Aircraft interiors equipment analyzed in Strand 7 | CDGudas
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Aircraft Interiors

Four views of rack internal structure and facings configuration. On side the tree structure of the sub assemblies and parts

 Strand7 solution displayed

Table with 1 g inertial forces applied to the rack

Brief of scope, configuration and representative loads

The side figure shows general characteristics for one of several configurations of 19 inch wide racks installed in the cabin of a commuter class aircraft for the purpose of hosting electronic equipment used in live data processing and imaging of electromagnetic information from radar and/or high optical resolution equipment used for example, in high altitude search and rescue operations with good visibly or when the visibility is obstructed by vegetation, clouds, etc.

In the case presented the racks is of light weight construction with the base attached to the aircraft seat tracks and with two additional attachments connected to the fuselage lateral structure.

The scope of analysis for this equipment was determination of the ultimate interface loads at the air frame for the purpose of showing compliance with the certification requirements applicable to this class of aircraft and operational profile.

The final finite element analysis was conducted per customer requirements, in Strand 7 (by Strand7 Pty Ltd) with an alternative code being developed and supplied in MSC Nastran. 

The model presented contains only 37 major parts, some fabricated from small thickness sheets of 4130 mild steel ( brackets, supports, hat sections, etc), other form 0.5 inch thick honeycomb panels with 2024 aluminium facings and core (side panels and shelves) and more than 250 fasteners like AN3 and AN525 bolts, MS24603 and MS27039 screws and honeycomb inserts.  Using a well defined system for the ids. of the nodes and elements of all components, detailed and extensive or targeted summary reports were generated for the relevant results in a semiautomatic manner using in this situation Excel and a suite of VBA subroutines to read. organise and extract the information from the results files.

A representative brief of the 1 g inertial forces applied by the equipment to the rack in this brief is shown in the table on the left.  This can be magnified by clicking inside the blue border

Pre-processing

For this initial stage two main pre-processing tasks are exemplified:

  • The systematic breakdown for all parts of the geometrical features where high stresses or high stress gradients occur often due to geometrical stress concentrations and/or due to the presence of interfaces for load transfer between the components in the assembly.   This systematisation is very convenient for the generation of data decks of meshes for similar features using scripts in a software of choice.
  • The use of different material property identifiers for quick selection and constructions of part sub -groups (in Strand7)

Examples of implementation are presented in the table and the figures below.

Table with systematic features break down and id allocations (extract)
Sample of part subdivision (by material prop. identifier)
Sample of part subdivision (by geometrical feature characteristics)

Post-processing

Two tables with summaries of results are exemplified in the tables below for fastener loads and principal stresses.  The systematisation and codification system developed in the pre-processing stage is fed automatically in the tables to provide quick identification of locations, orientation, load case etc.   In this case, when relevant, von Mises stresses were also included to ascertain if the results of linear analysis are within the validity range of the solution used.

Extracts of fastener loads summaries

Similar results for the other stress components in material, global or specific coordinate systems.

For this analysis over 450 coordinate systems were established in the modelling stage.

Extract of stress summaries (for fatigue and crack growth evaluation)
Global and local stress distributions (von Mises shown) in metal components _3

Global and local stress distributions (von Mises shown) in metal components

Stresses in the one of the facings of honeycomb panels

Max principal stresses in facings of honeycomb panels