3D-Printed Aircraft (3DPAC)

The 3DPAC rules require every part to be 3D printed, allow 8 seconds of powered flight, and cap altitude with a 35-foot ceiling, with score set by total flight time. That makes it a glide-endurance problem: minimize drag and wing loading so the aircraft stays aloft as long as possible. The team weighed a flying-wing layout but moved to a conventional-tail glider, which was far more structurally efficient to print.

For the aerodynamics I ran an XFLR5 study of six airfoils (Clark Y, Eppler 325, MH45, MH60, NACA 25112, SD7037) at the low Reynolds number of the flight regime, around 100,000. The Clark Y gave the highest lift (Cl near 1.32 at 11 degrees), the gentlest stall, and a low pitching moment, so it became the wing section. A SimScale CFD run on the wing returned a lift-to-drag ratio of 17.1.

Because the airframe is printed in PLA, handbook properties do not apply, so I characterized the real material. Following ASTM D638 I modeled and printed dog-bone coupons and pulled them on an Instron: five samples each for longitudinal PLA, transverse PLA, and longitudinal LW-PLA. The curves show the strong anisotropy of FDM parts and quantify the penalty of the lightweight foaming filament.

I used those measured properties in a SolidWorks finite-element model of the spar, loaded with the same 11.77 N distributed force as the physical wing-loading rig. Peak principal stress at the root was 16 MPa (11.29 MPa just off the mesh singularity) against a 44.4 MPa ultimate strength, a factor of safety near 2.7, with a 35.18 mm tip deflection. A modal study put the first bending mode at 7.73 Hz and the torsional mode near 46 Hz, far enough apart to rule out flutter.

I then verified the model physically. A vibration test measured the first bending mode at 6.5 Hz versus 7.73 Hz in the FEA, a 15.6 percent error. A sandbag wing-loading test brought the wing to roughly twice the aircraft weight before it failed at the root.

Selecting LW-PLA for the skin also meant a print study: I printed parts across a range of nozzle temperatures to trade the filament's active foaming, which can roughly halve density, against print quality, since LW-PLA prints cleanest in zero-retraction spiral-vase mode.

• 1st place at the 3D-Printed Aircraft Competition (3DPAC)
• Six-airfoil XFLR5 study selected the Clark Y; CFD lift-to-drag of 17.1
• ASTM D638 tensile tests (n=5) characterized PLA and LW-PLA
• Spar FEA: factor of safety near 2.7, 35.18 mm tip deflection
• Flutter ruled out (7.73 Hz bending vs 46 Hz torsion)
• FEA verified against a physical vibration test within 15.6 percent