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Advanced Modeling and Simulation of the C-5 Aft Cargo Loading System

This paper explores the comprehensive modeling and real-time simulation of the C-5 Aft Cargo Loading System, focusing on mechanical and hydraulic systems. It discusses the system's background, including the aircraft's aft pressure door, which serves crucial functions for aerial deliveries and drive-in loading. Utilizing CATIA, DADS, and EASY5 models, the development of solutions to address reliability and operational efficiency challenges is outlined. Results include hydraulic modifications increasing opening speed while maintaining performance criteria for aircraft operations, leading to optimized loading procedures.

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Advanced Modeling and Simulation of the C-5 Aft Cargo Loading System

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  1. Title Modeling and Simulation of the C-5 Aft Cargo Loading System J.B. Lojko Engineer II H.F. Smith Sr. Structural Specialist Engr. Lockheed Martin Aeronautics Company - Marietta

  2. Agenda • System Description & Background • DADS Model • EASY5 Model • Solution Development • Testing • Solutions, Part 2 • NASTRAN Model • Conclusions & Lessons Learned

  3. System Description& Background

  4. C-5 Aft Pressure Door

  5. Mechanical System Description • Plug-type Door - Seals Aft Cargo Envelope • Height - 11.4 ft • Width - 19.0 ft • Door Weight 1845 lb • Carries Cabin Pressure Loads in Flight & Cargo or Vehicle Loads for Drive-in Loading • Pressure Door Opens Up for Aerial Delivery & Truck-bed or Down for Drive-in Loading • 2 Sets of Hinges and Actuators, Upper and Lower, Left and Right

  6. Mechanical System Description • Aerial Delivery System • Aerial Delivery System (ADS) Requires Installation of a Pilot Parachute on the Lower Half of the Door • Pilot Parachute and Associated Hardware Weight 558 lb • Supporting Fuselage Structure Found to be Very Flexible

  7. Hydraulic System Description • 3000 psi System • Opening • 2 gpm Split to 1 gpm at Actuators • Ramp Blocker Valve • Balanced Relief Valve • Closing • Initial Lift - Fuse • Slow Down - Fuse

  8. First Contract • Fatigue Problems with Upper Hinge Prompted USAF to Place LM Aero-Marietta Under Contract to Improve the Reliability of this System • Initial Contract 1996 - Less Than Four Month Project • Geometry and Kinematics Created in CATIA • Ground Test Performed to Validate Simulations • Analysis Performed in CATIA Using CAT/DADS • Several Solutions Proposed • Hydraulic Modifications - Slow Door Opening • Structural Modifications - Increase Strength in Selected Areas

  9. First Contract

  10. First Contract Actuator Load Comparison, Normal Operation, Test vs. DADS

  11. First Contract Actuator Load Comparison, Slow Operation, Test vs. DADS

  12. Second Contract • Follow On Contract 1999 • Incorporate Hydraulic Modifications to Reduce Door Opening Speed • First Attempt Failed • Use DADS/Plant & EASY5 to Analyze All Proposed Hydraulic Modifications Prior to Testing • Using Analysis-Led Design the Second Attempt at Modifying the Hydraulics was a Success

  13. DADS Model

  14. Model Definition • Model Simplified - Flexibility Greatly Reduced • 16 Bodies • 6 Control Elements • Left & Right Actuator Distance, DistanceD, Force • Forces • 1 Contact Force - Door Stop • 2 TSDAs - Lower & Upper Fuselage Stops • 2 RSDAs - Flexibility in Torque Arm/Hook

  15. Model Definition • Approximately 20 Joints • Other • Curves - Door Stop Driver

  16. EASY5 Model

  17. Model Definition

  18. Model Definition • 62 Components • Main Control Valve • Custom - HV Library • Balanced Relief Valve (Simplification) • Pilot-to-Open Check Valve • Fuses - Variable Orifice that Closes After Specified Volume of Flow is Sensed

  19. Model Definition, cont. • Actuators - AP Component for use with DADS Model Extension Component • Ramp Blocker Valve - Critical that Pressure was Measured • Simple Fixed Orifice

