Towards an application of an active tendon in rotorcraft: A numerical and experimental study of coupled bending-torsion vibration of a beam-tendon system

This paper presents a numerical and experimental study of coupled bending-torsion vibration of a beam loaded by a tendon-induced axial force. The rotating beam-tendon system is described using a set of partial differential equations and free vibration analysis is performed. The model is validated against a benchtop experiment which features a reinforced open-section cantilever beam subjected to tendon loading. A satisfactory agreement between the numerical and experimental results is obtained and it is shown that the tendon not only reduces the natural frequencies of the beam, but also introduces frequency loci veering. The validated model is then used to perform a case study on the Bo105 helicopter to present some benefits of incorporating a tendon in a rotorcraft blade, making a first step towards an active tendon concept. This concept should eventually allow rotorcraft to operate with a variable rotor speed, thereby increasing their performance and efficiency.