1、REPORT 923EFFECT OF AFTERBODY LENGTH AND KEEL ANGLE ON MINIMUM DEPTH OF STEP FORLANDING STABILITY AND ON TAKE-OFF STABILITY OF A FLIING BOATBy ROLAND E. OEKIN and XOFIMANS. LANDSUMMARYTed were made to$ll partly the need for information on thefect of ajteTbody dimensions on the hydrodynamic stability
2、 of ajlying boat in smooth water. T7M dimensions investigated weredepth of step, angle of afterbody kel, and length of ajterbody.An analy”s of the data showed that a either the afunstablelandfngcberectdetfcs,FIwJrtE ms.u stable16ndfcuCkiWtWktf=.FtGL7E6.-Cantinned.Provided by IHSNot for ResaleNo repr
3、oduction or networking permitted without license from IHS-,-,-74 REPORT 923-NATIONAL ADVISORY COMMITfEE FOR AERONAUTICSmI I r I I I III I i I 1 1 1 I i1-2 “w,-, Trh,deg(C) Deil ofst?p,14Wlt stnblekl dk+ldtk%FIGURE 6.Conoluded.Provided by IHSNot for ResaleNo reproduction or networking permitted witho
4、ut license from IHS-,-,-EFFliWT OF AFIERBODY LJIXGTH AND KEEL ANGLE ONEffect of depth of step.The effect of depth ofs on meland stability of the model with oe of the afterbodiesis shown in figure 6. The curves showm in figures 6 to 8are envelopes of the extreme values of rise above the watersurface
5、at. the various landing trims, and actual test pointsarenot given inorder to aroid complication. The curves showa matium-rise peak which occurs near the hmding trimat which the afterbody keel is paraIleI to the free watersurface. b the depth of step was increased, the landingsbecame more stable. At
6、a depth of step which resulted inmarginal landing stability (13 percent beam) this peak isconsiderably reduced. With a depth of 14 percent the modelwas stable and no peak remained. This trend is character-istic of all the afterbodies tested.Effect of angle of afterbody keel.The effect on the Iand-in
7、g behavior of changing the angIe of afterbody keeI butmaintaining the same depth of step is illustrated in figure 7.As the keeI angle is increased, the landing behavior changesfrom stable to very unstable. The peak of each curve tendsto occur at a trim near the landing trim at which the after-body k
8、eel is parallel to the free water snrface-lHect of length of afterbody.-l%e efkct of changing theIength of the afterbody but maintah a constant depthof step on the landing behavior of the model is shown infigure 8. Increasing the length of the afterbody changedthe landing characteristh of the model
9、from margimd tovery unstabIe. The trim at which the peaks of the cumwsoccurred did not shift appreciably as the length of afterbodywas changed.5 i.- b i b 1 II “ -.4re af ofte.-bodyReefI II I.$f I I: Depthof Stqp-. oe.ce.fbear+j / II /733 w/If -1$ 1 /11 2 .gr/ i, / ,9 - -f: / 1,1x 1“ ,E/ .- ,%/, _ .
10、/ -If, /13 / I . 9 %/4 / 10 . /“1 ./ “-,- -II1-,*.6 8 10 12 4 6Trim,degFImns 6.Efleetof depthof stepon maxim- rke durinuIamUw3.We of sfkbodYkeeI,9.3%lengthof afterbdy, 261lxems.MINIMUM DEWJTE OF STEP FOB LANDLN”G STABIT.JIT 75Trim,degFIGLIU7.EEw of angleof n!lerbodg dh ofmeP.7-nt kProvided by IHSNot
11、 for ResaleNo reproduction or networking permitted without license from IHS-,-,-76 REPORT 92 and, therefore,the lines define the region of minimum acceptable depths ofstep. The depths of step at the limits of this region ofmarginal landing stability (shown in fig. 9) have beenplotted against afterbo
12、dy kmgth and keel angle in figure 10.These data clearly show tiat a Irn-weme-in depth ofstep was required to maintain marginal Ianding stability asthe afterbody length or keel angle was increased. The twocurves shown for each case may be regarded M the envelopesof a region of depths of step which wi
13、ll insure marginallanding stability of this model. A greatw depth of stepresulk in stable landings but the unnecessarily deep stepincreases the hump resistance and the air drag. A smallerdepth of step than the optimum leads to some Iandinginstability and somewhat higher water resistance at highspeed
14、s but dso leads to a lower air drag.Depth of sfep,percent.bearn(a) Eff of angleOfOftWbCdykeel.(b) Effectoflexhof OftdXdy.FIOUES9.EITcetof depthof step on maximumriseduringlandfngsmadewftb modelshavingvariousafwrbodydfmensione.Effect of gross load,Tho tests which were mnric todetermine the optimum de
15、pths of step were nll mmic at onegross Ioad. In order to find the.infhumcc of gross Ioml on theoptimum depth of step, one model with margina landiugcharacteristics at the design load was testml over a widevariation of gross load. This range of lode is 19 pmmmtto 25 percent of the design gross lend.
