| Aerospace

Flight Controller Software Protects Lightweight, Flexible Aircraft

Flutter prevention software can be used for better control of farm equipment, robots, and drones.

NASA has made profound contributions to aviation, including advancing our understanding of flight mechanics and devising ways to improve aircraft performance. In the late 1980s, NASA participated in the development of Robust Control theory, which aims to provide automated stability to a structure in response to various external forces. An important resulting application is called gain scheduling, whereby electronic controllers are programmed to apply those split-second changes.

Two pilots operate the X-56A MUTT from a ground control station.
In response to data picked up by onboard sensors, automated controllers are able to direct ailerons (hinged control surfaces attached to wings), rudders, and elevators to shift the plane’s trajectory, prevent structural damage, and otherwise improve flight quality for passengers.

In the early 2000s, a new type of airliner was drawn up called a lightweight, flexible aircraft. The plane’s body and wings would be made of lighter materials — carbon fiber instead of metal, for example — resulting in drastic reduction of fuel needed for transport and longer flight distances. But reducing a wing’s heft also increased susceptibility to a dangerous condition called flutter — uncontrollable vibrations that can cause a wing to break apart.

For lightweight, flexible aircraft technology to become viable, NASA advanced Linear Parameter-Varying Control (LPV) theory to account for the aeroelastic conditions that bring about flutter. Now the agency needed new gain scheduling tools capable of applying the theory so controllers could be programmed to prevent the dangerous occurrence.

Researchers at Armstrong Flight Research Center used the technology to synthesize flight control algorithms for an unmanned, lightweight, flexible aircraft called the X-56A Multi-Use Technology Testbed (MUTT). Developed by Lockheed Martin for the Air Force Research Laboratory, the X-56A MUTT’s successful deployment of flutter suppression algorithms would be an important step toward making lightweight, flexible aircraft technically feasible.

Founded in the early 1990s, MUSYN Inc. (Minneapolis, MN) was among the first companies to build on NASA’s Robust Control theory research and develop a software program, aptly named the Robust Control Toolbox (distributed by MathWorks of Natick, MA), to help manufacturers design controllers for their aircraft at specific flight conditions. In the late 1990s, when NASA’s new theories on flutter suppression arrived on the scene, the firm once again began working on a complementary set of software tools. In 2010, NASA put out a call for such a software program to be created.

The company’s proposal was approved, and later that year, NASA and MUSYN entered into a Small Business Innovation Research (SBIR) Phase I contract, followed by Phase II funding the following year. Much of MUSYN’s work centered on building on the software and theory developed for the Robust Control Toolbox, and overcoming its limitation: it can analyze the flight conditions of speed, altitude, and angle of attack only one point at a time. That means you’d have to look separately at conditions during takeoff, landing, and cruise altitude, and everything in between.

By 2013, MUSYN had overcome that roadblock with its LPVTools software toolkit that can synthesize flight control algorithms and set a controller’s gain schedule for not just a single point in time, but the entire duration of an airplane’s flight.

The software was made commercially available in 2014, and aircraft manufacturers designing similar lightweight, flexible aircraft will want to use the software. But the application is more than just a flutter prevention tool. Farming equipment companies, for example, can utilize the software to set controls for engines and active suspensions. Industrial plants that employ robots, and companies that develop unmanned aerial vehicles such as drones, can also benefit from the programming technology.

Visit http://spinoff.nasa.gov/Spinoff2015/t_3.html