The last days of noisy, gas-guzzling airplanes polluting the skies could be on the horizon as Japanese scientists have successfully — if briefly — flown an aircraft powered by water.

The revolutionary vehicle has no traditional power plant and, if the technology gets off the ground and is harnessed commercially, could mean a generation of aircraft that are both lighter and quieter than their present-day counterparts, less prone to malfunctions because of their simplicity, cheaper to operate and therefore cheaper for travelers too.

As an added bonus, a water-powered aircraft would not leave airlines at the mercy of the international oil market, while the propulsion system could be adapted to work similarly well in outer space, according to professor Takashi Yabe, 52, of the Tokyo Institute of Technology.

“It was initially conceived to propel a rocket into orbit, but there is no water in outer space, so the vehicle would either have to carry its own supply of water or collect it from another source, perhaps an orbiting space station,” he said.

For the present, Yabe and his team are concentrating on getting a small aircraft aloft, with laboratory experiments on replica planes proving successful so far.

The technique involves fitting the tail of the miniature aircraft with a small, curved aluminum plate that holds a few drops of water. A beam from a 0.2-joule yttrium aluminum garnet (YAG) laser is shot through the water and onto the aluminum dish, evaporating the metal, Yabe said. It is the evaporation of the aluminum that vaporizes the water, which is then funneled out of the rear of the vehicle, propelling it forward.

The force of the vaporized water is sufficient to push the paper plane used in the tests, weighing just a couple of grams, forward for about two seconds, at which point its aluminum plate must again be “shot” by the laser to force more water through the rear-facing nozzles. Surface tension quickly “seals” the hole left by the expelled water, while the amount of aluminum that actually evaporates is very small, meaning the bulk of the metal can be used many times over.

Yabe uses an infrared laser because it is a relatively cheap form of high-powered laser and it has the ability to pass through water — and as clouds are made up mostly of water, it will be able to cut straight through them, he said.

“The real merit of this airplane is that it does not even have to carry the laser, which would be very heavy and bulky to produce the required energy, so its engines are not even attached to it,” Yabe noted.

His team envisages a network of laser stations on the surface of the Earth that, in tandem with a network of orbiting satellites, continuously track the progress of the aircraft and shoot aluminum plates on the surface of the wings, encased in a sheen of water, every few seconds, providing a new jolt of power.

The aircraft will not even need to carry its own supply of water, Yabe said, as liquid in the form of condensation is readily available in flight.

He also dismissed concerns over the laser beam striking other airborne objects — vaporizing anything from birds to other aircraft — saying that it is possible to pulse a laser onto the surface of the human skin without damaging the skin; his gadget would use similar pulses that would touch, for example, a bird for a fraction of a second and leave no mark.

A greater concern, and one problem that he is trying to iron out, is finding a better way to store the laser’s energy aboard the aircraft to enable it to continue in flight should it miss a couple of “shots.”

There have been previous attempts to use lasers to propel rockets, Yabe said, but these focused on heating gas in the rocket, which produced very little propulsive power. Water, however, has a very high density and gives a strong force — 10,000 times that of a gas — when it acts as a propellant.

Yabe calculates that by using a 70-joule laser — 100 times more powerful than his present apparatus — he will be able to get an aircraft weighing 1 kg airborne. Lasers are developing rapidly, he said, and already a 1-megajoule laser is being built at the Lawrence Livermore National Laboratory in California.

A laser of that size “would be able to get an aircraft weighing many tons into the air,” Yabe said.

He is also not put off by the potential cost: “At present, setting up a system like this would be very expensive,” he conceded. “For example, the Livermore laser will cost $1 billion, but the technology is developing very fast and it will reach a manageable cost in a relatively short time. Look at my 0.2-joule laboratory laser: That would have cost millions of yen a decade ago, but now it’s next to nothing.”

Yabe and his eight-strong team are to present a paper on their work in the near future, with the initial objective of driving a small aircraft capable of monitoring climate changes and volcanic eruptions, although the sky could be the limit for the new vehicle, he said.

“It would be easier to fly a smaller airplane or an airship with this method,” he said, “But I see no reason why it can’t be applied to a much larger aircraft in the future.”

As yet, he has not approached any of the powerhouses in the aircraft industry. “It’s far too early. I doubt anyone would be interested at this stage, and we really need to do a lot more work on the project. But I’m confident they will be interested when we are at a more advanced stage in our studies,” he said.

And he is not particularly worried about passengers of the future being put off boarding an aircraft that has no engines and is powered from the ground.

“Why should they be?” he asked. “If the technology can be proven to be safe and efficient, I see no reason why anyone would be put off from flying in this aircraft. At least I hope that is the case. After all, 50 years ago, the first passengers aboard the first jet airliners still got aboard despite the fact that the engines had no propellers.”

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