A study on the conceptual design of wing in Surface Effect Ships (SES)

THE SIXTH INTERNATIONAL

,,_-_-w -,

SYMPOSIIJMON

-

_{PRACflCALDESIGNOFSHIPSAND} MOBILE UNS

PRADS

SEPTEMBER 17-22. 1995

A STUDY ON THE CONCEPTUAL DESIGN OF WING-IN-SURFACE EFFECT SHIPS

T.FUWA,T,TAKAHASHI,N.HIRATA and A.KAKUGAWA

Ship Research Institute, Japan

6-38-1, Shinkawa, Mitaka, Tokyo 181, JAPAN

ABSTRACT

In the present paper results of a study on the design methods of Wing -in-Surface Effect Ships (WISES) and an example of a WISES design are shown. The example is for an island route which carries 100 passengers at a speed of about 180 knots. Utility of WISES for passenger transport, and design features are also discussed. At present WISES is not economically promising as a high speed vehicle for civil use at sea, but the -fundamental study shown here is a useful example of a practical feasibility study of the safety of WISES and

high

speed marine vehicles in general, especially hybrid types.

INTRODUCT ION

Diversification of society and demands for marine transportation enable

various kinds of high speed marine vessels to be developed. A Wing-in-Surface Effect Ship (WISES) is a candidate for a super

_high

speed marine vehicle in the future. In the cruising condition WISES is sustained by the dynamic lift acting on aerofoils and runs above the sea surface. In the vicinity of a boundary surface, the lift on an aerofoil increases dramatically because of the so-called ground effect/surface effect. Better transport efficiency than the airplane is expected for a vehicle running near the surface like a WISES. Based on this principle there are many concepts for a WISES, and several types have already been developed in some countries,[l,2]. The safety and the

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Table 1: Requirements for WISES Design PURPOSE. ROUTE SIZE RANGE

MAX. WAVE HEIGHT

Passenger Transport Island Route 100 Passengers 300 n. nile 2m ( cruise 3m ( landing

economy of. WISES should be. compatible for marine transportation. Wave

disturbances and wave impact loads are quite important for the safety of the WISES because it runs close to the sea surface.

Di A study on the desigti nethods of a WISES was performed in the framework

T:

of a research project on the safety of WISES at the Ship Research Institute

t

of Japan,[3,4]. A comp.iter aided design (CAD) system for WISES shares many

a.

items with that for conventional airplanes, and includes the aerodynamic

ar

characteristics of the surface effects and the hydrodynamic perfOrmance in

rf

the system. Estimation of weight, performance and stability are the priOcipal

ti

items in the first stage of the design iteration. Main wings designed to have sufficient surface effect, tails for longitudinal stability to suppress the.

ar

instability due to the: surface effects and fuselages for good hydrodynamic

e: performance are points for W,ISES design.

p

Suitable size, range, speed, routes and sea conditions for WISES

er

operations

will

be shown based on economical evaluation by means of the

ta

estimation of direct operating costs (DOC) ftom airplane methods.

Si.

Plate 1: Solid Model of Designed WISES

Table 2: Principal Particulars of Designed WISES pe sç re de Range (nm) Passenger . Wing Loading(kg/m 2) Power Loading (lgtl,p) Takeoff Weight (kg) - 300 100 300 3.6 34,000 BodyLength (m) 30.1 Wing Span (m) 21.1 Neight (m) 8.4 Wing Area (m 2) 114.0

Mean Chord Legth (m) 5.3

Aspect Ratio 4

Wing Section NACA44O9

Tail Wing Area (m2) 45.6

Tail Wing Volume Ratio 1.47

Turboprop Engine(hp) 4762x 2

Cruise Altitude (m) 3.0. Cruise Speed (knot)

: 185 LJD(cruise) 14.0 CL at Cruise. 0.520 CD at Cruise 0.037

EXAMPLES 01 CONCEPTUAL DESIGNS OF WISES

Outline of the Design Results

The requirements for the WISES design shown in Table 1 were obtained after the investigations into the operating conditions of WISES for a conventional airplane. Applying the CAD program for WISES, the WISES shown in Figure 1

and Plate 1 with the characteristics in Table 2 was designed. The requirements and the CAD program for WISES design are described later, and the features of WISES design are outlined first.

