452,365. Aircraft with rotary-wing systems. LA CIERVA, J. DE, Bush House, Aldwych, London. Jan. 16, 1935, No. 1547. [Class 4] In an aircraft having an autorotative sustaining rotor, means, including a clutch for initiating rotation of the rotor and automatic means for varying the mean rotor-blade pitch-angle responsive to any or all of the forces acting on the blades, means are provided, responsive to a substantial decrease of driving torque with the clutch engaged, or operative on the aircraft becoming airborne with the clutch engaged to prevent the re-application of full driving torque to the rotor. In one form, the rotor is universally mounted on a pylon and is controlled from a lever. The starting torque is imparted to the rotor through bevel-gearing and a clutch controlled by the pilot through a tensionelement enclosed in a sheath. The rotor blades arc articulated to a member 32 rotatable on a member 31, connected to the pylon apex member by a universal joint, about axes 35, alpha alpha and # # ; the two latter may be concurrent and coplanar and the axis 35 may be arranged obliquely to the normal radial position of the blades as described in Specification 452,364. Each blade can flap about the axis 35 whilst rocking about the axes alpha alpha and # # results respectively, when the blades lead, in a decrease and increase in blade pitch, and conversely when the blades lag. As shown, pronounced lagging displacements of the blades as occur, e.g. when a driving torque is applied, are associated with progressive decrease of pitch and leading displacements which occur, e.g. when a brake is applied to the rotor hub also result in a progressive decrease in pitch. This result is obtained by the disposition of stops 47, 48b, 49, and two further stops which are nct shown in Fig. 5, which limit movement about the axes alpha alpha, # #, and a suitable choice of the aerodynamic and mass characteristics of the rotor blades. If the blades are constructed so that their aerodynamic centres of pressure are in advance of their mass centres then when the rotor is rotating leading displacements will take place about the alpha axis only and lagging displacements about the # axis only. The driving shaft 55 is supported in bearings 56 and comprises a quick-pitch thread 54 co-operating with a similar thread in a pinion 53 provided with a ring-member 61 and a friction collar 58 which engages a pad 59. A thrust bearing 60 is interposed between the pinion and the member 61 which is guided vertically. Toggle links 119, 120 are connected between brackets 122 and the member 61 and the links are extended against the action of a spring 124 bv a tension element 63 enclosed in a sheath 64 and attached to the clutch-actuating lever 65. Initial movement of the lever 65 closes the clutch, the pinion 53 begins to rise up the thread 54 to engage a pinion 52 to rotate the rotor, and subsequent movement of the lever 65 extends the links 119, 120 to prevent retrograde movement of the pinion 53. A catch 92 engages a projection 91 on the lever 65 to hold the clutch in its engaged position. On failure of the power plant with the clutch engaged the links 119, 120 are maintained extended and the rotor drives the power plant which then functions as a brake. On release of the clutch overrunning of the rotor causes disengagement of the pinions 52, 53. The catch 92 may be released to open the clutch by a spring-actuated plunger 77 which is held inoperative when the aircraft is on the ground by engagement with a projection 75 carried by a movable portion 73 of the undercarriage. The catch may also be released by operation of a hand lever 98. The rotor brake is operable through a tension element 83. In a modification, a catch 177, Fig. 13, retains the pinion 53 in its lower position. Movement of the clutch lover 65 to engage the clutch through a tension cable 173 and a lever 175 withdraws the catch 177 against the action of a spring 178., Simultaneously through a tension element 171 abutments 169, 57a, are drawn closer together against the action of a spring 172 to cause a striker 166, housed in a sleeve 167 connected to the abutment 169, to project from the catch 177. The tension elements are arranged so that the catch is projected after the clutch is engaged and the pinion 53 has risen. The engaging movement of the clutch lever tensions a spring 158 connected to a spring-actuated lover 159 held by a spring-actuated catch 162 and connected to a rotor brake which is operable by the usual tension element and by a tension element 160. Should, during starting, the power plant fail the rotor will overrun causing pinion 53 to descend and engage the striker 166 which through an element 164 releases the catch 162 to allow the rotor brake to be applied through the tension of the spring 158. Release of the clutch lever releases the rotor brake and consequently allows of the return of the various parts to their initial position. In a further modification, the blade root articulation is about axes 37, 41, Fig. 15, coplanar with the longitudinal axis of the blade in its normal radial position and this plane makes an acute angle with the axis of rotation. In a further form adapted for a three-bladod rotor the hub terminates in lugs 34, Fig. 17, supporting flapping pivots 35 on which are articulated drag links 36 terminating in pivots 37 such that the # # axis is inclined upwardly and outwardly and passes close to the flapping axis which is mounted as near as possible to the axis of rotation. Movements of the blade 46a about the txis # # are limited by adjustable stops 69. Owing to the offset between the intersection of the # # and flapping axes from the rotational axis relatively large blade displacements about the pivot 37 are required to bring into play centrifugal restoring moments of appreciable magnitude and due to the inclination of the # # axis the changes of pitch associated with blade movements are relatively small. When the mass distribution and profile of the blade are such that, for small angles of incidence at least, the pitching moment coefficient of the blade about its mass centre is in a direction tending to decrease the pitch, the drag pivot axis may be at or nearly at right-angles to the blade axis. Specification 420,322 also is referred to. Specification 444,485 is referred to in the Provisional Specification.