University of Minnesota
Aerospace Engineering and Mechanics
Winter 1998 Seminar Series

Improving Flight Control Automation Design Concepts and Processes

Tony Lambregts
Federal Aviation Administration


In this talk various aspects of the historic evolution of today's automatic flight control systems will be discussed, as well as new and advanced control concepts and methods. It will be shown that the piecemeal incremental development of new flight control functions over time has resulted in rather inefficient system architectures, with considerable functional overlap, unnecessarily high systems complexity, too much hardware/software and less than optimum system performance. The consequences in terms of safety and cost will be explored. It is concluded that automation in general has had a very positive impact on flight safety, although in some instances unnecessary operational complexity has contributed to pilot error and confusion, leading to some noteworthy accidents and incidents. Specific design deficiencies, which have long been known to exist in the current generation of automatic control systems, will be discussed and better design processes and concepts that have been developed to solve known problems will be described.

These new concepts are the Total Energy Control System (TECS) for longitudinal flight path and speed control, and the Total Heading Control System (THCS) for lateral-directional control. TECS and THCS each use a single generalized multi input / multi output core control algorithm to provide complete operational and performance consistency for all modes and flight conditions. The control error for each operational mode is normalized to feed into the generalized control algorithm. The result is a reusable building block system architecture that functionally integrates and consolidates all longitudinal and lateral directional control functions, previously provided by the pitch/roll autopilot, autothrottle, yaw damper, Flight Management Computer, and FBW augmented manual control computer. This design approach eliminates all control function overlap, reduces hardware up to 50% and control law software up to 70% and simplifies system interfaces.

The TECS design uses thrust to control total energy and the elevator to control energy distribution, to satisfy flight path and speed targets. The operation is directly compatible with the flight path angle/potential flight path angle display of a HUD system. The THCS design develops a roll angle command to control the sum of heading and sideslip errors (Total Heading Error), and a coordinated yaw rate command based on the difference between heading and sideslip error.

Implementation of the flight path vector based FBW augmented manual control modes as a simple add-on module to the core control algorithm will be described. This add-on module develops feed forward control commands based on the pilot control inputs.

The advantages of the reusable TECS/THCS designs will be discussed, e.g. the simplification and shortening the overall design development cycle, improved performance and reduction of overall cost and risk. Finally, some background comments will be provided about the NASA sponsored program, the pilot-in-the loop evaluations conducted on the B737 and B747 flight simulators and the flight demonstration results obtained on the NASA B737 airplane and the Condor Autonomous High Altitude Long Endurance aircraft.

Friday, February 27, 1998
209 Akerman Hall
2:30-3:30 p.m.

Refreshments served after the seminar in 227 Akerman Hall.
Disability accomodations provided upon request.
Contact Audrey Stark-Evers, Senior Secretary, 625-8000.