The main wing is a cambered rectangular wing with an aspect ratio of 4

and floats on the tips. Floats are effective in obtaining stronger surface effects on the wing similar to end plates. In front of the cabin there are pairs of propellers driven by two turboprop engines, which can tilt and

enhance the lift due to the power augmented ran (PAR) effect when the WISES

takes off and lands on the sea surface. The fuselage has a wide body and shallow bottom with dead rise and a step to provide better hydraulic

performance. The aft part of the fuselage rises up to avoid wave impacts and spray and to reduce the surface effect on the tail. The WISES has a

relatively large tail in a high position compared with conventional airplane designs to overcome an instability due to the surface effect.

Water Surface at Rest

at Cruise

1.

Investigation into the Design of WISES

Main Wing: Wing area, shape and position are assumed in the initial

stage of the design. Then the approximate size and performa.nce of the WISES is determined. In the case. of conventional airplane design, a. choice of a

high wing loading factor to enable the wing area to be small in order to reduce the total drag 'is the usual way. As seen in Figure 2, better fuel

efficiency is expected due to the increase of the wing loading factor. On the other hand, results

_for!WISES

with a rectangular or inverse delta wing show a different tendency in Figure 2. For simplicity a WISES with the rectangular wing is mainly

investigated,,

and an inverse

alternatives later.

For WISES designs with larger wings,

higher drag, is induced but at the same time relatively high lift isobtained due' to the surface .effect. For a. cruising height of 3m,

a constant increase in fuel costs is seen

due to the increases, in the wing loading

factor. For the 6rn cruising height the

optimum loading factor of 300kg/rn2 can be seen. With a lower cruising height, the lighter wing loading factor is preferable because greater surface effects can be

expected than with a higher cruising height.

'From the view point of the water impact'

forces in the landing process on the sea,

the lighter wing loading factor is also

preferable to attain a lower landing speed. The seaplane PS-I, used for search and

rescue in Japan, was referred to as a

guideline for the WISE'S design. From the

experience of seaplanes,(5], a wing loading factor less than 300kg/rn2 seems to be

delta wing is examined as the

4

.h=3m 6rn

s

_I

Rectangular Wing WISES

0 0

Inverse Delta Wing WISES

- Airplane (AR=8,h=6000rn) 0..

___..-_0

Wing Loading (kg/rn2) 200 300 400 500

Figure 2: Relation between Wing Loading and Fuel Cost

AspectRatio

h=3m Sm

Rectangular Wing WISES

o 0 Inverse Delta Wing WISES

W/S300k/m)

.Airplane (h=6000m)

1

2 4

'6'

8

Figure 3:Relation between Aspect Ratio and Fuel Cost

re he he, ob sti us ad as WI as of 11: th& cr ac Wi' ne s h 3m th tyl Wi, wa, as ex th Th im ef

required for the WISES of this size to possess seaworthiness up to 3m wave

height. Considering the minimum point of fuel costs for a 6m cruising

height, W/S was chosen as 300 kg/rn2 for the design.

For conventional airplane design, high aspect ratios are chosen to

obtain the high lift/drag ratio in spite of the increase in the wing

structural weight. In the case of WISES, a small aspect ratio wing can be

used, because a relatively high lift due to the surface effect can be

achieved for small aspect ratios. It can be seen in Figure 3 that a high aspect ratio is preferable to obtain better efficiency for every case. When WISES flies near the sea surface, however, the change in the fuel costs with aspect ratio is not so rapid as that of the airplane. Considering the risk of contact with the sea surface in the heel condition and the accumulative lift due to PAR effects, the smaller aspect ratios are considered better. If the aspect ratio is 3, better efficiency is expected in the case of a. 3m cruising height but less effective for a 6m height. Taking these factors into account, an aspect ratio of 4 was chosen.

