Aeroelastic stability of aircraft with circulation control wings

Abstract

The aeroelastic stability of aircraft with circulation control wings is examined. A beam finite element is used to model a high aspect ratio wing attached to a rigid fuselage. The fuselage is allowed to undergo rigid-body pitch and plunge motions about the aircraft center of gravity. Unsteady aerodynamic loads on the wing are calculated using a linear, time-domain unsteady aerodynamic model based on the indicia1 response method. Steady experimental circulation control airfoil data are used to determine the airfoil lift curve slope and aerodynamic center location as a function of Mach number and blowing level. Several aircraft configurations are examined, and a parametric study of design parameters is performed. The results indicate that when a high level of blowing is applied a instability of the first wing bending mode can occur. If the blowing pressure ratio is held constant, the wing restabilizes at higher speed. With high blowing the aircraft short-period mode also becomes unstable. The inclusion of rigid-body motion is shown to weaken the CC flutter instability due to inertia coupling of the wing elastic modes with the aircraft rigid-body motion. An improvement in stability also results when the fuselage pitch inertia is decreased and when the wing is swept aft. The effect of a horizontal tail and forward movement of the aircraft center-of-gravity was stabilizing for the 45-deg aft-swept wing configuration but is negligible on the 45-deg forward-swept wing configuration.