propulsion system for a wing-in-ground effect...

Propulsion System for a Wing-in-ground effect

model

Submitted by: Toh Boon Whye

Department of Mechanical Engineering

In partial fulfillment of the requirements for the Degree of Bachelor of Engineering

National University of Singapore

Session 2004 / 2005

I

Summary

The main aim of this project is to design and build a small scale Wing-in-surface

effect hull model that gives minimal water resistance and further integrates a

suitable propulsion system to demonstrate the phenomenon of ground effect.

This project sparked off initially as an industrial collaboration with a local

company, The Wigetworks Pte Ltd, who had plans to commercialize real Wing-in-

ground craft in Singapore. As this special marine craft has lots of potential

research, the interest conceived a project team of 4 members to design and build

a WIG scaled-model from scratch, involving not just textbook theory but the

application of engineering knowledge as well. All existing WIG crafts are huge

and nobody in Singapore has successfully designed and flew a truly small-scale

WIG craft. It is this project that has taken up the challenge in spearheading the

first-ever successful flight of its kind.

This Project started in August 2004 and over a period of 9 months there has

been numerous testing and troubleshooting. The hull design commenced from

day one of the project as it involves painstaking work: from designing on paper;

calculation of its many characteristics; building it for tow tank experiment

validation. It took 2 months to complete the hull, which was essential before any

integration work can be done to complete the prototype. Propulsion is a critical

element in flight design. In the sizing of the propulsion has been successful but it

was not without its challenges. The weight of the model, costing and most

II

importantly getting the right motors and the cheapest ones to validate the

concept of small scale WIG represent some of elements of real-life engineering.

Getting the right propeller sizes to match the motor has been done as part of this

project and likewise the theory, design and selection of different parts can all be

justified with the flight test of the final prototype. At project level, the challenges

became multi-disciplinary, where the hull and propulsion must integrate with the

wing design, structure and stability control for the entire craft to demonstrate the

concept.

Valuable experience has been gained when the project team presented on the

works of this multi-disciplinary project at the Air Technology Seminar in February.

It was a national level seminar organized by the Republic of Singapore Air Force.

The hull and propulsion design were successful. This thesis highlights the

achievements of the project and has been divided into 2 portions: hull and

propulsion. A short introduction covering existing WIG and seaplane hull design

is followed by the analysis of the model hull and the propulsion system. A

discussion of the results from the many flight tests that were conducted together

with the other team members: Ng Geok Hean of AM90 specializing in wing

design; Benedict Ng of AM91for the fabrication of the wings and Jonathan Quah

of AM93 in charge of controls.

III

Acknowledgements

The Author would like to extend his gratitude to the following persons for the very

important parts that they have played in the course of the project development.

A/P Gerard Leng Siew Bing, Project Supervisor, for initiating the project and

giving direction as well as guidance throughout the course of the project;

Encik Ahmad Bin Kasa, Mr Cheng Kok Seng, Ms Amy Chee and Ms Priscilla Lee,

staff of Dynamics and Vibrations Laboratory, for their invaluable support

throughout the project;

Staff of Engineering Workshop 2 for their guidance on woodwork for the model

hull construction;

And last but not least, Mr Tim Ming Boey and Mohd Thahir Jainulabidin from the

Marine Technology Department of Ngee Ann Polytechnic, for their generosity

and support in allowing the tow tank test to be conducted on the hull model.

IV

Table of Contents

Summary I

Acknowledgement III

Contents IV

List of Figures VII

List of Tables VIII

List of symbols IX

Chapter 1- Introduction 1

Chapter 2 – Theoretical calculations for analysis

2.1 Hull form and resistance analysis 3

2.1.1 Design of hull form 3

2.1.2 Calculation of hull form 5

2.1.3 Theoretical calculation of Hull resistance 8

2.2.1. Sizing of propulsion system 10

2.2.2 1st Prototype 10

2.2.3 2nd and final prototypes 12

Chapter 3 - Experimental Results and analysis 15

3.1 Tow Tank Experiment 15

V

3.1.1 Towing tank test for the hull model 15

3.1.2 Test Procedure for towing tank 17

3.1.3 Resistance values from the test 18

3.1.4 Discussion on the tow test results 20

3.2 Propeller and motor thrust experiment 21

3.2.1 Engine test stand 21

3.2.2 Calibration of test rig 22

3.2.3 Test procedure for measuring thrust 22

3.2.4 Thrust readings 23

Chapter 4 - Flight test and observation 26

4.1 Testing of the integrated model 26

4.1.1 1st flight test with the 1st prototype 26

4.1.2 2nd prototype flight test 27

4.1.3 Final flight test 29

Chapter 5 Conclusion 32

Chapter 6 Recommendation 33

References 35

Annex A – Propulsion theory 37

VI

Annex B – Resistance Theory 40

Annex C – Tabulation of hull readings 41

Annex D – Sample of the tabulated raw data logged during the

towing tank experiment 42

Annex E – Tabulated data for Towing tank experiment 44

(Lightship condition)

Annex F – Tabulated data for Towing tank experiment 45

(with hull weight of 2kg)

Annex G – Tabulated raw data for propeller and thrust measurements 46

Annex H – Constructing the hull model 48

VII

List of figures

Figure Description Page no.

1 A Lippisch WIG 1 2 Power Augmentation Ram Wing 2 3 The KM 2

4 Lines plan of the hull model showing front and stern 4

5 Station 8 transverse mid-ship section 7

6 Speed 400 and Speed 500 motor 12

7 Towing tank arrangement 15

8 Hull model attached to the transducer 17

9 Hull model undergoing test 17

10 Resistance Vs Speed (No load/loaded condition) 19

11 Engine test rig setup 21

12 Types of propellers used for the test 24

13 Thrust Vs Power of different propellers 25

14 Project maiden flight 26

15 Thrust beneath the wings at initial condition 28

16 prototype showing attempt to enter into ground effect 28

17 Modified hull to level with the wing 29

18 Entire hull off the water surface and free of hydro-drag 30

19 Model craft in ground effect 30

20 Full ground effect flight demonstrated at MPSH 31

VIII

List of Tables

Table Description Page no.

