naca arr 3i06 some analyses of systematic experiments on the resistance and porpoising...

7/27/2019 NACA ARR 3I06 Some Analyses of Systematic Experiments on the Resistance and Porpoising Characteristics of Fly

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3 1176013483715 , ~...,b_ . ~.. ...

p 10NATIONAL ADVISORY

.,.,,.=_ ::.!/.:._-.%..-b-. -.-. r..- .:

COMMITTEE FOR AERONAUTICS my.-,,%.,4+@A*@=

WUUIWIE IUMWRTORIGINALLY ISSUED

September 1943 asAdvance Restricted Report 3106

OME ANALYSES OF SYSTEMATIC EXPERIMENTS ON THE RESISTANCEAND PORPOISING CHARACTERISTICS OF FLYING -BOAT HULLS

By Kenneth S. M. Davidson and F. W. S. Locke, Jr.Stevens Instituteof Technology

NACA.

WASHINGTONNACA WARTIME REPORTS are repr in t s of pa pers or igimlly issued to provide ra pid dkt ribut ion ofa dva nce resea rch result s t o a n a ut hor ized group requiring them for the w a r effor t . They w ere pre-viously held under a secur it y st a tus but a re now uncla ssified. Some of these repor t s w ere not t ech-nica lly edit ed. All ha ve been reproduced w ithout cha nge in order t o expedit e genera l dist r ibut ion .

ARR INo.3106.&.-----$.+

W-68

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IIA!I!I019AL4DVISOEY COMMITTE?C rOE- A9%OH4UTIC5

ADVA??CE EESTEICTZD EMPOET

S-OME.AITAL?SES 011 SYS!I!EMA!I!ICKPEEIMMMTS ON THE E13SIWANCEAND PORPOISIEG CHAEAOTEEISTICS 03 lFLYIN&BOAT HULLSBy Kenneth S. M. l)8ViilEiC)n and F. W. S. Locke, Jr.

This report .dipcusses cartain analyaa dnd conden-sations of the test results obtained in the extensiveseries ef systematic experiments on the porpoloing cbar-terlstlcs of flying boats reported in referanc~ 1. Thework is believed to simplify arplicptlon nf the test re-sults to practical design problems and to aid in clarify-ing basic concepts regarding morpolslng.

The exrerlments were carried out according to ~trictsystem and considerable attention w=s given, in ref~rence1, to presenting the results In a form wklch would nrovideas clear a viau~l impression Rs mossible of the influencsnnd relative Importance of the different variables. Theradiating chart of variables in figurq 1 and th~ condensedsummary charts of test reoults in figures 2 and 3 nrt= takenfrom rqfereno- 1 and furnish tha genaral background for thatinalyees here considered.

It Is concluded in this report that:I - For a @_ven hull form under various combinations~- l


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3(b)

,..,,,., -.(c)

(a)

The lower lim~t at high speeds 1s notaffeoted (chart in fig. ~).Th; hurnp-trim- follows the changes in. .stern-post angle In the same way as thelimit curves in (a), and the hump re-sistance ia primarily a function of thehump trim (sec. 14, chart In fig. 15).The effectiveness of tha ventilation of .the main step determines the prssence orabsence of upper-llmlt porpoising at highspeeds, u ore eff~ctive ventilation summrss-sing this type of porpoislng (sac. 13).

These conclusions ar9 based umon a consideration ofthose variables on the radiating chart on figure 1 whichare not covered by cross-hatching. The remaining vsriabl=ishave not yet been considered, and the crosq-hntching hqsbeen added to the chart to make this clear. It Is believadthpt the remaining v%riables can be trented In a generallysimilar way to those considered mt this time, but the workto dnte Is being presented without wnltinp for furtheranalyses because it s=em9 of 9ufflcient intere~t In itsalf.

By considering the mnalys-g so fnr comnletatl ~nd bysore extant anticipating futur~ F.nalyees of vqrinbles noty-t comrleted, It ~qems clenr th~t when the stqbllltylimits ar~ expre~sed ng functions of ~~/CV withM

2(1) The positions of the upner gtablllty limit ~ndof the peak of the lower stnbility llmit nregoverned primarily by

(a) The stern-post angle (the angle between atwqgent to the forebody keel nt the stepand a line joining the ti

Tof the step withthe tip of the stern post

(b) The p~wer (I. e., dynamio llft) of the secondstep (,as Influenced by the plAn ~rea in thevicinity of the stern post, the general. angle


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(2)

(3)

of attack of this area with respect tothe line joining the tip of the sternpost with the tip of the main step, chineflare, etc. )

The position of the lower stability limit athigh speeds is governed primarily by(a) The dead rise and the effective warpingof the fo.rebod~ bottom, and probably alsothe curvature of tha forebody buttock6Suppression of upper-limit porpoieing at highspeed~ is governed primarily by(a) The effectiveness of the ventilation ofthe afterbody bottom in the vicinity ofthe main step

Of the foregoing, l(b) and 2(a), whilo based on the testdata reported in reference 1, are not analyzed In thisreport-These broad conclusions constitute R powarful tool

for clarifying porpoisimg phenomena, oven though they maynot be found otrictly applicable, in their antirety, to allcaOos. Qhe main concepts are brought out rapidly in thefollowing diagram:. - .! I iTrim angle

%n~tiDiagraaaetic Illustration of Tentatim &road Conclusl~nsrapardi~g Porpoisingshowingthe stabfllty llnits in nan~inensional foraand the regions influencedby the foreho~vby the aftarbodyb~ ventilation


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In this figure, the closed our~e surrounding thelower limit indioates the area within which changes to., tliefore body-.are effec.t%.l~e,,l~ltering the position of.tho lower limit of stability~ Elmllkrly. the. cl-osedcurvo surrounding the upper ltmit and peak of the lowerlimit indicates the area In which .changes to the after-body are effeotlve. Ll~wise, the line around the right-hand end of the upper limit indicates the area withinwhich step ventilation Is effective.. .

