Hovercraft seminar report

HOVERCRAFT

ACKNOWLEDGEMENT

I express my sincere gratitude to Mr. Sojan P Antony, Lecturer in mechanical

Engineering, on this occasion for his suggestion of this topic and presentation of this

seminar.

I also take this opportunity to express my sincere thanks to Mr. Jayachandran,

Hovercraft Seminar Report 2012-13

Head of Department, Mr. M V Revi and Mr. P.P Devdas for their valuable advice and

guidance in completion this seminar in pristine form.

At this juncture, I gratefully remember the moral support and co-operation

extended by my classmates on this seminar presentation. Their active participation

really brought life to my seminar.

My sincere thanks to one and all

MIDHUN VIJAY

Dept. of Mechanical Engg. S.R.G.P.T.C Triprayar
Page 1


ABSTRACT

The air cushion vehicle or “HOVERCRAFT”, as it is popularly known is the
newest vehicle in today„s transport scene. As well as being new, this vehicle is different
from other more conventional, terrestrial vehicle in that it requires no surface contact for
traction and it is able to move freely over a variety of surface while supported
continuously on a self-generated cushion of air. Though the concept is new, the rate of
development of hovercraft has been outstandingly faster than that of any other mode of
transport.

Modern Hovercrafts are used for many applications where people and equipment
need to travel at speed over water but be able load and unload on land. For example they
are used as passenger or freight carriers, as recreational machines and even use as
warships. Hovercrafts are very exciting to fly and feeling of effortlessly traveling from
land to water and back again is unique.

A hovercraft or air-cushion vehicle (ACV) is a craft designed to travel over any
smooth surface supported by a cushion of slow moving, high-pressure air, ejected
downwards against the surface below, and contained within a "skirt."

Hovercrafts are used throughout the world as a method of specialized transport
wherever there is the need to travel over multiple types of surfaces. Because they are
supported by a cushion of air, hovercraft are unique among all forms of ground
transportation in their ability to travel equally well over land, ice, and water. Small
hovercraft are often used in physical activity, combustion, or passenger service, while
giant hovercraft have been built for civilian and military applications to transport cars,
tanks, and large equipment into difficult or hostile environments and terrain.

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TOPIC NO.TOPIC NAME PAGE-NO.

1. INTRODUCTION 4

2. HISTORY 5

3. CONSTRUCTION FEATURES OF HOVERCRAFT 6

4. WORKING PRINCIPLE OF HOVERCRAFT 10

5. ADVANTAGES OF HOVERCRAFT 12

6. DISADVANTAGES OF HOVERCRAFT 12

7. APPLICATIONS OF HOVERCRAFT 13

8. FUTURE OF HOVERCRAFT 16

9. CONCLUSION 17

10. REFRENCE 18

Page 3


1. INTRODUCTION

Vehicles designed to travel close to but above ground or water. These vehicles
are supported in various ways. Some of them have a specially designed wing that will
lift them just off the surface over which they travel when they have reached a sufficient
horizontal speed (the ground effect).Hovercraft is such a vehicle.
Basically hovercraft is a vehicle that,
 Drive like a car but
 Flies like a plane.
 It can hover over or move across land or water surfaces while being
held off from the surfaces by a cushion of air.
 Float like a boat.

A hovercraft, also known as an air-cushion vehicle or ACV, is a craft capable of
travelling over land, water, mud or ice and other surfaces both at speed and when
stationary. Hovercrafts are hybrid vessels operated by a pilot as an aircraft rather than a
captain as a marine vessel. Hovercrafts are usually supported by fans that force air down
under the vehicle to create lift, Air propellers, water propellers, or water jets usually
provide forward propulsion. Air-cushion vehicles can attain higher speeds than can
either ships or most land vehicles and use much less power than helicopters of the same
weight.
Hovercraft is a transportation vehicle that rides slightly above the earth‟s
surface. The air is continuously forced under the vehicle by a fan, generating the
cushion that greatly reduces friction between the moving vehicle and surface. The air is
delivered through ducts and injected at the periphery of the vehicle in a downward and
inward direction. This type of vehicle can equally ride over ice, water, marsh, or
relatively level land
They operate by creating a cushion of high-pressure air between the hull of the
vessel and the surface below. Typically this cushion is contained within a flexible
"skirt". They typically hover at heights between 200 mm and 600 mm above any surface
and operate above 20 knots and can clear gradients up to 20 degrees.
The first practical design for hovercraft derived from a British invention in the
1950s to 1960s. They are now used throughout the world as specialized transports in
disaster relief, coastguard, military and survey applications as well as for sport or
passenger service. Very large versions have been used to transport hundreds of people
and vehicles across the English Channel whilst others have military applications used to
transport tanks, soldiers and large equipment in hostile environments and terrain.