1 Tabulation of sectional areas 5 2 Designed waterline areas 6 3 Weight breakdown of 1st prototype 10 4 Weight breakdown of final prototype 13

IX

List of Symbols

Symbol Description

A Area in m2

a Inflow factor

CF Frictional Coefficient of hull model

CM Mid-ship Coefficient

CD Coefficient of drag for wing Cp Prismatic Coefficient of power CR, Residual CT Coefficient of thrust CT, prop Thrust coefficient for propeller CT, total Total Coefficient for resistance D Diameter, m Dprop Diameter of propeller, m I Current / A K Amplification factor of test stand L Length M Mass, kg Mbl Reading of digital balance due to mass, kg M0 Reading of digital balance at 0 position, kg p Total pressure, Pa P Power, watts

X

RN Reynold’s number RT Total Resistance of water S Wetted surface T Thrust, N Ttotal Total thrust due to whole propeller system, N U Tangential velocity m/s V Flight speed/Design speed/velocity v Voltage V1 Velocity at propeller disk, m/s V2 Velocity at outlet, m/s W Weight of prototype, kg Vs Velocity of propeller slipstream, m/s V0 Mean velocity magnitude of propeller slipstream, m/s ρA ISA or Standard Air Density at 1.2256kg/m3 ρw Density of fresh water at 1000kg/m3

µA Kinematic viscosity of air at 1.714x10-5kgm-1s-1

µW Kinematic viscosity of water at 1.139 x 10-6 kgm-2s-1

WL Waterline

SM Simpson’s Multiple

1

Chapter 1 – Introduction

The phenomenon of wing-in-ground (WIG) effect has been in existence for the

last hundred years ever since the first airplane was invented. Most pilots in the

past regarded it as nothing more than a nuisance that changed the flying

characteristics of their aircraft during takeoff and landing. Only in the last few

decades1 that there have been efforts to conceptualize it as an application,

chiefly by Russia, Germany and Japan in producing a new class of highly

efficient, high-speed low altitude flying vehicle of what is termed now as the

Wing-in-ground/surface craft or Ground effect machine (GEM).

The most successful WIG craft have been developed by the Russians and the

largest WIG vehicle ever built is the Korabl Maket (KM), powered by 10 turbojet

engines and weighed up to 540 tons2. An unconventional method which the

Russian termed Power Augmentation Ram Wing3(PAR), thrust is intentionally

deflected underneath the wing to create an initial cushion of air that rapidly raises

the KM out of the water as compared to the moving through the water like the

typical seaplane. The Germans on the other hand have 2 designs in contrast to

the Russians: Lippisch and Tandem.

Fig. 1 – A Lippisch WIG.

2

Fig. 2 - Concept of PAR. Fig. 3 – The KM.

Up to this date, all WIG crafts including those described above are huge. There

have been no reports of WIG craft designed and built in small scale and this

project has created the opportunity to validate and demonstrate the possibility of

WIG craft in a rather small scale. In order to build a relatively small WIG craft, the

hull and propulsion pose the following challenges:

a. design of suitable WIG hull form that has low water resistance

b. Selection of suitable propulsion size

c. Fabrication of hull form for experimental testing

d. Integration of propulsion system and hull as prototype craft

e. Test flight of model

In the following chapters the justification works from designing to building the

prototype and experimenting with the model the concept of small scale WIG

model will be presented.

Propeller

Wing

3

Chapter 2 – Theoretical calculations for analysis

2.1 Hull form and resistance analysis

2.1.1 Design of hull form

Based on the technical surveys4 for the design of hull model there have

been at least 3 features that are essential to the seaplanes, which the

WIG model can adopt. The hull form should be of a deep-V configuration5

to facilitate the craft in high speed. Next, dead-rise angles do not exceed

240; 150 for moderate waves and any lower would be suitable for flat

water6. The third consideration would be the incorporation of a stepped

hull7. Research has shown that such hull will result hull planning and

assist in lifting off the water surface.

The length of the model has been decided by the project team to be a

maximum of 1metre with further input from Control Part AM93 that a

certain internal space is required for his control systems. A design is then

conceptualized on drawing based on these inputs as well as the essential

features. It has the following design elements:

a. 1m length with maximum 50% of the hull in water

b. A maximum beam of 0.1m. A wider beam will result in higher water

resistance

c. V-type hull of a dead-rise angle not more than 100

4

d. Stepped hull at mid-body of the model

The design requirements have all been translated into the lines plan8

where fairing of the hull form has been done to form a simple, streamlined

hull shape all for the purpose of constructing the physical model

subsequently.

4a

FIG. 4 – Lines plan of the model showing front (4a) and stern (4b) of model hull.

4b

5

2.1.2 Calculation of Volume and hull coefficients

Individual values of the hull lines were taken from the lines plan upon its

completion to calculate essential hull characteristics such as volume, hull

stability, CB, CP, etc., as well as translating them into coordinates that has

been used by the Aerodynamics part (AM90) for CFD and Structural part

(AM 91) for stress analysis respectively. A complete tabulation of the hull

lines values can be found in Appendix C.

2 steps are required to calculate the volume. It includes summing the

values of the lines plan values as a function of area f(a) in a particular axis,

followed by summing of the area, which is a function of volume f(v) as

shown below.

Table 1 – Tabulation of longitudinal sectional areas.

WL Area m2 SM F(v) Levers f(m)

0 0 ½ 0 0 0

1 0.0178 2 0.0356 1 0.0356

1.5 0.02529166 1 ½ 0.037937499 1 ½ 0.056090624

2 0.030416666 4 0.121666664 2 0.243333328

Design WL 0.34749025 2 0.06949805 3 0.20849415

Nose line 0.039975 4 0.1599 4 0.6396

80 0.0389375 2 0.077875 5 0.389375

10 0.035 4 0.14 6 0.84

12 0.01 1 0.01 7 0.07

∑ )(vf 0.652477213 ∑ )(mf 2.482493102

6

Both method make use of the mathematical tool known as the Simpson’s

multiple, based on the Basic Ship Theory9, to approximate the integration

of the areas calculated and hence each value has above 5 decimal places

to ensure accuracy in the final value.

Spacing for each station is 0.12 and the total number of stations is 8.

Thus, the interval h = 18

12.0−

= 0.017142857

Using Simpson’s formula, volume of the model = 31 x h x ∑ )(vf

= 31 x 0.017142857 x 0.652477213 = 0.003728441m3

The density of the balsa wood, measured experimentally, = 130 kg/m3

Total weight of the hull = 0.00372844 x 130 = 0.48540kg or 485.40g

The value subsequently validates with the actual weight of the model of

481g and is within acceptable error in similitude.

A second calculation has been done with respect to the designed

waterline mark, which the volume is required for calculating CB, CP and Cw.

WL Area m2 SM F(v) Levers f(m)

0 0 ½ 0 0 0

1 0.0178 2 0.0356 1 0.0356

1.5 0.02529166 1 ½ 0.037937499 1 ½ 0.056090624

2 0.030416666 4 0.121666664 2 0.243333328

Design WL 0.34749025 2 0.06949805 3 0.20849415

∑ )(vf 0.278199021 ∑ )(mf 0.6763627

Table 2 – Designed waterline areas.

