Further Results Further Results of Soft-Inplane Tiltrotor of Soft-Inplane Tiltrotor Aeromechanics Investigation Aeromechanics Investigation Using Two Multibody Using Two Multibody Analyses Analyses Pierangelo Masarati Pierangelo Masarati Assistant Professor Assistant Professor Dipartimento di Ingegneria Aerospaziale Dipartimento di Ingegneria Aerospaziale Politecnico di Milano (Italy) Politecnico di Milano (Italy) AHS International 60th Annual Forum & Technology Display AHS International 60th Annual Forum & Technology Display Baltimore, MD - Inner Harbor Baltimore, MD - Inner Harbor June 7-10, 2004 June 7-10, 2004
Authors and Contributors Authors and Contributors • David J. Piatak David J. Piatak NASA Langley Research Center NASA Langley Research Center • Jeffrey D. Singleton Jeffrey D. Singleton Army Research Laboratory Army Research Laboratory • Giuseppe Quaranta Giuseppe Quaranta Politecnico di Milano Politecnico di Milano
Outline Outline • Objectives and Approach Objectives and Approach • Experimental Model Description Experimental Model Description • Multibody Dynamics Analyses Multibody Dynamics Analyses • Key Analytical Results Key Analytical Results • Isolated Blade & Hub Results Isolated Blade & Hub Results • Control System Couplings Control System Couplings • Hover Performance & Stability Hover Performance & Stability • Forward Flight Stability Forward Flight Stability • Selected Nonlinear Analysis Issues Selected Nonlinear Analysis Issues • Concluding Remarks Concluding Remarks
Objectives Objectives • Compare multibody analytical techniques Compare multibody analytical techniques • Develop fundamental understanding of strengths, Develop fundamental understanding of strengths, weaknesses, and capabilities of two different codes weaknesses, and capabilities of two different codes 2. Assess prediction capabilities Assess prediction capabilities 2. • Compare response, loads, and aeroelastic stability in Compare response, loads, and aeroelastic stability in hover & forward flight. hover & forward flight. • Analysis vs. analysis Analysis vs. analysis • Analysis vs. experiment Analysis vs. experiment 3. Assess code/user fidelity Assess code/user fidelity 3. 1. Two different multibody codes Two different multibody codes 1. 2. Two different researchers Two different researchers 2. 3. Contrasting two codes helps eliminate errors in modeling Contrasting two codes helps eliminate errors in modeling 3.
Experimental Model Experimental Model Wing & Rotor Aeroelastic Test System (WRATS) Wing & Rotor Aeroelastic Test System (WRATS) Tested in the Rotorcraft Hover Test Facility and the Transonic Tested in the Rotorcraft Hover Test Facility and the Transonic Dynamics Tunnel at NASA Langley Research Center Dynamics Tunnel at NASA Langley Research Center Semi-Articulated Semi-Articulated Soft-Inplane Hub Soft-Inplane Hub (SASIP) (SASIP) 4 blades 4 blades articulated articulated soft-inplane soft-inplane elastomeric lag elastomeric lag damper damper
Multibody Analyses Analyses Multibody • Time domain - analyze via virtual experiments Time domain - analyze via virtual experiments • Can model components and mechanical Can model components and mechanical effects not typically included with effects not typically included with comprehensive rotor analyses comprehensive rotor analyses 1.Hydraulic components Hydraulic components 1. 2.Mechanical joints Mechanical joints 2. 3.Free-play in linkages Free-play in linkages 3. 3.No fixed-hub assumption No fixed-hub assumption 3.
