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Transcript of Boon Thesis
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Propulsion System for a
Wing-in-ground effectmodel
Submitted by:
Toh Boon Whye
Department of Mechanical Engineering
In partial fulfillment of the requirementsfor the Degree of Bachelor of Engineering
National University of Singapore
Session 2004 / 2005
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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
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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.
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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.
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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
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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
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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
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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
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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
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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
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X
RN Reynolds 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
A ISA or Standard Air Density at 1.2256kg/m3
w Density of fresh water at 1000kg/m3
A Kinematic viscosity of air at 1.714x10-5kgm-1s-1
W Kinematic viscosity of water at 1.139 x 10-6 kgm-2s-1
WL Waterline
SM Simpsons Multiple
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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.
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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
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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 configuration 5
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
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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
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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 0 0 0
1 0.0178 2 0.0356 1 0.0356
1.5 0.02529166 1 0.037937499 1 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
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Both method make use of the mathematical tool known as the Simpsons
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 Simpsons formula, volume of the model =3
1x h x )(vf
=3
1 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 0 0 0
1 0.0178 2 0.0356 1 0.0356
1.5 0.02529166 1 0.037937499 1 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.
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h =17
03.0
= 0.005
Volume of the model =3
1x h x )(vf
=3
1x 0.005 x 0.278199021 = 0.000463665m3
Block Coefficient, CB = draftxbeamxLength
Volume
=03.01.05.0
000463665.0
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
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The area of the mid-ship section calculated = 0.0025 m3
Mid-ship section coefficient, CP = draftxbeam
areamidshipTransverse
=03.01.0
0025.0
x= 0.833
Using the relation CB = CP X CM,
CP =M
B
C
C=
833.0
31.0= 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 =
2
1w x S x V
2 x CTotal
Where CTotal = CF + CR + CA
Given L = 0.5m, Cp = 0.372, = 1.139 x 10-6 m2/s, design speed = 10m/s
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Reynolds number, RN =v
VL=
610139.1
5.010x
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 Taylors 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 =2
1x 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.
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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
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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 =
2
1V2
2 S CD =
2
1x 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,3
63.20= 6.87 N
Now given T = 7.08 N, Design flight speed = 10 m/s and S = 0.0248m2,
thus
a + a
2
= 0248.0102256.12
87.6
2 xxx = 0.5069; a = 0.37
The ideal efficiency is =37.1
1
Useful power = TV, = 6.88 x 10 = 68.8W
The theoretical power required per airscrew based on Froudes
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
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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.
38mm52mm
28mm 38mm
Speed 400 Speed 500
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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 =3
29.17= 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 =35.1
1
New useful power = TV, = 5.77 x 10 = 57.7W
The new calculated power required per airscrew now is
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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.
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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
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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.
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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
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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.
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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)
WaterResistance(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)
Resistance(N)
Fig. 10(ii) Resistance Vs Speed (Loaded condition).
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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.
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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.
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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.
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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.
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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.
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Thrust Vs Power
0.00
0.50
1.00
1.50
2.00
2.50
3.00
55 75 95
Power (W)
Thrust(N)
Fig. 13- Thrust Vs Power of different propellers.
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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.
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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).
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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
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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 flushedwith the wing
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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 betweenthe water surface and hull.
Visible Gap
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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 visible5cm gap between the craft and the floor.
Gap of 5cm
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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.
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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.
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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.
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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.
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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
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Appendix A Propulsion Theory
A.1 Froudes momentum theory of propulsion
Froudes 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
VPo
P1VoP2
VsPo
Ideal actuator disc and flow in slipstream
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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 = ASV0 (1)
But with the increase of the momentum of the mass of fluid behind,
Equation (1) now becomes ASV0(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 +2
1AV
2 = P1 +2
1AV0
2 (4), P2 +2
1AV0
2 = P0 +2
1AVs
2 (5)
and equating (3) and (4), p2 p1 =2
1A(Vs
2 V2) (6)
Substituting (6) into (3) and equating the result to (2), yields
21 AS(Vs
2 V2) = ASV0(Vs- V) and dividing by ASV0(Vs- V),
V0 =2
1(Vs + V)
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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 =
2
1(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
dt
dE=
2
1ASV0(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 =
i =
)(2
1 220 VVSV
TV
s
i can be represented as
)(
2
1VV
V
s +
=
)(1
2
V
Vs+
=)1(
1
a+
Alternatively, the equation can be expressed in the following form:
V0 = V(1+a) and Vs = V(1+2a)
T = ASV0(Vs V) = ASV(1+a)[V(1+2a)-V]
= 2ASV2a(V1+a)
where it was utilized in the sizing of the propulsion in the thesis.
