Tank tests on a hydrofoil boat with incidence control (Hydrofin)

A i/-i,)'

1r.1n_

TECH. NOTE

AERO. 1922

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Act.-TECH. NOTE

-. AERO. 1922

T

a-C1

roÇ!

FA R

N B O R O U G- H. -

H A N

T S

TECHNICAL NÖTE No: AER0. 1922

TANK. TESTS OÑ A

HYDROFOIL BÓAT WITH

INCIDENCE, CONTROL

'¼

(HYDROFIN)

by

T. B. OWEN, B.A.

_/

7.

1b. v

RESTRICTED Class No. 532.582.4

Technical Note No. Aero.1922 November, 1947.

ROYAL AIRCRAFT ESTÀBLISHIv]ENT, FARNBOROtJCH Tank Tests on a Hydrofoil Boat with

Incidence Control (Hydrof in) by

T.B.Owen, B.A.

R.A.E. Ref: _{Áero.T./1739E/159}

SU1v1MRY

1 3 foot long stability model of a Hydrofin was tested in the R. A. E. seaplane tank to provide information on the stability of a variable incidence hydrofoil system. Ihe Hydrof in is a boat which travels supported on three hydrofoils with the hull clear of the water, _{A pair of awdliary planing surfacés is fitted ahead of} the boat, independently controlling the incidence of the two forward hydrofoils, desiied to enable the hydrofoil to run at constant.

draft under sea-going conditions. It was tested in a variety df wave systems and ran stably in regular vaves invoivìng +O.5g vertical

accelerations. By the use of springing and damping in the incidence control system, running in wave systems involving +1g should be

practicable if required. A drag:weight ratio of 0.16 ws obtained on the stability model with rather cnide hydrofoil and strut sections. It is thought that a drag:weight ratio of 0.10 should be attainable full scale up to about ₅ Irnots using suitable thin hydrofoil and

Tech. Note No. Aero.1922

LIST OF CONTENTS

Pago

i Introduction ₃

2 Description of Hyd.rofin ₃

3 Longitudinal Stability Tests

3.1 Calm water

3.?

Tests in waves

Drag Measurements _S

5 Lateral Stability 5

6 .Lif t and Moment Characteristics ₆

7 Pull Scale Behaviour and.Possib1 Design Developments 6

8 Conclusions 8

8.1 Longitudinal stability 8

8.2 Lateral stability 8 8.3 Resistance measurements 8 8.4. Lift and. moment characteristics 8

8.5 Pull scale behaviour 8

Notation ₉

References - 9

Circulation ₁₀

LIST OF APFDICES

ppendix Calculation of Forces and Moments

LIT OF TABLES.

Table prag Measurements on Hydrofin Model

LIST OF ILLUSTRATIONS

Figure Hydrof in Model 17 1 & 2

Auxiliary hydrofoil _3a

Main hydrofoil .3b

Tail hydrofoil 3c

Diagram of hydrofoil incidence control system 4.

Spray and wake formation in calm water and small waves ₅ Spray and wake formation at 12 ft per sec during one cycle each

cf 3", wave systems of length:rìeight ratios

50:1

and 30:1 6

Spray and wake formation in 1 in. waves, length :height ratio

30:1 at two weights 7

Hydrof in drag measurements 8

Tail hydrofoil 11f t curve ₉

-Tech. Note No. Àero.J922

i Introduction

Information was required on the stability of'hydrofoil systems with incidence control, as'part'of a general hydrof¿il research programme. Limited tests were therefore made in the' R.A.E. tank on a stability model of the "Hydrofin" hydrofoil boat, for which the stability was

claimed to give ful]. scalé. "A few drag measurements were also made. The basic feature of the design is that the hydrofoils are auto-controlled in incidence so that, at running speeds, they operate at almost constant draft relative to the water surface, the incidence decreasing 'with increaseof speed. This feature lends itself both to the possible achievement of high stability sud to some control of cavitation and aeration at high water speeds, when low incidence is essential.

