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N TION L
DVISORY
COMMITTEE
FOR
ERON UTICS
TECHNIC L
NO
TE
34 9
N C MODEL INVESTIG TIONS OF SEAPLANES IN W VES
By John B Parkinson
Langley Aeronautical Laboratory
Langley
Field,
Va
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
TECHNICAL NOTE
34 9
NACA MODEL INVESTIGATIONS
OF
SEAPLANES IN WAVES
l
By
John
B. Parkinson
SUMM RY
The characteris t ics of seaplanes in rough water
are
invest igated
experimentally in the Langley tanks by means of sel f -propel led dynamically
similar
models
having
freedom in the vert ical plane. Time
his tories
are
obtained of required quant i t ies during simulated
take-offs
and landings
into t ransverse waves
of
various s izes .
The maximum trim
r i se
vert ical
acceleration
and angular
accelera
t ion
during a number
of
landings are used as cr i te r ia for comparisons.
For
landings
in waves
of
a given height the
cr i te r ia
are primarily
depen
dent on wave length and usually peak a t a c r i t i ca l wave length.
Signif i
cant reductions
in the motions and
accelerations
are obtained
by pract ical
increases
in
hull
length-beam ratiO
afterbody
length angle of dead
r ise
and
sui table combinations of
these
features. The
normal
impact
load is
a
function of hull trim f l ight-path angle and
vert ical
veloci ty a t contact
referred to the
local
wave
slope and
wave veloci ty. The measure d maximum
vert ical
accelerations
and
the associated effect ive
contact
parameters
from
tes ts
in
various
heights of
waves
are
largely
functions of
the
wave
height-length rat io . Vertical loads
calculated
from the experimental con
t ac t
parameters
are
in reasonable
agreement with the
vert ical
accelerom
eter data. The mean resistance to motion through waves i s higher than the
resistance in smooth water. The increment is greatest
a t intermediate
speeds during take-off where
rebounds
are
most severe.
INTRODUCTION
Waves are
of
importance in
aeronautics
because even relat ively mild
sea
conditions
induce
cr i t ica l
loads
and uncontrollable
motions
on
sea
planes . These adverse effects have imposed severe
additional
design
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2
NACA
TN 3419
high
speed
portions
of the
runs
in waves; nevertheless the
problem of
the
all-weather
water
based ai rcraf t
has
not
yet
been
sat isfactori ly solved,
and there has
been
an increasing necessi ty for more effect ive solut ions.
The National
Advisory
Committee for
Aeronautics
conducts continuing
research programs on the fundamental aspects of water impact
loads
due to
waves and the rough
water behavior of seaplane
configurations. The pur
poses
of
th is act ivi ty
are
to
develop
improved methods
for
predict ing
water loads and pressures and better means of
al leviat ing
the
adverse
effects
induced
by
wave
encounter.
Experimental phases of the work a
re
carried out in the large-scale
hydrodynamic fac i l i t i e s of the NACA located a t the Langley Aeronautical
Laboratory
a t
Langley
Field, Va
. The
Langley
impact basin ref .
1) is
a
h
ighly
special ized fac i l i ty for establishing
basic
relat ionships among
the impact parameters . The Langley tanks are generally similar
in
func
t ion and operation to towing
basins
de s igned to
t es t ship
models except
that
they
have
relat ively
higher
ca
rr iage
speeds
to
accommodate
the large
Froude
numbers associated wi t h water based ai rcraf t
SYMBOLS
b beam of hull ,
f t
g
accelerat ion due to gravity
H
wave
height,
f t
L
distance from forward perpendicular
to sternpost ,
f t
R D
to tal- resistance coefficient
V
speed, fps
V
h
horizontal
veloci ty, fps
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N C TN 3419
3
wave
velocity,
fps
f l ight-path angle, deg
effective f l ight
path
angle,
deg
8
angle
of incl inat ion
of water
surface,
deg
wave
length, f t
T
trim
of straight portion of forebody, deg
effective
trim,
deg
DESCRIPT
I
ON OF T NKS
Langley
Tank
No.1
Langley tank no.
1 was placed
in operation in
1931
ref . 2) and
enlarged in
1937
ref . 3)
.
t has
a
width
of 24 feet , a
maximum
depth
of 12 feet , and a
maximum speed of
60 miles
per hour.
With
the ins ta l la -
t ion of a wave maker
and beaches
a t
the ends,
the working length
is
approximately
2,800 feet .
This ins ta l la t ion
i s shown in
figure
1.
The working element of the wave maker is a transverse f la t plate ,
hinged a t the bottom and
osci l la ted
by a
l ink
a t the top connected
to
an
adjustable-radius crank.
