The tests historically used a Compact Resonant Mass (CRM) system, a common test methodology used throughout the industry, to excite blades to the desired natural frequency. However the current CRMs were meeting an operational limit as they could no longer exert enough force through the entire length of the blades at the desired low frequency. This led to a switch to the Resonant Actuator Test (RAT), which has one single floor mounted actuation point that is coupled to the underside of the blade