CH-47 Helicopter Swashplate Test Stand

A complex multi-axis rotating test system for the CH-47 forward and aft swashplates was designed and built for the Army Redstone Test Center (RTC), with the assistance of the University of Dayton Research Institute (UDRI). This equipment was developed to give the Army the ability to test CH-47 swashplate bearings and new swashplate designs. It has also been used to evaluate the performance of currently fielded seals, new seal designs and greases, and to study the deflection of swashplates at flight loads and speeds. The test stand is not only capable of sine wave loading that has typically been used to test swashplate bearings but can reproduce the complex loading that occurs in the swashplate during flight. Dynamic behavior of the test stand is dependent upon the mechanical characteristics of the test plate, links, reaction plate, and frame - the plates and links, in particular, contain numerous joints that may exhibit backlash or hysteresis during motion under load. As result, dynamic wave shapes contain a product-dependent level of distortion or uncertainty (just as would be encountered in the airframe setup when acquiring flight load data). Using an active loop convergence algorithm, results have been obtained in which load peaks converge within 1% to 3% of the required values. Angular timing of the load peaks is achieved within a few degrees of desired rotation by adjusting phasing of the command signals and measuring the response of the system versus predicted values to determine model compensation factors. This paper describes the development effort for the test stand and describes the test programs that have been accomplished and are planned with the equipment.