Further Results of Soft-Inplane Tiltrotor Aeromechanics Investigation Using Two Multibody Analyses Pierangelo Masarati Assistant Professor Dipartimento.

Further Resultsof Soft-Inplane Tiltrotor Aeromechanics Investigation Using Two Multibody Analyses

Pierangelo MasaratiPierangelo MasaratiAssistant ProfessorAssistant Professor

Dipartimento di Ingegneria AerospazialeDipartimento di Ingegneria Aerospaziale

Politecnico di Milano (Italy)Politecnico di Milano (Italy)

AHS International 60th Annual Forum & Technology DisplayAHS International 60th Annual Forum & Technology DisplayBaltimore, MD - Inner HarborBaltimore, MD - Inner Harbor

June 7-10, 2004June 7-10, 2004

Authors and ContributorsAuthors and Contributors

• David J. PiatakDavid J. PiatakNASA Langley Research CenterNASA Langley Research Center

• Jeffrey D. SingletonJeffrey D. SingletonArmy Research LaboratoryArmy Research Laboratory

• Giuseppe QuarantaGiuseppe QuarantaPolitecnico di MilanoPolitecnico di Milano

OutlineOutline

• Objectives and ApproachObjectives and Approach• Experimental Model DescriptionExperimental Model Description• Multibody Dynamics AnalysesMultibody Dynamics Analyses

• Key Analytical ResultsKey Analytical Results• Isolated Blade & Hub ResultsIsolated Blade & Hub Results• Control System CouplingsControl System Couplings• Hover Performance & StabilityHover Performance & Stability• Forward Flight StabilityForward Flight Stability• Selected Nonlinear Analysis IssuesSelected Nonlinear Analysis Issues

• Concluding RemarksConcluding Remarks

ObjectivesObjectives• Compare multibody analytical techniquesCompare multibody analytical techniques

• Develop fundamental understanding of strengths, Develop fundamental understanding of strengths, weaknesses, and capabilities of two different codesweaknesses, and capabilities of two different codes

• Assess prediction capabilitiesAssess prediction capabilities• Compare response, loads, and aeroelastic stability inCompare response, loads, and aeroelastic stability in hover & forward flight.hover & forward flight.

• Analysis vs. analysisAnalysis vs. analysis• Analysis vs. experimentAnalysis vs. experiment

• Assess code/user fidelityAssess code/user fidelity• Two different multibody codesTwo different multibody codes• Two different researchersTwo different researchers• Contrasting two codes helps eliminate errors in modelingContrasting two codes helps eliminate errors in modeling

Experimental ModelExperimental 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 CenterDynamics Tunnel at NASA Langley Research Center

Semi-Articulated Semi-Articulated Soft-Inplane HubSoft-Inplane Hub

(SASIP)(SASIP)• 4 blades4 blades• articulatedarticulated• soft-inplanesoft-inplane• elastomeric lag elastomeric lag

damperdamper

MultibodyMultibody AnalysesAnalyses

• Time domain - analyze via virtual experimentsTime 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 analysescomprehensive rotor analyses• Hydraulic componentsHydraulic components• Mechanical jointsMechanical joints• Free-play in linkagesFree-play in linkages

• No fixed-hub assumptionNo fixed-hub assumption

Analytical Models & AnalystsAnalytical Models & Analysts

• MBDyn - MultiBody DynamicsMBDyn - 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 MasaratiWRATS-SASIP analyzed by Pierangelo Masarati

and Giuseppe Quarantaand Giuseppe Quaranta

• DYMOREDYMORE• Developed by (a team led by)Developed by (a team led by)

Prof. Olivier Bauchau, Georgia TechProf. Olivier Bauchau, Georgia Tech• WRATS-SASIP analyzed by Dave Piatak and Jinwei WRATS-SASIP analyzed by Dave Piatak and Jinwei

ShenShen

MBDyn - Analytical ModelMBDyn - Analytical Model

• Swashplate mechanicsSwashplate mechanics• Hydraulic actuatorsHydraulic actuators• Blades as composite-Blades as composite-

ready beams, with blade ready beams, with blade element aerodynamicselement aerodynamics

• Wing as modal element, Wing as modal element, with state-space with state-space aerodynamicsaerodynamics

• Analysis includes:Analysis includes:

ConventionalWRATS Model

DYMORE - Analytical ModelDYMORE - Analytical Model

• Blade ModelBlade Model• 4 element FEM4 element FEM• Lifting lineLifting line• 3D inflow model3D inflow model• Highly twisted: 34 Highly twisted: 34

degrees from root to tipdegrees 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 resultstest results

DYMORE Simulation ExampleDYMORE Simulation Example

Blade Modal AnalysisBlade Modal Analysis• All analyses consistentAll analyses consistent• Results agree with experimentResults agree with experiment

108.49108.49106.58106.58103.50103.50107.94107.94T1T1

61.4561.4562.4362.4364.2064.2061.1561.15F3F3

18.5118.5119.3719.3720.0120.0121.721.7F2F2

6.466.466.326.326.436.436.466.46L1L1

0.690.690.670.670.760.76--F1F1

DYMORDYMOREE

MBDynMBDynUMARCUMARCMeasureMeasuredd

ModeMode

Control System CouplingsControl 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-upHover Run-up• Current analytical model is a Current analytical model is a

simple, constant stiffness simple, constant stiffness equivalent spring hingeequivalent spring hinge

HoverHoverPerformancePerformance

• Blade elasticity and Blade elasticity and geometrical cross-couplings geometrical cross-couplings greatly influence greatly influence performance predictionsperformance predictions

Hover DynamicsHover DynamicsTransient time-series correlate with Transient time-series correlate with frequency analysisfrequency analysis Linear wind-upLinear wind-up

Forward Flight StabilityForward Flight StabilityComparison of Comparison of generic soft-generic soft-stiff inplane stiff inplane wing mode wing mode damping,damping,

WindmillingWindmilling

configurationconfiguration

Forward Flight StabilityForward 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 in powered flight, with low damping bucketlow damping bucket around zero around zero torquetorque

• High damping found in coupling with drive train dynamicsHigh damping found in coupling with drive train dynamics• Possible bucket explanation found by considering deadband Possible bucket explanation found by considering deadband

in drive trainin 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 dampinglike damping

• Soft mast slope controls Soft mast slope controls bucket widthbucket 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 transitiontransition

Concluding RemarksConcluding Remarks

• Multibody codes can:Multibody codes can:• successfully model complex systemssuccessfully model complex systems• improve predictions of rotorcraft dynamic behaviorimprove predictions of rotorcraft dynamic behavior• proficiently address nonlinearity issuesproficiently address nonlinearity issues

• Next steps are:Next steps are:• Conversion / maneuver simulationsConversion / maneuver simulations• Hub/blade maneuver loads correlationHub/blade maneuver loads correlation• Parametric study of SASIPParametric study of SASIP

Special Thanks To -Special Thanks To -

• Giampiero BindolinoGiampiero Bindolino(Politecnico di Milano, Dipartimento di Ingegneria Aerospaziale)(Politecnico di Milano, Dipartimento di Ingegneria Aerospaziale)

• Mark W. NixonMark W. Nixon(ARL: Army Research Laboratory, Vehicle Technology (ARL: Army Research Laboratory, Vehicle Technology

Directorate)Directorate)

• Jinwei ShenJinwei Shen(NIA: National Institute of Aerospace)(NIA: National Institute of Aerospace)