Airfoil Data
S1221-4DEG-FLAP

The S1221 w/ 4 deg flap is a 10.5% chord-thickness airfoil with a maximum camber of 5.2% at 28% 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 -5.2°.

Thin airfoil theory predicts a stall angle near 11.7° and a peak lift-to-drag ratio around 65 at typical UAV and light-aircraft Reynolds numbers — useful benchmarks before running a full XFOIL or NeuralFoil polar. The 10% thickness provides structural depth for main-spar placement without excessive drag penalty at moderate speeds.

Designers evaluating the S1221-4DEG-FLAP typically compare it against profiles of similar thickness: S1221 w/o flap, NACA 65(2)-415 a=0.5, 20-32C AIRFOIL, NACA M23 AIRFOIL, WB-140/35/FB 14%. The BOEING-VERTOL VR-1 AIRFOIL is another reference profile frequently considered alongside it.