Applications in airflow monitoring: stall detection. (a) Conceptual illustration of stall, with red region representing positive pressure while the blue region representing negative pressure [80]. (b) Schematic of the airfoil integrated with the iFlexSense skin (P: piezoelectric sensor; H: hot-film sensor; C: capacitive pressure sensor; T & S: temperature & strain sensors) [80]. (c) The electronic skin mounted on a standard NACA 0012 airfoil under varying AOA from 25° to +25° (an incremental step of 1°) [80]. (d) Time-averaged pressure of the suction peak under different free stream velocities from 4 m/s up to 11.16 m/s [80]. (e) Principle and structure diagram of digital-visualization array for turbulence stall sensing (DATSS) [81]. (f) DATSS system stall sensing T-signal after STD processing [81]. (g) DATSS system stall sensing raw P-signal [81]. (h) The photograph of fixed-wing remote control Cessna 182 aircraft with a wing length of 1420 mm for flight test, equipped with two DATSS units [81]. (i) The wireless flight signal of the arrayed DATSS system [81].