Patent GB-438660-A (GB)
Title: Improvements in and relating to blades for aircraft sustaining rotors
IPC: B64C27/02
Filed: 1934-05-16
Abstract: 438,660. Rotary aircraft-wings. CIERVA AUTOGIRO CO., Ltd., Bush House, Aldwych, London, and BENNETT, J. A. J., Genista, Newton Mearns, Renfrewshire. May 16, 1934, No. 14816. [Class 4] A blade for an aircraft sustaining rotor of the kind in which the blades are freely hinged to the hub member to swing perpendicularly to the plane of rotation and may also swing freely relatively to one another in the plane of rotation, comprises a tubular spar the leading portion of which conforms in external contour to the leading part of the aerofoil profile of the blade, or to part thereof, and extends over a considerably greater proportion of the upper surface than of the lower surface of the spar. The resistance to bending of the spar may be non-uniform along its length being graded so that the stress distribution approximates more closely to uniformity than with a constant cross-section spar, either in flight or when the blade is not rotating or under both conditions. The spar may have a non-uniform cross-section along its length, or a constant periphery and non-uniform thickness, or a constant thickness and non-uniform periphery, or a non- uniform periphery and thickness, or the spar may have a uniform cross-section and be reinforced locally by cover plates, or by internal or external sleeves, or the spar may be formed telescopically from two or more lengths of tubing riveted or otherwise connected together. Fig. 1 shows the metallic tubular spar 22 of a uniform cross-section blade 21 reinforced by an internal sleeve 23 having prior to insertion in the spar an external depth greater than the internal depth of the spar so that it is held in position frictionally. The rear fairing of the blade comprises spruce blocks 24, Fig. 2, bolted to the tube 22, solid balsa wood blocks 25 glued to the blocks 24, and a trailing-edge 26 of spruce connected by a plywood tongue or tongues 27 to the blocks 25. The balsa blocks may be reinforced by flat spruce ribs 33, Fig. 6. Lead washers 30 may be used as balance weights to balance the blade. In the construction shown in plan view in Fig. 6, the outer third of the blade is of increased chord and its aerofoil section, Fig. 8, is of smaller fineness ratio than that of the inner part of the blade, Figs. 1, 2. The blade has a rear fairing constructed similarly to that shown in Fig. 2, and a front fairing comprising a spruce block 24<x>, Fig. 8, bolted to the spar 22. The blade tip consists of upper and lower blocks 37, Fig. 9, of balsa wood glued to a separating sheet of three-ply wood 39, the inner end of the tip having a spigot 37<x> shaped to fit inside the tube 22 and riveted thereto. The leading edge of the tip is, from A to B, Fig. 7, a quadrant of a circle and the shape of the trailing edge B, G, D, is determined so that the cross-sections E, F, G are geometrically similar and the ratio EF /FG is constant. The blade root structure as shown in Figs. 12, 13 is formed by plugging the inner end of the spar tube with a solid block 45 of light alloy which is gripped between flanges 46<a> on the blade root socket member 46 and a flanged member 47 having a spigot 47<x> screwed into an internally-threaded spigot 46b on the member 46 which is forked at 46‹ to embrace the drag link (not shown), and drilled at 46<x> for the drag pivot pin (not shown). The end of the tube is reinforced by stepped cover plates 40 riveted to the spar and reduced in width between the two outer rows of rivets at 40<a> so as to equalize the loading on the rivets. Specification 399,446 is referred to.