Variation of hydrodynamic impact loads with flight-path angle for a prismatic float at 6° and 9° trim and a 22 1/2° angl...

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Material Information

Title:
Variation of hydrodynamic impact loads with flight-path angle for a prismatic float at 6° and 9° trim and a 22 1/2° angle of dead rise
Alternate Title:
NACA wartime reports
Physical Description:
6, 4 p. : ill. ; 28 cm.
Language:
English
Creator:
Batterson, Sidney A
Stewart, Thelma
Langley Aeronautical Laboratory
United States -- National Advisory Committee for Aeronautics
Publisher:
Langley Memorial Aeronautical Laboratory
Place of Publication:
Langley Field, VA
Publication Date:

Subjects

Subjects / Keywords:
Seaplanes   ( lcsh )
Airplanes -- Landing   ( lcsh )
Aeronautics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: Tests were made in the Langley impact basin to determine the relationship between impact normal acceleration and flight-path angle for seaplanes landing in smooth water. The tests were made at both high and low forward speeds and at trims of 6° and 9°. The model had 22 1/2° angle of dead rise and a gross wieght of 1100 pounds.
Bibliography:
Includes bibliographic references (p. 6).
Statement of Responsibility:
by Sidney A. Batterson and Thelma Stewart.
General Note:
"Report no. L-69."
General Note:
"Originally issued February 1946 as Restricted Bulletin L5K21."
General Note:
"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 previously held under a security status but are now unclassified. Some of these reports were not technically edited. All have been reproduced without change in order to expedite general distribution."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003638587
oclc - 71837422
sobekcm - AA00006240_00001
System ID:
AA00006240:00001

Full Text

NAJA L"A


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WARIlTIME REPORT
ORIGINALLY ISSUED
February 1946 as
Restricted Bulletin 1,021

VARIATION OF H11YODYNAMIC IMPACT LOADS WITH FLIGHT-PATH
A GLE FOR A RIMATIC FLOAT AT 60 AND 90 TRIK AND A

22 ANGLE OF IEAD RISE
2
By Sidney A. Batterson and Thelma Stewart

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 requring 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 withoutt change in order to expedite general distribution.


L 69


,;ME4 S rDEPAr-.I '.lT


SB No. L5K21




































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/variationofhydro001a








NACA RB No. L5K21 .ST.RICTED

NATICIAL A:."ISORY C<-"T 1T E FOR AERONAUTICS


PRSTRICTED BULLETIN


VARIATION 1C :' 'C.Ar:'IC I"?ACT LOADS 'TiITH FLIGHT-PATH

.A.GL. R. A PRITS.ATIC FLOAT AT 60 AND T.RI AND A
1o
22- A::GLZ OF DEAD RIE3

By Sidney A. Batterson and Thelma Stew'art




Tests were made in the Langley impact basin to deter-
mine the relationship beuw'een i.-.,act normal acceleration
end fli:ht-path angle for seaplanes landing in smooth
water. The tests were madCe at both hi'h and lowv forward
speeds and st trims of 60 and 00. ?e model had a
10
22- angle of desd rise and a r-.oss weight of 1100 pounds.
2
7. results of the tests indicated that, over the test
range of fliZht-pa th sngle y, the mraximum impact normal
acceleration was p:r'ortionl to Y for 6 trim and
to Y~-*3 for 90 trim. At low fli -:t-path anples the
dynamic lift forces resultin- from the downward deflection
induced in the water imoinii.-,- upon the flost bottom
predominated, wherees at hi.-'- flight-path ang,:les the forces
resulting f:-., the virtual rma-s oredorinated. i:: m
deoth of ir;mmersion and the imm-.ersion thct occurred at the
instant of maximum noriml force showed very little effect
of trim.





Tests made in the Langley impact basin to determine
the effect of flight-path 'anle upon impact normal acceler-
ation for seaolanes landing in smooth water have been
described in references 1 and 2. These tests were part
of an investigation undertaken to deterr.'tine the ffct of
flight-path angle upon impact acceloretions throughout
the r o.len of symmetrical lan'_ i;-s. Since the trim determines
the relative effect ucon the total impact load of the
dynamic li"t forces due to th' do-mniard deflection of the
water imrnpi:in upon the float bottom and the forces
resulting from the rate of ch-.n: of the virtual mass, the


TIL. ; *











2 NACA RB No. L5K21


investigation included tests at various trims. The results
presented in references I and 2 sho.w the variation of
impact normal acceleration with flight-path angle for
trims of 3 and 120, respectively. As a continuation of
the investi- -tion, data are presented herein to show the
variation of irprct normal acceleration with flight-path
enale at trims of 6 and 90. The tests wore made with a
10
model Ibvins orismstic form and a 22- angle of dead rise.
2
7he effect of ::eisht is not included, since the total model
weight was held constant throughout the tests.


SYMBOLS


V resultant velocity of float, feet per second

Vh horizontal velocity ccr:.-onent of float, feet
per second

Vy vertical velocity comionent of flost, feet per
second

g acceler-tion of gravity (52.2 ft/sec2)

Fiw impact force normal to water surface, pounds

W total model weight, pounds

ni_ maximum i: sect load f actor

T float trim, degrees

SfliTht--nath anrle, decrees (tan y =

y vertical displacement of float, inches




-'.e Lan;il- i-mpct basin float model .-1 tested,
10
whichh hns a 222 angle of dead rise, was the forebhJ" of
the float described in reference 5. !Th lines and
pertinent dimensions of this model are shown in figure 1.
The ,-ross wei :.t of the model including the .oo"i linkage










NACA RB No. L5?21


was 1100 pounds. The equipment and instruments used
throughout the tests were, with the exception of the
accelerometer, the same as those described in reference 3.
An NACA air-damped accelerometer with a frequency of
s roximately 21 cycles per second was used to determine
the impact nor-:lal acceleration.





