Tandem Wing Boats Could Suit Fast Freight Transport

While the original wing-in-ground (WIG) effect vessels used a single wing to travel above the water surface, German engineer Gunther Jorg focused on developing tandem wing versions of the technology, called “Flair boats.” There may be scope to develop the tandem wing concept for application on heavy-haul fast vessels capable of carrying shipping containers.

Introduction

When the Wright brothers first flew an airplane, they attached engines and propellers to a modified existing design of lifting kite, called a Hargrave kite that was essentially a widened box-kite with upper and lower wings. Other variations of lifting-kites featured the combination of two sets of upper and lower wings spaced horizontally along an elongated frame. When flown at certain angles, forward and rear wing sets both contributed to lift. During early 1920’s, Italian designer Gianni Caproni designed and built a plane with triple or wings spaced horizontally near the front, middle and rear of the aircraft. 

In 1998, Scaled Composites in the U.S. built the tandem wing Model 281 ‘Proteus’ airplane intended for long distance, high altitude flight. While the tandem wing configuration can increase airplane lifting capability by over 50 percent, manufacturers of large commercial freight aircraft that carry heavy loads have preferred to extend wingspan and wing surface area so as to carry additional payload. The combination of adjusting the trailing wing flaps to increase lift at certain angles of flight leaves the trailing wing set in the shadow of the forward wings and with insufficient air flow to maintain lift.

Ground-effect Transport

The wings of aircraft depend on generating smooth air flow over the entire upper surface or the wing to produce a vacuum effect which produces lift. By comparison, the wings of ground-effect vehicles maintain normal air pressure of minimal vacuum-effect on the wing upper surface and instead use forward motion to generate a dynamic cushion of air between the wing underside and the surface of water over which the vessel travels. For this reason, ground-effect vessels are classified as marine watercraft, and the so-called flight angle remains parallel to the water surface and including during lift-off.

The parallel flight angle allows WIG effect vessels to operate using comparatively narrow wings built to extended fore-and-aft length, as is the case with the reverse-delta shaped wings. It is also possible for WIG vessels to travel using the combination of horizontally-spaced forward and rear (tandem) wings built to identical wingspan. While the tandem wing configuration can travel without the aeronautical tail wing of other single-wing WIG vessels, there may be scope to further develop the configuration to carry additional weight inside extended length fuselages, perhaps even develop a triple-wing or ‘tridem’ wing configuration.

Kites and WIG Vessels

While the first airplanes were based on existing lifting kites, not all kite configurations may be suitable for high-elevation powered flight carrying a fuselage housing passengers and/or freight. However, the operational characteristics of WIG vessels eliminate the steep climbing angles required of commercial airplanes and allow for the application of kite and wing configurations that would otherwise be unsuitable or impractical for airplanes. Box-kites can be built in triangular, rectangular, hexagonal, elliptical or tubular wing cross sections with horizontally-spaced tandem or tridem wings, even multiple horizontally-spaced wing sets that can be installed lengthwise above WIG vessels to increase lift.

A tandem or tridem wing WIG vessel will be built with three hulls, with a main central hull carrying payload and a pair of narrow outer hulls to which the wings are attached. A series of multi-wing tubular box-kites may be installed at progressively higher elevations above the three hulls and remain in the neutral position when the WIG vessels operates in WIG Type-A mode close to the water surface. When additional elevation is required, the box-kite wings would be tilted to raise the upper forward edges to increase lift and transition the vessel into WIG Type-B operational mode.

Scale Models

Several aircraft hobbyists have built powered scale-models aircraft that use various multi-wing configurations and climb to higher elevation with the fuselage at gentle angles. The stepped wing or ladder-wings resembles an open staircase with the leading wing at the highest elevation and with trailing wings at successively lower elevations. The air stream that flows under the lead wing subsequently flows over the upper surface of the trailing wing to produce lift. There may be scope to adapt the ladder wing configuration to extended length WIG vessels that use tandem or tridem wings to produce the ground effect.

The stepped or ladder wing configuration allows for a comparatively narrow wingspan with lift being produced over an extended length involving the upper surfaces of the trailing wings. Adding stepped wings or extended length kite-wings to a WIG vessel simultaneously allows for short-distance flight elevation to 150 meters (500 feet) and to distribute the load carrying capability along the length of the fuselage. Extended length multi-wing WIG vessels would be able carry a greater payload of high-priority shipping containers than single-main-wing commercial aircraft and do so at lower transportation cost per container, even when operating between the runways of coastal airports.

Future Research

A large-scale WIG vessel built with tandem or multiple horizontally-spaced wings could theoretically be designed to carry extreme weight and be assigned to carrying double the number of containers of proposed heavy-haul commercial freight aircraft on trans-oceanic voyages. Future research would need to focus on evaluating and developing triple, horizontally-spaced ground-effect wings, with further research focused on the option of installing kite structures to the vessel provide short-distance flight capability at elevations of up to 150 meters. The weight of these vessels would restrict operation to water runways, requiring that hydrofoils be built into the hulls.

At the present time, the eight to 12-passenger Airfish-8 WIG vessel that incorporates a reverse-delta wing profile and built at Singapore has become commercially available. It is unknown as to whether this wing profile can be built in a tandem configuration and is a task that future research would need to discover, perhaps with the trailing edges of the forward wings being located at or slightly forward of the leading intake edge of the rear wings. If a tandem-delta wing configuration were possible, then future research could explore a triple wing layout.

Markets

The main market for heavy-haul would be high-priority trans-oceanic container transportation, carrying double to triple the number of containers of any future air cargo plane. While most overseas customers seem willing to delay arrival of containers to save on transportation costs, there are market segments that seek fast delivery and even at premium tariffs. While railway transportation incurs much higher transportation cost per container, container trains frequently undertake the journey between China and Europe. WIG vessels would carry containers where railway lines are non-existent and involves multiple pairs of cities located in different nations.

The large container carrier WIG vessels may operate remotely using radio control upon departure from ports and on the approach to and arrival at ports, with local crew guiding the vessel. On the open ocean, computer directed autonomous control would oversee operations. There may be scope for large passenger versions to operate overnight service on some westbound routes, where departure would occur during early evening for early morning arrival at the destination. The tour industry may wish to consider large WIG vessels for operation as mobile hotels on selected trans-oceanic routes, offering more relaxed journeys than aircraft.

Conclusions

The tandem-wing configuration has already been demonstrated using pilot operated WIG vessels called “Flair boat.” While a high-altitude tandem-wing aircraft has been flown, builders of the largest aircraft such as the Airbus A380 passenger plane, C-5 Galaxy military transport plane and Antonov 225 heavy haul carrier have preferred using single wing configuration that offers steeper climbing angles following take-off from a runway. In WIG vessels, there is scope for the tandem-wing layout to offer greater weight carrying capability, with the option to install aeronautical tandem wings to allow for flight elevations of up to 150 meters.