^(\C(\i-ic^ ^ EB No. L5K:21 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIMK REPORT ORIGINALLY ISSUED Fetruary 19^ as Eeetricted Bulletin L%21 VARIATION OF HrnROKfKAMIC IMPACT LOATS WITH FLIGET-PATH ANGLE FOE A PEISMATIC FLOAT AT 6° AND 9° TRIM AHD A 22^ ANGELE OF DEAD EISE 2 By Sidney A. Battereon and Thelma Stewart Langley Memorial Aeronautical Laboratory Langley Field, Va. MACA WASHINGTON NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were pre- viously held under a security status but are now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution. ® DOCUMENTS DEPARTMENT Digitized by tine Internet Arclnive in 2011 witln funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/variationofhydroOOIa 11^ MACA RB No. L5K21 RESTRICTED NATIONAL AD'VIiORY COMMITTEE FOR AEP.0NAUTIC3 RESTRICTED BULLETIN VARIATION 0? :-JYDRODYNA?,^IC IMPACT LOADS WITH FLIGHT-PATH ANGLE FOR A PRI3?;:ATIC FLOAT AT 6° tC^lD 9° TRIM AND A 22- ANGLE OF DEAD RIoE 3y Sidney A. 3attsrson and Thelrna Ste-.vart SU^iiARY Tests were made in the Langley Ir.ipact basin to deter- mine the relationship between impact normal acceleration and f lirTht-path angle for seaplanes landing in smooth y;ater. The tests '.vsre made at both nigh and low forward soeeds and st trims of 6° and 9°« The model had a ^ lo 22— anrjle of dead rise and a gross -A-eight of 1100 pounds. The results of the tests indicated that, over the test ran^-e of f li-^^ht-path an trie v, the msxim'om im.'oact normal acceleration was proportional to 'Y~ ' ^'^'^ 6° trim and to Y~*^^ for 9° trim. At low flight-path aiigles the dynam.ic lift forces resulting from the downward deflection induced in the water im.olnging upon the float bottom predominated, vvlieress at high flight-path angles the forces resulting from, the virtual ma£:s predominated. The m.axim.um. deoth of intnersion and the imiraersion thst occurred at the inst^-nt of maximum. normi?l force shovved very little effect of trim. . INTRODUCTION Tests made in the Langley impact basin to determine the effect of flight-path angle upon impact normal acceler- ation for seaplanes landing in sm.ooth v/ater have been described in references 1 and 2. These tests v/ere part of an investigation undertaken to determ.ine the effect of flight-path angle upon im.pact accelerations throughout the range of s"^7mirr;strical landings. Since the trim determines the relative effect uoon the total im/pact load of the dynamic lift forces due to thu downv/ard deflection of the v/ater impinging upon the float bottomi and the forces resulting fromi the i^ate of change of the virtual mass, the RESTRICTED 2 MCA R3 No. L5K21 invsstigation Included tests at various trims . The results presented in references 1 and 2 sho'.v the variation of impact normal acceleration with flight-path angle for trims of 5*^ ^-^^l 12°, respectively. As a continuation of the Investigation, data are presented herein to show the variation of impact norrr.rl acceleration with flight-prth ansle at trims of 6° and 9*^« The tests were made with a lo model having prismstic form and a 22p angle of deaa rise. The effect of '.vei^ht is not included, since the total model weight \'^HS held constant througliout the tests. SYMBOLS V resultant velocity of float, fset per second Vv horizontal velocity component of floau, feet per secona Vy vertical velocity component of float, feet per second g acceleration of gravity (52.2 ft/sec^) F^ impact force normal to water surface, pounds W total mcdel weight, v-ounds ni, maximum impact load factor \- ''max ^ T float trim, de^rrees "^ Y f lis:ht--oatli an"le, deftrees (tan y - t^I y vertical displacement of float, inches EOTJipr,-ENT ALT) INSTRUI'.SNTATIOK The Langlsy impfct basin float m.odel M-1 tested, 1° v/hich has a ?2-p an&'le of dead rise, v/as the forebody of the float described in reference 3' The lines and pertinent dimensions of this model are shown in figure 1. The gross weight of the model including the drop linkage MCA R3 No. L5K21 3 v/as 1100 pounds. The equipment and instruments used tiiroughout the tests were, with the exce-otlon of the accelercmeter , the same as those described in reference 3' An NACA air-damped accelerometer with a frequency of approximately 21 cycles per second v/as used to deterraine the im"oact nomal acceleration. TEST PR0C3DU.RE The model -//ps tested with 0° angle of yav/ at trims of 6° and 9°« The horizontal velocities for these tests ranged from approximately 1+'^ feet per second to approxi- mistely 100 feet oer second, and the vertical velocities 1 ranged from approximately Ip feet per second to 12 feet per second. The range of flight-path an.Tle was from 1° to li-!-*^. The depth of irnm.ersion \vas measured at the model stern per->Dendicular to the level water surface. During the impact process a lift equal to the total weight of the model wss exerted on the float by means of the buoyancy engine described in reference ^. All test measurements were recorded as time histories. PRECIS 1 0!T The apparatus used in the present tests yield meas- urements that are believed correct within the follov/lng limits : Horizontal velocity, foot -ner second -0.5 Vertical velocity, foot oer second '^0.2 Vertical displacement, inch '^0.2 Acceleration, g *0«5 Y;eight, poiAnds ±2.0 RESULTS AI>ID DISCUSSION For each run sn accelerometer record v/ss obtained from which the majcimum load factor for each impact was derived. Since the buoyancy engine contributed a force equal to tl^e total weight of the model, 1 g was subtracted from the values obtained from the accelerometer record to isolate the hydro dynamic force resulting from the impact. k MAC A RB No. L5K21 Inasmuch as the ris.ximian impact normal acceleration v/as sho'ATi in reference 5 "to be proportional to the square of the resultent velocit?