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2.HISTORY

2.1 EARLIEST EFFORTS :-

The first recorded design for a hovercraft was in 1716 put forward by Emmanuel
Swedenborg, a Swedish designer and philosopher. The project was short-lived and a
craft was never built. Swedenborg realized that to operate such a machine required a
source of energy far greater than any available at that time. In the mid-1870s, the British
engineer Sir John Thorneycroft built a number of model craft to check the air-cushion
effects and even filed patents involving air-lubricated hulls, although the technology
required to implement the concept did not yet exist.. In 1915 Austrian Dagobert Müller
built the world's first "water effect" vehicle.
In 1931 Finnish aero engineer Toivo J. Kaario began designing a developed
version of a vessel using an air cushion and built a prototype.
During World War II an engineer in the United States of America, Charles
Fletcher, invented a walled air cushion vehicle. Because the project was classified by
the U.S. government, Fletcher could not file a patent. From this time both American and
European engineers continued work on the problems of designing a practical craft.

2.2 INVENTION OF MODERN HOVERCRAFT :-

In the early 1950s the British inventor
Christopher Cockerell began to experiment
with such vehicles, and in 1955 he obtained a
patent for a vehicle that was "neither an
airplane, nor a boat, nor a wheeled land
craft." He had a boat builder produce a two-
foot prototype, which he demonstrated to the
military in 1956 without arousing interest.
Cockerell persevered, and in 1959 a
commercially built one-person Hovercraft
crossed the English Channel. In 1962 a
British vehicle became the first to go into
active service.

CHRISTOPHER COCKERELL

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3.CONSTRUCTIONAL FEATURES OF HOVERCRAFT

 Radar: apparatus that detects objects through the use of microwaves.

 Pylon: supporting post.

 Dynamic propeller: two-bladed apparatus that provides motion.

 Fin: steering device.

 Rudder: apparatus that prevents drift.

 Lift-fan air intake: opening to allow air to enter.

 Main level drive gear box: compartment that contains and protects the gear
mechanism.

 Skirt finger: part of the flexible skirt.

 Passenger entrance: opening on the side wall that provides access to the
passenger cabin.

 Flexible skirt: lower flexible part.

 Bow door ramp: opening at the front.

 Control deck: cubicle from which a hovercraft is operated.

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 LIFTING FAN :-
The volume of air needed is very large and a propeller is designed to be most efficient
in open air like on an aircraft. Also the fan needs to force air into the chamber below the
craft so creating a specific pressure under the craft. Propellers again are not efficient in
applications when an air backpressure will be applied to the propeller blades as they
rotate. Because of this the lifting fan on most Hovercraft uses what is known as a
centrifugal fan. This is a fan in which two discs and fitted together and looks rather like
a doughnut with angled slats at their edges.

When the assembly is rotated at high-speed air is sucked into the center hole in the fan
and the slats force it out at the edges. The advantages of the fan are twofold. They
operate efficiently in an environment when backpressure is high and they will move
larger volumes of air for a given rotation speed than a propeller with the same speed and
power input. The lifting fan is coupled via a gearbox to the engine. The engine also
drives the propeller on the craft, which provides thrust for forward motion of the
Hovercraft.

