A frequency selective damper for damping the low frequency natural lead-lag vibrations of an articulated helicopter rotor blade while leaving essentially unaffected the induced one per revolution frequency motion when the rotor is subjected to the combination of these motions. The damper comprises a hydraulic cylinder, a metering-type load valve connected via flow paths to either side of the cylinder piston, a three-way spool valve connected via flow paths to the load valve and to the flow paths connecting the load valve and the hydraulic cylinder, and a control cylinder connected mechanically to the piston rod of the hydraulic cylinder and via flow paths with the spool valve. The displacement of the valve spool is proportional to the time integral of the displacement of the hydraulic cylinder piston. Consequently, when the hydraulic piston rod velocity and the valve spool displacement are both in the extended or retracted mode or sense, the fluid displaced by the hydraulic piston is forced across the load valve. If, however, the piston rod velocity and valve spool displacement are in the opposite sense, the spool valve provides a low resistance bypass around the load valve. This selective bypass provides improved low frequency damping when the damper is subjected to the combined natural and forced vibratory motion.
A hydraulic vibration buffer for connection between two members with a case coupled with the first member, a piston rod with its top end coupled with a second member, a piston coupled with a base end of the piston rod and housed within the cylinder case so as to divide the cylinder case into first and second chambers, fluid source, a tank, and a control valve disposed in fluid paths connecting the cylinder case, the fluid source, and the tank with one another. The vibration buffer also includes returning-force application device constituted by a swingable link with its one and other ends coupled with the first member and the housing block through which the fluid paths extend, and a pair of springs disposed between a center portion of the swingable link and the spool of the control valve.
The hydraulic damper according to the invention has at least one restricted communication passage (47) between its two working chambers (8, 9) whose cross section is controlled by a viscous restriction valve (51) positioned via a control pressure of a fluid of a control damper with at least one secondary chamber (41, 42) delimited in a secondary cylinder (39) by a control piston (40), which cylinder and control piston are integrally attached, one to the main body (1), the other to the damping piston (4) of the damper, such that the damping law of the control fluid positioning said valve (51) is linked to the relative displacements of the main body (1) and damping piston (4). Application to the equipping of elastic-return struts with integral damping, in particular for helicopter rotors and blades. FIG. 2.
A snubber is disclosed for use on an airplane translating door hinge arm (13) comprising a hydraulic device (41) and a flow regulation system (40). The hinge arm (13) includes sprockets (25, 27) placed at the ends (15, 17) of the hinge arm (13). Roller chain pieces (31) rotate partially about the sprockets (25, 27). A pneumatic actuator (33) having a through-rod (37) and housing (35) is located on one side of the hinge arm (13). The actuator housing (35) is supported by a support member (23) integral with the hinge arm (13). The ends of the actuator through-rod (43) are each coupled to first ends of each of the roller chain pieces (31). The hydraulic device (41) comprising a housing (47), a through-rod (43), a piston 45, a first compartment (49), a second compartment (51), and hydraulic fluid, is also supported by the support member (23). The ends of the hydraulic device through-rod (43) are each coupled to second ends of each of the roller chain pieces (31). The hydraulic device (41) is located on the side of the hinge arm (13) opposite the side having the actuator (33). Also provided is a snubber fluid flow regulation system (40) comprising first and second flow regulators (59, 65) and first and second high pressure relief valves (61, 67), one each for use during door opening and door closing. A compensator (71) is also provided in the fluid flow regulation system (40) to hydraulically compensate the snubber (41) during temperature changes and to supply make-up fluid in case there is external leakage.
The invention relates to improvements in and relating to vertical axis wind turbines, particularly those of the "eggbeater" type. It has been found possible, in spite of previous beliefs that it was not so, to provide energy exchange means between the blades and the rotor to thereby smooth out cyclic variations in transmitted torque. The energy exchange means may be, for example, the provision of hinges between the blades and the rotor so that the blade is deflected in operation to transmit torque to the rotor in dependence not only on its fixed geometry but also in dependence on the deflection.
In a vibration absorbing device for rotorcraft, of the type having at least one vibration weight provided in the proximity of a structural member of the rotorcraft through which exciting forces are transmitted to the fuselage, and arranged in such a position and direction of vibration that a selected one of a plurality of forces and moment exciting forces may be offset by the force of inertia of said vibration weight, hydraulic means for imparting vibrations to said vibration weight and means for controlling said hydraulic means to impart desired vibrations to said vibration weight are provided.
