O) c: A no . A ; _L \l “M ~._,1 t * 5 . {553771111 ‘i Zlé’Q/zsv " QWMZZQQ {315/ v v ANC BULLETIN WATER LOADS Department or the'Air Force Air Materiel Command Department of the Navy Bureau of Aeronautics Department of Commerce Civil Aeronautics Administration Issued by the Subcommittee on Air Force-Navy-Civil Aircraft Design Criteria of the Munitions Board Aircraft Committee The contents of this Document shall not be reproduced in whole or in part without specific authorization of the Munitions Board Aircraft Committee. For sale by the Superintendent of Documents, U. S. Government Printing Ofl‘ice Washington 25, D. C. - Price 15 cents a.’ _,,.,-___‘ ANC-3 JUNE I950 NOTICE This bulletin is subject to revision and amendment when and where such revision or amendment is necessary to effect agreement with the latest improved information on aircraft design criteria. When using this bulletin, the reader should make certain that it is the latest revision, and that all issued amendments, if any, are known. Copies of this document, and amendments thereto, may be purchased from the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C. Engin. Ubrary .i’fr‘’ / J ALI“ ‘1" ‘kw, \.~v If A. , 9e" ‘\ m=3=%ma‘oI g9 THE 0 UNITED STATES OF AMERICA 8-» H15 WATER LOADS 1. General 1.1 Introduction 1.2 Water load parameters 1.5 Gross weight(s) 1 4 Distribution of mass items 1.5 Center-of-gravity positions 1.6 Power or thrust 1 7 Stalling speed(s) 1.8 Operations factor, Ka 1.9 Strength 2. symbols 3. Water pressures 5.1 Symmetrical water pressures for bottom design 5.2 Symmetrical water pressures for general design 5.5 Unsymmetrical water pressures for general design 5.4 Variation of numerical factor, K1 4. Symmetrical water loads 4.1 General 4.2 Hull or main float 4.5 Auxiliary floats 5. unsymmetrical water loads 5.1 General 5.2 Hull or main float 5.5 Auxiliary floats 1. GENERAL 1.1 Introduction. - This document describes a procedure for the computation of the magnitude and distribution of the water pressures and water loads imposed on the hull or main float and the auxiliary floats of seaplanes during landing and take-off. The procedures described are based upon the theory of seaplane impact suitably modified and adapted to practical design by the introduction of empirical constants, the values of which have been determined by the examination of a number of seaplanes known to have given satisfactory structural performance in landing and take-off. Inasmuch as this document is intended to describe design procedures, the development of the theory and the derivation of the formulas used herein have not been included. 1.2 water load parameters. - The loading conditions described in this document are defined in terms of stalling speed, angle of deadrise, airplane weight, airplane mass moment of inertia, power or thrust, and intended type of operation. 1.3 Gross weight(s). - The gross weight(s) for the loading conditions described in this document shall be those specified or approved by the procuring or certificating agency. 1.4 Distribution of mass items. - The distribution of mass items for the loading conditions described in this document are all those that are to be used in operations at the gross weight(s) specified in section 1.5 and for the center-of-gravity range specified by section 1.5. 1.5 center-of-gravity positions. - The center-of-gravity positions to be employed with the design gross weight(s) are the maximum forward position and the maximum aft position associated with the gross weight(s) specified in section 1.5. 1.6 Power or thrust. - For the loading conditions described in this bulletin the engines are to be delivering take—off power or thrust and also to be delivering zero power or thrust. 1.7 stalling speed(s). - The stalling speed(s) to be employed are the sea level stalling speed(s) at the applicable design gross weight(s) of section 1.5 with zero thrust and with landing flaps and other high lift devices in the operating positions corresponding to the take-off or landing conditions at the specified weights. 1.8 operations factors. - The loading conditions described in this document are set forth in a form in which the significant airplane parameters that affect water load are grouped together in the relationship indicated by theory. The magnitude of the actual water load resulting from this grouping is controlled by a factor, herein termed an operations factor and assigned the symbol K for the hull or main float and K4 for the auxiliary floats, the numerical value of which has been sefected so as to result in design loads compatible with those that will occur in operational use. The values of the factors, K3 and K4, for civil aircraft operation are considered to be 0.009 and 0.005, respectively. The values of the factors K3 and K4, for military aircraft operation are considered to be 0.015 and 0.007, respectively, unless otherwise required by the procuring agency. In those instances where the ratio of the design water load, as determined herein, to the weight of the airplane is less than 2.55 in the step landing case the value of the K3 factor shall be increased so as to result in a ratio of 2.55. 