Patent GB-353908-A (GB)
Title: Improvements in aircraft having freely rotative wings
IPC: B64C27/02
Filed: 1930-04-29
Abstract: 353,908. Aircraft with rotary wing systems. LA CIERVA, J. DE, Bush House, Aldwych, London. April 29, 1930, No. 13212. [Class 4.] Wings for autogyros are so constructed that the flexural rigidity of the wings is so great in the plane of its chord that the stresses in its longitudinal structural members imposed by the components of aerodynamic, inertia, and centrifugal forces acting in this plane are substantially unrelieved by deflection of these members while the flexural rigidity in a plane perpendicular to the chord is so small that the wing can deflect in the perpendicular plane to an extent capable of substantially relieving the stresses imposed. To this end the wing incorporates one or more longitudinal structural members of which the flexural rigidity is substantially constant from wing root to their outer extremities. A wing 20, Fig. 1, comprises a parallel portion 21 of maximum chord and of a length more than half the wing length extending to within a distance of the wing tip not exceeding twice the maximum chord, a second parallel root portion 23 of reduced chord joined to part 21 by a tapered portion 22 of a length not greater than twice the maximum chord, and a rounded tip portion 24. Part 23 has a high lift aerofoil section such as shown in Fig. 4. Wing 20, excluding the tip portion 24, comprises a single tubular main spar 27, Fig. 2, of which the centre line is shown at 25, Fig. 1, a leading edge former 28, ribs 29, a stringer 30, and a trailing edge member 31. The rib spacing is from one-fifth to one-sixth the maximum chord and the ribs are attached to clips 32, threaded on the spar and secured by screwed ferrules 33 or by sweating. The leading edge skin is of three-ply wood. The ribs 29 comprise flanges 292, Fig. 5, and apertured webs 291. The fabric covering 35 of the wing is secured by stringing 36 passing from top to bottom flanges through holes formed in grooves 293 into which the fabric is drawn so as to leave a smooth outer surface, the grooves being afterwards covered by doping on strips of tape with frayed edges. The wing tip 24 comprises a single sheet of aluminium or other light metal bent about the leading edge and joined by rivets at the trailing edge. A transverse channel stiffener 42, Fig. 10, is riveted between sides 39, 40 of the wing tip. Angle stiffening strips 43 and longitudinal channel stiffeners are also fitted. The edges of the sides 39, 40 are bent over at 44, Fig. 11, and are secured by screws 45 to wood blocks 46 at the outermost wing rib, a flange 47 of three-ply being placed under the leading edge skin 28. Spar 27 terminates in a spigot 49 passing through channel member 42 and having balance weights 52 secured thereon by a nut 50 which serves as an additional securing means for the wing tip. In an alternative form, Fig. 7, the spar is built up from corrugated metal strips 271 riveted together and has a metal leading edge skin 280 riveted directly to it. In another form the leading edge skin 28, 280 is continued back to the trailing edge and the ribs and stringer are omitted. In a further modification, Fig. 12, the wing comprises a main tubular spar 272 and a secondary channel section spar 273 braced together by diagonal members 274 and channel section ribs 290, the diagonal members being capable of resisting both tensile and compressive stresses. In all cases the centre of mass of any cross section of the wing lies behind the centre of pressure at normal angles of incidence so that a couple is produced by the lift and centrifugal forces tending to increase the pitch angle, the torsional stiffness of the wing being preferably such that the wing is twisted by this means to an angle of three to four degrees at the tip, the pitch angle of the wing in the unloaded condition being one to two degrees along its whole length.