Experimental validation of multi-mode tailboom passive vibration control using fluidic flexible matrix composite tubes

Helicopter tailboom vibrations are easily excited and decay slowly due to the tailboom's low inherent structural damping. The resulting vibration causes poor ride quality for passengers, fatigues structural elements, and increases maintenance requirements for the helicopter. Fluidic Flexible Matrix Composite (F²MC) tubes are an emerging technology which can provide lightweight, compact vibration control when attached to a vibrating structure and coupled with a fluidic circuit. This paper presents experimental results to validate a method for combining a finite element structural model of a laboratory-scale tailboom with a model of the F²MC tubes and fluidic circuit dynamics. Reductions of over 70% in both bending and torsional vibration are demonstrated in a coupled 26.7 Hz lateral bending/torsion tailboom mode, indicating that F²MC vibration control is viable at higher frequencies and for more complex vibration modes than previous research had explored. A second group of experiments is performed to demonstrate the effectiveness of a novel fluidic circuit configuration which targets two tailboom vibration modes, in contrast to the previous F²MC treatment which can target only one mode. On the lab-scale tailboom testbed, vibration reductions of over 60% are demonstrated in two modes simultaneously when targeting both a 12.2 Hz vertical mode and a 26.7 Hz lateral bending/torsion mode. The circuit designed to reduce vibrations in two modes has a nearly identical weight to a comparable single-mode treatment but is much more effective in reducing vibrations at the second mode.