1、Designation: F3331 18Standard Practice forAircraft Water Loads1This standard is issued under the fixed designation F3331; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates
2、the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides equations for calculating waterloads for aeroplane dual floats and single hulls. The materialwas developed through open consensus of internation
3、al expertsin general aviation. This information was created by focusingon Level 1, 2, 3, and 4 Normal Category aeroplanes. Thecontent may be more broadly applicable; it is the responsibilityof the Applicant to substantiate broader applicability as aspecific means of compliance.1.2 An applicant inten
4、ded to propose this information asMeans of Compliance for a design approval must seek guid-ance from their respective oversight authority (for example,published guidance from applicable CAAs) concerning theacceptable use and application thereof. For information onwhich oversight authorities have acc
5、epted this standard (inwhole or in part) as an acceptable Means of Compliance totheir regulatory requirements (hereinafter “the Rules”), refer toASTM Committee F44 web page (www.astm.org/COMMITTEE/F44.htm).1.3 UnitsThe values stated in inch-pound units are to beregarded as standard.1.4 This standard
6、 does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This interna
7、tional standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Com
8、mittee.2. Referenced Documents2.1 ASTM Standards:2F3060 Terminology for Aircraft3. Terminology3.1 A listing of terms, abbreviations, acronyms, and sym-bols related to aircraft covered by ASTM Committees F37 andF44 airworthiness design standards can be found in Terminol-ogy for Aircraft F3060. Items
9、listed below are more specific tothis standard.4. Significance and Use4.1 This practice provides one means for determining theaeroplane structural loads for either dual floats or single hullswhen taxiing on, taking off from, or landing on water. Thispractice satisfies the water loads requirements se
10、t forth in theDesign Loads and Conditions Specification for Normal Cat-egory Aeroplanes.5. Calculation of Aeroplane Water Loads5.1 Design Weights and Center of Gravity Positions:5.1.1 Design WeightsThe water load requirements mustbe met at each operating weight up to the design landingweight except
11、that, for the takeoff condition prescribed in 5.5,the design water takeoff weight (the maximum weight forwater taxi and takeoff run) must be used.5.1.2 Center of GravityThe critical centers of gravitywithin the limits for which certification is requested must beconsidered to reach maximum design loa
12、ds for each part of theseaplane structure.5.2 Application of Loads:5.2.1 Unless otherwise prescribed, the seaplane as a wholeis assumed to be subjected to the loads corresponding to theload factors specified in 5.3.1This practice is under the jurisdiction of ASTM Committee F44 on GeneralAviation Air
13、craft and is the direct responsibility of Subcommittee F44.30 onStructures.Current edition approved Sept. 1, 2018. Published October 2018. DOI: 10.1520/F3331-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book o
14、f ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized
15、 principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.15.2.2 In applying the loads resulting from the load factorsprescribed
16、 in 5.3, the loads may be distributed over the hull ormain float bottom (in order to avoid excessive local shear loadsand bending moments at the location of water load application)using pressures not less than those prescribed in 5.6.3.5.2.3 For twin float seaplanes, each float must be treated asan
17、equivalent hull on a fictitious seaplane with a weight equalto one-half the weight of the twin float seaplane.5.2.4 Except in the takeoff condition of 5.5, the aerody-namic lift on the seaplane during the impact is assumed to be23 of the weight of the seaplane.5.3 Water LoadsHull and Main Float Load
18、 Factors:5.3.1 Water reaction load factors nwmust be computed inthe following manner:5.3.1.1 For the step landing case:nw5C1VS02tan23!W13(1)5.3.1.2 For the bow and stern landing case:nw5C1VS02tan23!W133K11 1 rx2!23(2)5.3.2 The following values are used:5.3.2.1 nw= water reaction load factor (that is
19、, the waterreaction divided by seaplane weight).5.3.2.2 C1= empirical seaplane operations factor equal to0.012 (except that this factor may not be less than thatnecessary to obtain the minimum value of step load factor of2.33).5.3.2.3 VS0= seaplane stalling speed in knots with flapsextended in the a
