Abstract:
Researchers and practitioners spend much e ort in developing theoretical methods to
design and predict the performance of helicopter rotor blades. These blades have evolved
to become complex structures designed to operate in extreme conditions and over the exceptionally broad flight envelopes of helicopters. As a result, these vehicles are subject to
strict maintenance regimes that increase the overall operational costs. The need to reduce
such costs and improve aircraft performance together with the emergence of novel fibre
optic-based sensor technologies form the context of the research presented in this thesis.
Opportunities for blade health and usage monitoring created by sensor technologies such
as fibre Bragg gratings (FBG) for measuring strain and direct fibre optic shape sensing
(DFOSS) present today's industry with a critical question: Does the designer follow contemporary technological trends and adopt a preventative approach where he/she invests
in such instrumentation systems or is a reactive approach more appropriate where he/she
awaits to have sufficient evidence of operational need? A survey was carried out as part
of this research to understand this dichotomy faced by rotorcraft engineers and systems
architects. Adhering to the safety orientated culture within the aerospace community,
the aim of this research work is the numerical and experimental exploration of challenges
associated with the deployment of fibre optic instrumentation systems for future health
and usage monitoring. This was achieved through three objectives: (1) development
of a computational framework allowing the simulation of rotor blade dynamics at an
appropriate fidelity, (2) exploration of blade health monitoring capabilities using fibre
optic instrumentation systems and, (3) laboratory-based structural testing. Health and
usage monitoring capabilities were explored theoretically through a parametric damage
study using the computational framework. The experimental testing highlighted the need
for a sensor placement methodology for distributing FBG-based strain sensors over the
blade (both in terms of spanwise and chordwise locations) for accurately recovering mode
shapes. This was followed by investigating the accuracy of the novel DFOSS system by
deploying it on a bearingless main rotor blade along with other commercially available
instrumentation systems. Test results were used to (1) perform multi-step indirect finite
element modelling to increase the accuracy of the developed structural model and, (2)
to explore the suitability of FBG and DFOSS measurements for damage detection. The
main finding of this work is that future rotor health and usage monitoring systems based
on fibre optic sensing technologies require the development of a hybrid FBG and DFOSS
instrumentation system. Although numerous areas of further work have been identified,
it is hoped that the adoption of such an instrumentation system will not only help reduce operational costs but also provide much needed operational data on helicopter blade
dynamics to validate methods and improve designs.