BB No. L5E21a NATIONAL ADVISORy COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLY ISSUED February 19^6 as Eestricted Bulletin L5K21a VARIATION OF HYDRODYNAMIC IMPACT LOADS WITH FLIGHT -PATH ANGLE FOE A PRISMATIC FLOAT AT 12° TRIM AND WITH A 22i- ANGLE OF DEAD EISE By Sidney A. Batterson Langley Memorial Aeronautical Laboratory Langley Field, Va. NACA 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. 68 DOCUMENTS DEPARTMENT 7/ r ">if(*i> NAG A RB No. L5K21a RESTRICTED national advisory committee for aeronautics RESTRICTED BULLETIN VARIATION OP HYDRCDYNAMIC IMPACT LOADS ilTH PLIGHT-PATH ANGLE p OR A PRISMATIC FLOAT AT 12° TRIM AND V/ITH A ] o 22r- ANGLE OF DEAD RISE By Sidney A. Batter son SUMMARY Tests were made in the Langley impact basin to deter- mine the relationship between impact normal acceleration and flight -path angle for seaplanes landing on smooth water. The tests were made at varying resultant veloci- ties with the model at 12° trim. The model had a 1° 22-j angle of dead rise and a total weight of 1100 pounds The results of the tests indicated that the maximum impact normal acceleration was proportional to »r~ over the test range of flight -path angle y an d that maximum impact normal acceleration occurred prior to or at the instant of chine immersion. INTRODUCTION The initial phase of the research program at the Langley impact basin has been centered upon determining the variation of hydrodynamic impact loads with the prin- cipal flight parameters: velocity, flight-path angle, and trim. The variation of impact normal acceleration with resultant velocity is presented in reference 1. The variation with flight-path angle and trim ic being deter- mined from data secured by making a series of runs at a fixed trim and varying flight -path angles and then repeating the runs for a different trim. Reference 2 presents data obtained for 5° trim and reference 3, for 6° and 9° trim. The present report gives data obtained in a similar manner at 12° trim. The present tests were made over a larger range of flight -path angle than those of references 2 and J i n RESTRICTED NACA 3 No. L5 la j ■ order to secure valuer. Indicative of rough-water landings. This increased range c ' - ath angle also rmitted observations regarding the effect of chl lersion on the impact normal acceleration. 5YTTB0L3 resultant velocity of float, feet per second Vv horizontal velocity component of float, feet per second V v vertical ve loci by component of float, feet per second g acceleration of gravity (52.2 ft/sec-) Fa impact force normal to water surface, pounds W total model weight, pounds n* maximum xmoact load factor max t float trim, degrees V v flight -path angle, dt [ tan y = r vertical displacement of float, inches EO/ ! \ITD ENSTF The lines and pertinent dimensions of the Langley impact basin float model M-l tested are shown I . ure 1. The mode} was the forebody of the float described in reference 1 and has a 22— angle of dead rise with no chine flare. The model was tested at a tot light of 1100 pounds. The test equipment and instrumentation were, bh the exception of the accelercrr ter, the same as those described in reference 1. An rACA air-damped accel- erometer with a natural frequency of approximately 21 cycles per second was used to Treasure impact nor: acceleration. NACA RB No. L5K21a TEST PROCEDURE The tests Included runs at horizontal velocities ranging from approximately 2 feet, per second to approxi- mately 100 feet per second, and the vortical velocity ranged from approximately 1— feet per second to 12 feet per second. The range of flight-path angle resulting from the combination of vertical and horizontal velocities was from approximately 1° to 30°. The trim and angle of yaw were held constant throughout the tests at .1.2° and 0°, respectively. The depth of immersion was measured at the stern perpendicular to the level water surface. During the Impact process a lift equal to the total weight of the model was exerted on the float by means of the buoy- ancy engine described in reference 1. All test measure- ments were recorded as time histories. PRECISION The apparatus used in the present tests give meas- urements that are believed correct within the following limits : Horizontal velocity, foot per second ±0.5 Vertical velocity, foot per second ±0.2 Vertical displacement, inch . ±0.2 Acceleration, g ±0.5 Weight, pounds ±2.6 RESULTS AND DISCUSSION The Independent flight parameters, the maximum normal lead factor for each impact, and the immersion depth are tabulated for each run in cable I. Because the maximum impact normal