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experimentwascariedoutinstrongwindcondition，preventionefectagainstjumpsparksfrom the fire was also examined. In 19，the fire deterent efect when the water droped continuouslyfrommanyhelicopterswasexamined[3-4].Inadition，themagnitudeofthe crashedimpactofdropedwaterwasexaminedusingthelargehelicopter.For3yearsresearch work，fromtheaerialfirefightingexperiment，thelimitofaerialfirefightingandtheposibilityof efectiveuseweresugested.Manyproblemsareleftbehindstilmoreanditisbecomeclear thatthemethodofefectiveaerialfirefightingnedstobeinquired.However，sinceahugespace and an enormous budget are ne eded，it is dif ficult to carηout the real scale experiment frequently.
Therefore，inthisresearchwork，smalmodelexperimentwasproposedandsimilaritywithareal scaleexperimentwasverified.Asthefirststep，thescateringbehaviorofthewaterdroped fromthebuckettotheairwasreproduced.Althoughtherearemanyexampleswhichstudiedthe colapsephenomenonandthephysicalphenomenonofliquiddropswhichfalstheair[e.g.5-7]， therearefewexampleswhichstudiedforthesimilarityofthespreadsituationofthewaterwhile scateringhugeamountofwater.Inthispaper，thebehaviorofdropedwaterfromthebucketto theairwiththeexperimentsmalmodelwasreproduced，andthesimilarityofthebehaviorof dropedwaterwitharealscaleexperimentwasdiscused.Inadition，theimpactofcrashed wateronthegroundwasexamined.
Experimentalmethod
Fig.1isthephotographoftherealwaterbucketformidlesizefire-fightinghelicopterBKl17in Oitaprefecture，Japan.Watercapacityofthebucketis600liters，dischargeorificediameteris 200mm.Thebucketwashungunderthehelicopter，andincaseofwaterscatered，thefirefighter wasoperatedtheopeningandclosingofthedischargeholemanualy.Thesmalsimilaritytank modelwasproduced，andweconductedtwoexperiments，oneisforbehaviorofdropedwater andtheotherisforimpactofcrashedwaterontheground.
(a)Dischargehole (b)Exteriorview Fig.1.Waterbucketforfirefightinghelicopter.