Development of Control Laws for the Chinook Digital AFCS Program

When the Chinook Digital AFCS makes its debut on the CH-47F in the 3rd quarter of 2006, it will be the first production Army helicopter to meet all of the ADS-33 response-type requirements for operation in Degraded Visual Environments. This paper provides insight into the development process of these control laws and an initial look at how well these modern control laws may address the military’s needs based on the conclusions from flight test. The ADS-33 modern control law functions on the CH-47F include Attitude Command / Attitude Hold, Translational Rate Command, Precision Velocity Adjust, Position Hold, Precision Position Adjust and Altitude Hold. The Digital AFCS also provides for improved coupled modes through a new interface with the Rockwell Collins CAAS avionics suite and improves the utilization of the existing actuators. All this was incorporated on the partial authority Chinook helicopter in 30 months without any modifications to the existing actuators. In order to meet the aggressive schedule laid out for the program, maximum use was made of simulation and many advanced tools and processes were used throughout the control law development, coding, and testing. An extensive flight test program involving envelope expansion, sling load operations, ADS-33 Mission Task Elements, ADS-33 compliance evaluation, and Degraded Visual Environment evaluations capped the development of the control laws. The program requirements, control law development tools, processes and decisions, testing methodology and flight test results are all presented in this paper.