The
crank is driven through
a
gear reducer
by
a 75
horsepower
direct
current elect r ic motor.
The
rotat ional speed of
the motor
is controlled
by varying
i t s
input
voltage
from a
constant
speed
motor generator se t . The
length and
height
of the
waves are varied
by adjusting
the speed
of
the motor and the radius of the crank.
Tests of complete seaplane models in calm water are made
a t
the
6-foot level in th is tank to improve the a i r flow
over
the aerodynamic
surfaces,
and wave suppressors have
been ins ta l led
a t th is
level
to
reduce the time between runs. For tes ts in waves, the
water
is raised
to
the 8 . 5
foot level see f ig
.
1) to deactivate the
wave
suppressors and
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N C
IN 3419
maker as possible and
using only the
f i r s t waves
produced before in ter
ference patterns build
up .
With such precautions
and continuous
monitoring of the
waves
in the tes t region sat isfactory
duplication
of
tes t conditions and resul ts are obtained.
The ranges
of
wave size
available a t
the
8.5-foot level are
shown
in figure 2 . The heights are l imited by a
theoretical
upper boundary
de rived by
equating
the maximum t r iangular area swept by
the
plate to
the area of trochoidal waves of
various
sizes
above
the s t i l l -water
le
vel.
Actual
regular
waves
are obtained close
to
this
boundary. At
shor t wave lengths
the
heights become
irregular as indicated by the
le ft-hand shaded boundary .
Regular
wave
heights below
1 foot for
tests
of
sea
p
lane models
cannot
be produced with
length-height
ra t ios of
much
le
ss than
25
or 30.
Langley Tank
No.2
Langl
ey
tank no.
2 was completed
in
19
42 and i s
located
alongside
th
e f i r s t .
I t
has a
working length of approximately 1 730 feet
a
width
of 18 f e
e t
a uniform
depth
of 6
feet and
a
maximum towing speed of
60 miles per hour . From experience with
the
f i r s t tank the towing
carriage of Langley
tank
no. 2 was made much smaller to minimize aero
dynamic interference on complete
seaplane
models. This feature was made
possible by the use of closely spaced
ra i ls support
e d
by the roof-truss
system.
Langley
tank no.
2
i s
rectangular
in cross
section
with continuous
concrete
beaches along both sides a t
the
water
l ine
to suppress
waves
between runs . For
tests
in waves
the
water
level
is dropped
below the
b
eaches.
Since
the
water
depth
is
then
constant over
the
width t rans
verse waves remain uniform for a longer period
than
in
the
f i r s t tank
a
nd
regular waves
with
length -height ra t ios as low as
12
to 15 are
avai l
able.
The wave maker
and
end beaches
are
similar
in
principle
to
those
provided for Langley tank
no. 1 and the apparatus
and
procedures for
tests
in waves
in the
two
tanks are also similar.
DYN MIC MODELS
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NACA TN 34 9
5
adjustable
and the
elevators
are
adjustable
or
controllable
to
su i t the
conditions
to
be
simulated
.
The part iculars
of
the model are
necessarily
related to those
of
the fu l l - scale airplane
by
Froude s law
of
comparison to obtain
geometri
cal ly similar wave and spray patterns and proper scaling of the hydrody
namic
forces
. I f
viscous effects
are
neglected,
this law applies equally
to aerodynamic forces;
the wing, however, must
be f i t t ed with
leading
edge s la ts which are
not
on the fu l l - scale
seaplane,
to prevent a
large
loss of
l i f t
a t
high angles
of
at tack
due
to
the
low
model
Reynol
ds
number .
The
Froude
number
i s
also the
cr i ter ion
for dynamic s imilar i ty of
any geometrically similar systems moving under the predominant influence
of
iner t ia
and gravity forces . When
the
Froude relat ionships
for
speed,
s ize, mass, and mass dis t r ibut ion
are sa t is f ied
the relat ive posi t ions
of the systems af ter proportional
periods
of
time
are the same
an
d motion
paths
of
corresponding
points
in
space
are geometrically
similar.
This
general principle is
used
to advantage in aeronautical research for model
investigations
of
highly complex f l ight
problems,
such as the predict ion
of
flying
quali t ies,
spin
recovery, and
motions in gusts, as
wel
l as the
behavior of seaplanes
on the water.
With bal las t ing for scale el l ipsoid of iner t ia and
with the addition
of the side
s tabi l izing
floats of the ful l-scale seaplane, the tank
model
can be operated completely f r ee of the towing carriage for observations
of i t s three-dimensional behavior and can even be operated outdoor s for a
closer
simulation of
wind
and sea
conditions in nature .
