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design principls of hovercraft

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the chapter explains about design of a simple hovercraft and some tips and theories that must be known by a designer
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GOVT. RAJIV GANDHI INSTITUTE OF TECHNOLOGY
KOTTAYAM
DEPARTMENT OF MECHANICAL ENGINEERING
SEMINAR REPORT ON
“ DESIGN PRINCIPLES OF HOVERCRAFT ”
SUBMITTED BY
ANWAR SADATH K T

1
Department of Mechanical Engineering
Rajiv Gandhi Institute of Technology,
[Govt Engineering College]
Velloor P.O, Pampady, Kottayam, Kerala-686501
Ph: 0481-2505963; 2507763
CERTIFICATE
This is to certify that this seminar report entitled “Design Principles of Hovercraft” is
an authentic work done by ANWAR SADATH K .T, Reg. No : 52089, during the year 2007-
2011 in partial fulfillment of the requirement for the award of B.Tech in Mechanical
Engineering, Mahatma Gandhi University, Kottayam, Kerala.
Coordinator
Head of Department

2
ACKNOWLEDGEMENT
Let me take this opportunity to express my gratitude to all around me who helped
me in my work
I am grateful to God Almighty for guiding me to select the topic and supporting
me to finish the seminar successfully
I am indebted to Prof. J.T. Kuncheriah, the respected principal of Rajiv Gandhi
Institute Of Technology, Govt. Engineering College, Kottayam
I am also thankful to Dr. S. Sasikumar , Head of the Department, Mechanical
Engineering Department, Rajiv Gandhi Institute Of Technology, Govt. Engineering College,
Kottayam
I express my sincere thanks to Asst Prof Biju Augustine for his technical guidance
in my seminar work.
I express my gratitude to all my friends who have helped and co-operated with me
in the preparation and presentation of this paper.
Above all I am indebted to my parents for their support and help.
ANWAR SADATH. K.T

3
ABSTRACT
The Hovercrafts are designed in different ways in accordance with the practical
applications. It is generally used as commercial, civilian non-commercial, military, hobbyist,
hover barge & hover trains. Whatever is the application, all of it has general parts and general
design and some modifications are made in accordance with the application. Here we will
discuss a generalized study about the different parts, design, principles and its aerodynamics.

4
INDEX
Chapter
Topic
Page No:
1.
INTRODUCTION………………………………………………………...5
2.
CREATION OF HOVERCRAFTS…………………………………….…6
3.
HOW DOES A HOVERCRAFT WORK? …………………….…………7
3.1 PLENUM CHAMBER. ………………………………………………9
4.
MOMENTUM CURTAIN……………………………………………….11
4.1 CONSTRUCTION OF MOMENTUM CURTAIN………………….12
4.2 WORKING AND CREATION OF MOMENTUM CURTAIN….....13
4.3 OPEN PLENUM VS. MOMENTUM CURTAIN…………………...14
5.
THE PRINCIPLES OF DESIGN……………………………………...…15
6.
HOVERCRAFT HULLS - CORE MATERIALS………………….........20
7.
SKIRT……………………………………………………………,......….23
7.1 SKIRT DESIGN…………………………………………………........25
8.
LIFT FAN…………………………………………………..………...….27
9.
BUOYANCY TANK…………………………………………………….28
10. PRESSURE IN A DUCTED SYSTEM……………………….…………28
11. THRUST PROPELLERS…………………………………………...........31
11.1. PRINCIPLE OF WORKING………………………………………..32
12. INTEGRATED SYSTEM……………………………………………….33
13. RUDDER. ……………………………………………………………….34
13.1. WORKING………………………………………………..…………34
14. HOVERCRAFT DYNAMICS. ……………………………….……...…36
15. CONCLUTION. …………………………………………………………37
16. REFERENCES. ……………………………………………………,……38