1.9 strength. — The airplane structure must be capable of supporting without failure the design ultimate loads resulting from the loading conditions and ultimate factor of safety specified in this document. The loads which result from the design conditions specified herein are limit loads. The minimum ultimate factor of safety shall be 1.5, or as otherwise specified by the procuring or certificating agency. The magnitudes and distributions of limit and design ultimate loads that result from the loading conditions and factors of safety specified herein shall include in their determination the effects of the deformations of the structure which result from limit loads. The airplane structure Shall be capable of supporting the design yield loads that result from the loading conditions and the design yield factor of safety specified by the procuring or certificating agency without permanent deformation that will affect adversely the aerodynamic or hydrodynamic characteristics or the mechanical operation of any part of the airplane or that will be noticeable upon inspection. The bottom plating of hulls, main floats, and auxiliary floats shall support the design yield water pressures without permanent deformations that exceed one-half of one percent of the short span of the plating panel. The externally applied loads specified in this document are based upon treatment of the airplane as a rigid body. Because the airplane is elastic, the transient loads developed within the elastic structure under impulsive loading conditions may be significantly greater than the internal loads which would be determined if the structure were considered to be rigid. Transient loads which result from the externally applied limit loads specified herein shall be considered in the structural design of the seaplane. Particular attention should be given to the significant effect of transient oscillations in the determination of the loads acting upon such mass items as the tail group, forward and after sections of the fuselage, nacelles, and other items which are remote from the airplane center of gravity. ‘BC 13k Pa Pk 2. SYMBOLS angle of deadrise at chine, degrees (see figure 5.1) angle of deadrise at keel, degrees (see figure 5.1) angle between the hull reference line and the tangent to line b at each point on line b, in degrees (see figure 2.1) - coefficient of the tip float drag force coefficient of the tip float side force factor employed in the determination of the design water pressures (see table 5,1) radius of gyration of the airplane about the Y-axis, feet radius of gyration of the airplane about the X—axis, feet factor employed in the determination of the design water pressures (see table 5.1 and figure 5.4) factor employed in the determination of the hull or main float water loads (see figure 4.2) operations factor applicable to hull or main float loads (see section 1.8) operations factor applicable to auxiliary float loads (see section 1.8) distance from the step to the bow of the hull or the tip of the float, measured parallel to the X—axis, feet (see figures 4.2 and 4.5) distance from the step to the stern of the hull, measured parallel to the X—axis, feet component of the hull or float resultant water load parallel to the Z-axis, pounds component of the auxiliary float resultant water load parallel to the float ZX-plane, pounds water pressure, pounds per square inch water pressure at the chine of the hull or float, pounds per square inch (see figure 5,1) water pressure at the keel of the hull or float, pounds per square inch (see figure 5,1) mass density of sea water, 1.98 slugs per cubic foot volume of the tip float, cubic feet sea level stalling speed(s) of the airplane, power-off, miles per hour design gross weight(s), pounds distance from the airplane center of gravity to a point on the hull, measured parallel to the X-axis, feet distance from the X-axis to the auxiliary float plane-of-symmetry, measured along a line normal to the float plane-of-symmetry, feet (see figure 2.1) NOTES: 2! J ' __--- Line a is the projection of the chine on the plane of symmetry. Line b is in the plane of symmetry midway between the keel and line a. The hull (or main float) reference line is a straight line in the plane of symmetry tangent to line b on the forebody at the step. The X-axis is in the plane of symmetry parallel to the hull (or main float) reference line with the origin at the airplane center of gravity; the Z—axis is in the plane of symmetry normal to the X—axis; and the Y-axis is normal to the plane of symmetry. 8 is the angle between the hull reference line and the tangent to line b at the point at which any resultant water load acts. Positive directions are as shown. Figure 2.1 Coordinate system for water loads 3. WATER PRESSURES 3.1 Symmetrical water pressure for bottom design. - The symmetrical water pressures applicable only to the design of the bottom plating and stringers and their attachments to the supporting structure are those specified in table 5.1, rows 1 and 5, and in figure 5.1. These water pressures are intended to simulate the pressures occurring during high localized impacts on the hull or float. The bottom areas over which these pressures are applied shall be selected so as to result in the most critical local design loads except that areas so selected may be limited in size so as to not produce water loads greater than those resulting from section 4 of this bulletin. 