Final Report Summary - ADFLICO (Adaptive Flight Control for Advanced Aircraft Concepts)
Worldwide aviation traffic is predicted to increase manifold, putting challenges on the safety and environmental impact of air transport. Safety as well as “green” aircraft fit in the EU FP 7 Research Vision for Aeronautics. This will require advanced aircraft concepts. Advances in the development of nonlinear and adaptive control theory turn these control algorithms into enabling technologies for these advanced aircraft concepts. Two important examples are fault tolerant and next generation "green” aircraft. In the former category, a Fault Tolerant Flight System (FTFS) is capable to detect and adapt to changes in the aircraft behaviour. For next generation "green” aircraft to enforce energy efficiency and environmental compatibility (fuel consumption, emissions and noise), nonconventional strategies are required to control them.
Therefore, this project has focused on some key aspects of reconfigurable flight systems for these new concepts. In his PhD, the researcher has already focused on system identification and adaptive control. However, flight envelope estimation and flight path prediction, considered in this research project, are other crucial aspects which need to be included in the global setup of technological solutions for safety. This approach differs from others since it is physically inspired. This more transparent approach allows interpreting data in each step, and it is assumed that these physical models based on flight dynamics theory will therefore facilitate certification for future real life applications.
A nonlinear aircraft model has been used to develop an overall unified approach to estimate online the trim and manoeuvrability envelopes of the aircraft. A computationally efficient algorithm has been developed for estimating these envelope boundaries. Probabilistic methods are used to estimate the trim envelope through efficient high-fidelity model-based computations of attainable equilibrium sets. The corresponding manoeuvrability limitations of the aircraft are determined through a robust reachability analysis (relative to the trim envelope) through an optimal control formulation while making use of time scale separation and taking into account uncertainties in the aerodynamic derivatives. This method is by design suitable for the adaptive characterization of altered safe manoeuvring limitations based on aircraft performance after configuration changes or impairment. The results can be used to increase situational awareness of the flight crew by providing pilot feedback and/or be combined with flight planning, trajectory generation, and guidance algorithms to help maintain safe aircraft operations in both nominal and off-nominal scenarios. An implementation and evaluation in a relevant environment of this computationally efficient algorithm for estimating the safe manoeuvring envelope of aircraft has been done. The flight envelope limits are indicated in three axes on the primary flight display. These display features have been evaluated in the Advanced Concepts Flight Simulator (ACFS) at NASA Ames Research Center to investigate the impact on aircraft energy state awareness of the crew. Commercial airline crews flew multiple problematic approach and landing scenarios in a relevant environment. Results have showed that the additional display features have the potential to improve situational awareness of the crews and reduce the crew workload.
In a subsequent stage, this flight envelope information has been used for adaptive flight envelope protection. An efficient safe flight envelope protection method has been developed, for keeping a closed loop aircraft with manual control laws within the safe envelope bounds. This algorithm has been demonstrated as a concept, as well as evaluated with piloted simulations. The updated information of the safe envelope, as discussed before, is used in the flight control laws to prevent loss of control in flight. It has been found that a control architecture involving separate pilot command filtering is particularly well suited to incorporate these adaptive protections. This algorithm has been implemented in the DLR Robotic Motion Simulator at DLR Oberpfaffenhofen as a concept demonstration. Moreover, haptic feedback to the pilot controls can be included as well in this set up, based on the same adaptive bounds. This has the potential to further increase the flight crew awareness about the risk of losing control in flight. These algorithms have been evaluated in the Simona Research Simulator at Delft University of Technology, to investigate the impact on the awareness of the crew. Commercial airline crews flew multiple challenging approach and landing scenarios in a relevant environment. Results show that the algorithms support the flight crew significantly. They contribute to ’care-free’ flying and to avoiding loss of control in flight.
The photograph depicts the simulator set up at DLR, including the robotic motion simulator, outside visualisation and the primary flight display with adaptive envelope bounds.
Therefore, this project has focused on some key aspects of reconfigurable flight systems for these new concepts. In his PhD, the researcher has already focused on system identification and adaptive control. However, flight envelope estimation and flight path prediction, considered in this research project, are other crucial aspects which need to be included in the global setup of technological solutions for safety. This approach differs from others since it is physically inspired. This more transparent approach allows interpreting data in each step, and it is assumed that these physical models based on flight dynamics theory will therefore facilitate certification for future real life applications.
A nonlinear aircraft model has been used to develop an overall unified approach to estimate online the trim and manoeuvrability envelopes of the aircraft. A computationally efficient algorithm has been developed for estimating these envelope boundaries. Probabilistic methods are used to estimate the trim envelope through efficient high-fidelity model-based computations of attainable equilibrium sets. The corresponding manoeuvrability limitations of the aircraft are determined through a robust reachability analysis (relative to the trim envelope) through an optimal control formulation while making use of time scale separation and taking into account uncertainties in the aerodynamic derivatives. This method is by design suitable for the adaptive characterization of altered safe manoeuvring limitations based on aircraft performance after configuration changes or impairment. The results can be used to increase situational awareness of the flight crew by providing pilot feedback and/or be combined with flight planning, trajectory generation, and guidance algorithms to help maintain safe aircraft operations in both nominal and off-nominal scenarios. An implementation and evaluation in a relevant environment of this computationally efficient algorithm for estimating the safe manoeuvring envelope of aircraft has been done. The flight envelope limits are indicated in three axes on the primary flight display. These display features have been evaluated in the Advanced Concepts Flight Simulator (ACFS) at NASA Ames Research Center to investigate the impact on aircraft energy state awareness of the crew. Commercial airline crews flew multiple problematic approach and landing scenarios in a relevant environment. Results have showed that the additional display features have the potential to improve situational awareness of the crews and reduce the crew workload.
In a subsequent stage, this flight envelope information has been used for adaptive flight envelope protection. An efficient safe flight envelope protection method has been developed, for keeping a closed loop aircraft with manual control laws within the safe envelope bounds. This algorithm has been demonstrated as a concept, as well as evaluated with piloted simulations. The updated information of the safe envelope, as discussed before, is used in the flight control laws to prevent loss of control in flight. It has been found that a control architecture involving separate pilot command filtering is particularly well suited to incorporate these adaptive protections. This algorithm has been implemented in the DLR Robotic Motion Simulator at DLR Oberpfaffenhofen as a concept demonstration. Moreover, haptic feedback to the pilot controls can be included as well in this set up, based on the same adaptive bounds. This has the potential to further increase the flight crew awareness about the risk of losing control in flight. These algorithms have been evaluated in the Simona Research Simulator at Delft University of Technology, to investigate the impact on the awareness of the crew. Commercial airline crews flew multiple challenging approach and landing scenarios in a relevant environment. Results show that the algorithms support the flight crew significantly. They contribute to ’care-free’ flying and to avoiding loss of control in flight.
The photograph depicts the simulator set up at DLR, including the robotic motion simulator, outside visualisation and the primary flight display with adaptive envelope bounds.