APPARATUS ND
PROCEDURE
Towing Gear
For the determination
of
cr i t ica l behavior in the vert ical
p l
ane
during
take-off
and landing
runs,
t
is advantageous to use the towing
carriage to res train the model l a tera l ly and in ro l l and yaw as well
as to carry along
observers
and
equipment
. A side view of the model,
together
with
the towing
gear developed for
th is
purpose, is shown
in
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N C TN 34 9
vert ical motion
with
respect to
the
carriage, and
data are
preferably
taken
only
when
the
model is free of the stops. Connections to
the
model
are attached near
the
pivot to minimize the i r res t ra in t
on
the tr im
motions. The
arrangement
is shown
schematically
in figure
5.
The
model
is fixed
in
trim
during
a
landing approach with
fixed
elevators
by a
solenoid
-
operated
brake
that releases automatically
when
one of the keel contacts f i r s t
touches
the water.
This procedure
elimi
nates
rota t ion
due
to ground effect and simulates
more
closely
a
fu l l -
scale
piloted
glide .
After contact,
the
elevators
of the
model normally remain fixed.
They are also
on
occasion controlled from
the
carriage by
the
model
pilot or
automatically by
angular displacement and rate
senstive
mechanisms to
simulate the
rapid
corrective
actions
inst inct ively taken
by experienced pilots
Instrumentation
Vertical acce lerat ion
is
measured
by
an
accelerometer on the
s ta f f
attached to
the
model
and angular
acceleration,
by
a
matched pair
of
accelerometers
in the model
near
the
center of
gravity.
See
f ig. 5.)
These
units
are commercial oil-damped,
variable-resistance
types
having
fundamenta
l
frequencies
of
the order of
100
to 200 cycles per second.
The
small variations in
voltage
they produce
are ut i l ized
to modulate
a
stronger
carr ier
signal
produced by
a
5-kilocycle
electronic
osci l la tor
The modulated carr ier
is
amplified and
then
rect i f ied in a bridge
demodulator circui t to
provide
a
suitable
input
to the
oscillograph. The
recording
units of the la t ter have
lower
natural frequencies of the order
of 35 cycles
per
second to
minimize extraneous
hash due
to high
frequency
vibration.
Trim, r is e, and fore -and-a f t motiJn with respect
to
the
carriage are
recorded
by
resistance
sl ide -
wire
pickups
at
appropriate
points,
con
nected through direct-current
bridge
circuits to
the
oscillograph.
Con
t ac t
with the
water
a t various
points along
the
keel i s registered by
platinum
loops in
the
nonconducting
material
of
the model that
complete
circuits to
ground
when
wetted
.
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N C
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3419
7
The
instantaneous
speed
of
the
towing
carriage i s recorded by a
direct
-
current generator
geared
to
a
guide wheel.
The
distance
t raveled
by
the carriage is
regis tered by
a
light-beam photocell uni t
interrupted
by shut ters along the t rack . Oscillograph records from the photocell
unit
cal i brate the speed records from the generator. The towing
force
applied by the towing spring
is
recorded by
a
high-frequency resistance
strail i gage in
ser ies
with
the
towing l ine. Power
for
the
elec t r ica l
units is
obtained from the
carriage service t rol leys and
from storage
batter ies
as indicated in figure 5.
Records and Interpretat ion
A typical oscillograph
record of
a model landing in oncoming waves
is shown in figure 6. The
time
interval indicated is
1/10 of
a second.
On the
l e f t
the model
is flying
above the
water against
the rear stop
with landing power, the elevators are set for the landing at t i tude and
the
t r im
brake
i s
locked.
s
the
carriage
is
decelerated,
the
model moves
forward
off the rear stop
and
goes
into a free steady glide
as
indicated
by
the
s t ra ight
portion
of
the
r ise t race. At the f i r s t contact
with
the
water,
indicated by the
stop
contact
trace,
the trim brake is released
and
the model
goes
into a ser ies of
rebounds off
the waves during
which the
motions and
accelerations
become progressively more
severe unt i l
speed i s
lost and the model follows the waves to res t .
Although the f i r s t contact
is random,
the subsequent
t races
for
repeat runs in
the
same wave
t ra ins
are remarkably similar, and four to
eight
runs
are usually
suff icient
to establ ish
consistent
maximum
values
of
trim,
r i se
and
accelerations
re f
. 4 . This degree of reproducibi l i ty
is at ta ined because
in
regular
wave t rains the motions induced by the
in i t i a l contact
are
small in
comparison
with the subsequent
rebounds
below
flying speed, and
the l a t t e r
are largely the
consequence
of meeting the
next
wave upslope af ter contact,
even though
a
downslope
or
trough
may
be
contacted
f i r s t .
