Comparative Flight Test Evaluation of Passive and Active External Slung Load Dynamics

Abstract

The National Research Council of Canada and Université de Sherbrooke performed flight testing of an Actively Stabilized Slung Load on the NRC Bell 206 Research Aircraft. Hover, Attitude Capture, NRC designed Lateral Precision Hover, and Frequency Sweep mission tasks were performed for Bare Airframe, Passive Water-Filled Barrel and Active Slung Load configurations. Load Mass Ratios of 0.12 with pendulum modes of 1.3 rad/sec were identified for both configurations. Time domain response indicated that both loads remained controllable under excitation by pilot gain, winds, and helicopter-load mode coalescence. Frequency domain analyses confirmed pilot comments indicating HQR-4 handling qualities ratings for bare airframe and stable load behaviors. This degraded to HQR-5 for task execution with load oscillation effects rated at pilot induced oscillation tendency of PIO/T-4. Barrel load HQR degradation related to load inertial and surface area drag effects versus active tether feedback and roll-pitch actuation disharmony of the Active load. Though not optimized, this load’s swing behavior (consistent period and rate) can aid in management of aircraft rate response and pilot compensation. Overall, comparable passive and active test results indicate potential for magneto-rheological actuation to improve slung load mission task performance.