Experimental Assessment of the Poststall Performance of Two Highly Cambered Airfoils

Poststall aerodynamic data are required to design and validate propellers, rotors, and wind turbines. However, these data are scarce for (highly) cambered airfoils. This study provides poststall aerodynamic data for the E387 and the FX 63-137 airfoils, and it generates insight into the effect of airfoil camber on poststall aerodynamic behavior. Experimental lift, drag, and moment coefficients are presented for Reynolds numbers between 100,000 and 200,000 at angles of attack from -180 to 180 deg. Prestall performance is validated for the FX 63-137 airfoil, where hysteresis around stall is evident. Comparisons between the two airfoils and published results are made. The FX 63-137 produces a maximum poststall lift coefficient of 1.31 and a drag coefficient at 90 deg of 2.03, whereas the E387 generates values of 1.18 and 1.99, respectively. A geometric relationship is formulated to indicate if an airfoil should have a coefficient of drag larger than a flat plate at 90 deg, and it is found that the FX 63-137 is the only two-dimensional airfoil experimentally tested that conforms to this relationship.