Gianpietro Di Rito

Robust force control in a hydraulic workbench for flight actuators

The work deals with the design of the force control in a hydraulic workbench for primary flight actuators, to be used for hardware-in-the-loop simulations of a modern Fly-By-Wire Flight Control System. For this application, a high-bandwidth force response is needed in order to simulate aerodynamic loads on the control surfaces, but plant uncertainties can imply significant limitations. The variation of structural stiffness, due to hinge play and hinge local deformation, the uncertainties related to the flight actuator stiffness and the ones related to the hydraulic plant parameters lead to the necessity of a robust approach to the design of the force control. In the paper, a nominal LTI model of the plant is developed and the closed-loop force control is designed by means of a loop-shaping approach for different values of the bandwidth. The stability of the closed-loop force-controlled system is then verified by a robustness analysis, assuming the structural stiffness, the flight actuator stiffness, and some of the hydraulic plant characteristics as uncertain parameters. The bandwidth of the force control is determined by finding an optimal compromise between dynamic performance and stability margin. Finally, in order to overcome the additional problems related to the flight actuator movements due to aircraft manoeuvres, a compensation feedback based on the flight actuator acceleration is proposed.

Experiments and CFD Simulations for the Characterisation of the Orifice Flow in a Four-Way Servovalve

AbstractIt is well-known that the discharge efficiency of an orifice varies with the flow condition: it is very low for laminar flow, it reaches a maximum in “mixed” conditions, and it tends to be constant (i.e. insensitive to flow variations) when turbulence is fully developed. However, the classical approach to the modelling of servo-hydraulic actuators is based on the hypothesis that the flow through the servovalve orifices is turbulent, and this assumption can lead to significant errors if the dynamics of actuators operating in extreme conditions is concerned. This is the case of aerospace applications, since flight actuators can be commanded to move against high counteracting loads or at very low velocities, and a laminar (or rather “mixed”) flow pattern can be established in the servovalve orifices. In the paper, the flow through the Moog D633 four-way servovalve is studied by means of experiments and Computational Fluid Dynamics simulations (developed in the STAR-CD environment). Two are the basic ...

Self-monitoring electro-mechanical actuator for medium altitude long endurance unmanned aerial vehicle flight controls

This article deals with the reliability analysis and architecture definition of a fault-tolerant electro-mechanical actuator system for unmanned aerial vehicle applications. Starting from the basic layout of the flight control system of a medium altitude long endurance unmanned aerial vehicle, the attention is focused on the fault mode analysis of the single electro-mechanical actuator system, with the purpose of pointing out the effects of architectural choices on the system reliability. The electro-mechanical actuator system, developed to be a self-monitoring equipment, has three operating modes: normal, fail-operative and fail-safe. Reliability and safety budgets are quantitatively evaluated via fault tree analysis using typical failure rates of system components, and the most critical paths are identified and discussed.

Health monitoring of electromechanical flight actuators via position-tracking predictive models

This article deals with the development and performance characterisation of model-based health monitoring algorithms for the detection of faults in an electromechanical actuator for unmanned aerial system flight controls. Two real-time executable position-tracking algorithms, based on predictors with different levels of complexity, are developed and compared in terms of false alarm rejection and fault detection capabilities, using a high-fidelity model of the actuator in which different types of faults are injected. The algorithms’ performances are evaluated by simulating flight manoeuvres with the actuator in normal operation as well as with relevant faults (motor coil faults, motor magnet degradation, voltage supply decrease). The results demonstrate that an accurate position-tracking monitor allows to obtain a prompt fault detection and fail-safe mode engagement, while more detailed monitoring functions can be used for fault isolation only.