INTRODUCTION

The systematic experiment~ considered In reference 1radiated from a given flying boat taken as a basic Pointof depa~ture. Each of R number of variables was altered,separately from the othars, over a range of values embrac-ing the normal value for the flying boat and Intended tobe wide enough to cover all valueo likely to be encounteredin practice. The advantage of thie procedure la that Itmaterially simplifies the problem of coordinating test ro-Sults , It enables the effect to bo estimated of makingcorresponding changes In designs other than that of thereference flying boat in the Mjority of cases.

The vnriables fall naturallyinto the following groups:Group I Weight and In~rtla Loading(3rou:>11 A9ro@-:~.+mic ~oniiitionsGroup 1.11 Hul 1 FormGroup 111A &tcr30dy Form,Group Z?IF lorohody FormGroup IIIH. Hull ~or~ (as a wholo)

9!ho refetionce flying boat used In the experimentswas th~ XPE2ii-i, a modo~n de~ign having, for o.~ro~sweight of 145FO00 .~au.r?q, a wirg loading b~!; Of z8bopouuds,p~z sq.-wre Zoot and a bl~az ~CP.~l~g A J wlJ 3 of o.a9.The dimsusioas and particulars considered as normal aregiven in table 1.

The present discussions consider the variables ofgroups I and II and some of the variables of group TITA.All conclusions and generalizations are based upon tiiaranges of change of the variables covered In the ex-gerl-mentfi. Had the oh~ges been extended ad absurdum, comeof the conclusions would undoubtedly have been altered.


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Yhls investigation, conducted at the Stevens Instl-tute of Technology, was sponsored by, and conducted withfinancial assistance from the National Advisory Oommitteefor Aoronautios.

DISCUSSIONGroup X Group II

Weight and Inertia Loading Aero~ynamio Conditions

1. ~hose two groups include all of the vcriablota respon-sible for forces or uoments acting on the hull other thanhydrodynamic.

l!he variables of group I are obvious at once: thoseof group II are scarcely less obvious, thanks to therelatively 6imple configuration of the airplane. Thus itcan be said with some assuranco that the list given onthe ra$iating ohcrt In figure 1 includes all of the vari-ables in these two groups which affect forces and momentsapplied to the hull, both in steady motion and in porpois-Ing.

The mass In vertical oscillation is an additione,l -variable which, like the aerody~amic component of Zwand one or two other of the aerodynamic dorlvatives, canbe made Independent (in this case, independent of grossweight) in tho model but not in the ship~ Though notconsidered directly in the experiments, it was consi


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2. Regarding the six remalnlng varlat)~es , It Is apparentthat-- .... ..(i~ A Z~ and Zg, in oomblnatiop, fix a net foroew ioh~s, in fact, the net water-b o%nb loadin steady motion A(2) The oenter of gravity position and Mo, in com-bination, fix a net moment which det~rmines thotrim angle in dteady motion 7(3) Mq determines, by lt~elf, the tail dampingmomeats in porpoising motion

These combinations ~trongly euggest that, instead of SIX,the controlling vnriables are really three; namely,

(1) ~ water-~orne load A affecting reeiatanceand ~jj~B~ (2) Net moment H affecting resistance and por-.poising(3) Tail damning rate Mq affecting porpoioing

only, not re8i0tanco

NOW It is known to le~ln with, of courso, that tho 8teady-motion reslstanco IB co~.trollod hy the firGt two of thoseas Indicated nnd that Mq affects porpoising. Evidencethat, with q flxe)d, the $irrst two control porpoi8ingis supplied

(1) BY the upper charts (a) in fi~ure 4, whoreit is seen that tho upper and lower por-poi8ing linito obtained in the separateexperiments for altered values of Ao, 2.,and Ze, respectivel~, can ho expressedas unique functions of the net water-borneload A, with discrepancies of less than 1.It may be notod hero, though it boars malnlYon tha discussion 02 tho preceding section,that when A is altcrod by changing A. themass in vortlcml oscillntlon is affoctod indirect proportion but that when A I* ~ltoredb~ changing Z. or Zo t>o r3ass is uriaffOotQdOHence., a demonstration that A is the con-trolling PozialIle, whether the mnss ie variedor not, is in offoct a demonstration that them~ss in vertical oscillation does not affectporpoising.

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(2) By the more comprehensive charts of thesame sort in figures 5 and 6 discussed.in section 4.Tho lower charts (b) in figure 4 show that the shiftsin tho moneti curves obtained in the separate experimentsfor altered center-of-gravity locations correspond to theproduct of tha center-of-gravity shift times the not waterload, as would be expected; thus the net momont M isthe controlling vadiable.3. In practice, rcsiGtance is usually given as a functionof trim, lo~d, ?md speed, nnd por201slug li~its aro fre-quently ~xpicssed In terms of trim and speed - in bothceses withcut ?2ecial regcrd to the availability of themoments raqnlretl to produce the stated trims. In otherwords , rnoacnt in not ordinaril:r treated as an i~depbndentverinblo, trim being substituted arbitrarily as a pa~cimoteroThis substitution of trim Sor moment is discussed ia ~oredetc,il in the appendix. By aalcing th.s stihstitution, and byr eS ta t l : i g the c~i~c~->ts of the preceding section, It may beeaid that

(1) The r~sfstance characteristics ar~ a function-of trim, load, and speed.(2) The P !mpoisiilg cluzractaristic~ aro primarilyfunctions of load and speed, and socoadarilyfuncticng a- the tail--dampinfl rate.

