naca arr 3f12 some systematic model experiments on the porpoising characteristics of flying-boat...

7/27/2019 NACA ARR 3F12 Some Systematic Model Experiments on the Porpoising Characteristics of Flying-boat Hulls

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. . . ,# *.,.. AI/R No. 3F12

.>m~.---______ADVISORY COMMIT= FOR AERONAUTICS

~Y lSSIED. ->June 1043 as

Advance Restricted Report 3F12

SOME SYSTEMAIZC MODEL EXPERIMEN13 ON THE FORFOISINGCHARACTERISTICS OF FLYING -BOAT HULLSBy Kenneth S. M. Davidson aui F. W. S. Locke, J r.Stevens Institute of Technology

1, . . , W#l-UNGTON... . ,-, , .,.NACA WARTIME REPORTS -e reprlntefpapersoriglnUyIssuedoprovideapid dlstrlbutlon ofadvanceresearchesulteoanauthorisedrouprequiringhemforthewarefhrt.Theywerepre-vlouelyeldundera securitytatusutarenow unckeKled. Some althesereportserenottech-nicallydited.llhavebeenreproducedithouthangeinordertoexpediteeneraldletributlau.

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lWl!IOl?AL ADVISORY 00MMXTTEm

ADVANCE RESTRICTI!JD

~dtiArnROITAUTICS. .

REP ORT... . . r. . . . .SOMB SYSTEMATIC MODEL EKPERIMEET5 OMTHE PORPOISII?G----

CHARACTERISTICS Or FLYIITG-BOA!C HULLSBy Kenneth S. M. Davidson and F. W. S. Looke, Jr.

SUMMARY .

This report presents the results of eyetematlc! modelexperiments on the hydrodynamic oharaoterlsti.os of flying boats, aimed primarily at developing a comprehensive viewof the faotors Influencing porpolsing and of their rela-tive importance. The experiments radiatedW from a givenreferenoe ship; they embraoe changea, over reasonablywide ranges, in the value of eaeh of a number of variables,treated Independently.

The experimental results are summarized in a seriesof 26 flgurea, each of whloh gives the oomplete data forall the modlfioations of one variable. .The results are further oondensed for easy referenoeIn oharte 1 to 3, whioh follow the Summary. In thesecharts the prlnolpal portions of the eummary figures arereproduced at smaller soale and are arranged in groupsaooordlng to the type of the variable they represent.Here the relative influence of the variables Is brought ,out merely by the relative blaoknessn of the oharts.The ma~or conclusions which follow are based uponthe ranges of change of the variables indioated on thesummary flgureO:

1. The~etability limite for a given.hull under variousloadinge and aerodynamic conditions are determined (1)primarily by the three variables whioh govern the load onthe water in steady motion - gross load Ao, wing lift atarbitrary trim angle 201. . . . . . . and rate of change ofllft with..The aomplete eet of data from whioh the figures in thl~report were prepared and on which the analyses In thisreport were made may be obtained on loan from the Offloeof Aeronautical Intelllgen~e of the National AdvisoryCommittee for Aeronautics, Washington, D. c.


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trim Zfj and (2) secondarily by kh~ tall damplnp rateMl?Increasing the watsr-borne load raises both limite

w thout materially affecting.the width of the etable range:inoreasitig the tail damping rate lo~lers the lower limit nthigh speeds - the magnitude of the effect being greateet,however, at damping rate-s considerably below normal.2. Alterations to the afterbo~y, under piven lending andaerodynamic conditions, mny nlter the urmer limit qnd thep,~ak value of the lower limit In the vicinity.of the humn;theydo not alter the lower limit at hlphar ~needs. @h.humm trim and the humn rpsistmnce In eteqdy motion followth~ variation of the meak ef the lower limit. Assuming ar.~sonqble length, the most mowarful aft=rbod~ variable isthe anFle between a prol~n~ation of tha forebndy kel and aline joinlnr the tim of the m~in step with the tim of th=stern nest. Increasin~ this an~ls rais=s the kumn tr~m nndresistance and the Umasr limit of stab~l~t~: if carried far.enouph, it will sup~rees upn=r-limit mornolsinF at high .smeeds . Increasing the step h=lght qlso sumuresses umner-limlt porpolslng at high spe?ds. 3 Alterations to the fore~ody, under giv=+n londlng andaerodyn~mic conditl.ens, may alter bctk limits but. t+nd to affect princiual~y the low?r limit at high spe=fis. If. sufficient forebody lenfth to Drovide flotation nnd to pre-vent diving at low speeds Is atasumed, the most powerfulforebody variable is the emount. of warning. of the bottomin ths region just .ahe~:d of the main stem. Increasing thewarping lowers the lower li~lt at high spe~ds but r~isesthe hump resist rice.4. Finally, as a tentative, v-ry broqd conclusion: Honeof the modifications considered in the experimerits w~ssuccessful in eliminating. completely eith~r upper-limit orlower-limit morpoising and, In general, modificationswhicli t-nded to improve the. pornoising character~stlcstended to injure the resistance characterlstic~. B!od%flca-tions of thm loading or of the aarodynamlc conditions (thatis, of the .v~riable of groums I and IT shown In charts 1~nd 2) were found not to affect the chmract-~istics am-mreciably except as they influ~nc=d thq net water-bornelend; modifications of the hull form (tmking Froum .111,chart 3, in its entir=ty) had lar~er qff~cts, but thesemodifications .w?rflmalnlr v~riatlons on n plv+n parentform. It follows th~t.Lny significant improvement In %othnormoislng and resistance charactertstlcs must demend umonImnrovinp th~. basi,c m~jrent form of the hull.


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NACA CHART 1 GROUP r.- WEIGHTAND INERTIA LOADING 3

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/8 I ,..

CMAWGILSOF G-.-s WEIGH: Lm~., SEC Fi..6 M.-EMT -F IWERT, A, SEe Fir.. ?

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4 CHART 2 CROUP m - hmuu Ic timlm?u mm

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VUTCAL VELOCITY ~MPIN~. z, , %. F,.. II

u .m~ h+9

TAIL DAm PtMS, Mq , Su F16.13

] 1 1 1 1 I

WIW LIFT RATE, Ze , Scc Fu 10

nm-m A-s-4

- u- - -

-m

a

l_AIL fl.mmMT RATE, Ho , SEC FIa. IZ

1 -1+.. I


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I 1 1, I I , IA?nmma8Y Rmmaam, 8U Fla. 18

h I 1 1 1 I

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6 CHARr 3 (COUTIWED) GROUP =F - FORE BODV FORM NACAI 1 1 , 1 i f

I [ I , 1 1 I

r 1 1 , 1 ,

I 1 1I I T ,. , 6,, 1 11111


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IHTEODUCTIOIS... . - .-,


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Porpoisin# ph=nomsna hivs bem studied by th~oreti-CS1 analysis of the condition for stability, startin~from the basic eauations of motion (rsferencgs 1 and 2).To date, th~a qmroach has failed to advance materially ad~tnll~d underekandlng of the Dhenomena, rind-it reauireseo much time-consuming labor as tc render its nracticalapplication in individual cases neqrly Drohibitlva.

Yost of what is now known about ~orrolsing has beenlearned throu~h modsl experiments conducted with due re-gqrd to the d$nnmic retyulremente. The inh~r-nt dnng~r tothe actual ship limits the sco~e of systematic exu=rimentson pornoislng at full scale, and modal exm?rim~nts havethe Additional adv~ntaga that the test conditions c~ti bemore accurately controlled and th.s t~et results thereforemore readily interpreted. Sufficient evidmnc=. exiets toindicate satisfactory correlation between shin and modelporpoising In basic r~spects.

Because of the inherent. dangs~ to the shtn and theconsequent need of ~dvance warning on morpoising charac-teristics, mcd?l experiment~ in the Fagt kave tendpd toplace the emphasis on predicting the .characteristics oflndividu~l designs rathgr than on developing m brocd pie- .turn of the Influence and relativs imuort~nce of the vqr-Ious factors involved. The latter noint of view wasadomted for th? investlg~tion which forms ths subject ofthis ren~rt. In addition, through simmlific~tion of thetesting Drocedure ~nd the use of an unusually smnll mod-l,the experimental work h~s ban matsri=lly ~cc-lerated sothat considgrnble ground c=n b~ cover*d In a short tlm=.

The exmariments followed = nrogrfim designed nrimarilyto pqln persn=ctive, and con~iderqble attention has beengiven to presenting th~ test r=sults in sirmlp form. Onlythe basic cormoislng chr~ctmristics ar~ consider~d: namely,the umm~r and lo~~r limits, as these would be determined inan actual shtp by respectively raising or lowerinp th~ trimangle from R meqn vnlue in the st=lle rang-. Variations,particuljrly ofth~ hi~h-angle tymc of mor~oisin~, are knownto exist; these h~ve bq~n dlsreg.arded for th- pr~s~nt In theintereot of clarlfyin~ the basic t~eg.The werk was undertaken with the flnanci~l assistanceof the National Advisory Committafi for 4~ronautics. Thenrogram oriFlnally laid out was to pqr~llel similar workcontemnl~ted by them. In tha course of two years the mro-gram has be~n exmandd con~iderqbly along independent lin=s.

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sCOPg OF IMVES~I-QATION

It is. the purtiode of-this rsnort -to pr~s-nt -t.hn--r+eult~ of.certnin systematic model =xm-rlments on flylnp-.boat hulls; Pornoiqing ch-racteristlcs qnd steady-mottonre818ta~cm$ ~re considqr~d, but th= mrinclpal emphasis isoh thB porpoising characteristics. The exp-rimeints radi-atsd frem a given flying ho%t, taken ns a basic point ofd%p%rtur~. The refer~nce shim us-d was the XP.B2M-1, nrepiesentatiye modern design h~vlng, for n gross wsightof .lvO,O~O pounds, nwlng loading Ao/s of ~g.O poundsper squnre foot, and m benm lo~din~ Ao/wb3 of O.sg.Each of a number of varimhles was alterd, ssparqtslyfrom the ethers as far as nosslble, over a range of vll-ues embracing ths normal value for the refqr~noe shin mndintended to be wids enouFh to cover all vnlu~s likely tobe ericounter?d in pr%ctice. The advantage of this proc@-dure Is that it materially simplifies thp nreblem of co-ordinating test results. It does not necessarily restrictthe anplicsbillty of the rgsults to %h= ref=rence ship -providad that the renF+s of change of the v~riabl~s mresufficiently wid+. ..

