naca tn 183 static stability of seaplane floats and hulls
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NATIONALDJtSCFifHJM17TEEFORAEROiiAUTICs
NATIONALWISORY(lOMkJTTEEORAERONAUTICS.
NO.183
STATICSTABILITYF SEAPLAbiLOATSANDHULLS... By%. S.Diehl,Bureauof Aeronautics,.S.N.
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NATIONAII5VISORYCOMMITIHORAEROitAGTIC5.TECHNICALOTENO-183-
STATICSTABILITYF SEAPLANEFLOATSANDHULLS-*Bj7W. S.Diehl.
.Oneof theimportantactorsin seaplaneesignis the Sta --
bilityt rest on thewater.Ordinarilyhisis securedby .basinga newdesignon theproportionsollowedin someoldandsuccessfulesigq.Sufficientatahasbeencompiledrom.var- -ioussourcesto clearup thispointin eachof thecasesrequir- -ingstudy.Thesecasesarelateraland lon~itudinaltability---b of twinfloats,longitudinaltabilityf singlefloats,and lateralstabilityherefing tip floatsareused(aswitha sin-glemainfloator boathull). Thelongitudinaltabilityfboathullsis sogreatthatitmaybe neglected. .
Themethodfollowedinis to obtaina satisfactoryheightandstudythevalues
thecaseof singleandtwinfloats J-approximation.tohemetacentric .actuallysedin successfulesiOms-_
LATERALSTABILITY TWINFLOATS. .
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.
.-z-
thevolumeof displacement.et 6 be thespacingof tinefloa~son centerIinesjL thelength,and b thebeamof eachfloa~~.Then,assumingtheareaof thewaterplaneor eachflcattobe-Lb, themomentof inertiaof thetotalwaterplanereais
I ((s +b)3 - (s- b)3)= 12= +#6s2;+2b3)
Theweightof onecubicfootof seawateris 64lb.fore,thevolumedisplaceds
v = &* where ~ is thegrossweightof theseaplaneinpounds.ingtheexpressionsor I and V:
Themetacentriceight GM is thengivenbyGM= BM-BG=64L (6sb-+2b3) - h
where h is thedistanceof thec-g.abovethec.b.
..-
Thexe-
Combin-
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-3-
. GM = +whereA isthegrossdisplacementnpounds.
ThevalueofKI hasbeendeterminedroma seriesof testsat theWashingtonavyYardExperimentalodelBasin,andfoundtobe remarkablyonstantitha valueof 19.5as shownby Table .1. Theapplicationf thisformulatofullscaleindesignwill be discussedater.
LONGITUDINALTABILITY- SINGLEANDTWIHFLOATS.Followingher.ethodsedtodeterninehelateralrnetacen-tricheight,it tillbe assumedthatthewaterplane~ea.f each
floatisrectangularndofarea L X b, so thatY~emomentofinertiaof thetotalwaterplmeareais
1=%bL3where n is thenumberof floats.GM = 64nbL312A
.
Thisgives .--h
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-5-q
tobe sma21in comparisoniththemomentdueto inclination.tshou?.dherefozee alloxableoput
LI=CL2or A t COSCJ=.CWh sin6
ariddeterninehevalueof c correspo~dingo satisfac~y (and-.unsatisfactory)esigns.Thishasbeendonefortheseaplanes. .=listed.n TableIII,andit is foundthat C?variesfTOm~.~tO5.7. Onedesign,the YE-7 seaplane,avinga valueof C = 1.33,wasunsatisfactory.oublingthedisplacementf theWingtip --floatsothat C!= 2.67,q resultedin satisfactorytabi~..ity.Inviewof tieperfor~nceof thevariousseaplanesabulatedn.Table111,it is tobe concludedhatsatisfactoryateralsta-bilitywillbe obtainedThen C = 2.00.
APPLICATIONODESIGN.,.
Valuesof lateralad longitudir~le~centricheightsforVariOUS seaplaneshave been cal~la~ed by ~e~s of theapprOXi~te.formulajustderived.ThedataaregiveninTableIV. Upon .-
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-6-GM C 15 + .002~
GM beinginfeetandthegrossweightW inpoundsObviouslyhevaluesgivenby thesetwolinesareby no
meansfinal.Theyarebasedon a smallnumberof desiresand .refertoapproximatealueshm-ever,thatthevaluessorentpractice.Changesmaydatahavebeenaccumulated.