2 Descri?tion of Hydrof in

The Hydrofini's a boat

which

normal operating speeds is supported on three'hydrof oils with 'the hull clear of the water. A photograph of the model tested in the R.A.E. Seaplane Tank is shown in Fig.l. A G-.À. of the boat is given in Fig2 with details of the hydrofoils' in Fig.3. Two main hydrofoils 'are fitted aneaã. of the with a lateral spacing of about twice their span. Each of these is

separately connected tó one of two auxiliary planing surfaces ahead of theboa't so'that the rise and,fall of these t.jockeyu surfaces controls the incidence of' the hydrofoils. This system is shown diagraiatically in Fig.L.. The main hydrofoils are 'pivoted at about 307o back from the lêading edge so that very little moment is trans-mitted to the jockey by the hydrofoil. The jáckey therefore pianes lightly on the surface and will follow an undulating surface subject

only to inertia limitations.

It can be shown that, at a gïven speed and with the jockey planing at sensibly

constant

draft relative to the water surface,

the system constitutes a constant draft device for the main hydrofoil as a change in draft of the main hydrofoil from the equilibrium

position produces a restoring force proportional to the change in draft. (See Appendix.) The tail hydrofoil is fixed to the hull at a set attitude and this also constitutes a stable system as a change

in attitude produces a còrrespbnding restoring rnomnt (See Appendix.) The differential action of the twO jockey' systems produces stability in roll.

The above applies to calm ter and 'long swell ,wnere the curvature of the water surface is small. In smaller waves, 'when running head on to the sea, the jockeys act as predictors for the main hydzof oils and the main hydrofoils for the taiÏ hydrofcil, the boatj rising smpothly

to the wavewith'outlag. A varable damping devicQis f,tted to the

jockey system so 'that in small 'waves the ,jockey will skip from crest to creatwith the boat itself running evenly with the

hull

pisar of

the crests.

Apart from the three hydrofoils which supp'ort the boat at the normal running speeds, two auxiliary hydrofoils are fitted to assist in lifting the hull out of the water at low speeds On the full

scale boat: these are retracted upwards when the boat 'has riáen.to avoid pounding in waves, but for convenience they were at a fixed height onthe model. On themodèl testèd the auxiliary hrof oils were connected to the jockey 'system so that 'théi'r incidence varied with

that of the main hydrofoils, but on later boats the auxiliary i-ydro-foils 'have been set at a fixed angle to thehull ' 'A "feathering"

The ,model was tested. up. to 16 ft/sec.

sys teins

Tech. Note No. Aero,1922

device is incorporated be twen the jockeys _{and the. hydrbfoils to enable} the hydrofoil incidence to be reduced at displacement speeds so

decreas-ing. the drag (para.+).. .

Propulsion is b an aircraft engine. d'iving an air propeller.

j . Longitudinal Stability Tests

The model was towed from the C. C.. axis. and: was free . to pitoh and

heave but not to roll or yaw. No thru.st moment was applied. Cine-.

film records weze made of. the tests _{and the running attitude in calm} water observed.

3.1 Ca1mwater

The tests were made at _{5.8.3 1b corresponding to a hydrofoil}

loading (model) of 18 ib/sq..f t. Photographs of the mod1 rurning

at various speeds are shown inFig.5a. _{The model rose smopthly onto} the hydrofoils at about 6 ft/sec and, ran satisfactorily at speeds up to 12 ft/sec. _{At this speed the .water separá.ted from the main} hydro-foils, a bubble förming on the _{upper surface which, 'as tie spéed was} increased, extended further aft and upwards till at 20 ft/sec it had broken surface producing heavy spray. Separation from the, struts

supporting the hydrofoils first appeared at. .12 ft/sec and increased th speed, _{Very little spray oÏ' wake was produced up to 16 ft/sec,} when «spray was first thrown up from the.struts, but at ?. ft/sec the sprar was severe..

No oscillation was apparent at any speed apart from slight "pattering" of the jockey skids whiöh were set ata rather làrge incidence to the water surface.

.3.2 Tests in waves

at

5.83.lb

at speeds

. In 1 in. high waves, ,lèngth:height ratio

= 30:1, (pig.5b).

the

behaviour was similar to that in calm water except that intermittent flow separation first appeared at 8 ft/sec. The model rán steadily at higher speeds Wi:.th only about 2° pitàhing and was follówing a mean path rather than the wave profile.. Some spray was .throi up by the jockeys, wetting the.auxiuiary hydrofoils, ... "

.

