fJhcf\ I'^l AEE No. L5G19 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLY ISSUED September 19^5 as Advance Eestricted Eeport L5G19 EESISTMCE TESTS OF MODELS OF THREE FLYIHG-BOAT HULLS WITH A LENOTH-BEAM RATIO OF 10.5 B7 Jerold M. Bldwell and David M. Goldenliaim '1 Langley Memorial Aeronautical Latoratory Langley Field, Ya. NACA y 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. ^9 DOCUMENTS DEPARTMENT Digitized by tlie Internet Arcliive 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/resistancetestsoOOIang NACA ARR No. L5G19 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS ADVANCE RESTRICTED REPORT RESISTANCE TESTS OP MODELS OP TKRES FLYING-BOAT HULLS ViTTH A LENGTH- BEA?^ RATIO OF 10 . 5 By Jerold K. Bicwell and David M . Goldenbaum SUI^MARY Models of tl'jpee flying-boat hulls, each with a length-beam ratio of 10. 5, were tested at the Langley tank no. 1= The lines of these ir.odels were derived from the Deutsche Versuchsanstalt fiir Luftfahjrt (DVL) standard series. The thi'^ee models permitted tests with tv/o depths of step and two angles of dead rise. Fie si stance, trimming- moment, and v/etted-length data were obtained from general fixed- trim and free-to-trim tests at load coefficients ranging up to Ij..O. The results sho.'ed that these three models had low hj'drodynamic resista.-'ce at high load coefficients. At the free-to-trim hump, load-resistance ratios of ii.5 and 5.9 were attained at load coefficients of I.5 and 5.5^ respectively. Increasing the angle of dead rise, excluding chine flare, from 20^ to 2i4..5'^ tended to increase the resistance and ■crimraing moments at planing speeds. Changing the depth of step from 5 to 10 percent beam had little effect on the resistance. With conventional nacelle locations, excessive spray would enter the pro- pellers at load coefficients over ^ .Q , INTRODUCTION The effect of length-beam ratio on the water resist- ance of a flying-boat hull has been the subject of many investigations. Three independent studies (references 1 to 5) have indicated that, within the range of the NACA ARIt Ko. L5G19 investigations, increasing the length-bo am ratio results jn lowerriig the water resjstaiice. Lines of the Deutsche Versuchsanstalt f ur Lrftfahrt (DVL) standard series (refer- ence 1) were used in tha development of three models, each with a length-beai^. ratio of 10. 5. Tv/o of these models differed only in angle of dead rise; the third model was similar to the model with the higher dead rise but had a depth of step twice e.s great. The models used v^ere furnished to the NACA by- Consolidated Vultee Aircraft Corooration. MODELS The m.odels, designated in the Langley tanks as models 181;, 165? and 185-A, were derived from the DVL series by increasing the station spacing along the forebody and afterbody keels and keeping the beam the same as that of the DVL models (II.8I in.). Two of these models diffei-ed only in angle of dead rise (defined her?)in as angle of dead rise excluding chine flare): the angle of dead rise was 2C° for model I8I4. and 2i|.5° for modi-;! IO5. Tli© sections of the model with the higher angle of dead rise were fonned by multiplying the ordi- nate 3 of the lowei" angle of dead rise by 25/20. Use of this factor rlelds a dead-rise angle of 2i4..5° ^^^ ^ 3light].y dif'^eren:: radius of curvature for the chine fl?.;-c tL.r-n that oi^ model 181+. Lines of model l35 are give;:; ii; figors 1. The third model (model I85-A) was simils.r to morel I85 except that the depth of step was doubled by raising the whole afterbody vertically. Sec- tions of the three models at the step are shown in fig- ure 2. APPARATUS AND PROCEDURE The tests were made in Langley tank no. 1, which is described in reference Ix. General fixed-trim tests v;ere made by following the procedure described in reference if. In addition to the usual measurements, wetted lengths of both forebody and afterbody were observed. General free-to-trim tests were also made at speed coefficients up to 5 '5 (5*3 ^ps) or NaCa ARR Ko. L5G19 slightly over the hump speed. The schedule of loads and speeds used for the fixed-trim tests is given in figure 3 and the free-to-trim schedule is the same except for the elimination of all speed coefficients above 5 -J- Limita- tions in the capacity of the test equipment made it nec- essary to drop some points from the schedule. These limi- tations were the resistance (approx. 60 lb) and the trimming moment (approx. l80 lb -ft). RESULTS The results of the tests were reduced to the usual coefficients based on Froude's law to make them independ- ent of size. The nondimensional coefficients are defined as follows; load coefficient (A/.vb5) Cfj resistance coefficient \R/\'ib-^ ) Cy speed coefficient \V/\/gb_) Cy[ trimming-moment coefficient \_M/wb^y ^W.L. wetted- length coefficient (l/b) C^ draft coefficient ( d/b ) where A load on water, pounds w specific weight of water, pounds per cubic foot (65.1+ for these tests; usually taken as 6)4. for sea water) b beam (0.985 ft) R resistance, pounds V speed, feet per second g acceleration of gravity; (52.2 ft/sec^) M trimming moment, poun'i-feet (positive moments tend to increase trim) hr NACA ARR :To. L5G19 I wstted-length, feet d draft at main step, feet Any consistent system of units nay be used. The moment data are referred to the center of mcnents shown in figure 1. Trim t is the angle between the base line of the model and the horizontal. The data obtained from tests of rr.odel I85 £^re given in figures L. to 8. Resistance and trimming-nionent data from fixed-trin tests are presented in figures 1+ and 5» respectively. The triinining -moment data are arranged in a form unlike bhat used in previous NACA reports. Because of the large nianber of load paraii:eters used, the usual rr.ethod of presentation would result in a confusing inter- mingling of the