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Technical note | C-27J FEM Version 3.0 Enhancement and Verification

Abstract 

The Royal Australian Air Force (RAAF) has commenced a fleet acquisition of C-27J aircraft (AIR8000 Phase 2) to support RAAF tactical airlift capability requirements. As part of the Structural Substantiation Program, a global Finite Element Model (FEM) of the C-27J airframe was obtained from the Original Equipment Manufacturer, Alenia Aeronautica. A global airframe FEM is an important supplementary tool to aid in support of both current and future RAAF C-27J structural integrity management. In 2013, Defence Science and Technology Group completed a preliminary review of the C-27J global FEM and recommended several areas of model enhancement, including specific C-27J FEM verification and validation activities. The key enhancements are: inversion about the global x-axis for all model and load files, incorporation of beam element section properties representative of design section geometry, and finally, creation of a uniform set of engineering units to be used consistently for the model geometry, model materials, and applied loads. Model verification was carried out following application of each of these enhancements and reported. Pending experimental validation, the enhanced and verified C-27J global FEM, known as "C-27J_GFEM_DSTG-v3.0", is a linear elastic internal loads model that will be useful in providing global loads results such as wing tip displacements, field stresses, running loads, and connection forces.

Executive Summary 

The Royal Australian Air Force (RAAF) has commenced a fleet acquisition of C-27J aircraft (AIR8000 Phase 2) to support RAAF tactical airlift capability requirements. As part of the Structural Substantiation Program, a global Finite Element Model (FEM) of the C-27J airframe was obtained from the Original Equipment Manufacturer (OEM) Alenia Aeronautica. A global airframe FEM is an important supplementary tool in support of both current and future RAAF C-27J structural integrity management. In 2013, Defence Science and Technology (DST) Group completed a preliminary review of the C-27J global FEM and recommended several areas of model enhancement, including specific C-27J FEM verification and validation activities. The objectives of these enhancements were: alignment with DST Group model orientation norms, improved useability, alignment with design baseline data, and a reduction in the potential for usage errors.

Presented in this report, the key enhancements are: inversion about the global x-axis for all model and load files, incorporation of beam element section properties representative of design section geometry, renumbering and formatting of data files and finally, restoring the model to a uniform set of engineering units to be used consistently for the model geometry, model materials, and applied loads. The model is now structured in a manner that allows independent operation on any number of the sub-models constituent to the global FEM. Furthermore, substructures are numbered in an orderly fashion that allows new FEM entities to be introduced consistent with the numbering regimes applied, and thus easily spliced into the global FEM. Model verification was carried out following the application of the enhancements and is reported herein. However, assessment has also identified some remaining limitations relating to the applicability of the original applied loads as received from the OEM.

Pending experimental validation, the enhanced and verified C-27J global FEM, known as “C-27J_GFEM_DSTG-v3.0”, is a linear elastic internal loads model that will be useful in providing global loads results such as wing tip displacements, field stresses, running loads, and connection forces. The limitations associated with this model demand focussed consideration by all users.

Key information

Author

Michael Opie and Damion Hadcroft

Publication number

DST-Group-TN-1686

Publication type

Technical note

Publish Date

October 2017

Classification

Unclassified - public release

Keywords

C 27J, aircraft, stress analysis, Finite Element Model, FEM, FEA, Verification, Nastran , Royal Australian Air Force, AIR8000