7

h = 17

03.0−

= 0.005

Volume of the model = 31 x h x ∑ )(vf

= 31 x 0.005 x 0.278199021 = 0.000463665m3

Block Coefficient, CB = draftxbeamxLengthVolume

= 03.01.05.0000463665.0

xx = 0.31

Coefficient of mid-ship section CM, can be derived by calculating the

largest transverse mid-ship section in water. From the drawing below it

falls on Station 8.

FIG. 5 – Station 8 of the transverse mid-ship section highlighted in red.

Station 8

8

The area of the mid-ship section calculated = 0.0025 m3

Mid-ship section coefficient, CP = draftxbeamareamidshipTransverse

= 03.01.00025.0x = 0.833

Using the relation CB = CP X CM,

CP = M

B

CC

= 833.031.0

= 0.372

In general, none of CB, CP and CM, should exceed 1. For CB, a coefficient

of 0.45 represents a streamline hull; 0.8 to 0.9 is for a box-shape like hull

with the highest resistance. The same can be said for CP whereas CM is

usually ranging from 0.7 to 0.9 where largest transverse area of the hull is

usually at mid-ship.

2.1.3 Theoretical calculation of Hull resistance

Having obtained the basic values of the hull, the value of resistance can

now be approximated. Based on the basic formula for drag from Fluid

Mechanics,

RT = 21

ρw x S x V2 x CTotal

Where CTotal = CF + CR + CA

Given L = 0.5m, Cp = 0.372, ν = 1.139 x 10-6 m2/s, design speed = 10m/s

9

Reynold’s number, RN = v

VL = 610139.15.010−x

x = 4389815.62

Using the International Tow Tank Convention 1957 model-ship correlation

line9, where

CF = 210 )2(log

075.0−NR

= 0.00347

The wetted surface S is estimated at 0.0152m2 based on Taylor’s method7

of using the mid-ship coefficient and the formula S=c(∆L)0.5, where c is a

contour value.

Then CT = CF + CR, where CR is derived from towing tank test and

negligible in this approximation,

Calculated RT = 21

x 1000 x 0.0152 x 102 x 0.00347 = 2.637 N

The value of resistance calculated here indicates that the hull design may

prove to be acceptable in relation to its beam and hull form. As it is a new

hull design, there has been no other similar model to compare with which

also explains the neglecting of usually small term CR. To further validate

the accuracy of the value, a towing experiment on the model hull has been

carried out and is described in chapter 3. At this stage it represents a

rough estimate of the amount of resistance that the model will encounter

and is necessary as part of the propulsion sizing shall be described in the

next section.

10

2.2.1. Sizing of propulsion system

The components of thrust for the model consist of the weight of the model,

the aerodynamic drag and the water resistance value. While the latter two

components are predictable during design stage, the weight of the model

represents more of uncertainty due to the available servo components, the

motor and construction methods that can cause the model to become too

heavy for flight.

2.2.2 1st Prototype

The first prototype was completed in October 2004 with the following

weight break down:

Components Mass in kg % of total mass

Structural (Hull, wing and tail) 1.3 72.22

Propulsion (PAR, top engine mount,

propellers)

0.3 16.39

Control and system components

(servo, battery, speed controller and

wires)

0.23 12.56

Total mass 1.830 100

Table 3 – Weight breakdown of 1st prototype.

From the above, the required power for Prototype 1 has been calculated

and the wing has been sized by Aerodynamic part AM90 to give the

11

coefficient of drag, CD, for the wing as 0.028352 at the design air speed of

10m/s. CD is required as part of the thrust value, hence,

Drag force on wing = 21 ρV2

2 S CD = 21 x 1.2256 x 102 x 0.4 x 0.028352

= 0.69N

Weight of model in Newton = 1.830 x 9.81 = 17.95N

Thus total thrust calculated = model weight + Drag force of wing + water

resistance from tow test = 17.95 + 0.69 + 1.99 = 20.63 N

Since the configuration of the model must have 3 propellers (2 for PAR

and one for acceleration), it may be assumed that the total thrust is

divided by three with same type of motor. Thus, 363.20 = 6.87 N

Now given T = 7.08 N, Design flight speed = 10 m/s and S = 0.0248m2,

thus

a + a2 = 0248.0102256.12

87.62 xxx

= 0.5069; a = 0.37

The ideal efficiency is = 37.11

Useful power = TV, = 6.88 x 10 = 68.8W

The theoretical power required per airscrew based on Froude’s

momentum theory10, P = 68.8 x 1.37 = 94.25W

The power required is in the lower range and it is found that electric motor

is feasible rather than the usual Internal Combustion engine, chiefly due to

cost, weight and operability considerations. Upon narrowing down from

the wide range of electric motors available, the Promax Speed 400 motor

12

based on its specification can supply a maximum power of 96W. It

belongs to a class of cheapest, mid-range but powerful ferrite motor where

a single piece is suitable for a model of up to 600g (according to

manufacturer specification). Other ranges include Speed 300, 380, 500

and 600 but they are either too weak or too heavy to be used in terms of

the motor weight and the number of cells required. A picture of both the

Speed 400 and Speed 500 motor is shown below for comparison.

Fig 6. – Speed 400 and Speed 500 motor. Note the difference is size. The

weight of the Speed 500 is a staggering 56% more than Speed 400.

2.2.3 2nd and final prototypes

To improve on the initial prototype the model weight can be brought down

further because the initial construction method and consideration have left

much excess material on the hull, wings and tail that can be removed or

re-designed without compromising the structural integrity of the model.

38mm 52mm

28mm Ø38mm Ø

Speed 400 Speed 500

13

Both the motor and wing size are kept but the material weight for both the

hull and wing frames are reduced as much as possible. The final weight

breakdown can be as follows:

Components Mass in kg % of total mass

Structural (Hull, wing and tail) 0.745 50

Propulsion (PAR, top engine

mount, propellers)

0.421 28.25

Control and system

components (servo, battery,

speed controller and wires)

0.324 21.74

Total mass 1.49 100

Table 4 – Weight breakdown of final prototype.

Thus new total thrust = model weight + Drag force of wing + water

resistance = 14.61 + 0.69 + 1.99 = 17.29 N

Thrust required per airscrew = 329.17 = 5.76 N

With the following parameters, T = 5.76 N, V = 10 m/s and S = 0.0248m2,

a + a2 = 0248.0102256.12

76.52 xxx

= 0.4725; a = 0.35

The ideal efficiency is = 35.11

New useful power = TV, = 5.77 x 10 = 57.7W

The new calculated power required per airscrew now is

14

P = 57.7 x 1.35 = 77.895W

From the calculation it can be seen that the power required falls as the

weight reduces and that removes the need for a larger motor and propeller.