..Iui,».3

in. high waves, length:height 'ratio'=

30:1,

_thez was

slight pounding on tIi.ebottoitof the hullat 6 ft/sec when the boat had. just risen, arid heavy pounding on, the auxiliary hydrofdils at 12 ft/sec. _{Above 8 ft/seethe jockeys failed to follow the water} surface over some of the,wave crests and. the model skipped several

feet. . This was apparently due to the occasional "sharper" crests

produced by the. unstable, propagation of the wav.e system. _{Pig. 6b}

shows a sequence of' 'the model. running over one wave.

In 3 in. high waves, length:height ratio = 50:1, the :ode1 followed the waves smoothly at all speeds.

_though

at 16. ft/sec slight buffeting. was observed, on the auxiliary hydrofoils, which _{ul1 scale} would have been retracted, Separation was similar to that izi calm water but above.8 ft/sec.fairiy heavy spray was thrown up by the

jockeys. Pig. 6a shows a sequence of" the model running, over one wave. The model was also tested át the increased weight of 8.3 Ib in 1 in. high waves, length:height ratio = 30:1. At this' weight the

Tech. Note No. Aero. 1922

model rose onto the hydrofoils at just over 8 ft/sec. Separation appeared at 10 ft/sec and was severe at 16 ft/sec, the "bubble"

breaking the surface above

12 ft/sec. The model

ran smoothly

at

all speeds, the pitching amplitude, being reduced at the higher speeds

in the

ame way as at the lower weight.

Pig.7 shows

comparison

between the

two weights.

An attempt was made to examine the following - se case using a smaller model which ran on its hydrofoils at ¿4.

ft/sec, but this

was faster than the speed of propagation of all except very long

wave systems where the surface

curvature was insufficient to affect

the model any-way.

¿4-

Drag Measurements

The model was towed from the

drag

balanôe by a

thin string

attached to the nose of the boat, and the drag. determined over a.

range of speeds up tol6 ft/sec at 5.2+5. lb

and

8.95 lb weight.

These results are given in Table I and are plotted in Fig.8 in the

form of drag:weight

ratio against 1-/CL

where:-W/pV2 (2S1

+

s2)

W

weight of boat (lb)

p water density (slugs/cub.ft)

V =

water speed (ft/sec)

S1 =

area of one main hydrofoil (s.f t)

S2 =

area of tail hydrofoil (sq.f t)

It should be pointed out that the hydrofoils and struts on -the

test model had not been designed to give low drag values.

It is

apparent from the curves that their is some ttscale effect" present

between the two weights tested, the drag:weight ratio for the tests

at 8.95 lb being in general about 10% higher than those for the

tests at 5.)5 lb

at the same

CL.

This difference is presumably

due to separation effects.

The drag rises rapidly with increase of speed in the displacement region where the weight of the boat is supported mainly by the buoyancy forces on the hull. In the transition region where the weight of the boat is

being transferred to' the

hydrofoilá the drag reaches a peak value and, as the speed increases, begins to fall again.

This

peak value of D/W is O.23'which is reduced to 0.17 with the ain

hydrofoils partially feathered.

Froma

_0L

of

0.2+'

dowii to a

CL o

0.2 D/W remains sensibly

constent due

to the reduction of strut area immersed and improving

lift:d±ag rätìd of the hydrofoils compensating for the increasing

speed. As the speed increases still further the strut a±ea iersed

approaches a constant value indicated by the high speed water line in Fig.2.. This is nearly attained at a CL of 0.1 and from then on D/W incxeases proportional to V2 at a value of 0D = 0.021 (based on

the

hydrofoil

area 2S

s2).

