Experimental Investigations of Airplane Maneuverability and Stability in Stall

Nonlinear flight physics of the Lie Bracket roll mechanism

“…This deterioration of the aileron sensitivity near stall has been discussed in several efforts (e.g. [9,15,17,40]); Fig. 2 is quite similar to Fig.…”

“…Note that a zero-mean oscillation in the elevator and the aileron separately will lead to almost no-net motion; the airplane will oscillate around the operating condition. Interestingly, the aileron sensitivity derivative C L δa depends on the angle of attack in the high-alpha range [9,15,17,40,53], despite being constant in the linear range over small angles of attack. We can show this fact by through a simple analysis.…”

“…However, Von Karman discovered that at large angles of attack in the nonlinear regime, the equation has multiple solutions-some of which are asymmetric, as presented by Sears [49,50]. Hence, a purely symmetric wing under a purely symmetric flight condition at a high angle of attack may experience an asymmetric lift distribution causing a rolling moment [15,46]. Note that the asymmetry however slight between the two wing halves is inevitable, so if this asymmetric solution is stable, it would be certainly selected/preferred by Nature over the symmetric one; a large rolling moment would suddenly result [8,13,15,19,46,49,50], as typically occurs in the wing drop phenomenon [39].…”

“…Hence, a purely symmetric wing under a purely symmetric flight condition at a high angle of attack may experience an asymmetric lift distribution causing a rolling moment [15,46]. Note that the asymmetry however slight between the two wing halves is inevitable, so if this asymmetric solution is stable, it would be certainly selected/preferred by Nature over the symmetric one; a large rolling moment would suddenly result [8,13,15,19,46,49,50], as typically occurs in the wing drop phenomenon [39]. Almost every wind-tunnel operator testing a wing in stall experiences violently asymmetrical distributions and tremendous rolling moments [15,50].…”

“…The above discussion implies that an airplane during stall may experience a large, sudden rolling disturbance, which has to be balanced/corrected/rejected before worrying about decreasing the angle of attack to get out of stall. Unfortunately, the aileron control authority may drop significantly near stall [9,15,17,40]. In fact, its sensitivity may even reverse; a steering aileron command to the right may rather result in a left rolling, which exacerbates an already critical situation.…”