Stall Warning Using Flap Hinge Moment Measurements

Abstract

G ENERALLY, surface contamination of a wing leads to reductions in performance [1–3]. Premature stall due to contamination can also have devastating effects on the controllability of aircraft [4,5]. Currently, there is no established, effective method for monitoring aircraft performance and controllability in order to prevent stall under adverse conditions created by surface contamination. While angle-of-attack sensors are capable of providing an effective stall warning for an aircraft free of contaminants, the effectiveness of such systems greatly diminishes with the presence of contaminants on an aircraft wing. Gurbacki and Bragg [6] studied the steady and unsteady hinge moment behaviors of supercooled large-droplet ice-induced stall on a NACA 23012 airfoil model with a simple flap. In that study, it was found that the rms of the unsteady hinge moment increased 1 to 3 angles of attack before stall for the iced case. Thus, it was identified that the unsteady separated flow led to unsteady changes in the hinge moment, giving rise to the concept that unsteady hinge moment measurements could be used to predict ice-induced stall [7]. Such a method could be further applied to a system capable of monitoring aircraft aerodynamic performance and providing realtime predictions of the edge of a flight envelope. In addition to flight beyond the baseline-clean aircraft flight envelope, such a system could potentially detect a reduction in the envelope due to several inflight environmental contaminants resulting from icing encounters, heavy rain, surface contamination in the form of roughness, and structural damage, such as bird strikes or battle damage. To further this concept, additional development is needed beyond the initial work of Gurbacki and Bragg [6]. ThisNote reports the further development of such a technique. The specific focus of this Note is the development of a detection algorithm using the unsteady hinge moment from a simple flap on an airfoil with and without contaminants. The algorithm developed is used to predict stall several degrees before the event.