Optimization of Partial Authority Automatic Flight Control Systems for Hover/Low-Speed Maneuvering in Degraded Visual Environments

A ground-based piloted simulation study of a Partial Authority Flight Control Augmentation (PAFCA) concept for the UH-60 Black Hawk helicopter was performed to assess options for potential in-service upgrades and to expand the knowledge base on optimization of PAFCA systems. Two pitch and roll command model gain sets were synthesized for a model-following, attitude-command attitude-hold (ACAH) control law: 1) a gain set optimized for Level 1 handling qualities with respect to the ADS-33D handling qualities specification, and 2) a gain set optimized for minimum mismatch between the open- and closed-loop frequency response. The resulting configurations were evaluated at 10 and 15 percent authority levels in four hover/low-speed tasks. Comparison was also made with the standard UH-60 SAS. The tasks were performed in a simulated degraded visual environment (DVE) using night vision goggles (NVGs). The simulated DVE was judged representative of night operation using NVGs and was assessed as a useable cue environment of two (UCE = 2). Series servo hardover recovery at the 10 and 15 percent authority levels was also assessed. The following summary points were noted: • The ACAH control law was preferred to the UH-60 SAS for the tasks evaluated. • The “frequency-matched” ACAH control law reduced series servo activity, reduced series servo saturation, and improved control predictability in the region of saturation as compared to the ADS-33D optimized gain set. • Desired task performance was achieved with the frequency-matched ACAH control law using 10 percent series servo authority while increasing authority to 15 percent further improved handling qualities by one HQR. • A 15 percent authority series servo hardover was rated one failure rating point worse than a 10 percent hardover, but all failures were recoverable and tolerable.