TRANSILVANIA

UNIVERSITY OF BRA Ş OV

Faculty of Mechanical IngineeringAutomotive Ingineering

P ROJECT   :   Hoovercraft actuation systems

Name : Mita Sabin Ae1701

A well-designed hovercraft is superior to a boat because it has less

drag and requires less horsepower to operate. A hovercraft is 100% more fuel-efficient than a boat with similar capacity or size. Rising fuel prices and shortages are making the hovercraft a desirable form of transportation. It is conceivable that someday all watercraft will use the hovercraft principal due to its many advantages.

Hovercraft ride much smoother than boats because they travel over the surface of the water, not through it. It travels over water with no concern for depth or hidden obstacles. As the saying goes "if it looks good, it is good" refers to operating the hovercraft over land water or �ice, if the path looks relatively smooth your good to go. Hovercrafts will go against the current of a river with no speed reduction or decrease in fuel mileage. The hovercraft also works well in rapids and white water making it an excellent rescue vehicle.

Safety around swimmers and water skiers is far superior to a boat since there is nothing in or on the water. The hovercraft will pass safely over a swimmer or skier. This technique has proven useful when

returning the line to a fallen skier. Hovercrafts eliminate the need to climb in and out at crowded docks or piers. No more tying up every time you dock. Simply drive up onto land, shut off the engine and step out. Your hovercraft will launch from almost anywhere and does not require a special launching ramp like a boat. All hovercraft will float in water and can be docked for extended periods.

You can enjoy numerous year-round activities while investing in only one craft. Use it as a boat in the summer to go water skiing, fishing, or camping. In the winter the hovercraft is even more useful. It will travel over soft or heavy snow. You will never have to worry about the thickness of the ice you're traveling over. It makes no difference to the hovercraft.

How it Operates

A hovercraft is an air cushion vehicle (ACV) that flies above the earth's surface on a cushion of air. An engine that provides both the lift cushion and the thrust for forward or reverse movement powers it. It is a true multi-terrain, year-round vehicle that can make the transition from land to water without touching the surface. A Thrust propeller provides forward propulsion and directional control is accomplished via rudders mounted aft of the Thrust Fan.

The Lift Fan provides air to inflate the "Skirt" to create a semi-sealed �area between the hull and the ground permitting the craft to "Hover" in �ground effect. On the 19XR, lift is controlled by the lift throttle handle on the left side of the handle bars. This regulates air pressure and volume in and under the skirt. Steering is accomplished with moveable rudders mounted behind the thrust propeller. A horizontal wing acts as an in flight trim system

To properly operate your hovercraft you must become familiar with the machine and all of its components. This helps to build a general understanding of the mechanics and limitations of the craft.

Principals of Operation

A Hovercraft is a vehicle which travels over any surface on a cushion of air which is trapped in a chamber under the vehicle. This chamber is supplied with air under pressure from an axial 4-blade lift fan. The top and bottom of the chamber is formed by the vehicle bottom and the surface over which the vehicle is traveling respectively. The sides of the chamber are formed by the flexible skirt. The simplest skirt is the "C" skirt or the straight skirt shown in Fig. I.�

FIGURE I

A vehicle using a "C" skirt must have a round or nearly round platform �shape in order for the skirt to inflate and contain the air properly. This skirt should have a maximum height of about 10-15% the diameter of the vehicle. Any greater height will result in less stability. There must be a sufficient volume of air supplied to the chamber so the air escaping from gaps between the skirt and the surface is replaced. Operating over a smooth surface requires less air supply than operating over a rough surface. Operating over grass, especially tall grass requires a much higher volume of air than over concrete or ice.

Figure II shows the peripheral jet type Hovercraft, which traps air by means of a curtain or skirt formed by a jet or stream of fast moving air. This jet of air is aimed down and inward at a 45 degree angle for best efficiency and highest lift.

FIGURE II

The peripheral jet hovercraft was one of the first full size machines built. It was built in the late 1950's by Sir Christopher Cockrell in Great Britain. This type of Hovercraft required a large amount of horsepower for the weight it lifted. Too much power was required to maintain the air jet. This type of craft was later fitted with a flexible extension to the air jet to increase the total height of the hull with a corresponding decrease in the air jet height and power required, as shown in Fig. III.

FIGURE III

Experimenting with flexible skirts showed that the lifting efficiency and stability of the craft could be increased by using a bag skirt system. (Fig. IV.) The vehicle could be built to almost any platform shape and is simpler to build because air does not have to be supplied to a jet system all the way around the perimeter of the vehicle. The air could

be ducted directly into the bag and the chamber. The pressure in the bag could be equal to or greater than the pressure in the chamber. The greater the bag pressure, the harder the ride over rough surfaces.

Bag skirts generally give the best stability and the roughest ride. To get a smoother ride, Finger skirts may be added to (Fig. IV) the bag skirt or they may be used separately, with a decrease in the operating height of the hull. Finger skirts are difficult to build due to the large number of separate fingers that must be attached. The overall result of flexible skirts is to give greater operating height with less power required for lift.

With flexible skirts the power required for lift varies from 20 to over 200 lbs. per horsepower and depends on many factors. In general a vehicle that has about 100 to 150 lbs. weight for every horsepower of lift will operate well provided an efficient lift fan and duct are used.

Sources www.hovercraft.com

www.wikipedia.com

www.fuelcells.org

www.howstuffworks.com