Patent GB-496080-A (GB)
Title: Improvements in or relating to retractable undercarriages for aircraft
IPC: B64C25/20
Filed: 1937-08-19
Abstract: 496,080. Retractable aircraft undercarriages. AUTOMOTIVE PRODUCTS CO., Ltd., and THORNHILL, P.W. Aug. 19, 1937, No. 22782. [Class 4] A folding strut for an aircraft retractable undercarriage has a lever pivoted to one articulated part and connected by a link to the other articulated part and operating means acting on the lever to turn about its pivot on the strut and exert a thrust in the link when the strut is being folded to retract the undercarriage, the arrangement being such that the link approaches a position at right-angles to the second part of the strut as the folding operation approaches completion. In one form, Fig. 1, a strut comprises parts 1, 2 pivoted together about an offset hinge 3 and adapted to be connected to the aircraft structure and undercarriage leg, respectively, by pivot pins passing through apertures 4, 5. A pin 7 passes through a sleeve 6 and a slot 8 in strut part 1 so arranged that sleeve and pin are capable of limited movement in the direction of the axis of strut part 1. Pin 7 carries two triangular frames 11 of which the other two corners are connected by pins 12, 13. A link 14 connects pin 12 to strut part 2. Cylinder 16 of a hydraulic jack is pivotally connected to pin 13 and plunger 17 thereof is connected directly or indirectly to the aircraft structure. The pivot pin 7 of the triangular frames 11 passes through a plunger 18 slidable in strut part 1 between stops 19, 20, a spring 21 tending to move plunger 18 and thus sleeve 6 toward pivot 3. Sleeve 6 carries a wedge member 22 which in the closed position of the strut engages between part 1 and a cam 23 carried by part 2 and thus acts as a lock. Contraction of the jack initially produces axial movement of sleeve 6 to withdraw wedge member 22 and thereafter rotation of frames 11 about pivot 7 to fold the strut. The ratio of the angular movement of frames 11 to that of strut part 2 increases as the strut approaches the fully folded position in which link 14 is substantially at right-angles to strut part 2, Fig. 2, hence the mechanical advantage of the gear increases during the retracting operation. The jack mounting may be permitted a certain amount of lost motion which is utilized to control a latch holding the undercarriage in the retracted position. As shown, plunger 17 is pivoted to a lever 24 having limited angular freedom on pin 4 and formed with a stop 24a adapted to engage a fixed part of the structure 24b. During extension, when the jack is expanding, wedge 22 rides on the surface of cam 23 and when the jack is fully expanded, wedge 22 is entered between the cam and the leg part 1 but is forced home by the action of spring 21, the movement of pivot 7 during this operation being accommodated by the lost motion of the jack mounting. A hook 28 is pivoted on pin 25 and is urged in an anticlockwise direction by a spring link 31. Initial movement of the jack on extension forces hook 28 in a clockwise direction compressing link 31 and releasing the undercarriage. Link 31 becomes rigid after a certain movement and thus forms the stop limiting movement of lever 24 during extension. Alternatively, the arrangement may be such that link 14 passes beyond the position in which it is at right-angles to the part 2, thus preventing extension under the weight of the undercarriage. The hydraulic jack may be replaced by a pneumatic or screw jack. Specification 484,938 is referred to.