As we've seen with the ongoing X-Prize model, competitions can be a great way to provide incentive for technological advancements in transport. While the latest example, the Lunar X Prize, has its sight set on the heavens, NASA is running a competition with objectives a little closer to the ground. The Green Flight Challenge is enticing creative types with a USD$1.5 million prize in which designers need to create an aircraft that is low cost, quiet, has a short take-off, is 'road worthy' and gets excellent passenger-miles per gallon.

Hopeful entrants have until July 2011 to dream up and perfect a light aircraft, with the most likely end-market being PAVs (Personal Air Vehicles - check out our personal flight gallery for more developments). To the uninitiated, this is the closest we’re going to get to 'flying cars' in the foreseeable future without recruiting wild-haired scientists and DeLorean DMC-12s.

NASA’s light-aircraft collaborator CAFE (Comparative Aircraft Flight Efficiency) is running the competition and also is involved in PAV development. Key requirements are low cost, quiet operation, short take-off and ideally the ability to for the craft to fold up its wings and career around on a road until the driver/pilot feels the need to take to the skies. PAVs would require no more training than car drivers and though it sounds a bit far-fetched at this stage of development, the idea seems to have enough backing from high-profile suitors to suggest that it could become a reality.

The green credentials of such a craft are the focus of this particular challenge though, where the highest possible passenger-miles per gallon and cruise speed will take a higher priority.

CAFE states that: "A variety of innovative experimental aircraft that fly with either electricity, solar, bio-fuel or hybrid propulsion are expected to enter."

There's also a $150,000 prize for best score by a bio-fueled aircraft is also offered.

This brings us to the Pipistril, a battery powered glider that can reach heights of 6000 feet, that is expected to do well after further development. In order to enter the contest the Pipistril, like all other entrants, will need to match or beat a minimum of 200 passenger-miles per gallon in order to prove itself as a viable green alternative to a car.

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