The controlling vnriahles aro then reduced to two. ~urther-nore , th~ tni~danpia~ rato es~octs prii,lfirilytl:e lowerp=rpoising limit at high speeds (seo fig. 2) ~,nd is clearl~of loss iaportnuce thmn tho net water-borne load.

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In this form tile curves look more famlllar and theyare lesta distorted. .. . .- >..

The s~e simplificat-~oi-h~s been applied itithe pastwith reasonable sucoess to reelstance data for the plan-ing range (see references 2 and 3); its euccese for por-poisiug data IS not, therefore, very Surprising. Norneed the fact that it has never been widely used In daal-Ing with resistance data necessarily tifluence ite ado~tion for porpoislng data: the high precieion requiredfor resistance infornati,on is not ordinarily needed forstability limits. Its use reduces the statement of por-poising characteristics to a single chart with q asa perameter.

The extent of the speed rnntjes over which porpoisingoccv.i=sunder various conditions, and particularly thej?rese:~ce or absence of upper-limit porpoising at highspeoAs, are not Indicated by such ch=ts, Theeo are dia-cussoi!.in section 13.5. The tall-damping Cerivatlve % is directly pro-portional to speed. Hence, a statement of the proportion-ality iactor M /v1 is eufficiont to define values for allspeads. Taen d vialed by Pw/2 b4 ( Pw for water), thisfactor in made nondimcnslonal$ the expression qv Pw~ b4,is tLcirefore a s-tiitable criterion with which to expressthe tail-&.apin~ ratas for e. given deoign, at all speedsand S~Z(3Sm Its value is 0.249 for the e~criments inquestion.6. In summation It appe~s thmt the porpois,ing charactel)-isti.cm of a given hull can be e

7ressod (with the reserv:.-tion- noted et the ond of eec. 4 by-a eingle chart with

a single yarameter. Tho inherent porpokiiag oharacter- .istics, which fix the shapes ancl positions of the llmitcurvae on Iiy.lschart for a given value of the parameter,must thea depend on hull form only.

Group 111Hull Form

7. Tke choice of variableti for systematic studies of hullform is by no means straightforward. The hydrodynemio tom-


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10ponents of such quantities as Z9S M S and so forth, awe#ot clearly related to geometrio con Igurat ions and sizesof s~ecific elements of the hull form in the simple fash=ion that the aerodynamic components are clearl~ related.to geometric configuratioara and sizes of specific elementsof the airplane. Hull form must therefore be dealt withas ~uch.

!i!Iionds sought are easily statedt(a) To reduce hump and high~speed resistance(~) go eliminate porpoising or, failing this,

to widen the range of stable trim ~glesIt is iiesirable to im~rcve both characteristics, andimprovcmaut C: one at the e-spense of the other will not

usuzlly be very helpful.It vrill he v,nderstood that with -y hull form it isnece~sars to locate the center of gravity eo that thehum~ resistance is recsoneble, and so that t>e available

trim tracks are within tho stability limits at planingspeoce.8. In tio experiments (reference 1) the choice of vari-ables was governed by the underlying concept that thefore%ody unt. afterbody are separate parts of tile hullrerving di.ffeuent purposes and that in con~equence eachshould he altered Independently of the otkor.

Thio cczce~t was suggested by the comparison showmin figure 7, batweeo the charncterist+.cs of the completehull and thuse of the forehody done (under otherwiseidentical conditions). This comparison wap worked outbefore tie Ztot of htill nodifj.cations was fecidod Upon;as e.~gl~.ined in rei?arezce 1, it revaals in paiticular(a) T~.~t ti.a afterho&v is useful only in tho lowerhalf of the spoe~ range to tzlko-off and ti:at

!.tepreseilce at !Iigher speeds is [email protected] rh ce n t ai; that .

At rest and at displacement spoads, It pro-vtdes flotation .At moderate speeds up to the hu~p, it eon-trol~ trim and resistance and prevents

lower-limit porpoiaiag


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At high (planing) speeds, it is the direct. . cause of upper-limit porpoising and somb.. . what increas ed.resist ano,e.~.......... .,...,-_

(b) That the f orebody Is entirely self-suff Icientat planing speeds and needs no help from theafterbcdy

These ~.ndicqtions suggest clearly(a) That the forebody is the main hull - essentiallya steploss, V-bottom, planing boat with the cen-ter of gravity vary far aft(b) Tkat the afterbody is an appendage, the functionof which is to control trim (by providing nosin~down moment) until true planing of the main hullIs establishedGroup III IE accordingly divided into three subgroups

Group 111A Afterbody FormGroup 111~ 3orebody ~ormGroup IIIH Hull Morm (as a whole)The fir~t two of these are of more interest for prosentpurposes than the third and, as or.plained previously,cnly a part of the first is dealt with in this report.

Group 111AAfterboty 170rm

9. When a given set of vertical transverse sections (thatis, a given body plan) Is used to produce a eerles of hullfovrns differing in some consistent faehlon in their prc- .portions, the resulting forms are said to spring from theeamo parent fcrm. It is only when, rogardloes cf propor-tion, the ehape cf one or acre sectione is altered withrespect to the others that the parent form is said to havebeen altered.It is in accordance with these ideas to refer to thefollowing variables of group 111A as involvin~ no changesof parent form:

Im I . . - ..


