Contrasting Effects of Control System Delay and Visual System Delay on Helicopter Pilot Performance: Preliminary Findings.

Visually-coupled systems are designed to improve a pilot’s ability to fly a helicopter in degraded visual environments. However, a display imaging system which does not provide accurate imagery with a minimal processing delay may be disorienting to the pilot. There is an extensive database relevant to control system time delay effects, however there are few direct comparisons of visual time delay and control time delay effects. An experiment was conducted in the variable stability NRC Bell 205 research helicopter to compare visual and control delays. Three hypotheses were examined: first, that a time delay in either the helicopter control system or the pilot visual feedback loop would increase pilot workload and increase pilot errors in the maintenance of aircraft position; second, that time delay in the visually coupled system will have greater performance effects due to disorientation and motion sickness effects that may be encountered with visual delay conditions in a dynamic environment; and third, that time delay effects would be more pronounced in tasks that require large aircraft pitch or roll rates near the ground. In order to test these hypotheses an image buffer was inserted into the video stream of a visually coupled system, which could add programmable pure time delays. Additionally, incremental time delays were programmed into the helicopter fly-by-wire control system. Pilots performed a series of standardized maneuvers to evaluate the effect of the delays on their ability to control the aircraft. The results show that visual and control system delays degrade performance an equivalent amount, however long video delays also increased the incidence of reported motion sickness symptoms.