Should the weight remain the same a bigger motor may be required which

means more cells and much bigger propellers are required, resulting in

even heavier weight as well as affecting the other 3 fields of the projects

undertaken by the rest of the project members. Hence it remains essential

that the propulsion has not been re-sized and it remains as one of the last

parameters that the project team would want to change.

The subsequent chapters on the experiment and flight test results will

verify these theoretical calculations.

15

Chapter 3 – Experimental Results and Analysis

3.1 Experiments

3.1.1 Towing tank test for the hull model

The tow tank test conducted at the Marine Technological Department,

Ngee Ann Polytechnic works on the principle of towing the model on a

carriage through a 45m long tank at certain speeds. The transducer

picks up the opposing force felt when it tows the model as a value of the

water resistance encountered by the model hull. A picture of the towing

tank is shown below.

Fig. 7 – Towing tank arrangement.

The following support equipment is required for the test:

a. Water speed probe

16

b. Transducer

c. Load Cell (Holder) for the model

d. Desktop PC

e. PC 208W data logger

Running the test is rather simple and needs no calibration other than

warming up of the system. It involves a minimum of 2 persons for safety

reasons to allow emergency stopping of the carriage should there be any

mishap. The procedure is as follows:

a. Attached the model hull to the holder and fit it to the transducer

below the traveling carriage. (See Fig. 8 )

b. Switch on both the power to the carriage and data logger linked to

the desktop computer.

c. Adjust to the desired speed and start the tow.

d. Upon traveling to the cut of mark standby to press stop should the

carriage fail to stop. Travel back to the start point in reverse

direction.

e. Extract all readings that have been logged in the computer. No

conversion is required as they are direct readings of the resistance.

17

Fig. 8 – Hull model attached to the transducer.

Fig. 9 – Hull model undergoing tow test.

3.1.2 Test Procedure for towing tank

The following steps are to be taken:

a. Fit the model onto the load cell in which the X-axis must be in the

direction of tow. Loosen the stopper on the load cell-fitting jig and

18

adjust the angle to 00. Tighten the stopper screw firmly after

adjustment.

b. Test run the carriage at about 0.5 m/s and check whether the

reading of the force Y=0. If Y≠ 0, model fitting may not be in correct

alignment. Reset the angle of the model.

c. Set the desire towing speed at 0.9m/s

d. Run the carriage and check the reading on the water-speed probe

to confirm that the carriage is towing the model at the desired

speed.

e. Repeat the test with different speed (1.0, 1.1 and 1.2) and different

loading conditions (light ship and with weights up to 2kg). It is

essential to wait for the wave to settle down for a more accurate

result)

f. Extract and save the raw data in a disk.

g. The values of the measure resistance are then used to plot the

Resistance Vs Speed graph and further extrapolate for resistance

values of speed ranges above 1.2m/s.

3.1.3 Resistance values from the test

The raw data has been tabulated and due to the large amount of data (8

sets) only a sample is made available in Appendix D. The graph below

represents a plot of the direct resistance value measured during the tow

Vs the speed for (i) Light ship condition (no load) and (ii) loaded condition.

19

Resistance Vs Speed (Lightship condition)

0

0.5

1

1.5

2

2.5

0.9 1 2 3 4 5 6 7 8 9 10

Speed (m/s)

Wat

er R

esis

tanc

e (N

)

Fig. 10 (i) – Resistance Vs Speed (No load condition).

Speed Vs resistance (2kg hull weight)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0.9 1 2 3 4 5 6 7 8 9 10

Speed (m/s)

Resi

stan

ce (N

)

Fig. 10(ii) – Resistance Vs Speed (Loaded condition).

20

3.1.4 Discussion on the tow test results

The graph shows a very short linear relationship between the resistance

value of the model and the speed from start but curves up as speed

increases. It represents a typical characteristic of resistance of marine

craft. The graph of for the loaded condition shows that resistance value

increases 2 times, indicating that the overall model must not exceed 2kg,

or else the total thrust value will increase tremendously.

The tow results further validates the theoretical calculations done earlier

on the model hull during the design stage. Calculations has shown that the

hull resistance is comparable to the actual result of the tank test although

the calculated value only serves as an approximation for the purpose of

preliminary sizing of the propulsion. The difference where the actual test

result is at a much higher end is likely due to the following errors:

e. During construction the hull is not in perfect symmetry

f. Finishing of the hull surface can affect the reading

g. The next experiment could have been carried out before the

waves fully settled resulting in additional residual resistance to

the next test

h. Vibration of the carriage during travel may cause slight variation

in the readings.

Nevertheless these resistance values rare more accurate compared to the

calculated values as it is directly acquired from testing the model hull.

21

3.2 Propeller and motor thrust experiment

3.2.1 Engine test stand

The engine test stand is designed based on the lever principle which is

easy to setup with the following essential equipment:

a. 1 x Counter weight of 1lb

b. 1 x Modified camera tripod with bracket

c. 1 x Digital Balance

d. 1 x 1m aluminum beam with mountings

e. 1 x set of different small scale weights

Fig. 11 - Engine test rig setup.

22

3.2.2 Calibration of test rig

One requirement of the test rig is that it needs to be calibrated whenever a

new configuration is to be tested. Nevertheless the calibration process is

simple with little preparation before use and most of the time the

calibration results do not deviate significantly.

The procedure is as follows:

i. Place the 1lb counterweight on the digital balance and record

the value of M0 is

j. Attach the aluminum beam with motor to the digital balance and

read off the value known as Mbl from the balance.

k. Place another known mass (a 20g weight, etc.) on the motor

and read off the value

l. Repeat step c. with another known mass and obtain the mean

average.

m. Use the average to calculate the amplification factor K, where in

all subsequent values from the balance is use in the below

formula to calculate the thrust value:

T = K (Mbl – M0)

3.2.3 Test procedure for measuring thrust

The following steps are required:

a. Set the motor to full throttle.

23

b. Tabulate the following readings:

i. Angular Velocity of propeller

ii. Axial and Tangential airflow velocity

c. Reading at the digital balance

d. Voltage and current readings

e. The values obtain from the above are use to calculate the actual

thrust value based on the engine test rig and then tabulated

together with the rest of the readings.

f. Stop the running after 2 minutes to prevent motor from over-heating.

