Hot-Air Plane

by Barry Fox NewScientist.com, 29 Nov 2005 A drone aircraft powered by a 200-year-old engine design is the latest concept under wraps at Lawrence Livermore National Laboratory in California. The Stirling engine uses temperature difference to activate its gas-filed pistons. The engine is efficient at generating mechanical power, although slow. But the lab thinks it could be ideal for use in a solar-powered aircraft that needs to fly throughout the night on stored energy. Instead of using solar cells to convert sunlight to electricity, and storing this in rechargeable batteries, the new plane will use a thermal battery that stores heat in order to drive its Stirling engine. During the day, sunlight will be used to heat a mix of lithium and lithium hydride and a moving parabolic mirror will keep track of the Sun to focus its rays on the thermal store. While the Sun's rays will provide heat for the engine's gas, the cold air outside the plane will provide an ideal way of lowering its temperature. Read the hot-air plane patent