It _{is said that a cambered and a thin wing section is suitable for the}

wing in surface effect{6], so a NACA44O9 section was chosen. Further study is necessary for the optimum wing section of WISES. The position of the wing, shown in Figure 1, was chosen so that the nominal height of the main wing was 3m from the surface and the hull had a clearance of lm in calm seas. Thus, the hull did not impinge on waves smaller than 2m.

As an alternative to the rectangular main wing, a so-called Lippisch

type WISES, which was developed in Germany and posses inverse delta shaped wings of outstanding aerodynamic characteristics in the surface effects[3], was examined by means of a parametric study. For this type wing of a smaller aspect ratio than the rectangular wing is possible as seen in Figures 2 & 3.

Engine and Propeller: Development of a new engine for WISES is too

expensive considering the small size of the WISES market. Therefore design of the engines means selections from those available for conventional airplanes. The reciprocal engine has a relatively small power to weight ratio, and it is impossible to mount on the larger size WISES. The turbojet engine has reduced efficiency at low altitudes. So a turboprop engine was selected for the

desIgn. The required, horse power is

defined so as to overcome the hump

resistance and to take off. According to the design manual of seaplanés [5], even at the hump speed, the WISES should have 0.lg 0.2g acceleration in order to

take off safely. PAR effect is expected

W/BP

to be utilized for the, decrease of the

10

₅

100_

_,

/

-take-off speed. Standard values of W/HP

-plotted in Figuie 4 are 3.5 - 4.5 for airplanes, 3 4 for seaplanes, and 6

-10 for small WISES. Considering the requirement fOr the take-off ability in

waves and the PAR effects with tiltable thrusters, a W/HP = 3.6 was chosen for the design. Engine configuration, horse power for one unit and PAR effect lead to the present design. Propeller tip clearance to the still water level

is 2m and a 20 tilt angle is applied for operation in the take-off process.

Tail Wings: Usually tail design is performed according to the

examination of the tail-volume ratio of existing airplanes, but WISES lacks a reliable data base for the tail volume. Because of the surface effect, the

longitudinal stability of WISES is inferior to that of a conventional

airplane. In the ihitiá.l design of WISES, simple methodsand clear guidelines are expected to be developed from the practical point of view. Here, examination of static and dynamic stability is performed in connection with the tail design. Using the stability derivatives estimated by means of the DATCOM methods[71 for a height of 3m,. stability analysis is performed.

In the present WISES design procedure, the height stability (H.S.) is

ignored and only the pitch stability (P.S.) is examined for the static

stability; The. former is always negative and enhances the stability. The

latter is generalized with surface effects as P.S. _c - cL/CLxCs.

A value of P.S. -1.667 is taken as a temporary criterion of the static

stability of WISES. It is the P.S. for a conventional airplane designed by the same CAD system with a main wing of AR 8.

102-.0

o WISES A AiPLAJJE o SEAPLANE

( hp .

io2

Figure 4: Relation between Weight and Horse Power

ta su Th th re le th of to CA th th fo th st su an pr ba sh su - al

cruising HeigbL

V

MAIN NING DESIGN

Shape & Configuration

W/S W/llI AR. etc. PERFORMANCE ESTIMATION Aerodynamic Characteristics Surface Effect Engine Performance VEIGHT ESTIMATION Body Weight Fuel Weight STABILITY ASSESSMENT

Static Stability

Dynamic Stability ECONOMIC EVALUATION Fuel Cost DOC 0 C a, 0

Determination of Design

Figure 5: Flow Chart for WISES Design

CAD System for WISES

In practice various design methods and systems are established for each

specific object and production procedures of products, such as ships,

airplanes, plants etc. though they contain similar factors and common parts. The CAD system consists of a controller of design procedure, a data base and tools for design, i.e. drafting and processing manufacturing _data.

