Stability of asymmetric equilibrium flight states

Abstract

C dynamic stability of asymmetric trim states of a large, multiengine jet transport which are dictated by engine failure at low speed is considered. Eigenvalue (root) loci obtained from coupled equations of motion for a range of sideslip angles are presented. These loci indicate that as long as the equilibrium sideslip angle is kept small in magnitude there is little difference in the stability characteristics for symmetric and asymmetric thrust conditions. However, when a large magnitude sideslip angle is present in the equilibrium state the coupling effects due to sideslip result in appreciable differences in the coupled motion counterparts of phugoid, spiral, and Dutch roll modes. In particular, under a condition of left outboard engine out and large positive sideslip, the phugoid mode becomes unstable. The spiral mode, under the same engine-out condition, is unstable for both positive and negative sideslip angles.