In addit ion
to
the
in i t i a l
and maximum values of
the
motions
and
accelerat ions, the records
yield
corresponding
values
of the
horizontal
speed, ver t ica l
speed
slope of the r ise
curve),
and trim a t
each
con
t ac t
for detai led analysis
of
the impacts. Motion pictures
of the runs
are
also made to
aid
in
interpretat ion of the data and to record the
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NACA
TN
3419
TYPICAL RESULTS
ND DISCUSSION
Effects of
Hull Proportions
Figure
7
i l lus t ra tes
a
related family
of
hulls for the
same f lying
boat having
wide
variations in
the
basic design parameter of the length
beam
rat io . ~ lowest
ra t io
is
representative of
practice
as recent as
World War I I . The highest
rat io
represents
an extreme from
practical
considerations
.
The
size
and
aerodynamic
drag
of these hulls decrease as the
length
beam
rat io increases, whereas the smooth-water hydrodynamic qual i t ies
remain more
or
less comparable
throughout the
ser ies refs. 5 6 and 7).
Tank investigations
in
waves
of the
type
described have
demonstrated
significant effects
of
the higher rat ios with regard to
rough-water
qual
i t i es as
shown
in
figure
8 data
from
refs . 7 and
8). The maximum
values
of
the cr i te r ia for
behavior
are plot ted
against wave length in feet ful l
scale)
for
a
constant
wave
height of
4
feet ful l-scale) . The
curves
are
faired
upper
envelopes of the data
from
a number
of
landings
a t each
wave
length
tested.
Maximum t r im and r i se
are indicative
of the extent of
at t i tudes reached
above
the
s ta l l and
heights reached
above
the
water
d
uring rebounds.
The
accelerations
are
indicative of re la t ive load fac
tors on structures
supporting
concentrated
masses
in
the
airplane
ref .
9).
The plots
i l lus t ra te the
general
dependence
ref .
4
of
the adverse
effects
for
a
given
wave
height
on
wave
length.
Usually
there
is
a
c r i t i -
cal wave length
a t
which
the effects
are
most
severe. This cr i t ica l
length
does not
have a
universal relat ionship
to
hull
length
and must be
determined for each configuration and
wave
height.
As
the
length-beam ra t io
is
increased,
the
maximum values of tr im,
r ise , and
ver t ica l
acceleration
are progressively
reduced. See f ig . 8.)
These
effects
are interdependent since
the milder
impacts
resul t in lower
rebounds, and
vice versa.
The
narrower
beam
hulls
also
benefi t
from
the
fundamental
load-alleviat ing effects of
more chine
immersion
and lower
aspect
ra t io of the forebody wetted
area
involved
in
the impacts.
The
maximum angular acceleration increases somewhat because of
the
increase
in length inherent
in the
series , although
the accelerat ion for
Lib of
20 and 15
are approximately the
same . In
spite of
this
increase,
the
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X
NACA TN
3419
9
is
chosen
as
the upper
pract ical
l imit . The top
curves
in each
case
are
for
the
basic
hul l
of
length-beam
ra t io
15.
The
short-dash--long-dash
curves
from ref .
10) indicate
a marked improvement obtained
by
extending
the
afterbody
length
to
match the length required
by
the t a i l
surfaces.
The increase in
bearing
af t great ly reduces
the
trim and r ise motions and
the
accelerations
are
s ignif icant ly
smaller, part icular ly near
the cr i t i
cal wave length.
Similar resul ts were
obtained in an ear l ier investiga
t ion ref . 4 of a
model
with a low
length-beam
ra t io .
A
second
logical
improvement is
a
large
increase in V-bottom
dead
r ise
angle,
in this case from a conventional
20
to 40
ref . 11 . Fig
ure 9 shows
that the
motions
and angular
acceleration were
not
great ly
changed. The
large decrease in
vert ical acceleration, other things being
equal, i s
predictable
from
theory.
The important
contribution of
the
dynamic-model investigation ref . 11 is that
the
high-dead-rise form was
apparently sat isfactory in other respects and even higher dead-rise angles
than 40
0
may
be
of some pract ical
in teres t
for s t i l l greater load
al leviat ion.
The
short-dash
curves
from
ref . 12) indicate that the two previous
features can
be combined
for fur ther gains. In
th is modification, the
dead
-r ise angle
of the
long-afterbody
hul l
was progressively increased
from
the
step
to the bow. The
combination has
lower motions than the
basic hull
of
length-beam
ra t io 15
and the lowest accelerations
of
the
ser ies.