  20. Solution Development

  21. Simulations • Conduct Simulations to Determine the Best Combination of Flow Regulators • Performance Criteria - Load Reduction vs. Opening Time • Constraint - Slowing Opening Time Could Impact Aircraft Operation • Current Flight Profile Could Change for ADS Preparation

  22. EASY5 Results - Actuator Pressures & Position

  23. EASY5 Results - Ramp Position Valve, Pilot Line

  24. DADS/Plant Results - Actuator Load

  25. Testing

  26. Flow Regulators • Manifold, Cartridge Valve Flow Regulator • Fluid Regulators • Modify Current 2.0 gpm Flow Regulators • .5 gpm & 1.0 gpm • MS-Type Flow Regulator • Parker Hannifin • 1.5 gpm & 2.0 gpm

  27. Cartridge Valve Flow Regulator

  28. Tests • Baseline Test • Verify Door Operates Properly • 1st Test • 1.0/2.0 gpm Flow Regulators • Regulators Delivered as Specified • 2nd Test • .5/1.5 gpm Flow Regulators • Modified 2.0 -> .5 gpm Could Not Perform as Desired

  29. C-5 Aft Pressure Door

  30. C-5 Aft Pressure Door

  31. C-5 Aft Pressure Door

  32. Test Results • Baseline • Operated Properly • Approximately 10 second Opening • 1st Test • Approximately 19 second Opening • Predicted 21.29 second Opening

  33. Test Results, cont. • 2nd Test • Approximately 22 second Opending • Predicted 40 seconds with Constant .5 gpm Flow • 2nd Test - Better Performance • Re-Run Simulations with Variable Flow Rate Regulator

  34. SolutionsPart 2

  35. Loads & Pressures • Goal of First Model • Hydraulic Modification Will It Work? • How Long to Open & Close Door • Not Concerned with Loads • After Test, Model Fidelity Improved to Assist Loads & Structural Analysis Organizations • Variable Flow Regulator Simulated • Balanced Relief Valves Added

  36. Model Definition • Structural Flexibility in Fuselage Modeled • DADS/Flex Used to Model Torque Arm/Hook • Forces • 10 Bushings • MSC NASTRAN Model Used to Find Spring Constants • 4 RSDAs - Damping Only - Friction, Any Uncertainties

  37. Model Definition • Flexible Bodies • Left & Right Torque Arm & Hook • MSC NASTRAN • 1st Simulation Craig-Bampton Modes not Defined Properly • Continue Work Upon Return to Marietta

  38. DADS/Flex • Craig-Bampton Mode Errors • Fixed Constraints • Free Constraints • Axis Orientation • Local z-axis Parallel to Global y-axis for Revo & Cyli Joints • Several Axes Rotated about Global y-axis to Achieve Correct Load Path

  39. NASTRAN Model

  40. Torque Fitting Representation • Torque Fitting and Arms Isolated • Interface Points Defined • Shaft Inboard and Outboard Bearings • Actuator Attach • Door/Arm Contact • Inboard Roller • Restraint Hook • Structure Idealized in NASTRAN • Mirrored for Right Side

  41. Fitting Back-Up Representation • Fuselage Plug from FS 1964 to 2178 Used. Detailed Idealization of Back-up Frame Included. • Five Interface Points Chosen • Actuator Point • Inboard Upper Support Point • Outboard Upper Support Point • Inboard Lower Support Point • Outboard Lower Support Point • Mirrored for Right Side

  42. NASTRAN Analysis Run • Normal Modes • Imposed Deflection Force Matrix Generation • Unit deflections imposed on interface point DOF’s one at a time with remaining interface point DOF’s constrained. • Analyses performed for each side separately for each substructure.

  43. Fitting Idealization

  44. Back-Up Idealization

  45. Conclusion &Lessons Learned

  46. HYDRAULICS & CONTROLS MONODETAIL MODELS DYNAMICS MECHANICAL SYSTEM BUILDUP KINEMATICS (CAT/DADS) Methodology MECHANICAL SYSTEM PROTOTYPE

  47. Integrated CAE • CATIA • Work From One Geometry Model (CATIA) • DADS (CAT/DADS) • Define Load Paths • NASTRAN • EASY5 • Clearly Define Requirements for Interfaces • INTEGRATED CAE WILL SAVE TIME & MONEY

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