| The smart active blade tip (SABT) rotor is an on-blade rotor vibration reduction system, incorporating active blade tips that can be independently pitched with respect to the main blade.; The active blade tip rotor development included an experimental test program culminating in a Mach scale hover test, and a parallel development of a coupled, elastic actuator and rotor blade analysis for preliminary design studies and hover performance prediction.; The experimental testing focussed on a small scale rotor on a bearingless Bell-412 hub. The fabricated Mach-scale active-tip rotor has a diameter of 1.524 m, a blade chord of 76.2 mm and incorporated a 10% span active tip. The nominal operating speed is 2000 rpm, giving a tip Mach number of 0.47. The blade tips are driven by a novel piezo-induced bending-torsion coupled actuator beam, located spanwise in the hollow mid-cell of the main rotor blade.; In hover at 2000 rpm, at 2 deg collective, and for an actuation of 125 Vrms, the measured blade tip deflection at the first four rotor harmonics is between ±1.7 and ±2.8 deg, increasing to ±5.3 deg at 5/rev with resonant amplification. The corresponding oscillatory amplitude of the rotor thrust coefficient is between 0.7 · 10−3 and 1.3 · 10−1 at the first four rotor harmonics, increasing to 2.1 · 10−3 at 5/rev.; In general, the experimental blade tip frequency response and corresponding rotor thrust response are well captured by the analysis. The flexbeam root flap bending moment is predicted in trend, but is significantly over-estimated.; The blade tips did not deflect as expected at high collective settings, because of the blade tip shaft locking up in the bearing. This is caused by the high flap bending moment on the blade tip shaft. Redesign of the blade tip shaft assembly and bearing support is identified as the primary design improvement for future research.; The active blade tip rotor was also used as a testbed for the evaluation of an adaptive neural-network based control algorithm. Effective background vibration reduction of an intentional 1/rev hover imbalance was demonstrated. The control algorithm also showed the capability to generate desired multi-frequency control loads on the hub, based on artificial signal injection into the vibration measurement.; The research program demonstrates the technical feasibility of the active blade tip concept for vibration reduction and warrants further investigation in terms of closed loop forward flight tests in the windtunnel and full scale design studies. |
