Real-time monitoring of a variable-camber aileron rib by original strain-angle transducer

Abstract

The object of this work is the conceptual design and modelling of a transducer based on fibre optic sensor and conceived to measure rotations of rigid components around a pivot. The device, namely, post-buckling-fibre Bragg grating, is constituted of a flexible metal plate hosting a fibre Bragg grating strain sensor; the edges of the plates are hinged onto the rotating rigid bodies, eccentrically with respect to the pivot. In this way, any increase in rotation produces a further bending of the plate corresponding to a fibre Bragg grating wavelength shift. Among the different applications, an aileron morphing architecture is considered. This architecture is composed of a rib made of three rigid parts, hinged each other and moved through a dedicated kinematic chain. Two post-buckling-fibre Bragg grating devices are installed between the adjacent rib blocks giving a measure of their current angular rotation. A peculiarity of the proposed device is its ability in working in post-buckling configuration, with two main advantages: (1) easy, plug-and-play, installation (the device supporting plate can be manually bent and plugged within the connection hinges) and (2) tuning of the sensitivity or range of measure, on the basis of the fibre Bragg grating location onto the plate and of the initial post-buckling level. At first, the conceptual design was dealt with a theoretical model describing the post-buckling behaviour of beams, highlighting the effect of the main design parameters; then, the plate displacement field was related to rotation angle of the rib; a dedicated numerical (finite element) model was thus realized to prove the concept feasibility and simulate in detail its functionality. Finally, experimental set-up was provided in order to validate the design.