ω co cut-off frequency (rad/sec) σ ig RMS gust velocity (ft/sec) spatial frequency (rad/ft) τ d time delay (sec)

Modernized control laws were developed to provide an attitude-command/attitude-hold response type for the UH-60 BLACK HAWK helicopter and thereby afford improved handling qualities for near-Earth operation in night and poor weather. The inner-loop system modernized control laws were implemented using the 10% authority stability augmentation system actuators and was evaluated in an EH-60L helicopter. Central to addressing the significant resource and technical challenges of this project was the extensive use of a modern integrated tool set. System identification methods provided an accurate flight-identified aircraft response model and allowed the efficient isolation of discrepancies in the block diagram-based simulation model. Additional key tools were real-time rapid prototyping and a well-designed picture-to-code process. Control laws were tuned to achieve the maximum design margin relative to handling qualities and control system performance requirements. The optimized design was seen to be robust to uncertainties in the identified physical parameters. A flight-test evaluation by three test pilots showed significant benefits of the optimized design compared to the BLACK HAWK standard flight control configuration.

Updates to the military rotorcraft handling qualities specification are currently being considered that address the high-speed flight regime envisioned for the Future Vertical Lift platform of the U. S. Army. A team that features industry and academia has developed and evaluated a set of mission task elements (MTEs) that are defined to address vertical takeoff and landing (VTOL) high-speed handling qualities. Following the mission-oriented approach upon which ADS-33E-PRF is based, the MTEs were designed to meet different levels of precision and aggressiveness. Tracking MTEs based on a sum-of-sines (SOS) command signal were defined for precision, aggressive, and precision, nonaggressive applications. The command signals were derived from fixed-wing analogs that have long been used to evaluate aircraft handling qualities. While the precision, aggressive SOS tracking tasks, the primary subject of this paper, are surrogates for air-to-air tracking and nap-of-the-earth tracking, the known forcing function allows for complete open- and closed-loop pilot—vehicle system identification. The MTE objectives, descriptions, and performance criteria were assessed and refined via several checkout piloted simulation sessions. Formal evaluations were then conducted by Army test pilots at four simulator facilities, each featuring a unique high-speed platform including a generic winged-compound helicopter, two tiltrotor configurations, and a compound helicopter with coaxial rotors. To aid in the MTE evaluation process, baseline VTOL configurations were varied to achieve different handling qualities levels. Quantitative measures based on task performance and qualitative measures based on pilot ratings, comments, and debrief questionnaires were used to assess MTE effectiveness. The piloted simulation results demonstrated that the SOS tracking MTEs provided an effective means to discern precision, aggressive handling qualities in high-speed flight.

To provide the government with independent control-system design, handling qualities analysis, and simulation research capabilities in support of Future Vertical Lift, the U.S. Army Combat Capabilities Development Command Aviation & Missile Center has developed generic high-fidelity flight-dynamics models of several advanced high-speed rotorcraft configurations including a tiltrotor. Full-flight envelope explicit model following control laws were designed for the generic tiltrotor using a multiobjective optimization approach to meet a comprehensive set of stability, handling qualities, and performance specifications. Helicopter response types were used for hover/low-speed, while typical fixed-wing response types (normal acceleration and sideslip command) were used at high speed. The control laws were evaluated in a piloted simulation experiment at the NASA Ames Vertical Motion Simulator using a series of previously developed high-speed handling qualities demonstration maneuvers. This paper discusses the control laws and the results of the piloted handling qualities assessment which show overall assigned Level 1 handling qualities in high-speed and Level 2 in transition.