ACR No. L5FO7 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT OMQNALLY ISSUED June l9J<-5 as Advance Confidential Report L5FO7 EFFECTS ON LOW-SPEED SPRAY Cffi\EACTEEISTICS OF VARIOUS MODITICATIORS TO A POWERED MODEL OF THE BOEING XPBB-1 FLYING BOAT By Douglas A. King cind Newton A. Mas Langley Memorial Aeronautical Laboratory Langley Field, Va. UNIVERSITY OF FLORIDA DOCUMENTS DEPARTMENT 120 MARSTON SCIENCE LIBRARY P.O. BOX 117011 GAINESVILLE, FL 32611-7011 USA WASHINGTON NACA WARTIME REPORTS are reprints of papers originaUy 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 - 162 Digitized by tine 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/effectsonlowtspeeOOIang \^'> ' f V ( 5 ^ u MCA ACR 1^0. I,5F07 NATIONAL ADVISORY COMTHTTEE FOR AERONAUTICS ADVANCE COJIFIDE^'TT'TAL REPORT EFFECTS ON LO/.'-SPEED SPRAY CHARACT''RISTICS OF VARIOUS MODIFICATIONS TO A POWERED MODEL OF THE BOEING XPBB-1 FLYING BOAT By Douglas A. King and Nev/ton A. Mas SUrffilARY A size powered moael of the Boeing XP3B-1 flying 10 boat, which v/as dynamically similar to the full-size flying boat, was tested in Langley tank no. 1 to obsstrve the effects of trim and pov/ered propellers, of lengths of forebody and afterbody, and of various spray strips upon the Ic.v-speed spray characteristics. The effects of pov/ering the propellers were to lower the tri:?. and to pick up spray that would not strike the propeller disks when the propellers were v^findmllling. Lowering the trim increased the heirht of the spray with respect to the hull. Changes in the length of forebody or afterbody that incrseseci the ratio of forebody length to afterbody length raised the trim and reduced the intensity of spray in the propellers. Spray s jscting vert found to be striking the and the bott tiveness of spray strips spray as spr of dovm flar as to increa trips having the form of thin plates pro- ically dovi/nward from the forebody chines were very effective in preventing spray from propellers. Fillets betv,-een the spray strips om of the hull markedly reduced the effec- the spray strips. The unfilleted vertical were about as effective in controlling the ay strips of' the sarae length having an angle e of 30° and extending out from the chine so se the beam by alniost 13 percent. co^ipide:^ial naca acr iio. l5po7 totrotouction ■ • • In a relatively small range of speed, which is just below hvT.m speed, the spray from the forebodies of heavily loaded flying boats strikes the propellers. The quantity of spray increases with gross load and has become a factor limiting the gross load at v^hich some flying boats can take off.. The effects of load and forebody length, length -beam ratio, angle of dead rise, spray strips, and chine flare upon the tpray characteristics of various models have been reported in references 1 to 6, The tests of refer- en-.^zs 1 to 6 were made on unpovv'orcd models. Other model te.-^fs (i-eference 7) have shov.'n that the Inflov; of air to pov.'ered propellers picks up spray that does not hit the propeller disks when the propellers ^ are windmilling. In a:i''i: -icnj p'^v.'ering the propellsrs causes the trim of a povf.'rod :'!iodcl to be lower than that of the sam.e model without power. The spray chriractcristics of any hull are affootcd by trim. The effects lapon the spray characteristics of trim, powered propellers, length-beam ratio of the foi^ebody and afterbody, and of several types of spray strips attached to the f oT'eboily ciiines' v;ere investigated by tests of a powered model of the Boeing XP3B-1 flying boat. The effects of some of these modifications on resistance and longitudinal stability vjere also investigated. Cp resistance coefficient Cy speed coefficient ' p V^b COJTPIDENTIAL MCA ACR No. L5Fn7 CCNFTDS?ITIAL 5 where A^ gross load on