3.2 symmetrical water pressures for general design. - The symmetrical water pressures to be used in the design of the bottom plating, stringers, floors, and frames are those specified in table 5.1, rows 2 and 4, and in figure 5.2. These water pressures are the pressures to be used in conjunction with the procedures described in section 4 of this bulletin for the design of the general structure. 3.3 unsymmetrical water pressures for general design. - The unsymmetrical water pressures to be used in the design of the bottom plating, stringers, floors, and frame are those specified in table 5.1, rows 2 and 4, and in figure 5.5. These water pressures are the pressures to be used in conjunction with the procedures described in section 5 of this bulletin for the design of the general structure. 3.4 Variation of numerical factor, K1. - In determining the magnitude of the water pressures specified in this section 5 the variation of the numerical factor, K1, with hull or float length shall be that specified in figure 5.4. TABLE 3.1 WATER PRESSURES _ fK1vs2 f p — tan fl Applicable when Kl B Ka = 0.009 K3 = 0.013 in psi at K4 = 0.005 K4 = 0.007 1 2 3 4a 4b 5 6 Bottom plating. string- keel -0016 -0024 Bk ers, and attachments _ Hull or chm -0012 -0018 From 15.; main figure float(s) 5-4 Bottom plating, string— keel ers, floors, and frames and 0007 .0010 fi in combination with chine ' c over-all loading keel . . 24 . (see n te 2) Bottom plating, string— 0016 00 1 O fik o ers, and attachments . Auxiliary chine .0012 .0018 1.0 56 (see note 2) float Bottom plating, string— keel ?rs' fl9orsg and frames and .0007 .0010 1.0 Ba (see note 2) in combination with chine over—all loading NOTES: 1. Vs = stalling speed(s) in mph as defined in section 1.7 2. B = angle of deadrise measured at station where pressure is computed (see figure 5,1) except that for auxiliary floats the angle of deadrise shall be assumed constant along the length of the float and equal to the angle of deadrise one-quarter of the distance from the step to the bow UNFLARED COMPLETE FLARE \fi lac or J m * ‘ r r 1‘- p0 linear variation PARTIAL FLARE linear variation ' f1... ’fl'_figéi;?\lllinear variations NOTES: 1. 5k : angle of deadrise at keel 2. fie = angle of deadrise at chine 3. pk : pressure at keel (table 5.1) 4. pa = pressure at chine (table 5.1) ' Figure 5.1 Transverse variation of symmetrical pressure for bottom plating, stringers, and attachments .v ! I uniform distribution Figure 5.2 Transverse variation of symmetrical pressure for bottom plating, stringers, floona and frames. \ Q ~\‘ uniform distribution Figure 5.5 Transverse variation of unsymmetrical water pressure for bottom plating, stringers, floors, and frames. 0.75 1.0 i l 0.5 A ~ +_____Lf/2_____,_ Figure 5.4 Variation of numerical factor K1 with hullor float length 4. SYMMETRICAL WATER LOADS 4.1 General. — The external loads acting on the airplane are those specified in table 4.1 considering each loading condition separately. The water loads are considered as the summation of unit pressures applied over a loaded area. The external loads are to be reacted by inertia forces imposed on the mass elements of the airplane. The inertia forces are to be determined from a' consideration of the translational and rotational accelerations imparted to the airplane by the external loads and are to be utilized (in conjunction with the external loads) in obtaining net loads for design. 4.2 Hull or main float. - The envelopes of the X- and Z— components of the water loads versus the hull or main float length are computed in accordance with the procedures specified in figure 4.2. From these envelopes the particular water loads that are critical for design are to be selected. The transverse distribution of water pressures at any hull station within the loaded area that is required to produce a particular resultant water load shall be that shown in figure 5.2. The longitudinal extent of the loaded area shall be chosen such that the pressures specified in section 5.2 of this bulletin produce the specified load in magnitude, and point of application. Resultant water loads and their attendant pressure distributions should be computed at a sufficient number of stations on the forebody and afterbody to insure that critical loading conditions for design are adequately covered. However, as a minimum, strength shall be provided for the following four loading conditions: a. The condition involving the most forward load that can be developed on the forebody within the limiting positions shown on figure 4.2. b. ‘The condition involving the maximum nose-up pitching acceleration of the airplane. c. The condition involving the largest Z— component of the water load. d. The condition involving the most aft load on the afterbody within the limiting positions shown on figure 4,2. 