16、Thu extremes of lhcIoading range correspond to gross Ioad coecicnts CM of0.70 and 1.08, respectively, whereC.o=+andA. gross load, poundsw specific weight of Lonkwatw (63.4 lb/cu ft)b maximum beam of model (1.19 ft.)Typical records of the landings rnwlc aL the extreme vahlcsof gross Ioad are reproduc
17、ed in figure 11. Thcso rccorcisshow that the change iu landing bohtivior, which iY slight.over this rmgo of loads, is no grcatw thin tlmL obscrcdfrom runs made under supposedly tho same txmtiitions.With an optimum depth of step, selechl m previouslyexplained, the eflect of Ioad on tho hmding Mnvior
18、of Lhhmodel as small. Ang/eofofferbodykee degn%whereas anincresse in depth of step (conatant length of afterbody) raisesthe upper trim limits (reference 3). The eHect of increasingthe afterbody Iength and at the same time maintaining the -optimum depth of step is shown in .re 13 (b), in whichthe upp
19、er trim Limitsare shown to be Iowered slightly. Theeffect on the limits of stable Nsitions of the center of gravityis shown to be quite small in figure 14 (b). II the length ofafterbody is changed but the optimum depth of step is main-tained, the take-off stability is seen to be relatively un-change
20、d.CONCLUSIONSThe rwults of tmk tests made to determine the effects ofafterbody length and keel angle on the takeoff and Iandingstability of a dynamic model of a flying boat indicated thefollowing conclusions:1. An increase in length of afterbody required an accom-panyhg increase in depth of step in
21、order to maintain ade-quate Ianding stabiIity.2. Increasing the length of afterbody, and at the same timeincreasing the depth of step in such a manner as to maintainadequate landing stability, rawdted in onIy a slight changein the takeoff stabiJity.3. An increase in the angle of afterbody keeI requi
22、red anaccompanying increase in depth of step in order to maintainadequate Ianding stability.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-80 .- REPORT 923NATIoNAL ADVISORY COMMI-4-L-K!d -l-C!J 16Lothat where =2-61, a=6.2,and d= 9.5. Substituting th
23、e numerical due of the constanttlma obtaimd givesd=O.59 $ aData from other dynamic models that have been testedin Langley tank no. 1 are compared with the precedingfornnda in figure 17. The correlation is fairly good and theformula is, therefore, suggested for use in preliminary design.Several facto
24、rs, such as dead rise, step plan form, and pIanform of afterbody, may be espected to irduence the optimumdepth of step as selected from the aforementioned simpleformula. The model used for the tests had a transversemain step, an afterbody pIan form teatti a potat the second step, and both a forebody
25、 and afterbody withtin angle of dead rise of 20. The results shown in figure 17for correlation with the present test data were obtained frommodeIs vrith angks of dead rise of 20 and 22fi0, and tra-verse and 30 -ree steps, but all had pointed afterbodies.The depth of step at the centroid vras used fo
26、r models withLTo!FIG= 17.-Comparisan of tentntire afterlmdy desfau formula with data Ilom s?veraltankvee steps. These results =e mostIy from tests in whichthe landing stability was judged from records made of theIandings.REFERENCES1. Truscott, Starr: The Enlarged N.kCk. Tank, and Some of ItsWork. NA
27、C.A TM 918, 1939.2. Olson, Roland E., and Land, Norman S.: Methods Wed in theNACA Tank for the Investigation of the Longitudinal-StabilityCharacteristics of 310deIs of Flying Boats. NAC. Rep. 753,1943.3. Truscott, Starr, and Olson, RoIand E.: The Longitudinal Stabflit yof Plying Boats M Determined b
28、y Twts of Models in the NAC.1Tank. 11EiTect of Tariatious in Form of Hull on LongitudinalStability. NACA ARR, Nov. 1942.A Land, Norman S., and Lina, Lindsay J.: Tests of a DYnamioModel in NACA Tank No. 1 to Determine the Effect of Lengthof ,kfterbody, Angle of Afterbody Keel, Grws Load, and aPointed Step on Landing and Planing StabiIity. KAC.% ARR,hlarch 1943.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