 THRUST PROPELLERS :-
The propeller used to drive the hovercraft along is usually an aircraft type with variable
pitch blades. Its speed of rotation must remain fixed to that of the engine and the lift fan.
This is because the amount of lift air required dictates the engine speed to drives the lift
fan. In turn the amount of propulsion, which the propellers provide, must be obtained by
varying the propeller pitch and not its rate of rotation. This system is termed 'integrated
lift/propulsion'. A Hovercraft having more than one lift fan and propeller generally has a
separate engine for each fan-and propeller unit.
The propellers used on hovercraft can vary from four-bladed versions and about nine
feet in diameter on the smaller craft to the four propellers on the SRN4 cross-Channel
hovercraft. These are four-bladed and nineteen feet in diameter! On the SRN 4 the
pylons on which they are mounted can be rotated to change the direction of thrust. On
smaller craft, rudders like on aircraft, are used for direction control.

 MOMENTUM CURTAIN :-
When early models were built and analysis was done on the airflow using the plenum
chamber type of hovercraft it showed that there were problems with stability. In
addition the craft would require enormous power to maintain a reasonable hover height.
Stability of the hovercraft on its cushion of air remained a real problem despite some
design efforts and a new approach was needed. To solve these problems, a plenum
chamber with a momentum curtain was developed by Sir Christopher Cockerall.

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 HOVERCRAFT SKIRT :-
Despite the momentum curtain being very effective the hover height was still too low
unless great, and uneconomical, power was used. Simple obstacles such as small waves,
or tide-formed ridges of shingle on a beach, could prove to be too much for the hover
height of the craft. These problems led to the development of the 'skirt'.
The skirt is a shaped, flexible strip fitted below the bottom edges of the plenum
chamber slot. As the hovercraft lifts, the skirt extends below it to retain a much deeper
cushion of air. The development of the skirt enables a hovercraft to maintain its normal
operating speed through large waves and also allows it to pass over rocks, ridges and
gullies.

The skirt of a hovercraft is one of its most design sensitive parts. The design must be
just right or an uncomfortable ride for passengers or damage to the craft and the skirts
results. Also, excessive wear of the skirt can occur if its edges are flapping up and down
on the surface of the water. The skirt material has to be light flexible and durable all at
the same time.

For the skirt to meet all of its requirements the design and use of new materials has
slowly evolved. The current skirts use „fingers at the lower edge of the skirt envelope
which can be unbolted and replaced. By doing this there is a quick and easy way to
counter the effects of wear without having to replace the whole skirt structure. A
shocking example of the costs is the replacement of the skirt assembly on the SRN 4‟s
which used to cross the English Channel from the UK to France. The replacement cost
for a set of skirts for this craft is over 5 million US Dollars.

 THE ENGINE :-
The SRN 1 and other early hovercrafts used piston type engines and gas turbines. This
type of engine is smaller and lighter for a given horsepower and has been used
extensively in turbo prop aircraft.

The engine has a main shaft on which is mounted a compressor and a turbine. A starter
motor is connected to one end of the shaft and the other end is connected to the lift fan
and propeller gearboxes. Both compressor and turbine look like fans with a large
number of blades.
When the engine is started, the compressor compresses air from the engine intakes and
pushes it into combustion chambers mounted around the engine. Fuel is squirted into
the combustion chambers and ignited. The compressed air then rapidly expands as it is
heated and forces its way out through the turbine to the exhaust. As the gas pressure
rises, the turbine speeds up, thereby driving the compressor faster. The engine speed
increases until it reaches the engine's normal operating speed.
However, the use of these engines results in a very high level of engine noise outside
the craft. Also uses marine diesel engines that are much quieter and fuel efficient.

Page 8


 AIR BOX :-

The box-like structure at the rear of the hovercraft, right behind the propeller, the box-
like structure is called an air box. The air box takes about 10% of the air being pushed
backward by the propeller and forces it downward, underneath the hovercraft. There are
three small ducts cut into the base of the hovercraft, underneath the air box. Two of
these ducts lead into the skirt, which is basically a bag that goes all the way around the
perimeter of the craft, while the third duct leads directly underneath the hovercraft.

 RUDDERS :-

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. 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.
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.

