Aeromechanical Analysis of a Smart Helicopter Rotor in Forward Flight
This paper deals with a smart system integrated into a helicopter blade aimed at giving an anhedral shape to the blade tip region to alleviate the blade-vortex interaction phenomenon that may cause reduced helicopter performance in terms of noise and vibrations. The blade tip morphing is obtained through the joint action of a magneto-rheological fluid (MRF) device, a shape-memory alloy ribbons- based (SMA) device and a set of concentrated masses properly distributed spanwise. The presence of this smart actuator (particularly the concentrated masses) inside the blades modifies the aeromechanical behaviour of the rotor and may be detrimental in terms of hub vibratory loads, pitch control effectiveness and aeroelastic stability. Following a previous literature work concerning with the effectiveness of the smart actuated rotor in hovering conditions, the present paper focuses on the aeromechanical effects due to the inclusion of the smart device in a four-bladed helicopter rotor in forward flight where blade morphing is not needed. Aim of this work is to investigate on the compatibility of the smart system with the required aeromechanical performance of the rotor, highlighting the feasibility of its application on helicopters.
Experimental Results of the European HELINOISE Aeroaccoustic Rotor Test in the DNW
In a major cooperative research program between 8 European partners, a 40%-geometrically scaled and highly instrumented model of the ECD (formerly MBB) BO 105 helicopter main rotor was tested in the open jetanechoic test section of the German-Dutch Wind Tunnel, DNW, in the Netherlands. A comprehensive set of simultanious accoustic and aerodynamic bladde surface pressure data as well as blade dynamic and performance data were measured for the standard rotor with rectangular blade tips. The primary objective of this experimental study was to generate an extensive airload and acoustic database and to examine the relation between the blade pressure characteristics and the acoustic radiation. Initial quantitativeinformation on blade-tipvortex trajector ies and blade positions during blade-vortex interactions was obtained. The blade pressure instrumentation, the experimental equipment used, the test procedures applied, and the scope of the test matrix conducted are briefly explained.
Stability of elastic bending and torsion of uniform cantilever rotor blades in hover with variable structural coupling
The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, cantilever rotor blades without chordwise offsets between the elastic, mass, tension, and areodynamic center axes is investigated for the hovering flight condition. The equations of motion are obtained by simplifying the general, nonlinear, partial differential equations of motion of an elastic rotating cantilever blade. The equations are adapted for a linearized stability analysis in the hovering flight condition by prescribing aerodynamic forces, applying Galerkin's method, and linearizing the resulting ordinary differential equations about the equilibrium operating condition. The aerodynamic forces are obtained from strip theory based on a quasi-steady approximation of two-dimensional unsteady airfoil theory. Six coupled mode shapes, calculated from free vibration about the equilibrium operating condition, are used in the linearized stability analysis. The study emphasizes the effects of two types of structural coupling that strongly influence the stability of hingeless rotor blades. The first structural coupling is the linear coupling between flap and lead-lag bending of the rotor blade. The second structural coupling is a nonlinear coupling between flap bending, lead-lag bending, and torsion deflections. Results are obtained for a wide variety of hingeless rotor configurations and operating conditions in order to provide a reasonably complete picture of hingeless rotor blade stability characteristics.