Airfoil Data
E399

The EPPLER 399 AIRFOIL is a 12.1% chord-thickness airfoil with a maximum camber of 6.0% at 38% chord, suited to high-lift UAV wings, RC sailplanes, and low-Reynolds-number slow-flyers. At zero angle of attack the cambered geometry generates positive lift, giving an estimated zero-lift angle of -6.0°.

Thin airfoil theory predicts a stall angle near 11.6° and a peak lift-to-drag ratio around 69 at typical UAV and light-aircraft Reynolds numbers — useful benchmarks before running a full XFOIL or NeuralFoil polar. The 12% thickness provides structural depth for main-spar placement without excessive drag penalty at moderate speeds.

Designers evaluating the E399 typically compare it against profiles of similar thickness: S1210 12%, WORTMANN FX 05-191 AIRFOIL, GOE 621 AIRFOIL, GOE 612 AIRFOIL, NACA 63(3)-618. The NLR-1T AIRFOIL is another reference profile frequently considered alongside it.