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In a retractable aircraft undercarriage having a plurality of points of application of operative force constrained to move at varying rates, a differential device, adapted to allow for the relative rate of movement between the points of application, is provided in the transmission means. In one form, a landing‐wheel 5 is supported on resilient compression members 1 spaced apart to receive between them the wheel and pivoted to a supporting‐frame 6 also pivoted to a lever 8 rigid with a double‐grooved pulley 11. Retraction of the landing‐gear is accomplished by winding a cable 25 on to a drum 26. The cable is connected through a spring 24 to a pulley 23 over which and pulleys 22, 29, 30, 31 passes a cable 21, 21B secured at one end to the rod 6 and at the other to the pulley 11. Initial tension rotates the drum 11 anticlockwise which, through frictional engagement, rotates a lever to disengage a catch 14 co‐operating with a detent 16 having a slot 19 adapted to engage a pin 7A connecting the frame 6 and lever 8 for locking the landing‐gear in its operative position. Continued winding forces the pulley 31 and lever 8 anticlockwise, rotates the pulley 11 and pulls on the frame 6; thus the joint 7 is freed and moves past the line joining the pivot of the pulley 11 and the wheel axle 4. During retraction the pulley 23 allows for the varying rates of movement of the pulley 11 and the point of attachment to the frame 6. The landing‐gear is extended by rotation of a drum 27 integral with the drum 26 to wind up a cable 28 which has during the process of retraction been wound on the pulley 11. The cable 28 is secured to the pulley 11 or is made continuous with the cable 21B and secured to the pulley 11. The spring 24 allows for slight inequalities in the rate of paying out of cable 28 and hauling in of cable 25. The spring 24 may be omitted, in which case the drums 26, 27 are connected by a torsion spring. A brush for cleaning the landing‐wheel is provided. In a modification, a lever 51 connected to the frame 6 and the shock‐absorbers 1 are rotated for retraction or extension of the landing gear through gearing and toothed quadrants from a differential gear which is driven from a sprocket wheel 44, the quadrant on the lever 51 being driven from the differential through a chain 46 and a sprocket 47. The frame 6 is pivoted to a member 53 slidable in a bearing in the lever and provided with a rubber buffer 54 which bears, when the landing‐gear is operative, in a recess 55 in an anchorage secured to the rear wing spar. The wheels may project slightly when retracted.