When compared
with
the data in figure 8 for a length-beam ra t io
of
6,
t has
9
less maximum trim ,
8
feet less maximum r ise , and the
maximum vert ical
and
angular
accelerations are
reduced
in
the order
of
60 percent.
Effects
of Wave Proportions
The
resul ts
presented so
far were
al l for one height of wave.
Corre
sponding
data
have
been
obtained for the hulls
with
length-beam
rat ios
of 6
and
15
of
the
series
in
various
heights
of
waves
corresponding
to
2,
4,
and
6 feet full-scale) . See ref . 8 .) The
trends
obtained
are complex
in that
the
maximum
values
for the two
higher
waves remain
about the
same but
the cr i t ica l
wave lengths
are displaced; th is displacement
indi
cates a primary dependence
on
the maximum wave slope.
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N C TN 3419
The
symbol e is the local slope
of
the
wave surface a t contact)
T
is
the
trim of
the
s traight
portion of
the forebo
d
y)
and
r
is
the
f l ight -path
angle
or the
angle
of the
resul tant veloci ty
V
r
;
a l l
are
referred
to the horizontal .
A
simple
and
adequate assumption for the
v
eloci ty
increments of the wave)
according
to the theory
of
r e
ference
14)
is
that the wave may be considered a body of water in horizontal
t rans
la t ion
a t the wave veloci ty V
w
Adding w to the
horizontal speed
V
h
gives the
effe
ct ive resul tant
velocity
Vr .
e
From figure 10) the
effect ive
contact parameters determining the
water
load are
e + tan
-
l
Vv
Since the
angles
are small) the
normal load
i s
approximately
equal to
the
vert ical load measured on
the model
.
Figure
11 shows values
of
maximum vert ical accelerat ion and the
associated
effect ive
contact parameters for the model with a
length-beam
r at io
of
6 landing in various
heights
and
lengths
of waves plot ted against
th
e wave height - length
rat io .
The
pOints
shown
are for the
maximum
i mpacts
only obtained in the
three heights of wave)
and they were
com
puted
direct ly
from the
tabular
data
ref . 8
). Since
the
wave
speeds
and
slopes a t contact w
ere
not
actual ly measured) t
was assumed
that
the
maximum impacts
occurred
on the maximum slopes of the tank waves and that
these
waves were trochoidal. The slope for the
calculations
i s then
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
12/29
NACA TN 3419
v
w
where
H and A
are the
wave height and wave length, respectively.
Except
for the effective
trim,
the plot ted
points
for the
three
wave
heights l ie
for
the most par t along
smooth
upper envelopes
drawn
from the origins; this indicates the adeQuacy of
the
assumptions and
the
primary dependence
of the resul ts
On the
wave slope. The
effec
t ive
t r im
points
are
more
scattered
but
have
a downward
trend
wi th
increase
in
wave
slope as
represented
by the
mean l ine shown.
11
The
severi ty of the
impacts for
the
model configuration
invest i
gated appears to
peak
a t an H/A
of around 0.025
or
a length-height
rat io of
40. At
these ratiOS, the effective tr im is as
low
as
4
0
the
effective ful l -scale ver t ica l velocity is as high as 30 feet per second,
and
the effective
f l ight-path angle
is as much as
15
0
. Since
the
corre
sponding
loads
are
very high
from
a s tructural
point
of
view,
t
i s
of
interest to com
pute the ver t ical
accelerations by
the
method of
refer-
ence 14
for a r ig id prismatic
planing surface from values
of
the
con
tact parameters from the
mean
l ine
and fai red
envelopes of the figure.
The
resul ts are
shown by
the
dashed l ine see
f ig .
l l a))
and
indicate
reasonable agreement with
the
experimental data,
considering the
inherent l imitat ions of
both
methods . The fact that the experimental
accelerations
are
higher
than the theoret ical is significant
since
t
indicates
that
the instrumentation
chosen
i s
not
attenuating
high
freQuency loads of
importance.
Figure l l b )
presents
data for the
model
with
a
length-beam ra t io
of 15 ref .
8 .
The data show trends similar to those presented in
figure l l a ) ; hence, the trends are the same
over
a wide range of hull
proportions. The effect ive trims are as low as 0
f la t impact)
as
compared with 4
in
figure
l l a ) , the
maximum effective ful l -scale
ver t ical velocit ies are reduced from 30 to 25
feet
per second,
the
maximum effective f l ight-path
angle
from 15
0
to 12
0
and the
highest
maximum
ver t ical
accelerations
from
l2.5g
to 9
.5g.
