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

Fault-Tolerant Control of a Dual-Stator PMSM for the Full-Electric Propulsion of a Lightweight Fixed-Wing UAV

The reliability enhancement of electrical machines is one of the key enabling factors for spreading the full-electric propulsion to next-generation long-endurance UAVs. This paper deals with the fault-tolerant control design of a Full-Electric Propulsion System (FEPS) for a lightweight fixed-wing UAV, in which a dual-stator Permanent Magnet Synchronous Machine (PMSM) drives a twin-blade fixed-pitch propeller. The FEPS is designed to operate with both stators delivering power (active/active status) during climb, to maximize performances, while only one stator is used (active/stand-by status) in cruise and landing, to enhance reliability. To assess the fault-tolerant capabilities of the system, as well as to evaluate the impacts of its failure transients on the UAV performances, a detailed model of the FEPS (including three-phase electrical systems, digital regulators, drivetrain compliance and propeller loads) is integrated with the model of the UAV longitudinal dynamics, and the system response is characterized by injecting a phase-to-ground fault in the motor during different flight manoeuvres. The results show that, even after a stator failure, the fault-tolerant control permits the UAV to hold altitude and speed during cruise, to keep on climbing (even with reduced performances), and to safely manage the flight termination (requiring to stop and align the propeller blades with the UAV wing), by avoiding potentially dangerous torque ripples and structural vibrations

Design of a Fuselage-Mounted Main Landing Gear of a Medium-Size Civil Transport Aircraft

The subject of the present paper is the design of an innovative fuselage mounted main landing gear, developed for a PrandtlPlane architecture civil transport aircraft with a capacity of about 300 passengers. The paper presents the conceptual design and a preliminary sizing of landing gear structural components and actuation systems, in order to get an estimation of weight and of the required stowage. The adopted design methodology makes use of dynamic modelling and multibody simulation from the very first design stages, with the aim of providing efficient and flexible tools for a preliminary evaluation of performances, as well as enabling to easily update and adapt the design to further modifications. To develop the activity, the multibody dynamics of the landing gear (modelled using Simpack software) has been integrated via co-simulation with dynamic models developed in the Matlab/Simulink environment

Experimental validation of theoretical and numerical models of a DDV linear force motor

The performances of a Direct Drive Valve (DDV) mainly depend on the characteristics of its Linear Force Motor (LFM) and the availability of accurate models of the LFM plays an important role in the whole actuation system design. The present work deals with the modelling and the experimental characterisation of a LFM. By means of a specifically designed test equipment, the force provided by the LFM of an off-the-shelf DDV is measured as a function of the coil current and of the spool position. The experimental data are compared with the results of two models: a theoretical one, based on the magnetic circuit theory, and a numerical one, based on the FEM analysis of the electromagnetic components of the system. The numerical model provided good results over a wide range of test conditions and it allowed to evaluate correction factors for the theoretical model, related to the presence of secondary paths in the magnetic fluxes and to the distortion of the magnetic flux lines

Experimental implementation of a motion-compensated force control in a hydraulic workbench for flight actuators

The paper deals with the design and the experimental implementation of the force control in a hydraulic workbench for flight actuators, to be used for hardware-in-the-loop simulations of modern Fly-By-Wire Flight Control Systems. A basic problem affecting the plant performances is that the force response is sensitive to the flight actuator movements. Simulation results show that a suitable solution can be obtained including a compensation feedback based on the flight actuator acceleration, but sensor nonlinearities can induce relevant disturbances during experiments. In the paper, the model-inverting controller and the acceleration feedback are combined with a Kalman filter for compensating the accelerometer bias, and the performance of the closed-loop force-controlled plant is characterised by performing successive sessions of experiments, up to the simulation of the flight actuator dynamics during a typical flight manoeuvre

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 realtime 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 (71 C), cold (220 C), and extreme cold (240 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 concern

Experiments and CFD simulations for the characterisation of the orifice flow in a four-way servovalve

It 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 objectives of the investigation: to characterise the laminar-to-turbulent flow transition in the orifices of an aircraft-type hydraulic component, providing an original physical interpretation to the increase of the orifice discharge efficiency in “mixed” flow conditions, and to highlight the necessity of using Reynolds-dependant orifice equations for the modelling of high-performance servohydraulic actuators

AW149 de-risk actuator DDV test results (LLI control)

Il presente lavoro documenta le attività effettuate per caratterizzare sperimentalmente la risposta dinamica della servovalvola DDV dell’attuatore prototipo (De-Risk Actuator) utilizzato per le analisi preliminari e gli studi di fattibilità del sistema dei comandi di volo primari del nuovo elicottero AW149

ACT-TILT project (Work Package 1.2.1) - Hinge moments estimation - Summary of results

This paper summarises the results obtained by the staff of the University of Pisa and TELEAVIO Srl concerning a preliminary estimation of the hinge moments on the aerodynamic control surfaces of the tilt rotor (operating in the "Fixed Wing" mode), carried out in order to allow the pre-design of the actuators of the flight control system. The estimation was accomplished by means of two different methods (provided by ESDU and Hoerner ), whose results are then compared. The basic hypotheses are that the aerodynamic surfaces work in the linear range of incidence and control deflection. Nevertheless, an estimation of the hinge moments in the post-linear range of control deflection is also given