Introduction to hovercrafts
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A hovercraft is an amphibious vehicle mounted on an air cushion (a skirt), which allows it to fly - it's not a metaphor, a hovercraft flies - above all types of surfaces : land, water, sand, snow, ice, etc. The hovercraft can go from one to another without difficulty and without losing speed.
To sum up how hybrid a hovercraft is :
like a boat, a hovercraft must float, face waves and water currents
like a plane, it must be aerodynamic, light and well balanced
like a racing car, it must have enough engine power to reach high speeds
This scheme shows how a hovercraft works when it is equipped with a single propeller. The propeller provides both the air flow for the propulsion and for the air cushion (= the skirt) : a rigid flap deflects part of the air under the hovercraft. It is this flow of air, directed under the hovercraft, that allows it to "take off".
Here is the detailed operation of a "vented bag skirt" (it does not correspond to the illustration, but it's close enough) :
- air fills the skirt, which inflates
- air goes to the center of the hovercraft through several openings, allowing it to fully pull the hovercraft off the ground
- air escapes from the center of the hovercraft to the outside, creating a thin layer of air between the hovercraft and the surface
This thin layer of air under the skirt is necessary for the hovercraft to be able to move. This is why you need to let a few openings somewhere into the skirt. On our BR6 model for example, these openings are at the front and at the rear of the skirt.
In the 1960s, in the same way that the Concorde was seen as the future of aviation, large hovercrafts were considered to be successors of boats and ferries, due to their high speed and their low need for infrastructure.
Indeed, as shown in these pictures of the British SRN4 and the French N500, a hovercraft only needs a simple concrete runway to embark / disembark passengers and freight, which is cheaper and more convenient than having to use port infrastructures.
Unfortunately, these two emblematic hovercrafts have been retired when the Channel Tunnel was opened, for two main reasons :
their greed for fuel makes them expensive to operate (too expensive compared to the trains that now ran under the Channel)
since these large hovercrafts never went into mass-production like airplanes or cars, spare parts were - and are still - extremely expensive
Smaller hovercrafts are still used nowadays for sea rescue, coastal surveillance, crossing difficult terrain (swamps, polar environments, etc.), transporting passengers on short distances and racing.
On the military side, among other hovercrafts, we find the Zubr Class operated by Russia, China and Greece, the BH.7 operated by Iran, the Griffon 2000TD in service in British and Peruvian special forces...
In general, the autonomy of a hovercraft is sufficient for small maritime spaces such as the Aegean sea : Greece is one of the few countries in the world that can fully exploit the tactical potential of its four Zubr Class, bought from Russia and Ukrain. Conversely, the low autonomy of a hovercraft would make it incapable of navigating long distances and participating in the surveillance of the largest maritime spaces (USA, France, etc.).
In the same way that nuclear propulsion has been incorporated into submarines, some civilian ships and aircraft carriers, nuclear-powered hovercrafts were considered in the 1970s by the British. Such project would have corrected the weak points of hovercrafts: quieter engines, no CO2 emissions, up to 5 or 10 years autonomy... but unlike a boat, where the weight of a nuclear reactor can be supported by the water (Archimedes' principle), the lifting turbines of a hovercraft would need to be even more big and powerful to carry a nuclear reactor, which would reduce the space available for passengers... this is probably why such project would be difficult to carry out. Battery-based electric propulsion would be feasible, but we can guess that recharging would be too slow and that a company wouldn't find such a project viable.
To go further, there are many types of skirts, each with its own pros and cons :
A model of the french hovercraft "SEDAM N500", equipped with a "SEDAM bi-conical skirt", an assembly of several conical skirts.
This page will be completed over time. If you are interested in making your own RC hovercraft, check out our DIY guides (the BR6, the Qoum 3 or the Mower) or check out this page to design a custom vented bag skirt.
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