4.3 Aux111ary floats. - Two loading conditions only are specified for design. In each condition the X- and 2- components of the resultant water load are computed in accordance with the procedure specified in figure 4.5. In each condition the transverse distribution of water pressures is uniform over the full beam width. a. Bow—landing condition — The distance, d, in figure 4,5 shall be 0.75 times the distance from the step to the bow. The loaded area shall be that area forward of the station midway between the bow and the step. The longitudinal distribution of the running load shall be uniform and of sufficient magnitude to produce the specified load except that pressures in excess of that specified in table 5.1, row 4, may be neglected. b. Step-loading condition — The distance, d, in figure 4.5 shall be 0.25 times the distance from the step to the bow. The loaded area shall be that area aft of the station midway between the bow and the step. The longitudinal distribution of the running load shall be uniform and of sufficient magnitude to produce the specified loads except that pressures in excess of that specified in table 5.1, row 4, may be neglected. TABLE 4.1 SYMMETRICAL WATER LOADS Loading Air Load Alr ioad water load Water load See condition Z applled applied at figure , at X Z 1 2 3 4 5 7 8 9 Center ' Any point on line b of Hull figure 4.2 between the Forebody 2/5W Pltan 5 £3 maximum forward and 4.2 or maximum aft locations main of shown on figure 4.2 at float which the specified Afterbody 2/3W 0 P1 load can be developed 4.2 at the pressures spe- cified in section 4.2. gravity Line b of figure 4.3 Bow W Basin 8 Pzcos 8 at 3/4 the distance 4.3 Either from step to bow. auxiliary of float Line b of figure 4.3 Step W Pzsin 8 Pzcos 8 at 1/4 the distance 4.3 airplane from step to bow. tangent to line b at point of application of-load line'bifrcm figure 2.1 &~—hull reference line 0.8L Note ( O) 0-85L Note (18) 10. L1‘ w 2/3 2 KZKS 1 + x2/iy2 VS tang/3 fih ‘,pounds numerical factor illustrated in this figure 4.2 0.009 for seaplanes intended for civil operation and 0.015 for seaplanes intended for military operation, or as required by the procuring or certificating agency airplane design gross weight as defined in section 1.3, pounds radius of gyration of the airplane about Y—axis, feet distance illustrated.in this figure 4.2, feet stalling speed in mph as defined in section 1.7 angle of deadrise at chine at station where resultant water load is applied (see figure 5.1) pressure at station where resultant water load is applied, as defined in table 5.1, row 2, and figure 5.2 ' resultant water load shall act at any point on line b within the fore and aft limits defined. 0 Figure 4.2 Symmetrical water loads on hull or main float— l2 tangent to line b at point of application of load line b from figure 2.1 q \ \ v \4 P2 cos 8 5 LIE bull or main float reference line <_ Lf NOTES: w 2/8 K4 2 - 2 V 2 1 + y /1x 8 1, P2 = , pounds 2. W = airplane design gross weight as defined in section 1.5, pounds 5. ix = radius of gyration of the airplane about X-axis, feet 4. y = distance from the X—axis of airplane to plane of symmetry of tip float, measured normal to the tip float plane of symmetry, feet 5. Vs : stalling speed in mph as defined in section 1.7 . £6 = angle of deadrise at chine at station 1/4 of the distance from the step to the bow (but need not be less than 15 degrees) 7. p = pressure (need not exceed that specified in table 5.1, row 4) 8. K4 = 0.005 for seaplanes intended for civil operation and 0.007 for seaplanes intended for military operation, or as required by the procuring or certificating agency Figure 4.5 Symmetrical water loads on auxiliary float 5. UNSYMMETRICAL WATER LOADS 5.1 General. — The external loads acting on the airplane are those specified in table 5.1, considering each loading condition separately. Except for the fully immersed loading condition for the auxiliary float the water loads are considered as the summation of unit pressures applied over a loaded area. The external loads are to be reacted by inertia forces imposed on the mass elements of the airplane. The inertia forces are to be determined from a consideration of the translational and rotational accelerations imparted to the airplane by the external loads and are to be utilized (in conjunction with the external loads) in obtaining net loads for design. 5.2 Hull or main float. - The envelopes of the X—, Y—, and Z— components of the water loads versus the hull or main float length are determined by substituting the load P (determined in accordance with section 4.2 of this bulletin) in the formulas of table 5.1. T e transverse distribution of water pressures at any hull station within the loaded area that is required to produce a particular resultant water load shall be that shown in figure 5.5. The longitudinal extent of the running load and the loading conditions critical for design shall be determined in a manner analogous to that employed for the symmetrical loading conditions of section 4.2. 5.3 Auxiliary floats. - The unsymmetrical loads for either auxiliary float shall be determined in accordance with the formulas set forth in table 5.1 by reducing the pressures for the loading conditions of section 4.5 by fifty (50) percent on one side of the auxiliary float plane of symmetry, and adding an arbitrary incremental side load at the chine normal to the float plane of symmetry.’ Inboard and outboard acting total side loads shall be considered. In addition to the foregoing, strength shall be provided for the loads resulting from the fully immersed loading condition specified in table 5.1 and in figure 5.5. No water pressures are specified for this latter condition. TABLE 5.1 UNSYNHETRICAL WATER LOADS E’ Irndhg axnitkm Adr hxxlAdrjknd Z applhai at 'mnerlknd i’Y Whtfl‘ldfii amfliedat Figure 8 Hull or mani float Fbndxfiy 2/5wy (Enter Afuntndy 2/3W of Eiflxw mndlnuy float gmndty Sun) FulLy hnmnsed of ahmflane 0.75P1tan 8 tan fig 0' 25P1cos 8 0.75P1 0.25P1 tan ac (Jr/51>l Any point on line b of figure 4.2 beumxnitheimudmmn fonantiandlmndmum aft,hxxnionssmown a1f1gue1452at which the specified .kmd Qnibe