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12

Afterbody anglo}

for changing which, tho sameS~ep height after body was used in tho ox-perimentaAft orbodg length for changing which, tho afto~body station s~acing was uni-formly altered

rho praaont diSCUSSiOn iS limited to theso variables vithGone rcfcrcnce to the expor in eat s with tho f orobody alono.10. ~i&r~J 8 shows tf.e porpoising linits for the abovementioned variahlos. Zho lowor-limit curvo for thoforo~ody alone is ad&02 to these charts for rofez?onco.

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The indt.~idual points gor the upper-limit donot scatter more from the mean curve than the,-. , points In figure 6, the mean curves on thesetwo charts being conaitatent with eac~ other.

3lLwre 10 may be regarded as providing a furthersimplification {following fig. 6) in the statement ofporpois~ng characteristics. By eliminating differencesdirectly attributable to dlfferenc,es of stern-post angle,It clarifiee one more variable in the analysis of por-poieing characteristics. &lke figure 4, however, It failsto take into account differences in the ranges of speed(or of ~/~) over which upper-limit porpolsing oocursurider various condltionfi. It fixes the position of theupper-limit curve but not the extent. !Che latter is con-sidered further In section 13.11. It i~ olear from the discussion of the precedingsection that the limit curves in figure 10 are substan-tially intiependent of the forebody trim. It is seen, too,that the total range of stern-post trims embraced b

Tthetwo limit curves is quite smull (of the order of 4 .Theso observations ~uggest strongly that the wake, ortrough, loft by the forebody must be substantially in-dependent of the forebody trim and relatively flat at .all plantng speeds.

12. q~-e -photo,~aphs (fi~so 11 to 13) were taken In anattempt to throw furtkor light on tho nature of tho flowpatterns in the vicinity of the porpolslng limits. Threeregions aro shown, in separate figures:Lower limit at peak of broa.%away (Sig. 11)Upper limlt at moderate planing speeds (fig. 12)Upp~- llmlt at high planing speeds (fig. 13)

31ach i~g~oll 18 211uetrcted by three cases:Afterbody angle, 120L*torhotly angle, ~oAfterbody angle, 4+0

and aach case has threo photographs for trim angles cover-ing a range of 20 In the vicinity of the porpoising limitunder consicIeratlon.These photographs should be viewed as a first attemptto illustrate the flow patterns. They Indoicate, however,

1

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(1) Regarding lower-limit porpoislng (fig. 11) -that this type of porpoislng Is suppressedwhen, with Increasing. trim angler the tip ofthe afterbody first makes contact with thewater surface (this indication being amplyconfirmed by visual observations of the modelduring tests)g Since this occurs with stern-post depressions of the order of 1 to 3,It is evident that the forebody wake is de-pressed in about the same amount at the valuesof &/c~ in question.Regarding upper-limit yorpoising (figs. 12 and13) - that this type of porpoising developswhen , withoan increaso of trim of the orderof 10 to 2 beyond that required to suppresslower-limit porpoieing, a lnrge portion of theafterbody bottom becomes wetted. Zhis wettingand the fact that it Is followed, when the trimis further increased by about 1, by the fore-body coming clear, so that only the tip ofthe afterbod.y remains in contact with tlxe watersurface, seems to go far toward explainingthemechanism of upper-limit porpoising. Evidentlytho wetting of tha afterbody introduces forces(cad moments) which result in the forebodyjumping clear and this in turn breaks up thesituation which caused the afterbody wetting.

The photo~raphs in figure 14 wore taken to Illustratetti sii.lilarity of tho flow patterns at fixed values of dcA/c~ obtained with difforont combinations nf CA and Cv.As Sue?, tht3:-properly belon~ with the discussion of section4 rather than >ore. They are of inte?ost in connection withtho present uisci~sion, however, hccause the: Indicate thatmlcv is a very exact c=iterion of flow similarity whenother thi~gs are aqual, and they therefore provide a back-ground for saying that very small differences observed intho othor photographs - wkere othor thin~s we not equal -may bc si~al?icant.13. It has been noted, in sections 4 and 10, that theextent of tho 6peod range over whic]? upper-limit porpoisLnEoccurs is not necessarily shown in condensations of testdata upon the base ~/~m This speed range or, more

q


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especially, the rango of high speeds over which upper- llmit porpoising is absent, has considerable practicalImportance The absenoe of upper-limit porpo18i~g isobviously desirable In itself, and thero 1sa pos-e~bil- ity (now undqr Investigation) that its presanue or ab-sonoe is associated with undesirable or desirable, r-spectivelyc landing characteristics.

Itoferenoe to figizres 8 and 9 In&icates:(1) &hat , if thn upper-limlt ourvo stops shqrt oftalf-off, it tendm $0 stop at moro nearly aconstant value ~f ~/Cp (roughly 0.09)than a coastant valuo of spood(2) That tho upper-limit ourvo stopB short of take-off when

(a) The stern-poet angle is increased abovotho normal Talue of 8(b) Tho stop height Is tncruasod above thonormal value of 5 porcont of tho beam(c) In s ito Of a very low atop hei~ht (1 per-7ent , n su%etantial pasmago is providodto allow a!r to roach tho rear of thoatop

