Patent GB-420322-A (GB)
Title: Improvements in and relating to aircraft with freely rotative wings
IPC: B64C27/02
Filed: 1933-08-05
Abstract: 420,322. Aircraft with rotary wing systems. LA CIERVA, J. DE, Bush House, Aldwych, London. Aug. 5, 1933, No. 22105. [Class 4] In auto-rotative wing aircraft the power transmissions means are adapted to impart to the rotor an initial rotational speed in excess of the mean autorotative speed in flight during which period the rotational drag is decreased by decreasing the pitch angle of the rotor blades to less than that required in flight and when the starting torque ceases the pitch angle is immediately increased at least to the minimum value required for flight whereby the excess kinetic energy stored in the rotor generates temporarily a thrust sufficient to raise the aircraft vertically from the ground. The pitch angle is changed automatically with the rotor torque and the means for changing the pitch angle operates automatically to changes of centrifugal force, i.e. an increase of centrifugal force causes the pitch angle to increase and vice versa, The automatic pitch variation ensures an optimum value of pitch at all translational speeds, any cause decreasing the rotational speed being compensated for by a decrease in the pitch angle. The pitch angle varies up to 8‹ and restraining means are provided during the application of the starting torque for preventing the pitch angle of the blades increasing to a value sufficient to lift the aircraft as a result of a diminution of the starting torque and comprise an automatically operated frictional resistance or locking - device for the blades releasable by the pilot and being interconnected with the motor clutch. Where the rotor blades are pivoted about two independent pivots (flapping pivot and drag pivot) means are provided for varying the pitch angle of each rotor blade responsively to its movement on the drag pivot in such a way that movement of the blade relatively to the rotor hub in a direction opposite to the direction of rotation of the rotor causes the pitch angle to decrease and vice-versa. The rotor hub 25, Fig. 1, is pivoted about two transverse axes and is operable by control column 44. The airscrew 22, which may be of variable pitch, is driven by an engine 21 which is also connected by a clutch 36 to the rotor hub 25, the clutch-operating gear and airscrew pitch-operating gear being interconnected through a lost-motion device so that the pitch of the airscrew is a minimum when the rotor is speeded up at take off. Since the unbalanced rotor couple is small, the wheels 33 may be placed closer together and more underneath the centre of gravity g of the machine and in the case of an amphibian machine the wheels may be housed in the floats, the latter being constructed for minimum air resistance only. Each rotor blade is pivoted about a transverse or flapping pivot 60, Fig. 4, in the hub 25 through the intermediary of a stub axle 66 which lies in the plane of the vertical axis of the rotor and is inclined to the blade axis so that the blade turns in a conical path to vary the pitch angle. The hub 68 of the blade is connected by a hinge 80, 85 having a ball joint 82 to a friction plate 90, there being three plates each connected to a blade, the frictional resistance being varied by a compression plate 94. When the starting torque is applied the inertia of the rotor blades causes them to swing back on their drag pivots to zero pitch angle, the variation of pitch being limited by stops 78, Fig. 5, on a plate 76, attached to the hub 68. In this position the blade is restrained from rotation by a friction plunger 108 mounted on the hub 68 the friction being greatest toward the zero pitch position of the blade, and is inoperative within the oscillatory range of blade movement due to normal flight. This arrangement prevents premature take off. In a modification the plunger 108 is in the form of a tooth adapted to engage automatically in a recess in the member 65 at zero pitch angle and is released by the pilot through rod 116 and lever 113 when the clutch 36 is disengaged from the rotor. The tooth may be disengaged by a circular plate raising the rods 116 through the medium of Bowden cables operated by the rotor clutch control or by an independent lever. The mass centre M of the blade, Fig. 10, is situated nearer to the leading edge of the blade than a line p p drawn through one quarter of the chord dimension, by means of additional masses m mounted on arms a projecting from collars c secured to the main spar tube t. The direction of rotation of the airscrew as viewed from behind is the same as the direction of rotation of the rotor as viewed from above. A brake may be used on the rotor hub and the flapping movement of each blade is limited by stops. Specifications 393,976 and 410,532 are referred to.