Abstract:
A key objective of this work was to develop a quantitative rationale to explains some aspects of pilot rating variability, as this would point to the fundamental principles driving pilot response that may not be observable if averaged ratings are used as a handling qualities metric. This paper hypothesizes that the factors affecting a pilot's ability to stabilize and control an aircraft following abrupt control motion is neither the damping nor the frequency of the ensuing oscillation, but rather the length of time that the oscillation remains large enough to interfere with the task (i.e., the product of damping and frequency). A handling qualities metric is introduced called the decay rate parameter that reflects the decay rate of the closed loop dominant mode. Closed loop pilot-vehicle oscillation decay rates were generated by a pilot model employing pitch (visual channel) and pitch rate (vestibular channel) tracking strategies. These decay rates were used to predict minimum and maximum handling qualities ratings and pilot induced oscillation (PIO) ratings which closely matched actual pilot ratings from an inflight PIO study using a variable stability NT-33A aircraft. PIO frequency prediction results were excellent. Predicted handling qualities and PIO ratings from a piloted NASA Vertical Motion Simulator study also closely matched the actual ratings. The results indicate that even with the highest fidelity motion simulation, pilot control relies primarily on the visual channel and is constrained by its inherent limitations. Conversely, the dominant control strategy appears to be the vestibular channel when pilots conduct a visual task that is anchored in the physical, out-the-window environment. The vestibular channel is shown to incur effectively no time delay.