Periodic Tail Motion Linked to Wing Motion Affects the Longitudinal Stability of Ornithopter Flight

During slow level flight of a pigeon, a caudal muscle involved in tail movement, the levator caudae pars vertebralis, is activated at a particular phase with the pectoralis wing muscle. Inspired by mechanisms for the control of stability in flying animals, especially the role of the tail in avian flight, we investigated how periodic tail motion linked to motion of the wings affects the longitudinal stability of ornithopter flight. This was achieved by using an integrative ornithopter flight simulator that included aeroelastic behaviour of the flexible wings and tail. Trim flight trajectories of the simulated omithopter model were calculated by time integration of the nonlinear equations of a flexible multi-body dynamics coupled with a semi-empirical flapping-wing and tail aerodynamic models. The unique trim flight characteristics of ornithopter, Limit-Cycle Oscillation, were found under the sets of wingbeat frequency and tail elevation angle, and the appropriate phase angle of tail motion was determined by parameter studies minimizing the amplitude of the oscillations. The numerical simulation results show that tail actuation synchronized with wing motion suppresses the oscillation of body pitch angle over a wide range of wingbeat frequencies.

Bifurcation analysis and stability design for aircraft longitudinal motion with high angle of attack

Bifurcation analysis and stability design for aircraft longitudinal motion are investigated when the nonlinearity in flight dynamics takes place severely at high angle of attack regime. To predict the special nonlinear flight phenomena, bifurcation theory and continuation method are employed to systematically analyze the nonlinear motions. With the refinement of the flight dynamics for F-8 Crusader longitudinal motion, a framework is derived to identify the stationary bifurcation and dynamic bifurcation for high-dimensional system. Case study shows that the F-8longitudinal motion undergoes saddle node bifurcation, Hopf bifurcation, Zero-Hopf bifurcation and branch point bifurcation under certain conditions. Moreover, the Hopf bifurcation renders series of multiple frequency pitch oscillation phenomena, which deteriorate the flight control stability severely. To relieve the adverse effects of these phenomena, a stabilization control based on gain scheduling and polynomial fitting for F-8 longitudinal motion is presented to enlarge the flight envelope. Simulation results validate the effectiveness of the proposed scheme.

Aerodynamics of non-slender delta and reverse delta wings:Wing thickness,anhedral angle and cropping ratio

The effects of thickness-to-chord(t=c)ratio,anhedral angle(d),and cropping ratio from trailing-edge(Cr%)on the aerodynamics of non-slender reverse delta wings in comparison to non-slender delta wings with sweep angle of 45°were characterized in a low-speed wind tunnel using force and pressure measurements.The measurements were conducted for total of 8 different delta and reverse delta wings.Two different t/c ratios of 5.9%and 1.1%,and two different anhedral angles ofd=15°and 30°for non-cropped and cropped at Cr=30%conditions were tested.The results indicate that the reverse delta wings generate higher lift-to-drag ratio and have better longitudinal static stability characteristics compared to the delta wings.The wing thickness has favorable effect on longitudinal static stability for the reverse delta wing whereas longitudinal static stability is not influenced by wing thickness for the delta wing.For reverse delta wings,the anhe-draled wing without cropping has adverse effect on aerodynamic performance and decreases the lift-to-drag ratio.Cropping in anhedraled wing causes significant improvement in lift-to-drag ratio,shift in aerodynamic and pressure centers towards the trailing-edge,and enhancement in longitudi-nal static stability.