Patent GB-443764-A (GB)
Title: Improvements in aircraft sustaining rotors
IPC: B64C27/51
Filed: 1935-08-09
Abstract: 443,764. Aircraft with rotary-wing systems. CIERVA AUTOGIRO CO., Ltd., Bush House, Aldwych, London. Aug. 9, 1935, No. 22489. Convention date, Aug. 18, 1934. [Class 4] In an aircraft sustaining rotor of the kind having blades rotatable about a substantially vertical axis and wherein the individual blades are pivotally attached to the hub so as to be freely and independently displaceable out of their plane of rotation, the rotor blades are each formed in two or more parts each of appreciable extension in the direction of the blade length, the adjacent parts being connected with one another and capable of substantially unrestrained movement (at least to a limited extent) on an articular joint or joints whose axis is substantially parallel to the flapping axis of the blade root articulation and which is so formed as substantially to prevent relative displacement of said adjacent parts otherwise than about the joint axis. A further feature of the rotor blades consists in concentrating the effective lift of the blades in the outer region thereof and relatively reducing, if not eliminating the effective lift of the inner or root portion thereof. The Specification includes a detailed statement of the aerodynamic behaviour of such blades with reference to an aircraft incorporating fixed wings fitted with ailerons and a normally auto-rotative three bladed rotor system. In one form, Fig. 2, the blade comprises a shank portion 18a extending over 57 per cent of the radius of the blade tip from the rotor axis and a blade portion proper 18b. Shank portion 18a is of double-ended bi-convex section of somewhat greater camber above the chord line than below and having a high thickness ratio, for example, 42 per cent and is set on the hub at about 6¢‹ positive incidence relative to a plane perpendicular to the hub axis. Outer panel 18b is of substantially elliptical plan and may have a maximum chord of from five to eight times that of the shank and is of a thin section (e.g. N.A.C.A.23 with a thickness ratio of 9 per cent) set at about 5‹ positive lift incidence relative to a plane perpendicular to the hub axis. Blade portion 18a comprises a large diameter spar 25 which may act as a core, the blade section being completed by balsa wood fillings and a fabric covering, whilst outer portion 18b comprises a smaller diameter spar 25a truss bracing 25c of metal tubing and wing ribs covered with plywood or fabric the weight per unit length in the two sections of the wing being the same. Member 25a may be reduced in diameter at 25b although given an increased wall thickness. The differential angular setting of the two blade portions is shown in Fig. 4, in which y-y and z-z represent planes perpendicular to the rotor axis x-x. Chord line a-a of wing section 18a is set at an angle of +1¢‹ to plane y-y, the no-lift line of the aerofoil section being at -5‹ to the chord line. The chord line of aerofoil 18a is set at + 4‹ to the plane y-y, to no lift line in this case being at -1‹ to the chord line. The blade is connected to the hub by a flapping pivot 19 lying in a plane substantially perpendicular to the rotor axis and by a drag pivot 20 lying substantially in a plane containing the rotor axis. Upward limiting stops and droop stops 21, 22, Fig. 3, are provided on extension link 23 in positions to react on hub 16 and one of the pivot forks 24 of tubular blade spar 25 is provided with a tongue 26 positioned to engage one or other of limiting stops 27 on angular movement of the blade from its radial position. Blade portions 18a, 18b are connected by a pivot pin 19a, Fig. 5, carried by a bearing sleeve 28 mounted in a horizontal transverse aperture in fitting 29 secured in the outer end of spar 25 by pins 33. The ends of pin 19a are fitted in fork-ends 31 of a fitting 32 secured in the inner end of outer spar 25a. Relative angular movement between the inner and outer blade portions is limited by a tongue 34 integral with fitting 29 which co-operates with abutment surfaces 37, 38 formed in the inturned flange 36 of fitting 32. The clearance between tongue 34 and abutment 37 when the two spars are in alignment is made less than that between tongue 34 and abutment 38 since the average cone angle of the outer blade portion in flight will be slightly greater than that of the inner portion. For this reason the inner part of the blade need not be provided with such a large negative coning range as in the case of a non-articulated blade hence the upward coning stop 21, Fig. 3, may be given a clearance of 10‹ or more and droop support 22 a clearance of about 4‹. The gap between the adjacent ends of panels 18a, 18b may be bridged by an elastic sleeve 39, Fig. 2, which may be cemented in place to pair together the two wing sections and to enclose the joint 19a. Fig. 8 shows a blade of uniform chord and aerofoil section throughout its length comprising a main spar 25 divided by horizontal pivots 19d, 19e and articulated to the hub by horizontal pivots 19c and vertical pivot 20. A subsidiary spar 25d may be provided which is not connected to the hub but is divided by pivots 191 coaxial with those of main spar 25.