Rotor blade lead-lag hydraulic damper with centrifugal force compensating damping characteristics

A lead-lag damper for a helicopter blade, the damper comprising:

• a housing having an inside surface that defines an inner chamber that extends from a first axial housing end to a second axial housing end, a first bore extending through the second axial housing end into the inner chamber;
• a first shaft connected to the first axial housing end of the housing;
• a second shaft extending through the first bore of the housing;
• a piston assembly comprising:
• a piston-rod extending from a first piston-rod axial end to a second piston-rod axial end, the piston-rod comprising a tubular member having an interior area defined by a first inside surface and a second inside surface, a piston-head extending radially outward from the piston-rod and located between the first piston-rod axial end and the second piston-rod axial end, the piston head having a first axial face facing towards the first piston-rod axial end and a second axial face facing towards the second piston-rod axial end, a first port extending through the piston-rod and located axially away from the first axial face of the piston-head and a second port extending through the piston-rod and located axially away from the second axial face of the piston-head;
• a sleeve positioned in the piston-rod and engaging the second inside surface, the sleeve having a first annular passage in fluid communication with the first port and a second annular passage in fluid communication with the second port, the sleeve having an interior engagement surface;
• a valve spool disposed in the sleeve and slidingly engaging the interior engagement surface, the valve spool having a radially outward opening channel which is in variable fluid communication with the first annular passage and the second annular passage;
• a biasing member engaging the valve spool such that the valve spool is biased axially away from the second port;
• and
• wherein the channel has an axial width of a magnitude configured to variably regulate fluid flow between the first port and the second port to variably control dampening of the piston-rod in response to centrifugal forces applied to the valve spool, generated by rotation of a rotor of the helicopter blade;
• the piston-rod being disposed in the inner chamber, a radially outermost circumferential surface of the piston-head being in sliding engagement with the inside surface and the piston-head bifurcating the inner chamber into a first inner volume and a second inner volume;
• and
• the second shaft being connected to the second piston-rod axial end of the piston-rod.

A valve arrangement for a lead-lag damper for a blade mounted on a rotor of a helicopter, the valve arrangement comprising:

• a sleeve having a first annular passage and a second annular passage formed in the sleeve and having an interior engagement surface;
• a valve spool disposed in the sleeve and slidingly engaging the interior engagement surface, the valve spool having a radially outward opening channel which is in variable fluid communication with the first annular passage and the second annular passage;
• a biasing member engaging the valve spool such that the valve spool is biased axially away from second annular passage;
• and
• wherein the channel has an axial width of a magnitude configured to variably regulate fluid flow between first annular passage and the second annular passage to variably control flow of fluid through the valve arrangement in response to centrifugal forces applied to the valve spool.

A housing assembly for a lead-lag damper for a blade mounted on a rotor of a helicopter, the housing assembly comprising:

• a housing-body comprising a wall structure having an outer wall and an inner wall, the wall structure having a valve interior area formed in the wall structure between the outer wall and the inner wall, the valve interior area being defined by a valve inside surface, a first port extending from the interior area and through the inner wall and a second port extending from the interior area and through the inner wall, the second port being located axially away from the first port;
• a sleeve positioned in the valve interior area, the sleeve having a first annular passage in fluid communication with the first port and a second annular passage in fluid communication with the second port, the sleeve having an interior engagement surface;
• a valve spool disposed in the sleeve and slidingly engaging the interior engagement surface, the valve spool having an exterior surface having a radially opening channel which is in variable fluid communication with the first annular passage and the second annular passage;
• a biasing member engaging the valve spool such that the valve spool is biased axially away from the second port;
• and
• wherein the channel has an axial width of a magnitude configured to variably regulate fluid flow between the first port and the second port to variably control damping of the piston-rod in response to centrifugal forces applied to the valve spool, generated by rotation of the rotor.