How it will bo soon that, In all three of the cases listedunder (2), there has boon an incroaso in tho amount ofstep vontilatlon, this term being used broadly, to inoludoany moans by which a supply of air to tho stop oan bo ac-complished and not moroly the provision of air ducts. !Cheinforonao Is obvious that tho avoidance of high-spood uppor-llmlt porpolslng dcponds directly on the provision of suffi-oiont ventilation. !Chio inforenco, furthermore, appearsto ho cntiroly consistent with tho point of view dovolopedin section 12 that tho wetting of a l,argo portion of theaftorbody bottom marks tho beginning of upper-llmit per-poislnfi, for general tvetting of the aftorbody bottom Isprobably assoclatod olosoly..with .t~~ offoctlveness of stopvontllation.14. Figure 15 is a chart of zaxtmum hump resistance plottad against maximum hump trim. Values are forthe true hump (in tho vicinity of 10 Zt/sec modol.spood) and not for tho vontllation hump (In the vi-cinity of 8 ft/sot). Data aro Included for ono or two


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16 variables in addition, to those listed in eeot ion 9 Inorder to euphaslze that it is the hump trim itself,rather than the exaot means taken to get it, which oon-trols the hump resistance. The exoess of the total re-sistance over the value of A tan (T+2) is seen to beroughly constant for high trims hut to increase rapidlywith low tsims ao that the total resistance is a rclnlmumat around 3~0 trim.

The arrows on the chart indicate the difference .between the maxluurn hump trim and the maximum trim on thecurve of lower-limit porpoising (which usually occurs atmuch tho same speed). The hump trim exceeds the lowerporpoising limit to a moderate extent except when thehump triu i~ very low.

CONCLUSIONS

The ~rincipal conclusions to be drawn have alreadybeen ~t:~ted in the Stumcrr of t3e report.Particular attention is called to the three charts:Fitqne 6 - which 3hOWS that~ for a given huli underVt i-LOUS co~l)+.n a t t o ils o f loading and aerodynamic COE-Gitions, the stahil.ity limits uay be exprepsed asfunction:: of t:]e tiinonsionless oriterion ~/CV~~~~ Q as a parameter,~pWb4

2~l~ne 10 - which s?.ows that, for zo


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APPSNTDIX..Uhile not strictly a part- of the present. thesis,

a brief discussion of the substitution of-trim for domentas a criterion In the statements of resistance ad por-poising charactoristlos may be useful.Moment is, In fact, an Independent variable andfailuro to consider it as such does not dispose of It.There can be little advantage in knowing best trims (withrespect to elthor resistance or porpoising) without know-ing whether they can be obtained. The general lack ofemphaBis on moment is perhaps explained in part by thedlfficultiee which still stand in the way of accurate de-

terminations of the aerodynamic moments during tak-offqnd landinc. There iS another aspect of the matter, ho-ever, which is considered In what follows.Tho chart in figure 16 showo tho usual data for thenorGal X232M-1 flying boat and, at ths four speeds forwhich cross plots are drawn, tho moments due to(1) 2!hrust -Corresponding to tho thrust curve shown.(2) Haximun ~hlft of center of gravity -

Corresponding to 2* feet either way in theship or lE?.5 percent of the beam. (Thf wingIG afi6umo& to be shifted with the e.g.(3) Maximum elevator deflact Ion -

Assuming Q!max aero = 0.4 (or CLt = 1.0)These are the principal moments; they are aclditive (al-gebraically), except ior the thrust moment, in any desiredcombination- The magnitudes shown aro not claimed to haveprecise absolute significance; they are intended. only toindicate approximate maxfmurns.With this understa~dlng,It will be observeti that

(1) At the Ioweet opeed (CV = 2.79), which Is aboutat the hump and for which the power-on case istherefore of most @terest, the possiblo effecton trim of altering the moment combination isabout ~ and thatAny trim within this range is near the trimfor best resistance,..


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(2) At tho highest speed (CV = 5.57) the elevatormoment is so large that, with an~ combinationof the other two uoments, the trim can he heldbetween the porpoising limits sad at the valuefor beet resistance

For these-two speeds, then (and for all lowor and higherspeeds, respectively) moment Is of necondary interestonly. I?owever ,

(3) At the first intermediate speed (CV = 3.71),tho tein for least resletancc can be roachedwith any posslbla combination of tho moments ,but thifi trim is less than the lower porpols-ing limit, m:d thero are many combinations ofthe moments , particularly in the power-on case ,with wLich the maximum trim cannot be Inad9 toexcoe? tho lower limit.

Thus, Tor spcods in the vicinity of this ono (a littleabove the hump) aamsnt , though still secondary frcm thepoint of viaw of steady-notion rc~Lstance, takes on pri-mary iqortonco froa the point of view of porpoisin.g limits.These speeds, too, era oepecially iuportmt l]cca~~sein.accelorated take-off the triu is felling rapidly from itspeak value ncor the hump: thug initial ?.isturkences are

?N31n ir.duce porqoising.rovidod to -In gon:3ral, ther~foro, norent has to ho qiven noroconsideration is dealin~ with porpoislag than in dealinfi

with rosistancfi. Sut t:mre does not sGorI ta !a any groatnoot. :or a xors nccurato knowledge of th% aorodynamlc(olovator ) noncnt ; the principal roo.ulr~uent is to aottho cantor of gravity in the nest advantageous position.Shifting the center-of-gravity position Is zmch thosimplest way to alter tho mouont co~biaation in an existing

flying bo~.t, ar.d tests to determine the best position - ortho Ziniti.ag pract?.cable rango of positons - aro ordinarilyc.arricd out on a now flying heat. Ia this case, howevnr, theconsequences ~f a sk-ift differ somewhat froJm t-hos,>dlscu~sedin section 2 because tho wing is not shifted with the canter03? Cra~StFm Irom tho point of view of design, with whichthis paper is primarily co~cerned, tho ving ou~ht usuallyto bc s:liftod whoa tho c[+ntor o! gra~it~ Is shift?d to avoidintroducing m additional aonon.t whilG flying, This was


20/48

. . .. .___19

simulated In the experiments vhloh form the background forthe present work and allowed for in calculating the momentsfor. the chart6 -in figurs 16. When the wing ie not shifted,the ~omont Is greater, as indiaate-d- inthe-f-ollowing .sketches :

Directionf of motion

A. Lo.Wing shifted Wing not eld.fted

(l%angemoment = (A. - L) a me moment = A. a

2he differ onoe Is montionad here to avoid possiblemisunderstanding.

