Reduction of Vibrations due to Dynamic Stall in Helicopters using an Actively Controlled Flap

This paper presents a successful treatment of the helicopter vibration reduction problem at high advance ratios, taking into account the effects of dynamic stall. The ONERA model is used to describe the loads during stall, in conjunction with a rational function approximation for unsteady loads for attached flow. Single and dual actively controlled flaps are used to reduce vibrations. Several control laws are considered in this study. Successful vibration reduction is demonstrated over the entire range of advance ratios considered (0.3 ≤ µ ≤ 0.45). This study represents the first successful implementation of vibration reduction in presence of dynamic stall, and physical explanation for the vibration reduction process is also provided. Finally, saturation limits on the control deflections are imposed, which keep flap deflections in a practical range. Effective vibration reduction is achieved even when imposing practical saturation limits on the controller.

[1]  Carlos E. S. Cesnik,et al.  Vibratory loads reduction testing of the NASA/Army/MIT active twist rotor , 2001 .

[2]  P. Friedmann,et al.  Actuator saturation and its influence on vibration reduction by actively controlled flaps , 2001 .

[3]  V. K. Truong,et al.  A 2-D dynamic stall model based on a Hopf bifurcation , 1993 .

[4]  Peretz P. Friedmann,et al.  New developments in vibration reduction with actively controlled trailing edge flaps , 2001 .

[5]  O. Dieterich,et al.  Stall Effects and Blade Torsion - An Evaluation of Predictive Tools , 1999 .

[6]  Peretz P. Friedmann,et al.  Vibration reduction in helicopter rotors using an actively controlled partial span trailing edge flap located on the blade , 1994 .

[7]  W. Johnson,et al.  CAMRAD - A COMPREHENSIVE ANALYTICAL MODEL OF ROTORCRAFT AERODYNAMICS AND DYNAMICS , 1994 .

[8]  Peretz P. Friedmann,et al.  Vibration reduction in rotorcraft using active control - A comparison of various approaches , 1995 .

[9]  Friedrich K. Straub,et al.  Comprehensive Modeling of Rotors with Trailing Edge Flaps , 1999 .

[10]  Peretz P. Friedmann,et al.  Active Control Of BVI Induced Vibrations Using A Refined Aerodynamic Model And Experimental Correlation , 1999 .

[11]  M. J. D. Powell,et al.  UOBYQA: unconstrained optimization by quadratic approximation , 2002, Math. Program..

[12]  Peretz P. Friedmann,et al.  Application of a New Compressible Time Domain Aerodynamic Model to Vibration Reduction in Helicopters Using an Actively Controlled Flap , 2001 .

[13]  J. Gordon Leishman,et al.  Principles of Helicopter Aerodynamics , 2000 .

[14]  Carlos E. S. Cesnik,et al.  Forward flight response of the active twist rotor for helicopter vibration reduction , 2001 .

[15]  Friedrich K. Straub,et al.  Active Flap Control for Vibration Reduction and Performance Improvement , 1995 .

[16]  David A. Peters,et al.  Toward a Unified Lift Model for Use in Rotor Blade Stability Analyses , 1985 .

[17]  Khanh Nguyen,et al.  Active control of helicopter blade stall , 1996 .

[18]  Robert A. Ormiston,et al.  SMALL-SCALE ROTOR EXPERIMENTS WITH ON-BLADE ELEVONS TO REDUCE BLADE VIBRATORY LOADS IN FORWARD FLIGHT , 1998 .

[19]  Wayne Johnson,et al.  Self-Tuning Regulators for Multicyclic Control of Helicopter Vibration , 1982 .

[20]  Peretz P. Friedmann,et al.  Rotary-wing aeroelasticity - Current status and future trends , 2001 .