Means for securing fabric to a wing or the like comprises a rib or similar member having an up‐right limb a, Fig. 2, of U‐section and horizontal flanges b with downturned ends d, the limb a being traversed at intervals by eyelets such as c, rivets or the like, around which the fabric securing cord/ is passed as shown in Fig. 1 so that the fabric is pulled down partially into the concavity in the virtue of their' nature or construction numerous small perforations or interstices spaced substantially uniformly over the area so as virtually to render the area uniformly porous to air. Perforations or interstices of the order of 420 per square inch are stated to be suitable to give the desired porosity. As shown, an aero‐engine 3 drives a centrifugal blower 5 to suck air through the wing covering, ducts 7, 6 having guide vanes 8, and exhaust it above the fuselage. Passages are formed in the wing beneath the covering and are provided with valves 13 operable together or severally. According to the first Provisional Specification, porous fabric may be stretched over closely perforated sheet‐metal.
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