Feasibility of an Acoustic Liner Applied to a Fenestron™

A helicopter antitorque system significantly contributes to radiated noise. The Fenestron™ antitorque system used on Airbus helicopters reduces this noise through masking effects and blade distribution modulation. This paper explores integrating acoustic treatments similar to those used in aircraft engine nacelles into the Fenestron™ to further decrease the antitorque system noise. Numerical simulations are performed to identify the optimal acoustic impedance for these liners, followed by proposing and assessing several liner designs on small-scale experimental benches. Finally, a larger-scale, more representative measurement campaign on a Fenestron™ mock-up with integrated liners demonstrates that a likely significant noise reduction can be attained.