Patent GB-898248-A (GB)
Title: Landing gear for aircraft
IPC: B64C25/34
Filed: 1959-04-02
Abstract: 898,248. Aircraft undercarriages. BOLKOW - ENTWICKLUNGEN KOMM.-GES. [trading as BOLKOW-ENTWICKLUNGEN KOMM.-GES]. April 2, 1959 [April 5, 1958], No. 11234/59. Class 4. Landing gear for vertical take-off and landing aircraft, such as helicopters, is movable relatively to the fuselage, and means are provided to lock the landing gear automatically against such movement during landing when the landing gear conforms with the ground configuration In Fig. 3, an undercarriage strut 31 is secured to a piston 32 sliding in a hydraulic cylinder 30 in a helicopter fuselage, there being a by-pass pipe 35 containing a valve 36 operable by an electromagnet 42. Two other undercarriage struts 28, 29 are similarly mounted, only their by-pass valves 37, 38 and electromagnets 43, 44, being shown. In addition, each strut on starting to retract from the extended position closes a switch 39, 40, or 41. Prior to landing, valves 36, 37 and 38 are open, and the struts 28, 29, 31 extend under their own weight, so that switches 39, 40 and 41 are open. On touch down or uneven ground, the two struts which first contact the ground are free to move upwardly towards the fuselage, closing their respective switches. When the third leg contacts the ground, the open one of switches 39, 40 and 41 is closed, and completes a circuit to energize electromagnets 42, 43, 44 from a battery 48 through two way switch 49. Valves 36, 37 and 38 are closed, and the undercarriage struts are thus locked. After take-off, switch 49 is manually changed over, to energize electromagnets 42, 43, 44 with reverse polarity independently of switches 39, 40 and 41. Valves 36, 37, and 38 re-open, and the struts 28, 29, 31 extend under their own weight. A modification in which retraction and extension of the strut is power assisted is shown in Fig. 4. The piston 52 divides the cylinder into chambers 50, 51 communicating with bores 54, 55 in the piston rod 53. The strut 60 is slidably engaged on the piston rod, and urged apart therefrom by a spring 61. Relative axial movement between the rod and strut is limited, and relative rotation prevented, by a pin 62 in the strut engaging a slot in the piston rod. The strut 60 has three parts co-operating with two branches of each of bores 54, 55, and connected to pipes 56, 57, and 59. Pipe 59 leads through valve 58 to pipe 57, and pipes 56 and 57 lead through valves 63 and 64 to hydraulic pressure and return pipes respectively. The latter pipes are connected by pipe 66 containing valve 65. Fig. 4 shows the strut prior to landing valves 58, 63 and 64 being open and valve 65 shut. Fluid circulates through valve 63, pipe 56, the lower part of bore 55, pipe 59, valve 58, pipe 57, and valve 64, to drain. When the strut touches down, spring 61 is compressed, and the registry of pipes 56, 57, 59 and bores 54, 55, is changed, so that fluid under pressure enters chamber 50 through valve 63, pipe 56 and bore 54. Chamber 51 is connected to drain through bore 55, pipe 57, and valve 64, should the pressure on leg 60 cease, spring 61 expands and the disposition shown is resumed. Normally, however, the first two legs to touch down continue to retract until the third leg touches down, when valves 63, 64 and 65 on each leg are changed over, in the same way as valves 36, 37 and 38 of Fig. 3. This locks the legs, and by-passes pressure fluid through pipe 66 and valve 65. After take-off, spring 61 expands, valves 63, 64 re-open, and valve 65 closes. The struts can be extended hydraulically by closing valve 58. Fluid under pressure then flows through valve 63, pipe 56, and bore 55, to chamber 51. Chamber 50 is connected to drain through bore 54, pipe 57, and valve 64.