Aircraft Active Inceptor Dynamics under Vibration Loads

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Aircraft with fly-by-wire control systems often incorporate so-called active inceptors (stick, throttle, pedals, etc.) that provide the interface between the pilot and the aircraft control surfaces. These devices are complex electro-mechanical gimbal systems utilising motors, servo-actuators, torsional springs, linear springs, ball bearings, spherical bearings and displacement and force transducers - all interconnected via a series of mechanical linkages and a pilot's grip assembly. The system controls the grip force-to-displacement relationship to allow real time variation in feel characteristics to support aircraft operational modes. The dynamic response of the individual elements in an inceptor, and of the system as a whole, is critical in maintaining the level of performance required throughout its service life. Whilst the fatigue life is partly driven by the pilot-applied cyclic loads, aircraft vibration loads can be the primary design driver. The effects of aircraft harmonic vibration loads, as in a helicopter, are difficult to assess: some of the resulting inceptor system resonances can fall within aircraft frequency ranges that must be avoided. This PhD project involves the derivation, development and study of a suitable mathematical model of an active inceptor, which can be used for assessing its dynamic characteristics. BAE Systems will provide a development helicopter collective stick unit and the associated CAD models for this investigation. The mathematical modelling, at least initially, be focused on this collective stick. Any experimental testing of this unit needed to support the modelling will be conducted either by BAE Systems or within the University. The objective of the study is to enhance the understanding of the dynamics of this candidate inceptor system, including under the influence of harmonic excitation representing helicopter vibration, and to explore methods for ensuring that resonant-frequency responses are avoided. Related topics such as friction modelling, force sensing and pilot arm interactions could potentially be incorporated at a later stage.