Patent GB-543609-A (GB)
Title: Improvements in or relating to undercarriage legs for aircraft
IPC: B64C25/20
Filed: 1940-07-03
Abstract: 543,609. Pneumatic and hydraulic shock-absorbers. ROLLASON AIRCRAFT INSTRUMENTS & EQUIPMENT, Ltd., and THOMAS, A. H. J. July 3, 1940, No. 11186. [Class 108 (iii)] [Also in Group XXXIII] A retractable undercarriage leg comprises a telescopic member pivoted to the air frame for retraction and normally braced by a radius member pivoted at one end about an axis parallel to and spaced from the leg pivot and connected at its other end to the pivoted part of the telescopic member, means being provided for disconnecting the radius member from the pivoted part of the telescopic member and connecting it to the axially moving part so that by shortening or lengthening the telescopic member the leg will be retracted or lowered about its pivot. Normally the telescopic member acts as an oleopneumatic shock-absorber and hydraulic pressure is used to effect the shortening. A cylinder 31 Fig. 22, is pivoted to the air frame at 36 and a wheelcarrying ram 37 slides within the cylinder. The wheel fork is connected also to two parallel rods 41 sliding in guides 42 on the cylinder and connected together by cross members 50, 51. A radius member 46 pivoted to the airframe at 47 has a forked end 48 with upper and lower notches 53, 52 Fig. 3, the latter normally engaging a lug 49 extending between the lower guides 42. Pivoted within the forked member 48 about a pin 55 is a latch member 54 with two arms 56, 57 the latter normally engaging beneath the lug 49 where it is retained by a pair of springs 70 acting through a detent 60 pivoted on the latch member. The other ends of the springs 70 are anchored to members 64 pivoted at 65 to the radius member 46 and connected together by a bar 67 which engages the detent 60, cam surfaces on the lower guide 42 co-operating with the members 64 to cause the bar 67 to hold the detent 60 normally clear of the member 46. While the aircraft is on the ground the ram 37 is partially forced into the cylinder 31 and the cross member 50 on the guide rods 41 is clear of the notch 53. When the aircraft leaves the ground the bar 50 descends into the notch 53 whereupon the pilot actuates a control to tighten a Bowden cable 329 and tilt the latch member 54 so as to bring the arm 56 above the bar 50 and the arm 57 almost clear of the lug 49. Pressure fluid is simultaneously admitted beneath the piston of the oleo-pneumatic device to telescope the leg and, the bar 50 being now anchored to the radius member 46, the arm 57 of the latch member slides clear of the lug 49 and causes an undercut end 61 on the detent 60 to come opposite a lipped opening 63 in the radius member. As the members 64 slide clear of the cam surfaces on the guide 42 the detent 60 is pulled into engagement with the lipped hole by the springs 70 and the latch member 54 is held in its new position. Continued shortening of the legs causes the cylinder to swing about its pivot 36 until a hook 332, Fig. 22 engages a spring-urged up-lock 330. To lower the leg the lock 330 is released and the leg allowed to fall helped by the stored air pressure within the cylinder or pressure fluid may be supplied above the piston to force down the leg. The Bowden cable 329 is slackened simultaneously with the release of the lock so as to enable the latch mechanism to resume the position shown in Fig. 3 when the leg is fully lowered. Fig. 10 shows the interior of the cylinder 31. The member 37 is connected to a piston 38 working in the cylinder 31 the lower and upper ends respectively of which are connected by passages 101, 102 to a control valve 34 which normally puts these two passages into communication with a passage 105 leading via a variable restriction valve 35 and passage 120 to an oil reservoir and air chamber 32. Oil can flow freely from one side of the piston to the other but the oil displaced by the plunger 37 has its flow to the reservoir 32 restricted by the valve 35. Oil returning from the reservoir to the cylinder can reach the passage 105 relatively freely past a non-return valve 106. The valve 35 is gradually closed as the leg telescopes, a lever 117 on the valve having a forked end engaging a pin 115, Fig. 22 on one of the guide rods 41. When the valve is completely closed the pin can move clear of the lever which is then held against a stop by a spring. Should further displacement occur under landing shocks oil is forced through a chamber 123 and through a valve 130 to force up a floating piston 124 into a chamber 122 containing air at a higher pressure than that in the reservoir 32. Normally the piston 124 seats down on the valve 130 which has a narrow passage 128 through its stem. To raise the leg the valve 34 is turned to put the passages 101, 102 into communication respectively with passages 109, 108 leading to the delivery and input sides of a closed circuit pump 114, a passage 107 to the reservoir 32 also being put in communication with the passage 102, and the passage 105 is closed. When the leg is raised into engagement with the uplock 330 the valve may be turned to close all the passages, or it may be turned to the original position to enable the pressure in the chamber 32 to lower the leg as soon as the uplock is released. Should this pressure be insufficient the valve 34 may be turned to a fourth position in which the passages 109 and 102 are connected and the pump actuated and the passages 101, 107 and 108 connected. A modification is described which is similar in operation but suitable for an open circuit pump, a spring loaded valve preventing oil from being returned to the pump intakes until a predetermined pressure has been built up in the chamber 32. For controlling the valve 34 a four position lever 301, Fig. 22 moving in a gate is employed, the lever actuating sprockets connected to the valves on each leg by chain and Bowden wire gear. A cam-actuated lever in each valve control box 316 ensures that two oppositely moving Bowden cables 329, 328 connected respectively to the latch member 54 and uplock 330 cause the latch 54 to be lowered as the uplock is released, and raised as the uplock is rendered ready to receive the projection 332. A clutch actuated by a hand wheel 320, Fig. 10, enables the valve to be moved by hand from the ground for raising or lowering the airframe relative to the wheel. The device may be applied to seaplane.floats.