water, pounds w weight density of water, pounds per cubic foot {bj).h, for these tests) b beam of hiai, feet R resistance, pounds V speed, feet per second g acceleration due to gravity, 52.2 feet per second per second and 6^ flap deflection 5q elevator deflection Lp forebody length L^ afterbody length d depth of spray strips of forebodies F]_o and Fn T trim, degrees r radius of fillet between spray strip and bottom of hull of forebodies F]_2 and F^t Any consistent system of units .r.ay be used. MODEL The basic model, Lang ley tank model 17i|F]_A[,, was a 1 ^ size model of the -Boeing XPBB-1 flylnc: boat and was 10 fo .. ^ dynaiuically similar to the fxill-size flying boat. A sketch showing the general arrangement of the model is given in figure 1. The basic model was supplied by the Boeing Aircraft Company. COOT' IDE NTIAL i; COIIT^ID^JITIAI, FACA ACR No. LpPO? The model differed from the actual flying boat In that the bow gun turret and pilot's canopy were replaced by a simpler deck and the waist gun turrets v;ere omitted. As is customary at the Langley tanks, leading-edge slats were added to the model to correct for the loss in maxi- mum lift that would be obtained with the model wing with- out slats at the ] ow Reynolds number required in tank tests of d;^mamlc models. The. model was powered by two 2-horsepower variable- frequency alternating-current motors, v/hlch drove three- blade metal propellers I.65 feet In diameter. The pro- pellers operated at such a combination of blade angle and rotational speed that the variation of thrust with forward speed approximated that corresponding to the full-size flying boat . Two forebody lengths, two afterbody lengths, and seven spray strips were tested. Sketches and designations of the various parts and modifications of the model are given in figtire 2. The basic forebody F, (fig. 2(a)) had a length of 14.2,65 inches and an angle of dead rise of 17. 9°- The bottom adjacent to the chine was horizontal, Forebody F|, (fig. 2(b)) v;as I4. Inches longer than the basic forebody. All the spray strips (figs, 2(c) to 2(h)) were attached to the basic forebody F;j_, The spray strips that Increased the beam had an angle of down flare of 5^° and projected 0,8 inch out from the sides of' the hull. They differed only in length. A length of 9,75 inches was removed from the aft ends of the spray strips of forebody Fg to form forebody F^. The forvard part of the spray strips of forebody Fj was faired into the hull to form forebody Fg. The spray strips that did not Increase the beam were formed from -ir-inch metal 16 strips projecting vertically downward from- the chines and had approximately the same shape in elevation view as the spray strips of forebody Fg. The depth of the sprajr strips of forebody F]_o ^^^ 0,8 inch and that of the spr'ay strips of forebody F-i -1 was 0,)^. inch. Fillets of 1-lnch and - — inch radius were Inserted between the k spray strips of forebody F-^-, to form forebodies P-j_2 and F-,7, respectively. CGNFIDEriTlAL NACA kCR No. L5F07 CC^-Ii^IDENTIAL 5 The basic afterbody A^ (fig. 2(i)) had a length of 33 '^l- inches and an angle of dead rise of 20°. The length of the extended afterbody A^ (fig. 2(j)) was li3 »h inches. The keels of both afterbodies were at an angle of 5 .