Airfoil Data
M685

The M6 (85%) is a thin 7.0% chord-thickness airfoil with a maximum camber of 3.5% at 30% chord, suited to high-speed UAVs, sailplane tip sections, and propeller blade design. At zero angle of attack the cambered geometry generates positive lift, giving an estimated zero-lift angle of -3.5°.

Thin airfoil theory predicts a stall angle near 11.9° and a peak lift-to-drag ratio around 55 at typical UAV and light-aircraft Reynolds numbers — useful benchmarks before running a full XFOIL or NeuralFoil polar. The slim profile minimises pressure drag at higher speeds but leaves limited spar depth for structural integration.

Designers evaluating the M685 typically compare it against profiles of similar thickness: NASA/LANGLEY RC12-64C AIRFOIL, S1048 14% (Danny Howell), NASA SC(2)-0714 AIRFOIL, SG6041, SC(2)-0714 | Supercritical airfoil (coordinates from Raymer w/ one correction). These coordinates are actual model coordinates, not coordinates as designed. Ref: NASA TP-2890. The NACA 64-215 AIRFOIL is another reference profile frequently considered alongside it.