US Navy Tests "Flying Wing Underwater Glider"

Underwater Travel Takes Wing By David Snow, Wired News Mar. 03, 2004 The U.S. Navy plans to begin testing a prototype for an unmanned underwater glider with a flying-wing design in March, according to the Office of Naval Research, which funds the project. If successful, tests of the Flying Wing Underwater Glider could lead to a new generation of gliders that researchers expect to be the largest and fastest to date. They would be capable of traveling thousands of miles under ocean waves, quietly conducting surveillance and gathering data for military and civilian purposes, researchers said. "Gliders have the potential of providing long-endurance mobile platforms for employing sensors," said Thomas Franklin Swean Jr., team leader for Ocean Engineering and Marine Systems Science and Technology at the Office of Naval Research, which has spent $500,000 on the project so far. "The endurance is measured in months rather than hours or days." The Flying Wing isn't the first glider to "fly" underwater, just the first of its kind. Over the past seven years, projects at the Scripps Institution of Oceanography, the University of Washington School of Oceanography and Woods Hole Oceanographic Institution have developed gliders whose designs incorporate torpedo-like shapes. The new wing design, akin to that of a B-2 stealth bomber, could be superior to them in some ways but inferior in others, sources said. New craft based on the flying-wing prototype, which has a 20-foot wingspan and a theoretical top speed of 5 nautical mph -- 10 times the speed of existing gliders -- might be effective in the open sea, but their size could hinder them in shallow waters and make them more difficult to deploy than existing gliders. The Flying Wing Underwater Glider's likely civilian applications include ocean science research, environmental study and fisheries monitoring, Swean said. It could map currents or follow marine animals without disrupting their behavior, according to Scott Jenkins, a senior engineer at Scripps who spearheaded work on the glider's design. Jenkins described two scenarios in which the glider could play a vital role. In the first, oil companies use it to monitor the activity of sperm whales. The industry's use of seismic refraction shootings to detect undersea oil deposits -- explosions are detonated and the resulting shock waves are studied -- is restricted when whales are nearby. In the second scenario, a glider monitors an offshore waste field to help determine its relationship to beach closures. "Nothing else is capable of doing that (kind of research) in an economical way," he said, pointing out that the use of ships is expensive, whether data gathering is carried out onboard or the ship is hired as a delivery vehicle for instruments on moorings. Moorings are susceptible to damage from storms, ship collisions and vandalism. The glider's other major applications are military, Swean said. They include surveillance and reconnaissance. "Homeland security applications would involve coastal monitoring, perhaps ship traffic," he added. In the future, gliders could take on other roles, such as payload delivery. "We're talking very large gliders," Jenkins said. "One practical thing would be to move underwater robots (vehicles) around. All of those devices have a mother vehicle. A glider could do it in a very clandestine way." The Navy's tests scheduled for March will take place in a vast basin at Space and Naval Warfare Systems Center in San Diego. Tests scheduled for April will take place at sea off Point Loma, which lies between San Diego Bay and the Pacific Ocean. Precise test dates have yet to be determined, but the goals are clear. "These are basic tests to validate hydrodynamic design," Swean said. "We will observe glide trajectory at a prescribed net buoyancy to confirm the wing is flying as designed. Subsequent phases will integrate sensors and prove endurance (and) range." The prototype wing, built by Legnos Boat Building of Groton, Connecticut, is 1.3 feet thick and made up of fiberglass covering foam ribs, Swean said. Inside the glider, a steel pressure hull will protect inner workings during deep-sea diving, Jenkins added. The internal volume of 40 cubic feet will be enough space for control systems and research instruments. The most essential control system is the buoyancy engine, which uses battery power to drive the wing, Jenkins said. It powers a high-pressure pump that inflates a bladder, which displaces enough water to cause the glider to rise. Evacuating the bladder displaces less water and causes the glider to descend. As Swean described it, the wing moves forward when changes in its buoyancy create vertical forces; the wing uses the pressure of the water's mass to transform those forces into forward movement. In other words, it moves forward by changing its elevation. Jenkins added that the onboard computer will adjust the craft's center of gravity by sliding the batteries along a track, which will also help with steering. The new design's potential superiority over existing underwater gliders involves the efficiency of the wing shape, Jenkins said. With nearly all of the surface area creating lift, the vehicle can travel over long distances using only a small amount of energy. "The wing is the most efficient shape we know," Jenkins said. "The prototype for it is a bird. Nature's the most demanding of all engineers." The glider will surface to transmit data to a satellite or stay submerged to send acoustic communications, Swean said. The Navy isn't the only party interested in the outcome of the flying-wing glider tests. "We will certainly follow what Scott (Jenkins) has done and look into the capabilities of that (glider)," said Clayton Jones, a project engineer with glider manufacturer Webb Research.