Airfoil Data
E639

The EPPLER 639 AIRFOIL is a 11.1% chord-thickness airfoil with a maximum camber of 5.5% at 29% chord, suited to general-aviation and UAV wing design. At zero angle of attack the cambered geometry generates positive lift, giving an estimated zero-lift angle of -5.5°.

Thin airfoil theory predicts a stall angle near 11.6° and a peak lift-to-drag ratio around 66 at typical UAV and light-aircraft Reynolds numbers — useful benchmarks before running a full XFOIL or NeuralFoil polar. The 11% thickness provides structural depth for main-spar placement without excessive drag penalty at moderate speeds.

Designers evaluating the E639 typically compare it against profiles of similar thickness: EPPLER 433 AIRFOIL, GOE 480 AIRFOIL, NACA 64(3)-418, AH 93-W-145, GOE 584 AIRFOIL. The NACA 747A315 is another reference profile frequently considered alongside it.