Locke, F W S , Jr

English

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NATIONALADVISORYCOMMITTEE
FORAERONAUTICS
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TECHNICALNOTE
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ANANALYSISOF!imM4m EmfHC!HmA-smcs
OFS(243FUtL-SIZEMULTIEKtNEFLYINGMATS
ByF.I/.S.Locke,Jr.
Bureauof-
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ANANALYSISOFTEEMAINSERAY03ARACTERISTICS
OFSOMEl?UllG-S12J3MULTIENGINEFLYINGBOATS
Ansnalysisismade
heightofthemainspray
boats.ItiS foundthat,
ByF.W.S.ticks,Jr.
SUMMARY
ofavailableful.1-scaleandmodeldataonthe
atthepropellerplaneofmultienginedflying
withfixedCA and ~/b, increasingthe
beamtillincreasethesprayheightata“slightlygreateratethan
wouldbeexpectedbyFroude~sLaw.
Byadjustingthedatatoa commonbeam,a goodcorrelationofspr~a heightandforebodylength/besmratiois obtained. Thiscorrelationin-
dicatesa veryappreciablereductioni sprayheightcanbeobtainedby
w increasingL-f/b.
Appro&iatecombinationofthecorrelationsy~ovidesa designchart
whichwillenabledeterminationofthenecessm hullhei~ttokSeD the
propellersclear of themainsprqy.Thischart-
tiengineflyingboatsofgenerallyconventional
INTRODUCTION
isspeciflcallyfor”mul-
dwsign.
Theincreasingsizeandweightofmodernflyingboatshasernpha-
sizedtheabsolutenecessityofobtaininggoodwaterperformanceinnew
designs.Inthelast,a greatdealoftroublehasbeencausedbyspr~.
Propellers,flaps,andtailsurfaceshavebeenseriouslydemqedby
impactithsprsyinrelativelysmoothwater,andvisionthrou@the
d windshieldhasbeenbadlyobscuredbysprsythrownupthebowinrough
water.Itwouldbeverydesirabletohavemans forpredictingthehei@t
ofthesprsyasaffectedbytheloadanddimensionsofproposeddesigns.
w-
Itispointedoutinreference1 thatsprqyhastwoprincipal
.
origins:(1)The“mainspray,”whichexiateinsmoothandroughwater,
l
originatesfromtherear80percentor so oftheforebody;and(2)the
“bowsprsy,”whichnormallycanbeavoidedexceptinroughwater,orig-
* ina.tesfromtheforwardsectionsoftheforebody.
Parkinson(reference2)correlatedsomefull-scaleexperienceon
mainspr~intermsoftheforebodylength/beamratioanda spr~ “inten-
sity”constant.However,sincehiscorrelationdoesnotincluaesprsy
height,itwouldbepossibletodesigna hullhavinga low value ofthe
spray-intensityconstantandunknowinglyocatethepropellerssothat
theywereoperatinginthespray.Inotherwords,theactualcombination
ofhullandairplanemustbeconsideredasa unity.Becauseoftheim-
portanceofsprayheight,itisthepurposeoftheworkconsideredin
thisreportoattemptodeterminea correlationforthemainsprey
heightinrelative~smoothwater.Thecorrelationisbasedonquanti-
tativefull-scaledataonthespreyheightatthepropellersof
multienginsflyingboats,Noqumtitativefull-scaledataareavailable
atotherlocations,which,fortunately,areofsomewhatlessimportance.
Byusingthecorrelationitshouldbepoesibletopredicta hull
heightwhichwillensurepro~ellerclearance.Hence,thesprqyinten-
sitywillbeoflessimportance,provided,ofcourse,thehullsizeis
notdecreaseda absurdum.
*
DATA
Onfull-eizemultienginedflyingboats,theheightofthemain
sprsyinrelativelysmoothwaterisdifficulttoestinate,anywherebut
atthepropellerplane.ThelocationoftheTropellerdiskisknow
sothattheheightofthesprayatthispointmaybeestimatedwith
reasonableaccuracy.Underpracticallyallconditionsa verylightmist
of spraywillbedrawnupbythepropellers,butwhentheheavygreen
waterstrikesthepropeller,itcanbefeltaswellasseen.Itisthe
heavymainspr~enteringthepropellerinsmoothwater,andnota light
mist,withwhichthisreportisconcerned.
