Abstract: An automatic roll, pitch, and heave stability device for air-cushion-borne vehicles equipped with semi-rigid planing bow and stern seals, the latter which may be divided into separate port and starboard seals, and with rigid side-walls. Each seal at its trailing edge is mechanically linked to, and controls, a bypass duct valve. The linkage is arranged so that pressure in the seal increases as the seal is forced up due to a wave crest, and decreases as the seal drops away from the vehicle body in a wave trough. Vehicle stability in heave is achieved by the bow and stern seals operating in unison; in pitch, by the bow and stern seals operating oppositely; and in roll, by the split port and starboard seals operating oppositely. The system operates both while the vehicle is underway, and with changes in load on the vehicle in calm water.

Abstract: An automatic pitch stabilization and motion alleviation device for air cushion borne vehicles, equally applicable to fully-skirted and to rigid sidewall vehicles. The vehicle's air cushion plenum is divided into bow and stern compartments by a transverse seal. Vehicle lift fans and a unique ducting arrangement supply air flow to the air cushion compartments and seal system. A valve, in a portion of the duct feeding air to the forward compartment, regulates the pressure drop from the stern compartment to the forward compartment. The valve is capable of providing 30-100% higher mean pressure in the aft compartment relative to the forward compartment. The valve is actuated automatically by height, motion, rate, acceleration, and pressure sensors, the outputs of which are fed to the valve servomechanisms to provide effective underway dynamic control of the pressure differential between compartments for motion stabilization in pitch and for improvements of ride quality.