Patent GB-452364-A (GB)
Title: Improvements in and relating to aircraft with autorotative wings
IPC: B64C27/02
Filed: 1935-01-16
Abstract: 452,364. Aircraft with rotary-wing systems. LA CIERVA, J. DE, Bush House, Aldwych, London. Jan. 16, 1935, No. 1546. [Class 4] In an aircraft of the gyroplane type having a rotor starting transmission including a starter clutch, means for varying the mean pitch angle of the rotor blades, means for overspeeding the rotor at a decreased pitch angle and utilizing the exceess kinetic energy for obtaining a direct take off, means are provided operating independently of the pilot's actions for regulating the rate of change of blade pitch angle during a part at least of the "take-off" period intervening between the initiation of disengagement of the starter clutch and the establishment of normal autorotation, for the purpose of minimizing thrust fluctuations of the rotor during the take-off. The pitch changing means may be either of the type in which the blade pitch angle is positively controlled by a train of mechanism operative directly on the rotor blades ("mechanical" class) or of the type in which the pitch angle is controlled by means responsive to any of the thrust, torque, inertia and centrifugal forces and elastic characteristics of the rotor blades (" automatic " class). A combination of "mechanical" and "automatic" pitch regulation may be used. In one form, the invention is applied to a gyroplane, Fig. 1, having a propulsive engine 80 arranged to drive the rotor hub by means of a transmission comprising a shaft 86 ; a clutch comprising a fixed element 90, Fig. 4, and a movable element 89; bevel pinions 91, 92 ; and a shaft 88 coupled to the shaft of a bevel pinion 126 meshing with a gear ring 125 secured to the rotor hub. The rotor hub assembly, Fig. 5, is of the type described in Specification 410,532, incorporating means for cyclically changing the pitch angle of the blades to effect a change in the plane of rotation of the blade tips and separate means for varying the pitch angles of all the blades together. The first mentioned means are controlled by a universally rockable control column 79, Fig. 1, connected to the rotor head by means of rods 119, 120, longitudinal control being effected by fore-andaft movement of the control column which produces endwise movement of rod 120 and lateral control by sideways rocking of the column which produces endwise movement of rod 119. The second mentioned means is controlled by endwise movement of rod 45 which is connected at its upper end to sliding sleeve 118 upon which blade pitch control collar 117 is journalled. The lower end of rod 45 is guided in a support 46, Fig. 7, and the rod terminates in a stud 44 engaging a curved slot 43 formed in a cam plate 31 pivoted at a fixed point 32 and including a projection 36 engageable by a catch 37. Catch 37 which is slidable in an abutment 39 is spring urged into engagement with projection 36 and may be withdrawn by actuation of a hand lever 42 which is connected therewith by a tension element 40 enclosed in a flexible sheath 41. Cam plate 31 is connected on one side of pivot 32 by a tension element 33 enclosed within a flexible sheath 34 to a hand lever 35 and on the other side is connected by a rod 100 and bell-crank 99 with starter clutch actuating rod 98, Fig. 4, and also to piston rod 47 of a spring loaded dashpot device comprising an oil-filled cylinder 49 in which slides a piston 48 formed with oil throttling orifices 51 and downwardly urged by spring 50. The cam slot is so shaped that when cam plate 31 is rocked in a counter clockwise direction from the position shown, rod 45 is raised to increase the pitch angle of all the blades. The mechanism operates as follows :-to engago the starter clutch, lever 35 is moved in a clockwise direction until it reaches the position shown, the motion of lever 35 is communicated by tension element 33 to cam plate 31, thereby causing rod 47 to raise piston 48, thus compressing spring 50 and causing rod 100 to move upwardly rocking bell-crank 99 in the direction to cause engagement of clutch elements 89, 90, Fig. 4. At the same time stud 44 is brought to the left-hand end of the cam slot, thus lowering rod 45 and decreasing the rotor blade pitch angle to its minimum limit (substantially zero). Clockwise movement of the cam plate causes projection 36 to spring over catch 37 which thereafter holds the cam plate and the pitch - varying and clutch - controlling mechanisms in the position shown in Fig. 7. On depressing lever 42, catch 47 is withdrawn from projection 36 whereupon cam plate 31 is rotated in a counter-clockwise direction by spring 50 assisted by clutch spring 97, Fig. 4, thus disengaging the clutch and increasing the pitch angle from its minimum to its maximum value. The rate of change of pitch angle is determined by the characteristics of the dashpot and by the shape of the cam slot. The cam slot of Fig. 7 is designed to produce a more rapid increase of pitch in the early than in