Variation of hydrodynamic impact loads with flight-path angle for a prismatic float at 3° trim and with a 22 1/2° angle ...

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Material Information

Title:
Variation of hydrodynamic impact loads with flight-path angle for a prismatic float at 3° trim and with a 22 1/2° angle of dead rise
Alternate Title:
NACA wartime reports
Physical Description:
5, 3 p. : ill. ; 28 cm.
Language:
English
Creator:
Batterson, Sidney A
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 on smooth water. The tests were made at both high and low forward speeds with the model at 3° trim. The model had a dead-rise angle of 22 1/2° and, with the drop linkage, weighed 1100 pounds.
Bibliography:
Includes bibliographic references (p. 5).
Statement of Responsibility:
by Sidney A. Batterson.
General Note:
"Report no. L-211."
General Note:
"Originally issued February 1945 as Restricted Bulletin L5A24."
General Note:
"Report date February 1945."
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 - 003594136
oclc - 70914994
System ID:
AA00009366:00001


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Full Text

4C L-21(


RB No. L5A24


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS




WARlTIE I REPORT
ORIGINALLY ISSUED
February 1945 as
Restricted Bulletin L5A24

VARIATION OF HYDRODYNAMIC IMPACT LOADS WITH FLIGHT-PATH
ANGLE FOR A PRISMATIC FLOAT AT 30 TRIM AND WITH A
221- ANGLE OF DEAD RISE
2
By Sidney A. Batterson

Langley Memorial Aeronautical Laboratory
Langley Field, Va.






NACA


WASHINGTON
NACA WARTIME REPORTS are reprints of papersoriginally 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.


L 211


DOCUMENTS DEPARTMENT


/







I-f -f


NACA RE Jo. L5A24

I!ATTCHAL ADVIT 9 'Y CO r."'TTTTE 'B r. A '.'AUITTCS


R STFRICTELD 3'.LLETITN


VARIATION OF :F'rRODYIAMIC IMPACT LOADS V.ITH FLICHT-PATHt

Ai'GLZ FOR A PEI3T.'TIC FLOAT L.T 30 TRIr.1 AND ':.ITH A
S10

By Sidney A. r.tte--r-


ST II.: I', 41,"J


Tests were made in tihe Lariler impact basin to
determine the relationship bet een ir.:.pact normal accel-
eration and flilght-path ancle for seaplanes landing on
smocth water. The tests were made at both hiPh and low
forward 'speeds with the model :.t ,33 trim. The model
10
had a dead-ric angl of 22- andc, 4itth the drop linkage,
we' ced 1100 pounds. Ti'h re.silts of the tests indicated
thmt the maximiut im pact normal tcccr-leration was propor-
tioial to y1.3.6 over the test ran-e of flihit-path
an-le -- and t1.-t the efifctc of Pravity forces appeared
during the i~m,': rsirn rn.ocers i-ftr- the maximum impact
norms] acceler.atin hbi tccurr cd.


ItI" T-.OD j CT IO:


The time histor:.,' of the impact acceleration that
occurs during s' Tnmetricl smoot1h-wivter landinris of a
seaildnne i dependent upon t'Lce e crr4incipal fli;-'ht
par.i-rm t i's: vclocit:', fli-ht-path anle, and trim. The
variation of impact ijormn3l ac'Ce]er:,,tion with resultant
velocity is presented in reference 1. It has heretofore
been i-.p-ssible to establish experimental>]; the relation-
shij. betvwern impact load and fliiht-path angle. Data
derived from tests of full-scale airplanes h-ve not been
ap--licabl t- the problem of determining this relation-
ship because of insufficient accuracyr in the measurement







IJACA RB'No. L5A24


of the test parameters. The Laniley Impact basin,
hov.ever, affords controlled as well as accurate means
for obtaining data relevant to thi s problem (ref r-
ence 1). Tests were r ade in the Lanjlc.y Impact barin
to d3tcrmrine an empirical variation of impact normal
acceleration with flight-path angle within the rarEe of
smooth-water landings. The results of there te-tr,
which included runs at both bigh and low speeds, are
representative of a prismatic form because m the model
(reference 1) was tested without the afterbody. The
effect of trim is not included in the present report
since all runs were made with the model at 50 trim.


T"E.CLS


V resultant velocity of float, feet per second

Vh horizontal velocity component of float, feet
-pr second

Vv vertical velocity con'ponent of float, feet per
second

g acceleration of gravity (32.2 ft/sec2)

y flight-path angle, -derees tan y = Vh

y vertical displacement of float, inches

Fi .impact force, pounds
V4 total dropping weight, pounds

ni impact load factor, g (1)

T float trim, degrees


EU.IFr.!.T AN.D I:USTRUrJE'I!TAT IOT


The model tested (fig. 1) was the forebody of the
float described in reference 1, whichh has an angle of
10
dead -ise of 22- The dropping weight, of the model was
held at 1100 pounds throughout the tests. The instruments








.'.CA R3 1o. L5EA24


and equipment used throughout were thr same as those
described in reference 1, except that an NACA air-da:niped
accelerometer with a natural frequency of approxim-ately
21 cycles per second replaced the galvanometer-type
accelerometer previously used.