/, the hydrodynamic load factor WPS divided by v2 to make it independent of velocity. The values of ni,., /v2 for both float trims of 6° and 9^^ s^'3 plotted in figure 2 against flight-path angle at the instant of water contact. Vvithin the scatter of the test T^oints appearing in this flgtire, the variation cf n^ with Y is a simple power function over the max test renge. figure 2 shows that for 6° trim niw cc y max ..5^ an d for 9° trim n-" *ma:c yl'33 Figure 2 indicates that at low flight-path angles the impacts for ^^ trim resulted in higher loads than those for 6° trim; hovvever, es the flight-path angle incra"sed, the tv;o cui'ves tended to intersect. This condition is described in reference I4. and is attributed to the fact that at low flight-path angles the increased trim, oroduces greater downward angle of v/ater deflection, which results in greater impact acceleration. On the ether hand, at the high flight-path angles the increase of virtual mass primarily governs the magnitude of the Irapsct accelerations since the depth of imDiersion increases as the flight-path angle becomes larger. The mass effects are obviously gx-eater in the case of the lov;er trim. Maximum depth of immersion and depth of immersion at time of n^ are olotted acainst flight-path angle '^max for trim of o*^ in figure 5 s^d^ for trim, of 9 i^^ figure 14., A comparison of figures 5 and 14. shoves them to be nearly identical and indicates that the difference in trim, had no significant effect on depth of immersion. The test range of flight-path angles was not sufficient to show the very marked effect of chine immersion upon the depth of penetration at the time of maximum force as observed MCA RB No. L5K21 5 in rsference 2; however, for both the 9° and 6° trims the curves exlilbitsd reduced slopes at the higher flight-path p.ngles . C0MCLU3I0NS Tests were made in the Langley impact besin to deter- mine the relationship between the ii'npect normal accel- eration and flight-path angle for senplanes landing In smooth v;ater. The results ' of the tests, which v.-ere made at constant v/eight and model trimc of b° and 9°> lesd to the following conclusions: 1. The maximum impf^ct normal acceleration for 6° trim v/as proportional to y-*5M- over the test range of flight- path angle v. 2. The msximuta impact normal acceleration for 9° trim v/as proportional to y-^*^> over the cest range of y ^, The experimental data provided a check for the ■oreviously drawn theoretical conclusion that: at low flight-path angles the lift forces resulting from the do^ATiv/ard deflection induced in the water impinging u'^on the float bottom predoruinated, whereas at high flight- path angles the forces resulting from the virtual mass predominated. k-' The maximum depth of ijiimersion and the iiTinisrsion that occurred at the instsnt of iria;iiramn normal force shov/ed very little effect of trim.. Langley Memorial Aeronautical Laboratory National Advisory Conii-rdttee for A3ronautics Langley i''i3ld, Va. NAGA RB No. L5T<2i REFERENCES 1. Batterson, Sidney A. ; Variation of Hydrodynamic Impact Loads vvith Flight-Path Angle for a Prismatic Float 1 o at 5° Trim and witli a 22-| Angle of Dead Rise. NAG A R3 No. L5A21+, 19^+5. 2. Battarson, Sidney A.: Variation of Hydrodynamic Impact Lo.'^ds with Flif.ht-Path Angle for a prisnatic Float 1° at 12° Trim and with a 22^: Angle of Dead Rise. 2 NAGA RB No. L5F21a, 19l|5. 3. Batterwson, Sidney A.: The NAG A Impact Basin and Water Landin;~ Tests of a Float Kodel at Various Velocities and ;Veights. FAG A ACR No. li4-H15, ISiiii. q.. Mayo, Wilbur L. : Theoretical and Experimental Dynamic Loads for a Prismatic Float Plaving an Angle of Dead 1° Rise of 22-.. NAGA RB No. L5FI5, 191+5. NACA RB No. L5K21 Fig. 1 BODY PLAN STATION 259 21 /20 75 PROFILE 120. 7 5 NATIONAL ADVISORY COHMrTTEE FM AERONAUTICS Figure: l- Lines of float model mi tested iai langley impact basin. Fig. 2 NACA RB No. L5K21 /on K/o 6.0 60 4.0 JO // // / 20 // / / r 9 ') / / / \ r-'6 c /o 0, "^ / <^ 1 ' / /\ / \^ / ^ / %. / / ^ f ' f r-a' r=6' u Vf-,"^ 45 fps a ^ V^~ 98fp5 ^ / / 4 / / ~^ A } i 3 / / -- — - / / / > / / 7 ^/ / NATIONAL ADVISORY COKMITTEE FOft AERONAUTICS ■ / / / / Z 3 ^ 6 d /O 20 30 40 60 SO /CO FZ/c^hf -pafh ong/e^ -r , deg F/oure 2 - Van a f /on of para/ne^er n,^ V^ with f/iahf--pa^h an^/e for /-r/ms of 6°and 9";W-IIOOpounds. NACA RB No. L5K21 Fig. I 5b ?D r U/ 'n'UO/SJ3LUU// JO l//d9Q ^ ^ ^ ^ 1^ Fig. 4 NACA RB No. L5K21 -Uf '^/I'uO/S^jaUULU/ JO Lf^c/dQ 5? II k 1. 5 ^ ^ UNIVERSITY OF FLORIDA 3 1262 08105 013 9 UNIVERSITY OF FLORIDA 0SCUMENTSDEPAR»^ 1 20 MAP,STON SCIENCE UBRnrtY To. BOX 117011 7niillSA GAINESVILLE. FL 3261 1-7011 USA