3.2.4 Thrust readings

A graph of the Thrust Vs Power consumed is shown in Fig. 13. The

tabulated raw data readings are available in Appendix G. From the graph

it can be observed that power consumption on the same type of motor

increases as the propeller size increases and generally for the thrust as

well. Actual testing proves that small diameter propellers like the 2-blade

5.5” offer higher revolutions but give mediocre thrust and are mostly fixed

in pitch which do not allow optimum matching of the propeller and motor to

the model. A significant improvement over the 5.5”, the 4-blade 5.6”

propellers at 3” setting increases the thrust by 50g more but as the test

flight will show it is yet to be the optimum propeller for the model. In

addition at 4” setting and above the thrust value decreases, possibly due

to stalling effect.

24

Most importantly the graph shows that the 7” x 3” diameter propeller

delivers the most thrust and with no sudden jump in the power

consumption. A 2-blade and 4-blade 7” propeller make further difference

by churning more air, hence increasing the propeller efficiency (nearer the

condition of an ideal disc in the momentum theory) by 20%, which is the

same amount of increase over the motor specification through actual

testing. Again, any setting in the propeller angle above 4” will result a

decrease in thrust and the propeller at 6” setting will actually overload the

motor. Therefore for optimum flight results the 4-blade 7” x 3” propellers

should be used to deliver the maximum thrust.

Fig.12 – Types of propellers used for the thrust test. Note the size in

comparison of the various propellers. From left: 2-blade 5.5”, 6”, 7”, 4-

blade 5.6” and the optimum 4-blade 7” propeller selected.

25

Thrust Vs Power

0.00

0.50

1.00

1.50

2.00

2.50

3.00

55 75 95

Power (W)

Thru

st (N

)

2-blade 5.5" X 4.5"4-blade 5.6" X 3"4-blade 5.6" X 4"4-blade 5.6" X 5"4-blade 5.6" X 6"2-blade 6" x 5.5"4-blade 7" x 3"4-blade 7" x 4"2-blade 7" x 5"4-blade 7" x 5"4-blade 7" x 6"

Fig. 13- Thrust Vs Power of different propellers.

26

Chapter 4 – Flight test and observation

4.1 Testing of the integrated model

The project team conducted numerous test flights of the completed WIG model

over a period of 5 months at West Coast Park where it is most suitable to

demonstrate the amphibious capability of the model. The results can be grouped

under 3 significant milestones of the flight tests described in this chapter.

4.1.1 1st flight test with the 1st prototype

When the first flight test was carried out in December 2004 with the 1st

prototype the results proved disappointing.

Fig. 14 – Project maiden flight.

27

It was done using the 4-blade 5.6” X 3” propellers and Fig. 14 showed that

though there was sufficient power for slight planning of the hull to take

place, a large portion of the hull could not lift off the water. The fact that

the prototype was at the initial design load of 1.8kg also contributed to the

failure of the test as the wetted surface area of the model had

unexpectedly increased. Water also entered the craft from top due to the

propeller splashes and the gaps in the wing. This resulted in additional

weight. Wind and water condition was calm and these did not contribute to

the failure.

4.1.2 2nd prototype flight test

Trouble-shooting on the 1st prototype has led to a major weight reduction

on the model. The weight of the hull has halved, from a weight of 0.745kg

to 0.352kg without affecting the structure integrity. Final weight of the craft

is kept at 1.49kg with no change to the propulsion and the wing

dimensions. Optimum propellers, the 4-blade 7” x 3”, has been used for

the 2nd prototype and the result then has been promising. Large amount of

thrust has been generated beneath the wings and this has enabled the

craft to rapidly lift off the water surface initially before stabilizing in forward

motion (Fig. 15). The craft is attempting to enter into ground effect (See

Fig. 16).

28

Fig. 15 - Thrust beneath the wings at initial condition.

Fig. 16 - 2nd prototype showing attempt to enter into ground effect.

The most significant observation regarding propulsion during most of the

flight tests for 2nd prototype has been occasional stalls and flips. The stern

portion has been observed to be heavy. Nevertheless it has shown that

there is sufficient thrust for the craft to take off and only requires minor

29

modifications for the model to get into ground effect despite water entering

the craft. Hence no further changes to the propulsion system would be

required.

4.1.3 Final flight test

In analyzing all the flight tests conducted for the 2nd prototype it has been

determined that a minor flaw in design exists at the bottom of the craft.

The hull should be further leveled (See Fig.17) to the wing to achieve 2

objectives: further reducing excess weight and improving the lift

underneath. Since the initial thrust of the model would have lifted the hull

out of water, by leveling it with the wing would mean that hydrodynamic

drag on the hull is removed from start and the entire craft would have

maximum lift due to the flat plate configuration.

Fig.17 – The modified hull. Bottom was cut to level with the wing.

Hull flushed with the wing

30

Fig. 18 – Entire hull off the water surface and free of hydro-drag.

Further testing has led to the success of the project as the craft flew in

ground effect with a visible gap in between the hull and water surface as

shown below.

Fig. 19 – Model craft in ground effect with a minor gap observed between the water surface and hull.

Visible Gap

31

To prove the effect further another test at the NUS Multi-purpose Sports

Hall has conducted where the medium is hard ground and that has

successfully demonstrated the full ground effect of the craft.

Fig. 20 – Full ground effect flight demonstrated at MPSH. Note the highly visible 5cm gap between the craft and the floor.

Gap of 5cm

32

Chapter 5 - Conclusion

The project overall has been successful, as shown in the validation of ground

effect with the flight test of the final prototype both on water and hard surface.

The objectives to design a small scale WIG hull and to size the propulsion in

relation to the design have been fulfilled.

The theoretical calculations used to predict the characteristics of the hull form

have been rather accurate and verified by the tow-tank experiments. The results

form part of the essential parameter or consideration in the sizing of the

propulsion ultimately. For propulsion, the power and thrust calculations have

assisted in the selection of the right motor and the optimum propellers. This has

contributed to the success at project level as propulsion is a critical element in

flight design. In addition, the selection of the electric motor has been the correct

to fly the model. It is proven to be more advantageous over traditional Internal

Combustion engines in the area of small scale WIG model.

Lastly, it has been very enriching and challenging to work as a team that involves

multi-disciplinary aspects to put together a flying machine that is able to

successfully demonstrate the phenomenon of ground effect. It would have never

been possible without the tremendous effort of every team member.

33

Chapter 6 - Recommendations

Though the project has been a success it is not without its room for

improvements. They are as follows:

Hull Design

a. The hull form can be further refined or faired such that it is more

streamlined than the existing model. If the internal space required by the control

part at the design stage is smaller the beam of the model can be reduced as well.