It is recommendedhat
for thesedesigns=It is thought,indicatedrea reliableguideto cur-be raieas founddesirablehenmorethelongitudinalndlateralmetacen-.
tricheights be ~~e equalandof thevaluegivenbyGM= 15 + .002w. Theproperlen@h or ~uacing~equiredtoatisfytheindicated.
valuemaYthenbe obtainedfrcmsubstitutionn theapprOXim~te _formulaeformetacentriceight.
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.
. -7-
ltodel
, Loening. CT
IIIIII11TS-1DT .Ss
q TABLEI.LATERALSTABILITYF TWINFLOATSFORSEAPLANES.
DETERMINATIONF KI IN TKEFORMULA
LengthLft.
2:332.0832.0832.0832.0832.0831.8322q 0451.75
Beambft.-:292.34s.348.348.348.348.241.296.245
Spacingon&,sft..875
1.0001q0001.Ooe1.0001;000q777-833.791
Dis-place-rlenAlb.4-676.075.084.353.632.722.733.942.61
Heta-centricheightGMft.2-1192.3282.9?3.174.015.061.9551.8902.030
Lbs2A
.1117
.1192
.1423
.1663
.1993.2660
.0983
.1067
.~028
19.013.5 .=20.9 -:19.120.1 .19.019.9 .17:719.8
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.-8-
.
Model
q LoeninIICTII
II
n
H
TS-1DT
TAE.LE1.LONGITUDZNAHTABIJTYOl?SIIAPL&NELOATS.DeterminationF Q IN THEFOR.KULA
LengttLft.
2.332.312.0832.0832.0832.0832.0831.8322.945
GM . ~nbL3AMODELTESTDATA.
Beam1liumbe~ofb floatsinft.I ._J..,__
.2921 2t
i.348 2.348.348.241.296
2222
Dis-place-mentAlb.4-674.906.075.084.353.632.722.713.94
Meta-centricheightGMft.3.1642.6142.0532.903.473.i94.142.3602.423
nbL3A
1.581.2531.0341,~371.4431.7302.3101.0931.284
.
K2-.
-- - -2.00 -.1.99 --....2.34....1
:.-. s2.40. ...,. .-2q07 _.=;1,79 .:...2.16 :..--__,,1.89 ._,
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-$j -
TABIJ3II.LATERALSTABILITYEAPLANESITHWINGTIPFLOATS.
.
Seaplane
N9HS-2 qHS-33-16F-5-LNCMI?iFVE-7VE-7Mod.40
GroBSweightw
lb.24006430643010900135002200024908850260026002467
Dis- .*place- a;o$ement c.b,eachwing htipfloatil.lb. ft.160 I 5.7
WingtipfloattoG1.f-h19.1
275 I 4.9 I26.4*O 4.51170 6.01175 6,0laoo ?.5160 4.01000 5.0190 6.0380 6.0265 4*3
26.430.433.241.515.6Z.513.513.514.75
Angletosub-mergewingtipfloato$977874*.5.1097710
tan9
.158
.123,123.140.123*079.176~158q 123.123.176
c?
1.421,875.033.883.925.7019433.231.332.672.08
Remarks-
.
.,
-.-+ .
lJnsatis-,fat- .tory
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Seaplam
bening~~TS-1
DTSsVTR6BoeingWATG
q N9* NcGB
TABEEIV.FULLSCALEMETACENTRICEIGHTOF SEAPLANES. 6
(CALCULATEDY FORMULA)Dis-place-mentAlb.2450100002025697546158615.395024554~(30..~8~24002200065000
Lerqth Beamofboat~ bft. f-t18.67I 2.3325.00 4.716.50 2.1824.53 3.5521*O I 2.9325.75 3.6120.0 [email protected] 2.2E!25.06 3.2521.251.2517.83 3.4844.8 I 10.064.g6 I14.6
Number;Spacingon&
Tn sft.2z
222,22211111
7.012*O
\ 70I IO*OI 9.0I\ 11.83II 11.0I1 7.5
I
Longitu-LateraldinalGM GMft ft.
26.027.420.331.624.829.921.316.025.623.317.386.0129.0
17.029.317.0 _24.320.9..29.429.816.4
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Fig.1,