The agreement
of
the measured accelerations with those calculated
from
theory i s
closer
than that
for
ib
=
6 because the
additional
al lev ia t ion
due to
chine
immersion associated with the higher length-beam
ra t io
i s not taken
into
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
13/29
12
NACA TN 3419
s
ometimes lead to
dubious
resul ts
by
not
taking into
account a l l the
influences
on
the motions
prior
to
the c r i t i ca l impact.
In such cases
the range of
contact
parameters deduced
from
model t es t s provide
a
more
rea l i s t ic basis
for
design
estimates of the maximum loads.
Take -
Off
Resistance in Waves
The resistance of seaplanes
during
take-off
remains
a problem of
s
ome importance in
spite
of
the increases
in thrust
afforded by
present
d
evelopments
in
powerplants..
The
resistance
becomes
greater
in
rough
water because
of the added energy in
the
motions and
the
increased
wetting of parts of
the
a i rplane that remain dry in smooth-water
o
peration.
The magnitude of
the
increase
in the case of
a
configuration Slml
la r to
figure
3
i s indicated
by
the
data plot ted
in figure 12.
The
points
are the to ta l average
resistance
R
D , measured by
the strain-gage
dynamometer
described
previously,
a t
a
succession
of constant
speeds
throughout the take - off range . The center -of-gravity posi t ion and eleva
tor deflect ion are constant . The ordinate and
abscissa
are in terms
of
Froude nondimensional
coeff ic ients
proportional
to
to ta l
resistance
and
speed,
respectively.
The take - off
thrudt
available, in terms of a corre
sponding coeff ic ient , is shown on the plot for comparison .
The lower
sol id curve is for the smooth-water resistance
and
i l lus
t ra tes
the
c r i t i ca l
points of
mi nimum
thrust
available for
accelerat ion
a t the
hump
speed
and near take -
off
.
In
2- and 4
-foot
waves, the
resistance is progressively higher a t intermediate planing speeds, where
the motions and extra
wetting
due to waves and spray thrown are greatest .
At the hump
speed,
where the model can more
or
less follow the wave con
tours, the
resistance
i s about the same as in smooth water. Near take
off
where
the model is nearly airborne, the motions
and wetting
again
b
eco
me
small,
and the
resistance tends
to again
approach the smooth-water
v
alues.
In
6-
foot
waves,
the
hump
resistance
becomes much
higher
because
t he
model
can
no
longer r ide
over
the crests and the
e r o ~ i c components
are heavily wetted .
Figure
12
indicates
that with the
available
thrust shown the design
w
ould
not
take
off in waves higher than 2 feet . This
conclusion of
course
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N C TN 3419
13
CONCLUDING REM RKS
The N C seaplane tanks
have
been provided
with
wave makers
appa
ratus and instrumentation
for investigations
of
seagoing
qual i t ies of
water-based i rc r f t . The operation
of Froude
dynamic models in
the
tank
waves
has served to aid
in
defining the problems
and
the relat ive
importance of some of the many parameters. Several pract icable design
improvements
offering
s ignif icant al leviat ion of the adverse effects
of
waves
have been
developed. General
relat ionships
of
the
qual i t ies
of
importance in rough-water
take-offs
and landings
with
wave
length
and
length -height r t io
have
been demonstrated. The increase in take-off
resistance
due
to rough
water has been
invest igated
br ief ly
and
appa
rent ly can be c r i t i c l for operation in large waves.
Langley
Aeronautical Laboratory
National Advisory Committee
for
Aeronautics
Langley
Field
Va.
May
25 1955.
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14
N C TN
3419
REFERENCES
1 .
a t t e r s o n ~
Sidney A.: The N C Impact Basin and Water Landing Tests
of a
Float
Model a t Various Velocities
and
Weights.
N C
Rep . 795,
1944 .
Supersedes N C WR L-163.)
2 . Truscott, Starr: The N.A.C.A. Tank - A High-Speed Towing Basin for
Testing
Models of Seaplane
Floats. N C
Rep. 470, 19
33.
3 .
T r u s c o t t ~
Starr:
The
Enlarged
N.A.C.A. Tank,
and
Some
of
I t s
Work.
N C T 9
18,
1939 .
4.
Benson,
JamesM., Havens, Robert F . , and Woodward, DavidR.: Landing
Characterist ics in
Waves of
Three
Dynamic Models of
Flying Boats.
N C
TN 2508, 1952 . Superse des
N C
R L6L13.)
5 . Yates,
Campbell
C., and Riebe, John M.: Effect of Length-Beam Ratio
on
the
Aerodynamic
Characterist ics
of Flying
-
Boat
Hulls.
N C
TN 1305 , 1947.