The radiating chnrt (fir. 1) shows th~ thre= groups :into which the variables fqll nntur~lly:Groun I - N~iFht end In~rtln TendingGroup II - Aero~ynmmlc ConditionsGroum III - Full Form

end also tht= comror.ent v~rlnbles of 4ncb Rroun which h~~eb~en covered, to date, by the ~xnarirr~nt~. Tt will beseen that the l%st groun is subdlvid~d irtoGroup 111A - Afterbody PormGroup ITIF - Furebody Form .Group IIIH - Hull Form (As m iihol~)

The dimensions and particulars considqrd ns normalwfor ship and model (1/30 soale) are giv~n In table I. Thebasic hull lines are shown in fi.nre 2... . .-Gandeased S.umrnqryfigures Qf test r~sults (ft&s.- 6.t~30) Include all the pertinent dqta; all conclusions or generalizations are bas?d on the ranges of ch%qge of theva~lables which they show: Hadth~ r~n~ss of chanpe~ . ~been extended !!ad absurdum, ~ SOtiq of th~ conclusions mndgenernllrntions would undmbtedly have been altered.


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10TEST METHOD

Teste of a dynamio model, complete with wings andtall taurfaoea, are a recognized method of investigatingtheporpoieing oharaoteristios of individual flying-boatand eeaplane designta (references 3 and 4). Difficultiesinherent in this method are .(1) That the magnitudes and the influence onporpoising of the separate aerodynamic and hydrody-namic components of the variablep involved are noteaelly evaluated .(2) That ecale or interference effet!ttamayeaeily prevent accurate reproduction.of the full-size aerodynamic foroes and momente(3) That the time and cost Involved in construct-ing and altering models ie high

The method uned In.the preeent Investigation wae de-signed to overoome these difficulties as far ae poesibleand to permit direot tatudiea of the hydrodynamic charac-teristics under rigidly controlled aerodynamic condi-tlone. A dynamic model of the hull is ueed without wingeor tail aurfaoeeg The equivalent of the aerodynamloforces and moments are applted by

(1) A calibrated hydrofoil for lift foroes andforce derivative(2) A calibrated spring and a calibrated daeh-pot for aerodynamic moments and moment derivativeta

All these are readily adjustable to produoe magnitudeoorregpondlng to any de~ired air etructure.

DESCRIPTION 03 APPARATU6

A diagrammatic sketch and a photograph of the appa-ratus used in the porpoising experiments are shown in fig-ures 3 and 4.The main frame in fitted With vertical traoks guided .by rol.lerm EIO that it is free to move vertically but


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otherwise restrained with respect to the towing carriageof the tank. The model iB attaohed to the forward end ofthie frame through pivots at the oenter of gravity whlohallow freedom in pitch; the after end of the frame oarrlesthe supporting oolumn for a hydrofoil. This framo--trase-mits the lift of the hydrofoil to the model; its weight,with all the attachments moving with it, is a part of thegroeta weight of the model.

The walkingbeam, pivoted on the main frame, changesthe angle of attaok of the hydrofoil in proportion tochanges In the angle of trim of the hull. Through the de-sign of the hydrofoil .Itself, and by means of the ad#utit-mente provided, the aerodynamic lift oan be made to corre-spond to prescribed values of20 lift at arbitrary trim angle (Lo)Ze rate of change of lift with trim angle (dL/dT )Zw rate of ohange of lift with vartioal velooity (dL/&w)

A torsion spring, mounted in the axis of the modelpivot, is provided with the neceaeary ad~ustmente for mak-ing the resultant aerodyqamio moment correspond to pre-earlbed values ofM moment at arbitrary trim angle (Mo)Me rate of ohange of moment with trim ahgle (dM/dT)

The dashpot shown is provided with a number of cali-brated pistons which, together with adjustment of theradius of aotlon, provide for making the aerodynamic taildamping moment correspond to prescribed values ofq rate of ohange of moment with angular velocity (dM/dq) .

The following two aerodynamic derivatives are neg-leoted in thle arrangement of the apparatus: .q rate of change of lift with angular velocity (dL/dq)Mw rate of change of moment with vertiaal velocity (dM/dw).A taeriee of Bpecial teate described later, oonflrmed theassumption made In designing the apparatue that these two

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derivatives probably had negligible ef f eot s on the stabil-tty limits.Graphioal records of porpoieing are obtained from aecf4ber, attached to the model and located at an arbitraryheight directly above the oenter of gravity when 7=0,whioh moves over a smoked .glaee fixed with respect to thetowing carriage. The records are reproduced photograph-ically.The drive gear of the Stevens Tank Is arranged toprovide a series of fixed, reproducible speeds. A de-scription of the tank will be found in referenoe 5.

TEST PROCEDURE

All tests were made at oonetant speede and in eub-etantially atlll water. It ia considered that teste at aeteady speed are more likely to bring out porpoislng tend-enoiee than accelerated teete, because they allow time forany instability to develop. In alloaees in which proposi-ng ooourred, a eteady-etate ayole wne developed after avery few initial traneient oyclee. It wae found that thetransient cyoles depend upon the amplitudes of the initialdisturbanoee whioh start porpoieing, as oompared with thenteady-state amplitude, a larger number of transientoyoles oocurring when the initial dlsturbanoee are rela-tively small and a emaller number when the initial dis-turbances are relatively 18rge.The amplitude of the final steady-state oycle islargely unaffected, however, by the magnitude of the ini-tial disturbances and is therefore a convenient measureof the inherent porpoislng tendency under given condi-tions. The principal requirement in teeting ie that the

initial disturbances shall be euff!clently severe to in- .suredevelopment of the eteady state within the llmlte of .the test run. TO this end the mo~el ie accelerated rapidlyin a dletanoe equal to about three or four timep Ite ownlength.The teste under each combination of hull form, aero-dynamic conditions, and loading followed the came basioprogram. In detail:

(1) Teete were made at each of a number of fixedspeeds, covering the range from a little below the

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hump to get-away in approximately equal steps.(2) At each speed, tests were made with varia-

tions of the applied moment (oorreepondlng to result-ant aerodynamic moment), oovering a range efficientto produce trim angles em%raolng the upper and lowerstability limits, ae. ordinarily defined. The momentsetting (obrYespondlng to elevator setting) wa8 notaltehedduring the course of any one test.. . . . . .(3) At each speed and applied koment, a teetwas m+de with each of three values of the tail damp-ing dM/dq corresponding coneeoutively to one-half,one, and two times the normal value given in table 1,

unless stab?.lity occurred with less than the maximumof these v~iuee. In the latter event no furthertests ware made. When the maximum value failed tocauee etability, an additional tefit Qaa made with alarge e~oess of tail damping to define the steady-motlon attitude.(4) The tests with normal particulars were madefirst and were carried out very completely. In thelater tente with modified particulars, certain caeeswere omitted which the ftrst teste had shown to berelatively unimportant.

state(5) Graphical records were made of the steady-fully developed, porpoising cyole for allteetsin which propoi~lng occurred.(6) Thestablllty limit is arbitrarily definedas the trim at which the total eweep In trim angleduring porpbising (that 1s, the double amplitude) Is2. ThIS deflnitiop IS of greetest eignificanOe inconnection with lower-limit porpoieing, where theamplitude tends to blow up progres~ivcly; In theease of upper-llmit propolslng, wh~ch tands to etartsuddenly and may often consist principally of verti-cal motion, an arbitrary definition of the stability.limit is largely unneaesearymThe limits shown In the charts are for normaltall damping, and ars lifted from auxiliary chartsof the sweep measured on the graphlcal recordsagainst the steady-motion trim angle, at constantspeed.


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ACCURACY .The nccurncy of the rendinps from the v=trlous martsof the Dnarntus and to-line gear has be9n chucked by fre-quent calibration, mnd it IS b-lieved thqt thq valu=sused In preparing the curves era corr-ct within the fol-lowng limits:

Speed, foot ner second . . . . . . . . . . . . . . +0.01Resistance, povnd . ..o q q ..- q . ..* q ... . q +~o 01Trim, degree. . . . . . . . . . . . . . .~. . . +0.3Trimming mom~nt, mound-inch . . . . . . . . . . . +0.1Disml~cr=ment, mound . . . . . . . . . . . . . . . ().~5Anoth?r method for anprnislnp th- mccurqcy of thnt~st~ Is to compar= the ram~oduclbil!tv of fully davelopedPornoislnp cycles. Wh=n the ampqrqtus w-a fir8t nut intoUS9, this mntt~r wns giv~n considerable mttention. It wnqfound that records of mornoisinfl CYCIPS obtained nt inter-vals of s=vrnl months, under presumn%ly identicml condi-tions, were ~s n~arly alika as they could h= m-asured.In n mora rec+nt c-8P, two modele built to the same linasand testsd 2 r=~rs mr~rt FRV* practic~.lly 5fi9nticql re-sults over the entire sp99d rhnga. Thug it was not con-sidered worth vhile to c~.rry on nny syst~matic nro.rram of

check tests during the nr-se~t investigation.The models were very c~rafully constructed nnd it isbeli~ved th=t the avarage deviation from tha lin~e was notmore th,n +0.01 inch. SD3ci.11 cnr? wns t%k~n to ~roducesharp edges at the stop ~nd chines ~ad to Avoid eny smnlllocnl irregulmriti9s. ?h~ models wve mqde of white nineand covered with four Cents of spar v~rnlsh rubbed downto Q very smooth finish with wet s~n?maper between coats.The avera~e length of time required to construct a modelwms shout 48 man-hours witk qn n~~itional ~ m4n_hourg for

setup nr?psrmtory to testinp.TEST R?ISUITS

Ths graphicnl records of the tnst result~ w+rmmountqd directly on lqrg9 chnrts, one for t=achs-t ofparticul~rs. One of these larpe charts, for th~ rpfpr-ence shim, hss bnnn suf~ici~ntly rn~ucafi in sigma to p=r-mit:includinp it im this rmmort mnd is shnvn ES firurm fj.

