/^M/--;iiY 1* [ NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGlNALLy ISSUED January 19^5 as Advance Restricted Report L5A13a WDTD-TDKNEL TESTS OF A DDAL-EOTATIBG PROPELLER HATIHG OHE C(»IPOBSNT LOCKED OR VrrWT MTT.T.TM ; , By Walter A. Bartlett, Jr. I Langley Jfeonorial Aeronautical Laboratory Langley Field, Va. ri* , 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. J 1 oil. DOCUMENTS DEPARTMEN I 16)9 0\^ (f1 NACA ARR No. L^AlJa NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS ADVANCE RESTRICTED REPORT WIND-TTOINEL TESTS OF A DUAL- ROTATING PROPELLER HAVING ONE COMPONENT LOCKED OR IVINDMILLING By Walter A. Bartlett, Jr. Smir.TARY Tl'ie effect on the oroD-'jlsl ve efficiency of locking or windniilling one oroneller of a six-blade dual-rotating- Dropeller installation was determined in the Langley propeller- research tunnel. Tests v»rere made of both pusher and tractor configurations, Vi-ith the unpowered propeller both leading and ^"ollowirg the po.vei-ed pro- peller, which was set at a blade angle of h,0° , The maximum propulsive efficiency of the powered propeller in combination with the locked or v/indmilling propeller was, in all cases, lower than that of the powered propeller operating alone. The locked propeller gave greater maximum propulsive efficiencies v.'hen used as a contravane to remove rota- tional energy from the slipstream than v;hen used as a means for imparting initial twist to the air. The windmill ing nropeller, however, was equally efficient both leading and follov/ing the driven propeller. In the tractor installation, smallest losses in maximum propulsive efficiency were obtained when the unpowered following propeller v;as locked at a blade angle of 90° S-i^^ vvhen the unpowered leading nropeller was allowed to windmill at a blade angle of l\.^^ . In the pusher installation, equal losses in maximum pro- pulsive efficiency were obtained 'vhen the unpov;ered following propeller, was either locked at 90° or wind- milling at 55°j t»ut the unpowered leading propeller gave smallest losses when windmilling at 55° • NAG A ARR No. L5Al^a INTRODUCTION In the event of engine failure in multiengine airolanes 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 unpov/ered 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 v;ith the unpowered component both leading and following the powered component. The blade angle of the powered propeller was held at 14.0° and the blade angle of the unpowered propeller varied from 25° to 100°. This variation depended upon v^hether the installation was tractor or pusher and whether the unpowered component was windmilling or locked. Because of the limitations in tunnel airspeed (100 mph) and rropeller rotational speed (Jj-50 rpra ) , 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~i'^dius station was of the order of 1,000,000, and the highest tip speed was approximately 2l].0 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 51^5-6 (right-hand) and 5156-6 (left^ hand). The geometric characteristics of the blade are NACA ARR No. L^AlJa -> given in figure J. The front (right-hand) propeller disk was separated from the rear (left-hand) propeller disk by approximately 10 inches. RESULTS AND DISCUSSION The results are presented in the form of dimen- sionless coefficients, which are defined as follows: Cfp thrust coefficient ,P n2D^) Gp power coefficient / p-\ \pnVJ V/nD propeller advance ratio n propulsive efficiencv ( — — 1 \Cp nD/ where T actual thrust of oowered 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 0.75^, degrees Subscripts ; F, R front and rear propellers, respectively k NACA ARR TTo. L5Al3a The results obta:^.ned for the various combinations of a powered cojnponent with a locked or wlndmilling 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 ij.. Test points included in figure l\.{&) 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 figiore Ij., 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 90° 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 90° locked propeller following or leading the powered pusher propeller lowered the maximum propulsive efficiency 4. and 6 percent, respectively. The data show that smaller efficiency Irsses 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 r^owered propeller, the maximum propulsive efficiency was found to be essentially independent of the location of the wind- milling component for blade-angle settings from ij-0° to 55°' (See fig. 6.) The maximum propulsive efficiency of the tractor installation with the windmill ing 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 NAG A ARR No. L^AlJa I|. percent. Very little friction opposed the windmilling propeller, and results Indicated that the value of V/nD at which the propeller windmilled 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 or without the driven propel] er. Aerodynamic characteristics are nresented in figure 7 for the three-blade propeller operating alone and in optim-um 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 wl-en loc'ced at ^0°. Vi/hen the unpowered propeller led the pov;ered proDoller, the maximum efficiency was greatest for the combination with the windmilling propeller set at a blade angle of I|.5°. For the pusher installation, with the unpovv-ered prooeller following the powered propeller, the maximum propulsive efficiencies of the combinations with the locked pro- peller at a blade angle of 90° sind with the windmilling propeller at a blade angle of 55° were of the order of 3o percent, "/hen the unpowered propeller led the driven propeller, highest efficiencies were obtained with the windmilling component at a blade angle of 55°- SmiMARY OF RE3TTLTS Wind-tunnel tests of a six-blade dual-rotating- propeller installation with the operating propeller set at a blade angle of [(.0° and with the inoperative propeller locked or windmilling indicated the following conclusions : 1. In all cases, the maximum propulsive efficiency v;ith the locked or windmilling component was lower than that obtained with the three-blade propeller operating alone . 2. The locked propeller was raost efficient when used as a contravane to remove rotational energy from the slipstream. 6 NACA ARR Ko. L^AlJa 3. Per blade-angle settings from [t.0° to 55°> the windmilling propeller was almost equally efficient both following and leading the powered propeller. I4.. In the tractor-propeller installation, smallest losses in maximiim efficiency were obtained when the inoToerative following nroDeller was locked at a blade o angle of 90 and when the inoperative leading propeller was allowed to windmill at a blade angle of lj-5°. 5. In the pusher-propeller installation, equal losses in maximum propulsive efficiency were obtained with the following propeller locked at a blade angle of 90° or windmilling at a blade angle of 55°> '^'^■'^ the inoperative leading propeller gave smallest losses when windmilling at 55°« Langlejr Memorial Aeronautical Laboratory National Advisory Committee for Aeronautics Langley Field, Va. REFERENCES 1. Biermann, David, and Gray, W. li, : Wind-Tujinel Tests of Eight-Blade Single- and Dual-Rotating Pro- pellers in the ""ractor Position. NACA ARR, Nov. I9J+I. 2'. Bierm.ann, Da^'id, and Hartman, Edwin P.: Wind- lYuinel ""ests of Four- and Six-Blade Single - and Dual-Rotat 'ng Tractor Propellers. NACA Rep. Fo. 7lj.7, 19)42. NACA ARR No. L5A13a Fig. i^ O UJ o o •4» H « •rt a> l-l fl o • *< u a OS d « a 5§ a » H I « 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.arch ive.orgWetails/windtunneltestng NACA ARR No. L5A13a Fig. 2a o ■.H ■H> o (U CO ■^ . to .-( . 0) a; c ■ij c o c •w c 3 *J ■ H +J (d .— 1 X) C .— 1 0) o td ■p u ♦J c cd to 3 0) c O to ■H t 0) i-i u (D 1 > — 1 QO i-i rH C t- OJ CO O,—) — O (tj U W-, • — a. o a; u 3 NACA ARR No. L5A13a Fig. 2b o •H +J 03 •— 1 • •—\ 13 cd 0) *J T3 Cfl 3 c r— 1 .—J o i- ^-l o iV o •-H r-i 1 0) . 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