Validating the Carbon-Fiber Airframe with FEA

A 2.4 kg UAV doesn't look all that harmless trackside; motor vibration and sudden maneuver loads hit the airframe hard. We didn't start manufacturing without running FEA (Finite Element Analysis) first. The reason: CNC cutting carbon-fiber plates is expensive, and one mistake means throwing the part away. We ran three different analyses. Two of them changed the design.

Strain analysis

We mapped out the load distribution on the structural components during flight. We confirmed the critical joints stayed within strength limits. In the first run there was local stress concentration where the motor arms meet the frame; we increased the corner radius, and the problem went away.

Stress analysis

We measured the micro-deformations that form in the parts under applied forces. The material stayed within its elastic limit. This analysis also helped us optimize the design's form stability under dynamic loads, especially for the sudden load transfer at the moment of landing.

Displacement analysis

We measured how far the components deviated from their original positions under static and dynamic loads. This is how we quantified structural rigidity. We found that the flex occurring during flight stayed within limits that wouldn't disrupt the aerodynamic shape. This analysis actually proved most useful on the wing shaft; the first concept was 6 mm in diameter, exceeded the flex limit, so we moved to an 8 mm carbon-filled polymer.

Decisions that made it into manufacturing

• Main airframe plates: 3K carbon fiber, CNC-cut to 0.1 mm tolerance.
• Wing mounting columns manufactured on a 4-axis CNC (the shape was too complex for 3-axis).
• Parts like motor mounts, wing attachments, and the payload bay are 3D-printed in ABS filament.
• Wing carbon-fiber tube: 8 mm, carbon-filled polymer; the first concept was 6 mm.

So field repairs don't become a nightmare

The arms and landing gear are bolted on. If something breaks, swapping the part takes under 10 minutes. That's not just a design preference, it's a lesson from last season's field stories. We heard it from a former teammate: on competition day a wing cracked, they tried gluing it back together with epoxy in half an hour, and of course it didn't fly. We didn't want to end up in the same situation.