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This iype of ohart IS ooneidered an important presentationof the results beoauee it provide~ a oomplete comprehen-sive view of-all the porpoising oharacte.rlstio.s UrI@@X agiven net of partioulare and not merely of the takabilitylimits.

Desorlptlon of Large Chart - One forEach Series of !l!este(fig. 5)*

(1) The ordinates are trim angles that are meae-ured from the base line, which make~ an angle of 2with the forebody keel; the abeclesas, speeds.Speed soalee are given for model and chip speeds andfor the speed coefficient Cv q The Stevens Tankspeed numbers for the various fixed speeds at whiohteete were made are given at the foot of the verticallines drawn at these epeeda.

(2) The graphioal records of porpoleing areplaoed on the chart with the small cross, which ln-dioates the steady-motion attitude, at the height ofthe observed trim and longitudinally to the right ofthe vertioal speed line, on this line, or to theleft of it, depending upon whether the tall dmmpingwas one-half, one, or two times the normal tail damD-ing, respectively. Values of the trill damping areIndicated at the tops of the vertioal speed linee.

(3) A cirole with alternate a.uadrants blaokedIndicates that a test was made but that the motionwag stable.(4) The reoords are placed on their sides, eothat inoreaslng heave oorr6sponds to progressiontoward the left of the chart and increasing trim,

progression toward the bottom. The short horizontaland vertioal lines, respectively above and to theright of a reoord, Indioate %ero trim angle and ~eroheave from the etatfc flotation corresponding to140,000 pounds in the ship.(6) I!?otee-are givdn defining the ~anges of trimangles within which the forebody or afterbody waeobserved to be wet or olear.

~This desoriptlon applies partiou~arly to the larger sizeof theee oharts, In reduoing, for fig, 6, oertaln detailshave been omitted.

re-m-m , ,. . . .. ------ .-.


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(6) The thrqe curvqs .ranrssent th= fre=-to-trimtrack* for the hull In gt~mdy mot!on, the umnar stq-billty limit, Rnd the low~r stpbillty limit.

(7) ~hg atbility limit is arbitrarlqy dt=fln~dss th= trim at which t~s total sv-qn in trim snFle durinp morpolsing Is 2 . Th=! limits shown are fornorm-l trill dmmping =nd are lifted from auxiliarycharts of trim ewe?m, ns m~n%ur=d o= the pr%nhicalrecords, plotted against st-a~y-motion trim anple ntconetmnt appqd.In order to pmmlt remdw comnariaon of the tpst rrn-aultao the atablllty llmlta have been taken off the lqrfecharts described abov9 and presented In the form of sum-mnry figures, each of which shows the atabllity llrcitafor all the modification of oE~ vmrlnble. These summmryflgurea conatltute the princirnl presentation in thte re-port :

Description of Summary Fi@rea - One for All Modificationof Each Variable (figs. 6 tin 30)

Included are:Stability limits (fer 2 oscillation) -solid curves cross-hatch-d onunstable aideFree-to-trim trncks -center-lin~ curvesTake-off trim tracka -

dashed curves

Free-to-trim r=sist~ncqs---.--- ------- ------- ------- ------- ------- ------- ---------*The trim track correamondine to reaultnnt n~rodyrn~micmomenta about the canter of pravity equal tri zaro, aa ob-tnin~d by interpolation. It Is for tha hull, mlfin-, andnot for the comnli=t~ airnlanp.

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Applied moment and resletanoe against trim (at thebottom)-.. . . .. .... ...Oroee plots at four fixed speeds indicate-d

DISCUSSION Or RESULTS

The effects of eaoh yariable or modlfloatlon coveredby the teste are discussed below In come detail. It ISIntended that referenoe be made, in following the disous-slon, to the summary figures described in the precedingsection.

It has been mentioned previously that the aim In lay-ing out the program of experiments was to change only one variable at a time, thereby isolating its effects. l?atu-rally the program was not entirely successful in this re-spect; in certain cases, two or more of the variableslisted were found to eonetltute essentially the eamechange from a hydrodynamic point of tilew. Where this 5sclearly the aa8e, It is noted in the discussion.

Group I - Weight and Inertia Loadings (Chart 1)(1) Modification

120,000140,000160,000200,000Porpolsing.

of gross weight (fig. 6)pounds 86 percent(normal) 100114143Increasing the groes weight move~ the

range of stability in the direction of higher trimanglen and leaves the width of the stable range vir-tually unaffected. The speeds at which porpolsingetarts are delayed by increasing the gross weight,and the free-to-trim track Is shifted to higher trimanglee In the viwinity of the hump. The free-to-trimtraok tendg to cut across the middle of the stableranges f or all groes weights. .,Eeeletance. Not Inveetlgated (exoept for the normaloaee).

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(2) Modification of moment of inertia (fig. 7) .o.g16 x 10e slug-faeta . 60 percent1.366 (normal) 100 ..1.716 IZ62.049 150Pornoislnr. Increasing the mom~nt of inertia re-duces very slightly the range of stability mt lowsp~eda. The mrincipsl consequence of increasingthemom~nt of int=rtia is to increase the -ormoisingamplitudes und-r othfirwise identical conditions,The norpoisinp freauency is r~duce~ nlso, anmrnxi-mately in Proportion to the increasin the recim-roc.1 of th9bti~ qresistanc~.

(3) Modification ofgrnvity (fi@.

square root of th= radius of gyrntion.This modifieat.ion could not aff9ct the

lcngituflinnl position of center nfq)67 inches forward of step zJ.Tpercent bw+mforwardofstep70 (normal) 3.250 30. gThe center of gravity was shifted by altsring thelocation of the mod~l pivots and rehqllastinp.Since the hydrofoil lift is annlied throuph themodel pivots, this procedure is equival~nt tn Plter-ing ths centar of grnvit~ and thm wing nosition si-multaneously and does not introduce an additionalmoment du9 to lift.

Pornoising. Shifting th center of gravity sitherforward or nft has only n vpry slight eff~ct on therqnge of stability at moderate smeeds. The nrinci-DR1 consq~uence of shifting the center of ~rnvitF isto shift bodily the curves of ~pplied mnm~nt, theresult b9ing that a different moment is renuireil tomrcduce the s~me trim angle in stnnd? motion. Aswould be expected, th+ rea~ired chqnpe in annli~duoment is eaual to the net wipht on thq watr timesthe shift of tk~ center of pravity and the vin~,~m q Hot investigated for the free-to-trimcondit!on (~xcemt for th~ nnrm=l cas~).


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&oup II - Aerodynamic Conditions (Chart 2)(1) Modification of wing lift !?0 nt T = 5(fig. 9) .

. - . ,, , . . -.4:m~3V8a poundta . 67 p9rcent -6.95 Vaa (norm=l) 1009. 27 V~a 133Chi:nging the.wing lift was accomplished by ohmneingthe angle b9tween the normal hydrofoil ~nd the hullbase line .which eimulmtes P chnnge in the inaid~nceof the wing. This left dL/d? and dL/dw. unchav?d.~orpolsing. Increasing the wing lift mkk~s thb stP-ble rang9 ~ppreclahly wid-r, chiefly b?r lowerlng th?lower limit at moderwt9 sr.eeds. The largest lifttested prevented up~er-llmit pfirpoising at hi~hspe~du . Increaslnfi ths lift low-rs the fre=-to-trimtrack at modsrate speeds just nbove the hump, sothat its relation to th~ lower limit of stability isvirtunlly un%ffectmd.Res3stnnce. Not Investigated.

(2) Yodificmtlon of win~lift rate TQ (fIF. 10)0.344 Vsa pounds ner degr~e 75 m=rcento.45t? Vsa (normal) 1000.6s7 V*= 150Changing tha wing lift rate was accomplished b= al-tering the hydrofnll size. This produc~d a corre-spnndi~ change In the value of dL/dw. The lift atT = 5 wae unchanged from ths normal lift in allcmsea. (In later teste, describ~d below, dL/dwwas changed independently.)PorDolsing. Increasing the wing lift rate has prac-tically no effect on the stabil~ty limits at moder-at9 spends and decre%ses the range of stability veryslightly at high spends. !Chq freq-to-trrim -trmck isunaffected .at moderate speeds just over the humm.Eesistance~ Rot lnveati~ntqd.


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20 .

(3) Modification of vertic~l velocity dqmping & (fig. 11)0.J5g ti~ pound-seconds per foot (normal) 100 pero~nt0.916 VB 200By means of a specially constructed dnshnot which wasattached to affect only th~ haawlng motion, the rateof chsnge of lift with vertlcnl velocity wqs doubled.l!his chanpe in the ap~sratus Is shown in the secondsketch in figurs 31. Thta t.gts were l~~ited to thrt=espeeds nnd to normal tnil dnmning.Pornolsinp. Study of the mormoising cycl=s on thagranhical recnrd8 flle to r~vmnl an?? ~nnrecia~~edifferences when dL/dw iS dfiublad.W9sistnnce. This mmdificatlon cnuld not nff=ct theresistance.

Note, The r=sult~nt aerodynamic moment M. is altered inthe course of each smies of tssts and is not mroprlyconsidered an independent varihble.(4) Modification of tail moment rate Me (fig. 12)

O.gg v~ pound-feet per deprae 71 perc=nt1.37 Vs (normnl) 1002.05 vs 150?0 rpoislnu. lncr~asing the tail moment rate hmslnonoticeable effect OE either stability limit or on therange of stability. Ths largest moment rat~ used n.p-preciably reduced thei size of the steady-stnte cyclesIn lower-limit porpoislng at high speeds, and therewas also a tendency to supprsss umer-limit porpolsingat very highR9sistmnce.r9slst~nce.

(5) Modification

sp9ads q -.

