Rotorcraft Modeling Formulations

Models of different order may be used depending on what is known about the measurements available, the frequency range of interest, and the degree of coupling between the longitudinal and lateral-directional motions. Generally, a 6DOF model is the minimum required for a highly coupled rotorcraft. The 6DOF rigid body model for rotorcraft consists of the usual EOM derived from Newton’s law.

Equations for linear accelerations

U = X — g sin U — qw + rv

v = ~ + g cos U sin f — ги + pw (3.44)

W = Z + g cos U cos f — pv + qu

Equation 3.45 can be further simplified by assuming the product of angular rates to be small and neglecting the corresponding terms in the moment equations. Equation 3.45 in that case reduces to the form

P = L

q = M (3.50)

r = N

The rigid body states described in Equations 3.44, 3.46, 3.47, and 3.50 are used to characterize rotorcraft dynamics. Since the forces and moments are presented as specific quantities in the equations, mass and moment of inertia no longer explicitly appear in the mathematical model.