Dynamic modelling and stability of hingeless helicopter blades with a smart spring

The aeroelastic stability of a uniform, untwisted hingeless 'smart' helicopter rotor blade in hover has been analysed. The concept of a 'smart' blade is achieved by implementing a piezoelectric stack at an appropriate location along a host blade such that upon actuation it enters the load path becoming an integral part of the host structure. Thus, the stiffness characteristics of the rotor are altered causing modal damping augmentation of the blade. The perturbation equations of motion for the 'smart' blade that describe the unsteady blade motion about the equilibrium operating condition are obtained using Galerkin's method. These differential equations with periodic time coefficients are analysed for stability utilising the Floquet method. Six different regimes of actuation are investigated, and a parametric study is carried out by considering six different design cases. It is shown that, compared to a 'host' blade the stability characteristics of the 'smart' blade are not affected adversely. In fact, a judicious design and actuation of the 'smart' spring has the potential of improving the stability boundaries of individual blades.

[1]  Hughes Helicopters,et al.  On Developing and Flight Testing a Higher Harmonic Control System , 1983 .

[2]  Maurice I. Young,et al.  A Theory of Rotor Blade Motion Stability in Powered Flight , 1964 .

[3]  J Mayo Greenberg,et al.  Airfoil in sinusoidal motion in a pulsating stream , 1947 .

[4]  D. H. Roberta. Hodges,et al.  Stability of elastic bending and torsion of uniform cantilever rotor blades in hover with variable structural coupling , 1976 .

[5]  Fred Nitzsche,et al.  Using adaptive structures to attenuate rotary wing aeroelastic response , 1994 .

[6]  D. G. Zimcik,et al.  Development of the Smart Spring for Active Vibration Control of Helicopter Blades , 2004 .

[7]  Dewey H. Hodges,et al.  Linear Flap-Lag Dynamics of Hingeless Helicopter Rotor Blades in Hover , 1972 .

[8]  John C. Houbolt,et al.  Differential equations of motion for combined flapwise bending, chordwise bending, and torsion of twisted nonuniform rotor blades , 1957 .

[9]  C. E. Hammond,et al.  Wind Tunnel Results Showing Rotor Vibratory Loads Reduction Using Higher Harmonic Blade Pitch , 1980 .

[10]  C. E. Hammond,et al.  A Unified Approach to the Optimal Design of Adaptive and Gain Scheduled Controllers to Achieve Minimum Helicopter Rotor Vibration , 1981 .

[11]  Earl H. Dowell,et al.  Nonlinear equations of motion for the elastic bending and torsion of twisted nonuniform rotor blades , 1974 .

[12]  J. V. Lebacqz,et al.  NASA/FAA experiments concerning helicopter IFR airworthiness criteria , 1983 .

[13]  Richard S. Teal,et al.  Higher Harmonic Control: Wind Tunnel Demonstration of Fully Effective Vibratory Hub Force Suppression , 1985 .

[14]  F. Nitzsche,et al.  A comparative study on different techniques to control rotary wing vibration using smart structures , 1999, The Aeronautical Journal (1968).

[15]  D. G. Zimcik,et al.  Control laws for an active tunable vibration absorber designed for rotor blade damping augmentation , 2004, The Aeronautical Journal (1968).