Active/Adaptive Flexible Motion Controls with Aeroservoelastic System Uncertainties

Most aeroservoelastic analyses of modern aircraft have uncertainties associated with model validity. Test-validated aeroservoelastic models can provide more reliable flutter speed. Tuning the aeroservoelastic model using measured data to minimize the modeling uncertainties is an essential procedure for the safety of flight. However, uncertainties still exist in aeroservoelastic analysis even with the test-validated aeroservoelastic model due to time-varying uncertain flight conditions, transient and nonlinear unsteady aerodynamics and aeroelastic dynamic environments.

For flexible motion control problems, we need a control law that adapts itself to such changing conditions. Active and adaptive control of these coupled mechanisms is mandatory for stabilization and optimal performance in such time-varying uncertain flight conditions. The basic concept behind adaptive control is the ability to follow the system changes during flight. The most attractive feature of this approach is the ability to handle mildly time-varying nonlinear systems, such as encountered in transonic aeroelasticity. Therefore, the proposed control technique is applicable for the linear subsonic and supersonic aeroelasticities as well as mildly nonlinear transonic aeroelasticity.

The primary objective of this research is to study the application of a digital adaptive controller to the flexible motion control problems. This can be achieved by introducing online parameter estimation together with online health monitoring. Structural response information at the selected sensor locations will be used for the online parameter estimation. The second objective of this research is to develop a simple methodology for minimizing uncertainties in an aeroservoelastic model.

Work to date: The team has modeled known uncertainties.

Looking ahead: Future activities involve further refinement of the models, which will involve flight tests currently planned for 2015.

Partners: Lockheed Martin Advanced Development Program has provided the X-56A finite element model and test data. The Air Force Research Laboratory will provide X-56A vehicles and ground control systems. Other NASA centers have contributed to this effort, as well as the University of Texas at Austin.

Benefits

• Economical: Enables high-precision simulation prior to expensive flight tests
• Smoother ride: Permits superior ride quality control

Applications

• Resulting models apply across a wide range of aircraft