 HOVERCRAFT OPERATION :-

Piloting a hovercraft is an interesting proposition. Since very little of it actually touches
the ground, there isn't much friction, making it very difficult to steer and also very
susceptible to strong winds. Imagine trying to drive around on top of an air-hockey
puck! We've discovered that the best way to drive it is treat it like a jet ski, i.e. leaning
back and forth and steering very carefully. It is also possible to do a 360-degree turn
without stopping, which is quite a sight.

 AERODYNAMICS :-

Aerodynamics is defined as the branch of fluid physics that studies the forces exerted by
air or other gases in motion. Examples include the airflow around bodies moving at
speed through the atmosphere (such as land vehicles, bullets, rockets, and aircraft), the
behavior of gas in engines and furnaces, air conditioning of buildings, the deposition of
snow, the operation of air-cushion vehicles (hovercraft), wind loads on buildings and
bridges, bird and insect flight, musical wind instruments, and meteorology. For
maximum efficiency, the aim is usually to design the shape of an object to produce a
streamlined flow, with a minimum of turbulence in the moving air. The behavior of
aerosols or the pollution of the atmosphere by foreign particles are other aspects of
aerodynamics.

Page 9


4. WORKING PRINCIPLE OF HOVERCRAFT

Hovercrafts work on the two main principles of lift and propulsion. When
dealing with a hovercraft, the existence of lift is imperative for the proper
function of the vehicle. Lift is an essential factor because it is that which allows
the craft to ride on a cushion of air several inches off the ground. This process,
the process of attaining lift begins by directing airflow under the craft.

In order to quarantine the air under the air cushion, a skirt is required. This is
done in order to create pressure under the hovercraft which forces the vehicle off
the ground. Attaining the proper amount of airflow is imperative for the
maintenance of the crafts stability. If too much airflow is directed under the
craft, it will then hover too high above the ground, resulting in the hovercraft to
tip. Not enough lift will cause the craft to remain on the ground which defeats
the very purpose of the hovercraft altogether. 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.

It is 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. The
fan produces more than enough force for the hovercraft to move. 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.

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.

Page 10


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.

Page 11


5. ADVANTAGES OF HOVERCRAFT

 Can carry a relative size payload.
 Can be launched from ship (ex: interception, deploying troops to shore from
a carrier, travel where larger/mother vessels cannot).
 Travel over any surface.
 Shortcutting routes.
 Travel Rivers up as fast as down, irrespective of the current.
 Travel in dry water-beds.
 No collision with debris, logs etc.
 Access to 75% of coastal area instead of only 5% with conventional vessels.
 Hovercrafts are very fuel efficient (CO² friendly) as Hovercraft do not have
to plough through the water but "fly" above the surface. At maximum speed
fuel consumption of a Hovercraft is approx. 70% less than of a fast patrol
boat with similar payload capacity.
 No turbulence or impact in water as no propeller churns up the water so sea
life remains untouched.
 Travel in dry water-beds independent from harbors, piers and jetties.

6. DISADVANTAGES OF HOVERCRAFT :-

 They move a lot of air and can be relatively loud.
 Steep grades can be issue.
 Potential of skirt damage/puncture.
 Not exactly agile (e.g.: cornering).
 The Hovercraft is bulky and its high speed makes it difficult to control
while on land.