5 Lat.eral Stability

No tests were

made specifically to examine the lateral stability

but, during the drag tests, the model

was freely towed. by a

single

Tech. Note No. Aero.l922

long

string prom the nose, No oscillation in roll was apparent at any speed and the model in all cases rose onto the two main hy.rof oils simultaneously without "lurching". The boat in most cases ran straight but at the smallest CL reached, at 16 ft/sec and 5.2i.5 lb wt., a large oscillation in yaw was set up in, spite of the stabilising moment pro-duced by the nose towizg poin1. When running at the draft indicated by the high speed water line in Fig.2 the moments about the C.C.. of the vertical areas, submerged are ₄₅ ins3 for the ni.dder and 35 ins3 for the main hydrofoil.struts. The difference, which is an approximate criterion of the directional stability, is comparatively small and is very sensitive to changes in draft of the tail hydrofoil. In addition to the main hydrofoil struts the jockeys also contribute a destabilising moment which is not readily calculable.

6 Lift and Moment Characteristics

The lift contributed. by the tail hydrofoil can be calculated from a knowledge of the weight drag and C.C. position of:

the

model. Further, if the running attitude of the boat is measured and assuming that there

is no interference beteen, the main hydrofoils and the tail hydrofoil, a curve of lift against attitude for the tail hydrofoil can be produced. This is plotted in Fig.9 calculated from the tests in calm water at

5.83 lb. Due to separation effects this is not a unique curve but is dependent also on draft and speed, a decrease in draft and an increase in speed causing a reduction of CL2. Ari approximate CL - a relationship at any condition can be 'obtained by joining the mea ured value to the no lift angle (assumed constant) by a straight line as indicated in Fig.9. On this basis the value of dCL2/da2 varies from about

0.06

per degree at 6 ft/sec with the hydrofoil running at

1.5

chords below the surface to '0.04. per degree at 16 ft/sec with the hydrofoil at 0.4. chord below the surface c.f. the theoretical value

of

0.08

for hydrofoils of th aspect ratio employed.

If these experimental figures are assumed applicable to the main hydrofoils as well as to the tail hydrofoil the various moments can be calculated using the formulae deduced in the Appendix. At 16 ft/sec the restoring force due to a change in draft of the main hydrofoils is

9 lb/in, and the restoring moment in pitch 2.0 lb.ft/degree. In

roll the restoring moment at 16 ft/sec is 0.85 lb.ft/degree correspond-ing to a metacentric height of 9 ft for a model weight of

_5.5

lb.

7 Full Scale Behaviour and Possible Design Developments

The incidence control of the main hydrofoils is a very powerful method of draft control - at running speeds a change in attitude of 2° produces 1g normal acceleration on the boat, The response of the boat to chaiiges in hydrofoil incidence is therefore very rapid and it

is apparent that in waves the motion applied to the main hydrofoils must be accurately representative of the path the boat is req.uired. to

follow. The hull is carried, well clear of the water so that the boat need. not be affected by small waves or irregularities, responding only to waves or swell longer than about twice the length of the boat*.

On the model tested the jockeys were connected directly to the hydrofoils, the inertia of the system providing the only damping.. This

* _{Waves 2-3 ft high in coastal waters are rarely shorter than 20:1}

length:height ratio while the longer waves encountered. In the open sea are nearer 50:1 length:height ratio..

Tech. Note No. Aero, 1922

functioned satisfactorily in regular wave systems

involving

up

to

O.5 vertical accelerations, but above this the

jockey skids failed

to follow over the crests of the waves, causing the model to skip out of the water. Sna1l irregularities near the crests were sufficient to make the model skip in waves

involving

only ±O.3g vertical accelertioris. It is proposed on the full scale boat to apply damping to the upwards motion of the jockey arms which should reduce the response to small waves and irregularities but without affecting the behaviour in

regular

waves.

The limitation of i-O.5g imposed by the system tested is probably higher than that required for comfort, but if higher speeds, involving higher vertical accelerations, are required the jockey system needs modification. Improved following in regular waves necessitates an increase in the ratio of the load carried by the ,ockeys to the inertia of the jockey system.

This can most easily be accomplished by spring loading the jockey arms, which besides increasing the jockey load, at the same time permits a reduction in weight of the jockeys

and

hence a. reduction of the inertia. The ratio in this way could easily be doubled, enabling watres involving up to +1g to be negotiated, though at the expense of heavier impacts on the jockeys. The attachment of the oc1cey skids

:to

the arms by a

damped..spinging system (similar to theHsuspension of a land vehicle) would sthó9th out the impacts and at the same time assist in reducing the response to small waves and irregularities. In attempting to reduce the lag in the system it is essential to ensure that there is no 'feed backt' from the hydrofoils to the jockeys i.e. that the resultant force on the hydrofoils passes through the hinge line of the system as closely as possible.