acceleration was shown In reference 1 to be proportional to the square of the resultant velocity, the hydrodynamic load factor was divided by V to eliminate the eff-jcts of velocity. The values of n* /V 2 thus obtained are plotted in w max/ figure 2 against the flight -path angle at the instant of water contact. Within the scatter of the tost uoints ** iCA R3 No. 1,51121a the variation of ru with y is a simple power ff aax function over the test range. Evaluation of the slope of the curve in figure 2 showa that for 12° trim 1 22 w max Maximum depth of immersion and depth of immersion at the time of nj_ are plotted against the f light - w max path angle in figure 3. The distance from the keel to the chine at the stern of the model is 8.0 inches (fig. 1). Since the model was tested at a trim of 12°, an immersion of J .8 inches would cause the level water line to inter- sect the chine at the model stern; further immersion would serve to move the water line and chine intersection forward. Figure 3 shows that for flight -path angles up to l r )° the maximum impact normal acceleration occurred "before a depth corresponding to chine immersion at the stern in level water was reached. For impacts occurring at flight-path angles exceeding 15° , however, the curve leveled off abruptly and the maximum acceleration occurred at a depth corresponding approximately to chine immersion at the stern. lost of the scatter in the test point. 3 is believed due to inaccuracies in time correlation between accelerometer and displacement records. "he remaining curve in figure 3 shows that the maxi- mum depth of immersion continues to increase as the flight- path angle increases. Since this curve presents the results of a single instrument, time correlation cannot be a source of error: however, these runs wore made at widely different values of number. In the tests of reference 2 different maximui srsiona were obtained fcr similar flight-pal ;les when the value of Froude number was varied, 3ince bhe pres nt test runs were made at varying resultant velocities, the scatter of the test points is believed to be a result of this effect. It 3hould be noted in figure 2 that there is no apparent change in the variation of m >r with flight- w max path angles extending well beyond those resulting in chine immersion. NACA RB No. L5E21a CONCLUSIONS Tests were made in the Langley impact basin to deter> mine the relationship between impact normal acceleration and flight-path angle for seaplanes landing on smooth water. The results of the tests, which were made for constant model weight and a model brim of 12°, indicate thw f oil owing e one lus ions ; *o 1. The maximum impact normal acceleration was prc- onal angle y , portional to Y x over the test range of flight-patl 2. The maximum impact normal acceleration occurred prior to or at the instant of chine immersion. Langley Memorial Aeronautical Laboratory National Advisory Committee for Aeronautics Langley Field, 7a. REFERENCES 1. Batter son, Sidney A.: The NACA Impact Basin and Water Landing Tests of a Float Model at Various Velocities and Weights. NACA ACR No. li^il^, I9A4J4.. 2. Batterson, Sidney A.: Variation of Hydrodynamic Impact Loads with Flight-Path Angle for a Prismatic Float at 3° Trim and with a 22^° Angle of Dead Rise. NACA RB No. LSA2I;, I9I4.5 . Batterson, Sidney A., ard Stewart, Thelma: Variation of Kydrodynamio Impact Loads with Flight -Path Angle for a Prismatic Float at 6° and 9° Trim and a 1 , 222 An £ le of Dead Rise. NACA RE No. L5K21 I9I4.5 . Digitized by the Internet Archive in 2011 with funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/variationofhydroOOIang NACA R3 No. L5K21a TABLE I DATA FOR MODEL M-l TESTED IN LANGLEY IMPACT BASIN 1100 lb; t = 12 ol Run 1 v h V Y n iv; r Ttnax y at n i w max kfps) 1 (fps) (fps) ('leg) max (in.) (in.) 1 1 1 1.9 96 b 96.1*. 1.1 1.1 2.0 ' 1 1.9 2 1 o 96.6 96.7 2.2 5 * 2 3.2 I 98.2 op 5 , 2 *£ - -1 2o!S 3.1 li.B k-3 12. b 6^ 8 2,k 7.9 5 12.1 5.1 1 * ? 66.9 2 .[(. 20.1 7.0 6 i ill. 5 5.6 12.9 6k. 1 2 - •3 20.2 7- 6 7 112.0 7-6 Ik. 2 57.7 2.6 19 ,k 8.1 11.1 2-7 lk.8 I48.7 2,6 17.6 7.5 9 11.9 8,8 1.4 . 8 ? 3 ° 1+3.9 2.6 !«•§ n 2 10 12.1 t 12.5 17 -4 2.8 16. s 7:3 |u 112.0 10.5 15.3 I48.9 ? 1 <- . 1 17.]+ 7-5 12 ill .2 6.9 13.2 58.1 2 r^ V Iri 0, SO r 6.0 Mlf / 40 / p 20 / < / *?" 6 .6 4 A < z / .1 NA COMMI riONAL fTEE F< AOV )» AEI ISO ON* 5Y JTIC s 4- 6 8 IO 20 40 60 SO /OO Fl iaht -path ang/e, V , dey 2 f~/gure 2. - Von at /on of the parameter n w mm JV wirh fl/ght-path angle. T*J2 9 - W-- 1100 pounds. NACA RB No. L5K21a Fig. 3 ui'fi'uoirjzuJUJi jo Ljj.d9