As the aircraft approaches the ground, the flow around it is changed because the downwash generated by the aircraft is modified. From a flow perspective, the ground or sea surface acts like a mirror. Pilots and their passengers are familiar with ground effect as a cushioning influence felt as the aircraft flares for touchdown. Incidentally, the upwash outside the wing tips is why migrating geese travel in large V-shaped formations – each bird is exploiting the upwash outside the wing tip of the neighbouring bird ahead of it, reducing the energy it needs for flight. However, despite this, the model works surprisingly well, in describing the flow about a lifting wing. This is a simplified representation is valid for low-speed flows without considering air viscosity. Considering this model a little more, we can see that a lifting wing will generate an upwash ahead of the leading edge and outside the wing tips, and a downwash behind the wing, and between the trailing vortices. In a steady flow, this representation will result in additional local air speed above the wing, and reduced speed below, and the pressure difference between the two surfaces of the wing will generate lift. If we want to consider a simple representation of a lifting wing, we can represent this as a ‘bound’ vortex, lying across the span, with trailing vortices at the wing tips (this is called a lifting-line representation by aerodynamicists). The circulation is generated as a result of the shape of the aerofoil, its camber and its angle to the airflow. These are the familiar vortices, often seen behind manoeuvring aircraft, but also visible as part-span vortices trailing from flaps, because of the change in circulation at the end of the flap. So, let’s unpack Wing-in-Ground-Effect craft, to explain their operating principles, and from there, discuss their potential applications, and some of the issues that may affect their operation.Ī conventional lifting wing can be thought of as generating lift through circulation about the wing, the circulation being shed at the wing tips as trailing vortices. The envisaged role was as a high-speed, high-payload, troop or equipment carrier, flying below radar detection over the sea. The KM could cruise at up to 230 knots and was designed to operate at about 10 m above the surface of the water. The best-known example of an Ekranoplan is the Caspian Sea Monster, otherwise more properly known as the Central Hydrofoil Design Bureau KM, a very large WIGE weighing 240 tonnes empty, and up to 500 tonnes at maximum weight. What is an Ekranoplan? Well, Ekranoplan is the Russian term for a class of air vehicle otherwise known as a Wing-in-Ground-Effect craft, or WIGE. Here’s an explanation of how they work, and perhaps why the big breakthrough has not yet happened. Ever when Ekranoplans or ‘wing-in ground-effect’ vehicles are not warlike giants they are unique. It was 20 metres longer than a Boeing 747, weighed over a million pounds and flew faster than a Spitfire just above the surface of water. The Soviet KM remained the largest aircraft in the world during the entirety of its existence. Ekranoplans are among the most extraordinary machines ever built.
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