(CNN) — The dream of sustainable air travel is now one step closer to reality, after a team of researchers in Germany flew a plane that emits nothing but water vapor into the atmosphere.
The plane runs on fuel cells -- devices producing an electrical current from a supply of hydrogen and oxygen -- aided by a battery for extra oomph during takeoff.
The four-seater aircraft, called HY4, had its maiden flight from Stuttgart Airport in Germany in September. It's the result of a collaboration between aircraft manufacturer Pipistrel, fuel cell specialists Hydrogenics, the University of Ulm and the German Aerospace Center (DLR)'s Institute of Engineering and Thermodynamics.
"This is the first time that somebody has built an airplane that can carry more than one person and which is driven by hydrogen," says Andre Thess, director of the Institute of Engineering Thermodynamics at DLR, who sees HY4 as a major leap toward decarbonizing air travel.
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The team aims to use fuel cells to power small and medium-sized passenger planes, which could change regional air travel and provide an alternative to carbon-emitting airplanes, buses and trains.
Josef Kallo, HY4 project leader at DLR and a professor at the University of Ulm, thinks we could also see emission-free air taxis flying from city to city within the next 20 years.
"Say you want to go between Irvine and Ventura in the Los Angeles area. It can take you between one and a half and three hours if there are traffic jams, but by plane it will take you around 35 to 40 minutes.
"And within a controlled airspace you could have a lot of these planes flying around."
The electrical system is also very quiet compared to conventional planes, as it does not have the same loud combustion roar as a jet engine, which makes it ideal for flying near residential areas, Kallo says.
"I can envision having a lot of these planes landing in the middle of Los Angeles, for example."
The team are also looking at placing the system in larger aircraft.
HY4 is powered by a hybrid fuel cell
Kallo, a pilot himself, says a 40-seater flying a distance of a thousand kilometers may not be far off.
The ultimate goal is to cut carbon emissions from air travel, the researchers say.
Although aviation contribute around 2% to the overall total of global greenhouse gas emissions, for someone looking to cut their personal carbon footprint, flying plays a major part. A flight from London to New York generates roughly as much emissions per person as the average European generates by heating their home for a whole year, according to the European Commission.
The aircraft is powered by a hybrid fuel cell and battery system.
The fuel cells mix a supply of hydrogen and oxygen, which trigger a controlled explosion. This generates an electrical current to power the motor which drives the propeller.
The battery supplies additional power required for takeoff and climbing.
The fuel cell itself is not unlike the science experiments mixing hydrogen and oxygen to spark a small explosion that some may remember from school, Thess says: "But there is no bang. Just electricity and water vapor as the exhaust gas. It's a way of taming this explosion and extracting electric energy directly from hydrogen and oxygen."
Fuel cells are reliable and provide a steady power flow while cruising, but they are not ideal for quick power boosts, which is where the battery comes in handy for takeoff and emergencies, Thess says.
"In the unlikely event that all fuel cells break down, the power of the battery would still be sufficient for a safe emergency landing."
Electric cars and NASA space shuttles already use hydrogen fuel cells for power. The system could theoretically be placed into any small or medium-sized aircraft, according to Thess.
"In a similar way that a Rolls Royce engine can be attached to a Boeing Airbus, our battery hybrid fuel cell systems can in principle be integrated into any aircraft that's already powered with a battery or other means."
The four-seater plane has a maximum distance of 1,500 kilometers
The maiden flight was the first step in showing off this technology to the world. Next on the plane's schedule is a tour around Europe and a flight between San Francisco and New York next year.
There are limits, however, and researchers will spend the next three years testing the system's potential and find out just how high it can go and how it reacts to different temperatures and rapid changes in power requirements.
This plane has an estimated range of 1,500 kilometers, but with a larger plane this could soon increase, Thess says.
"Over the next few years DLR will work on developing a 19 passenger electrically powered aircraft."
With energy storage among the main limitations, those hoping to fly long haul in an electric aircraft will have to wait.
"The vision of having a thousand passengers go 10,000 kilometers could be feasible in 50 years or so," Kallo says.
"Today, the maximum range is around 2,000 kilometers, but if I'm wrong, that would be nice."