Flight Envelope Protection System Research Articles

Flying by Feeling: Communicating Flight Envelope Protection through Haptic Feedback

ABSTRACT Modern aircraft can be equipped with a flight envelope protection system: automation which modifies pilot control inputs to ensure that the aircraft remains within the allowable limits. Overruling the pilot inputs may lead to mode confusion, even when visual or auditory feedback is provided to alert pilots. We advocate using active control devices to make the flight envelope protection system tangible to the pilot. This paper presents the main findings of an evaluation of three haptic feedback designs for flight envelope protection. The first concept used both force feedback and vibro-tactile alerts, producing promising, yet inconclusive, results. The second concept used asymmetric vibrations to give directional alerting cues, which did not result in improved performance on initial use, but which did yield improved learning rate for the task. The third system employed force feedback to physically guide the pilot away from flight envelope limits, which yielded safety improvements from the first use, but created dependence: pilot performance degraded immediately after the force feedback was removed. From this, we advise to use asymmetric vibrations during training for flight envelope excursions, to leverage active control interfaces for providing force feedback during operation, and reevaluate a combination of both to combine their advantages for single-pilot operations.

Database-Driven Safe Flight-Envelope Protection for Impaired Aircraft

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.

Online Safe Flight Envelope Protection for Icing Aircraft Based on Reachability Analysis

Icing encountered by an aircraft in flight can pose a great threat to flight safety, which is the foremost concern in aviation. Ice accretion has nonlinear and coupling properties, and therefore, a conventional envelope protection system cannot successfully deal with the condition. A safe flight envelope based on reachability analysis is proposed in this paper as a basis for designing an online envelope protection system for aircraft under icing conditions. This system uses a neural network method to identify changes in the aerodynamic coefficients and to classify the degrees of icing and uses a database-driven approach to solve the onboard safe flight envelope computation problem. The database of icing safe flight envelopes is created offline and can be retrieved in real time. The Research Civil Aircraft Model (RCAM) encountering icing conditions in the climbing phase was taken as an example to verify the feasibility of the online safe flight envelope protection system. The simulation results showed that the system can classify the degrees of icing efficiently, prevent the aircraft from deviating from the safe flight envelope, guide it back to the envelope along the fastest path, and reduce the risk of loss of control under icing conditions.

Design of a Haptic Feedback System for Flight Envelope Protection

Several modern aircraft use a passive control manipulator: a spring–damper system that generates command signals to the flight control computers in combination with a flight envelope protection system that limits pilot inputs when approaching the aircraft limits. This research project aims to increase pilot awareness of this protection system through the use of force feedback on the control device, that is, haptics. This paper describes in detail how the haptic feedback works and when it triggers; another paper will discuss the results of an experimental evaluation. With the current haptic design, pilots can get five cues: first, a discrete force cue when approaching the limits; second, an increased spring coefficient for control deflections that bring the aircraft closer to its limits; third, a stick shaker for low velocities; fourth, if a low-velocity condition requires an input, the stick is moved forward to the desired control input; and finally, the stick follows the automatic Airbus “pitch-up” command during an overspeed condition. This novel system is expected to help pilots correctly assess the situation and decide upon the right control action. It will be evaluated in two scenarios close to the flight envelope limits: a windshear and an icing event.

Probabilistic Flight Envelope Estimation with Application to Unstable Overactuated Aircraft

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-constraint-based 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.

Automation Situation Awareness Display for a Flight Envelope Protection System

This paper presents an interface system display that is conceived to improve pilot situation awareness with respect to a flight envelope protection system, developed for a midsized transport aircraft. The new display is designed to complement existing cockpit displays by augmenting them with information related to both aircraft state and control automation. In particular, the proposed display provides cues about the state of automation directly in terms of pilot control actions, in addition to flight parameters. The paper also presents results of a piloted simulation-based evaluation, which was designed to validate the developed interface by assessing the relevance of the displayed information, as well as the adequacy of the display layout.

Adaptive Control Within a Flight Envelope Protection System

An adaptive control augmentation is presented for desired systems containing a feedforward term and is applied to a controller within a flight envelope protection system for a transport-class aircraft. By recovering the baseline controller’s nominal performance in the presence of failures and disturbances, the proposed controller is able to improve aircraft performance, reducing pilot workload and allowing pilots to focus their attention on determining a course of action to prevent the offnominal condition from propagating into a loss-of-control sequence. Combined with the flight envelope protection system and other technologies, the proposed algorithm can form an integrated system for preventing aircraft loss of control. Nonlinear simulation results show the efficacy of the proposed control law.

