Patent GB-569724-A (GB)
Title: Improvements in helicopters
IPC: B64C27/41
Filed: 1943-05-18
Abstract: 569,724. Helicopters. WEIR, Ltd., G. & J., and PULLIN. C. G. May 18, 1943, Nos. 7910 and 10389. [Class 4] A helicopter having blades so mounted that as the blades respectively rise and fall about flapping axes their incidence is reduced and increased, and particularly where such change of incidence is considerable compared with the change of flapping angle, is provided with compound pivots incorporating limit stops in the blade articulations so that the changes of incidence are confined to a limited range of flapping movement while permitting more extended flapping displacements without further substantial change of incidence. In one form, Fig. 3, each blade spar 55 is rotatably mounted upon a link 50 pivoted about a hollow horizontal pivot 48 fixed to a drag-link 46 which in turn is fixed to a vertical pivot 44 rotatable in upper and lower lugs 42 on the rotor hub. The hub rotates about a member 36 mounted upon gimbals supported by a fixed tubular member 34, the member 36 being tiltable in any direction by connections to the flying controls as described in Specification 567,989. A yoke 58 pivoted about vertical trunnions 57 on the trailing side of the spar engages the ball-end of a lever 61 on a forked member 62 pivoted on vertical trunnions on a plate 66 which is bolted to a face cam 141 and to a sleeve 139 rotatable within the fixed pivot 48. The face cam 141 is normally pressed into engagement with a corresponding cam 142, on the end of the fixed pivot 48, by a spring 144 acting upon a shoulder 143 within the sleeve 139 and bearing against the head of a bolt 146 secured to a cap 148 which holds a disc 150 in contact with the opposite end of the pivot 48. The disc 150 has an integral sleeve splined at 149 to the sleeve 139 which is normally held stationary by the cam 142.- Two projections on the link 50 engage two notches, not shown in Fig. 3, in the disc 150. Within the limits set by these notches, any flapping movement of the spar 55 is accompanied by a rotation about its own axis as a result of the lever, 61, 62 being held against vertical movement by the cam 142, but any movement in excess of these limits causes the disc 150 and with it the plate 66 to rotate against the resistance of the cam 142 and spring 144 and there is no longer any appreciable relative movement between the end of the lever 61 and the yoke 58. Stops on a projection 68 on the drag-link 46 limit the ultimate flapping displacement of the spar by engaging the interior of the link 50. In another form, Figs. 12 and 14, the spar 160 is rotatable in a member 162 which has lateral recesses tiltable about circular bosses 164 on two side-plates 165 bolted to distance pieces 173, 176. A slotted lever 172 fixed to one of the side-plates 165 controls the incidence of the blade by engaging a block 170 on a pin 169 adjustably clamped to the spar 160 to vary the ratio of change of incidence to change of flapping angle. The side-plates 165 have each two transverse pins 174 engaging slots 175 in the sides of the drag-link 46x, centrifugal force on the blade normally keeping the pins at the outboard ends of the slots. The blade spar can rise or fall relative to the side-plates 165 within the limits set by the outboard distance pieces 173 during which movement the lever 171 varies the incidence of the blade. Flapping movements of greater extent cause the side-plates 165 to tilt about either the upper or the lower pin 174 until the opposite pin is checked by encountering the inboard end of the slot. During this movement there is no relative displacement of the lever 172 and the spar.