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Chinese reportedly working on submarine that would ‘fly’ in an ‘air bubble’

A supercavitating submarine creates a bubble of air that encompasses the whole vehicle by ejecting gas through the nose with enough force that it forms water vapor. This greatly reduces drag and allows it to travel at high speeds not possible by standard submarines. (Sources: Defense Update, Popular Science, South China Morning Post. Graphic: Tobey – The Washington Post)

In the annals of vehicular locomotion, the submarine is the equivalent of the Walkman. It dazzled the masses when it hit, flexing nuclear-tipped missiles that completed the “nuclear triad” of deterrence.

But other technologies soon surpassed it in terms of speed and agility. Now, years later, the submarine may be making a comeback — at least theoretically. Researchers at the Harbin Institute of Technology in northeast China tell the South China Morning Post that they’re hard at work on a submarine that the newspaper claims could travel the 6,100 miles from “Shanghai to San Francisco in 100 minutes.”

That’s not in the cards. But there’s plenty of reason to believe a submarine could be built that would significantly exceed the speed of today’s fastest models, which lumber along at a speed of 40 knots (about 46 mph.) It all has to do with friction and how to conquer it.

The reported plans for the super-fast Chinese submarine draw on research that reaches back to the Cold War on “supercavitation,” a technology that creates a friction-less air “bubble” around a vessel that allows it to “fly” underwater, facilitating incredible speeds. The Russians have developed torpedoes that travel faster than 230 mph using that approach.

Now researchers at Harbin’s Complex Flow and Heat Transfer Lab are reportedly figuring out how to use that science to build submarines.  “We are very excited by its potential,” lead researcher Li Fengchen, a professor of fluid machinery and engineering, told the South China Morning Post. “… Our method is different from any other approach, such as vector propulsion,” which involves engine thrust. Rather, he would lubricate the vessel in a special liquid that would reduce water friction until the vessel would reach speeds high enough to enable “supercavitation.”

How could a vessel reach such high speeds in the first place? And how would it be steered? Li says the liquid membrane would navigate the vessel. “By combining liquid-membrane technology with supercavitation, we can significantly reduce the launch challenges and make cruising easier,” he told the Chinese publication.

Increasing or decreasing the liquid membrane would manipulate friction to steer the ship. The specifics of the research are being kept under wraps for now, South China Morning Post reporter Stephen Chen told the Washington Post.

“These studies in China do not go to academic papers, but the technology is being tested in the laboratory,” he wrote in an e-mail. “The scientists have received pressure from authorities due to the sensitivity of the research and they hope the matter can cool down a bit.”

The potential of supercavitation has not gone unnoticed by the U.S. Navy. “Some technologies innovations have so significant an impact on our way of doing business that they are often described as ‘disruptive technologies,’ with the potential to change the future,” said a 2002 paper published in Undersea Warfare, the official publication of the submarine force. One of them, it said, was ” ‘supercavitation’ techniques.”

The Defense Advanced Research Projects Agency was once reported to be doing much the same, and Popular Science says the project would have allowed the “delivery of men and material faster than ever.” That’s exactly the end game for the Chinese research team: civilian transportation — or even swimming.

“If a swimsuit can create and hold many tiny bubbles in water, it can significantly reduce the water drag,” Li explained. “Swimming in water could be as effortless as flying in the sky.”

Still, questions remain. Wang Guoyu, who leads the Fluid Mechanics Laboratory at Beijing Institute of Technology, expressed doubt at its success. “The size of the bubble is difficult to control, and the vessel is almost impossible to steer,” he told the South China Morning Post, adding that if any part of the ship breaches the bubble, it would snap off due to the density difference.

Plus, he said, “the primary drive [behind the research] still comes from the military, so most research projects are shrouded in secrecy.”