Design of a Flight Envelope Protection System for NASA’s Transport Class Model

This paper presents a flight envelope protection system for NASA’s Transport Class Model. The developed protection scheme is based on a command-limiting architecture that accounts for aircraft adverse aerodynamics, unusual attitude, and structural integrity and is designed to augment a standard gain-scheduled flight control law. The scheme also includes an energy protection system, which relies on an automatic throttle control loop that implements a total energy control law. In the setup adopted, the limits of the protected envelopes are actively adjusted to ensure, on the one hand, that the aircraft always stays in a safe flight condition and, on the other hand, that the pilot has enough control authority to perform aggressive maneuvers, if needed. Batch simulations demonstrate the efficacy of the protection system in maintaining the aircraft within desired safe conditions.

Design and evaluation of a Flight Envelope Protection haptic feedback system

Abstract: This paper describes the design and evaluation of a shared control, haptic feedback system to communicate Flight Envelope Protection System intent. The concept uses a combination of stiffness feedback and vibration to communicate proximity of the aircraft state to flight envelope boundaries. In addition, a stick center shift can be applied by the envelope protection system to cooperatively perform corrective actions in case of severe excursions of the envelope margins. Results from the evaluation experiment show improved performance with haptic feedback in both scenarios. Workload ratings were unaffected. Pilot opinion was unanimously positive, especially with regard to the combination of stiffness feedback and vibration cues.

Flight envelope protection of aircraft using adaptive neural network and online linearisation

Flight envelope protection algorithm is proposed to improve the safety of an aircraft. Flight envelope protection systems find the control inputs to prevent an aircraft from exceeding structure/aerodynamic limits and maximum control surface deflections. The future values of state variables are predicted using the current states and control inputs based on linearised aircraft model. To apply the envelope protection algorithm for the wide envelope of the aircraft, online linearisation is adopted. Finally, the flight envelope protection system is designed using adaptive neural network and least-squares method. Numerical simulations are conducted to verify the performance of the proposed scheme.

Design of a Flight Envelope Protection System Using a Dynamic Trim Algorithm

Most large commercial aircrafts and high performance military aircrafts use fly-by-wire (FBW) or fly-by-light systems to improve their controllability, comfort, and safety. A flight envelope protection technique is used with flight control systems utilizing the FBW technique. Such flight envelope protection systems prevent these aircraft from exceeding the structural/aerodynamic limits and control their surface limits. This is accomplished by predicting the values of the future state variables and adaptively compensating the control action. In this study, the conventional dynamic trim algorithm of the flight envelope protection is modified to increase the method accuracy and to handle cases with multiple variables. Numerical simulation is also performed to verify the performance of the proposed method.

Investigation of Practical Flight Envelope Protection Systems for Small Aircraft

Personal air transportation using small aircraft is a market that is expected to grow significantly in the near future. However, seventy times more accidents occur in this segment as compared with commercial aviation. The majority of these accidents is related to handling and control problems, which are closely linked to the experience level of the pilots. In commercial aviation, the combination of fly-by-wire technology and flight envelope protection is used to prevent these types of accidents. Instead of downscaling advanced and high-cost fly-by-wire platforms, a low-cost solution should be considered for the general aviation market. This paper focuses on a flight envelope protection system for small aircraft. Preliminary results are obtained from an empirical comparison study in the time domain between a proportional-integral-derivative-based control limiting approach, a command limiting approach, a constrained flight control law approach using model-based predictive control and incremental nonlinear dynamic inversion, and a virtual control limiting approach, which also uses incremental nonlinear dynamic inversion. Comparison is done not only using a nominal model but also in cases of parametric uncertainty, sensor noise, time delays, wind gusts, and turbulence. Investigation of the results reveals that, for this study, control limiting should be avoided, and for practical implementation command limiting is the best option.

항공기의 수평속도에 대한 비행영역 보호 시스템 설계

Recently developed aircrafts use Fly-By-Wire(FBW) or Fly-By-Light(FBL) system. These systems have some merits; they can perform very complicated missions, they can expand the flight region and improve the reliability of the aircrafts. With the development of flight control systems that use FBW technique, flight envelope protection concept is introduced to guarantee reliability of the aircraft and improve the efficiency of mission achievement. In this study, flight envelope protection system is designed using a dynamic trim algorithm, a peak response estimation, and a gain scheduling technique. The performance of these methods are compared by performing numerical simulation.

Path Planning for Autonomous Vehicles by Trajectory Smoothing Using Motion Primitives

We present a novel planning strategy which is applicable to high performance unmanned aerial vehicles. The proposed approach takes as input a 3-D sequence of way-points connected by straight flight trim conditions, and ldquosmoothsrdquo it in an optimal way with the goal of making it compatible with the vehicle dynamics. The smoothing step is achieved by selecting appropriate sequences of alternating trims and maneuvers from within a precomputed library of motion primitives. The resulting extremal trajectory is compatible with the vehicle and therefore trackable with small errors; furthermore, it is guaranteed to stay within the flight envelope boundary, alleviating the need for flight envelope protection systems. Yet it can be computed in real-time using closed-form expressions, all nonlinearities due to the vehicle model being confined to the stored library of motion primitives. The new method is demonstrated for the aggressive maneuvering of a helicopter.