Stall warning using flap hinge moment measurements

The development of a detection algorithm using the unsteady hinge moment from a simple flap on an airfoil with and without contaminants is studied. To obtain hinge moment data to be used in the detection algorithm development, a series of wind-tunnel tests were performed on a flapped NACA 3415 model. Hinge moment measurements were acquired at a sample rate of 3 kHz for 10 s. Before applying the hinge moment data to the stall detection algorithm, the hinge moment measurements were digitally low-pass filtered at 50 Hz to minimize the influence of structural frequencies. The unsteady hinge moment data obtained from the NACA 3415 test were operated on to increase the signal-to-noise ratio to provide more reliable estimates of the stall angle of attack. While boundary warning predictions were not generated for threshold boundaries other than 2°, there appears to be sufficient signal from the outputs of the detector functions to set the threshold boundary 1 to 4° before stall.