Flight Stability and Control of Tailless Lambda Unmanned Aircraft

Abstract

Marques P. (2013). Flight stability and control of tailless lambda unmanned aircraft. International Journal of Unmanned Systems Engineering. 1(S2): 1-4. This paper illustrates the unique challenges with which Aerospace Engineers are presented in achieving dynamic stability and autonomous flight control in tailless lambda unmanned aircraft. The static margin in lambda configurations is short, making the aircraft unstable. To compensate for the short static margin, a priority in lambda UAV design is to obtain a small linear pitching moment. Negligible pitching moment is implemented using reflex camber airfoils that complement the longitudinal dihedral provided by combined wing sweep back and washout. The reflex airfoil permits a wider choice of wing planform and enhances control authority with minimum elevon deflection. Stability analysis shows that a lambda UCAV is longitudinally unstable in ground effect, in both the flaps extended and flaps retracted configurations. Vortical flow and asymmetrical vortex bursting unsteadiness in a rapidly maneuvering next generation near-lambda 1303 UCAV are responsible for unexpected changes in pitch, roll and yaw coefficients and illustrate the difficulty in maneuvering the UCAV beyond certain critical angles of attack. The primary mechanism of lateral-directional control in a W–shaped flying wing UAV is provided by drag rudders, however lateral-directional control in such aircraft requires a sophisticated on-board flight control system. © Marques Aviation Ltd – Press.