Abstract:

This paper presents one kind of aggregation for linear system modal reduction. The aggregational matrix of reduced system is given bythe solution of a general Lyapunov equation——SA11-A22S-A21 =0,in whichA11, A21 and A22 are the block matrices of the parameter matrix of initial linear system. Matrix （-S I） is the aggregational matrix. Then, by means of the method given above, the linearized dynamic equations of longitudinal motion and lateral-directional motion of aircraft are separated, and the approximate formulas of phugoid, short period, roll-spiral and Dutch-roll modes are derived. Some calculation results show that the approximate formulas have a goad precision, espscially increasing the estimation accuracy for the dampings of phugoid and Dutch-roll modes.

Key words: modal aggregation, modes of aircraft, longitudinal motion, lateral-directional motion