Testing and Analysis of a Simplified Nonlinear Horizontal Stabilator of an Aircraft

The horizontal stabilator (H-Stab) of a fighter aircraft develops freeplay as the control surface mechanism ages. Modal tests on a simplified model of a H-Stab structure were performed to investigate the behavior of frequency and damping ratio of the spindle and bushing interface on different levels of wear on the structural dynamics. Testing on this simplified model successfully revealed critical changes in its dynamic properties. The H-Stab structure was represented by a rectangular aluminum block (exciter plate), attached to a steel rod as a spindle fixed to a mast. A set of bushings with varying diameters was used at the center of the plate to simulate different levels of freeplay, which was controlled in the order of 0.034° to be comparable with the MIL-A-8870 standard. Steel bushings were fabricated that represent three freeplay cases: tight fit, nominal clearance, and double clearance.