Page 12


7. APPLICATIONS OF HOVERCRAFT

 Downdraft associated with helicopters, & a fraction of the cost to purchase,
operate & maintain. Rescuers can reach floods, mud, and sand& ice victims
without exposing rescuers to life threatening danger.
 Distribution of famine or flood aid support craft. Relief work (United
Nations).
 Civil emergency & infrastructure support
 Oil industry survey, exploration & pipeline patrol.
 Electrical Power-line patrol & safety.
 Remote mining access support vehicle.
 River, lake & port geological surveys.
 Mud & riverbed sampling.
 Environmental projects & clean-up operations.
 Airport bird scaring/support/rescue services.
 Coastal civil engineering & bridge construction & repair/maintenance.
 Transport, service & safety craft for river & low tide coastal work where
24-hour access is vital for staff safety.
 Fish farm & low tide access.
 Leisure & family fun. Rental Operations, Corporate entertainment.
Education, schools. Summer fetes & shows.
 Access to Riverside, lakeside & island properties. Hovercraft travel over
mud, sand & ice. Hovercrafts are not restricted by tide, or fast running
water. Or shallow water, or submerged rocks, coral, or marine life.
 Super Yacht Tenders
 Filming & TV work. Store sales & advertising (Harrods).
 It can be used on fast flowing water e.g. flooded rivers as current has little
Effect on craft when hovering. This means the pilots able to maintain speed
and direction or even remain stationary, maintaining position to carry out
Rescues etc. without fighting the water current. Can be launched onto rivers
and floodwater without use of a slipway Providing a reasonably low bank
can be accessed. No need to back a trailer down into the water. The
hovercraft can be flown (or reversed) in. Hovercraft can be operated over
underwater obstructions such as fences, Walls and debris without hindrance
and there is no propeller to foul. No propeller in the water means less risk to
casualties in the water or crew when working close to the craft. Extreme
maneuverability and controlled reverse capability as well as the ability to
stop quickly means this type of hovercraft can be operated in Confined
spaces such as narrow streets and flooded caravan sites. Hovercraft can be
used on mixed surfaces where boats cannot be effective.

Page 13


SOME APPLICATIONS

Single Seated Racing Hovercraft.

A Formula 1 Racing Hovercraft.

Passenger-Carrying Hovercraft

Hovercraft Lifeboats.

Page 14


The Hovertravel Service.

Fire Department Using A Hovercraft To Practice A Rescue.

Military Hovercraft.

Coastal Cruising.

Page 15


8. FUTURE OF HOVERCRAFT

The future of hovercraft seems uncertain, but there is a good chance there will
be huge hover ports all over the world, like the one in the picture. Thinner
hovercraft might be built so civilians can drive safely on roads. Hovercrafts,
once only used by military bureaus and coast guard agencies that delivered
disaster relief, and carried out rescue missions, are now used in commercial
capacities, both public and private, as well as for personal transport and sporting
activities, including fishing, hunting and group outings.

The future is more promising than ever before, exciting outdoor
enthusiasts across the globe with their possibilities of maintaining the craft for
their personal enjoyment, realizing the dream of owning a craft that was once
relegated to professionals.

Page 16


9. CONCLUSION

Hovercrafts are generally simple mechanisms in theory. Yet the process from
theory to manifestation is not as easy as it may seem. A plethora of problems exist and
must be faced in order to attain a well-functioning hovercraft. The plans and designs
must be flawless. One must take under consideration the weight and the shape of each
component in order to avoid problems such as instability and dysfunction. This is a
marvelous machine which greatly cuts down the friction which in turn helps it to attain
greater speed and more stability.

Varieties of problems and factors have to be taken into account in designing and
constructing a hovercraft. The difficulties involved in maintaining stability and
functional competency has limited the application to only transportation or for military
purpose. The cost involved in the developing of a hovercraft is also another impediment
to the widespread use of this machine.

Page 17


10. REFRENCES

1. http://www.totalairdominance.50megs.com/articles/hovercraft.htm
2. http://en.wikipedia.org/wiki/hovercraft
3. http://en.wikipedia.org/wiki/acv
4. http://en.wikipedia.org/wiki/hovercraft
5. http://www.resonancepub.com/images/hovercraft.gif
6. http://images.google.co.in/images
7. http://science.howstuffworks.com/question69.htm
8. http://www.espionageinfo.com/Sp-Te/hovercraft.html
9. http://www.hovercraft design.info/51.htm
10. http://www.hitechweb.genezis.eu/hovercraft /image013.jpg
11. http://www.maruine.com/hovercraft /scm.html
12. http://www.razorworks.com/enemyengaged/chguide/images/hovercraft.gif
13. htp://www.x20.org/library/thermal/pdm/hovercraft.htm
14. http://en.wikipedia.org/wiki/aircushion
15. http://www.military-heat.com/43/hovercraft /
16. http://homepage.mac.com/ardeshir/hovercraft.pdf
17. http://www.scribd.com/doc/7393272/hovercraft
18. http://www.megaessays.com/essay_search/hovercraft
19. http://www.termpapersmonthly.com
20. http://www.marinetalk.com/articles-marine-companies/art/hovercraft

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