This modification could nnt affect the

of tail d~mplng rate Mq (fig. 13)o x 104 V8 nmnd-foot-s=conds mer radi~n ~ p.r~ent2.024.05 Vss ;:g.lo Va (nbrmal) 10016.2 Vs 200


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21

. .PorpoiOing. Inoreaeing the damping due to the hor.i-sorital tail surfaoes lowers the lover limit at allspeedsf the amount inoreaeing with speed- from nearly%ero at the epeed at which lower-limit porpoie~n-getarte to a very large amount at high epeeds; at agiven high speed, the effect on the lower limit pro-gre08ively deoreaaee ae the tall damping Ie Increaaed.Increasing the tail damping has no appreciable effeot on the poeition pf the upper limit but has a tendenoyto delay the speed at whloh this type of porpoleingetartsm The largest damping used (twlee normal) pre-vented upper-limit porpolsing in the region of get -away mpeede.It 1s worth noting that, at 19 feet per seoondi mod-el speed (about 70 mph ship speed), upper-limit por-polelng frequently could not be suppressed dith 20times the normal tail damping and occasionally 80times was not sufficient~ In a few instanoes, lower-llmit porpoising wag not entirely suppressed with 20timee the normal damp5ng.Resistance. This modification oould not affect theretaistanoe.

(6) Inolusion of phase angle between qXMq, and q (flgJ 14)

It had been auggeeted that, in the full-size atrplaherthere might be a time lag between the pitching ve-looity and the pitch damping moment produoed by thetail. Speolal teste were therefore run to investi-gate this matter. The phaee angle was Introduced byputting a small calibrated spring between the dashpotpiston and Ite pleton rod. Teets were run at approx-imately the three lagging phaee anglee ehown above,at eaoh of three epeede, and with various valuee ofthe tail damping rate.Porpoising. The teet reeulte ehowed that the great-eet of the lagging phaee anglee ooneidered wae theonly one which had any noticeable effeot whateverand that ite only effeot wae to ralee the lower limit .very slightly at the loweet speed Investigated.


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. . .


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24 .

that, at rest and at displacementn speeds,it provldee flotationthat, at moderate epeedg up to the hump, Itcenitrols trim and resistance and preventmlower-limit porpolslngthat , at planing speeds, It is the dlreotcause of upper-limit porpoising and some-what increases resistance

(b) That the forebody 1s entirely self-suffi-cient at planing speeds and needs no helpfrom the afterbodyThese indioatione suggest clearly that the forebody Is the main hull and that the afterbody Is an append-age, the function of which is to control trim (byproviding nosing-down moments) until true planing ofthe main hull is established.

(2) Modification of afterbody angle (fig. 17)2 between forebody and afterbody keels~o4050607 (normal)94012The afterbody angle vas increased by rotating theafterbody at the model deck and shifting It vertl-oally so that the step height was unchanged; It waereduced by rotating the afterbody at Its keel, leav-ing the step height unchanged. .Porpoisin~. Increasing the afterbody angle raieeethe lower limit at moderate epeedsand causes it tostart at a slightly lower speed but has no appreci-able effect on the lower limit at high speeds; theupper limit is raised and, with the two greatestaftorbody anglee, the upper limit is suppressed athigh speeds. Reducing the afterbody angle lowersthe lower limit at moderate speeds and ehift8 its .starting point to progres~ively higher speeds butagain hae no effeot on the lower limit at very high


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. ... .. . . . . . .. . . . .. .. .. ... ... . .. .

as....-

upeede. The upper limit is lowered at all speeds.and Its .etarting point shifted to progressivelyhigher epeeds. With afterbody anglee lees than nor-real, the high-speed upper-l-trnl% porpolslng beoomesincreasingly ~iolent ae the angle is reduced.Resistance. The afterbody angle for optimum hump re-sistance appears to be about 3* for this. hull; withangles greater or less than this the hump.resistancesare oonslderably tnoreaeed. Thie is consistent withthe Findings of reference 6 in a general way. Atvery high bpeeds, the optimum trim and resistance arenot partloularly affeoted by afterbody angle.

(3) Modlfiaatlon of afterbody length (fig. 18)2.25 times beam at main etep2.76 (normal )3.25

The afterbody length wae altered by applying a oon-stant multiplier to the station apaoing and movingthe stations in or out along the afterbady keel.Thuo the afterbody angle and the etep height wereunohanged.Porpolsing. Decreasing the afterhody length raisesthe upper limit elightly an-d hae only a very smalleffeat on the lower limit at moderate epeede #ustpast the hump; the speed range over which the free-to-trim traok passes below the lower limit ielengthened slightly. The ehortest afterhody testedstopped high-speed upper-limit porpoielng in thepresent Inetanoe. The effectm are generally similarto thoee resulting from modifying the afterbodyangle.Resistance. Only the free-to-trim re~iatinoe wan in- .vestigated in thie case. Inoreaeing the .afte~~;dy - wlength lowers the hump resistance eomewhat.ehortest afterllody ueed had a very high resletanaepeak Just before the true hump, though thle presum-ably might have been elim.tnated by relocating thetail oone. ---- .-

. - -_ - - ___ ..


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.

a6(4) Modification of afterbody

Chine flare removedNormalExtended .

chine flare (fig. 19)

. .The normal afterbody chine flare ends abruptly, form-ing a partial step a little forward of the sternpost. Two modifications were tried (1) extendingthe chine flare aft so that it washed out at thestern poet (2) removing all the chine flare.Porpoislng. Extending the afterbody chine flarelowere the lower limit very elightly at moderateepeeds and leaves the upper limit praotioally unaf-fected. Removing the afterbody ohlne flare raldesthe lower limit elightly at epeeds ~uet beyond thehump and raises the upper limit ellghtly, and pre-vented ?aigh-epeed upper-limit porpoieing in thepresent tests.Resistance.. Removing the afterbody chine flarecaueee a high peak in the resistance before the truehump and slightly Inoreaees the true hump. The veryhigh peak appeared to result from water clinging tothe afterbody eides and running up the tail oone.Eemoving the afterbody chine flare had almost no ef-fect at h~gh speeds. Reelstance tests were not runwith the afterbody chine flare extended.

(5) llo~~~~ca;;yn of height of main step - firet eeriee91 peroent of beam36 (normal )7

The etep height wae altered in thie seriee by ehift- .Ing the entire afterbody vertically with reePect to .the forehody.Porpoielng. Increaelng the etep height in this wayraieee the lower limit at moderate epeedo juet pastthe hump but hae no appreciable effect at higher~peede. The upper limit Is raleed at all epeede andupper-limit porpoiaing at very high speede ie sup-

.

,.


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27

preeeed. When the step height is ~eoreased, the vlo-lenoe of the high-speed upper-limit porpolslng isprogressively Inoreaeed until, with the lowest height-tried,. thi-s t~e- ofporpotdihg. id eiibdjtSonallyio-lent in the region of get-away.Reslstanoe. Only free-to-trim resistance was invee-tlgated. Inoreaslng the step.height .elightly.in-oreases the hump r.esietanee and reduoes the high-apeed reaiatamoe. . The8e ind~oations are.consistentwith those found in reference 7. . .

(6) Mo~~~;oa~;fn of height of main step - seoond seriesq

1 percent of beam5 (normal)913The step height was ~ltered in this series hy rotat-ing the afterbody about the intersection of theafterbody keel and the ~tern post in the normal hull..Thue the posl.tion o.f the stern post was unaltered.. The tests were oarri ed to a greater maximum stepheight than in the fir~t eerles.Porpoising. Increasing the step height In this way.has practloally no effect on the lower-limit at anyspeed or .on the position of the upper limit. Theetep heights greater than normal again suppres~ed thehigh-speed upper-limit porpoising tind the 1 percentstep height gave exceptionally violent high-speedupper-limit porpolsing.The position of the free-to-trim track suet pact the hump IS not affeoted when the step height Is alteredI n thie way.Eeelstanoe. Increasing the step height has praoti-.oally no effeot on the true hump but deoreases thepeak before the true hump. At very high speeds theresistance appears to be slightly decreased by in-oreaslng the etep height to Greater thaa n~rmal.

(7) M.odifloations of afterbody dead r i s e at stern point -no ohine flare (fig. 22)


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28

-10 dead ~ise at afterbody stern post00100 . .200 (normal)~oo

The afterbody was warped by leaving the dead rise atthe main step unchanged and altering the dead riseat the stern post; the buttooks were kept straightlines. The Step height and the angle of the after-body keel were unaltered. No afterbody chine flarewas used.Porpoising. Decreasing the afterbody s~ern-postdead rise has ~ractioally no ~ffeat on the lowerlimit at any speed but lowers the upper-limit at all

. speeds, Possibly because of the absenoe of after-body chine flare, the high-speed upper-limit porpois-ing was suppressed in all oases. The stern-post deadrise whioh-~auses the greatest suppression of thehigh-speed upper-limlt porpoi.sing was found to be. about 200. lrom the standpoint of upper-limit por-poising, stern-post dead-rice angles between 10and 20 appear to give the b;st all-round results.

. Resistance. Decreasing the afterbody dead r i s e atthe stern post causes an appreciable deorease of thediscontinuity that appears before the hump. !Chetrue hump resistance is also lowered but to a muoh

. lesser extent. At very high speeds, the resistanceis not altered materially, but 10 dead rise appearsto be about the best angle.(8) ventilation of main s tep for step heiglit of 1 percentrough preliminary trial (fig. 23)

.

}Ho ventilationVentilation Step height 1 percent beam

Ventilation of the ma~n step was accomplished byshifting the afterbody (set for 1 percent stepheight) aftward along its keel by 5 percent of thebeam and leaving open the gap thue causnd. Theafterbody angle remained unchanged from the normal.The teet~ are looked upon as very preliminary innature.

.

.

-.


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.

29

. Porpoising. Ventil~tlng tihe ~inetep in this wayraises the upper limit slightly and entirely aup-preeees high-speed upper-limit morpoising. Thelower limit waO not invet3tSgated.The effect of this ventilation, even though impos-sible to construct f~om a praotioal viewpoint, isremarkable in that it suppressed entirely the veryviolent high-speed upper-limit porpoising (the mostviolent yet encountered.) whiob oocurred with an un-ventilated 1 peroent step.BesietaE3e. Hot investigated. .9

.Group IIIE - Eorebody Dorm (Chart 3) a

Drawings of modifications are ehown in figure 33. Themanner In which the various modifications were car-ried out should be especially noted. .(1) Modification of forebody form - first series of warp-ing (fig. 24).

