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Optimal Design for Aircraft Sub-assembly Structure

The Client

The client is an aircraft Original Equipment Manufacturer (OEM).

Business Need

The client required an overhaul of the sub-assembly, which is part of the landing gear support structure. It comprises inner fixed trailing edge wing skin panel extensions with attached stringers, stiffeners and brackets. The upper and lower skin extensions form part of wing covers over the landing gear support structure and is the most critical part of the sub-assembly. The client sought to develop an optimal design for the sub-assembly from concepts and achieve seamless integration with the wing box structure. Besides weight optimization and re-design for freight, and the next MSN were also commissioned.

Challenge

Aircraft Finite Element Grid Structure

Infosys had to address several challenges:

  • The sub-assembly structure is witness to a complex set of loads. It is designed with different load cases in different zones. It had to be designed for strain matching loads from the wing box bending, the local loads from flap tracks and spoilers, the landing and ground loads, crashworthiness loads and discrete failure cases such as tyre debris
  • Identify case-consistent critical load cases for each part or region of the structure from thousands of load cases, instead of a simple approach of max-max enveloping
  • Certain parts and interfaces had to be protected for higher weight variants and design protection was sought for reparability against possible impact from discrete failures
  • Irregular and non-standard geometric features render an application of standard sizing methods, complex and necessitate rigorous analysis through fine grid finite element methods

Our Solution

Salient features of our solution include:

  • Different design concepts were evaluated jointly and optimal configurations were selected. Chordwise and spanwise stringer configurations were evaluated for wing bending critical areas. The number of stringers, stiffeners, positioning, section types and sizes, materials, and joining methods were decided based on rigorous analysis of diverse options
  • Sizing templates were established with macros to interface with client tools, FEM software and methods helped run sizing calculations rapidly for multiple load releases
  • Potato plot technique was employed to enable selection of case-consistent critical load cases among number of maximum and minimum cases, which helped achieve a light weight design
  • Parameterized 3D-CAD models were created for quick updates to sizing and regular uploads to DMU databases. ICAD was effectively used for automated design model development of skin panels and stringers

Benefits

  • A number of automations were established for efficiency in CAD modeling and sizing calculations. Designs were released on time despite delays in load and interface releases and several iterations
  • The design solution achieved desired weight target in the first design iteration, and realized additional weight saving of 20 kgs against the target of 15 kgs
  • Re-design performed on two variants resulted in cycle time reduction of 30 percent – 40 percent

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