^t-° ^o the forebody keel. TESTING APPARATUS AND PROCEDURE Tests were conducted in Langley tank no. 1 v/ith the apparatus substantially as described in reference 8 except that in the present tests the model was tov;*d under the main carriage. The ranges of speed in which spray entered the pro- pellers were determined visually uuj?ing runs made at low accelerations . o 31 The Tests were made at grosr-load coefficients Ca u of 0.91* 1.1^^ and 1.28, which correspond, respectively, to gross loads of 65,500, 82,300, and 92,11.00 pounds . Th condition for the tests was for full-povifer operation, free to trim, at a flap deflection 5^ of 20° and an elevator deflection 5g of -10°. The center of gravity was located at 28 percent of the mean aerodynamic chord. Measurements of resistance v/ere made during runs at constant speed with propellers wlnd:-,iilllng. The resist- ance includes both the vater resistance and the air drag of the model but not the air drag gf the towing gear. In the tests made to determine the effects of trim and of air flov; into the propellers on the spray charac- teristics, the gross-load coefficient was 0.91 (full-size gross load, 65,S00 pounds) and the flaps were deflected [|.5°. Photographs of the soray were taken at several constant speeds at pover-off and power-on conditions. For each speed tested, two fixed trims were used, which corre- sponded to the free-to-trim trims for the tvi/o conditions of power . CONFIDENTIAL CONFIDENTIAL MAC A ACR No. L5PO7 RESULTS AND DISCUSSION Effects of Trim and Powored Propellers The effects of trim and powered propell characteristics are shown in flgiji-'e 5. Thes were taken with the model operatin,;^' at a gro ficient of O.9I and a speed coefficient of 1 Lowering the trim approximately 2'^ Increas of the hew spray approximately 1 inch v/ith r model. The powered propellers picked up spr how "hlisters" even though the blisters were far bolovv' the propeller disks. ers on spray e photographs ss-load L coef- .73. ed the height espect to the ay from the relatively Effect of Length of Forehody and Afterbody The effect of length of forebody and afterbody on the range of speeds in which spray struck the propellers is given in figure l± and in the following table: Range of Cy Range of Cy Model Lp ^-A in which spray struck propellers Trim (deg) in which spray struck propellers Tr im (deg) Ca = 1.1^1- "0 CAo = °-51 ^lAb. 1.28 1.5 to 2.3 6.0 to8.9 1.6 to 2.0 6.2 to 7.0 P[i.A2 1.08 1.1; to 2.6 k.k to 6.7 1.6 to 2.2 k'k to ^.0 F1A2 .93 l.k to 2.7 ;.7 toT.O 1.6 to 2.5 5.8 to 5.3 For convenience, the length of the forebody is taken as the distance, measured parallel to the base line, from the step to the intersection of the keel and chine at the bov/. ]'']xtending the basic afterbody 30 percent of the original length (80 percent of the beam) to form model 17i|.F2^A2 lowered the trim approximately 3° in the range of speed in which spray struck the propellers and CONFIDL'.TTIAL NACA ACR No. L5PO7 CO!'!FIDEOTIAL 7 greatly increased the intensity and voliime of spray in the propellers. The range of speed in which spray struck the propellers was greatly increased. Extending the length of the forebody of nodel 171^2^2 9 percent of the •original length (32 percent of the beam) to form model 17i|Fj,A2 raised the trim approximately 1° and decreased the intensity of the spray that struck the propellers. This decrease in Intensity woiild be expected from the results of reference 1. Decreasing the ratio of forebody length to afterbody length lov/ered the froe-to-trim trim, increased the range of speed in which spray struck the propellers, and increased the intensity of the spray. As has been shown, lowering the trim increased the height of the spray and brou^-lit it more under the influence of the inflow to the propellers . The 'effect of length of forebody and afterbody on the variation of trim and resistance with speed is shown in figure 5« The extended afterbody Ag lowered the trim in the speed range in vjhich spray struck the pro- pellers approximately 3'^ ^-^d. caused a'high'peak in the resistance curve at a speed less than hump speed. At the high trims caused by the ' load coefficient and elevator deflection in the planing range, the extended afterbody lowered the trim approximately 2°. The hump resistance was decreased approximately I3 percent and the resistance at high speed was decreased slightly. Extending the length of the forebody (changing from model I'^k'^i^z ^° model 17l^F|, A2 ) raised the low-speed trim approximately 1° and decreased the resistance at all speeds to a value below that of the basic mbdel.