Con~tant eaotion (mi~imum warping)I?ormal foreto~yLinear dead-~iae variati.n (maximum warping,dead rise &hanges 9.7 per beam forward ofA

step)The firet forebody In this group had the same lengthas the nor=al forebody, but all the eections of thenormal foreLcdy were compressed into the forwardhalf. !i!heafter half had the un~form seotion found at.the main step in the normal hull.The Xhird model was constructed with a linear varia-tion of deaa rise from the forepoint to the mainstep. The step section, the profile, the chine pl~form, and the deaa r i s e near the forepoin.t were un-altered.Both modele were tested with the normal afterbody.These models ~ be oonsiaered as belonging to agroup in whioh warping of the forebody bottom nearthe etep is the variable, the ohange of warpingbeing-small between the first and the normal modelsand large between the normal and the third =odelm.

- .. ..- . . --. .. ----


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. . _ - . .. . - . ______.

q

Porpoising. Inoreased warping of the forebody bot-tom l~wers the lower limit very materially at allexcept the very lowest speeds and very slightlylowere the upper. limit at sJ1 speede. At humpspeeds, inoreaeing the warping of the forebody bot-tom hae no great influence on the free-to-trim trackbut #overs it materially at higher speeds.

. R6eietance.. Increasing the forebod.y warping in-creases the hump resistance appreoi~bly, and also in-creasee the resistance at high epeeds when the after-body is clear. This ie consistent with the findings. of referenoe 8. .

.

(2) ~o~~~~oa::;n of forebody warping - eecon~mseriesq

.Dead:rise changes 0 per beam forward of step2. 7 .. . 5. 40 . .8.1010.8.

The forebody warping in eaah aase wae linear from. step to forepoint in exa,otly the same manner as Inthe linear-dead-rise-variation model referred toab ov.e. This resulted in having ver~ low dead risein the forward half of the forebod~ in most oases.The serlee wae built to explore the effect of fore-body warping more s~stematically than in thd firstseries. qP0rpo3.elng. Increasing the warping of theforebodybottom very appreciably lowers the lower limit athigh speeds but only slightly at speeds Just.beyondthe hump.. The uppe r limit 1S aleo lowered, but to avery much leseextento Increasing the warping of theforebody lowers the free-to-trim track at high speeds.These effe~ts are similar to thoee found in the firstserietit. .

It was found that the two models with a dead-riseohaage of 0 per beam and 2.7 per beam had noticea-ble tendencies toward diving at very high speeds andlow trim angles.. Thie iS undoubtedly due to the howseo%ions having insufficient dead rice and ie of lit-tle interest here. q . ..\:#

q.

.

..

-~~:::.:.,+~-% F . . .. .. .-. .... ----- . ..+... . . . . . . ,*:*#< ., ,.. -.


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Resistance.creaee~ theepeeds.

(3) Modification

Inoreaelng the forebody warplngreeistanoe, at both the hump and

of forebody length (fig. 26)

31

in-planiag

2.82 times beam at main stepa.44 (normal)4.07The models In this group all used the same forebodyseotions; the alteration consisted of applying a oon-stant multlplter to the station spacing. The sta-tions were shifted in or out parallel ts a line tan-gent to the normal forebody keel at the step. !Chemultipliers for station spaaing were the same as forthe modifications of afterbody length (group IIIA.ohart 3).In the planing range, the alterations in this groupmay be considered as oonstitutlng small ohanges inthe warping of the forebody.Porpoising. Decreasing the forebody length slightlylowers both the lower @nd upper limits. With theshortest forebody, the hull swamped at speeds belowthe hump; no difficulty was found at high speeds,however, when steps were taken to support the modelwhile it passed over the hump.Resistance. Decreasing the forebody length increasesthe hump resistance appreciably and the resistance atplaning speeds sllghtly.If the alterations are considered as changes of fore-body warping near the step, then the trends in re-sistance and porpoising are the same an for the twopreceding series.

Group IIIH - Hull Form (As a Whole)(Chart 3)Drawings of modifications are shown in figure 33. Themanner in which the various modifications were oar-ried out should be especially noted.

(1) Modification of hull length (fig. 27)

.. .. ---- ---- . ..- ---- . . . . . ----- ----- .- ..-. . . . .. . . .. . .


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. .. &- .... -

#

... ...

32~.~~ timgs b?am nt main step .. (nnrmal)7:32

The hull length was altered by joining the altered-length forebofi.les (group IIIF) to the simllmrly al-tered afterbodles (group 1114). The stap height andthe afterbody angle remaln~d unaltered.Porpol.sing. Increasing the hull length lnwers thelower limit ~er~ slightly -t low speeds and raises itslightly-at higher spe=ds; the umpsr llmit is loweredvery slightly. The frae-to-trim track in the regionjust pact the hump, where It is important, is virtu-ally unaltered.. .Resistance. Increasing the hull length very appre-ciably reduces the hump resistance. At planingspeeds, the-resistance Is v~ry slightly reduced.These effects -.re consistent with those uentioned inreference a. .

(2) Modification of hull dmd rise (fig. 2g)0.5 tdmes normddeadz%ee at-e& stat~on(10 at step) .1.0 (20 )(normal)1*5. ( 300 ) ...The hull dqad rise was altered bv multinlyin~ thede~d rise at e=ch etation by the same constant. Thekepl prnfile was unaltered, but the chlnqs werech~nped ms necessnry. Th~ chine fl~r.s w-re in-creased In-proportion to the dead rise.

K%%#i Incr~asing the hull d~ad ris~ raisgaimit quite mntsrially and lowers the upmerlimit scmewhst. The spe~ds at which both the ummerand the lower limits start are proprasqlvely increasedwith increasing hull dead rise. .In the vicinity of 14 f-et mm sqcnnd, model smfied(about 55 mphfor thq ship), the upmer and lowerlimitg almost come togeth=r wh~n the hull dsad ~iseis 10 . Thus it would be nearly impossible for such.ahull to take off without passin~ through a regionof instability. dhen the dend rise is 30, there isonly a small gap between the upper nnd lowqr limitsat eneeds near get-nway.

.


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33R98i8tance. Increasing the hull dem.d rise increas~sthe .reslstance appreciably at nll planinf sm~=ds.!l!he.true hump .r?si-stance $s got preatly affected but..ie learnt with 20 hull d~ad rise. Jith both 10 and300 de~d rise, the nfterbody chine flare Pppsared in-sufficient to prevsnt con?id~ra?)le nid~ mnd tail-cnn9wetting at low eps~ds and, thus, 4 lmrge reslstnncepeak before the true hump. Thesa findings are ingenerml agreement with thoss In referance 6.Spray. No mmasurem?nts wera mad~ of volume or heiphtof the spray, but increasing the hull dend rise ap-pear=d to lowsr the height of the spray rindto mak~~he hull much cleaner running. - -

(3) Modification of lon~ltudinnl sten pmsition (fi~.541 inches fitoffor=pcAlt[h&?tt~)10.5ercentbeam forward)ssg57g (shlfkd 12.4 merc~t %e~m-t)The lrnritudinal nflsition of th mnin qtm wa= altredby mxtendin~ or chom~ln, off the nri~inql fort=bofly andnlterinp theafterboily length in the omnosit= e=ns~.The stem heipht, the angle betwe~n ths qfterbody ke~land b9se lln9, =nd the longitudinal locntion of theetern Dnst were kent unmlterd.The net result is that of combining several of them~difications alrec:dy considered. ?h.n th~ ste~ ismoved forwnrd, the forebody ie short~ned and itswarping very slightly increased, the afterbofi.y islengthened, and the afterbody snple -is in ~ff~ctslightly reduced; also, the center of pravity isfarther sft rslmtlve to the step.This modification wqe includ9d mainly becnuss shift-ing the step is a r~latlvely simnle change to cnrryout in full size.Porpoisinu. Moving the mnin stem forw~rd lflwers tkelower limit v-by slightly at =11 spe=ds, as ul~ht baexpected from the slightly increms~d wq~$ng of theforebody hottnm. The upper limit is sl~btly lowsredat all speeds, agnin ns ml~ht be expected from thedecreased equivalent afterbody angle.


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.34

Moving the main step forward has substantially thesame effeot on the moment curves as shifting thecenter of gravity aft by the came amount. The shiftof the moment curves ie equal to the weight on thewater tlmem the diatanoe the step 1s moved.Reeiatanae. Not investigated.

(4) Modification of plan form of main etep (fig. 30)45 ewallow tallTransverse (normal)450 v .

The plan form of the main step was altered withoutchanging the keel lines of either the forebody orthe afterbody. The amount of planing area shiftedaft of the normal transverse step was balanced byremoving an equal area forward of the normal trans-verse step. This left unaltered the Imeanltrans-verse step and. step height.Porpoieing. In going from a swallow-tail etep to aV-etep, the position of the upper limit Is raisedappreciably and the in~ensity of the upper-limitporpoislng, increased. At moderate speeds the V-steplowers the lower limit, acd the swallow tail raisebit. The situation is reversed at high epeede butthe effects ar e not HO marked.Resistance. The plan form of the main step does not .have any appreciable influence cn the true hump re-slstano refere~ae g ). The V-step, however, de-creases the height of the peak in the resistancecurve before the true hump. At high speeds, the V-step appear~ to have highest reslstanoe and the swal-low tail the lowest resistance in the region Inwhloh the afterbody is wetted.

COMMENTS ON THE TESTS

In a broad sense, lower-limit porpoislng and upper-limit ~orpolslng are distinguished, beyond the differencein the general region of trim angles in whioh each oocurs,by the differing character of the porpoising motions.


36/74

Lower-1imit porpolslng IS largely a phenomenon of the fore-body alone, while upper-limit porpoising depends upon boththe forebody and the afterbody and their relation to eaohother. In low6r-limit porpo~eing, the motion 1s smoothand regular and the afterbody is, in general, olear of thewater. In upper.-limit porpolsing, the motion is very. ir-regular, though consistent in suooessive eyoles in a givenease, and the hull appears to be thrown baok and forth,the forehody and afterbody alternately carrying the bulkof the water load; the motton tends to have large ampli-tudes Sn heave and relatively small amplitudes In pltoh.