the later stage of movement. Alternatively a "humped" cam slot 43, Fig. 8, may be used such that when the stud passes over the "hump" the blade pitch angle attains a maximum value and is thereafter decreased to its normal autorotative flying value when the stud reaches the right-hand end of the slot. According to a modification, Fig. 9, disengagement of the clutch is not damped, the clutch operating mechanism being connected not to the cam plate itself but to a lever 31x mounted on pivot 32 and movable by lever 35. Clockwise movement of lever 31x to engage the clutch is accompanied by similar movement of cam plate 31 by reason of the engagement of the lever with a projection 31a formed on the plate. The projection 36 is in this case formed on lever 31x. With any of the foregoing arrangements means may be provided whereby release of catch 37 is effected by movement of the control column rearwardly from the extreme forward position, Fig. 11, or alternatively whereby the control column is locked in its extreme forward position until freed by downward movement of hand lever 42, Fig. 12. As applied to a gyroplane of the type shown in Fig. 29 in which the rotor apex member is universally mounted in the manner described in Specification 393,976 and is tilted by means of a control lever 132, the rotor blade is articulated to drag link 55, Fig. 13, by a drag pivot pin of which the axis, alpha-alpha, is inclined upwardly and outwardly at an acute angle to the longitudinal blade axis b-b so that movement of the blade on the drag pivot is associated with a change in blade pitch angle, such that when the blade lags the pitch. angle is decreased and vice versa. Thus the effect of application of starting torque is to cause the blade to lag and therefore reduce its pitch angle whilst when the starting torque disappears on disengagement of the starter clutch, the blade swings approximately into its normal mean radial position, thus increasing the pitch angle to about the value obtaining in autorotative flight. The rate at which the pitch angle is varied on disengagement of the clutch is automatically regulated by a friction damping device operative between drag pivot housing 56 and drag link 55 and comprising a cylinder 58 mounted on a bracket 59 secured to drag link 55 and a piston 60 slidable within cylinder 58 and formed with a rod 63 terminating in a ball 64 engaging in a socket 65 mounted on pivot housing 56. Piston 50 carries a friction ring 61 and is urged by a spring 62, toward the bottom of the cylinder, i.e. toward the position in which the blade is in its mean radial position. The lower part of the bore of cylinder 58 is enlarged in such manner that for movements of the piston corresponding to small oscillations of the blade about its mean radial position, friction ring 61 is out of contact with the wall of cvlinder 58. In order to obtain the effect of the humped cam of Fig. 8, i.e. a graduated increase of pitch angle to a maximum followed by a slight decrease to the normal autorotative value, a rotor blade is employed in which the mass centre is in advance of the mean aerodynamic centre of pressure as described in Specification 420,322. The effect of this is shown in Fig. 15 which shows a blade B in its means radial position in which #-# is the flapping pivot axis, alpha-alpha the drag pivot axis, m the mass centre, and p the centre of pressure. On account of the upward coning of the blade the centrifugal force F applied at m may be revolved in components F<1> acting along blade axis b-b and F<2> acting downwards at right angles thereto. The lift L acting upwards at p constitutes with component F<2> a couple about axis b-b. Owing to the pivot axis alpha-alpha being inclined at an angle other than 90‹ to axis b-b couple LF<2> has a component A rotating blade B about axis alpha-alpha in a direction to reduce its pitch angle, this displacement being limited by the centrifugal restoring couple set up on movement of the blade from its mean radial position. By this arrangement an automatic correlation is established between the ratio thrust-centrifugal force and blade pitch angle such that if the thrust alpha increases relatively to the centrifugal force F the pitching couple LF 2 is increased relatively to the centrifugal restoring couple and the pitch angle is decreased. On disengagement of the starter clutch, the pitch angle increases and the excess kinetic energy of the rotor is utilized to obtain a temporary helicopter effect. It is stated that owing to delay in building up of the downward inflow through the rotor disc the thrust reaches a minimum not when the upward velocity is a maximum but slightly later. Concurrently the speed of rotation and hence the centrifugal force decreases ; since, however, the decrease of thrust after attainment of the peak valve is the more rapid, the ratio thrust/centrifugal force decreases resulting in increase of pitch angle and producing a tendency to maintain the thrust at a useful positive value. The effect of dependence of the