Riding on Air—by Hovercraft
By “Awake!” correspondent in the British Isles
ON April 30, 1966, two small hovercraft, each capable of carrying thirty-eight people, established a new link between England and the continent of Europe. The vessels neither sailed across the Strait of Dover (part of the English Channel) like ships nor flew high above the water like aircraft. Instead, each skimmed across the twenty-eight miles on a cushion of air.
Today, on many round trips a day during the busy season, the latest hovercraft carries two hundred and eighty-two passengers and thirty-eight cars over the same route at a cruising speed of 60 m.p.h.
Experiment with Coffee Cans
About twenty years ago an electronics engineer made a rough experimental model with the aid of two empty coffee cans, one slightly smaller than the other, and a small industrial blower rather like a home hair dryer. The engineer, Christopher Cockrell, took the larger can and drilled a hole in its base just large enough to take the nozzle of the industrial blower. Next, he fixed the smaller can inside the larger can so that a gap was left between the two walls. Now, with the can bases facing each other, any air blown from the nozzle must be diverted down through the gap between the sides of the cans to emerge as a ring-shaped curtain of air, only a fraction of an inch thick.
The contraption was fixed to a stand so that the pressurized curtain of air could be directed down onto the weighing pan of a pair of domestic kitchen scales. Cockrell now had a crude method of measuring the pressure of the air leaving the cans. As he expected, the air pressure leaving the industrial blower nozzle had more than tripled during its passage through the gap. From this, Cockrell concluded that a curtain of air so produced, if directed onto a solid base, would not only support the weight of the producing unit but also carry an additional load. Further, if some method of propulsion could be added, the unit, plus a load, would move quite safely on a controlled cushion of air in any direction. This marked the birth of the air-cushion vehicle (ACV), from which the hovercraft and many other devices originated.
Development
In 1959 the National Research and Development Corporation (NRDC), a body sponsored by the British government to bring any promising invention to manufacturing stage, showed interest in the ACV principle. Soon NRDC launched a company to control the project and a manufacturing contract was awarded, which resulted in the construction of the world’s first hovercraft. This craft was launched at East Cowes on the Isle of Wight. It weighed three and a half tons and had a 435-horsepower engine, which provided not only the air cushion but also the means of propulsion by auxiliary jets located along the vessel’s sides.
The hovercraft was initially tried out on land, but within a month sea trials also took place, and passengers on the Solent Ferry plying between Southampton and the Isle of Wight were amazed one day to see a strange-looking craft passing them at a surprising speed of 25 m.p.h.
Modifications had to be made, as the original craft proved to be unstable over obstacles (waves and ground irregularities) more than eighteen inches high. Eventually, a flexible segmented skirt was fitted around the bottom of the craft to delay the escape of air from the jet. This not only increased the efficiency of the air seal but gave the extra lift necessary to clear greater obstacles. In fact, the skirt came to be one of the most important factors in hovercraft development, transforming it from little more than an elaborate toy into a useful workhorse capable of transporting great loads.
Other Uses
The air-cushion-vehicle principle has developed in many directions since its discovery. For instance, the hover load-remover has made it possible to load great weights onto an air-cushion platform, hitch it to a conventional towing vehicle and transfer the load to another location. In July 1967 two giant storage tanks at a depot near Manchester, England, each seventy tons in weight and fifty feet in diameter, were moved two hundred yards to a new site by this method. Air, pumped into an air-cushion load-remover until it reached a pressure of sixty pounds per square foot, raised each tank seven inches off the ground. The transfer went smoothly despite having to negotiate a zigzag path.
Today, transformers weighing two hundred tons are moved by the same method along public roads without the bridges over which they pass having to be reinforced. On a smaller scale, hover-pallets are regularly used for moving heavy loads in factories and warehouses.
The medical profession has adapted the ACV principle to its own specialized use. In June 1967 an article in the British medical journal The Lancet told of two seriously burned patients who were treated successfully on a hoverbed, which can be best described as an upside-down hovercraft.
The hoverbed has a rigid framework with a nylon-coated bag suspended inside. The top of the bag has two rows of fingerlike pockets similar to the segmented skirt of a hovercraft. Warm sterile air, which is pumped into the bag at a pressure of one quarter to one third of a pound per square inch, inflates the “fingers,” which form a seal by meeting down the middle of the top side.
When the patient is lowered onto the bed his body passes through the ends of the inflated fingers. He is then supported solely on the cushion of air underneath, and the fingers form a seal by automatically following the contours of his body.
One of the two patients was severely burned over one third of his body, and the other on his right side only. When laid on the hoverbed the first one was kept there for fifteen hours, and the second for six hours. Each had extensive weeping areas on his body, but in both cases the burns dried rapidly. The hoverbed has been responsible for the alleviation of a great deal of suffering since its first appearance.
Welcome Aboard
Many people have made use of hovercraft passenger service. Have you? Why not join us for a trip? A helpful stewardess is on hand to give personal attention, guiding us to our seats, explaining life-jacket procedures and showing us how and where to stow our hand luggage. The time has now arrived for the actual flight.
The first indication of movement comes immediately after the engines have warmed up. We detect an almost imperceptible lift as the vessel raises itself on its cushion of air. The hovercraft is no longer in contact with the surface and will remain in suspension until the destination is reached. Now the vessel is moving forward so smoothly that only a lively spume of spray rushing from its sides indicates that it has traveled from land to sea.
As the sea is calm today, the hovercraft will take the direct route from Pegwell Bay to Calais, France. This involves crossing the Goodwin Sands, which lie roughly north to south along the Strait of Dover. Treacherous to conventional surface craft, especially when submerged just below the water, they present no problem to an amphibious ACV. In bad weather the hovercraft changes course slightly by hugging the calmer coastal waters for as long as possible and then making a straight run across the sea at the shortest distance between the two coasts.
In the forty minutes it takes to cross the Strait of Dover there is time to think. What if the engines fail? Will the hovercraft sink? Will it collide at high speed with other shipping in these the world’s busiest sea-lanes? A glance at a booklet describing the flight is reassuring. In the unlikely event of all engines failing simultaneously the vessel is designed to float on its buoyancy tank. Even with just one engine functioning it can proceed at reduced speed to land. But what about all the other ships traveling across the hovercraft’s path? The captain is provided with constant information on the craft’s position while the second officer operates two marine radars, which reveal the position of all other shipping in the vicinity, even in thick fog.
On arrival at Calais, on the French coast, the hovercraft leaves the water and glides onto the landing platform. No bumps, no squeal of brakes, just a contented sigh, like settling into a comfortable armchair, as the cushion of air is dispersed.
The flight in the world’s newest form of transport is over. Land and sea have been crossed by riding on a cushion of air.