Though WISES is _{categorized as a high speed ship and shares marine}

operating procedures with ships, it will be designed properly by means of

Passengers

Range

_{Sea State}

E

Co

iCr_{Cruising Height Landing Speed}

/

Take-off Speed Fuel Weight

J

Pay Load *W7HP - Required Take-off Weight Engine Power Estimation

Aerodynamic Body Weight Characteristics

Surface Effect

Ando' s Jormula,[6J) Take-off

Tai I Area Locat ion

Fuselage

Length Breadth

v

\

Main Wing

Tail Wing

Area Area

Shape Location AR etc. _{Tall Volume}

\1V

N Fuel Weight Engine Thrust Weight : EYALUAT ION: STABILITY cruising static stab dynamic stab take-off landing ECONOMY Fuel Cost DOC SAFETY Wing Area. Shape AR ONFIGVRATION: MARK: ,r Choice Flow

Figure 6: Schematic Diagz'am of Composition and Process for WISES Design

V

I INPUTS: Design Eequireent:... Design Requirements Range Passengers Sea State '1'

airplane design method.. A CAD system for WISES will have factors similar to thOse for ships and which are common with airplanes because WISES is a hybrid of a ship and an airplane.. A prototype of a CAD system for WISES has been built by modification of a system named ISAAC (Interactive-CAD System

Advanced Aircraft Configuration) for the conceptual design of a STOL airplane developed in the .Nationl Aerospace Laboratory of Japan.

Figure 5 shos th flow chart for the WIS-ES conceptual design, which is

almost the same as thai for airplanes. In Figure 6 the process and the design.

system are summarized. Some ready-made tools are applied in the CAD system. The main body of the CAD program is composed of the ISAAC Program. A data

base, estimates of the.! aerodynamic characteristics with surface effect{6-,7],

and seaworthiness are added.

Conthtions for WISES Operation

WISES is expected to be applied to passenger transport for island routes.

Here comparisons between WISES and airplanes are. mainly shown, because conventional high speed ships have different properties and offer different services, i.e. -slower speeds and lower fares. -For the design and operation of

WISES, the cruising height is a _key factor. Because sea conditions near

Japan, especially during winter time, are quite severe.

As the result of a parametrIc study for the economical efficiency by

means of the ISAAC Proram, the requirements for the designed WISES have been obtained. It assimed that the design conditions of WISES will enable a

hull clearance In the cruising condition for 2m regular waves. Parameters include the numbers f passengers, from 20 to 200, and the range of operation, from lOOn.rn. to l000n.m. A lighter wing loading factor and smaller

Table 4: Specific.tion.s of Design for WISES and Airplanes

Marks-: *5 -- 1SES As -- Airplane w:- -I' a: cc cc s 2( ti-0 r fi

it

dr lo pa to pr

Number of Height(m) */S(kg/m') Aspect Ratio Type of

Passengers *$ -. As ** As ** As Engine 20 3.0 1.500 150 200 4 - 8 Turboprop 50 3.0 4,500 200 300 4 8 Turboprop -100 3.0 6. 000 300 500 4 8 Turboprop 200 3. 0 6. 000 400 600 4 8 Turbofan I-r pe ma ar

c

wc

wing aspect-ratio than ordinary _{Table 5: Results of Comparison of Fuel Cost} airplane are assumed for WISES.

In Table 4 specifications for

WISES and a conventional

airplane are summarized.