By referring to the ohart In figure 5, vhioh showsthe graphioal reoords of porpoising for the normal alr- plane, It is apparent at onoe that the amplitude of lower-limit porpoising is relatively insensitive to ohanges totrim angle and damping rate at speeds near the hump butthat it beoomes increasingly sensitive to both as thespeed inoreases and is extremely sensitive at high speeds.This menns, in effect, that from a praotioal point of viewlower-limit porpolsing Ismuoh more dangerous at highspeeds than at low.

Upper-limit porpoising starts at higher speeds thanlower-limit porpolsing. It develops very euddenly a~ thetrim angle exoeeds that at whioh the afterbody takes anappreciable fraotion of the load, though a large changeof moment is ordinarily required to bring this about.The droop of the upper-limit curves with Inorease of speedappears to be oaused by progressive ohanges in the shapeof the roach left by the forebody. As opposed to lower-llmlt porpoising, the amplitude of upper-limit porpoisingIs ordinarily quite insensitive to ohanges of dampingrate and to the epeed; the motion is essentially violentat all times. The speed range over which it ooours oanoften be slightly reduoed at its ends by inoreased talldamping; at speeds in the middle of the range, however,Inoreaslng the damping rate to 80 times normal quite fre-quently hae little effeot.

A few speoial tests were made under the normal par-tloulars to explore the range in trim angle of upper-limit porpois.iqg. ,The indication that upper-l~mit por-poising was encountered when, with increasing ~rlm angle,the afterbo-dy would have taken an appreolahle, fraction Ofthe total load if the motion had remained steady suggeste~ .that this type of porpoising might be eliminated and sta-bility reestablished if the bulk of the load were trane-

-


37/74

mm. .. . . . . . . . ..-. ..- - . . . .. -. mmm . n . . ... -. . m . ,,, -,,-,,.., s I

ferred to the afterbody. This was found to be the caee.Very large stalling moments - far beyond any magnitudesposeible in practice - w=~e required, as had been antic-ipated, and the return .+i~stable motion usually ooeurredonly when the forebody came clear - the entire load thenbeing supported by the afterbody. What had not been an-ticipated 1s the faat that the trim angle under theee con-ditioris can be less than that of the ordinary upper-limituurveg

CONCLUSIONSGroup I - Weight and Inertia Loadings

1. Increasing the gross load raiaes the trim anglesat whioh both the upper and lower limit~ of stability oc-cur and delays their starting to higher speeds.2. Neither moment of inertia in pitch nor the center-of-gravity position has any appreciable influence on thelimite of etabillty, though the latter has a pronouncedeffect on the moments and thus on the available trim range.

Group II - Aerodynamic Conditions1. The actual llft at arbitrary trim Z. and therate of change of lift with trim Zfj are the only aero-

dynamic variables which Influenoe the position of bothlimits. It will be noted that these two variables, incontradistinction to any other aerodynamic variables, af-fect the net load on the water in stead? motion. -2. The aerodynamic pitch damping rate q has a

large effect on the lower limit of stability at highspeeds, but its effect decseases ae the damping is in-creafled and is much less at damping rates near normalthan at lower damping rates. The damping rate has prtao-tloally no effeot on the upper limit of stability.3. None of the other aerodynamic derivatives has -appreciable effeots on either stability limit.

, , ,,.-. ,. -, ,, -. . ...,.. . . . .. , . ,,


38/74

Group 111A - Afterbody Sorm1. Modifioatione .whieh raise the stern poet have

the following general effeo t s :(a) Tofar enough,high s p eed s(b) .Toof the hump(0) Tovioinity of

ralee the upper limit and,. If carriedto Bupprees upper-limit porpolsing at

ralee the lower limit In the vioinity

raise the free-to-trim traok Sn thethe hump and the hump resietanoeThey do not affeot the lower llmit at high speeds.

20 High-speed upper-limit porpoielng was suppressedIn the present test~ by increasing the step height, byventilating the step, or by removing the afterbody ohineflare. This point needs further lnveStlgatlon.

Group IIIF - Borebody Yorm .1. Modlfioations which inorease the warping of theforebody bottom lower the lower limit of stability veryappreciably and the upper limit very slightly.

Group IIIH - Hull Berm (As a Whole)1. Increasing the hull dead rise raises the lowerlimit appreolably and lowers the upper limit moderately. .2. The step position has very little influenoe onthe stability limits, its ohief effect being to shift thernomeht ourves, as in the ease of a aenter-of-gravity ehi f t .3 . Ohanges of hull length have the oombined effeoteof Intependent ohanges of forebody and afterbody length.4. A ewallow-tail step has less intense high-speedupper-limit porpoising than a normal transverse step, butthe usual step has on the whole better stability oharao-teriotlos than either the V- or swallow-tail steps.

Experimental Towing Tank,Stevens Institute of Technology,Hoboken, N. J.


39/74

38

1.

20

3.

6.

6.

7.

8.

9.

. . .

..

Perring, W. G. A., and Glauert, H.: Stability onthe Water of a Seaplane in the Planing Condition.R. & M. Ho, 1493, British A.R.C., 1933.Klemin, Alexander, Pierson, John D., and Storer,Edmund M. : An Introduction to Seaplane Porpoislng.Jour. Aero. Soi., vol. 6, no. 8, June 1939, pp. 311-318.Coombes, L. P., Perring, W. G. A., and Johnston, L.:The Use of Dynamically Similar Models for Determin-ing the Porpoising Characteritatice of Seaplanes.R. & M. No. 1718, British A.R.C., 1935.Olson, Rolqnd E., snd Land, Norman S. : The Longl-tudlnal Stability of Flying Boats as Determinedby Tests of Models in the HACA Tank. I - MethodsUsed for the Investigation of Longltudinal-Stabllity Characteristics. llACA A.3.R., NOV. 1942.Murray, A. B. : Stevens Institute Opens ExperimentalModel Towing Tank. Marine Engineering and ShippingAge, vol. 40, no. 8, Aug. 1935, pp. 300-304.Bell, Joe W., and Willis, John M , Jr.: The Effectsof Angle of Dead Rise and Angle of Afterbody Keelon the Resistance of a Model of a Flying-Boat Hull.NACA A,R..R. , Feb. 1943.Bell, Joe W.: The Effect of Depth of Step on theWater Performatice of a Flying-goat Hull Model -I?.A.C.A. Model 11-C. T.II. HO. 535, NACA, 1935.Shoemaker, James M, and Parkinson, John 3.: TankTeste of a Family of Flying-Boat Hulls. T.Y. YO.491, NACA, 1934.Dawson, John R.: A General Tank Test of I!?.A.C.A.Model 11-C YlyinH-Boat Hull, Including the Effectof Changing the Plan Form of the Step. T.H. NO.538, NACA, 1935.

..... ., ..--, .,.,. , .


40/74

..... c

39TABLEI

DIMENSIONS lUIDPARTICULARS (lKU?MAL)FWIRIOLIAZEYLYIHG B(2AT~2M-1 &lD ~SCAIJd MOIXUL -

Dimensions Full sizeieamatmaineteg, i.n . . . . . . . ...162alngle between f orebody keel andbase line, deg 2.0bgle between after~o~k~ei ~ base llne, deg...... . . . . ...5.0Height of main step at keel, In . . . . . g.1Center of gravity forward of mainstep (26.5g percent M.A.C.), in . . . . 70Center of gravl~ above base line, in . . 146.7Gross weight, A, lb . . . . . . . . . l@,000Load coefficient, CA (EeaW8t~) . . . . O.ggMoment of inertia in pitch, slug-fta . 1.366 x 10=lb+na . . 6.32g X 109Wingspan, ft . . . . . . . . . . . . . .200Wing area, S, aqft . . . . . . . . . 35a3Mean aerodynamic chord, M.A.C., in . . . . 249Aspect ratio (geometric) . . . . . . . . . 10.C7Horizontal.tail area, sq ft . . . . . . . 50gElevator area, aqft . . . . . . . . . . . 143.7Distance e.g. to 35 percent M.A.C.horizontal.tail (tall length), ft . . . 63.6Thrust line above base line atmainetep, In . . . . . . . . . . . . .230.3-at line inolined upward tobasellne, deg . . . . . . . . . . . . 5.5

1/3 O-scale model5.402.05.00.27

5.19 f.w.2606.674.~2&3010.670.5650.1602.127.6g5=5

Ratios & n-sizeModelIlnveloolties, A . . . . . . . . . . . . 5.477linear dim&eions, A . . . . . . : . . j.ox 10areas, i% 9.OX 1083-0 0 q * = q vohnesg A . . . . . . . . . . .= . .4 27.ox 103momenta, A . . . . . . . . . . . . . . En.ox 10:moments of inertia, As . . . . . . . . 2QJ.OX 10

aSee footnote on p.40.


41/74

---- ___ ______ __ ----

. .40 %

!l!KSEEIDINEHS1ONS AND PAIITI(XJIARSNOIUUZ) RORFUL&SIZE ELYING

BOAT .XE62M-1AND ~-S~ Mm (Continued)14erodynamlccharacteristics Pull size l/30-scale model~&3tT=0

7(relative to base line,fl&ps,30 . . . . . . . . . . . ..l.slvj l.ggb

Lat TsbO . . . . . . . . . . . . . 695 v:(c) 7.72 X10-3 V=d~/d T . . . . . . . . . . . . . . . . 0.1045 0.1045dL/d7 (dZ/de), lb/deg . . . . . . . . 0.4513v~ .0.509 x 10-3v~

()dL/dw (dZ/dw), l&sec/ft ~$ . . . . o.@3 Va 0.509 X10-3Vq#%L=%w/d+J ====o 0=0150 0.0150dh! /dT (dM/dQ), lb ft/deg (ay.) . . . 1.365vgI 5.05 x 104 VabdM/dq,lb ft see/radian . . . . . . . . ~020 x Va 9.90 x 10-3 vdM/dw, lb sec (m.) . . .. . . . . . .. 7g.3 Xve 2.90 )(10-~ v

+dlf dq ft/radian . . . . . . . . . . 102.5dlidw /dq /Tail length, l/radian . . . . .dM/dw 1.61

3.411.61

Get-ew~epeed, f@... . . . . . . . 130 23.74Get-av~ ~ . . . . . . . . . . . . . 1.E90 l.ggoGet-away T. deg. . . . . . . . . . . g.g g.g

~All trim angles measured relative to the baee line.Contributionof horizontal tail rirface only.csub~cript s is for full size.


