Flight Testing a Digital Flight Control System. Issues and Results

The AFTIF-16 Advanced Development Program modified an F-16A to be a testbed for evaluating new flight control related technologies. The program has completed its first phase of flight testing. Some of the technologies being developed are a triplex digital fly-by-wire flight control system which operates asynchronously, an analog independent backup unit IBU, eight separate digital task-tailored control laws, and six decoupled controller options. Included among these task-tailored modes are normal operation modes, air-to-air combat and air-to-surface combat modes. One unique aspect of this program was the heavy involvement of the AFTIF-16 Joint Test Force throughout the entire system development pre-flight test phase. This forced early design consideration to be given to pilot-vehicle interface issues. Through use of a General Dynamic GD simulator, the test pilot became an integral part of the flight control normal digital mode, seven different sensor reconfiguration digital modes, and the analog IBU. Much concern surfaced prior to first flight as to how landable these different modes were this resulted in all the landing modes being extensively tested on the GD Simulator, the Flight Dynamics Lab LAMARS, and the NT-33 Inflight Simulator. Two of these modes, the normal mode and the IBU, have been flight tested on the AFTIF-16 itself and the flight test results were different from any of the simulators predicted results. This has raised several issues on the use of simulators to accurately represent todays highly augmented fighter aircraft.