499,632. Aeroplanes with rotary-wing systems. HAMMOND, E. V. April 14, 1938, No. 11470. [Class 4] In an aeroplane provided with a retractable rotarywing system, means are provided for correcting or preserving the stability of the aircraft in flight and are adapted to become operative when the rotor is extended. As applied to a passengercarrying aeroplane, a rotor 1 is mounted on a shaft 2 slidable in a guide 3 to raise the rotor from a nested position in a housing 4 in the cabin roof. The rotor 1 is of the type having articulated blades, Fig. 4, and is adapted to auto-rotate but is driven for starting by power means. Shaft 2 is splined at 6 or has a splined sleeve secured thereto, the splines engaging in the splined bore of a bevel-gear pinion 7, and is guided within the bore of the guide by bearings 12, 12a, a thrust bearing 13 being fitted below bearing 12a. Vertical movement of the shaft is effected by a geared electric motor 21, on the spindle of which are mounted sprockets 24 over which pass lengths of chain 25 connected by wires 26 passing over pulleys 20 and by wires 26a with trunnions 16 fixed in shaft 2 and projecting through slots 17 in guide 3. Guide 3 is divided above and below pinion 7 and each part has welded thereto one part of a split housing 42 which carries bearings for the pinion 7 and for pinion driving shaft 9 to which power is applied through means including a clutch and freewheel from a source which may be one of the main engines. Pulleys 20 are mounted on a spindle 19 carried by guide 3 to which spindle is also secured a sprocket which serves to transmit the drive of motor 21 through chain and wire transmission to a screw jack controlling the incidence of the tail plane. A drum 46 for a band-brake (not shown) is formed integrally with pinion 7. Automatic switch means may be employed to stop motor 21 when the rotor shaft is fully extended and also when the rotor shaft reaches the end of its travel on retraction. In addition to increasing the tail plane incidence concurrently with rotor extension means may be provided for depressing landing flaps 47, Fig. 5; these means comprise cables 29, 29a, passing over pulleys carried by guide 3 and secured to the trunnions 16. An alternative hydraulic means for operating the rotor shaft and the tail plane is shown diagrammatically in Fig. 9, and comprises a gear pump 58 adapted to draw oil from a reservoir 59 and to supply oil under pressure to cylinders 60 and 60a in which move pistons, of which the rods are connected to the rotor shaft and the tail-plane front-spar, respectively. Oil above the pistons is forced into hydro-pneumatic accumulators 62, 62a. The pump is of the continuously running type and a relief valve 70 serves to return excess fluid to reservoir 59 by overflow pipe 67f. To return the rotor and the tail plane to their initial positions the pump 58 is stopped and valves 70a, 70b are opened, whereupon the pistons are forced down by the compressed air in the accumulators 62a and 62b. A similar circuit also including a hydro-pneumatic accumulator may be supplied by pump 58 through branch pipes 67b to actuated flapoperating jacks. Similar power means may actuate a jack 60c, Fig. 8, to effect the retraction and extension of a pivoted undercarriage leg 75 carrying a wheel 78 by an offset axle 77. Leg 75 is mounted on and braced by a strut 80 to a hinge-pin 76 carried by front and rear walls of a built-up box-spar. In this case the undercarriage is held in the " down '' position by the pressure of the air in a hydro-pneumatic accumulator and may be maintained " up " by positive locking-means. The valves in the undercarriage circuit are controlled independently of those in the rotor, tail plane and flap circuit. As an alternative to an adjustable tail plane, a variable-area tail plane may be employed comprising separate tip portions of which the spars are slidable into and out of front and rear spars of the main portion of the plane. Spars may be directly acted on by the rams of hydraulic jacks, each comprising a single cylinder with two oppositely moving rams, or by screw jacks. In the first case control is by means similar to that shown in Fig. 9 and in the second the screw jacks are operated by chain and wire transmission from the sprocket driving-chain 25a, Fig. 4. As a further alternative aerofoils normally nested in the fuselage enter side by side or one above the other and toward the tail of the machine are swung out into the airflow in synchronism with extension of the rotor. In one such arrangement, Fig. 14, an aerofoil 32d comprises spars 32e which converge at the root and terminate in bearings mounted on the driving shaft of a, geared electric motor 21a. The spars are guided and supported by means of brackets carrying rollers engaged between spaced arcuate guide rails 85. The upper rail is formed or provided with a toothed rack 88 with which meshes a spur pinion 89 carried by spar 32e and driven by chain gearing from the motor shaft. When the aerofoils are nested one above the other they may be so arranged that their angles of incidence when projected differ slightly to compensate for their asymmetric arrangement. Hydraulic operating means may be employed as shown in which piston rods of pistons working in a common cylinder are connected by links and levers to lever extensions of spars. A still further alternative an autorative rotor may be housed in the tail plane and projected therefrom by means similar to those used for the main rotor. In this case the electric motor may also be arranged to drive the rotor through means which only come into action when the rotor reaches the operative position. The main rotor may incorporate automatic pitch-changing devices. In one form, Fig. 22, the flapping pivot is carried by a sleeve 97 rotatable on hub arm 55b and retained by a tension bolt 99, a thrust bearing 14d being inserted between the sleeve and the retaining nuts. The hub is loose on shaft 2b and the sleeve 97 is formed with a toothed gear segment 101 which meshes with teeth 102 formed on a rack integral with a driving member 95 pinned to shaft 2b. Stops limit relative movement of the gears. The arrangement is such that when shaft 2b is driven for starting, one stop contacts the end tooth of segment 101 and the rotor blades are at an autorotational pitch angle. When the drive ceases the friction between the gears is stated to be adequate to prevent relative movement between the gears but when shaft 2b is braked to arrest rotation of the rotor, the latter overruns the shaft changing the' blade-pitch angle to a large negative pitch angle and thus the rotor is brought quickly to rest. In another arrangement the driver is above the hub and in this case the blades are caused to assume a negative pitch angle when the shaft is driven and a positive pitch angle when driving the shaft. A single-bladed main rotor may be employed using a leadfilled steel shell as a counterweight.