TEST PRCCE.DUIRE


The tests included two series of runs: the first at
a forward speed of approxrinately C9 feet per second and
the second, at approxirately 45 feet per second. The
trim and yaw an-le were held constant throughout the
tests at 9o and 0C0, rcspectively; wherreas the vertical
velocity -rar varied to vive an approximate ran-e of
Vy/VL fr3m 0.015 to 0.130 for each series of tests.
The depth of i -lmer.iDn was Aeasred at the step. During
the i;iipact process, a lift equal to the dropping weight
was exerted on the float by reans of the buoyancy engine
described in reference 1. All test measurements were
recorded as time histories.


FR2CISIOr


The apparatuF used in the present tests give meas-
urenents that are believed correct within the following
limits:

Hcrizortal velocity, ft/ec ... 0.5
Vertical velocity, ft,/sec .. . 0.2
Vertical displacement, in. ...... ... .0.2
Acceleration, . 0.5
eight, Ib . .. 2.0


FRESULTS A::D DISCUSSION


The maximrran normal lad factor for each impact was
derived from' the accelerometer record for each run.
Inasmuch as the buoyar-nc- enpine contributed a force
equal to the dropri',.n7 w'eiht, 1 g was subtracted from
the accelerometer record to isolate the hydrodynamic
force resulting from the impact. Because the maximum







TACA RB No. L5A24


impact norrral acceleration w-is shwrw In reference 1 to
be pro p rtional to the square :f the resultant velocity,
the iydrcdylnamr c loadc factor w'rI~ divided by 7J to
eliminate the effects of velocity. The values of
ni /V2 thus obtained are Plotted in figure 2 against
map.
the fli-Tht-p-ath angle at the instant of water contact.
Within the scatter of the test points,.the variation of
nimax with y is an evronential function over the test
rance. Evaluation of the slo.-' of the curve ir. figure 2
shows that for 30 trim
n,1.36
ni ma ccY
ma:

Ma::"i:um depth' of irni-iersion and depth of immn.ersonr
at the time of ni aare plott. i .Min-t the flirht-
at the .t o ,
path angle in figure 3. The curvre.s repre-.erting t:.,
immersion at !r:axi,nrl ni for tlhe two velocity series
coincide and .hereby show no effect of velocity; however,
the curves for maximum immersion show a defirnit separation
and thus indicate a velocity effect dur'iir t.li period.
It is quite easy to show that the maximum depths of
immersion for I'i.-iacts of equal flight-path anpl s but
different velocities are the same providede d trE acceleration
at any instant is proportional to the square of the
velocity an.. all other parameters are ass.i,-d conreant.
The instantaneous .rrpact accelerations result from n
suumation of .-5rnamic forces and gravit- force-, both of
which vary in magnitude during different stt:fr- of
imm-ersion. The' di'-anic forces are proportional to V2
but the gravity forces do not follow the V2 law. It
is therefore evident fr.r" fir-' re 3 that the effect. of
gravity forces, which are' a f -:nction of 1rsude's nurbcr,
become apera.nt during the imrersion -:rocess -z:me time
after the maxm.um normal impact acceleration 1as o'curr d.
The accuracy of tnc data, however, is in.-ufficiEnt to
pe:r.it evaluation of the -malnitude ano Fe::t.Jnt of this
effect.


CO'CLUSIC N" :s


Tests were.- ifldt in the' L.n7ly:; impact basin to
detcr-inr: the relationship b~-twecn the impact normal









NACA RB No. L5A24


accelcraticn nnd flight-poth angle for scaplaner landing
on smooth Vwatcr. Thc results of the tests, which were
made at ccnsttnt .wviht and 30 trim, indicated the
following conclusions:

1. The maxiLnum Imruct normal acceleration was pro-
portionr-l to c.ui'3 ovr' the test range of flight-path
angle .

2. The effects of gravity forces appeared during
the imT.crsion process, after the max.im .n rn impact normal
accclE ration ihad occurred.


Langlev !Lkmor'ial Aer-ron-utical Laboratory
IIjtior.l Advt"iVlry Co' 'ittee for Aeronautics
L-n l--y Fi'.ld., V ia.










1. E.attrrson, Sidnc' : A.: The ':AC.t, Trmp ct Basin and
',.teAr Lnr!ii Te'-ts of a Float Moi-l at Various
Vlocitl e -nc d';e'. hts. 'AC.-. ACR No. L4H15, 1944.






































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NACA RB No. L5A24


Figure 1.- Side view of model fastened to boom
in Langley impact, basin.


Fig. 1






NACA RB No. L5A24


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- Variation of the parameter ni /V
with fligh- paTh angle. r=3= mo


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NACA RB No. L5A24 Fig. 3






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UNIVERSITY OF FLORIDA
DOCUMENTS DEPARTMENT
120 MARSTON SCIENCE UBRARY
P.O. BOX 117011
GAINESVILLE, FL 32611-7011 USA
















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