Low interaction wind tunnel balance

Claim 1

A strain gage balance for measuring component forces and moments applied to the body of a test model disposed in a flow field of a test wind tunnel, said balance adapted for mounting at one end to said tunnel by means of a sting and at the other end to said model comprising: first and second means for measuring pitch and yaw load applied to said model, said sting being connected to the first of said pitch and yaw means, a roll moment measurement section integrally connected to said first pitch and yaw means, said roll section having a plurality of torsion webs spaced at the upper and lower periphery of said roll section and capable of allowing twist deflections for the balance for roll load measurement but providing a constraint on deflections along the pitch and yaw axes, a plurality of beams connecting the forward and aft non-webbed portions of said roll section, said beams consisting of a support beam integral with the forward portion of said roll section, said support beam having a recess therein defining a thin beam, a thin intermediate beam integral with said thin beam, said intermediate beam being integrally connected to a roll gage beam capable of deflection in response to a rolling moment, whereby said thin beam has the capability of reducing any deflections induced in said roll gage beam due to an axial force or pitching moment, said intermediate beam is capable of reducing any side force and yaw load which said roll gage beam may experience; an axial force measurement cage attached to said roll section, said axial cage being integral with said second pitch and yaw means, said axial cage having longitudinal beams of cruciform construction acting as an integral unit, a plurality of axial deflection beams integrally formed with said longitudinal beams allowing said longitudinal beams to respond as a unit under an axial force without transmitting roll moments or pitch and yaw loads, a central beam fixed to said roll section and integrally formed with said axial deflection beams, a cross beam integrally connected to said central beam at one end and at its other end to an axial gage beam which is capable of deflection in response to an axial force, said axial gage beam also being integrally formed with said longitudinal beams via thin flexure beams, whereby said longitudinal beams transmit said axial load to said axial gage beam, said axial deflection beams being capable of carrying pitch, yaw loads and roll moments without allowing much deflection of the axial gage beam due to pitch, yaw loads and roll moments acting on said model, said thin flexure beams, acting like pin joints, reduce interaction and transmit the axial force loading to said axial gage beam, and; means responsive to the deflection of said roll and axial gage beams for indicating the magnitude and direction of said rolling moments and axial forces, respectively.