Active Twist Rotor Research Articles

Active twist rotor blade modelling using particle-wake aerodynamics and geometrically exact beam structural dynamics

An active aeroelastic and aeroacoustic analysis of helicopter rotor systems is presented in this paper. It is a tightly coupled computational aeroelastic code that interfaces a particle-wake panel method code with an active nonlinear mixed variational intrinsic beam element code. In addition, a Ffowcs-Williams–Hawkings equation-based acoustic component is incorporated to complete the numerical implementation. The theory behind each component is summarized here as well as the method for coupling the aerodynamic and structural components. Sample acoustic and aeroelastic results are given for different model-scale rotors. Comparisons with available (passive) results show very good agreement. Preliminary study with an active twist rotor is also shown.

Acoustic Aspects of Active-Twist Rotor Control

The use of an Active Twist Rotor system to provide both vibration reduction and performance enhancement has been explored in recent analytical and experimental studies. Effects of active-twist control on rotor noise, however, had not been determined. During a recent wind tunnel test of an active-twist rotor system, a set of acoustic measurements were obtained to assess the effects of active-twist control on noise produced by the rotor, especially blade-vortex interaction (BVI) noise. It was found that for rotor operating conditions where BVI noise is dominant, active-twist control provided a reduction in BVI noise level. This BVI noise reduction was almost, but not quite, as large as that obtained in a similar test using HHC. However, vibration levels were usually adversely affected at operating conditions favoring minimum BVI noise. Conversely, operating conditions favoring minimum vibration levels affected BVI noise levels, but not always adversely.

Hover Test of Mach-Scale Active Twist Rotor Using Piezo-Bending-Torsion Actuators

The active twist rotor investigated in this research is a derivative of the previously developed smart-activeblade-tip (SABT) rotor. On the SABT rotor, the blade tips are independently pitched, with respect to the main blade. A novel piezo-induced bending ‐torsion coupled actuator beam, located spanwise in the hollow midcell of the main rotor blade, is used to actuate the blade tip. When the blade tip is locked to the main blade, the actuator beam twists the entire blade. A Mach scale rotor with a 1.542 m diameter was hover tested, open loop, to evaluate the control authority for vibration reduction. A nonrotating tip-twist amplitude of 0.78 deg was achieved (below resonance, 150 V rms ). Analysis indicates that no signie cant twist actuation degradation is expected at full rotor speed. In 2000-rpm hover (tip Mach 0.47 ), at 8-deg collective, and for a single blade actuation of 150 V rms at 1, 2, and 3 per revolution, respectively, the measured oscillatory thrust coefe cients are 1 :4 £ 10 3 , 0:55 £ 10 3 , and 0:7 £ 10 3 . The corresponding e nite element model estimated blade twist amplitudes are 0.8, 1.0, and 1.9 deg. Good correlation of the predicted and measured rotor thrust was achieved up to 3 per revolution. The hover test demonstrates the potential of the active twist rotor system using an internal actuation beam and warrants further research for a dedicated next-generation model-scale design and full-scale feasibility study.

Vibratory Loads Reduction Testing of the NASA/Army/MIT Active Twist Rotor

Recent studies have indicated that controlled strain-induced blade twisting can be attained using piezoelectric active fiber composite technology, and that such advancement may provide a mechanism for reduced rotorcraft vibrations and increased rotor performance. In order to validate these findings experimentally, a cooperative effort between the NASA Langley Research Center, the Army Research Laboratory, and the MIT Active Materials and Structures Laboratory has been developed. As a result of this collaboration a four-bladed, aeroelastically-scaled, active-twist model rotor has been designed and fabricated for testing in the heavy gas test medium of the NASA Langley Transonic Dynamics Tunnel. Initial wind tunnel testing has been conducted to assess the impact of active blade twist on both fixed- and rotating-system vibratory loads in forward flight. The active twist control was found to have a pronounced effect on all system loads and was shown to generally offer reductions in fixedsystem loads of 60% to 95%, depending upon flight condition, with 1.1o to 1.4o of dynamic blade twist observed. A summary of the systems developed and the vibratory loads reduction results obtained are presented in this paper.

Dynamic response of active twist rotor blades

Dynamic characteristics of active twist rotor (ATR) blades areinvestigated analytically and experimentally in this paper. The ATR system isintended for vibration and potentially for noise reductions in helicopters throughindividual blade control. An aeroelastic model is developed to identifyfrequency response characteristics of the ATR blade with integral, generallyanisotropic, strain actuators embedded in its composite construction. An ATRprototype blade was designed and manufactured to experimentally study thevibration reduction capabilities of such systems. Several bench and hovertests were conducted and those results are presented and discussed here.Selected results on sensitivity of the ATR system to collective setting (i.e. blade loading), blade rpm (i.e. centrifugal force and blade stationvelocity), and media density (i.e. altitude) are presented. They indicatedthat the twist actuation authority of the ATR blade is independent of thecollective setting up to approximately 10P, and dependent on rotational speedand altitude near the torsional resonance frequency due to its dependency onthe aerodynamic damping. The proposed model captures very well the physics andsensitivities to selected test parameters of the ATR system. The numericalresult of the blade torsional loads show an average error of 20% in magnitudeand virtually no difference in phase for the blade frequency response.Overall, the active blade model is in very good agreement with the experimentsand can be used to analyze and design future active helicopter blade systems.