Both characteristics will ensure a lower water resistance for the model.

b. Special computer software, such as AUTOSHIP, SWAN or SHIPFLOW

can be used to compute the initial hull characteristics of the hull form as well as

to validate the tow-tank test results. This would enable changes to the hull form if

necessary or allow the drafting of a few more designs without going through too

much manual work.

Construction

a. The method of construction used for the model has been based on the

butter and bread method which is more time-consuming. Another method known

as the frame method maybe used to reduce construction time.

34

b. Water-proofing the top such that minimal water enters the internal space

would allow the craft to fly without excess weight and free-surface effect.

Motor

a. Better electric motors (at higher cost) such as 3-phase AC motor maybe

used for a 10 to 15 percent increase in motor efficiency. Alternatively larger

motors can also be used but its consequences can be huge with increase in

weight and bigger propellers required.

35

List of references

1. Historical Review of WIG Vehicles, Volume 14 page 65-76, Journal of

Hydronautics, July 1980.

2. A.V. Nebylov and P.A. Wilson, Ekranoplanes – Controlled Flight Close to

the Sea, WIT Press Southampton, UK 2002.

3. http://www.se-technology.com/wig

4. Hugli, William C., Hydrodynamic Investigation of a Series of Hull Models

Suitable for Small flying Boats and Amphibians, NACA TN 2503, 1951.

5. Darrol Stiniton, The Design of the Aeroplane, Blackwell Science, Osney

Mead, Oxford 2001.

6. Roger Marshall, Powerboats – Understanding Design and Performance,

International Marine/Mcgraw-Hill, Camden, ME 2002.

7. Henry B Suydam, Hydrodynamic characteristics of a Low-Drag Planning-

Tail Flying-Boat Hull, NACA TN2481, 1952.

36

8. Edward V. Lewis, Principles of Naval Architecture Volume 1 and 2,

Society of Naval Architecture and Marine Engineers (SNAME), 1967.

9. K.J. Rawson and E.C. Tupper, Basic Ship Theory Volume 1 and Volume 2,

Longman Inc., New York 1984.

10. E L Houghton and P W Carpenter, Aerodynamics for Engineering

Students, John Wiley & Sons, Inc. New York 1993.

11. Dietrich Kuchemann and Johanna Weber, Aerodynamics of Propulsion,

Mcgraw-Hill Book Company, Inc. 1953

37

Appendix A –Propulsion Theory

A.1 Froude’s momentum theory of propulsion

Froude’s momentum theory of propulsion is a rather simple tool that can be used

in estimating the requirement for the propulsion. It involves the concept of

assuming the propeller or as an ideal disc that supplies energy to the incoming

air. The ideal disc is treated as an infinitely thin disc of area S and offers no

resistance, drag or loss to air that passes through it. Thus when the air pass

through the disc energy from the disc is imparts pressure energy to the air. It is

assumed that the air velocity passing through the disc is constant over the whole

area and hence all energy supplied to the disc is transferred to the air.

As a fluid moving uniformly at a speed of V and pressure P0 and passing the 2

streamlines at the side and approaches the ideal disc it accelerates to a speed of

V Po

P1 Vo P2

Vs Po

Ideal actuator disc and flow in slipstream

38

V0 and pressure decreasing to P0. At the disc the pressure is increased to P2 but

law of continuity prevent the sudden change in speed. Therefore the air behind

the disc expands and further accelerates well behind the disc and returning to

pressure P0. The flow behind the disc is also known as slipstream.

Given:

Mass of fluid passing through the disc = ρASV0 (1)

But with the increase of the momentum of the mass of fluid behind,

Equation (1) now becomes ρASV0(Vs- V), (2)

which is also the thrust on the disc.

If the pressure before and after the disc is known, then

T = S(p2-p1) (3)

Since the flow can be separated into two region then Bernoulli Equation can be

applied where

P0 + 21 ρAV2 = P1 +

21 ρAV0

2 (4), P2 + 21 ρAV0

2 = P0 + 21 ρAVs

2 (5)

and equating (3) and (4), p2 – p1 = 21 ρA(Vs

2 – V2) (6)

Substituting (6) into (3) and equating the result to (2), yields

21 ρAS(Vs

2 – V2) = ρASV0(Vs- V) and dividing by ρASV0(Vs- V),

V0 = 21 (Vs + V)

39

This showed that the velocity through the ideal disc is an average of the inlet

velocity and the out flow velocity.

Letting a be the inflow factor, V0 = 21 (Vs + V) can be written as V0 = V(1+a) and

that Vs + V = 2 V0 = 2V(1+a). Therefore, Vs = V(1+2a).

The rate of increase of fluid energy in the system is describe as

dtdE =

21 ρASV0(Vs

2 – V2)

To assume that the disc is moving from one point to another at speed of V into

the initial stationary fluid, this is term as the useful work done TV. The efficiency

of the disc as a propulsion system =

iη = )(

21 22

0 VVSV

TV

s −ρ

iη can be represented as )(

21 VV

V

s + =

)(1

2

VVs+

= )1(

1a+

Alternatively, the equation can be expressed in the following form:

V0 = V(1+a) and Vs = V(1+2a)

T = ρASV0(Vs – V) = ρASV(1+a)[V(1+2a)-V]

= 2ρASV2a(V1+a)

where it was utilized in the sizing of the propulsion in the thesis.

40

Appendix B – Resistance Theory

B.1 Components of resistance and propulsion

If the hull of the ship is driven through the water by some device which in no way

interacted with the hull or water, it would experience a total resistance RT which

would be the summation of several types of resistance of the following:

a. Frictional

b. Wave-making

c. Eddies-making

d. Appendages

e. Air

All except the frictional resistance are group as residual resistance and usually

only the frictional is of the greater concern as the hull is directly in contact with

the water. Method of comparison has been develop by Froude but not used

universally to derive the skin friction resistance and a universal standard friction

line has since been reached in 1957 during the International Towing Tank

Conference at Madrid, known as the ITTC 1957, with the below formula to

calculate for frictional resistance.

CF = 210 )2(log

075.0−NR

; CT = 2

21 SV

RF

ρ

Since CT = CF + CR, hence the residual resistance CR can also be obtained.

41

Appendix C – Tabulation of hull readings

The following hull values were taken from the lines plan upon its completion for

the purpose of calculating areas.

