Project Goal:

To design and optimize a fuselage with beam and truss members for maximum stiffness and minimum weight.

Project Summary & Impact

This project was for Mech 485 - Airplane Structures Design, a course that I took as an elective. This upper-level mechanical engineering course focuses on the main components of airplane structures including wing box design, fuselage design, design of connections such as rivets and bolts, and calculating different stresses and loading cases. As a capstone project for this course, I optimized a wing box structure to solve for a minimum mass and maximum stiffness using the Finite Element Analysis software, Abaqus. This software allowed for the utilization of modeling physical responses of the system under a pre-defined load of 4000N.

<aside> 💡 This project highlights the use of Abaqus an FEA software used for simulating physical responses to environmental conditions. Through many iterations, I was able to increase the performance of the design by 46.78% measured by the increase in load-to-weight ratio. These skills apply to any product design as we look to decrease mass/cost and optimize performance.

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Process

The process for this design was to first model the structure based on geometry given by the professor. Then, by incorporating design principles and my knowledge of statics and dynamics, reduced the weight and increased the stiffness of the design. I sectioned these designs into five main iterations which had considerable changes in geometry, though many more were done to fine-tune the design. Rather than simply guess and check (a time-consuming process) I utilized resources from the course, and other courses, watching YouTube modeling videos, and papers online to get an optimized structure and 100% on this report.

The design

The parameters given by our professor were the following:

The question posed for the report: Perform the wing box analysis using beam elements and compare the stresses with the truss model. What are the differences in stress and displacements?

My Theory behind Wing Box Simulation:

• Beam Elements: one-dimensional line element in three-dimensional space that has a stiffness. Beam elements can deform via axial stretch, bending, or torsion.
• Truss Model: one-dimensional bars or rods that are assumed to deform by axial stretching only

Unlike truss elements, beam elements can undergo bending and torsional stresses, not just axial stretch. Truss elements do not have the ability to transmit moments! Typical spars in aircrafts are solid extruded aluminum or multiple aluminum extrusions riveted together. This type of joint tells us that these elements should be modeled by beam elements as they will be able to carry a bending load. This contributes to a more realistic modeling of our spar elements as these components will undergo bending since they are not rods connected by ball joints (spherical joints) at both ends – this is what trusses essentially model.

In aircrafts typically the ribs are supported by diagonal elements. These support elements are the case when we do want to see these elements deforming only axially and not transmitting moments. These diagonal components help translate this force to be undertaken by the fuselage. The use of joints in the ribs (the portion defining the airfoil shape) allows the defining shape to stretch or compress axially under load so the joints can easily be bent changing the airfoil’s shape.