Phugoid approximation for conventional airplanes

An improved closed-form approximation for phugoid motion in conventional ai rplanes is presented, Although several closed-form approximations for phugo id motion are currently available and widely used, none of these approximat ions accurately predict all of the fundamental characteristics of phugoid m otion. The new approximation accounts for changes in angle of attack as wel l as the effects of pitch stability and pitch damping. The total phugoid da mping is shown to depend on pitch damping as well as aircraft drag. In addi tion, this solution points out another important contribution to phugoid da mping called phase damping. It is shown that the phase-damping contribution to the real component of the phugoid eigenvalue is always positive and ten ds to reduce the total phugoid damping. Under certain conditions this phase damping can cause the phugoid mode to become divergent.