The stability in roll is enormously greater than that of a dis-placement craft and no difficulty should be experienced in a cross or partially cross sea, the boat rolling just sufficiently to remain perpendicular to the local water surface The runñing speed of the boat should normally be greater than the speed of the wave system so that a following sea can only occur for very fast waves, which in practice means waves of very large iength:height ratios and hence small surface curvatures. The rate of change of the angle of the surface at the boat will therefore b very small, giving ample time

for the boat to respond.

On the model tested thedirectional stability was

borderline and.,

unless the rati.o of the rudder area to the area of the struts supporting

the main hydrofoils is considerably increased, the

stability will be

very critical to the

rudder area

iniiered,

i.e. to

the draft

of the roar

hydrofoil which in turz:i depends on the longitudinal C,C-, location. The size of rudder necessary to al1ov for variations of C.C. position

can

,bereducéd however by making the aft hydrofoil setting angle adjustable

and

setting

it

to give a suitable hydrofoil draft for

any particular

condition.

The lift:drag ratio of 6:1 on the model was obtained using hydrofoil and strut sections.consisting of flat plates sharpened at the leading

and. trailing edges. Using suitable thin sections for the hydrofoils1

and

struts2 a 11f t:drag ratio of 10:1 is thought to be attainable full

scale up to about

50 kts. providing strut interference

can

be kept

small.

The drag could possibly be further reduced by the use of

higher aspect ratio hydrofoils

and,

at high speeds, by some method of

reducing the wetted area.

The limitation on thiclmess and

aspect

Tech. Note No. Aero.1922

supporting struts to the hydrofoil because of the possibility of forced water separation bn the hydrofoil by air running down thestruts.' The

limitation

on area is given by- the maximum CL which can be achieved.

without flow separation at the design

speed1,

assuming

that a sufficient

auxiliary hydrofoil area is available to lift the hull clear of the water at low speeds.

8 ConclusionS,

8.1 Longitudinal stability

Disturbances in pitch and heave appeared to be very highly damped and. no oscillations were observed in the tests inwaves other than

those involved in following the waves. In small waves the model followed a mean path rather than the water contour at ruiining speeds, and. in large waves ran smoothly over regular waves involving up to +O.5g vertical accelerations though small irregularities near the

crests were sufficient to reduce this to 0.3g.

8.2 Lateral stability

No òscillations or unsteadiness in roll were apparent in the free-towing tests, and oscillations should be as highly dampe. as

those

in heave since the rolling stability is due to the differential

action of the jockeys.

The directional stability

was borderline with

the ratio of rudder area to main hydrofoil strut area employed. on the model.

8.3 Resistance measurements

The drag:weight ratio rises to a value of 0.22 in the transition region where the weight is being transferred. to the hydrofoils, falling again to 0.16 at a CL of O.L. when the hull is clear of the water. The peak value of 0.22 can be reduced to 0.17 by partially feathering the main hydrofoils. From a CL of 0.4 down to 0.15 the dragweight ratio remains sensibly constant at about 0.16, then rising again, till at values of _0T below 0.1 it increases proportionally to y? at a value

of CD (based on total hydrofoil area) of 0.021. 8.4 Lift and moment characteristics

The value of CL/da falls from about 0.06 per degree at 6 ft/sec

with

the hydrofoil

running at 1.5

chords below the surface

to 0.04 per

degree at 16 ft/sec with the hydrofoil running at 0.4 chord below the surface c.f. a theoretical value of 0.08 for hydrofoils of the aspect ratio used assuming nb separation. Using the experimental figure the restoring force at 16 ft/sec due to a change in.draf t at the main

hydrofoils is 9 lb/in and the restoring moment in pitch 2.0 lb.ft/d.egrce. In roll the restoring moment is 0.85 lb.ft/degree at 16 ft/sec corres-ponding to a metacentric height of 9 ft for a model weight of 5.5. lb.