42/74

NACA Fig. I

eradicating CHART OF VARIABLES

zr

GROUPm

SECOND STEPFig. I


43/74

..

IT

/

Fig. 2

PARENT FORM / /

7

III I /// I

/

----- ----1StationNumbers are Inches Aft of Forepoint on Full Size.

Fig. 2


44/74

d

WALKINGBEAM

TRACK~ mnY 11?@i;I

1 TOWING CARRIAGEROLLERSUPPORT- GUIDEROLLERS

w SMOKEOOLASSHOLDERGLASS-_ :

tI*

m--=-xRAMEWORKMOUNTED - ,1 ~::ONTRACK + 7a%-&Ju\ I I \ /\-K L-xcRBERppOR> . . . . . . .. . .. . . .. ... . . . . . . . . . . C.OFGDASHPOTTRACKr - J - - ,~HYO~OFOIL SUPPORT

HYDRoFOILAPPARATUS FOR PORPOISINGTESTS

Fig.aT

(CHANGESANGLEWITHMOOEL)


45/74

Figure 40 Apparatus for porpolsing test~

T


46/74

@ul alE4UNE,

WI&iiiLIMIT TASEN [05L3LL%IE OP ~-il I ~1 2=-$3 I ltlii~;:~yyz~

PITCH DAW!NKLB. P7.SEG/lW.a159aa7s. .I1353mn aoM. .03M194ml a4E4am IMW,$EAEaul am ~

I I I

LsHpE5i252k9471 am all~ 9514am am. ,.

I rw*f. L - \lx.

(lSPEcDCOEPFICICvu

m Y Y 1 II I I I I I I I I I 1 ~HOOELKED, n. PER.s5e .

Figure 5. - Stahl lIty limit S and free-to-trim track for the parent modal, ehowIng thegraphical records of the porpo ising cycles.

P


47/74

,

I I I I 1 I I I I EXIIERHMTALTcwsw TANK1 1 TEwas hsmlns OFTwMoLom

I2 Lsu_l .8 -i NOSOKEM,L8

FREE-TO-TRIMTRACK4 \./

7/

RiLiYxv.1 ,$ : f;m-~ XPB2M+A. \ 4F 140,000: LBS> . ....m- . . CHANGES

/ 1 1 I 1 1 ~~. .= OF... - 5 10 15 20 25 GROSSWEIGHTMODEL SPEED, FVSEG

1 Y- . -

nRESISTANCE

1.2

.1

(mmos)FREE-;-Z mmD 120,00086% OF -1

0.8 140,000100%OF NORMALl140,000 160,00011% OF NORMAL]s -200,000(143%OF NORMAL]g -0.44

5IIlQ8 140,000

m -0.4a 140,000 km--.0

o -. --- ~60t-K% I a RESJSTAIWE-- I vs.Fig. 6 TRIM ANGLE, DEG m


48/74

I I I InRIM ANGLE*=ED/ :*.

sF -4 REE-mTR!yy

/-~.-

1. 5 101 I MOD

1

-- .-

+/sEC.

I EXPERIMENTALTDWINGTANKSwwENs INSTITUTEw TkcwmowHOBOKEN.NJ.I XP82M-I

Z2!z#bJ (sLGFT.2d

Fig. 7

25

ERESISTANCE~D 1.82(60% OF NORMAL)1.37 (100%OFNORMAL)1.72126%OFNORMAL)2.05(150% OFNORMAL)4 25I I II I

:cm+Y$s454z!i8 12 4 8 12 4 8 12

TRIM ANGLE, DEG

:nP

-n-.0.-J


49/74

s REE-ToTR7*/y mF -4/--

I 1 I-.- 5 10 15

I I I I I EXPERIMENTALowuw TANK

w c1

STEVENS4STlTUTEOF .~CHNa06YTRIM ANGLE& -1$? ~N, N.4S:ED XPB2M-I\. .&L ~\&. 7 %= 140,000LBS.CHANGES

I.-1A.zm FREE-TO-TRIURESISTANCE,: 0.8~$ 0.4 I MODEL SPEED, P;YSECI I I-1 .- 1 -imt+(NORMAL) I + (W. FWDo OF MM STEP)-1 . i%!i%a[;&kk&ti8 12 4 8 12 4 8 12 812Fig. 8 TRIM ANGLE, DEG


50/74


51/74

-,.L . . .3

.

k12I I I I I I EXPERIMENTALTWING TANKn TRIM AN6LE S-* INSTITUTEOF Tkcw+oLo6Y. HOSOKEN,NJ.6&D8 /FREE-TO-TRIMRAM4 \./

,/--- 5 Is 20 -

J-MODEL SPEED, FT/8Ec r

. L2 I II IIIUIT_ _,~ ( xv;,i&G]I&l !.344 ( 7s% OF NcRMNJ0.456 OOO%OFNa?wOE87150/0FNoRMAut-uI I I NOTE:LIFT AT 3X 5= 6.95Vf

[l+L%&-:5:,%lii812 4 8 12 4 8 12 481Fig. 10 TRIM ANGLE, DEG.

z9nP

5


52/74

I 1 Ic1RM AHGLE*=EDE-wTRT./~

/-1. -

I5 10

1 I

.

-- ..

I I15 20

I

* .

n?ESWAMCESs1

EK?EMNENTALTOWINGTANKWEWW INSTITUTEOF TmwaowNaWKEN, N.JIXPB2M-I%=140,000 LBS.

VERTICALVELOCITYDAMPINGz.

0.458 V, ( 100% OF NORMAL)0,916 V~(200% Of NORMAL)

NOEFFECTg -0.41 I I I 1 I

Allslxf I MdL !&ED. F I I\ I

31) \ 1/ l\ -1 i!u!:&t2L&EbcEz!!a-- 48!2 4 8 12 4 8 12 4 8 WTRIM ANGLE, DEGig. I I


53/74

I I * I

(nRtNAIWJLE12 S&o

8FnEE-T&Trnu lkAaf

4 \./- /--/1 1-~I 5 10

1 I I..

0.s81.37 -. -2.05

15 20

l\

I ~UNTAI. Ti)wwo TASU

XP82M-I~ 140,000L6S.*%. - ;TAIL MOMENT RATEUWR LWTt, ., , m Memu ( V* , LB.n.tc=)

Ci98(71%OF NORMAL)MOO~L SPEED, WSEG

Izl 1 I I5IIlg 08;b 5 -0.4 b]!Zaw +[o-8z -.0 00~2~ -IO- I 1 I 1 Il&=4812 4 8 12 4 8 12: Fig. 12 TRIM ANGLE, DEG

1.37(100%F NORMAL)2.05(150% OFNORMAL)+

NO EFFECTes1 I II I


54/74

EXPERIMENTALTOWINGTANKSTMNS INSTITUTEw lkcnmcwmHOIEJOKEN.J

I I I 1 I I I I I 1 I$ E fin 5 ITT 7~~E~FT~=T -F 2700100 Ja

XPB2M-I~4=140,0008STAILDAMPING

Mq(x I04VS LEFT SEC.lRAD0.00( o %oF NORMAL:2.02 ( 25%0 NORMAL:4.05 ( 50%0 NORMAL:8. 1 ( 100%0 NORMAL:

1

~&Pd5r+-dTEE812 4 8 12 4 8 12 4 8 12TRIM ANGLE, DEG.ig. 13


55/74

I I I I I EXPERIMENTALTOWINGTANK

o El

STEvsasINSTITUTEW lkcwomwTRIM ANGLE H09DKEN,NJS~ED XPB2M-I

/ \ ~ 140,000 L6Sa .=F - REEmTR


56/74

I I I I I EXPERIMENTALTDWWSTANK

n

Slstms lNsTITUTEoF lkcHmoimyTRIM ANGLE~ -12 HDSDXEN,NJ.w S~ED * UPPER LIMIT XPB2M-1.. \,4 ~ 140,000 LBSa N,*@s E-*RT#,/~ - - \ .*O*P- 4 .,/ INCLUSIONOFMU~ ZqI I I I n WITHMq,COMPARED. - 5 10 15 20 25

MODEL SPEED, F~/sECd n-

REWjTANCE TOMq ALONE-1.2q F;~;&~N s~Dg -0.8ge# -0.4 NO EFFECT

1 I511g! -d .!w-1Z*

+- z -0.4 wL H?O= _..=go TR~MMI#k#I#Tzz &N@LEE -lo I I I 1 1 I I I 1 I I 1 AT FIXEDS?EEDSb 4812 4 8 12 4 8 12 4 8 12Fig. 15 TRIM ANGLE, DEG


57/74

+ FREE-TO-TRIM TRACK\I I I I I EXPERIMENTALTOWINGTANK1===1

, APTERO~ REMOVED SIEvEms lNSTITuTEm TechnologyI HOSOKEN,NJ.\ COU~ ~LL WLY I XPB2M-Izs REE-wTRT./-EEL ---- -y,.P-4 ,/-- AFTERBODYREMOVEDLOUER LIMIT

I I I-.- 1 Z-5 15 20 25 .APTERSODYREWED~ MODEL SPEED, WSEC i

n-RESISTANCE. -1.2m F::;~A-n %&

: -0.8~al OOWLETE W; -0.4

I I Iy := ~~ I 1, &Eq F&c 2: >


58/74

-?