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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
Since CT = CF + CR, hence the residual resistance CR can also be obtained.
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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
Station0 WL 1 WL
1.5
WL2 WL
Design
WL
Nose
Line8 WL
10
WL
12
WL
0 (FP) 0 0 0 0 0 0 0 0 0
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 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
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Appendix D Sample of the tabulated raw data logged during the towing tank experimen
Testnumber Year Days Time
Carriage-speed(Tachometer) m/s
Water speed (Water-Probe)m/s
106 2004 288 1450 -0.014 -0.003 106 2004 288 1450 -0.015 -0.005
106 2004 288 1450 -0.014 -0.006
106 2004 288 1450 -0.014 -0.003
106 2004 288 1450 -0.015 0.098
106 2004 288 1450 0.368 0.329
106 2004 288 1450 0.58 0.501
106 2004 288 1450 0.817 0.734
106 2004 288 1450 0.985 0.906
106 2004 288 1450 0.984 0.973
106 2004 288 1450 0.98 0.948
106 2004 288 1450 0.983 0.939
106 2004 288 1450 0.985 0.977 106 2004 288 1450 0.981 0.973
106 2004 288 1450 0.98 0.978
106 2004 288 1450 0.985 0.942
106 2004 288 1450 0.964 0.943
106 2004 288 1450 0.984 0.928
106 2004 288 1450 0.985 0.935
106 2004 288 1450 0.981 0.949
106 2004 288 1450 0.985 0.957
106 2004 288 1450 0.985 0.921
106 2004 288 1450 0.985 0.937
106 2004 288 1450 0.985 0.955
106 2004 288 1450 0.985 0.957 106 2004 288 1450 0.989 0.922
106 2004 288 1450 0.973 0.933
106 2004 288 1450 1.005 0.988
106 2004 288 1450 0.985 0.966
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106 2004 288 1450 0.985 0.944
106 2004 288 1450 0.989 0.957
106 2004 288 1450 0.978 0.914
106 2004 288 1450 0.984 0.93
106 2004 288 1450 0.725 0.765
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Appendix E Tabulated data for Towing tank experiment (Lightship condition)
SpeedV m/s
Length(m)
Gravity(m/s)
FnRT
(gram)RT (N) CT RN W CF
0.9 0.5 9.81 0.40 53.1 0.520911 0.115806 395083.41 1.14E-06 0.005798
1 0.5 9.81 0.45 61.9 0.607624 0.109418 438981.56 1.14E-06 0.005653
2 0.5 9.81 0.90 70.1 0.687303 0.030942 877963.13 1.14E-06 0.004823
3 0.5 9.81 1.35 81.6 0.800953 0.016026 1316944.69 1.14E-06 0.004419
4 0.5 9.81 1.80 91.5 0.89799 0.010107 1755926.25 1.14E-06 0.004163
5 0.5 9.81 2.25 111.7 1.095375 0.00789 2194907.81 1.14E-06 0.003979
6 0.5 9.81 2.70 129.7 1.272465 0.006365 2633889.38 1.14E-06 0.003838
7 0.5 9.81 3.16 147.9 1.451017 0.005332 3072870.94 1.14E-06 0.003724
8 0.5 9.81 3.612189 166.2 1.629961 0.004586 3511852.50 1.14E-06 0.003630
9 0.5 9.81 4.063713 179.5 1.761224 0.003915 3950834.06 1.14E-06 0.003550
10 0.5 9.81 4.515236 203.2 1.992931 0.003589 4389815.63 1.14E-06 0.003480
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Appendix F Tabulated data for Towing tank experiment (with hull weight of 2kg)
SpeedV m/s
Length(m)
Gravity(m/s)
FnRT
(gram)RT (N) CT RN W CF
0.9 0.5 9.81 0.406371 63.8 0.626074 0.139185 395083.41 1.14E-06 0.005798
1 0.5 9.81 0.451524 84.0 0.82404 0.148389 438981.56 1.14E-06 0.005653
2 0.5 9.81 0.903047 110.8 1.086948 0.048933 877963.13 1.14E-06 0.004823
3 0.5 9.81 1.354571 134.4 1.318464 0.02638 1316944.69 1.14E-06 0.004419
4 0.5 9.81 1.806095 177.2 1.737879 0.019559 1755926.25 1.14E-06 0.004163
5 0.5 9.81 2.257618 211.7 2.076375 0.014956 2194907.81 1.14E-06 0.003979