Mostofthedataweretakenfromf’lighttestreports.Theda% are
taken from experienceinrelativelysmoothwaterandwiththeaircrsft
headedirectlyintothetind.Alllongitudinalaccelerationswerevery
10%7,Thesprqywasobsemedbyeyewithreferencetothepropellerdisk
. andhence,whileeub~ectoa fairlylargedegreeoferror,maybecon-
sideredquantitative.Inaddition,variouspeoplewhoeitherhaaflown
theairplanesor beenconcernedwiththeiroperationwereconsulted.
- Reasonablygoodsgree~ntofopinionswasobtained.
Thedata,togetherwithpertinentparticularsofthevariousflying
boats,aretabulatedintableI.
2
IWCATION
Throughoutthisreyort thefollowing
coefficientsareused:
Initialead coefficient
Speedcoefficient
Webernumber
Longitudinalspraycoefficient
Verticalspraycoefficient
Sprayheightcoefficient
Forebodylengthcoefficient
where
A.
w
b
v
g
Y
P
x
z
initialoadonthewater,~ounds
specificweightofwater,
beamatmainstep,feet
s~eed,feetpersecond
poundsper
otationandnondimensional
cubicfoot(64.c)forseawater)
accelerationof gravi-@, 32.2feetpersecondpersecond
surfacetensioncoefficientofwater,poundsperfoot
massdensity of water,poundsecondsper foot4
longitudinalpositionofmainspr~peak,masuredfore
(positive)oraft(negative)ofthemainstep,feet
vertical positionofmainspreypeakmeasuredfrctuthetemgento
theforebodykeelatthemainstep,feet
forebodylength,measuredfromtheintersectionofchineandkeel
tothestepcentroidalonga linep~alleltothetangentothe
keelatthestep,feet
3
NACATNNo.1~1
# Figure1 definestheprincipaldimensionsdataconsideredherein,X,Isthedistanceof
lerarcaheadoftheuainstep,and Z isthe
l heavyspr~atthatpointabovethetangento
ANALYSIS
Noneoftheflightestreportsconsulted
u ed.Forthefullsize
thebottomofthepropel-
maximumheightofthe
theforebodykeel.
gavea definitespeedat
whichthespraythro@hthepro~ellers wasati~sworst,though~heyall
statedthatitwasa fairlylowspeed- around15to20knots.Examina-
tionofmodeldataIndicatesthattheworstsprayinthepropellers
shouldoccurbetweenabout~ = 1.5 and 2.0.Sincethisspee-disso
low,noveryappreciableerrorisintroducedbyassumingthattheload
onthewaterisequal tothegrossweight,forworstsprayattheyrope~
lerplane.
Inreference3, /itisshownthatwhen CX/CAL3 isfixed,the
sprayheightcoefficientCZ/CAtillalsobeconstantformostmodels.
IttillbenotedfromtableI that,whilethev=iationsof C& ona
givenflyingboatarenotlarge,@/CA. appearstobepractically
l constantforemyparticularfull-sizehull.Thus,despitetheincon-
sistencyoftherelationCZ/C&, whichisdiscussedinreference3,
itappearedtobequitesuitableforhandlingfti scaledata.
l /ForalltheflyingboatsconsideredCx/CAoL3 atthepropeller
planeisreasonablycloseto1.5,andthevariations of grossloadin
practiceonanyofthegivenairplanesdonotalteritsvalueappreci-
ably.
A plot(fig.2) of CZ/CAoagainstL-f/bfor CX/~1~3= 1.5
waspreparedfrom thedatafortheseriesofmodelsderivedsystemati-
callyfromtheXEB2M-1,endgiveninreference4..Onthissamefigure
isplottedtheavailablefull-scaledatafromtableI. Ineverycase,
themodelvalueislowerthsnfullscale,contrsryto expectations by
Froude~sLaw.Howeverjinonlyonecase,theXPB2M-I.R,wasthere
reasonablyclosesimilarityinhullformbetweenthefsmilyofmodels
endfull scale.(TheXH32M.IRhassomewhatmoreforebodychineflare
thantheXPB2M-1andlessafterbodychine flare.)Thechsrt,figure3,
. showsthedifferenceb tweenthefullscaleandmodelvaluesof CZ/C~
plottedagainsthefull-sizeb am.
