Session: 07-13-01 Optimization, Uncertainty and Probability I

Paper Number: 71095

Start Time: Tuesday, 03:40 PM

71095 - Multiphysics Modeling of a Faulty Rod-End and Its Interaction With a Flight Control Actuator to Support PHM Activities 

Spherical joints, or rod-ends, are used in flight control systems to connect the actuator to the aerodynamic surface, on one end, and to the airframe on the other side, hence performing a safety critical function at the aircraft level. As any mechanical component, rod-ends are subjected to a wide range of failure modes. Focusing only on the spherical joint, most of the degradation modes are shared with the journal bearings (wear, lubricant oxidation, surface denting and so forth). Looking instead at the joint within the context of the actuation system, three major failure modes can be observed. The first and most critical is the opening of a crack in the external element, often referred as “open-eye” failure in flight control literature. This rupture is particularly dangerous for the aircraft safety, since it might cause the decoupling between the actuator and the aerodynamic surface. Depending on the number of actuators operating on the same surface, this failure could cause the complete loss of control of the aerodynamic tab or severe limitations to the system performances. The increase of backlash due to advanced wear is instead the most common occurrence; since it is usually impossible to monitor the position of the rod end, a backlash outside of an acceptability window may cause excessive loss of precision in the surface positioning. Finally, the excessive increase of friction forces within the spherical joint can cause excessive bending stresses on the actuator. In a few reported cases, this condition led to the permanent deformation of the actuator and hence to severe limitation of its performance and movement capabilities. As noted, most of the degradation modes affecting the rod-ends cause critical failure or excessive loss of performances in other components. Despite this, literature on the subject is mostly focused on the single component and not on the interaction between a faulty rod-end and the actuation system. Aiming to define a Prognostics and Health Management system (PHM) for flight control actuators, the understanding of the interdependency between the actuator behavior and the rod-end health status is instead critical. To pursue this objective, a high-fidelity dynamic model of a rod-end was prepared and linked with an experimentally validated model of an Electro-Hydraulic flight control actuator employed in long-range civil aircrafts. The model solves the equation of hydro-dynamic lubrication through a finite difference method and is able to describe the trajectory of the pin as a function of the forces exchanged between the aerodynamic surface, the actuator and the airframe. A contact model and a simplified methodology based upon the Tallian parameter was adopted to compute the force exchanged in the contact zone and to estimate the friction forces. Finally, the rod-end model is attached to a high-fidelity representation of an Electro-Hydraulic servo actuator with a deformable rod. A few simulations under realistic scenarios are then performed for nominal and degraded health conditions. Results are hence provided, and early indication on the detectability of the degraded conditions presented.

Presenting Author: Antonio C. Bertolino Politecnico di Torino

Authors:

Alberto Bacci Politecnico di Torino
Antonio C. Bertolino Politecnico di Torino
Andrea De Martin Politecnico di Torino
Massimo Sorli Politecnico di Torino