1.

9,,0

3.

.DaTi LsoQ, Kenneth S. K., and Locke, r. W. S., Jr. :Somo SystomRtic Mo?.el Xxporlmonts on the Porpoie-ing Charactoriattcs of illying-Boat Hulls. 33ACAA.E.IL., Juno 1945,Schr~der , Paul: The Take-Off of Seaplanes , Based on a30W Hydrodynamic Rrduction Thsory. T.;{. No. 621,rAcA, 1931.Anon. : A Coapa?isos oftho Planinf; Eaane ofT.M. XO. 47, StevQae

. .Stovan B and 117..C.h. Test~ Inthe Navy i{~rk V Seaplane Hull-Inst. l!och., 1940.

. --- . .. _. .- - ..


21/48

20

!CABIiEDIMEt@IOES MD PARTICUZAIE (MCM?MAL)B(IRRII&SIZE

Dimensions 3%11 size l/30-Ocale modelBeamatmain step, in... . . . . . . . 162 5.40aAngZe between forebody keel aadbaee line, aeg 2.0 2.0@gle between after&&k~e; ~~ base lfne, deg...... . . . ...5.0 5.0Height of main step at kesl, in . . . . . 6.1 0.27Cen%er of gravity forward.of mainstep (26.58 percent M.A.C.), in . . . . 70 2.33Center of gravity above base line, in . . 146.7 4.89Gross weight, A, lb . . . . . . . . . . 140,000 5.19 f.w.Load coef~ici.ent, CA (sea water) . . 0.89Moment of inertia inpitch, slug-fta . 1.366 X 106lb-in8 . . 6.328 X 109 260Wingspan, ft . . . . . . . . . . . . . . 200 6.67Wtng area, S, eqft . . . . . . . . . . 3683 4.092Mean aerodynamic chord~ M.A-C., in . . . . 249 8.30Aspect ratio (geometric) 10.87 10.87Horizontal tail area, ~q ft . . . . . . . 508 0.565~levatorar~, Sqft . . .. . . . . . . . 143.7 0.160Distance c,g. to 35 percent M.A.C.horizontal tail (tail length), ft . . . 63.6 2.12Thrust line above bame line atmainetep, in . . . . . . . . . . . . . 230.3 7.68TIUUS3 line inclined upward tobass line, deg . . . . . . . . . . . . 5.5 5.5 .

ofofofofofof

veloci.tle8,AVa . . . . .. m.... . 5.477linear dlnemions, A . . . . . . . . . 3.0 x 10a rea s, Aa 9,0 x lo~rolumss, A;:::::::::::: :: 27.0 x 103moments, A 81.0 X 104moments of ine;tiaz Ai I I I I I I I I 243.0 X 10footnote on p. 2tI..

L


22/48

21

.TABLE I

DIIDIUSI~S ABIlPARTI- .@OBl@ EOEllJI&SIE ~YIHG

Aero-loCLat T=

BOAT XPB2M-1 AND &-SOALl MODEL (Continued)

characteristics fill size l/30-scale model5 (relative to base line,

flapa,30) . . . . . . . . . . . . . 1,585 1.585Lat T=6 . . . . . . . . . . . . . -3695 ~:(c) 72 x 10 Tra t ic~ dh . . . . . . . . . . . . . . . 0.1045dL/dT (dZ/d~), lb/deg . . . . . . . . 0.458 Vaa

()dL/dw (dZ/3w), lb-aec/ft ~~ . . . . 0.458 v~ITT%@%L =dC%G/d7 (av.) . . . . . . 0.0150d?iCG/drdM/d6), lb ft/deg (sw.) . . . 1.365 v:

bdM/dq, lb ft aecfradian . . . . . . . . 8020 x TSdM/dw, lbaec(av. )..... . . . . . 78.3xv~&A/qa ft/raaiian . .. m..... . la2,5Idq /Tall length, I/radian . . . . .a 1.61

Get-away speed, fpa . . . . . . . . . . 130Get-away ~ . . . . . . . . . . . . . 1.890Get-away ~, deg . . . . . . . . . . . 8.8

aAll trim angles measured relative to the base line.bcontrl~ti.on of horizontal tall s~ace only.cSubacript a is for full size.

0.10460.509 x 10-3 Va0.509 x 10-3 v

0.01505.05 x 10-5 Va9.90 x 10= vZ.go x & v

3.41

1.61

23.74

1,8908.8

I 11111 Ml ,,, ,, . .. . . . . . . . . .


23/48

NACA Fig. 1RADIATING CHART OF VARIABLES

_- *SECONDSTEPFigure l.-mo no effeot on steady-motionresistanoe olwaoteriaticw.

m little or no effeot on porpoisingoharaoteristiosm


24/48

NACA WART 1 CROW. ~ - WEIGHT *O INERTIA LOAOING Fig.2.a

nW=&w-w -

L_. /; I.tI m m

+--!


