-rotating propeller}]avi]lgCurtiss ~j3~- and 857-1C2-15 blades has beenincreased by addin~ extension flaps .to th-e trailing edge .The method of analyzinS the new blade-section characteri-stics in this case was av:~lied to a particular 9ropellerfor ormration. at a very l.o-~vadvance-diameter ratio, butthe m~thod. may be anpl~ed to arty propeller section underanj~ operating condition. The :Oitch distribution of thepropeller with flaps may be :held constant or, if desired,may be varied for differen-t design operating conditionsby properly setting the flap ang:le.
Langley lle-mor~-alAeronautical La?]oratoryNat5.onal Advisory Committee for Aeronautics
Langley Fieldj Va.
NACA ACR No. L5A11 ~ 9
REFERENCES.
1. Theodorsen, Theodore, and Stickle, George W.: Effectof a Tralllng-Edge Extension on the Characteristicsof a Propeller Section. NACA ACR NO. I@21, 1944.
2. Stack, John: Tests of Airfoils Designed to Delay theComprosslbllity Burble. NACA TN No. 976, hC. 19&(Reprint of ACR, JunB 1939.)
Crigler, J. L. DIVISION, Propellers (11)SECTION, Aerodynamics (1 )CROSS RefERENCES, Propellers - Aerodynamics (75476);Propellers - Lift-drag (7~Z~.95); Propeller blades -
AUTHORIS) . . Trailin~ edze extensions l7OXJ601'*
ORIG. AGENCY NUMBEB
ACR-L5All
REVISION
AMER, T1TLE'The effect of trailing-edge extension f.laps on propeller characteristics
FORG·N. TITLE,
National Aovi s ory Committee for Aer onaut i cs , Was hing t on , D. C.
u. S.CLASS. OA TE PAGES IlLUS. FEATURESUnc l as s . Jan '45 19 9 . graphs
A13$VMCV, Method of calculating chanr.es in ideal ang l e of attack, an gle of zero lift, and decignlift coefficient of propeller blade section having trailing-edge ex t e ns i on flap was utilized to calculate performance of six-blade dual-rotating propeller:J with extension flapsval1'i r.g up to 40% chord. l!ethod was us ed to detennine the angle whi ch flap extensionmus t make with chord to obtain a particular load dis tribution. Analysis was made forwind-tunnel propeller designed to ope rate at 101\' advance-diameter ratio, but method isapplicable to any propeller section under any operatinp, cc~dition.
~ Propellers - l'erfonnance (75479.21$)NOTE: Requests for copies of this report mus t be addressed to: II.A.C.A., \':aslingt"",D.C.
T·2,HQ. AIR MATERiel COMMAND & IR 'iJ'ECHNICAL ONDEX WRIGHT FielD. OHIO. US""FWF-O-21 MAR ~ ~
