Traditional methods of flight flutter testing analyze system parameters such as damping levels that vary with flight conditions to monitor aircraft stability. In the past, the actual flight envelope developed for aircraft operation was essentially determined only by flight testing. The edges of the envelope are points where either the aircraft cannot fly any faster because of engine limitations, or, with a 15% margin for error, where the damping trends indicate a flutter instability may be near. After flight testing, the envelope empirically determined is used for regular operations.

An online method of producing a robust flutter margin envelope was developed that is essentially model-based so that it not only has the desired predictive nature of a traditional method, but also uses flight test data to obtain the desired accuracy of predictive estimates. This combines the strengths of both the traditional p-k method and the new method of online estimation of the damping method. This new method, referred to as a unique .mu. method of flight testing for flutter margins, is for online flight test prediction based on both analysis data of the aircraft model and flight test data in order that analysis data be updated during the testing procedure for continual correction of the aircraft model data.

The method may be used for flight testing or post-flight analysis of aircraft flying at or near flutter boundaries. During flight testing, the technology can compute flutter margins at each test point and calculate an optimal flight envelope. The in-flight data is acquired through accelerometers, strain gauges, Armstrong’s fiber optic strain sensor (FOSS) system, or other structural or aerodynamic sensors, depending on the application and modeling.

This work was done by Richard C. Lind and Martin J. Brenner of Armstrong Flight Research Center. NASA is actively seeking licensees to commercialize this technology. Please contact the NASA Armstrong Technology Transfer Office at 661-276-3368 or by e-mail at This email address is being protected from spambots. You need JavaScript enabled to view it. to initiate licensing discussions. Follow this link for more information: .