GB1218554A - Helicopter landing gear - Google Patents

Abstract

1,218,554. Aircraft undercarriages. DOWTY ROTOL Ltd. 23 Sept., 1968 [19 Oct., 1967], No. 47709/67. Heading B7G. [Also in Division F2] Helicopter landing gear, which may be contracted on landing to lower the helicopter centre of gravity by selection of negative blade pitch and locked in a contracted position, comprises an hydraulic cylinder 11 and piston 12 carrying wheel 13, and an hydraulic flow control valve 21 operated by a solenoid 38 in response to settings of pitch selection mechanism 43. On landing with positive pitch, hydraulic oil flows from chamber 18 to chamber 16 through damping valve 20, chamber 16 being allowed to expand by piston 14 and air chamber 15. Oil also flows from chamber 18 to annular chamber 19 by way of control valve 21, passing through chamber 22, by-pass 36, chamber 34, valve 32, 37 which solenoid 38 has opened, spring chamber 33, orifice 35 and duct 26. On take-off the flow is reversed. With negative pitch selected, however, spring 41 closes valve 32, 37 since the solenoid 38 is inoperative, so that flow from chamber 22 to chamber 19 is through valve 27 formed by spring-loaded piston 31 and valve seat 25 into chamber 24 and along duct 26. No reverse flow through the control valve is possible, because orifice 35 equalizes the pressures in chambers 24 and 33, so that spring 30 closes the valve 27; hence the landing gear remains contracted until positive pitch is selected and reverse flow through valve 32, 37 is possible. A valve 44 may be closed to maintain the contracted position over a length of time.