06-04-2012, 11:01 AM
A SIX LEGGED WALKER
Hovercraft - A Model, Review III Report.docx (Size: 956.73 KB / Downloads: 63)
Introduction
Air-Cushion Vehicle, also hovercraft, is a craft that operates above the surface of water or land. The vehicle is supported on a cushion of air. The air cushion is provided by a large fan that pushes air downward within a flexible skirt attached to the perimeter of the vehicle. The skirt maintains the cushion by restraining the air. It makes the vehicle appear to be operating only a few centimetres above the surface.
Literature Review
The Cushion Effect
In conventional winged aircraft lift, associated with circulation round the wings, is used to balance the weight, for helicopters the 'wings' rotate but the lift generation is the same. A radically different principle is used for sustaining of the hovercraft. In machines of this type, a more or less static region of air, at slightly more than atmospheric pressure, is formed and maintained below the craft.
Dynamic effects of hump drag
In the situation where a hovercraft begins to hover over water, its cushion pressure will displace the water under the craft. The total weight of water displaced equals the gross weight of the hovercraft. As the hovercraft accelerates, the cushion pressure continues to depress the water under the skirt as it moves along. As the speed of the hovercraft increases so does its need for more energy. This is because the water under the craft is depressed downward by the cushion pressure.
Lift
Hovercrafts are supported by a fluid air, which allows the hovering with little or no friction. The amount of air pressure that is needed is directly related to the weight of the craft. Therefore, the less the weight is for a hovercraft, the less the air pressure required, which in turn results in energy savings.
Thrust
When designing a system to provide thrust, there are some criteria that must be considered. When using a fan, its diameter plays a very important role in the effect of the thrust output. Large diameters cannot be incorporated into small hovercraft. The next best alternative is the propeller. Its major drawbacks are the difficulty of guarding such large devices and the high thrust line. Ducted fans are safer, more compact, have lower thrust lines, and, consequently, are favoured, despite their lower thrust capability.
Methodology
Brainstorming:
We started with brainstorming and thought of making Ergonomic chair and then we shifted to making Portable Laptop Stand. We finally decided, to make a model of Hovercraft, as we felt that the project met the constraints of time and capabilities and expertise.
Prototype:
We decided to test the feasibility of the concept and made a simple prototype. The idea worked, and the craft was lifted above the ground.
Model:
Body
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. Longer and narrower shapes increase speed but decrease stability. Most hovercrafts have rounded ends, and offer both stability and speed.
Conclusion:
This report, briefly describes the methodology and the steps of manufacturing involved in this project. The various tools and manufacturing processes are described. The experiment clearly shows that the hovercraft lifts up and the friction force reduces considerably, when the blower is switched on. Therefore, very small force will be sufficient to propel the force, as compared to the case when no lift force is exerted.