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). 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. Air-cushion suspension has also been applied to other forms of transportation, in particular trains, such as the French Aero train and the British hover train.

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.

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 craft’s 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.

That which makes hovercrafts so efficient and 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. However odd as it may seem, the fan produces more than enough force for the hovercraft to move. This is achieved through the existence of another major factor:

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.

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.

When riding a hovercraft the natural state of motion is easily seen to be constant vector velocity with a constant rate of rotation. A sloping floor will definitely change your velocity vector without changing your rate of rotation. In addition to Newton’s three laws of motion it will become obvious that to avoid spinning or tilting the hovercraft you must apply the forces in line with the center of mass of the combination of the craft and your body.

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.

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