Longitudinal stability of an agriculture aircraft during low-altitude flight operation

The longitudinal aerodynamics of agriculture aircraft during low-altitude flight operation was analyzed. And the longitudinal static stability criterion in ground effect was discussed, including the effects of major aerodynamic derivatives on longitudinal static stability. By the five-order small-disturbance linear equation in ground effect, the influence on the mode properties of agriculture aircraft during low-altitude flight operation was computed. And the approach of mode vectors was used to investigate the dynamic stability, which is useful to understand the major variables acting in different modes. The longitudinal dynamic stability was analyzed by Routh's criteria. To ensure dynamic stability, the favorable position of the center of gravity was deduced by approximations. The results show that the longitudinal aerodynamics and stability influenced by ground effect should not be ignored for the agriculture aircraft during low-altitude flight operation.