Investigation of the Flare Maneuver Using Optical Tau

Abstract

Airline transport operations are carried out in a wide range of visual and instrument meteorological conditions. However, the pilot can choose to land the aircraft manually using the visual cues available for all but the most limiting of degraded visibilities. How this is achieved may seem rather obvious, but has challenged researchers for some time. Optical flow theory offers a solution: pilots detect motion from the surfaces over which they move. In a relatively recent incarnation, flow theory transforms motion into the temporal, time-to-contact parameter, tau. Research conducted at Liverpool has applied this theory to low-level helicopter flight. The present paper extends the application to the fixed-wing flare. Flight simulation results show that tau-guidance strategies exist for this maneuver. It is shown that, as expected from tau theory, the pilot-selected values of the rate of change of tau with time, tau-dot, and the tau-guide coupling constant, directly influence the acceptability of the touchdown rate achieved. