LOS ANGELES — Researchers are installing the first set of flexible wings on the X-56A Multi-Utility Technology Testbed (MUTT) to prepare for flight tests designed to probe to the edge, and beyond, of the destructive flutter envelope.
Built by Lockheed Martin Skunk Works, the 28-ft.-span unmanned aircraft has been specially designed to test control technologies to counter flutter, a potentially catastrophic aeroelastic instability to which aircraft with slender, high-aspect ratio wings are particularly vulnerable. The research is vital as long, thin wings are considered key to the design of many potential future unmanned, long-range surveillance systems and fuel-efficient transport concepts.
The U.S. Air Force Research Laboratory (AFRL) and NASA therefore plan to use the MUTT to evaluate flutter suppression and gust-load alleviation technologies. But before the work can begin, initial flight testing has been under way to characterize the basic flying qualities and clear the envelope of the X-56A with conventional wings. Flight tests have been conducted from the relatively secluded North Base at Edwards AFB, Calif., since early August.
Eight flights were completed during this first phase, some of which included tests of a revised nose leg damping design which incorporates a motorcycle part to overcome a “pogo” effect uncovered with the original configuration. The downtime for the wing retrofit also includes uploading new software into the flight control system, which will attempt to suppress aeroelastic instabilities in real time. These will be induced by transferring water ballast in the wing in flight to change the mass distribution and mode frequencies.
Given the realistic potential for inflight wing failure, the fuselage is equipped with a ballistic parachute recovery system. Lockheed has built two fuselages and multiple wing sets. In addition to the initial conventional wings, the aircraft will be tested with up to three sets of flexible wings.