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Hovercraft Construction Materials

Designing and building a hovercraft

Building a hovercraft isn't the easiest of tasks as there are a number of essential design and construction principles to adhere to. But with some good guidelines or instructions, some handiness with tools, time and patience, success is assured. Of course you can always buy one instead and the price of small hovercraft are coming down all the time.



The basic principle

The basic principle of an air cushion is that if you lift an object off the ground using air you reduce the force needed to move the object. Because the object is no longer in contact with the ground the friction this causes (surface friction) is reduced, making it easier to move the object. This also implies that the smoother the surface the less the friction. This is also true. Uneven surfaces with rocks and other obstacles can significantly slow down or even stop and damage an air cushion vehicle if the chamber containing the air cushion (the plenum chamber) was made of rigid materials.Hence the use of a flexible skirt and the need for sufficient lift. This allows the craft to pass over (smaller) rocks and other uneven terrain obstacles without (too much) trouble or damage or slowing down.

The basic parts

That said with a hovercraft we can identify four basic construction necessities - 1) the hull, below which is attached the skirt system, 2) the carriage or cabin part which needs to hold the passenger(s), crew or freight, 3) a propulsion system to move the craft, and 4) the lift system to feed air into the plenum chamber below the craft in order to create the air cushion.Some hovercraft use a single engine system to provide both the air for the plenum chamber and propulsion. The difficulty in using one engine is to provide optimal efficiency for both systems, dividing the power for propulsion as well as for the fan to produce enough air for the lift. Many modern air cushion vehicles use separate systems for air and propulsion. But advances in engines have made it possible to choose between one and two engine systems, especially for smaller, recreational hovercraft. Bigger, industrial, commercial or military hovercraft can have anywhere up to eight engines for propulsion and lift.

Power-to-weight ratio

Although an air cushion vehicle does not require the critical power-to-weight ratio precision as does an airplane in order for it to still operate, it is nonetheless necessary to consider the power-to-weight ratio at the design stage of an air cushion vehicle, rather than find out later that there isn't enough power to lift or move the craft. The power-to-weight ratio determines in large part the amount of ground clearance between the skirt and the ground surface. The greater this ground clearance the more efficiently the propulsion system operates. That is not to say that the higher the hovercraft lifts into the air the better. Lifting it too high will cause instability. Such is the power of the lift that even a severely overloaded and miscalculated power-to-weight ratio hovercraft construction will still work, but it is far from ideal.

Military Use Of Hovercraft

Its well known that any scientific development or discovery is quickly exploited for military purposes, and the hovercraft industry is not different from any other in that respect. In general, an air cushioned vehicle cannot change direction very quickly, so would be no good in a combat situation for example, but the fact that it rides on a cushion of air without touching the surface of the ground raises very interesting possibilities.

Imagine a military commander needing to transport men and equipment many miles over marshy terrain, sometimes hard ground, sometimes shallow water and in places a sticky mud. The variety of surface conditions requires a mode of transport that isn't land based, nor marine in nature. A hovercraft simply glides over any surface and the flatter the better. Water, mud, slippery ice and snow are no obstacles to a hovercraft.

Although the principle of using a contained air pressure as a means of transport was known for decades, it was mostly seen as a novelty having no real commercial value. After all, steering the craft was difficult. It couldn't stop very quickly, or manoeuvre tight corners, but then neither could large ships. In fact, sea travel was the most interesting early application of ACVs, both for private commerce and the military.

After World War 2, Russian hovercraft manufacturers built an enormous craft, possibly still the largest in the world, which could carry hundreds of tons of men and machines. Russia is of course a vast country with plains and ice which are easy to traverse using a vehicle that hovers just above the surface. It's not how nimble the craft is, but it's carrying capacity for this type of work. It doesn't get bogged down because it has no wheels. If it cannot stop quickly then it's relatively easy to allow more time to stop, it's a simple as that! A bit of planning will ensure that the terrain to be hovered over has plenty of space for turning.

The engines used for thrust and lift are of course much bigger than a comparable size commercial hovercraft. In fact, the supersized model has many engines. If you think about it, military vehicles of all kinds are always much heavier than regular machines, due to the fact they they are intended for rough and frequent use. It's also true that military hovercraft maintenance schedules are second to none, so that the motors are always in tip-top condition.

Specialist training is required to pilot such a craft. It isn't an aircraft, marine craft or land vehicle therefore a different approach has to be taken to controlling direction and speed.