2CONTENTS INTRODUCTION HISTORY DESIGN AND OPERATION OTHER APPLICATIONS ADVANCEMENT IN TRANSPORTATION METHODFUTURE OF HOVERCRAFTSOME AVAILABLE HOVERCRAFT
3INTRODUCTION Known as Air Cushion Vehicle (ACV). It flies like as an aeroplane , float like a boat ,can drive on land like a car.Its engine provides the power to drive large fans that blows air under the craft, this air is retained by a rubber skirt that helps to move the hovercraft.
5Tchnical definitionAny of the machines characterized by movement in which a significant portion of the weight is supported by forces arising from air pressure developed around the craft, because of which they hover in close proximity to the Earth’s surface can be put under the category of HOVERCRAFT or GROUND EFFECT MACHINE.
6HISTORYFirst man to introduced the concept of ACV was Sir John Thornycroft in 1870.First practical use was made in 1929 by German Dornier DO X flying boat.Work went on its peak during World War -2.In 1960s,American aerodynamicist developed an experimental craft.Experiment went on many more experimental craft. But they remain experimental.Finally invented by Christopher Cockerell of UK.He patented it on Dec. 12, 1955.
7Theory of sir Cockerell If air were pumped under the vessel through a narrow slot running entirely around the circumference, the air would flow toward the centre of the vessel, forming an external curtain that would effectively contain th ecushion.this system is known as the Peripheral Jet. Once air has built up below the craft to a pressure equaling the craft weight, incoming air has nowhere to go but outwards and experiences a sharp change of velocity on striking the surface. The momentum of the peripheral jet air keeps the cushion pressure.
8DESIGN AND OPERATION Basic elements Skirt arrangement Power plant Thrust propellerACV operation
9BASIC ELEMENTSA HULLA SKIRT SYSTMA PROPULSION SYSTEMA LIFT SYSTEM
10Skirt system is beneath the hull Skirt system is beneath the hull .On the skirt system accomodation for passenger, crew and fright is built.Lift system feeds air into the plenum chamber below the craft in order to provide a cushion.The propulsion and lift system can be driven by the same power plant or by separate unit.The power to weight ratio is very critical and it detrmines not only the payload and performance of the craft but also the ground clearance between the surface and the skirt.Hull structure are of marine aluminium skin,welded or riveted onto aluminium webs or frames.The cavity or chamber in which the air is kept is called a ‘plenum’ chamber.
11SKIRT ARRANGEMENTThe 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. It is of semicircular shaped .
13POWER PLANT Early crafts used piston type engine. After that gas turbine engines were evolved.The engine has a main shaft having a compressor and a turbine .A starter motor is connected to one end of the shaft and the other end is to lift fan and propeller gearbox.These engine creates a lot of noise.Newer engines are made to make engine noise low and greater fuel efficiency.
15THRUST PROPELLER Usually an aircraft type with variable pitch blades. The propeller can vary from four-bladed versions and about 9 feet in diameter to the 4 propeller and 19 feet in diameter.
16ACV OPERATIONSConfined to commercial passenger-carrying ferry service(5 to 40 KM), military operations.Also used for seismic survey parties,either over shallow-water areas or in deserts, search and rescue operations.US used these in Vietnam operations. Later used as mine-countermeasure works,antisubmarine works,aircraft carrying and missile launching.
17OTHER APPLICATIONSExperiments are going on for hover car and hover train.This principle is used for moving large or heavy objects.
18Advancement in the transportation method Air cushion concept was used for passenger carrying trains.In 1970s 235 mile/hr. speed was achieved.French French got 300 mile/hr.Many experiments are going on this project but now emphasis has diverted to magnetic trains
19Future of hovercraftACV vehicles have not yet fulfilled their origianal promise. These hovercrafts are not economical although they are idle in military application.So research is mainly going on for military purposes.
22Special Purpose Hovercrafts: AIRLIFT 950A (Ambulance)Type Enclosed Cabin. Installed ambulance equipment.Length 9.5 metresWidth 4.2 metresCapacity 1 crew + 14 seats, centre 6 seats can be converted to 2 stretcher spaces or operating table.Engine 2 x Cummins 6BTA 5.9 diesel, 2 x 2600rpmApplication Ambulance, health services.
23AIRLIFT 1060FT (Fire Tender) Type Fire-Fighting and Rescue hovercraft.Length 10.6 metresWidth 4.6 metresCapacity 2 to 6 crew plus equipmentEngines 2 x Cummins 6BTA 5.9 diesel, 2 x 2600rpmApplication Fire fighting, Pollution control, Dive tender, Rescue.