6 .
a r t e r ~
Arthur W., and Haar, Marvin
I . :
Hydrodynamic Qualities
of
a
Hypothetical Flying Boat With a Low-Drag Hull Having a Length-Beam
Ratio of 15. N C
TN
1570, 1948.
7 .
Carter,
Arthur W., and Whitaker, Walter E., J r . : Effect
of an
Increase
in
Hull
Length
-
Beam
Ratio
From 15
to
20 on
the
Hydrodynamic
Characterist ics of
Flying
Boats . N C
R
L9G05, 1949.
8 . Carter, Arthur W.:
Effect
of
Hull
Length-Beam Ratio on the Hydro
dynamic Characterist ics of
Flying
Boats in Waves.
N C
TN 1782,
1949 .
9 . Parkinson,
John
B.:
Appreciation
and Determination of the Hydrody
namic Qualities of Seaplan
es
. N C
TN
1290, 1947.
10 . Kapryan, Walter
J .
and Clement, Eugene
P.
: Effect of Increase
in
Afterbody Length on the Hydrodynamic Qualities of a
Flying-Boat
Hull of High Length-Beam Ratio.
N C TN
1853, 1949.
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
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NACA TN
3419
15
13 .
Milwitzky Benjamin
:
Generalized
Theory
for Seaplane Impact. NACA
Rep .
1103)
195
2.
14 .
M r )
Robert :
Hydrodynamic
Impact
Loads
in
Rough
Water
for a
Prismat
i c Float
Hav
i ng an
Angle of
Dead
Rise of
3
0
. NACA
TN
1776) 1948 .
15.
Schn
zer
Emanuel :
Theory
and
Procedure
for Determining
Loads
and
Motions
in
Chine-Immersed
Hydrodynamic Impacts
of Prismatic
Bodies.
NACA
Rep .
1152) 1953.
Supersedes
NACA
TN
2
813
. )
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
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SUPPORTING TRUSS
PL TE -------.J11 M I
11 5
1
GEAR
R ~ D U C E I-
24
CONTROL
P NEL
ADJUSTABLE
C R N K ~
DC
MOTOR
MOTOR GENERATOR SET
SLOTTED
BEACH
PLATE
8.5 FT WATER LEVEL
4
1
1
P I
Figure 1 . Wave maker and beach in Langley tank
no
1
TANK
NORTH
END
f-
0 \
f
1- 3
\ N
.j::
>
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
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2.0
WAVE
HEIGHT
FT
1.5
1 0
.5
o
IRREGULAR
HEIGHTS
16
LENGTH
HEIGHT
RATIO
2
THEORETICAL
MAXIMUM HEIGHT
120
3
8
6
WAVE LENGTH FT
Figure
2.- Working range of Langley tank no. wave maker at 8.5-foot
water
leve
1.
x>
\.).J
0-
f-
--J
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
19/29
Figure 3. TYPical powered
dynamic
model for
t s t s
in wav
es
.
L 89316
I-
O
t>
\ . )J
=
0
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
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N
C
TN 3419
19
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
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SERVICE
TROLLEY
IIOVAC
r--=--=-:-:-:=-=-----
l S ~ L ~ 5
KC
635 V DC OSCILLATOR
SCILLOGRAPH
MOTOR \ OC DEMODU CARRIER
G E N E R T O R ~ MASTER CONTROL
BOX
LATOR AMPLIFIER
.--=-.. -
~ i W / 4 - . . . / , . / : : . v -
/ j I VYVII\I\ J t
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
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R ~ f -
IMPACT
1
J I I
I
I ' J J J
I
I
I l I
I
I
f c ~ f ~ i ~ < : ~ o ~
I
~
1111111
1
2,
'II'
~
I
~
r t ~
11111 ~ l __.lli H
ME
I N t E R V A L ( O J 5 I r ~ ) I r-
J I
A N ~ U L A R
~ C C E ~ E R A T O N
. 1 I 1'.j)(
, I >;
.1::
- 'I,.. '
] I
'
cci
S,
TERNPOST
FOR'T
~ t : P - I t F T POSITION
,
~ E ~ ~ R ~ ~ CE
-'
1
1
r f II t
l
V
{l
1l l 1. lr u /.
I
1.
1
11
,,.J
11
1J.
' T ' J
BOW
VJ\
1/ \ If IT -
71
III H.,
\
~ i & ' J L l ~ tf1
i'J
fili
i :. ' V
/ I\
J
V ' I 1 \ \
1
r 'Ic
T
1 L
1\ r\
, i\ J f\. \ 9 ( ~ T ~ N C E " V. W'FORWARD WAVE
T uT
j
,, ;
Fi
g
ure 6.-
Typical oscil logr aph
record
of
landing.