20、ppropriate landing position and with noslipstream effect.5.3.2.4 = angle of dead rise at the longitudinal station atwhich the load factor is being determined in accordance withFig. 1.5.3.2.5 W = seaplane design landing weight in pounds.5.3.2.6 K1= empirical hull station weighing factor, inaccordance
21、 with Fig. 2.5.3.2.7 rx= ratio of distance, measured parallel to hullreference axis, from the center of gravity of the seaplane to thehull longitudinal station at which the load factor is beingcomputed to the radius of gyration in pitch of the seaplane, thehull reference axis being a straight line,
22、in the plane ofsymmetry, tangential to the keel at the main step.5.3.3 For a twin float seaplane, because of the effect offlexibility of the attachment of the floats to the seaplane, thefactor K1may be reduced at the bow and stern to 0.8 of thevalue shown in Fig. 2. This reduction applies only to th
23、e designof the carry through and seaplane structure.5.4 Hull and Main Float Landing:5.4.1 Symmetrical Step, Bow, and Stern LandingFor sym-metrical step, bow, and stern landings, the limit water reactionload factors are those computed under 5.3. In addition:5.4.1.1 For symmetrical step landings, the
24、resultant waterload must be applied at the keel, through the center of gravity,and must be directed perpendicularly to the keel line.5.4.1.2 For symmetrical bow landings, the resultant waterload must be applied at the keel, one-fifth of the longitudinaldistance from the bow to the step, and must be
25、directedperpendicularly to the keel line; and5.4.1.3 For symmetrical stern landings, the resultant waterload must be applied at the keel, at a point 85 % of thelongitudinal distance from the step to the stern post and mustbe directed perpendicularly to the keel line.5.4.2 Unsymmetrical Landing for H
26、ull and Single FloatSeaplanesUnsymmetrical step, bow, and stern landing con-ditions must be investigated. In addition:5.4.2.1 The loading for each condition consists of an up-ward component and a side component equal, respectively, to0.75 and 0.25 tan times the resultant load in the correspond-ing s
27、ymmetrical landing condition;5.4.2.2 The point of application and direction of the upwardcomponent of the load is the same as that in the symmetricalcondition, and the point of application of the side component isat the same longitudinal station as the upward component butis directed inward perpendi
28、cularly to the plane of symmetry ata point midway between the keel and the chine lines.5.4.3 Unsymmetrical Landing; Twin Float SeaplanesTheunsymmetrical loading consists of an upward load at the step ofeach float of 0.75 and a side load of 0.25 tan at one float timesthe step landing load reached und
29、er 5.3. The side load isdirected inboard, perpendicularly to the plane of symmetrymidway between the keel and chine lines of the float, at thesame longitudinal station as the upward load.FIG. 1 Pictorial Definition of Angles, Dimensions, and Directionson a SeaplaneF3331 1825.5 Water Loads-Hull and M
30、ain Float Takeoff Condition:5.5.1 For the wing and its attachment to the hull or mainfloat, the aerodynamic wing lift is assumed to be zero; and5.5.2 A downward inertia load, corresponding to a loadfactor computed from the following formula, must be applied:n 5CTOVS12tan23!W13(3)where:n = inertia lo
31、ad factor;CTO= empirical seaplane operations factor equal to 0.004;VS1= seaplane stalling speed (knots) at the design takeoffweight with the flaps extended in the appropriatetakeoff position; = angle of dead rise at the main step (degrees); andW = design water takeoff weight in pounds.5.6 Hull and M
32、ain Float Bottom Pressures:5.6.1 GeneralThe hull and main float structure, includingframes and bulkheads, stringers, and bottom plating, must bedesigned under this section.5.6.2 Local PressuresFor the design of the bottom platingand stringers and their attachments to the supporting structure,the fol
33、lowing pressure distributions must be applied:5.6.2.1 For an unflared bottom, the pressure at the chine is0.75 times the pressure at the keel, and the pressures betweenthe keel and chine vary linearly, in accordance with Fig. 3. Thepressure at the keel (psi) is computed as follows:pK5C2K2VS12tank(4)
34、where:PK= pressure (psi) at the keel;C2= 0.00213;K2= hull station weighing factor, in accordance with Fig.2;VS1= seaplane stalling speed (knots) at the design watertakeoff weigh twith flaps extended in the appropriatetakeoff position; andk= angle of dead rise at keel, in accordance with Fig. 1.FIG.
