Tau guidance in boundary-avoidance tracking: new perspectives on pilot-induced oscillations

Abstract

Tau theory, introduced to the flight control discipline as a model for natural guidance, is shown to provide an
approach to predicting a class of adverse aircraft-pilot couplings described as boundary-avoidance tracking events
and pilot-induced oscillations. These have previously been modeled a posterior as discrete events using timedependent
feedback gains. Drawing on the prospective nature of the time-to-contact variable optical tau �, a new
method is proposed for modeling such phenomenon and also for determining the critical incipience for this class of
aircraft-pilot coupling. In the present study, the approach has been applied to tau guidance in a rotorcraft trajectory
tracking maneuver, to predict the conditions under which aircraft-pilot couplings may occur. In addition, a strong
correlation between motion and control activity and the derivatives of tau adds substance to the hypothesis that the
pilot’s perceptual system works directly with invariants in the optical flow during visual guidance. Results from flight
simulation tests conducted at the University of Liverpool and complementary flight tests carried out with the
National Research Council (Canada) advanced systems research aircraft in-flight simulator support the tau control
hypothesis. The theory suggests ways that pilots could be alerted to the impending threat of such adverse aircraftpilot
couplings