Frequency Domain Verification & Validation of a UH-60A FLIGHTLAB Model with a CONEX Sling Load

This paper details the first step in a process to use simulation modeling as a prediction tool for helicopters with external loads. Using Advanced Rotorcraft Technology's (ART) FLIGHTLAB® software, the U.S. Army Aviation Engineering Directorate (AED) developed a simulation for a UH-60A Black Hawk with a 4,000 pound (4K), container express (CONEX), sling load. The aerodynamics model for the CONEX contains a full mapping of forces and moments in angle of attack (±90 deg) and yaw (±180 deg), but due to limitations of the FLIGHTLAB® software, the cable properties of an "equivalent" one-cable sling replaces the tested four-cable sling. The verification and validation procedure consisted of on-axis, cyclic frequency sweeps processed using Comprehensive Identification from FrEquency Response (CIFER®). The results, in the form of attitude responses, handling qualities, stability margins, and slung load dynamics, show good comparison between the simulation model and the NASA Ames flight test data. Future work involves a cooperative effort between the Army, Navy, and ART to improve and test the FLIGHTLAB code to predict helicopter and external load behaviors.