The model wps tested with 00 P. le of yaw at trims
of 60 and 00. The horizontal velocities for these tests
ranged from a"-.roxis.ately 45 feet per second to approxi-
mately 100 feet per second, and the vertical velocities

ranged from approximately 1- feet -:t second to 12 feet
per second. The range of flight-peth an.:le was from 10
to J0o. The depth :f immersion was measured at the model
stern -"erendicular to the level water s:rface. During
the impact process a lift equal to the total weight of
the model was exerted on the float by means of the
buoysncy engine ascribed in reference 5. All test
measurements were recorded as time histories.


P?-C VISION


The apparatus used in the present tests yield meas-
urements that are believed correct within the following
limits:

Horizontal velocity, foot ner second ..... 0.5
Vertical velocity, foot oer second .. 0.2
Vertical displacement, inch . .. C*0.2
Acceleration, g .0 . 0.5
:ei-'.t, pounds . . 2.0


7-' LTS AND DTSC'UICKN


For each run an accelerometer record was obtained
from which the maximum load factor for each impact was
derived. Since the buoyancy enirne contributed a force
equal to the total weight of the model, 1 g was subtracted
from the values obtained from the accelerometer record to
isolate the hydrodynamic force resulting from the impact.










NACA RB No. L5K21


Inasmuch as the maximum impact normal acceleration
vwas sho,:n in reference 5 to be proportional to the square
of the resultant velocity, the hydrodynamic load factor
was divided by V2 to make it independent of velocity.
The values of ni,, V2 for both float trims of 60
and 90 are plotted in figure 2 against flight-path angle
at the instant of water contact. Within the scatter of
the test points appearing in this figure, the variation
of ni max with y is a simple power function over the
max
test rar.--:. Evaluation of the slopes of the curves in
figure 2 shows that for 6 trim


n., acc Yyl54


and for 90 trim


ni. Yl" 33


Figure 2 indicates thst at low flight-path angles
the impacts for 9 trim resulted in higher loads than
those for 6 trim; ho.:ever, as the flight-path angle
increased, the two curves tended to intersect. This
condition is described in reference 4 and is attributed
to the fact that at low flight-path angles the increased
trim produces greater downward angle of water deflection,
which results in greater impact acceleration. On the
other hand, at the high flight-path angles the increase
of virtual mass primarily -iorns the magnitude of the
impact accelerations since the depth of immersion increases
as the flight-path anrle becomes larger. The mass effects
are obviously greater- in the case of the lower trin.

;~ .-.1a. deathh of immersion and depth of immersion
at time of n, are olotted a-ainst flight-path angle
for trim of 60 in figure 5 and for trim of 90 in figure 4.
A comparison of figures 3 and ;4 shows them to be nearly
identical and indicates that the difference in trim had
no significant effect on depth of immersion. The test
range of fligiht-path angles was not sufficient to show
the very marked effect of chine immersion upon the depth
of oenetrrtion at the time of maximum force as observed









IACA RB No. L5K21 5


in reference 2; however, for both the 9 and 60 trims the
curves exhibited reduced slopes at the higher fll-lht-path
angles.


CO'iCLUSIONS


Tests were made in the Langley impact basin to deter-
mine the relationship between the impact normal accel-
eration and flight-path angle for seaplanes landing in
smooth water. The results of the tests, which were made
at constant weight and model trimr of 6 and 90, lead to
the following. conclusions:

1. The maximum impact normal acceleration for 6 trim
was proportional to y1'54 over the test rn-e of flight-
path an le y.

2. The mnximui impact normal acceleration for 9 trim
was proportional to yl. over the tsst rasne of y.

Th- experimental data provided a check for the
previously drawn theoretical conclusion that: at low
flight-path angles the lift forces resulting from the
downward deflection induced in the water impinging unon
the float bottom predominated, whereas at high flight-
path angles the forces resulting from the virtual mass
predominated.

4. The maximum depth of iiLinersion and the immersion
that occurred at the instant 1' ro % irmium normal force
showed very little effect of brim.


Langley Memorial Aeronautical Laboratory
National Advisory Co~lmittee for Aeronautics
Len.-ly Field, Va.










NACA RB No. L5T21


1. 3Btterson, Sidney A.: Variation of Hydrodynamic Impact
Loads .vith Flight-Path Angle for a Prismatic Float

at 30 Trim and with a 22- Angle of Dead Rise.
TTACA RB No. L5A2+, 1945.

2. Batterson, Sidney A.: Variation of Hydrodynamric Imypact
Lopds -with Flight-Path Angle for a Prismatic Float
10
at 120 Trim and with a 22- Angle of Dead Rise.
NACA RB No. L5K21a, 1045.

5. Batterson, Sidney A.: The N.'.A Impact Basin and wster
Landin, Tests of a Float Iodel at Various Velocities
and .':eights. 7ACA ACR No. L-H15, 19L1.

+. ayo, v Wilbur L.: Theoretical and ExperimentEl Dynamic
Lo,;ds for e Prismratic Float Hvin, an Angle of Dead
10
Rise of 22-. NACA RB No. L5F15, 1945.






NACA RB No. L5K21


HALF-BREADTH


22-


BODY PLAN


5 TA TON


NATIONAL ADVISORY
PROFILE CO.,ITTEE FO ..TIS.


F/GU16RE I- LINES OF FLOATMODEL M-/ TES TED /N LANGLEY IMPACT BASIN.


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NACA RB No. L5K21


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NACA RB No. L5K21


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