25/48

NA CA CHART 2I 1 1 1 I I

GROUP Jz - ACROOYNAMICmDITIOMS Fiq.2b

I I I I I 1

n. wS& /;


26/48

NACA CHART 3 CROUP IU A - AFWR800Y FORM FIq. $

e

Maa *D. ~V9EC

I

, I

I / I 1, I , JA.SLC Btrwcc. FM. AR. Arrcmeaw KEELSI 1 1 , , 1

m*J -.. 4r I I 1 1 1

H,t, GI.IT 0, MAIN STEP , z. 5.,,,.

ArT, m.. w W.,,. S?r., Vt. T8LAT,0m,T=. H*ICHT 11.


27/48

SEE FIGS. 5 ~ 6 FOR SYMBOLS 2

0 02s 50 T6 100 12s 1s0

w-UPf ER i JM l T

/ daLoWER LINIT

*

10 !4go P8 r-# tin LmlT

6;0

(0)4F

UWER Mm

2* *

0 -0 2sso Tsloo=lsoSTABILITY LIMITS AS FUNOTIONSOF NET WATER LOAD FOR EXPERIMENTS ON & ,Z ,Zc= 3.71(14.13Ds) Gv= 4.64 (1765 fp8) %, :5.#7(21.18fpd

IED MOMENT CORRESPONDING TO SHIFT OF C. G.I IC.G..IINS FwDOF MAIN STEP

o 68 Dt202 8~120246 80 12

(b)

*


28/48

STABILITY LIMITS VS. A/@ AND~/@ FOR&Zo, 2014 FORGROSSWEIGHTS,Ao= 120,000 LBS. ~140,000 Im. qW,cm Les @12 2oo,0cm LOS Q

LIFTS ATT =W, ~ = 4.63 V* *UPPERLIMIT z~ ~ S24 Vt #

IO Zg, tildv = m44v~ 40 / Z@, (LAM S am?+ *

# $8 4~o o Fz

6 * #c1 LOWERLIMIT$>

4(5%zE @21-

CAK~ [=* CLIFTCOEE, h/b*@ejJ~3

~TAKE-OFF A/vE(SHIP)Figure 5.-


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ISTABILITY LWITS vs.6A/Cv FORAo,Zo, Z@GROSSWEIGHTS,AO= 120,000 LBS. o ~14qooo LBs. q

160,000 LBs. ~200#00 LBS. 0. 12LIFTS ATV =5: ~ ~ 4.63 # #

h = 9.24 # j,~, dL/d7 a 0344 Vt 1.0 Z., dL/d7 = 0.6G7 Vt k 0

s9 s 8

#o #d # n

# z6ELOWER LIMIT > 1-Od) 4

0 Mq = 0.249yp(m 2#

A ~ ~ oCJCV TAKE-OFF~0.25 a20 OJ5 QIO 0.05 [


30/48

& FREE-TO - TRIM TRACK\ AfTEREOOY REUOVW EXFUMIENT&L TowmaTANKSTEVEU9twmm OFlmt19LoBYHmaEn, WA.

COWU1CHULL OULY XPB2M-I~ 140,000 LBS

/- AFTERBow FEMwED. - 5 w LO, F:/sEc to 25WTU80DY WmVm G

l\ 1.- I I I I I

FiQure 7.- lklM AMaE, m


31/48

l=: --rlgure u.-


32/48

=g*

STABILITY LIMITS VS.&@v ;

!0 ~i ~x /I 8 rOmww A1.au 3 #

Iy

16 I I I TAK-&F ~8 k +14 Iz- #E II

/II

12ii

I /

B10 ~ Ont.ta IIOAUAL STIY W!NTILAIIOM-IW \

?s.

8 X*C58$

CIJSTEPVCNTILATICN-1%

o AFTERBODY ANGLE6x STEP HEIGHT, AFTERB~Y RAISEDA AFTERBOOY LENGTHn STEP HEIGHT, STERNFC6T ~ =S4

2 = 0.249

0.35 0.30 azs 0.20 0.5 0.10 aos


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=!gST~lLITY LIMITS +

ON THEBASIS OF STERNPOST TRIMOvs. ~/CV

+4 II I \ I //////N////////M /7//1/ .%% Liq r WK:MIKUO, FIGS. 5AII06I/

-t

M STEP W6HT, AFTERBDDY RAISED MA AFTERBODY LEWTH -+ stL2498 u STEP HEIGHT, STEWOST ~ u & qP.

(p

G/cv +nI 0.3s Qio (I25 Q2Q am alo aos 1Figure 10.-


34/48

NACA Fig. lla

\~

= ~..- Afterbody-------1P F angle, deg124.5*79 74.s ,,4.5

1.02.766.620

Afterbodyangle 12Stern-postangle 13Abs. forebodytrim = 13.4Abs. stern-posttrim = 0.4

Afterbodyangle 7Stern-postangle 8Abs. forebodytrim = 8.7Abs. stern-posttrim = 0.7

Afterbodyangle = 4.5Stern-postangle = 5.5Abs. forebodytrim = 5.5Abs. stern-posttrim = O.OO

K~cv0.298.224.181

(a)

Figure 11.- Steady-motion photographs at lower limit, peak of IIbreakaway!t.

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


35/48

NACA Fig. llb

..

Afterbody mangle, deg12 1.027 .7664.5 .620

Afterlmdyangle = 12Ste~n-po_stangle = 13Abs. forebodytrim 14.4Abs. stern-posttrim 1.4

Afterbodyangle = 7Stern-postangle 8Abs. forebodytrim = 9.7Abs. stern-posttrim = 1.7

Afterbodyangle = 4.5

Abs. forebodytrim = 6.5Abs. stern-posttrim = 1.00

.224

.181

(b)Figure 11.- Continued.


