Rajeev Chandramohan

Guidance and Control of Airplanes Under Actuator Failures and Severe Structural Damage

This paper presents control algorithms for guidance and control of airplanes under actuator failures and severe structural damage. The presented control and guidance algorithms are validated through experimentation on the Georgia Institute of Technology Twinstar twin engine, fixed-wing, unmanned aerial system. Damage scenarios executed include sudden loss of all aerodynamic actuators resulting in propulsion-only flight, 25% of the left wing missing, sudden loss of 50% of the right wing and aileron in-flight, and injected actuator time delay. A state-dependent guidance logic is described that ensures the aircraft tracks feasible commands in the presence of faults. The commands are used by an outer-loop linear controller to generate feasible attitude commands. The inner-loop attitude control can be achieved by using either a linear attitude controller or a neural network-based model reference adaptive controller. The results indicate the possibility of using control methods to ensure safe autonomous flight ...

Vortex Model Based Adaptive Flight Control Using Synthetic Jets

Presented at the AIAA Guidance Navigation and Control Conference, Chicago, Illinois, August, 2009.

Flight Test Results of Adaptive Controllers in Presence of Severe Structural Damage

rst is a proven MRAC based method employing a single hidden layer NN. The second is the recently introduced Derivative Free MRAC (DFMRAC) method. The results establish the feasibility of these methods for ensuring safe autonomous ight in presence of severe structural faults.

Experimental Results for Kalman Filter Modication in Adaptive Control

Modern flight control systems are expected to perform beyond their conventional flight envelopes and exhibit robustness and adaptability to uncertain environments and failures. Adaptive control has been shown to improve the performance of a flight control system in the presence of uncertainties and failures. It is well known that modification to standard laws such as e-modification, σ-modification and others are employed in adaptive control schemes to ensure boundedness of the adaptive parameters. In this paper flight test results from a small twin engine aircraft with a novel Kalman filter implementation of of an adaptive loop recovery modification term that preserves loop properties are presented.

Experimental Evaluation of Derivative Free Model Reference Adaptive Control

Modern flight control systems are expected to perform beyond their conventional flight envelopes and exhibit robustness and adaptability to uncertain environments and failures. Adaptive control has been shown to improve the performance of a flight control system in the presence of uncertainties and failures. Recently, a new adaptive design named DF-MRAC has been developed which offers the possibility of improved adaptation and smoother error transient characteristics compared to conventional MRAC designs. In this paper flight test results using a small twin engine aircraft with DF-MRAC design is evaluated and compared with conventional MRAC design in the presence of failures.

A Process to Obtain Robustness Metrics for Adaptive Flight Controllers

*† * ‡ * This research effort seeks a process to draw parallels between the classical stability metrics of gain and phase margins for classical linear control systems with stability margins for adaptive controllers. The method uses a Monte Carlo simulation to yield stability threshold results for the adaptive controller based on problem-specific performance metrics. By fitting a linear controller’s analytical robustness results to the adaptive stability data, the gain and phase margin for the performance-fitting linear system are considered to be the worst case equivalent gain and phase margin for the adaptive controller. This paper also discusses some experiences successfully obtaining time delay margin in a flight test setting.

Flight Test Results for Kalman Filter and H2 Modication in Adaptive Control

Flight control systems designed using linear control theory do not perform adequately over the entire operating range of aircraft. Furthermore flight control systems developed for unmanned areil vehicles are expected to meet performance specifications in the presence of nonlinearities and/or failures. Adaptive controllers are ideal candidates for flight control sytem design due to their inherent ability to adapt to compensate for nonlinearities and or failures. Modification terms like e-modification, σ-modification and others are added to standard adaptive laws to ensure boundedness of the adaptive parameters. In this paper flight test results for Kalman filter implementations of ALR-modification for a Nonlinear in parameters neural network adaptive controller are presented. In addition flight test results of an H2 adaptive control with e-modification are also presented.

Modeling of a 3-DOF Dynamic Wind Tunnel Traverse

A 3-DOF (pitch, plunge, and roll) programmable dynamic traverse has been designed and constructed for dynamic testing of aerodynamic models in the wind tunnel. The system design allows an experimentalist to carry heavy models with all of the needed sensors for evaluating true unsteady aerodynamic flight qualities. Controlling the forces and moments applied to the model allows the experimentalist to drive the model through predetermined trajectories. The desired forces and moments can also be applied to the model independent of the model motion with very low impedance. This allows for the model motion to be controlled by relatively weak aerodynamic forces, essentially simulating free flight in the tunnel, while still providing necessary forcing to remove unwanted effects such as gravity. Using feedback on the applied force and moments, the dynamic characteristics of the model can be actively modified to alter dynamic characteristics such as the system’s natural frequency, damping, and mass and inertia properties. In this paper a dynamic model of the traverse is obtained using experimental data for simulation and control design purposes.

Autonomous Guidance and Control of Airplanes under Severe Damage

This paper presents an overview of the fault tolerant control work performed at Georgia Tech. Flight test results on the Georgia Tech GT Twinstar xed wing twin engine aircraft are presented. The algorithms presented were ight tested under di erent structural damage scenarios, including multiple actuator failures, propulsion only control, ight with 25% left wing missing, and sudden loss of 50% right wing and aileron in ight. A state dependent guidance logic is described that ensures the aircraft tracks feasible commands in presence of faults. The commands are used by an outerloop linear controller to generate feasible attitude commands. The innerloop attitude control can be achieved by using either a linear attitude controller or a neural network based model reference adaptive controller. The results establish the feasibility of using control methods to ensure safe autonomous ight in presence of severe faults for a transport category aircraft.

UAV Flight Control Using Flow Control Actuators

The use of active flow control devices that affect the flow field over the wing and tail planes sufficiently to create moments and forces that can be used for controlling the aircraft has attracted interest over the last decade. Using flow control actuators to control aircraft attitude have several potential benefits as compared to conventional control surfaces. These benefits are in reduced structural weight, lower power consumption, higher reliability and potentially faster response times. This paper presents preliminary flight test results and lessons learned concerning the use of flow control actuators for both open and closed loop control of the DragonEye UAV.