2 - Air cushion theory

Abstract

Development of the air cushion theory is closely related to the development of hovercrafts themselves, particularly of flexible skirts. Early air cushion vehicles were conceived with the object of drag reduction for a marine craft. The concept of injecting lubricating air over the wetted surface was replaced by the use of a thicker air cushion. The chapter deals with the air cushion theory from early research and discusses the flow rate coefficient method. It also introduces the wave-pumping concept and its requirements; the determination of the heaving damping coefficient; and the heave stability derivatives of air-cushion vehicles (ACVs). The relation between the cushion airflow rate and the pressure of the craft hovering on a rigid surface and calm water is derived. The chapter discusses the air cushion stability and hovering damping concerning the longitudinal and vertical motion of ACVs hovering on a rigid surface. These parameters will greatly affect the natural heaving frequency, seaworthiness, and comfort of craft, and are relative to the static air cushion characteristics of ACVs.