Assessment of Digital Flight-Control Technology for Advanced Combat Rotorcraft

Digital flight-control systems are critical to the mission success of advanced combat rotorcraft. Single-pilot and nap-of-the-earth operations require handling qualities that minimize the involvement of the pilot in basic stabilization tasks. To meet these requirements demands a fullauthority, high-gain, multimode, multiplyredundant digital flight-control system. The gap between these requirements and the current lowauthority, low-bandwidth flight-control technology of operational rotorcraft is considerable. The work reported here aims at smoothing the transition between current technology and advanced design requirements. A review of the state of the art of high-bandwidth digital flight-control systems is presented with special emphasis on areas of concern for such systems in modern combat helicopters. Important design and analysis aspects of high-gain, digital systems are illustrated, using results from a detailed case study involving a current rotorcraft system. Frequencydomain methods for design and analysis are stressed as being essential for the practical implementation of high-gain control systems for rotorcraft. Approximate and exact methods are introduced and illustrated for treating the important concerns that are unique to digital systems.