Development of External Load Handling Qualities Criteria for Rotorcraft

The dynamic motions of external loads are known to have a negative impact on the handling qualities of helicopter/external load systems during hover and low-speed operations. Although criteria have been proposed, currently there are no external load quantitative requirements in the U.S. Army Aeronautical Design Standard for rotorcraft handling qualities, ADS-33. To collect data to support the development of quantitative criteria to address this need, the U.S. Army Aeroflightdynamics Directorate has conducted a series of external load flight tests with an EH-60L Black Hawk helicopter at Moffett Field. Three experimental test pilots performed evaluations of two Mission Task Elements from ADS-33E-PRF. These were flown without an external load, and with multiple external load configurations (five load weights and four sling lengths). Frequency sweeps of selected configurations were also conducted to provide quantitative data to validate a simulation model of the helicopter external load system. Pilot comments and assigned handling qualities ratings from testing indicate that the effects of external loads on handling qualities are most pronounced with the combination of long sling lengths and heavy external load weights. Based on the qualitative results, the attitude frequency responses obtained from the validated simulation model were analyzed and parameters were identified that correlate well with the assigned handling qualities ratings. Using these parameters, a quantitative criteria has been developed that can be used to predict the hover and low-speed handling qualities of helicopters with an external load.