. Withtheaidoffigure3al$thevaluesof @A., bothmodelend.
fullsize,wereadjustedtoa beemof10feet,andplottedagainsthe
forebodylengt~~beamratioonfigurek. Thischartindicatesa fairly
4
NACATNNO. 1~1
e goodcorrelationofthesprayheightcoefficient,egainstIf/b;soa
finaldesignchartwasprepared.Thedesignchart(fig.5),showscon-
toursof cz/c&.
It wasderivedby
again=t‘Lf/bwithf’ull~sizebeamasthe-parameter.
conibiningfi ures3 ad 4.
DISCUSSION
Thew inwhichthelinewasdrawnthroughthedataonfigure3
requiresexplsnatlonoThethreeblackpointsarefor“dirty”boats.
TheorighalS-43wasclesnedupappreciablybytheaddittonofpowerful
spraystripsontheforebody.TheJ4F-2hasnochineflare,butonlya
smallsprsystrip,andisvery“dirty.”TheRCAFisunderstoodtohave
installedspraysuppressorsonthisaircraftbutthetrdataon the re-
sultarenotavailable.SincetheSaro37alsofallsa longwayabove
thecurveonfigure3, itispresumedthatitshouldalsobe classed
asa “dirty”hull.
Figure3 inMcatesthatthedifferencesinthemodelandfull-size
spr~height,thoughnumerically small, are sufficientlylargetobeof
practicalimportance.@heexactcauseoftheUfferenceisnotatall
* clem-~at shouldbenotedthatthemodels{fromreference4)were
teste~withoutmotor-drivenpropellers,andhencetheiresultsdonot
includeanyeffectofslipstream.Thusthedifferencemsybeduetothe
l slipstream.However,Qt is just as reasonabletoassumethatthediffer-
encesinmodelandfull-scalesprayheightaredueonlytodifferencesh
thesurfacetensionumber(Webernumber).>Thefactthatitispossible
toplotthecorrectionegainsthebeamwouldappeartosupporthis
idea.Inreference6 soresexperienceisrecoz@edwhichinticatesthat
heelangle~ bethesourceofmuchofthedifference.Whenthemodel
washeeled,thespraywasappreciablyhigherelativetothemodel.Ac-
tua~ thedifferenceb tweenmcdelandfullscaleprobablyisduetoa
combinationofallofthese ffects.Sottorf?sdata(reference 5),also
obtainedfrommodelswithoutrunningpropellers,indicatea f= more
rapidincreaseofspr~heightwithincreasingsizethanisshownhere.
Becausea survey(reference6)ofchangeofspregheightwithsizeindic-
ated that nopronounceddifferencen edbeexpected,anathisissup-
portedbythepresentinvestigation,Sottorfrsesultshavebeen
neglected.
.. Withinthelimitsofabout15°to25°(reference6)ti~ riseaoes
not havemuch
thedeadrise
. location.In
uncertainties
effectonthespr~-atthepropeller plane,butincmaslng
doesproaucea beneficialreductionfsprayattheflap
usingmodeldatatodeterminesprayheight,aespitethe
Involve&inthiscorrelation,theuse oftheaddition
5
NACATNNo.l@l
/
r
givenbyfigure3atlongitudinallocationsotherthan CX/C~L3 = 1.5
probablyis~ustlfied.,atleastuntilbetterinformationbecomesavail-
able.
.
Theamountofchineflareontheforebodywillinfluencethespray
heightInsmoothwateraccordingtobothmodelandflightests.How-
ever,bothmodelandfull-scaleflightestsalsoindicatethatinrough
waterpronouncedchineflarehasverylittleffect,andinfaotsome-
times~ beevenharmful.Henceja designercencountonsom reduc-
tionofsprayinsmoothwateroverthatshownbyfi$ure5 byusingpro-
nouncedchineflare,butshouldnotexpecta proportional.reductioni
roughwater.
