G. Di Rito

Development and experimental validation of real-time executable models of primary fly-by-wire actuators

The availability of practical real-time models of primary flight actuators is a key aspect for performing hardware-in-the-loop simulations of fly-by-wire flight control systems. The solution could be offered by empirical models tuned on experimental data, but this approach would imply that hardware-in-the-loop simulations could be performed only after the actuators have been designed, constructed, and tested. The alternative approach, to which this work refers, is to develop high-fidelity actuator models based on the component physics and to reduce their complexity by trying to obtain a compromise between accuracy of results and real-time execution requirements. In the paper, real-time models of a servo-hydraulic actuator for primary flight controls are developed, taking into account the basic features of the fly-by-wire implementation (the non-linear direct-drive servovalve dynamics, the structural compliance, the oil compressibility, the saturation of commands, and the digital controls) as well as other physical phenomena, which are often disregarded in hydraulic actuator modelling (the hinge play, the flow forces on the servovalve spool, and the laminar servovalve flow). The simulation results of models characterized by different levels of complexity are compared with experimental data obtained by testing the aileron actuator of a modern fly-by-wire aircraft, and the relative importance of the model characteristics is highlighted and discussed, providing useful guidelines about actuator model reduction for real-time applications.

Experimental and theoretical study of the electrical failures in a fault-tolerant direct-drive servovalve for primary flight actuators

The current paper deals with the study of the electrical failures in fault-tolerant flight actuators, with particular reference to the short circuits of the servovalve coils. A high-fidelity model of the servovalve of a modern fly-by-wire actuator is developed and validated through experiments, focusing attention on the characterization of the component dynamics in case of partial and total short circuits of the direct-drive motor coils. The servovalve model is then used to simulate a typical on-ground built-in-test procedure to determine the limit condition for the detection of a partial short circuit. Finally, once different possible combinations of short circuits are injected, the degradation of performances of the whole actuator is characterized through experiments, and the servovalve model is used to justify the test results, highlighting and discussing the effects of the failures on the system dynamics.

Impacts of safety on the design of light remotely-piloted helicopter flight control systems

Abstract This paper deals with the architecture definition and the safety assessment of flight control systems for light remotely-piloted helicopters for civil applications. The methods and tools to be used for these activities are standardised for conventional piloted aircraft, while they are currently a matter of discussion in case of light remotely-piloted systems flying into unsegregated airspaces. Certification concerns are particularly problematic for aerial systems weighing from 20 to 150xa0kgf, since the airworthiness permission is granted by national authorities. The lack of specific requirements actually requires to analyse both the existing standards for military applications and the certification guidelines for civil systems, up to derive the adequate safety objectives. In this work, after a survey on applicable certification documents for the safety objectives definition, the most relevant functional failures of a light remotely-piloted helicopter are identified and analysed via Functional Hazard Assessment. Different architectures are then compared by means of Fault-Tree Analysis, highlighting the contributions to the safety level of the main elements of the flight control system (control computers, servoactuators, antenna) and providing basic guidelines on the required redundancy level.

Experimental assessment of the dynamic stiffness of a fault-tolerant fly-by-wire hydraulic actuator

The stiffness of an actuator depends on the closed-loop position control (architecture and parameters), on the load frequency, and, for fault-tolerant actuators, on the operative mode. The stiffness response is of basic importance for the design of actuators for primary flight controls, especially for high-performance aircrafts. Actually, during flight conditions characterized by high speed and high angle-of-attack, the dynamic interactions between aircraft structure, actuator, and aerodynamic loads can induce aeroservoelastic effects, which, if not controlled, can imply performance degradation and even instability. The study and the compensation of such concerns require the assessment of the resonant frequencies of the aeroservoelastic system, which can be performed only by characterizing the dynamic stiffness of the actuator. This article reports the experimental activities carried out for the characterization of the stiffness response of a fault-tolerant fly-by-wire actuator for the primary flight controls of a modern jet trainer, starting from the feasibility studies of the experiments up to the execution of the vibration tests. The actuator stiffness performance is evaluated in different fail-operative modes by artificially injecting hydraulic and electrical failures, and the experimental data are interpreted by means of an LTI model of the flight actuator, highlighting and discussing the effects that the failures induce on the stiffness performance.

Experiments and simulations for the study of temperature effects on the performances of a fly-by-wire hydraulic actuator

The paper deals with the study of the temperature effects on the performances of fly-by-wire hydraulic actuators. The activity is developed via both experiments and simulations, using a primary flight actuator of a modern fly-by-wire jet trainer as reference hardware. A dedicated experimental set-up is arranged, by integrating a thermal chamber with a real-time actuator control system developed in the MATLAB-Simulink-xPC Target environment, and an extensive test campaign is performed on the actuator in environmental control conditions. In particular, both the static and the dynamic performances are concerned, characterizing the valve threshold, the valve motor gain, the open-loop, and closed-loop frequency responses. The tests are performed at ambient, extreme hot (71u2009°C), cold (−20u2009°C), and extreme cold (−40u2009°C) temperatures. Experimental results are reported and discussed, providing a physical interpretation of temperature sensitivity effects. Concerning the simulation studies, they started from a detai...The paper deals with the study of the temperature effects on the performances of fly-by-wire hydraulic actuators. The activity is developed via both experiments and simulations, using a primary flight actuator of a modern fly-by-wire jet trainer as reference hardware. A dedicated experimental set-up is arranged, by integrating a thermal chamber with a real-time actuator control system developed in the MATLAB-Simulink-xPC Target environment, and an extensive test campaign is performed on the actuator in environmental control conditions. In particular, both the static and the dynamic performances are concerned, characterizing the valve threshold, the valve motor gain, the open-loop, and closed-loop frequency responses. The tests are performed at ambient, extreme hot (71u2009°C), cold (−20u2009°C), and extreme cold (−40u2009°C) temperatures. Experimental results are reported and discussed, providing a physical interpretation of temperature sensitivity effects. Concerning the simulation studies, they started from a detailed model of the actuator dynamics, previously developed and validated by the author at ambient temperature. The model is adapted for taking into account the temperature effects, and an experimental validation is obtained at servovalve level. The influence of temperature at actuator level is predicted by simulation, highlighting and discussing the expected closed-loop control concerns.