~
;t>
\..N
+-
~
I\)
f-
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
23/29
L
ct
-E=:-C
l
--
b-- I : - ~ : ~ : : ~
= == ==
-
= =
~ = = ~ ~ =
L //--?
Cg
b
\ ~ O ~ 6 / r : ; : / ~
: : : ~ : :
6 15 :20
~ ~ ==
Fi gure
7.
Series of hulls of var i ous length beam
rat ios
for
the
same
flying boat .
f\
f\
~
f
;t>
t-3
~
\.>J
(0
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
24/29
2 ~
MAX. TRIM,
OEG
10 ,
MAX.
ANGULAR
ACCEL
1
RAO/SEC2
OL
2 ~
8
4
LENGTH-BEAM RATIO
6
~ ~
-- ==---
- 2 0 -
~ 5
2
MAX. RISE,
FT 10
MAX. VERT.
ACCEL.
,
9
OL
12
8
4
WAVE HEIGHT,
4 FT (FULL-SCALE)
6
~
~
I I I
L
I I I
o
1
2 3 0
1
2 3
WAVE LENGTH,
FT
Figure 8 . Maximum motions and
accelerations for three length beam ra t ios .
Data
from references 7 and 8.
f
1 3
\>I
-t=
f--
\.0
f\
\>I
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WAVE HEIGHT
4 FT FULL-SCALE)
2
2
= = = ..
MAX. TRIM, I , : : : : . : : : . . : = : : . : .
MAX.
RISE,
DEG 1 ~ \ W R P E FOREBODY FT
10
LENGTHENED
AFTERBODY
~ = -
-
...
/
/ -LENGTH EN ED
'I
AFTERBODY
OL- I I I a
I
12r
12
INCREASED
DEAD
RIS
E
MAX
.
8
/ ~
8
ANGULAR
,
MAX.
V
ERT.
/ - , ~
CCE
L.,
A
CCEL.
4
4
/
,
RAD/SEC2
/
, , ~
I I I
L
I
I
a
100
2 3
0
1
2
3
0
WAVE
LENGTH
FT
Figure 9 .- Maximum motions and
accelerations for
modifications of the
model with leng
th beam
rat io of 15 .
Data
from refe rences 10 l l}
and 12 .
f\
+:-
~
:t>
~
\..N
+:-
0
>
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MO EL
W VE
..
igure 10
Relation of
geometric and effect ive contact parameters
;p
1 3
\ N
f\
V
8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf
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~ M E N
LINE
EFFECTIVE
30
8 ~
FULL-SCALE
EFFECTIVE VERT
VELo
2O
l
-
WAVE HEIGHT
RIM,
Vv FPS
FULL-SCALE
Te
DEG
4
0
e 10
~ 2 FT
o
4
FT
o 6 FT
0
0
ENVELOPE OF
EXPERIMENTAL
E N V E L O P E ~
12r
DATA \
15r
0
, , -
,&
/
/
8
/
EFFECTIVE
1
MAX. VERT
P
~
LIGHT -PATH
ACCEL., 9
/ CALCULATED
NGLE,
4
' / / FROM CONTACT
e DEG
5
/ PARAMETERS
1
I
0
.01
.02 .03 0 .
01
.03
WAVE
HEIGHT-LENGTH RATIO, H/A
a ) Model
with length
- beam
r t io
of
6.
D
ata from
references 8 and 14
Figure 11 - Effect ive contact parameters and maximum ver t ic l
accelerations .
_ ~ ~ ~ ~ ~
f\
0 \
~
f
~
\..).I
=
t:;
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_ _ ._
8
EFFECTIVE
TRIM,
Te DEG
4
I
0
15
EFFECTIVE
10
F
LIGH
T-PATH
ANG
LE,
Ye , DEG 5
o
\MEAN
LINE
\R n
'-
\ J
I()
ENVELOPE,
EFFECTIVE
30
FULL-SCALE
VERT.
VEL.,
20
0
VVe
FPS
6
WAVE
HEIGHT
~ FULL-SCALE
10
62FT
o
4FT
o
6FT
0
12.
ENVELOPE OF
EXPERIMENTAL
8
MA
X. VERT
ACCEL
.,
9
4
\TA.JtC
,
~
- C A L C U L A T E D
F
ROM
CONTACT
PARAME
T
ERS
I I
.01 .02 .03 0 .01
.
02
.
03
WAVE
HEIGHT-LENGTH RATIO,
H/A
b)
Model with
length-beam
r t io of 15.
reference 8 .
F
igure
1
1.
- C
oncluded
.
Data from
~
f
~
8
~
\.)oJ
+
I\
..l
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z
n
>
t '
.?-