36/48

NACA Fig. llcAfterbodyangle 12Stern-postangle 13Abs. forebodytrim = 15.4Abs. stern-posttrim = 2.4

Afterbodyangle 7Stem-postangle = 8Abs. forebodytrim = 10.7Abs. stern-posttrim = 2.7

Afterbodyangle = 4.50Stern-postangle = 5.5Abs. forebodytrim = 7.5Abs. stem-posttrim 2x+2~.... Afterbody ZW--- @~--- angle, deg12 7 12 1.02 0.2984. se?* 7 .766 .2244.50 4.5 .620 .181

(c)Figure 11.- Concluded.


37/48

NACA Fig. 12aAftertndyangle = 12Stem-postangle 13Abs. forebodytrim = 15.4

Afterbodyangle = 7Stem-postangle = 8Abs. forebodytrim 10.4

Afterbodyangle = 4.5Stern-postangle 5.5Abs. forebodytrim = 7*9O

%Jqe -.-~-l& 707 4.504.s0 Am=o.493, ~hv=o.143,,(a) Absolute stern-post trim, 2.4.

Figure 12.- Stesdy-motion photographs at upper limit, moderate plsning speed


38/48

NACA Fig. 12b

Afterbodyangle 12Stern-postangle = 13Abs. forebodytrim = 16.4

Afterbodyangle 7Stern-postangle 8Abs. forebcdytrim = 11.4

Afterbodyangle 4.5Stern-postangle = 5.5 Abs. forebodytrim = 8.9

,X2-----1 ., ,o~y+ WV2=0.493,A.,C,= 0.143I I

(b) Absolute stern-post trim, 3.4.Figure 12.- Continued.

.?


39/48

NACA

Wq23 -. -.. -..12 7070 4 54 50(c) Absolute

Figure 12.- Concluded.

Fig. 12c

Afterbodyangle 12Stern-postangle = 13Abs . fcrebodytrim ~ 17.4

Afterbodyangle 7CStern-posta ngle = 8Abs. forebodytrim = 12.4

Afterbodyangle = 4.5Stern-postangle = 5.5Abs. forebodytrim = 9.9

AT2 = 0.493, ~/cv = 0.143

stern-post trim, 4.45.


40/48

1VACA Fig. 13a

Afterbodyangle = 12Stern-postangle = 13Abs. forebodytrim 13.2

Afterbodyangle = 7Stern-postangle 8Abs. forebodytrim 8.2

Afterbodyangle = 4.5Stern-postangle 5.5Abs. forebodytrim = 5.7

E ~~lvz = 0.146, /CA/C~ = 0.0425(a) Absolute stern-post trim, 0.2.

Figure 13,- Steady-motion photographs at upper limit, highPlaning speeds.


41/48

NACA Fig. 13b )

AfterbodYangle 12Stern-postangle = 13Abs. forebodytrim = 14.2

Afterbodyangle 7Stern-postangle = 8Abs. forebodyt r im = 9.2

Afterbodyangle = ~.~oStern-postangle = 5.5Abs.forebodytrim = 6.7

1%4z~.~ -.. ---120 704 5070 f12 0.146, ~/Cv =0.04254 5(b) Absolute stern-post t rim, 1.2.

Figure 13.- Continued.

..., ,..., --- ,. . . . . . ., -, . , ,, ,.,, . . . ,,i, .


42/48

NACA Fig. 13c -

.

I 1

Afterbodysngle = 12Stern-postsngle 13Abs. forebodytrim = 15.2

Afterbodyangle 7Stern-postsngle = 8Abs. forebodytrim = 10.2

Afterbodyangle 4.5Stern-postsngle 5.5Abs. forebodytrim = 7.7

%+4~.w -- ---12e 78 m=o.146, @~=o.0425. w70 4.50(cI Absolute stern-Post trim, 2.2.

Figure 13.- Concluded.


43/48

NACA Fig. 14a

c~ = 4.636

CA = 0.444

c~ = 4.173

CA = 0.361

c~ = 3.701

CA = 0.285

(a) Absolute forebody trim, 15.4.Figure 14.- Steady-motion photographs to illustrate similarity of flowpatterns at constemt values of ~\Cv obtained with different combinationsOf CA~d Cv. Afterbody angle, 90; qlcv = 0.144.


44/48

NACA Fig. 14b

Cv = 4.636

C* = 0.444

Cv = 4.173

CA = 0.361

Cv = 3.701

CA 0.285

(b) Absolute forebody trim, 16.4.Figure 14.- Continued.


45/48

N4CA Fig. 14c

c~ = 4.636CA = 0.444

c~ = 4*173

CA 0.361

c~ = 3.701

cA = 0.285

(c) Absolute forebody trim, 17.4.Figure 14.- Concluded.


46/48

/0,0

Y h/,/,0

I Ax,8

/f 0,0

,/ 0

DEG.Jh10 16

*AAN (3+2)-1=

MAXIMUM HUMP RESSllUWVs

MAXIMUM HINP TRIMonAx

I

AFTE~ ANGLESTEP FEIGHTAFTERBODYLENGTH _AFTERBODYGIINE FLAREAND STERNPOSTIXADRISE


47/48

I I i I InW AM8U Hllmq u&D UPPER LIMIT XP8ZM-I/ \ A=140,000BS

-m I$ ~8; k 0.4 FbWER ON#no APPLIEDMMENTY$ -10 14 a t2 1 J I I AT IXEO SP~4 8 II! ?-r---r Figure 16.- ~lM ANQLE, DEG


48/48

...-~-,_ ..- ..>

Illllllllluiir[llfllmilllllllllll~._3_l176013483715 ;.._..

naca arr 3i06 some analyses of systematic experiments on the resistance and porpoising...

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