Analysis Of Potential Helicopter Vibration Reduction Concepts

Several recent helicopter vibration reduction research programs of the United Technologies Research Center (UTRC) are described. Results of analytical investigations to develop, understand, and evaluate potential helicopter vibration reductionn concepts are presented in the following areas: identification of the fundamental sources of vibratory loads, blade design for low vibration, application of design optimization techniques, active higher harmonic control, blade appended aeromechanical devices, and the prediction of vibratory airloads. Primary sources of vibration are identified for a selected four-bladed articulated rotor operating in high speed level flight. The application of analytical design procedures and optimization techniques are shown to have the potential for establishing reduced vibration blade designs through variations in blade mass and stiffness distributions, and chordwise center-of-gravity location. Analytical evaluation of a computerized generic active controller for implementing higher harmonic control indicates the potential for good controller performance and extensive fuselage vibration reduction with low pitch amplitudes for three controller approaches investigated. Exploratory evaluation of a passive tuned blade tab concept indicates considerable sensitivity of vibratory load alleviation to design parameters with an improvement in inplane hub excitation but an increase in vertical excitation. The prediction of vibratory airloads, attributable to rotor/wake, rotor/fuselage, and rotor/empennage interactional aerodynamics, is also described.