- These trends are in accordance with the results of reference 3« The upper trim limits of stability of model 17l4.F]_A2 (basic forebody, extended afterbody) were about 1° lov;er than those of model 17l;F]_A[^ (basic model) and about the same as those of model l'jh-F]j^A2 (extended forebody and afterbody) . The low-speed peak of the lower trim limit of stability of the models with the extended afterbody A2 occurred at a lower trim and higher speed than that of the basic m.odel. At higher speeds the lov^er trim limits of stability of all three models wer'e approximately the same. These trends are in accordance with the results of refer- ence 9> in which a general discussion of trim limits of stability is presented. CONFIDE^TTIAL 8 CONFIDENTIAL NACA ACR No. L5FO7 Effect of Angle of Dead Rise As shown in figure I4., the range of speed In which spray entered the propellers of the model with an angle of dead rise of 23"^ v/as about the ;jan;e as that of the basic model, which had an angle of dead rise of 17»9°» The intensity of spray in the propellers was approximately the same for both models. Those results are not in accordance with the results of references 5 and i;, the tests of which were made on unpowered models. Effect of Various Spray Strips In indication of the eff octiysness of the various spray strips on the basic forobody in controlling the spray is given in table I, Spray gtrips t hat increased beam .- The. spray strips of forobodiTs F^T^, and Fg pro jeotud O.G inch (0.06l\. buam) beyond the chin.. s, v/hich increased the beam 15 percent, and had an angle of down flare of 30°. They differed only in length. Tho; load and speed coefficients of the models with forebodies F^, Fj, and Fp were based on the beam at tho step, which v/as the linear dimension used in computing the coefficients of the basic model. I'.qual load and speed coefficients therefore represent equal loads and speeds in all cases. The spray strips were similar to spray strips that had been shown to be effective in tests of another model ,in the Langley tank no.,l» These spray strips were reported by the m.anuf acturer to be effective when applied to the full-size flying boat. In the present tests, tho spray strips of fore-bodies F^, Fy, and Fg were also effective in keeping spray out of the propellers. Short- ening tho spray strips made the spray slightly more intense, but, as shown in a photograph in table I, the spray of the model with tho shortest spray strips (model 17l|-FoA. ) did not strike the propellers. The spray appeared in the form of individual drops instead of the smooth blister that may be observed in tests of most models . , The angle of down flare of the spray strips of fore- body Fq v;ae changed from 50° to 20° v/ith a resulting CONFIDEITTIAL :^TACA ACR No. L5FO7 COWTDEIMTTAL slight loss in effectiveness in controlling the spray. Only visual observations were raade and no .model niunber Vv'as assig-ned to this modification. The variation of trim and resistance with speed of model lYilFoAji is compared with that of the basic model in fi^tire 6. Below the hump speed, the spray strips increased the trim and resi-stance slightly. The hump resistance of model 17i4-FQAi was about J percent greater ^than that of the basic model. .The ■ additian of these spray strips to the forebody lowered the trim limits of .stability slightly. Spray strips that did not increase beam .