curves at low speeds. In figure 5> there- fore, trim T is the parameter Instead of the conventional load coefficient C^ . Data from the free-to-trim test on this model are given in fir re 6. The static properties are shown in figure 7- Similar data for models iSi^ and 185--H are not given because these data differ only slightly from those for model I85. Wetted-length data for model I85 are given in fig- ure 8. CorresDonding data for model I8/4. were obtained but are not presented herein. No data on wetted lengths were obtained for model I85-A. Observations of wetted lengths wore made whenever practicable but, because of the heav7/ spray, the data at heavy loads are not complete. No wetted lengths on the afterbody keel are given because of the difficulty of observing them. Best-trim curves derived from fixed-trim data for model 185 are given in figure 9' 'j^he best-trim data for models iSh. and IS5-A are given in figures 10 and 11, respectively. Photographs of the forebody spra^'' of model 185 are shown in figure 12. DISCUSSION The spray and resistance characteristics observed were similar on all three models. Some relatively minor effects on the resistance were produced by the change in angle of dead rise ai.i depth of step. Relatively high NACA ARR No. L5GI9 load-resistance ratios ware maintained at very high- load coefficients hj each of the tliree iiiodels. Effect of angle of dead rise .- The effect of changing the angle of dead rise from 20^' to 2l.u5'^ on the load- resistance ratio at hump speed and at high speeds is shown In figure 13 . The mcdel vi'ith the lower angle of dead rise shows slightly lower resistance at both hump and high speeds. Trimming moments are less positive for the m.odel with the lower angle of dead rise at best trim beyond the huinp. Below hum.p :;peed the effect of the change in angle of dead rise was negligible. These results are in agreement with those for conventional length-beam ratios reported in reference 5- Effect of depth of step .- The effect on the resist- ance of changing the depth of step from 5 to 10 percent beam is indicated in figure ll{. by a comparison of load- resistance ratios under several conditions of trim and speed. The effect is small, the trend for the model with the deeper step being toward higher resistance at hump speed and lower resistance at Mgh speed and light loads. Greater positive trimming moments were observed on the model with the deep step than on the model v;ith the shallow step. These results are siiriilar to thoce for conventional length-beam ratios of reference 6. On a hull of the form of model I85, if a step as deep as 10 percent beam is required to attain good landing sta- bility, no m.arked increase in take-off time may be expected over that for a hull with a shallow step. Fo rebody spray .- Photographs of the lorebody spray of m.odel It^ Cxve given in figure 12. The model is shown running free to trim at several load coefficients and at several speeds. The effect of the change in angle of dead rise on the snray v/as imperceptible, and therefore no photographs of the model with low angle of dead rise are given. The criterion for^ forebody loading (refer- ence 7) is given as C^ = '"^V") ' vvhere Lf is the length of the forebody and k is an empirical coeffi- cient. The follov;ing C^ values have been computed for this m.odel having a forebody length-beam ratio of 5.8: L^'G19 ic C. ■--o 0.119 l.o .0975 (excessive) 5 .2.3 .C825 (heavy) 2.77 .0675 (satisfactory) 2.27 .0525 (light) 1 1.76 Prom this table, model lOS would be expected to produce extremely heavy forebody spray at a load coefficient of h-.O. The spray actually ooserved and shown in fig- ure 12 verifies this expectation. With nacelles and wing located according to current design practice, a flying boat having a hull si'';ilar to model ibU or I83 would have an excessive amount o:' spray in its propellers when oper- ating at load coefficients ver J> .0 , CONCLUSIONS 1. The thr^ee models tested maintained relatively id-resistance ratios to' higher load coefficient; p. 9 3 '3 > I'espectively . 2. Changing the angle of dead rise (excluding chine flare) and the depth of step on these models had the same effect on their resistance as similar changes made on models of conventional length-oeara ratio. 3. Excessive spray was shown for the three models tested at conventional propeller locations with load coefficients greater than 5.0. o-^ Langley Memorial Aeronautical Laboratory National Advisory Committee for Aeronautics Langley Field, Va . FAG A ARR Fo. L5G19 RSPSRENCSS 1. Sottorf, vV.: The Design of Floats, NACA TIvI No. 860, 1958. 2. Bell, Joe W., Garrison, Charlie C, and Zeck, Howard.; Effect of Length- Beam Ratio on Resistance and Spray of Three Models of Flylng-Eoat Hulls. NaCA ARR No. 3J25, I9U3. 5. Davidson, Kenneth S. I"., and Locke, F. Vv . 3., Jr.: General Tank Tests on the H^'^drodynami c Character- istics of Four Flying-Boat Hull Models of Differing Length- Beam Ratio. NACa ARR No. I|-F15, 19Ut-. k-. Truscott, 3tarr: The Er''.arged N.A.C.A. Tank, and Some of Its v/ork. NACA TM No. 918, 1939. 5. Bell, Joe W., and Vi'illis, Joiin M . , Jr.: The Effects of Angle of Dead Rise and Angle of Afterbody Keel on the Resistance of a Model of a Flying-Boat Hull. NACA ARR, Feb. I9J+3 . 6. Bell, Joe v;.: The Effect of Depth of Step on the Water Perforraance of a Flying-Boat Hull Model - N.A.C.A. iLOdel 11-C. NACA TN No. 535, 1935. 7. Parkinson, John B.: Design Criterions for the Dimen- sions of the Forebody of a Long-Range Flying Boat. NACA ARR No. 5KO8, 19i|5 . NACA ARR No. L5G19 Fig. >■ h- <^ 3 > 2 -■? < <•■ Z ul ii o w ^ I I I Fig. 2 NACA ARR No. L5G19 Model 184 Model 186 Model I65'A NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS Fiqure ^.'Comparison of^ hull ^ccfions at fhe. step. 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