Abstract: Elbow nozzles in VTOL aircraft engines, are highly stressed when operating, in that they act as high pressure vessels. The invention provides a means for varying the outlet area of such a nozzle without weakening its structure. A single flap is inserted inside the nozzle and connected to the nozzle extremity for pivoting about an axis which lies across the outlet between a position wherein its edges seal against the nozzle side and so restrict the nozzle outlet area and, a position wherein it lies parallel with a wall of the nozzle so that exhaust gas can pass both sides and out of a bigger outlet.

Abstract: Use of bulk sound absorber-backed spaced-cell honeycomb structures as sound attenuating liners in the flow ducts of gas turbine engines involves the disadvantage that the bulk absorber may soak up water or fuel present in the honeycomb after entry thereinto from the flow duct. In order to drain away liquid before it comes into contact with the bulk absorber, each honeycomb cell communicates with surrounding cells via apertures in the cell walls through which the liquid can drain, and a perforated sheet is provided between the honeycomb layer and the bulk absorber layer. The perforations are such that sound can enter the bulk absorber layer, but the liquid does not, each perforation being a hole having a peripheral flange which protrudes away from the bulk absorber layer into the interior of a respective cell.