- '^he spray strips of fcrebodies F^o* ^llt F]2> ^^'^ Fx3 were formed from inch metal strips projectinf^ vertically downwara from the chines. The spray strip of forebody Viq, baving a depth of O.S inch (O.06I4. beam), was very effective in keeping spray out of the propellers. Only occasional and momen- tary splashes of spray struck the propellers at speed coefficients from I.55 to 2,07. Decreasing the depth ol' the spray strips to 0.0i4. inch (0.052 beam) to form forebody F]_2 increased the inten- sity of the spray very slightly. As shown by the photo- graphs in table I, the vertical spray strips of forebod^r p were about as .effective in controlling the spray as were the spray strips of forebody Fg. Adding fairiilps of 1-inch and —-Inch radii to form k forebodies F-jo and F-,?, respectively, almost com- pletely nullified the effectiveness of the spray strip of forebody P-,-, in keeping the spray out of the pro- pellers. The intensity of the s;oray of forebodies F]_2 and F2_z was somewhat loss than that of the basic fore- body F]_, and appeared in the form of individual drops rather than in the more usual relatively smooth blister. The effects of the spi'ay strips of forebodies Ftq' ^11» •^12 > ^^"^ F]_z vipon the resistance and stability characteristics of the model were not determ.ined. GONFIDSOTIAL 10 COI^IDEOTIAL ■ NACA ACR No. L5F07 The addition of spray strips to any flying boat would probably increase the air drag of the flying boat. In this regard, the vertical spray strips .of forebody F]_]_ offer an advantage over other types in that they could be retracted vertically upvi/ard on the sides of the hull. . . C0FCLUSI0N3 Tests of a —-size model of the Boeing XPBB-1 flying 10 boat, which was dynamically similar to the full-size fl^Hng boat, were made with propellers operating in order to determine the effects of trim and powered propellers, length of forebody and afterbody, and various spray strips on the low-speed spray characteristics. The tests, which may reasonably be expected to apply to other types of flying boat, indicated the following conclusions: . Spray strips that extend vertically dovmward he forebody chines without appreciably increas: 1. from, the loreDody chines without appreciably increasing the beam were about as effective in controlling the bow spray as spray strips that extend outward and downward from the chines and Increase the beam. Both types of spray strips were effective in keeping spray out of the propellers . 2, Changes In the length of forebody or afterbody that increased the ratio of forebody length to afterbody length raised the trim and decreased the Intensity of spray in the propellers. 3, Lowering the trim increased the height of the bow spray with respect to the hull,. Langley Femorlal Aeronautical Laboratory National Advisory Committee for Aeronautics Langley Field, Va, CONFIDEI'ITIAL iiACk Ar;n fo. t,5F07 cotifideittial ii refj;r::nces 1. Parkinson, John E. : Desi0;r. Criterions for the Dimen- sions of the ForehodY of a Lon'3:-Ran<3;3 Flying Boat. NaCA Ai-.R No. 5K0o, 194^. 2. Bell, Joe v; . , Oarrlson, Charlie C, and Zeck, Howard: Effect of Length-Beam Ratio on Resistance and Spray of Three Models of Flying-Boat Hulls. MA,CA ARR* No. 5J23, 19ij.3. 5. Parkinson, John B., Olson, Roland £., and House, Rufus 0,: Hydrodynamio and Aerodyna-nlc Tests of a Family of Models of Seaplane Floats with Varying An^c'.les of Dead Rise. N.A.C.A. Models 57-A, §7-B, and 57-C. NACA TN No. 716, 1939- I4.. Bell, Joe Vi,' . , and 'ViiUs, John i:., 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. 19i:-5 . 5. Truscott, Starr: The Effect of Spray Strips on the Take-C.^f Performance of a '\Todel of a Flying-Boat Hull. NACA Rep. No. 503, 193ii. 6. Bell, Joe W., and Olson, Roland E.; Tanl: Tests to Deterriiine the Effects of the Chine Flare of a ^lying-Boat Hull - N.A.C.A. Model Series 62 and 69. NACA TF No. 725, 1939. 