As the promise of electric cars grows, so too does the potential of electric planes. These aircraft, whose motors are far more efficient, reliable and quiet than internal combustion engines, could help transform how we fly — if a few problems could be solved.

Electric motors are three to four times better than internal combustion engines at driving an airplane propeller. And the reliability of electric motors is "perhaps 10 times or even 20 times that of a piston engine," said Brien Seeley, president of the Comparative Aircraft Flight Efficiency (CAFE) Foundation, an independent flight test agency which hosts NASA'sCentennial Challenges for Aeronautics.