Abstract: A current-driven signal conditioning system comprising a first terminal, a second terminal, a strain gauge, and an instrumentation amplifier is disclosed. The strain gauge is adapted to measure a deformation of a structure and to generate a resistance which corresponds to the measured deformation. The instrumentation amplifier is adapted to be connected between the first terminal and the second terminal. The instrumentation amplifier is further adapted to be connected to the strain gauge and to place an output current on the second terminal. The output current is proportional to the resistance generated by the strain gauge. An output resister is coupled between the strain gauge and the second terminal, and a capacitor is coupled between the resister and the first terminal. A zenor diode is coupled between the first terminal and the strain gauge, and a diode is also coupled between the first terminal and the strain gauge.

Abstract: The system is used in power-assisted control systems to provide a restoring force to the control stick indicative to the pilot of the deflection of a control surface. The feel system is trimmable in that the neutral position can be altered. In prior systems trimming was accomplished by releasing a brake which permitted movement of a part of the control stick linkage toward an equilibrium position in response to the restoring force. In prior systems the released part acquired sufficient momentum to cause it to overshoot and oscillate about the equilibrium position. If the brake were engaged prematurely, the momentum was imparted to the control stick resulting in a disagreeable "kick" felt by the pilot. To overcome these problems, the brake is repetitively disengaged and engaged at a repetition rate in the range 5-40 Hz. The small amount of momentum built up in each of the successive cycles results in an almost imperceptible vibratory reaction on the control stick rather than a single large "kick".

Abstract: In some helicopters power is transmitted from a gearbox adjacent the engine to the tail rotor by a long shaft. To minimize weight, a tubular shaft is used, which rotates at supercritical speeds. Vibrations resulting from shaft unbalance are magnified by resonance as the shaft passes through its critical speeds making it essential that the shaft be finely balanced. This is accomplished by slowly rotating the shaft about its axis while measuring at a chosen station along its length both the wall thickness of the tubular shaft and the distance from a fixed reference plane to the outer surface of the shaft. From these data are determined the local cross sectional area and the location of the center of gravity at the chosen station. From the latter two quantities are determined both the amount of counterweight required and its required angular location around the shaft, for the chosen station. The measurements are repeated at a large number of stations along the shaft.