The aeroelastic stability of a uniform, untwisted hingeless 'smart' helicopter rotor blade has been analysed. The concept of a 'smart blade' is achieved by implementing a piezoelectric stack at an appropriate location along the length of a host blade such that upon actuation it acts as a 'smart spring' that enters the load path becoming an integral part of the host structure. As the result, the stiffness characteristics of the rotor can be altered causing modal damping augmentation of the blade. The blade is modelled as an aeroelastic cantilevered slender beam undergoing lead-lag, flap and torsional motion. As a first attempt, hover condition is considered with no offsets between the elastic, aerodynamic and tension axes, with the pre-cone angle set equal to zero. In anticipation of future experimental verification of this concept, a reduced scale model of a Eurocopter BO 105 helicopter blade has been designed and used as the base rotor in this investigation. The corresponding linearised perturbation equations of motion for the smart blade that describe the unsteady blade motion about the equilibrium operating conditions are obtained by applying Galerkin's method to the nonlinear, partial, differential equations of motion of the system. These differential equations whose coefficients are periodic functions of time are solved using Floquet method. The stability of motion is then investigated using the standard techniques. Inc1uding the base line cases, six different regimes of actuation are investigated, and six different design cases are considered. It is shown that using a judicious actuation scheme, the smart spring has the potential of acting as a damper to eliminate divergence and flutter instabilities of the individual blades.
Aeroelastic stability of a helicopter blade with a smart spring
Aeroelastische Stabilität eines Hubschrauber-Rotorblatts mit einer intelligenten Feder
2004
11 Seiten, 4 Bilder, 1 Tabelle, 25 Quellen
Conference paper
English
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