naca model invastigation on seaplanes in waves.pdf

8/10/2019 NACA MODEL INVASTIGATION ON SEAPLANES IN WAVES.pdf

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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


2/29

X

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


3/29

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


4/29

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


5/29

4

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


6/29

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


7/29

6

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

.


8/29

N C

TN

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


9/29

8

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


10/29

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.


11/29

10

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


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


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


14/29

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.


15/29

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.


16/29

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

. )


17/29

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::

>


18/29

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


19/29

Figure 3. TYPical powered

dynamic

model for

t s t s

in wav

es

.

L 89316

I-

O

t>

\ . )J

=

0


20/29

N

C

TN 3419

19


21/29

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


22/29

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-


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


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


25/29

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

>


26/29

MO EL

W VE

..

igure 10

Relation of

geometric and effect ive contact parameters

;p

1 3

\ N

f\

V


27/29

~ 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:;


28/29

_ _ ._

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


29/29

z

n

>

t '

.?-

naca model invastigation on seaplanes in waves.pdf

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