5
1. INTRODUCTION
Over the centuries there have been made many efforts to reduce the element of friction
between moving parts. Shipbuilders have always known that 'drag' results from the skin friction
of water acting on hulls. Early attempts at forcing air through tiny jets either under the hull or all
around it failed simply because the engine needed to produce too much air and the propulsion
engines put the cost way above any advantage in speed. Many other ideas where tried during the
early 20th century until they came together in the genius of one man - Sir Christopher
Cockerell. Although Cockerell's fIrst tests were carried out on dry land the main aim was to
prove that drag or friction between boats and water could be substantially reduced if the 'craft'
floated on an air cushion. And so the 'hovercraft' came in to being.
Nowadays there are several types of hovercrafts, but a definition of a hovercraft can still
be given: A hovercraft is a self-propelled vehicle, dynamically supported by a self-
generated cushion of slow moving, high-pressure air which is ejected against the surface
below and contained within a flexible “skirt” such that it is totally amphibious and has
some ability to travel over less than perfect surfaces. Propulsion is not derived from contact
with the water or the ground.
Hovercrafts are used throughout the world as specialized transports. This vehicle differs
from other vehicles in that way, it needs no surface contact for traction. Because they are
supported by a cushion of air, hovercraft are unique among all other forms of ground
transportation in their ability to travel equally well over land, ice, and water. Small hovercraft are
used for sport, or passenger service, while giant hovercraft have civilian and military

6
applications, and are used to transport cars, tanks, and large equipment in hostile environments
and terrain.
Hovercraft can be powered by one or more engines. Small craft, such as the SR.N6,
usually have one engine with the drive split through a gearbox. On vehicles with several engines,
one usually drives the fan (or impeller), which is responsible for lifting the vehicle by forcing
high pressure air under the craft (air cushion chamber). The air inflates the "skirt" under the
vehicle, causing it to rise above the surface. Additional engines provide thrust in order to propel
the craft. Some hovercraft use ducting to allow one engine to perform both tasks by directing
some of the air to the skirt, the rest of the air passing out of the back to push the craft forward.
Obstacles such as gullies and waves can be taken very easily like it is a flat surface.
2. CREATION OF HOVERCRAFTS
When building a hovercraft it is imperative that you are sure you have a firm grasp of the
important concepts and principles involved. An elementary knowledge of physics is required.
Ease of use, cost, availability and safety are all significant considerations when building a
hovercraft. Care must be taken in selecting a motor and propeller for the proper function and
stability of the hovercraft and to meet your needs for thrust and lift. A good skirt design is
essential for stability and of course, body designs must be well thought-out in order to meet your
needs for speed and stability. Finally, the rudders must be well weighed out in order to avoid
weighing down your hovercraft and also well shaped in order to move air as efficiently as
possible.

7
3.
3 HOW
H
DOES
DOE A
S H
A OV
H
E
OV R
E C
R R
C A
R F
A T W
F
OR
T W
K
OR (pr
( i
pr n
i c
n i
c pl
i e
pl )
e
Hover
Hove c
r r
c a
r f
a tfs
t swork
wor on the
t
he two
t
ma
m i
a n
i pri
pr nc
i i
nc pl
i e
pl s
e sof
of lilfitf tand
a propul
pr
s
opul i
s on.
i
Whe
W n
he dea
de l
a ilng
i
ng wit
wi h
t a
hover
hove c
r r
c a
r f
a tf,
t the
t
he ex
e is
i t
s e
t nc
e e
nc
e of
of lilfitf tis
i sim
i pe
m r
pe a
r t
a itve
i
ve for
f
or the
t
he prope
pr
r
ope rfun
f ct
c iton
i
of
of the
he vehi
ve c
hi l
c e
l .
e Li
L fitf tis
i san
a
es
e s
s e
s nt
e i
nt a
i l
a lfa
f c
a t
c or
t bec
be a
c us
a e
us
e iti tis
i stha
t t
ha twhic
whi h
c al
a llows
l

ows the
t
he cr
c a
r f
a tf tto
t rirde
i
de on a
a cus
c hi
us o
hi n of
of ai
a ri rseve
e r
ve a
r l
a linc
i he
nc s
he
off
of fthe
t
he gr
g ound.
r
This
Thi spro
pr ce
c s
e s
s ,
s the
t
he proc
pr e
oc s
e s
s sof
of at
a tta
t i
a ning
ni
ng lilfitf tbeg
be i
g ns
i
ns by
y dir
di e
r c
e t
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i
ng ai
a rifrlfow
l
under
e rthe
t
cr
c a
r f
a tf.
t In
I orde
or r
de rto
t quar
qua a
r nt
a i
nt ne
i
ne the
t
he ai
a ri runder
unde rthe
t
he ai
a ri rcus
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us on,
hi
a
a ski
s r
ki tr tis
i srequi
e r
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r d.
e This
Thi sis
i sdone
done in
i
n orde
or r
de
to
t cr
c e
r a
e t
a e
t
e pre
pr s
e s
s ur
s e
ur
e under
unde r the
t
he hover
hove c
r r
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r f
a tf t whic
whi h
c fo
f rc
r e
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t
he vehi
ve c
hi l
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e off
of f the
t
he gr
g ound.
r
Att
At a
t i
a ni
i n
ni g
g the
t
prope
pr
r
ope ram
a ount
m