The results for fuel costs of WISES and a

conventional airplane under the same conditions are shown in

Table 5. Except for the case of

20 passengers, it can be seen

that WISES can have advantages over an airplane in the shorter range. The reason stems mainly

from the fuel consumption

involved in climbing to high altitudes. At high altitude low

drag and high efficiency of jet engines are possible for airplanes, therefore longer range operation is more suitable for airplanes than for WISES. For 20 passengers the scale of the total wing and body is relatively small compared to the cruising height for sufficient utility of the surface effect to

produce better transport efficiency, and a different tendency is seen.

CONCLUDING REMARK

In order to clarify the points of WISES design, a conceptual design is

performed. The conceptual design is quite helpful for understanding the

nature of WISES, which is essential as background for the safety assessment and regulation of WISES. By the application and modification of an existing CAD system for a conventional airplane, a prototype of a CAD system for WISES was built. With emphasis on the nature and safety of WISES design, a

Nvrnber of

Passengers Range

(nrn)

DOC(fuel) (c/s-rn) Ratio of DOC WISES/Airplane WISES Airplane 100 4.775 5.288 0.903 ** 20 300 4.063 4.251 0.956 * 500 3.965 4.247 0.934 *X 1000 4.035 5.130 0.787

***

100 2.856 4.139 0.690 *xx 50 300 2.444 2.520 0.970 * 500 2.367 2.294 1.032 1000 2.314 2.058 1.124 100 2.125 3.778 0.562 *** 100 300 .822 1.996 0.913 ** 500 1.770 1.656 1.069 1000 1.741 .445 1.205 100 2.503 3.500 0.715 x*x 200 300 1.950 1.956 0.997 * 500 1.826 1.669 1.094 1000 1.657 1.427 1.161 Marks:

*ss < 0.9< ** < 0.952 < * < 1.0

<

conceptual design for passenger use has been performed. Though the design was obtained in only the first 'stage of its design iteration, it seems to possess features' of WISES and resembles the Russian WISES.

At present WISES is still just at the beginning of its history, and

there is very little data available. Various experimental and theoretical

data, and trial and errbf of the WISES design are necessary for. the

development and optimization of the WISES. Reduction of the required engine horsepower is essential in practice to have reasonable economy. Therefore.

investigations should be carried out into high lift devices with PAR effect, and control systems for stability in the take-off and landing conditions as well as cruising; Many other items such as maneuverability and seaworthiness are included in the design iteration in practice.

The authors would like to express their thanks to Mr. K. HARA, Shin

Maywa Co., and the people involved At the National Aerospace Laboratory fOr their kindness in allowing, the use of the ISAAC Program and for their. advice

i-n the airplane arid seaplane designs. The authors also wish to express their

gratitude to their colleagues at SRI for their discussion and support.

REFERENCES

011ila, R.G., Historical Review of WIG Vehicles," J. of

ffydronautics,

Vol.14, No.3,pp.65-76, 1980..

Rozhdestvensky, K.V '& Synitsin, D.N., " State-of-the-Art and Perspectives of Development of Ekranoplans in Russia," FAST'93,Vol.2,pp.1657-l67O, 1993.

Fuwa, T. ,Hirata, N. &. others,, Fundamental Study on Safety Evaluation of Wing-in-Surface Effec.t Ship (WISES) ,' IAST'93,Vo'l.2,pp.1585-l596, 1993. Takahashi., T. & Fuwa, T., " WISES Design Methods and Their Application,"

J. of Kansa'i Soc. N.A.,, Japan,

No.222,pp.183-190, 1994.(in Japanese) Kikuhara, S., " Aircraft Design Experience,"

J.

of

Japan Soc. Aero. Space

Sd., Vol.39, No.451,pp.379-387, 'l991.(in Japanese)

Ando, S., " Note on Prediction of Aerodynamic Lift/Drag Ratio of WIG at Cruise," FAST'93,Vol.2,pp. 1561-1572,. 1993.

USAF,

Stability and

Control

DATCOM, Air Force Flight Dynamics Lab.,

Wright-Patterson Air Force' Base,, Ohio, 1968 & 1978.

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