Tethered Flight Completed Recently, Free Flight Tests Planned In The Fall

NASA has flown a concept electric-hybrid VTOL aircraft dubbed "Greased Lightning" as part of a study was designed to explore the possibility of combining two diametrically opposed requirements, specifically, high efficiency cruise with vertical takeoff and landing.

The study considered both near-term and higher risk advanced concepts. During the second phase of this study, 35% and 50% scale prototypes were fabricated to analyze and validate the ability of the advanced vehicle concepts to transition from hovering flight to wing borne flight and back again. Currently ongoing in the third phase of this study is a different vehicle concept using the lessons learned from phase two with more substantial resources to design to a greater degree of confidence.

In forward flight the control of Greased Lightning is similar to that of conventional aircraft, with a couple of notable exceptions. Pitch control is accomplished via rotation of an all-moving tail. Due to the inertia of the tail, it will be for low bandwidth control only. Elevators are added to the inboard portion of the tail to provide high bandwidth control. The elevators alone do not provide sufficient pitch control power, but the combination of tail rotation and elevators will sufficiently control the pitch axis of the aircraft.

The wing incorporates six control surfaces that function as both ailerons and flaps, and therefore are called flaperons. These flaperons are located between each pylon. During transition, they deflect trailing edge up in order to increase the stall angle of
attack of the airfoil. Also in hover, the flaperons are used to supplement yaw control as they are washed in the propeller slipstream.

In hover, the vehicle is controlled like most quad copters. Pitch and roll control are accomplished via thrust modulation of the props. Yaw control is accomplished by modulating the thrust of the clockwise versus counter clockwise propeller rotation.

NASA released an image of the first tethered flight of the GL-10 "Greased Lightning" aircraft on Tuesday ... National Aviation Day. Free-flight tests of the aircraft, which has a 10-foot wingspan, are planned in the fall of this year.

NASA says this research has helped the Aeronautics Research Mission Directorate efforts to better understand the potential of electric propulsion across all types, sizes and missions for aviation. The aircraft is one of four being studied by the agency.

FMI: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140001088.pdf