Neuromuscular Response Comparison for Center and Side Stick Positions

Four Army pilots participated in a simulation experiment to examine the influence of stick location and sensitivity (gain) on pilot neuromuscular (NM) response, performance, and workload. The experiment employed an active inceptor that was positioned between the pilot's legs or, adjacent to the pilot's right side with an armrest. Two stick sensitivities that varied by a factor of four were evaluated using a single-axis compensatory tracking task in the longitudinal and the lateral axes. The experiment results identified two prominent NM modes at roughly 10 and 25 rad/s; stabilizing the elbow implicated the 10 rad/s mode with forearm motion, and wrist/finger motion with the mode at 25 rad/s. With the longitudinal task using the low stick gain, workload ratings were significantly higher for the side stick than the center stick. A preliminary analysis indicated that the greater resisting force between the forearm and non-compliant armrest (side stick configuration) relative to the resisting force between the forearm and leg (center stick configuration) may be a key factor in the higher workload. This suggests that a side stick's gain in the longitudinal axis should be a function of task such that control displacements are generally small. Overall workload during manual tasks would benefit if this approach were applied to all control axes. A second study was conducted to investigate the significant effect of stick gain on crossover frequency that was observed in the first experiment. These results showed that the ratio of stick rate to stick amplitude is directly proportional to crossover frequency, and that a tradeoff between rate and amplitude reflected by changing crossover is similar to the phenomenon described by Fitts Law, where manual movement time is related to the distance travelled. The implications for design are that stick travel can affect performance much more than stick force provided the stick dynamics do not adversely interact with the NM system. It is recommended that the feel system mode should lie between the forearm and wrist/finger NM modes, and that stick sensitivity selection should be based on mission and operating environment.