Patent ID: 6926500

Claim:
A drag damper designed to be fitted between a hub of a rotary-wing aircraft rotor and a flapping mass which comprises one of the blades of the rotor and a device for connecting said blade to the hub so as to damp the angular drag movements of said flapping mass relative to the hub, said flapping mass having by construction a natural drag frequency (ωδ) differing from the nominal rotation frequency (Ω) at which the rotor is designed to be driven, the drag damper comprising: a tubular damper body closed by two end faces, a piston fitted and slidable axially in the body and delimiting in and with said body two opposing variable volume working chambers, a rod moving integrally with the piston and passing substantially axially through at least one end face of the body, a spring bias acting on the rod and/or the piston and bearing on the body, and tending to return the rod-piston assembly towards a neutral position in the body, said body and said rod each comprising a connector for connecting respectively to one of two components which are the hub of the rotor and said flapping mass, a fluid filling at least the two working chambers in the body, and at least one restrictor port made in the piston and/or between the piston and the body, and restricting fluid passing from one working chamber to the other when the piston is moved in the body, wherein the drag damper further comprises at least one bypass channel of length (Lc) connecting the two working chambers and filled with fluid, the length (Lc) Of said bypass channel being greater than a main dimension of its cross-section (sc), which is itself smaller than the cross-section (Sa) of the body, with the body and the bypass channel having dimensional characteristics and said fluid having physical characteristics such that the damper has an anti-resonance frequency (ωa) substantially equal to the rotation frequency (Ω) of the rotor so as to filter the Ω dynamic component in damper loads, and wherein said at least one restrictor port is calibrated so as to dampen the relative movements of the rod-piston assembly and of the damper body at a frequency which is substantially equal to the natural drag frequency (ωδ) of the flapping mass.