35、2 Hull Station Weighing FactorFIG. 3 Transverse Pressure DistributionsF3331 1835.6.2.2 For a flared bottom, the pressure at the beginning ofthe flare is the same as that for an unflared bottom, and thepressure between the chine and the beginning of the flare varieslinearly, in accordance with Fig. 3
36、. The pressure distribution isthe same at that prescribed in 5.6.2.1 for an unflared bottomexcept that the pressure at the chine is computed as follows:Pch5C3K2VS12tan(5)where:Pch= pressure (psi) at the chine;C3= 0.0016;K2= hull station weighing factor, in accordance with Fig.2;VS1= seaplane stallin
37、g speed (knots) at the design watertakeoff weight with flaps extended in the appropriatetakeoff position; and = angle of dead rise at appropriate station.5.6.2.3 The area over which these pressures are appliedmust simulate pressures occurring during high localized im-pacts on the hull or float, but
38、need not extend over an area thatwould induce critical stresses in the frames or in the overallstructure.5.6.3 Distributed PressuresFor the design of the frames,keel, and chine structure, the following pressure distributionsapply:P 5C4K2VS02tan(6)5.6.3.1 Symmetrical pressures as computed as follows:
39、where:P = pressure (psi);C4= 0.078 C1(with C1computed under 5.3);K2= hull station weighing factor, determined in accordancewith Fig. 2;VS0= seaplane stalling speed (knots) with landing flapsextended in the appropriate position and with noslipstream effect; and = angle of dead rise at appropriate sta
40、tion.5.6.3.2 The unsymmetrical pressure distribution consists ofthe pressures prescribed in 5.6.3.1 on one side of the hull ormain float centerline and one-half of that pressure on the otherside of the hull or main float centerline in accordance with Fig.3.5.6.3.3 These pressures are uniform and mus
41、t be appliedsimultaneously over the entire hull or main float bottom. Theloads obtained must be carried into the sidewall structure of thehull proper but need not be transmitted in a fore and aftdirection as shear and bending loads.5.7 Auxiliary Float Loads:5.7.1 GeneralAuxiliary floats and their at
42、tachments andsupporting structures must be designed for the conditionsprescribed in this section. In the cases specified in 5.7.2 5.7.5,the prescribed water loads may be distributed over the floatbottom to avoid excessive local loads, using bottom pressuresnot less than those prescribed in 5.7.7.5.7
43、.2 Step LoadingThe resultant water load must beapplied in the plane of symmetry of the float at a pointthree-fourths of the distance from the bow to the step and mustbe perpendicular to the keel. The resultant limit load iscomputed as follows, except that the value of L need notexceed three times th
44、e weight of the displaced water when thefloat is completely submerged:L 5C5VS02W23tan23s1 1 ry2!23(7)where:L = limit load (lb);C5= 0.0053;VS0= seaplane stalling speed (knots) with landing flapsextended in the appropriate position and with noslipstream effect;W = seaplane design landing weight in pou
45、nds;S= angle of dead rise at a station34 of the distance fromthe bow to the step, but need not be less than 15; andry= ratio of the lateral distance between the center ofgravity and the plane of symmetry of the float to theradius of gyration in roll.5.7.3 Bow LoadingThe resultant limit load must be
46、ap-plied in the plane of symmetry of the float at a point one-fourthof the distance from the bow to the step and must beperpendicular to the keel line at that point. The magnitude ofthe resultant load is that specified in 5.7.2.5.7.4 Unsymmetrical Step LoadingThe resultant waterload consists of a co
47、mponent equal to 0.75 times the loadspecified in 5.7.1 and a side component equal to 0.25 tan times the load specified in 5.7.3. The side load must be appliedperpendicularly to the plane of symmetry at a point midwaybetween the keel and the chine.5.7.5 Unsymmetrical Bow LoadingThe resultant waterloa
48、d consists of a component equal to 0.75 times the loadspecified in 5.7.2 and a side component equal to 0.25 tan times the load specified in 5.7.3. The side load must be appliedperpendicularly to the plane of symmetry at a point midwaybetween the keel and the chine.5.7.6 Immersed Float ConditionThe r
49、esultant load mustbe applied at the centroid of the cross section of the float at apoint one-third of the distance from the bow to the step. Thelimit load components are as follows:vertical 5 gVaft 5CxV23KVS0!22side 5CYV23KVS0!22(8)where: = mass density of water (slugs/ft3);V = volume of float (ft3);CX= coefficient of drag force, equal to 0.133;CY= coefficient of side force, equal to 0.106;K = 0.8, except that lower values may be used if it isshown that the floats are incapable of submerging at aspeed of 0.8 VS0in norma