6 0.5 9.81 2.709142 259.7 2.547765 0.012744 2633889.38 1.14E-06 0.003838
7 0.5 9.81 3.160665 295.9 2.902897 0.010668 3072870.94 1.14E-06 0.003724
8 0.5 9.81 3.612189 343.2 3.366331 0.009472 3511852.50 1.14E-06 0.003630
9 0.5 9.81 4.063713 379.5 3.723224 0.008277 3950834.06 1.14E-06 0.003550
10 0.5 9.81 4.515236 417.2 4.092271 0.007369 4389815.63 1.14E-06 0.003480
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Appendix G Tabulated raw data for propeller and thrust measurements
Propeller type andpitch RPM Rad/s Voltage (v) Current (A) Power W M0 (kg) Mbl (kg) AmpFac K T (g) T (N
2-blade 5.5" X 4.5" 11041 1156.36 6 9 54 1.078 1.12 2.34 98.3 0.96
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
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
4-blade 5.6" X 3" 10478 1097.40 6 9.3 55.8 1.078 1.147 2.34 161.5 1.58
4-blade 5.6" X 3" 10501 1099.80 7 9.5 66.5 1.078 1.151 2.34 170.8 1.68
4-blade 5.6" X 3" 10595 1109.65 8 9.5 76 1.078 1.165 2.34 203.6 2.00
4-blade 5.6" X 4" 10283 1076.97 6 9.4 56.4 1.078 1.138 2.34 140.4 1.38
4-blade 5.6" X 4" 10310 1079.80 7 9.55 66.9 1.078 1.142 2.34 149.8 1.47
4-blade 5.6" X 4" 10375 1086.61 8 9.6 76.8 1.078 1.15 2.34 168.5 1.65
4-blade 5.6" X 5" 10037 1051.21 6 9.4 56.4 1.078 1.136 2.34 135.7 1.33
4-blade 5.6" X 5" 10099 1057.70 7 9.8 68.6 1.078 1.14 2.34 145.1 1.42
4-blade 5.6" X 5" 10112 1059.06 8 9.9 79.2 1.078 1.145 2.34 156.8 1.54
4-blade 5.6" X 6" 10099 1057.70 6 9.9 69.3 1.078 1.126 2.5 120.0 1.10
4-blade 5.6" X 6" 10118 1059.69 7 10.1 70.7 1.078 1.132 2.5 135.0 1.32
4-blade 5.6" X 6" 10129 1060.84 8 10.3 82.4 1.078 1.14 2.5 155.0 1.52
2-blade 6" x 5.5" 10081 1055.82 6 10 60 1.079 1.139 2.5 150.0 1.47
2-blade 6" x 5.5" 10107 1058.54 7 10.2 71.4 1.079 1.144 2.5 162.5 1.59
2-blade 6" x 5.5" 10119 1059.80 8 10.5 84 1.079 1.152 2.5 182.5 1.79
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Propeller type andpitch RPM Rad/s Voltage (v) Current (A) Power W M0 (kg) Mbl (kg)
AmpFac K T (g) T (N
4-blade 7" x 3" 9799 1026.28 6 10.5 63 1.076 1.175 2.5 247.5 2.43
4-blade 7" x 3" 9843 1030.89 7 10.7 75 1.076 1.179 2.5 257.5 2.53
4-blade 7" x 3" 9981 1045.34 8 10.8 86.4 1.076 1.184 2.5 270.0 2.65
4-blade 7" x 4" 9705 1016.44 6 10.6 63.4 1.076 1.164 2.5 220.0 2.16
4-blade 7" x 4" 9789 1025.23 7 10.8 75.6 1.076 1.176 2.5 250.0 2.45
4-blade 7" x 4" 9865 1033.19 8 11 88 1.076 1.179 2.5 257.5 2.53
2-blade 7" x 5" 9711 1017.07 6 10.8 64.8 1.079 1.147 2.5 170.0 1.67
2-blade 7" x 5" 9841 1030.68 7 11.1 77.7 1.079 1.151 2.5 180.0 1.77
2-blade 7" x 5" 9994 1046.70 8 11.4 91.2 1.079 1.167 2.5 220.0 2.16
4-blade 7" x 5" 9599 1005.34 6 11.3 67.8 1.079 1.148 2.5 172.5 1.69
4-blade 7" x 5" 9674 1013.19 7 11.6 81.2 1.079 1.162 2.5 207.5 2.04
4-blade 7" x 5" 9743 1020.42 8 11.7 93.6 1.079 1.174 2.5 237.5 2.33
4-blade 7" x 6" 8753 916.73 6 11.6 69.6 1.079 1.146 2.5 167.5 1.64
4-blade 7" x 6" 8812 922.91 7 11.8 82.6 1.079 1.161 2.5 205.0 2.01
4-blade 7" x 6" 8994 941.97 8 11.9 95.2 1.079 1.17 2.5 230.0 2.26
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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.
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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.
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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.