Airfoil Data
HT21

The HT21 is a thin 2.6% chord-thickness airfoil with a maximum camber of 1.3% at 20% 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 -1.3°.

Thin airfoil theory predicts a stall angle near 12.1° and a peak lift-to-drag ratio around 43 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 HT21 typically compare it against profiles of similar thickness: HT12, HT08, GOE 443 AIRFOIL, HT05, GOE 444 AIRFOIL. The HT 14 is another reference profile frequently considered alongside it.