Airfoil Data
E421

The EPPLER 421 AIRFOIL is a thick 15.6% chord-thickness airfoil with a maximum camber of 7.8% at 33% 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 -7.8°.

Thin airfoil theory predicts a stall angle near 10.4° and a peak lift-to-drag ratio around 73 at typical UAV and light-aircraft Reynolds numbers — useful benchmarks before running a full XFOIL or NeuralFoil polar. The 16% thickness provides structural depth for main-spar placement without excessive drag penalty at moderate speeds.

Designers evaluating the E421 typically compare it against profiles of similar thickness: GOE 434 AIRFOIL, GOE 462 AIRFOIL, USA 31 AIRFOIL, WORTMANN FX 72-MS-150A AIRFOIL, GOE 522 AIRFOIL. The GOE 415 AIRFOIL is another reference profile frequently considered alongside it.