Analysis of the Lateral-Directional Stability of Gliding Peregrine Falcon

Peregrine falcon can perform stable gliding without a vertical tail. This paper assumed that the spanwise distribution of wing dihedral angle can affect the lateral-directional dynamic stability of Peregrine Falcon. The dynamic model of gliding Peregrine Falcon was built and the model was considered to be rigid. Thus, the falcon model can be treated as a fixed-wing aircraft. Its lateral-directional dynamic stability was analyzed based on linearized small perturbation theory under different spanwise distributions of wing dihedral angle. The product of natural frequency and damping ratio was used to assess the characteristic of the Dutch roll mode, and the eigenvalues were used to evaluate the stability of the spiral mode and the rolling mode in this paper. The criterion detailed in piloted airplane flying qualities was used as the reference value. Results show that all of the analyzed configurations have a well-convergent rolling mode and the dihedral angle changing has only a slight effect on the rolling mode stability. Peregrine Falcon can obtain a good Dutch roll mode characteristic by changing its wing dihedral angle. Most analyzed configurations have divergent spiral mode and meet the level 1 criterion.