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Though air travel represents only about 3% of total world emissions, traffic is increasing quickly even as concerns over climate change multiply. To make matters worse, because airplanes fly at high altitudes, they give off large amounts of nitrous oxide, which is estimated to produce double the warming effects of carbon dioxide.

Plane travel is more energy efficient than car travel per passenger mile, but far less so than going by train, leading some advocates to push for the outright elimination of airline flights. But with transcontinental and transoceanic flights still facts of life and few options for their replacement, environmentalists, government regulators, and manufacturers are considering improvements to aircraft that will reduce emissions.

Here we’ve detailed a number of advances that may make airplanes a more acceptable mode of transport in a carbon-reduced future.

Waggling Wings

One of the major impediments to reducing the fuel consumption of air travel is drag — simply put, the air resistance airplanes encounter when they’re moving through the sky at up to 550 mph. Winglets, which are increasingly standard on new aircraft, are vertical tails at the end of each wing. They allow airplanes to reduce drag during takeoff and they provide additional lift.

Winglets provide the basis for a new look into how to redesign wings to increase efficiency. Ideally, a wing that could literally move up and down during flight would work best. But that’s not a realistic solution for mainline aircraft.

New research argues that an effective improvement to airplanes would be the addition of tiny vertical protrusions or air jets placed all over the wings that would direct wind sideways and dramatically reduce fuel use. Duncan Lockerby, a physics professor in Coventry, England, is leading a team with Airbus that will research how to design wings that better redirect airflows perpendicular to the travel direction in order to reduce drag. Experimental wings could be ready for testing by 2012.

Biofuels

Last year, Virgin Atlantic airlines flew a Boeing 747-400 jumbo jet from Amsterdam to London with biofuels powering one of the airplane’s four engines. The flight was the first of its type for a commercial airliner and demonstrated that airlines could rely on something other than carbon-heavy jet fuel to fly.

Yet the biofuels used for the Virgin flight, derived from coconut and babassu oils, have negligible carbon savings, because the production of the plants themselves results in negative environmental effects. Meanwhile, their use, displacing food crops, increases food prices and hinders efforts to feed the third world. So while Virgin’s mission was a technical success, it wasn’t a long-term solution.

Boeing, the aircraft manufacturer, however, thinks it has a solution in new biofuels based on non-food sources such as algae. Using such plants as a fuel source would produce more energy per plant than existing soy or corn-based fuels. But we’re years away from production; no algae fuel conversion plant currently exists, and it’s unclear whether today’s jet engines would even be able to handle such fuels.

Silent Aircraft

The Concorde was the world’s fastest commercial airplane, and that made it attractive to the most hurried business passengers. But many people living near airports where the plane landed were happy when the aircraft were removed from service in 2003. The Concorde’s introduction caused massive controversy because of the loud noises emanating from the jets during takeoff, landing, and sonic boom.

But regular, standard speed airplanes also make a lot of sound, and so getting rid of the Concorde was just the first step in a worldwide effort to reduce the noise pollution resulting from air travel.

A research team at Cambridge and MIT called the Silent Aircraft Initiative is designing a new type of airplane that will be virtually silent outside the boundaries of airports. This experimental jet will have a radically different shape than today’s plans, with its wings blended directly into the delta-shaped body, encouraging lift and reducing drag. Engines will be located above the fuselage so that their sounds will be muted; their exhaust pipes will be mutable in form, able to adjust to different power demands. Wings will be specially shaped at the leading and trailing edges to promote reduced noise.

The overall effect would be a jet not only much quieter than existing planes, but also with about 50% higher passenger mileage per gallon. As a result this “Silent Aircraft” would be quite fuel efficient.

Hydrogen Airplanes

In the car industry, hydrogen has long been bookmarked as the “fuel of the future” — the world has a virtually unlimited supply of the gas once it has been extracted from water, and when using fuel cells, it can be burned emissions-free. Similarly, airplane manufacturers have looked into using hydrogen technology for flight, with the assumption that similar advances would eventually allow airlines to fly without releasing carbon.

Preliminary research has been done using military drone planes, operated without a human pilot. The U.S. Army recently experimented with the “Orion”, whose hydrogen power gives it a special property: the ability to stay aloft for four days straight. That could be quite beneficial for future spy planes. The problem? The test vehicle can only carry about 400 pounds of cargo.

Last year, Boeing introduced the first piloted hydrogen aircraft. The tiny plane, only capable of holding one person on board, ascended to 3,300 feet on a battery and then cruised using its hydrogen reserves at 60 mph for twenty minutes.

To put it mildly, the technology is still limited by capacity problems — and it’s hard to conceive of a hydrogen-powered commercial airplane in the next few decades, absent some unforeseen advance. No manufacturer has so far been able to overcome the significant problems with the fuel, including extracting it from water, storing it without causing explosions, and using it safely at extreme temperatures. Yet once those barriers fall, we can all make like the 1960′s and fly guilt-free again.

Con trails photo

Tags: NEWFANGLED THINGS