µSky-1 in low cruise
Designing a WIG boat is much more challenging than designing a ship or an aircraft. Especially in the preliminary design phase many problems have to be adressed at the same time. One cannot isolate wing, tail and fuselage design, which is common practice to a certain extent in aircraft design. Rules of thumb are hardly available and simple analytic calculation methods for performance and stability of a WIG boat do not exist. The only way to confirm stability are wind tunnel or full-scale tests or CFD (panel method) calculations. These are tools that are generally not intended for the preliminary design phase, but they are inevitable to generate a design with at least some potential to survive the next design phase.
The only help in the initial conceptual design phase is given by existing craft, although many times their characteristics are not known in detail. Over the last decades a large number of very different WIG boats have been designed and built. All designers faced the same problems, taking off and stability, but they have found different solutions. Without going into too much detail some basic solutions can be recognised: the ram wing, the Lippisch delta, the tandem and the ekranoplan. It may be argued that more categories can be recognised, based on the type of take-off aid that is used, but many of them are applicable to all concepts.
Although the general concepts may be a guideline in the conceptual design phase, choosing one of the existing concepts does not guarantee that the resulting design will be successfull. Many parameters, such as dimensions, weight, power and airfoil shape are critical.
Nearly all WIG boats utilise high pressure ram air for increased lift, but the plain ram wing WIG boat is considered to be one that does not have any of the advanced features described in the other concepts.
Some of the early WIG boats were based on this concept, usually they had a low aspect ratio wing (almost square) and a (large) horizontal tail mounted out of ground effect which provides the necessary stability. The wing is usually fitted with endplates in order to enhance ground effect.
µSky-1 in low cruise
The Lippisch concept is a special case of a ram wing, where the wing is a reversed delta with negative dihedral along the leading edge. This layout is in itself more stable than a square ram wing, so that a smaller T-tail is required for longitudional stability.
X-114 in a low banked turn
The tandem wing concept has only been used successfully by the German Jörg so far. It basically consists of two ram wings in line, both wings of almost equal size have a relatively small gap inbetween and no horizontal tail. This configuration provides excellent stability in strong ground effect, but its inability to fly stable without ground effect makes it marginally stable at intermediate heights.
Joerg VI in a harbour with Joerg II-2
Ekranoplan is the Russian word for WIG boat, but it is also used to refer to a specific concept of a WIG boat. All the large WIG boats so far were Russian and were based on this concept. It is basically a plain ram wing with flaps and the addition of engines (jets or propellers) mounted in front of the wing, that blow under the wing at take-off. Western literature often refers to the ekranoplan type WIG boat as a PAR-WIG craft (Power Augmented Ram Wing in Ground Effect).
All ekranoplans have an enormous horizontal tail and a wing of aspect ratio 1 to 4 with endplates and flaps. Dozens have been built in different types and sizes, the largest exceeding 500 tons.
Lun is the most recent example of a big Ekranoplan
Apart from these rather conventional WIG configurations, some have proposed very exotic vehicles utilising ground effect. An example is the hybrid airship (e.g. ref.309), this is a vehicle which is partly supported by helium and partly by aerodynamic lift in ground effect.
A not so exotic concept is the aforementioned WIG assisted ship, an example is the Wing from Incat. In this concept WIG technology is only used to lift the boat partially out of the water, so that propulsion can still be under water. This results in a significant drag reduction compared to a conventional ship at the same speed.
Japan developes a WIG train as an alternative to the MagLev concept
Another recent development is the use of WIG technology for trains. Especially in Japan there is much interest in this subject. A concept for the next generation Shin Kansen is based on this technology. The train is running inside a U-shaped concrete bed. At low speeds the train runs on wheels which are retracted when its wings lift the train from the concrete at higher speeds. The train is propelled by ducted fans. In theory this train would use only one third of the power of the Maglev at 500 km/h and be much cheaper to build, especially the infrastructure.
