The Supersonic Maritime Option

sound barrier

Published Jun 5, 2015 1:08 AM by Harry Valentine

During the mid-1940s, Air Force pilots encountered a strange phenomenon during steep dive maneuvers, like some kind of an invisible barrier. A decade later, aircraft designers were busy seeking to develop an airplane capable of passing through the invisible barrier – the sound barrier.

Some 50 years later, a research team sought to develop a high-speed car capable of passing through that same invisible barrier while travelling on the Bonneville Salt Flats in the U.S. A three-wheeled jet-powered car actually passed through the sound barrier on two successive runs.

Now, an Australian boat enthusiast announced his interest in developing a boat capable of exceeding the speed of sound, possibly on a calm lake in Australia.

The lateral thinking approach would seek to combine known precedents from supersonic flight and the supersonic car with a known maritime technology - the wing-in-ground (WIG) effect craft that rides above the water surface like a sea bird gliding above the water surface. When in low-elevation flight, sea bird wing tips push an air stream downward and some of that airstream rebounds off the water surface as an updraft to help keep the seabird aloft. The same approach keeps WIG-craft aloft, and that concept may be combined with precedents in supersonic flight and supersonic ground transport to explore a possible option of supersonic maritime operation.

Designers of the supersonic car had to confront the phenomenon of the vehicle generating a shockwave as it exceeded the sound barrier. Repeated laboratory investigation and testing of supersonic aircraft revealed a sudden rise in air pressure across the shockwave that travelled with the vehicle.

With supersonic ground transport, the sudden pressure rise would occur around the vehicle and especially below the vehicle where the underside profile had to redirect the high-pressure air up and around the side. Textbook theory advises that if the vehicle is travelling 20 percent faster than the speed of sound, or Mach 1.2, the (absolute) air pressure across the shockwave would rise by 50 percent.

Theoretically, a WIG-craft built with a supersonic cross-sectional profile that includes swept-back wings would generate a shockwave that would envelope it as it exceeds the speed of sound. Since it would fly close to the water surface, the shockwave would cause a zone of lower-speed (Mach 0.8422), high-pressure air to develop between the underside of the wings and the water surface, with air rebounding between the wings and water surface.

The dynamic of air under the wings offers a possible updraft capable of carrying the weight of a high-speed WIG-craft travelling at low supersonic speed (Mach 1.2). On the top side, high-pressure air would rise upward and rearward relative to the WIG-craft, otherwise exerting minimal downward force on the wings.

Worldwide, a fraternity of interested people are involved doing research into future possibilities for WIG-craft technology, many of them building scale models or small versions of WIG-craft. The present discussion focuses on a relatively narrow wingspan with extreme length of wing, or extended-length wing chord measurement relative to the fuselage. It is a configuration that could be lengthened with a swept-back profile at the leading edge of the wings, perhaps with a rectangular ‘intake’ to the underside of the wings to ensure a high-pressure, low-speed zone of air and a supersonic profile at the bow section. There is much precedent for WIG-craft researchers to use as they explore the possibility of a supersonic version of the technology.

A previous article suggested that it would be possible to fly WIG-craft that include landing gear and carry freight between coastal airports. Supersonic WIG-craft could operate between the same coastal airports. At subsonic speeds, WIG-craft offer the prospect of burning less fuel than conventional aircraft. On extended westbound flight, conventional aircraft have to fly into powerful headwinds known as the jet-stream, while near the ocean surface the effect of the jet-stream is far less powerful, even non-existent depending on local, low-elevation wind direction. While winds may blow in one direction at low elevation at a location, more powerful higher elevation winds may blow at much higher speed in the opposite direction above the exact same location.

If the Australian adventurer who seeks to develop a boat capable of supersonic speeds were to consider a WIG-craft, he could set a precedent for future commercial development involving passenger transportation.

In the future, it may be possible for a supersonic WIG-craft to travel between the coastal airports of Los Angeles and Sydney at a speed of Mach 1.2 and with comparable fuel consumption to a commercial airliner flying into a more powerful headwind. It offers the possibility of reducing the 14-hour flight to a 10-hour voyage close to and above the ocean.  There are several possible routes between coastal airports across the Asia-Pacific region where supersonic maritime transport may be a future option. – MarEx

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.