8.5 Full scale behaviour

It should be possible to raise the limitation of waves involving not more than 0.4g vertical acceleration to +1g if required by

suitable combined, springing and damping of the jockey system. Though

prediction

of full scale resistance cannot be made accurately, a

11f

t:drag ratio of 10:1 is

thought to be attainable up to

about

50 kts. using suitable thin hydrofoil and strut

sections.

Though

only the behaviour in head seas could be investigated on the model,

Tech. Note No. Aero.1922

Notation

CL1 Lift/p V2S1 for main hydrofoil.

-CL2 Lift4pV2S2 for tail hydrofoil. D = Total model drag (lb).

= Distance of .jockey ahead of main hydrofoil pivot (f t). Distañce of main hydrofoil pivot ahead of C.G. (f t)..

¿3 = Distance of tail hydrofoil aft of C..G. (ft).

¿

Lateral distance of main hydrofoil centre line, from boat

centre line (f t).

L = Rolling moment (lb.f t). M = Pitching moment (ib.f t).

S1 = Area of one main hydrofoil (sq.f t).

S2 = Area of tail hydrofoil (sq.ft). V. Foiw.rd speed (ft/sec).

W = Weight of boat (Ib).

z = Draft of main hydrofoil (f t).

Z . LIft of main hydrofoil, positive dovìnwards (f t).

= Attitude of main hydrofoil.

= Attitude of tail hydrofoil.

p Water density (slugs/cub.f t).

¶ = Attitude of boat. Angle of roll.

References

Ref. No. Author Title, etc.

i d.H. E.Warren A théoretical approach to the design of

hydrofoil lifting surfaces. R.A1E. Aero T.N. No. 1826. à.R.C.9L176. S.550. 2 _C.H.E.Warren A theoretical approach to the design of

hydrofoil strut sections. R.A.E. Aero T.N. No. 1739. A.R. C. 10181.

S.573.

Attached: Appendix :t Drg. Nos. 20e46S-20850S Neg.Nos. 751+82 - 751+85 Circulation: P. D. S. R. (A) A.D.A.R.D. (Res.) A.D.S.R. (Records) P.D.T.D. (A) D.A.R.D. D. M. A. R. D. T.P.A3/T.LB. 170 D. C. A. R.D. A.D.R.D.A.C.l D.D.R.D. (Pere.) A. D. R. D. S. A. D. R. D. N. lvl.A.E.E. 2 N.P.L. 2 D.N.C. (Admiralty) 2 R.D.S.2 Director, R.A.E. D. D. R. A. E. Library M.E. Dept. Aero (i) T/A Supersonic P

w

T .. 10

i.e.

oz =

dz dz - pV2S2 I

-

-pv2sl

da1

where p= water density (slugs/cub.ft), V foiward speed (ft/sea),

.d.CL1

S1 = ¡nain hydrofoil area (sq.ft), =slope of hydrofoil lift - da1

ourve arid di.staiice of jockey forward. of hydrofoil pivot (f t).

The attitude of the tail hydrofoil to the boat is fixed so.a change of attitude of the boat ô produces a moment about the front hydrofoils

dC L2

-

_pVS

_ô

( +

where S2 tail hydrofoil area (sq.. hrdrof oil 3ift curve and (2 + ¿3) = of the main hydrofoils (f t).

d-CI ( + da2 d-CL2 ft), - slope of tail da2

distance of tail hydrofoil aft Tech. Note No, Aero.1922

Appendix I

Calculation of Forces and Moments

The boat is assumed to be running at a uniform speed in calm water with the jockey skids running at a small constant draft. Then from Fig.L a change in draft ôz of a main hydrofoil produces a -change of hydrofoil attitude ôa1 ôz/e,. This is turn produces a force

In roll a change.in angle ô, produces a change in draft = ¿. ÔØ at one main hydrofoil and ôz = - ¿. at the other (pig.2) producing a moment

¼

ÖL

24.

2 dal ¿, ÔÇ6 i. e. dL

-d-CL1 2 a1 1

where 2¼ = distance apart of the two main hydrofoils (f t) measured from centre line to centre line.

