Systematic Simulation Approach to Aircraft Landing Gear Shimmy Analysis 2012 Aerospace Users Symposium Presented By: Patrick McNally Co-Author: Colin McNally September 14, 2012 MSC Software Confidential 2012 Aerospace Users Symposium Agenda • Introduction of Shimmy Problem • Two Models for Analysis • Characteristics of Problem, Models, Method • Results • Impact of Results • Credits MSC Software Confidential 2 2012 Aerospace Users Symposium Introduction of Shimmy What is Shimmy? “Shimmy is an oscillatory, combined lateral and yaw motion of the landing gear, caused by an interaction between dynamic tire behaviour and landing gear structural dynamics” MSC Software Confidential 3 2012 Aerospace Users Symposium Key References for Shimmy Analysis • Reference (A) • “Modeling and Analysis of a Dual-Wheel Nosegear: Shimmy Instability and Impact Motions” – – G.X. Li, Heroux Inc. SAE 931402 • Reference (B) • “An Investigation of Landing Gear Shimmy: Tire Models, Tire Test Methodologies, Analysis and Parameter Studies” – – – John Medzorian Air Force Research Laboratory SAE 1999-01-5527 • Reference (C) • “Preliminary Nose Landing Gear Shimmy Analysis Using MSC.ADAMS Aircraft” – – Chris Hetreed, MSC.Software MSC.ADAMS NA User Conference, 2002 References analyze a specific configuration and/or make limiting assumptions. Our goal is to describe general techniques. MSC Software Confidential 4 2012 Aerospace Users Symposium Two Analytical Models For analysis of shimmy MSC Software Confidential 5 2012 Aerospace Users Symposium Two Models for Shimmy Studies Light Aircraft Nose Gear Transport Nose Gear FAR Part 23 Business Jet Small Military Jet UAV MSC Software Confidential FAR Part 25 Typical Boeing and Airbus aircraft 6 2012 Aerospace Users Symposium Light Aircraft Nose Gear Details • Effects of layout including – – – – Static trail Cant angle Upper cylinder length Lower cylinder length • Tire effects including – Choice of tire model – Relaxation length – Aligning moment coefficient MSC Software Confidential 7 2012 Aerospace Users Symposium Transport Aircraft Nose Gear Details • Stiffness effects – Mounting – Strut – Steering MSC Software Confidential 8 2012 Aerospace Users Symposium Key Characteristics of Both Models MSC Software Confidential 9 2012 Aerospace Users Symposium Key Characteristics of Both Models • Subsystem or System level analysis • Nonlinear nature of problem • Parametric construction • Method of shimmy stimulus • Detection of shimmy • Overall process MSC Software Confidential 10 2012 Aerospace Users Symposium Subsystem or System Analysis • Same gear model can be used in test rig or attached to aircraft • Mimics physical testing done on test rig or aircraft taxi • Instrumentation, stimulus, and detection are same MSC Software Confidential 11 2012 Aerospace Users Symposium Parametric Variation – Kinematic effects • – Joint compliance • • – Hydraulic system stiffness Torsional backlash/free play Flexible components • • • • • – – – – Joint stiffness (through use of bearings) Free play Steering compliance • • – Advanced parametrization of model to permit “one click” cant angle and trail length studies LG Strut Parts Torque arm Drag link Supporting Structure (Subframe) Bogies/axles Flexible Bearings Damping Friction Internal dynamic tire states (e.g. Swift, FTire) MSC Software Confidential 12 2012 Aerospace Users Symposium Method of Stimulus “Pinger” force added to model to push axle laterally Step function used MSC Software Confidential 13 2012 Aerospace Users Symposium Detection of Shimmy • Sensor used to detect lateral velocity exceeding a threshold • Action is to capture the forward velocity when shimmy occurs MSC Software Confidential 14 2012 Aerospace Users Symposium Automation of the Shimmy Analysis Process Parameter Variables MSC Software Confidential ADAMS + VI-Aircraft automation 15 modeFRONTIER DOE and optimization 2012 Aerospace Users Symposium Results MSC Software Confidential 16 2012 Aerospace Users Symposium Typical Results – Time Domain • Time domain plot • Monitor lateral force until exceeds threshold • Determine velocity and time when threshold has been exceeded • Optionally run an eigenvalue analysis MSC Software Confidential 17 2012 Aerospace Users Symposium Typical Results – Frequency Domain • Eigenvalue analysis • Shift to right half plane when unstable • Animation confirms shimmy mode MSC Software Confidential 18 2012 Aerospace Users Symposium Parallel Coordinates MSC Software Confidential 19 2012 Aerospace Users Symposium Scatter Matrix Parameter Variables MSC Software Confidential ADAMS + VI-Aircraft automation 20 modeFRONTIER DOE and optimization 2012 Aerospace Users Symposium Scatter Matrix – Trail Length Effect MSC Software Confidential 21 2012 Aerospace Users Symposium Impact of Results • SAE A5 Document • Upcoming meeting in Bar Harbor, ME MSC Software Confidential 22 2012 Aerospace Users Symposium Summary and Conclusions • Simulation models used to predict nonlinear behavior such as shimmy • Trends of the models used to understand key factors – model specifics are realistic • Approach to excite shimmy in simulation is based on physical testing • Simulation method is being used to describe general methods which are used as best practices and should become standard practices in aircraft development MSC Software Confidential 23 2012 Aerospace Users Symposium Acknowledgements • Jack Hagelin, Boeing Aircraft Company • Brandon Wagoner, ESTECO • Colin McNally, VI-grade MSC Software Confidential 24 2012 Aerospace Users Symposium
