Multivariable flight control for an attack helicopter

This paper discusses advanced flight control for the Apache YAH-64 helicopter. The control laws have been flight tested and were extensively evaluated with fixed-base piloted simulation as part of the Advanced Rotorcraft Technology Integration Flight Experiment. The control system employs as sensors normal and lateral acclerometers and three body rate gyros; for control, it uses collective, tail rotor, and lateral and longitudinal cyclic controls. The control laws were developed to provide decoupling, gust attenuation, desensitization, and stability augmentation in the face of aircraft modeling uncertainty. A multivariable proportional-plus-integral element is the basic ingredient of the control. Various analyses are presented, including frequency and time responses and stability robustness properties using singular-value and structured singular-value techniques. Responses of the controlled helicopter to pilot and gust inputs are examined using time histories.