Active tab, a new active technique for helicopter noise reduction

This paper presents the concept of the active tab which is a new active technique for the helicopter noise reduction, the policy for its aerodynamic design and the results of the experimental activities performed in 2D configuration to evaluate the effect of the active tab with regard to the potential for the noise reduction. The static wind tunnel test was performed in 2002 to study whether a realistic size tab has the aerodynamic capability equivalent to the noise reduction. It is shown by the test result that the tab of around 8% blade chord with more than 6deg. deflection can achieve the sufficient aerodynamic work for the rotor noise reduction. The dynamic wind tunnel test was carried out in 2003 to study the unsteady aerodynamic effect of the active tab and to conclude that the more than 11%c active tab extension with 10deg deflection has the sufficient capability for the rotor noise reduction. Finally, the outline of the future work of this research activity is described. Introduction The several active techniques for the helicopter noise and vibration reduction, such as HHC (Higher Harmonic Control) (Refs.1-3), IBC (Individual Blade Control) (Refs.4-6), active flap (Refs.7, 8), active twist (Refs.9, 10) and the like have been proposed, researched and developed so far. Some of them were flight-tested and others are in the phase just close to flight test evaluation. The outlines of each existing active technique, for example on 2 bladed rotor, are depicted schematically in Fig.1. (a) HHC