7. Parkinson, John E., and Olson, Roland E.; Tank Tests of a 1/5 Full-.^-ize Dynamicallj-^ Similar Model of the Army OA-9 A;nnhibian with Motor-Driven Pro- pellers - NACA Model II7. NACA ARR, Dec. l^lil . 8. Olson, Roland E., and Land, Norman S.: The Longitu- dinal Stability of Flying Boats as Determined by Tests of Models in the MCA Tank. I - Methods Used for the Investigation of Longitudinal- Stability Characteristics. NACA AT.R , Nov. l^k^ . 9. Trascctt, Starr, and Olson, Roland E.: The Longitu- dinal Stability of Flying Boats as Determined by Tests of Models in the NACA Tank. II - Effect of Vpx-lations in Form of Hull on Longitudinal Stability. NACA ARR, Nov. 191^2. CONFIDEI'ITIAL NACA ACR No. L5F07 12 TABI£ I.- EFFECTIVENESS OP VARIOUS SPRAY STRIPS Traneveroe half-eeotlon Forebody Spray oharacterlstlos at C. = l.ll(. W 0.064 b FjA)^; Cy = 1.90 Heavy apray In propellers at apeed ooefflclente from l.l+V to 2. J} Some reduction In Intensity of apray and In range of speed In which spray struck the propellers Pg and ■ Py No spray struck the propellers FqAj^; C^ = 1.90 Spray slightly more Intense than for F^, but no spray struck the propellers Only occasional and momentary splashes of spray struck the propellers at speed coefficients from I.55 to 2.07 005 b Fj^q; d = O.OfiUb rk---i JLa( L 1^0.005 b 0.032 b Fj^j; r = 0.02b ■ 10 "11 FnA, \- Cv = 1-90 About the same as F^^q except splashes more frequent Heavy apray struck propellers at speed coefficients from 1.55 to 2.07; somewhat less spray struck propellers than for Pj^ "15 About the same as for P 12 RATIONAL ADVISORY COTOITTEE FOR AERONAUTICS NACA ACR No. L5F07 Fig. 1 NATIONAL ADVISORY COMMITTEE FOB AEBOHAUTICS Figure I.- General arrangement of Boeing XPBB-I flying boot. NACA ACR No. L5F07 Fig. 2a-c -^Dec/t of model 17.9 (a) Basic forebody, F,. 46.65' (b) Extended forebody, F^ (c) forebody Fg NATIONAL ADVISORY COMMITTEE fO« AEBOM*UTICS Figure 2 .- Sketches of forebodies and afterbodies used in tests. NACA ACR No. L5F07 Fig. 2d-f (d)Forebody Fj 42.65 (e)Forebody Fg. ^.8' //I6l k (f)Forebody F/q Figure 2- Continued. NATIONAL AOVISOBY COMMITTEE FM AfBONlUTICS NACA ACR No. L5F07 Fig. 2g-i (g) Forebody Ff, . '/'radius (h) Forebody F/^ -1/4' radius (i) Forebody F,y . Figure 2 .- Continued. NATIONAL ADVISORY COMMITTtE FM AEKOtlAUTICS NACA ACR No. L5F07 Fig. 2j,k (j) Basic afterbody , A^ (k) Extended afterbody, A2. Figure 2 .- Concluded. NATIONAL ADVISORY COMMITTEE F0« AERONAUTICS NACA ACR No. L5F07 Fig. o to S2 o > ^ Z lu o j;; o «0 I 1.^ li ^ Uj ►o 5 .& NACA ACR No. L5F07 Fig, ^P ' J.USI0!JJ3OZ> pVO/'S-^OJQ NACA ACR No. L5F07 Fig. /2 ^ 8 ^ h ^^ _rr^ ./ Yl-A ^ H [^ ^"^ -^<^-e< -.--A X Cr<^'^ / ^u "^-^ [D- F^A^ o t i £ ■> J ^: 5 6 .<9^ ^ O Speed coefficient , C^ ■^ e>cfs/c model IT^F/A^ ° D Basic forebodj, expended afterbody 174 f[\ O -0 Extended for^body and afterbody IT'l-f^fii^ T 1 r n 1 \ \ NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 2 3 4 Speed coefficient) Cy Figure S - Effect of length of forebody atnd atterhodj on the variation of trim and resistance with spe.ecl Gross-load coefficient C^ , f 14 i power off. .¥ ^kCk ACR No. L5F07 Fig. 6 12 (4) O 1^ O ^ \^ , '°^ Y" ^^ ^^ ^v r,A^ x^^ ^ / '/ ^ o .32 V? 1.2^ 1) ■5 .OS ci; 2 3^ Speed coeffic/ent^ C^ r :^^ ^ XI. A kc '^ FiA^ '^:o 7 *^-^<- V ^tro / J_ a o Basic model □ Spray strips on fore body 174 F^/^^ NATJ COMMIT! ONAL ADVISORY EE FOft AERONAUTICS 12 3^56 3pe ed co efficie nt ,C^ Figure 6 Effect of adding spray strips of forehody FS fo f/je hps/c /vode/ on ffie yar/off/on of fr/m and ' res/sfcfnce ^viff) speecf. Gross-foQd coeff/c/e/?/' Ca. . IJ4 ' poy/er off. UNIVERSITY OF FLORIDA 3 1262 08106 449 4 UNIVERSITY OF FLORIDA DOCUMENTS DEPARTMbNT 120 MARSTON SCIENCE LIBRARY P.O. BOX 117011 GAINESVILLE, FL 3261 1 -701 1 USA