In recent years, hub active vibration control (HAVC) technologies have been developed to attenuate blade pass frequency vibration on helicopters. While these systems provide superior vibration control with reduced weight compared to passive options, in the event of electrical power loss they can exacerbate the vibration problem in a manner that is problematic for helicopter and tiltrotor aircraft. This paper presents an offset hub active vibration control system (OHAVCS) designed to attenuate vibration during a power loss by offsetting the centers of rotation of two imbalance masses. The equations of motion for this system are developed using Lagrangian methods; analysis, simulation and experimental validation of these equations indicate that offsetting the imbalance masses effectively mitigates 1/Rev vibrations during a rotor hub power loss while continuing to cancel N/Rev vibrations during normal operation. These offsets create stabilizing centripetal torques that rotate each imbalance mass to a unique equilibrium angle. Experimental data also indicate that these offsets do not hinder control of the imbalance masses during normal (active) operation, though they do increase system power requirements.
This paper presents an overview of the efforts associated with integrating a new torque measurement system for T408 engines into an NCH-47D airframe and performance of the torque measurement system during operation on the aircraft. The effort described was performed collaboratively between GE Aviation, The Boeing Co, Parker LORD, and DEVCOM AvMC. The Torque Measurement System was utilized in the T408 Engine Control System during its demonstration on an NCH-47D airframe at Ft. Eustis, VA. In addition, based on DEVCOM AvMC program requirements, health monitoring capability was successfully implemented and demonstrated during the NCH-47D T408 Engine Demonstration. Lessons learned from the torque measurement system's health monitoring features are included.
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