819,214. Rotary wing aircraft. WILFORD, E. B., and LEMONT, H. E. Nov. 14, 1956 [Nov. 17, 1955], No. 34772/56. Class 4. A rotary wing aircraft rotor system comprises a drive shaft, a hub universally mounted thereon and connected thereto by flexible means so as to bias the hub towards a normal position of equilibrium, a plurality of blades journalled radially in the hub, and means to take up spanwise forces between the blades. In Fig. 1, the rotor shaft 24 is driven through a gear 122 and has an extension 22 ending in a spherical part 20 forming with a bearing member 16, a universal joint for the hub 11. A multiarmed flexible spider 26 is secured to the hub at 30, and a similar spider 32 is secured to the drive shaft at 32. These spiders are connected at the ends of their fingers as at 40, and transmit uniform rotation to the hub while allowing tilting thereof and biasing the hub to a central position. The hub is formed with four cylindrical arms 12 each journalling through roller bearings 52, a cylinder 50 having a flanged end 51 clamped by a ring 56 to a flange 45 on a blade root 44. A tapered pin 58 passing through the cylinder 50 and blade root 44 serves as an anchor for a tension and torsion strap 74, each strap also being attached to a member 78, Fig. 2, relieving the hub of centrifugal forces. A collar 64 is splined to the inner end of each cylinder 50, and bears an arm 66 connected by a rod 108 to the inner ring of a conventional swash ring 94, Fig. 1. Each arm 66 is adjustable to vary the " lead" of the pitch control mechanism. Stops 80 on the hub abut the upper surface of member 78, and a resilient ring 82 surrounds the drive shaft 24 within member 78, to restrain the hub tilt beyond a predetermined point. The spherical member 20 contains an oil reservoir lubricating the bearing 16 through ducts 118. The two spiders 26 and 32 may be replaced by a bellows extending between the fastenings 30 and 34, and the bearing 16 may be replaced by ball bearings. U.S.A. Specification 2,648,387 is referred to.