Method and apparatus for minimizing axial friction forces in a cylinder-piston shock absorber

In an aircraft load measurement system of the type including a landing gear shock strut having a circular cylinder member, a piston member mounted for axial reciprocation in said cylinder member and cooperating therewith to define a variable volume fluid confining pressure chamber therebetween, a fluid within such chamber having a pressure representative of a load on said strut, and means for measuring said fluid pressure, the combination therewith comprising:

• annular bearing means coaxially disposed between said cylinder and piston members for axially guiding the reciprocation of said piston member within said cylinder member, said bearing means being formed and mounted for rotation about its axis relative to said members;
• and
• actuator means connected between said bearing means and at least one of said members for rotating said bearing means relative to said members during measurement of said fluid pressure, thereby minimizing axial friction effects between said piston and cylinder members so that the pressure of said fluid substantially equals the load on said strut.

An aircraft load measurement apparatus comprising a landing gear shock strut for supporting an aircraft on the ground and including a cylinder member and a piston member disposed for axial reciprocation in said cylinder member forming a variable volume fluid pressure chamber between said members, a fluid within said chamber subject to a compressive load on said strut and having a pressure representative of such load means for measuring said fluid pressure, and means for reducing axial friction forces between said piston member and cylinder member comprising an annular bearing means disposed coaxially with and radially between said cylinder and piston members for guiding axial reciprocation therebetween, said bearing means being disposed for rotation about its axis relative to said members, and actuator means mounted on said shock strut for rotating said bearing means relative to said piston and cylinder members during such pressure measurement.

In a method of determining the weight supported by an aircraft landing gear shock strut, including the steps of measuring the pressure of a fluid within a variable volume chamber defined between a shock strut cylinder and cooperating axially reciprocating piston wherein such piston is reciprocatively guided by an annular bearing structure disposed coaxially between the piston and cylinder, and concurrently reducing axially oriented friction forces between the piston and cylinder, the improvement in said step of reducing friction forces comprising rotating the bearing structure about its axis and relative to said piston and cylinder.