Unsteady aerodynamics and flow control for flapping wing flyers

Active flutter suppression, which is a part of the group of flight vehicle technologies known as active controls, is an important contributor to the effective solution of aeroelastic instability pr...

https://arc.aiaa.org/doi/pdf/10.2514/1.C034442

Aircraft Active Flutter Suppression: State of the Art and Technology Maturation Needs

This paper demonstrates the importance of analyzing proposed modern control system designs with classical frequency response techniques. When classical constraints such as open-loop crossover frequency are ignored, apparently robust modern control designs may go unstable for relatively innocuous plant perturbations. Modern control system designs of successively more complex plants are analyzed to reveal some problems that may occur in the design of real systems and to show how these problems can be solved so that modern control methods will be more useful to practical'control system designers.

Why Modern Controllers Can Go Unstable in Practice

In this paper, an adaptive feedforward control framework is proposed for the suppression of aircraft structural vibrations induced by gust perturbations to increase the resilience of the !ight control law in the presence of the aeroelastic/aeroservoelastic interactions. Currently, aircraft with nonadaptive control laws usually include roll-off or notch "lters to avoid aeroelastic/aeroservoelastic interactions. However, if changes in the aircraft con"guration aresigni"cant,the frequencies of the!exible modesof the aircraft may beshifted, andthe notch"lterscould become totally ineffective. With the proposed approach, the !exible modes can be consistently estimated in real time via a proven system-identi"cation algorithm. The identi"ed !exible modes information is used in the proposed adaptive feedforwardcontrolalgorithmtoadjusttheparametrizationofthebasisfunctionsinafeedforwardcontroller.Along with the recursive least-squares estimate, the feedforward controller is adjusted, and the structural vibration of the aircraft induced by the gust perturbation can be largely suppressed. An F/A-18 active aeroelastic wing aeroelastic model with gust perturbation based on the linear aeroelastic solver formulation is developed as a test bed to demonstrate the proposed adaptive feedforward control algorithm.

/pdf/adaptive-feedforward-control-for-gust-load-alleviation-56rj3k4n4j.pdf

Adaptive Feedforward Control for Gust Load Alleviation

This paper describes an analytical and experimental investigation into the use of active lifting surfaces with distributed strain actuators for dynamic aeroelastic control A detailed analytical aeroelastic model is developed for analysis and control law design using the Rayleigh-Ritz assumed mode method, kernel function unsteady aerodynamics, and modern state-space techniques The models are used to design multivariable dynamic compensators for applications such as gust alleviation, command following, and flutter suppression The effectiveness of the control laws is assessed analytically and verified experimentally through closed-loop wind-tunnel testing The experiments demonstrate that distributed strain actuation can be effectively employed for aeroelastic control, with gust alleviation of 8-dB broadband and an increase in flutter speed of 11 %

Multivariable active lifting surface control using strain actuation : Analytical and experimental results

This paper describes the application of linear quadratic Gaussian (LQG) methodology to the design of active control systems for suppression of aerodynamic flutter. A wind tunnel model of a research wing with associated sensors and actuators comprises the system to be controlled. Results of a synthesis methodology that provide small values of rms response and robust stability are presented. Results of control surface and sensor position optimization are also presented. Both frequency response matching and modal residualization are used to obtain practical flutter controllers. Scalars b c E( ) h (x,y,t) J km /_ q s t u V w x,y

Control Law Synthesis for Flutter Suppression Using Linear Quadratic Gaussian Theory

Additional insight is provided into the use of the Doyle-Stein (1979, 1981) technique in aeroelastic control problems by examining the application of the method to a flutter control problem. The system to be controlled consists of a full-size wind tunnel model of a wing, plus an aileron, an actuator, and an accelerometer used to sense the motion of the wing. A full-state feedback controller was designed using linear optimal control theory, and a Kalman filter was used in the feedback loop for state estimation. The filter design procedure is explained along with that to improve closed-loop properties of the system. The locus of the poles of the filter is examined as a scalar design parameter is varied. The Doyle-Stein design procedure is shown to substantially improve the stability properties of an active flutter controller designed using the linear quadratic Gaussian control theory.

Robust Kalman filter design for active flutter suppression systems

This paper describes the application of Linear Quadratic Gaussian (LQG) methodology to the design of active control systems for suppression of aerodynamic flutter. A full-size wind tunnel model of a supercritical wing with associated sensors and actuators comprises the system to be controlled. Results of a synthesis methodology that provide small values of rms response, insensitivity to flight condition, and robust stability are presented. Results of control surface and sensor position optimization are also presented. Both frequency response matching and residualization are used to obtain practical flutter controllers.

J. K. Mahesh

Papers

Control Law Synthesis for Flutter Suppression Using Linear Quadratic Gaussian Theory

Robust Kalman filter design for active flutter suppression systems

Active flutter suppression using Linear Quadratic Gaussian theory