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Overview
Problem: Design a hat-stiffened fuselage segment to survive 10,000 lbf axial compression within a strict weight budget.
Hat stiffener selected over blade stiffeners — closed trapezoidal section distributes load through a loop, improving buckling resistance
DOE across 4 parameters (flange width, web height, crown width, wall thickness) run at 3 simulation levels — isolated stiffener, plate, full panel
Final geometry: 30 ksi peak stress, sub-1 lb mass, 1.54 in deformation across 36 in structure
2° tapered interference-fit interface eliminates adhesives and fasteners while constraining all 3 DOF
6 segments assembled into 36 in fuselage — Teamcenter PLM used to manage drawing releases and design iterations
Siemens NX · ANSYS FEA · Teamcenter PLM · Design Of Experiments · 3D Printing
Why a hat stiffener?
The hat stiffener forms a closed trapezoidal cross-section when bonded to the fuselage skin. That closed geometry transfers compressive load through a continuous loop rather than concentrating it at discrete points — giving it a higher moment of inertia and better torsional and buckling resistance than open-section alternatives like blade stiffeners. The same principle drives its use in the Boeing 787 and Airbus A350.
Parametric optimization
Four stiffener geometry parameters were studied: flange width, top width, web height, and wall thickness. To isolate the effect of each variable, only one parameter was varied at a time across five versions while the others were held constant. Initial values were set at the 3D printing minimum feature threshold (0.050") given the competition's manufacturing constraints.
Each version was evaluated across three progressive simulation configurations — isolated stiffener, stiffener bonded to a flat plate, and an array of stiffeners on a larger panel — to capture behavior from individual cross-section performance all the way up to panel-level stiffener interaction.
Final optimized dimensions:
Parameter Optimized value
Flange width 0.080 in
Top width 0.054 in
Wall thickness 0.069 in
Stiffener height 0.064 in
Full fuselage FEA
With optimized dimensions locked in, the full cylindrical fuselage segment was simulated under the same 10,000 lbf axial load. Small fillets (0.010") were added at internal corners to avoid artificial stress concentrations and produce more physically accurate results.
The final 36-inch assembly — six 6-inch segments joined end-to-end — achieved a peak von Mises stress of 30,347 psi against an average of 24,943 psi. The tight gap between peak and average stress indicates that the stiffener geometry and joint interface are distributing load efficiently rather than concentrating it. Total mass: 0.99 lbs.
Assembly interface: 2° tapered interference fit
The competition prohibited adhesives and fasteners. To connect six printed segments into a structurally continuous 36-inch fuselage, I designed a friction-fit interface: one end of each segment features an internal tapered receptacle with a 2° inward draft; the opposite end is a matching male protrusion. During assembly, the male end elastically deforms against the taper, generating a high-contact-pressure interface that constrains axial, radial, and rotational degrees of freedom simultaneously. No hardware required.
Results
10,000 lbf axial load sustained across 36-inch assembly
Peak stress: 30,347 psi / Average stress: 24,943 psi
Max displacement: 1.54 inches
Total mass: 0.99 lbs
6 segments, hardware-free assembly via tapered interference fit
Physical prototype was sliced to G-code and prepared for print within the 6×6×6 in build volume constraint. Printing could not be completed within the project timeline — physical validation and tolerance testing of the friction-fit interface remain future scope.
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