Fig- !7 TRIM ANGLE, DEG


59/74

.I I I I I EXPERIMENTALTOWINOTANK

mTRIM ANGLE Swnms lNsllTuTE m TkCHNOLMY~ -12 H090KEN, NJua S:ED UPPER LIMIT

u// m

: #~/ , 2.25 X?B2M-I%-8 2.75 \& ;3~ 4=140,000 LBS.~REE-~oTN..~~~,~j$, ,#!

pE-+ b1- .// ,

,/:~ AFTERBODYLENGTHLOWERLIMIT

1 I I -.,,,,~ q (TIMES BEAM ATMAINSTEP)-. - 5 10 15 20 25

iL3EtaiiKEaizmx- 4812 4 8 12 ~ 4 8 12 4 8 12Fig. 18 TRIM ANGLE, DEG.


60/74

!-TRIM ANGLE

ti%EtI%&g..!:;

FREE-TO-TRIMTRACK

>

,2J- NORMAL

./1 I. - 5 10

1 9

. 1.2 ONINE FLARE REMFREE-TO-TRIMRESISTANCE# 0.8 7

g mMAL

g 0.4

I

-u I-p-+# MODEL SPEED, F

G I

I

E REMOVED

RE EXTENOE-- -.

+!SE(j.

LOWER LINK~ ,0ESISTANCESK?D

EXPERIMENTALTOWINGTANK;TEvms mt7uTE W lkt3tNoLoelHIXOKEN, NJ.

XPB2M-I~ 140,000 LBS

AFTERBODYCaiuwFLAFu

+25I I 11

md zggElJ- m-0.4z;w +lo_=

2 -.0 DTRIMMINGMOMENTgosz~ -lo I I AT FIXED SPEEDS4 8 !2 4 8 12 4 8 12 4 8 12Fig. 19 TRIM ANGLE, DEG


61/74

ElRIMANGLE.12 S:ED 7 7,c~-8 75- 5i ~FREETO-TRI~TRACK ./,/&H2A *3 I.4 I -. .- ;/.-

/f/-.

/ I 1 I~.-~/~ 5 10 15- .-= -- 20MODEL SPEED, F~&c..L2 I I IF~:;&:-u

0.8

-0.4

uESISTANCEs?&EXPERIMENTALOWINGTANKTEVENSNSTITUTEOF IECHNOLOWHOFIOKEN,.J

XPB2M-I6F 140,000 iLBS.

HEIGHTOFMAINSTEP% BEAM1%BEAM3% BEAM5% BEAM

i7%BEAM

l~tsERIEsFTERBODY RAISED

I!!! 5I IIg

J ogg ~1= ~ -0.4zwq)!!!zs -o DTRwN6 MOMENTgos I3r -lo I4812 AT FIXED SFEEOS4 8 12 4 8 12 4 8 12

;D

-n-.(n.Fig. ZO TRIM ANGLE, DEG No


62/74

..

I I I I I -IMENTAL TDWIrnTAUK

,0Tw AH6LE STEWNShslmm DF l kcMwoLavHaoKEm NJ.

SD 1l-m I ,-*5%1%

1 AW- I ,- {

S-)-G Lm-ok.. I I 4 XPB2M-I,% N,~s% ~4-._ A= 140,000 LBS.HEIGHTOFMAINSTEPSTERNPOST ANGLE= 8

I 10 OF BEAM5% OF BEAM(NORMAL)9% OF BEAM13% OF BEAM

2!@SERIES

I I

Fig. Zl TRIM ANGLE, DEGI4 8 12


63/74

{ + ~ \

MODiL SPEED, FT/sEc

nRESISTANCE1.2 ~~.,,100

FRu-;A-~ ,00 !&:Dw 0.8s N&T/ rl

[

EKPERINENTALTowwe TANKINSTITUTEof ~cwaoslHoeoKEN,N.J.XPB2M-I4=140,000 LBS.

AFTERBODYWARPEDNO CHINE FLARE

1

DEADRISE AT STERRJPOST-1oo102030-1I 1 I I 1, I I I I

1TRIMMINGMONENITRIM ANGLE, DEG


64/74

d-12 nRIM ANGLES~ED8

azfi - 4 E-m-TRy./~/-- I- -I 5 10

UPPER LIMIT--- .-

+kc

1 I$l_ 1151 ~+ti

=QYL E =

1 mW*NEXPERIMENTALOWINGTANKSTEvENsINsTITuTEof lECMNOLOGYSASEsoAh4 ~= 140,000 LBS%]

+. o~+.-STEPM STEP VENTILATIONLOWER LIMIT I STEP HEIG~T l%25 1qRESISTANCE ONLY UPPER LIMIT INVESTIGATE**ED

1

t

25 I I I%

L,

\ \

XPB2M-I

bds&rbzxe12 48t2 4 e 12 8Fig. 23 TRIM ANGLE, OEG m-.


65/74

Fig=24 TRIM ANGLE, DEG


66/74

--a

~ .$-48 FREE-TO-TRIUTRACK -< 0.0Vb ,,2.7yb4 g;! /-.~:-, m.aqb :----../ ,-===-4 5 10I I Mo()[

lo.ovb - I I2.7 yb EXPERIMENTALOWINGANKSTEVENSNSTITUTEOF lECIINOLOGs.4 Vbo.I Yb HOSOKEN,J.tik15

! tomSPEED, F ./sEc a, ~~

I

-+I I I15 20

I UEE!!-J I

45I I IXPB2M-IA=140,000 LBS.

FOREBODYWARPINGDEADRISEINCREASESFWD.OF STEP

0.0 Yb27 Yb5.4 Yb8.1 ?b10.8Yb

(/JJ Gg zcl-- 7zId+~

E7s TRIMMINGMOMENIu) 8 RESWANCE

: TRIMv~Ii&EAT FIXED SPEEDS;-1-Fig. 25 TRIM ANGLE, DEG

2@ SERIES

I I

z

-n-.n.Nm


67/74

,I I I I I EKIIERIMENTALTOWINGTANK

, -12 mSTEvEwMITWE OF ~~tioov

H060KEN, ?&J.L =Cw J 3.44 XPB2M-I

8 4.07 ~ 140,000 LBSFREE-WJ-TRINRAUfs

E -4 . FOREBOIYYLENGTH. I I (TIMESBEAM.ATMAWSTEP)--. 5A 10 15 20 I 25 .

r&!kil31iEk-;:Z,ti- 4812 4 8 12 4 8 12 8Fig. 26 TRIMANGLE, DEG

T-.D.


68/74

I1 I 1190 nRIM AN6LES&o 6.19 u- LIN17 4

/A? j .+.z - 7.X ~%5.07Ua FREE-TO-TRIMTRACKa

9/ - \&

F -4 7.3E

v&07

I 1 I?--- .f5 10 Is 20 25J2-:d>o,=n -1 n616TANcE,%:0 1

=RIMENTAL TOWINQANK7tmi6 hR3TITUnOF lWNoLo6v-EN, MAXPB2M-I4= 140,000 LBS.

HULL LENGTHx (= m ATMAWm)

I

5.07 x BEAM6,19 X BEAM7,32 X BEAM

. [6.19XBEAM=NORMAL]

1 1

Fia.27 TRIM ANGLE, DEG-n-.


69/74

TRIM ANGLE, IIEG


70/74


71/74

.I1-.,.,

8FRSE-I&TRIM TRACN

44S. SWALLOW TAIL

. STEPPLAN FORM1 CHANGESOFWD I mm

I .-1 .-MOO~ %EED, F@EC - I I REslslawos 11 45 V-STEPI ~ I 45SWALLOWTAILAl 7-1

l- SWALLOW

zgo 1- ~ENls 45:Pl~LLow

45, v.~Ep 45. swALLow 45, swAL~TAIL TAILNORMAL

E -10 I 1 I I4812 4 8 12 4 e 12 4 8 12Fig.30 lhIM ANGLE, DEG-n-.3JJ3


72/74

L

NACA Fig.31SCHEMATIC SKETCHES SHOWING

ARRANGEMENT OF APpARATLJS FoRVmlousTYPES OF DAMPING

CARRIAGE

FOR TAIL DAMPING DERIVATIVE Mq ONLYSEE.PAGE 20

CARRIAGE

Mq

-FOR TAIL DAMPING Mq AND VERTICAL VELOCITY DAMPING ZW

SEE PAGE 20

CARRIAGEII ,Mq ,Mw m Zq

FOR TAIL DAMPING Mq, AND THE AERODYNAMIC MOMENTSAND FORCES ATTRIBUTABLE TO MW AND Zq

FIG. 31 SEE PAGE 22


73/74

NACA GROUP IIIA AFTERBODYANOLE WTWCEN FHC AND APTERBODY=ELBACCONPLISHEOHOLOINO STEP HEIOHT CONSTANT

MODIFICATION F i9.132

.--------1

ER 1$!6 Ido 44 do 646 7+4 E$4 1098 g2040APTERDOOY LENBTH

ACOOMPLIBHEOBY EXPANOINOOR GONTRACIINO STATION SPACINO

1 I 1

AFTCRDOOY CHINE FLAREI

CNINE FLARE REMNEONII r I r I

sERIES IHEIOHTOF MAIN STEP

ACOONPLISHEODY RAISIN@ OR LOWERINO AFTERBOOY

SERIES JIHEIf3HTOF MAIN STEP

ACCOMPLISHED BY RAISINO OR LOWERlN6 AFTERBOOY AT STEP

.. - ----------- - -I

DEAORISE AT AFTERBOOT STERNPOSTNO CHINE FLAREI

s ------------I

VENTILATION OF MAIN STEPSTEP HEIONT 1% SEAM

I I I I mm@L

------------ER 126 270 414


74/74

&

NACA GROUPII F & H,CHANSES OF FOREBODYFORM

HULL CHANGES Fig. 33I I 1I1 CONSTANTSEOTION ,,---------------

RR 128 MB Bss 7b It&?4

I

CHANGES OF FOREBOOYWARPINCI I I I

I I I I

CHANOES OF FOREBOOYLEN6TH::- ZGr,---- -. ---

CHANQESOF HULL LENOTH~----.--,

..-- -

1

GHANQESOF HULL DEADRISE

-------------------------- --------------------------------------1

CHANGES OF LONGITUDINALSTEP POSITIONS

041, 550(NORMAL), 57S IN.AFT OF P.R

naca arr 3f12 some systematic model experiments on the porpoising characteristics of flying-boat...

Documents