hovercraftseminarreport-midhunvijaynewedited-130303030343-phpapp02

Hovercraft

Seminar Report

2012-13

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. Ja yachandran, 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

Hovercraft

Seminar Report

2012-13

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 the y 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.



Hovercraft

TOPIC NO.

Seminar Report

TOPIC NAME

2012-13

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



Hovercraft

Seminar Report

2012-13

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 f orce 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 an y 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.



Hovercraft

Seminar Report

2012-13

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 protot ype. 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 twofoot 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



Hovercraft

Seminar Report

2012-13

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.



Hovercraft 

Seminar Report

2012-13

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 aircr aft 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 rotati on. 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 hei ght. 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.



Hovercraft 

Seminar Report

2012-13

HOVERCRAFT SKIRT :-

Despite the momentum curtain being very effective the hover height was s till 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 eas y 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 compress es 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 i s 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.



Hovercraft 

Seminar Report

2012-13

AIR BOX :-

The box-like structure at the rear of the hovercraft, right behind the propeller, the boxlike 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.



Hovercraft

Seminar Report

2012-13

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.



Hovercraft

Seminar Report

2012-13

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.



Hovercraft

Seminar Report

2012-13

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.



Hovercraft

Seminar Report

2012-13

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 eff ective.



Hovercraft

Seminar Report

2012-13

SOME APPLICATIONS

Single Seated Racing Hovercraft.

A Formula 1 Racing Hovercraft.

Passenger-Carrying Hovercraft

Hovercraft Lifeboats.



Hovercraft

Seminar Report

2012-13

The Hovertravel Service.

Fire Department Using A Hovercraft To Practice A Rescue.

Military Hovercraft.

Coastal Cruising.



Hovercraft

Seminar Report

2012-13

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.



Hovercraft

Seminar Report

2012-13

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.



Hovercraft

Seminar Report

2012-13

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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