Waterline

Station 0 WL 1 WL

1.5

WL 2 WL

Design

WL

Nose

Line 8 WL

10

WL

12

WL

0 (FP) 0 0 0 0 0 0 0 0 0

½ 0 0 0 0 0 0.015 0.006 0 0

1 0 0 0 0 0 0.025 0.01 0 0

2 0 0 0 0 0.016 0.036 0.034 0 0

3 0 0 0 0.022 0.034 0.05 0.05 0.05 0

4 0 0 0.02 0.034 0.045 0.05 0.05 0.05 0

5 0 0 0.034 0.042 0.049 0.05 0.05 0.05 0

6 0 0.028 0.043 0.048 0.05 0.05 0.05 0.05 0

7 0 0.044 0.048 0.05 0.05 0.05 0.05 0.05 0

8 0 0.049 0.05 0.05 0.05 0.05 0.05 0.05 0.05

9 0 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05

9 ½ 0 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05

10 (AP) 0 0 0.05 0.05 0.05 0.05 0.05 0.05 0.05

42

Appendix D – Sample of the tabulated raw data logged during the towing tank experiment for speed 1m/s

Test number Year Days Time

Carriage-speed(Tachometer) m/s

Water speed (Water-Probe) m/s Fx (g) Fy (g) MZ

106 2004 288 1450 -0.014 -0.003 -4.199 18.48 0 106 2004 288 1450 -0.015 -0.005 -4.199 18.48 0 106 2004 288 1450 -0.014 -0.006 -3.359 18.48 0.84 106 2004 288 1450 -0.014 -0.003 -1.68 18.48 0.84 106 2004 288 1450 -0.015 0.098 -15.12 23.51 1.68 106 2004 288 1450 0.368 0.329 -38.63 25.19 2.519 106 2004 288 1450 0.58 0.501 -48.71 25.19 4.199 106 2004 288 1450 0.817 0.734 -57.11 26.87 4.619 106 2004 288 1450 0.985 0.906 -57.11 26.87 4.199 106 2004 288 1450 0.984 0.973 -58.63 23.51 4.199 106 2004 288 1450 0.98 0.948 -58.55 23.51 3.359 106 2004 288 1450 0.983 0.939 -56.87 23.51 2.519 106 2004 288 1450 0.985 0.977 -55.19 23.51 3.359 106 2004 288 1450 0.981 0.973 -54.35 23.51 4.199 106 2004 288 1450 0.98 0.978 -52.31 23.51 2.519 106 2004 288 1450 0.985 0.942 -52.31 23.51 2.519 106 2004 288 1450 0.964 0.943 -52.31 23.51 1.26 106 2004 288 1450 0.984 0.928 -52.31 23.51 0.84 106 2004 288 1450 0.985 0.935 -52.31 23.51 0.84 106 2004 288 1450 0.981 0.949 -52.31 23.51 0.84 106 2004 288 1450 0.985 0.957 -52.31 23.51 0.84 106 2004 288 1450 0.985 0.921 -52.31 23.51 2.519 106 2004 288 1450 0.985 0.937 -52.31 23.51 2.519 106 2004 288 1450 0.985 0.955 -52.31 23.51 2.519 106 2004 288 1450 0.985 0.957 -52.31 23.51 2.519 106 2004 288 1450 0.989 0.922 -52.31 23.51 1.26 106 2004 288 1450 0.973 0.933 -52.31 23.51 0.84 106 2004 288 1450 1.005 0.988 -52.31 25.19 0.84 106 2004 288 1450 0.985 0.966 -52.31 25.19 0

43

106 2004 288 1450 0.985 0.944 -52.31 25.19 0 106 2004 288 1450 0.989 0.957 -52.31 23.51 0.84 106 2004 288 1450 0.978 0.914 -52.31 23.51 1.68 106 2004 288 1450 0.984 0.93 -51.83 23.51 1.26 106 2004 288 1450 0.725 0.765 15.12 21.83 0.84

44

Appendix E – Tabulated data for Towing tank experiment (Lightship condition)

Speed V m/s

Length (m)

Gravity (m/s) Fn RT

(gram) RT (N) CT RN µW CF CR ρw Sw V2

0.9 0.5 9.81 0.40 53.1 0.520911 0.115806 395083.41 1.14E-06 0.005798 0.110008 1000 0.0111065 0.8

1 0.5 9.81 0.45 61.9 0.607624 0.109418 438981.56 1.14E-06 0.005653 0.103765 1000 0.0111065 1

2 0.5 9.81 0.90 70.1 0.687303 0.030942 877963.13 1.14E-06 0.004823 0.026119 1000 0.0111065 4

3 0.5 9.81 1.35 81.6 0.800953 0.016026 1316944.69 1.14E-06 0.004419 0.011606 1000 0.0111065 9

4 0.5 9.81 1.80 91.5 0.89799 0.010107 1755926.25 1.14E-06 0.004163 0.005944 1000 0.0111065 16

5 0.5 9.81 2.25 111.7 1.095375 0.00789 2194907.81 1.14E-06 0.003979 0.003911 1000 0.0111065 25

6 0.5 9.81 2.70 129.7 1.272465 0.006365 2633889.38 1.14E-06 0.003838 0.002527 1000 0.0111065 36

7 0.5 9.81 3.16 147.9 1.451017 0.005332 3072870.94 1.14E-06 0.003724 0.001608 1000 0.0111065 49

8 0.5 9.81 3.612189 166.2 1.629961 0.004586 3511852.50 1.14E-06 0.003630 0.000956 1000 0.0111065 64

9 0.5 9.81 4.063713 179.5 1.761224 0.003915 3950834.06 1.14E-06 0.003550 0.000366 1000 0.0111065 81

10 0.5 9.81 4.515236 203.2 1.992931 0.003589 4389815.63 1.14E-06 0.003480 0.000109 1000 0.0111065 100

45

Appendix F – Tabulated data for Towing tank experiment (with hull weight of 2kg)

Speed V m/s

Length (m)