TheBV222isa goodexampleofwhatmighthappenbyusing
Parkinsonrscriterion(reference2)alone:65,~ poundsisapproxi-
matelythelimitingweightwhichcanbecarriedwithoutexcessivesprsy
throughthepropellers,yet ParkinsonrsK=, C~/~&/b)2,iseqti to
theverylowvalueof0.0414.Atthedesignweightof99,000poundsthe
aircraftisreportedtobeverydirty.A laterdesign,theBV238,has
almosthesamehullproportionsexcepthatthepropellersarelocated
a gooddeal fartherabovethekeel.Thisismntionedtoemphasizethe
. necessityoffittingaircraftand.hulltogethersothatthecombination
.
willgivesatisfactoryperformance,andthefactthathavinga lightly
loadedhullisnotsufficienttosnsuredesirablespr~characteristics.
.
The.designchart(fig.5)shouldbeveryuseful. in preliminaryde-
sign,providedtheforebodyformatleastresemblesthoseonwhichthe
chartisbased.Thechartdoesnotnecessarilyrepresentoptimumsob-
tainablewithconventio@forebodes,becausebothefterbodyangleand
M’terbodylengthareknowntohavefairlylarge ffectsonthespr~
characteristicsthreughtheirinfluenceontheforebodytrim.However,
byusing tie design chart, the Usigner can determine hullhei@ts,for
a givenpropellerclearance,withvariousforebodydimensions.Hecan
thendeterminetheinfluenceoftheforebodyontheperfozmsnceofthe
airplaneheisdesigning,withs~ecifiedsprayclearancetotake-off.
Withtheaidofinformationobtainedfrom figure5 a goodframeworkcan
beobtainedinwhichtomakea designstudyfora proposedairplane.
ThedatainthisreportwereobtainedfrommultiengineflyinghoatS.
Becausethereasonforthedifferenceb tweenmodelandfull-sizesprw
heightisnotclear,thedesignchartproducedfromthedataisstrictly
. applicableonlytomultienginedflyingboatsofgenerallyconventional
configurations.
..+ Itwillbenotedthatthe&signchart(fig.5)willleadtomuch
lowerloadcoefficientsthenhavegenerallybeenusedinpastpractice,
regardlessoftheforebodylength/beamratio. This till result in con-
servatived signs.However,itisverydesirablethatfurtherworkbe
6
NACATNNo.1091
r donetocorrelateaccuratelymodeieM full-scalesprayinordertoput
theprocessof-predictionona firmerfoundation.mis tilltekea g~d
dealoftires.Intheinterim,thedataInthisreyortshouldproveuse~..
. ful.
CONCLUSIONS
AnalysisofavailablemodelandfullscaledataonWe hei@tof
themainspreyatthepropellerplene,in relativelysmoothwater, indi-
cates:
1. CZ/C~ isa constantfora givenhull.
2.Witha fixed.$/b,CZ/CAoincreasesslowlywithincreasing
bean.
3.Witha fixedbeam,C@Ao decreasesrapidlywithincreasing
forebodylength.
l
BureauofAeronautics, Navy Department,
Washington,D.C.,October1945.
.
,
NACATNNo.Lwl
r RFJIEREI?CES
* 1.Locke,F.W.S.,Jr.: SomeSystematicModel~erimentsonthe
Bow-Spr~CharacteristicsofFlying-BoatHullsOperati~atLow
SpeedsinWaves.NACAARRNO.3L04,1943.
2.Parkinson,JohnB.:DesignCriterionsfortheDimensionsofthe
Forehodyofa Long-RangeFlyingBoat.NACAARRNo. 3K015j9~3.
3.Locke,F.W.S.,Jr.: “General”Main-SprayTestsofFlying-Boat
ModelsintheDisplacementRange.NACAARRNo.5A02,1945.
4.Davidson,KennethS.M.,andLocke,F.W.S.,Jr.:@ner~T*
TestsontheHydrodynamicCharacteristicsofFourFlying-Boat
HullModelsofDifferingIm@h-BeamRatio.NACAARRNo.@15,
1944.
5.Sottorf,W.: ExperimentswithPlaningSurfaces.NACATMNO.739,1934.
6.Locke,F.W.S.,Jr.,an&Bott,HelenL.:
QuantitativeStudiesoftheMainSpray
FQing-BoatHullModels.NACAARRNo.
A Method for MsJsing
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An analysis of the main spray characteristics of some full-size multi-engined flying boats

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