NASA Flies Hybrid Electric VTOL
NASA has flown its tilt-rotor hybrid electric concept aircraft and hopes it will result in a practical VTOL unmanned aircraft. Greased Lightning flew for the first time Aug. 19 (tethered) and it represents a new take on an old design first pioneered by Canadair in the 1950s and used by the V-22 Osprey. The wings and tail surfaces swivel, allowing the engines to be turned into lifting rotors. In Greased Lightning's application, however, most of the engines are shut down for cruise flight and the rotors/props fold to reduce drag.
The engines are powered by a bank of high-density lithium-ion batteries that are charged in flight by a couple of 8-horsepower diesel engines driving alternators. The diesels are housed in the fuselage. Although Greased Lightning is about the size of a big RC model aircraft, NASA says the concept is "scale free," meaning it could be used on much larger aircraft. Untethered flights are planned for later this year.