ÔM =

ai

12

-Tech. Note No. Aero.1922

Table I

Dra' Measurements on Hydrof in Model

Weight lb 8.95 Main Hydro-foils Normal Partially Feathered Normal Partially Feathered Speed (f t/ sec) 1/CL Drag (lb) D/w Drag (lb) D/ _'/CL Drag (lb) D/w Dra (lb) D

/

2.8

0.57

_1.03

0.189 0.71 0.130 0.35 1.32 0,147 0.82 0.092 ¿4.2 1.06 1.17 0.2114. _0.85 0.156 0.64 1.92 0.214

1.30

O.:Uf5 6.3 2.38 0.86 0.158 0.83 0.153 1.14.5 2.10 _0.234 1.60 0.179 8.4 4.23 0.82 0.151 2.58 1.51 . 0.169 1.49 0.166 12.5 9.52 1.06 _0,194 .5.80 _1,49

0.166

16.7

16.92 1.80 0.330 10.17 2.02 0.226

IR.A.E. NEC. NO.75482 /47v

FIG.1. HYDROFIN MODEL

42O

FIG

rAhTIc

WATER LINE HIH SPEED WATER LINE

2. HYDROFON MODEL Il

!O 847.5

f-FIG.3o.) AUXILIARY HYDROFOIL

FIG.3.e,)MAlN

HYDROFOIL

70"

U)

I>

A..

.1

FIG.3c) TAIL HYDROFOIL

FIG..3 .DETAILS OF

HYDROFOILS

TN. ARÒ 19Z

FIG.3

SCALE.:-'/Z MObE.L SIZE

MAIN'

I

HThROIL

JCKEY

SKIb

AUXILIARY }

kYROFOILJ

C:.

'WATER 5URFACE _TAIL

- tH'rbROFOIL

-4 ft./sec. 6ft./sec. 8ft./sec. I 2ft./sec. T.N: AERO. 1922

FIG.5

/

l6ft./sec.

-

_I A

(a) CALM WATER (b 1. inch WAVES

LENGTH: HEIGHT RATIO = 30:1

FIG.5.

SPRAY AND WAKE FORMATION

IN CALM WATER AND SMALL WAVES

A.U.W.= 5831b

L

-/

(a) LENGTH; HEIGHT RATIO = 5OT _L(.) LENGTH: HEIGHT RATIO = 30:1

FIG 6

SPRAY AND WAKEIIFORMATION AT 12 ft Isec DURING

ONE CYCLEEACffQE3jnch WAVE SYSTEMS OF

LENGTH HEIGHT RATIQS5O1IAÑD 30L A U W = 5 83 lb

MODEL POSITION _{T.N: AERO. 1922}

(WAVE HEIGHT _{FI G .6}

E XAG G E RATE D

N o z t, z a Bft./sec. l2ft./sec.

l6ft./sec.

A.U.W.= 5.831b.

_{A.U.W.= 8301b.}

FIG.7.

_{SPRAY AND WAKE FORMATION}

IN

I inch WAVES,

LENGTH: HEIGHT RATIO=30:I

AT TWO WEIGHTS

T.N: AERO. 1922

FIG.7

/.

I.

I I

i.

o

i'

.

0.Z5

i MAIN HYDROFØIL.$ DEbUED FROM IN RUNNING TESTS AT &95,t5. POSITION

I ' bEDUC! FROM

I.

1ESTSAI545L8.

fMAINIfroroILs

rIA3.LY

1 FeATHREb

2.

4

G

8

IO

14,

1G IC1,

FIG.8. HYDROFIN DRAG MEASUREMENTS

la

-3.5

40

50

-7.0

-8.0

-I00

.0

b

LP (n

0.4

_Ii

0.3

i

QZ

I

0l

I 0.12 I i

OI

0.09

i

.00B

i

007

i C1,

0.OG

2

.4

oL _ATTI1'U

(bREzs)

MEASURED TO LOWER 3URFAC

FIG.9. TAIL HYDROFOIL LIFT

.

CURVE

'#IEJHT 5.63 LB.)

/

20850.5

NA&O i9z