ount of
of ai
a rifrlfo
l w is
i sim
i pe
m r
pe a
r t
a itve
i
ve for
f
or the
t
he ma
m i
a nt
i e
nt na
e nc
na e
nc
e of
of the
t
he cr
c a
r f
a tf’s
’ sst
s a
t bi
a l
bi iltiy.
y IfI ftoo
t
muc
m h
uc
ai
a rifrlfow
l
is
i sdir
di e
r c
e t
c e
t d
e under
unde rthe
t
he cr
c a
r ftf,
t iti twil
wi ll lthe
t n
he hover
hove rtoo
t high
hi above
a

bove the
t
he ground,
gr
re
r s
e ul
s t
ul itng
i in
i the
t
hover
hove c
r r
c a
r f
a tf tto
t titp.
i Not
Not enoug
e
h
noug lilfitf twil
wi ll lca
c us
a e
us
e the
t
he cr
c a
r f
a tf tto
t re
r m
e a
m i
a n
i on the
t
he gr
g o
r und whic
whi h
c def
de e
f a
e t
a s
t sthe
t
ver
ve y pur
y
pos
pur
e
pos o
e f t
f he
t hove
he
r
hove c
r r
c a
r f
a tf a
t l
a tloge
t
t
oge he
t r
he .r
Fi
F g
i 3.1
3
A dem
A de ons
m
t
ons rta
r t
a iton of
i
h
on of over
ove c
r r
c a
r f
a tf pr
t i
pr nc
i i
nc pl
i e
pl

8
The source of the airflow which propels the craft of the ground is a fan. The fan can be
used for lift and thrust. It can be dedicated to lift or thrust or even both simultaneously. In either
case the passage where the air flows through to reach the air cushion affects the stability of the
hovercraft. This passage is a hole located on the base of the craft. Another vital component is the
motor. The motor is usually located in the rear of the vehicle and is the heaviest of the
components. Due to the weight of the motor, extra pressure is required under the area where the
motor is positioned in order to attain hovering capabilities. Which makes hovercrafts so efficient
and different from other vehicles of its category is that very little force is required for it to move.
Propulsion is that which makes the craft move. The source of this effect is the fan, which is used
to move the air for propulsion.
Hovercrafts have no contact with the ground; therefore any resistance the ground may
produce under other circumstances is now non-existent for the craft. As explained above, the
propulsion of the craft requires a fan but a normal fan is not sufficient. This is because a normal
fan does not blow air straight back. Instead it spins the air in a spiral shape. Therefore engineers
decided to use turbines or stationary blades, that un-spin the air. When air does not spin more of
its kinetic energy can be used for translation and less is required for rotation.
The shape of the body also affects the stability of the hovercraft. The larger the area of
the base, the more stable it will be. Wider base implies greater stability. Longer and narrower
shapes increase speed but decrease stability. Most hovercrafts have rounded ends, and offer both
stability and speed.

9
The skirt is another vital component. The common skirt is known as a bag skirt. It is
comprised of a bag that covers the bottom of the base and has holes in it to allow air to escape
and push the craft off the ground. Each part of the skirt inflates independently which makes
repairs much easier and improves stability. Unfortunately, the more stable a skirt, the slower it
will go.
When the hovercraft is finally able to move it will most definitely require steering
capabilities. This is achieved through the use of rudders. These rudders can be controlled by a
variety of devices including computers. Rudders cannot be too heavy otherwise they will weigh
down the craft because they are located very close to the motor. The shape of the rudder dictates
how well it will be able to move air.
When riding a hovercraft the natural state of motion is easily seen to be constant vector
velocity with a constant rate of rotation. A sloping floor will definitely change velocity vector
without changing your rate of rotation. In addition to Newton’s three laws of motion it will
become obvious that to avoid spinning or tilting the hovercraft you must apply the forces in line
with the center of mass of the combination of the craft and your body.
3.1 Plenum chamber
A plenum chamber is the main part of all hovercraft. This is a pressurized housing
containing a gas or fluid ( typically air ) at positive pressure (pressure higher than
surroundings). The function of the plenum is to equalize pressure by the air supplied by a lift fan
which helps for thrust of the craft.

Document Outline

  • ANWAR.pdf
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