Analytical Models & Analysts Analytical Models & Analysts • MBDyn - MultiBody Dynamics MBDyn - MultiBody Dynamics • Developed by (a team led by) Developed by (a team led by) Prof. Paolo Mantegazza, Politecnico di Milano Prof. Paolo Mantegazza, Politecnico di Milano • WRATS-SASIP analyzed by Pierangelo Masarati WRATS-SASIP analyzed by Pierangelo Masarati and Giuseppe Quaranta and Giuseppe Quaranta 2.DYMORE DYMORE 2. 1. Developed by (a team led by) Developed by (a team led by) 1. Prof. Olivier Bauchau, Georgia Tech Prof. Olivier Bauchau, Georgia Tech 2. WRATS-SASIP analyzed by Dave Piatak and Jinwei WRATS-SASIP analyzed by Dave Piatak and Jinwei 2. Shen Shen
MBDyn - Analytical Model MBDyn - Analytical Model Analysis includes: Analysis includes: Swashplate mechanics Swashplate mechanics • Hydraulic actuators Hydraulic actuators • 3. Blades as composite- Blades as composite- 3. ready beams, with blade ready beams, with blade element aerodynamics element aerodynamics 4. Wing as modal element, Wing as modal element, 4. with state-space with state-space aerodynamics aerodynamics Conventional WRATS Model
DYMORE - Analytical Model DYMORE - Analytical Model Blade Model Blade Model 4 element FEM 4 element FEM Lifting line Lifting line 3D inflow model 3D inflow model Highly twisted: 34 Highly twisted: 34 degrees from root to tip degrees from root to tip Structural and Structural and geometrical properties geometrical properties tuned to match WRATS tuned to match WRATS SASIP ground vibration SASIP ground vibration test results test results
DYMORE Simulation Example DYMORE Simulation Example
Blade Modal Analysis Blade Modal Analysis All analyses consistent All analyses consistent Results agree with experiment Results agree with experiment Mode Measured UMARC MBDyn DYMORE Mode Measured UMARC MBDyn DYMORE F1 - 0.76 0.67 0.69 F1 - 0.76 0.67 0.69 L1 6.46 6.43 6.32 6.46 L1 6.46 6.43 6.32 6.46 F2 21.7 20.01 19.37 18.51 F2 21.7 20.01 19.37 18.51 F3 61.15 64.20 62.43 61.45 F3 61.15 64.20 62.43 61.45 T1 107.94 103.50 106.58 108.49 T1 107.94 103.50 106.58 108.49
Control System Couplings Control System Couplings Typically difficult to Typically difficult to • model. Elastic model. Elastic deformation can have a deformation can have a significant contribution. significant contribution. Non-linear modeling - Non-linear modeling - • classical analyses classical analyses typically use constant or typically use constant or tabulated lookup tabulated lookup coefficients. coefficients. Multibody codes capture Multibody codes capture • nonlinear effect. nonlinear effect.
Hover Run-up Hover Run-up Current analytical model is a Current analytical model is a • simple, constant stiffness simple, constant stiffness equivalent spring hinge equivalent spring hinge
Hover Hover Performance Performance Blade elasticity and Blade elasticity and • geometrical cross-couplings geometrical cross-couplings greatly influence greatly influence performance predictions performance predictions
Hover Dynamics Hover Dynamics Transient time-series correlate with Transient time-series correlate with frequency analysis Linear wind-up frequency analysis Linear wind-up
Forward Flight Stability Forward Flight Stability Comparison of Comparison of generic soft- generic soft- stiff inplane stiff inplane wing mode wing mode damping, damping, Windmilling Windmilling configuration configuration
Forward Flight Stability Forward Flight Stability Comparison of Comparison of generic soft-stiff generic soft-stiff inplane wing inplane wing mode damping in mode damping in powered and powered and windmill. windmill. Windmilling case Windmilling case correlates well. correlates well. Initial results for Initial results for powered mode powered mode did not (no drive did not (no drive system system dynamics) dynamics)
Powered Flight Damping Bucket Powered Flight Damping Bucket Experimental evidence of high damping in wing beam mode Experimental evidence of high damping in wing beam mode in powered flight, with low damping bucket low damping bucket around zero around zero in powered flight, with torque torque High damping found in coupling with drive train dynamics High damping found in coupling with drive train dynamics Possible bucket explanation found by considering deadband Possible bucket explanation found by considering deadband in drive train in drive train
Powered Flight Damping Bucket Powered Flight Damping Bucket Stiff-inplane experimental results have generally show only Stiff-inplane experimental results have generally show only small differences in wing damping between powered and wind- small differences in wing damping between powered and wind- milling flight mode. milling flight mode. Soft-inplane experimental results have significant differences. Soft-inplane experimental results have significant differences. Reason is ‘chance’ coupling of drive dynamics with wing: Reason is ‘chance’ coupling of drive dynamics with wing:
Powered Flight Damping Bucket Powered Flight Damping Bucket Deadband yields windmill- Deadband yields windmill- like damping like damping Soft mast slope controls Soft mast slope controls bucket width bucket width
Powered Flight Damping Bucket Powered Flight Damping Bucket
Powered Flight Damping Bucket Powered Flight Damping Bucket Damping Damping peaks at peaks at bucket bucket borders may borders may be explained be explained with with identification identification close to close to deadband deadband transition transition
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