Propulsion flow modulating system

Claim 1

An aircraft propulsion flow modulating system comprising: a jet engine having a fan driven by the engine to produce a propulsion air stream; a core cowl surrounding the engine; a streamlined shroud surrounding the engine and fan having an inner wall radially spaced from the cowl wall to define therewith a generally annular duct for rearward flow of the propulstion air stream delivered by the fan; the shroud terminating forward of the trailing edge of the cowl in a plane transverse to the axis of the engine and defining with the cowl a rearwardly discharging nozzle exit; and means for varying the flow area of the duct in the vicinity of the nozzle exit comprising an elongate band of elastomeric material extending substantially around the periphery of the cowl wall; the band having generally parallel fore and aft margins located forward and aft of the plane of the nozzle exit and being air-tightly secured to the cowl wall; in which the band comprises an elongate; laminated flexible strip having one or more outer layers of a high-stretch elastomer and a reinforcing core including multiple substantially straight strands of a lowstretch material serving to limit the extensibility of the band to a predetermined degree corresponding to the limit of stretch of the strands; the band in contracted position lying against the cowl wall; a plenum chamber underlying the cowl wall and substantially coextensive axially and peripherally with the band and air-tightly secured to the interior of the cowl wall; the latter being perforated in the coextensive area to allow passage of pressure fluid between the plenum chamber and the band; and a conduit communicating at one end with the plenum chamber and at the opposite end with a source of pressure fluid to introduce the fluid into the plenum chamber and under the band to force its intermediate peripheral portion toward the shroud wall and reduce the flow area of the duct.