QL = CS(h ± X6 (2) The plenum pneumatic capacitances are based on isentropic compressibility. The pressure rates associated with the inner circular skirt plenums and the inskirt plenum, which lies between the inner circular skirts and the outer peripheral skirt, vary with vehicle motion in pitch and heave where dP/dt = (kP/V)[2Q + A(dZ/dt ± xd8/dt)] (3) The equations of vehicle motion in pitch and heave represent a rigid craft operating over a nondeforming surface with zero forward speed and are simplified by limiting the motion to small perturbations. A body-fixed coordinate system is used with the origin fixed at the vehicle center of gravity. A further simplification is realized due to symmetry about the x-z and y-z planes of the vehicle. The equation of motion in heave for the multiple-skirt ACV is 2 = 9 ~