In this paper, an online flight envelope protection system is developed and implemented on impaired aircraft with structural damage. The whole protection system is designed to be a closed loop of several subsystems, including system identification, damage classification, flight-envelope prediction, and fault-tolerant control. Based on the information given by damage classification, the flight envelopes are explicitly retrieved, processed online from the database, and fed into the fault-tolerant controller, which makes the protection system adaptive to a wide range of abnormal conditions. Simulation results show that with envelope protection, loss-of-control accidents are more likely to be prevented, since excessive commands to the controller are restricted based on the updated information of the changed flight envelopes. In this way, the fault tolerance of the impaired aircraft can be effectively enhanced.

@en

In this paper, an online flight envelope protection system is developed and implemented on impaired aircraft with structural damage. The whole protection system is designed to be a closed-loop of several sub-systems, including system identification, damage classification, flight-envelope prediction and fault-tolerant control. Based on the information given by damage classification, the flight envelopes are explicitly retrieved and processed online from the database and fed into the fault-tolerant controller, which makes the protection system adaptive to a wide range of abnormal conditions. Simulation results show that with envelope protection, loss-of-control accidents are more likely to be prevented, since both the controller and pilots are aware of the shrunken flight envelopes after damage and excessive commands are restricted. In this way, the fault-tolerance of the impaired aircraft can be effectively enhanced. @en

This paper proposes a novel and practical framework for safe flight envelope estimation and protection, in order to prevent loss-of-control-related accidents. Conventional analytical envelope estimation methods fail to function efficiently for systems with high dimensionality and complex dynamics, which is often the case for high-fidelity aircraft models. In this way, this paper develops a probabilistic envelope estimation method based on Monte Carlo simulation. This method generates a probabilistic estimation of the flight envelope by simulating flight trajectories with extreme control effectiveness. It is shown that this method can significantly reduce the computational load compared with previous optimization-based methods and guarantee feasible and conservative envelope estimation of no less than seven dimensions. This method was applied to the Innovative Control Effectors aircraft, an overactuated tailless fighter aircraft with complex aerodynamic coupling between control effectors. The estimated probabilistic flight envelope is used for online envelope protection by a database approach. Both conventional state-constraintbased and novel predictive probabilistic flight envelope protection systems were implemented on a multiloop nonlinear dynamic inversion controller. Real-time simulation results demonstrate that the proposed framework can protect the aircraft within the estimated envelope and save the aircraft from maneuvers that otherwise would result in loss of control. @en

Among all the contributors to fatal accidents, in-flight loss of control (LOC-I) remains one of the largest categories, as indicated by statistics of investigations into past civil aircraft accidents. In flight LOC generally refers to accidents in which the flight crew was unable to maintain control of the aircraft in flight, resulting in an unrecoverable deviation from the intended flight path. Compared with other accidents occurrence categories, LOC-I is more challenging to predict and prevent, since it is often the result of a highly complex combination of a wide range of contributing factors. Many in-depth researches into loss of control accidents have been conducted to find out how these events unfold, and to develop effective intervention strategies for preventing LOC. @en

This paper proposes a novel and practical framework for safe flight envelope estimation and protection, in order to prevent loss-of-control-related accidents. Conventional analytical envelope estimation methods fail to function efficiently for systems with high dimensionality and complex dynamics, which is often the case for high-fidelity aircraft models. In this way, this paper develops a probabilistic envelope estimation method based on Monte Carlo simulation. This method generates a probabilistic estimation of the flight envelope by simulating flight trajectories with extreme control effectiveness. It is shown that this method can significantly reduce the computational load compared with previous optimization-based methods and guarantee feasible and conservative envelope estimation of no less than seven dimensions. This method was applied to the Innovative Control Effectors aircraft, an over-actuated tailless fighter aircraft with complex aerodynamic coupling between control effectors. The estimated probabilistic flight envelope is used for online envelope protection by a database approach. Both conventional state-constraint-based and novel predictive probabilistic flight envelope protection systems were implemented on a multi-loop nonlinear dynamic inversion controller. Real-time simulation results prove that the proposed framework can protect the aircraft within the estimated envelope and save the aircraft from maneuvers that otherwise would result in loss of control. @en

A study addresses offline construction of the database. The main focus and contribution of this study are database building and interpolation for the Database-Driven Safe Flight Envelope Prediction System (DEFEND) system. More importantly, through complexity analysis, the database approach is shown to be feasible for onboard real-time implementation within the aircraft control laws. Reachability analysis as the method to compute safe flight envelopes, as the theory provides a set-valued insight into safety and control design of dynamic systems. One advantage of this method is that all possible trajectories can be computed from all available control strategies and initial states, which naturally meets the safety guarantees. The computed results are called reachable sets, which are defined as a set of states that reach a certain target set within a certain time horizon and current control authority. Two sets of envelopes are computed using the level-set method toolbox. One is the pitching envelope, referred to the motion in the longitudinal plane with horizontal tail damage. The other is the rolling envelope, referred to the motion in the lateral plane with wing tip loss.

@en

Safe flight-envelope prediction is essential for preventing aircraft loss of control after the occurrence of sudden structural damage and aerodynamic failures. Considering the unpredictable nature of such failures, many challenges remain in the process of implementing such a prediction system. In this paper, an approach to online safe flight-envelope prediction is proposed that is based on the retrieval of information from offline-assembled databases. One of the key steps of this approach is determining the structural damage of the state of the aircraft by using the identification, detection, and classification methods presented in this paper. The estimated damage cases will lead to structural damage indices in the database corresponding to those safe flight envelopes that are “closest” to the actual safe flight envelope of the damaged aircraft. The feasibility of the proposed database-driven approach is proved by simulation results, where three damage cases are successfully detected and classified.
@en