Gravity (m/s) Fn RT

(gram) RT (N) CT RN µW CF CR ρw Sw V2

0.9 0.5 9.81 0.406371 63.8 0.626074 0.139185 395083.41 1.14E-06 0.005798 0.133388 1000 0.0111065 0.8

1 0.5 9.81 0.451524 84.0 0.82404 0.148389 438981.56 1.14E-06 0.005653 0.142736 1000 0.0111065 1

2 0.5 9.81 0.903047 110.8 1.086948 0.048933 877963.13 1.14E-06 0.004823 0.044110 1000 0.0111065 4

3 0.5 9.81 1.354571 134.4 1.318464 0.02638 1316944.69 1.14E-06 0.004419 0.021961 1000 0.0111065 9

4 0.5 9.81 1.806095 177.2 1.737879 0.019559 1755926.25 1.14E-06 0.004163 0.015396 1000 0.0111065 16

5 0.5 9.81 2.257618 211.7 2.076375 0.014956 2194907.81 1.14E-06 0.003979 0.010977 1000 0.0111065 25

6 0.5 9.81 2.709142 259.7 2.547765 0.012744 2633889.38 1.14E-06 0.003838 0.008906 1000 0.0111065 36

7 0.5 9.81 3.160665 295.9 2.902897 0.010668 3072870.94 1.14E-06 0.003724 0.006944 1000 0.0111065 49

8 0.5 9.81 3.612189 343.2 3.366331 0.009472 3511852.50 1.14E-06 0.003630 0.005842 1000 0.0111065 64

9 0.5 9.81 4.063713 379.5 3.723224 0.008277 3950834.06 1.14E-06 0.003550 0.004728 1000 0.0111065 81

10 0.5 9.81 4.515236 417.2 4.092271 0.007369 4389815.63 1.14E-06 0.003480 0.003889 1000 0.0111065 100

46

Appendix G – Tabulated raw data for propeller and thrust measurements

Propeller type and pitch RPM Rad/s Voltage (v) Current (A) Power W M0 (kg) Mbl (kg)

Amp Fac K T (g) T (N)

Air speed m/s U m/s Ct

2-blade 5.5" X 4.5" 11041 1156.36 6 9 54 1.078 1.12 2.34 98.3 0.96 8.1 1.83 0.0152032651 2-blade 5.5" X 4.5" 11197 1172.70 7 9.2 64.4 1.078 1.129 2.34 119.3 1.17 8.2 1.99 0.0193123726 2-blade 5.5" X 4.5" 11231 1176.26 8 9.3 74.4 1.078 1.143 2.34 152.1 1.49 8.4 2.09 0.0256687384

4-blade 5.6" X 3" 10478 1097.40 6 9.3 55.8 1.078 1.147 2.34 161.5 1.58 8.9 2.19 0.0279764623 4-blade 5.6" X 3" 10501 1099.80 7 9.5 66.5 1.078 1.151 2.34 170.8 1.68 9.1 2.2 0.0264247227 4-blade 5.6" X 3" 10595 1109.65 8 9.5 76 1.078 1.165 2.34 203.6 2.00 9.5 2.33 0.0329446356

4-blade 5.6" X 4" 10283 1076.97 6 9.4 56.4 1.078 1.138 2.34 140.4 1.38 7.4 2.1 0.0217189502 4-blade 5.6" X 4" 10310 1079.80 7 9.55 66.9 1.078 1.142 2.34 149.8 1.47 7.7 2.17 0.0242351343 4-blade 5.6" X 4" 10375 1086.61 8 9.6 76.8 1.078 1.15 2.34 168.5 1.65 8.0 2.26 0.0284330641



2-blade 6" x 5.5" 10081 1055.82 6 10 60 1.079 1.139 2.5 150.0 1.47 9.9 2.14 0.0266482478 2-blade 6" x 5.5" 10107 1058.54 7 10.2 71.4 1.079 1.144 2.5 162.5 1.59 10.5 2.19 0.0287721121 2-blade 6" x 5.5" 10119 1059.80 8 10.5 84 1.079 1.152 2.5 182.5 1.79 11.2 2.24 0.0245551171

47

Propeller type and pitch RPM Rad/s Voltage (v) Current (A) Power W M0 (kg) Mbl (kg)

Amp Fac K T (g) T (N)

Air speed

m/s U m/s Ct 4-blade 7" x 3" 9799 1026.28 6 10.5 63 1.076 1.175 2.5 247.5 2.43 10.1 1.98 0.0438221400 4-blade 7" x 3" 9843 1030.89 7 10.7 75 1.076 1.179 2.5 257.5 2.53 11.6 2 0.0346462611 4-blade 7" x 3" 9981 1045.34 8 10.8 86.4 1.076 1.184 2.5 270.0 2.65 11.9 2.1 0.0201550011

4-blade 7" x 4" 9705 1016.44 6 10.6 63.4 1.076 1.164 2.5 220.0 2.16 9.2 1.59 0.0296006891 4-blade 7" x 4" 9789 1025.23 7 10.8 75.6 1.076 1.176 2.5 250.0 2.45 9.9 1.68 0.0186620381 4-blade 7" x 4" 9865 1033.19 8 11 88 1.076 1.179 2.5 257.5 2.53 10.1 1.71 0.0196766078

2-blade 7" x 5" 9711 1017.07 6 10.8 64.8 1.079 1.147 2.5 170.0 1.67 8.9 1.38 0.0126901859 2-blade 7" x 5" 9841 1030.68 7 11.1 77.7 1.079 1.151 2.5 180.0 1.77 9.2 1.46 0.0137545219 2-blade 7" x 5" 9994 1046.70 8 11.4 91.2 1.079 1.167 2.5 220.0 2.16 9.6 1.54 0.0163798969



48

Appendix H – Constructing the hull model

As mentioned in Chapter 2 during the conceptualizing of the hull design and the

basic requirement which have the following:

a. V-hull

b. Dead-rise angle of not more than 150

c. Stepped hull

d. A beam of 0.1m

e. Shallow draft (low design waterline)

f. Lightweight

g. Easy to repair

h. Easy to shape

With all this criteria in mind and after a careful analysis the choice of balsa wood

has been decided over normal wood or other material such as resin or foam,

chiefly due to weight or material strength limitations. The choice of balsa is

necessary as it is light and easy to shape and only those of a stronger, short

grain balsa planks are used. Due to the fact that blocks of balsa cut to the

required model length is not available locally, an improvised method has been

devised by joining thick planks of balsa. The planks are glued together using

normal white glue and then fully clamped overnight to ensure that the planks are

fused as an entire block as shown below.

49

A block of balsa formed from planks.

On the part of lofting the hull curves on the block, upon the completion of the

lines plan cardboards are used to trace the longitudinal and transverse section at

each station. These cardboard forms the templates that will be utilize for

checking the correct angle and area while cutting the block. Methods of removing

the balsa wood on the external surface to the required shape mainly involve

cutting of the main portions of the unwanted material before filing or chiseling to

the marked out curves.

Cutting of large amount of unwanted material.

50

To remove the chunks of material in the internal space a good and effective way

is to make use of milling machine to cut them. The boundaries are first marker

out and then drilled before proceeding to mill.

Milling of the internal space.

The final process to complete and protect and water proof the hull model is the

use of wood lacquer and apply 3 coatings, with each coating to dry before the

next. As the skin of the hull is critical particularly for the towing tank experiment,

sanding between coatings is necessary so that substantial unevenness or

roughness on the surface is properly removed.

The completed hull model.

propulsion system for a wing-in-ground effect...

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