Hovercraft

Overview

A hovercraft is an amphibious vehicle that supports itself on a cushion of slightly pressurised air rather than on the surface beneath it. Because nothing solid touches the ground, the same craft crosses water, mud, ice, sand and grass without caring which is which, and with almost no contact friction it slides over them at speed. The trade-off is that it has little grip to steer or brake with, so handling a hovercraft is a distinct skill.

The craft is built around a buoyant Buoyancy Hull that also forms the floor of the air cushion, sealed to the surface by the flexible Flexible Skirt around its edge. Two airflows do the work: the Lift System pumps air down into the cushion to raise the craft, while the Thrust System drives it forward and its rudders point it. Both fans are turned by the Petrol Engine, commanded through the Controls. The pilot and passengers sit in the Cabin, fed by the Fuel System and Electrical System systems.

How it works

The centrifugal fan in the Lift System forces air into the plenum and the inflated Flexible Skirt bag. Pressure builds until it just lifts the craft clear, then air escapes continuously under the skirt fingers; the craft floats on this thin, constantly replenished layer. The skirt is the key trick: it lets the cushion follow uneven ground and waves while keeping the air gap small, so the lift fan does not have to fight large leaks.

Forward drive comes from the ducted Thrust System propeller, which throws air rearward; the reaction pushes the craft ahead. Steering is by air rudders in that slipstream plus shifting crew weight, since there are no wheels or keel to bite. The Petrol Engine burns petrol from the Fuel System to power both fans, and the Electrical System battery runs ignition, charging and the cabin instruments. Because the cushion carries the weight, the same modest engine that would barely move a boat this size can push a hovercraft across water at speed.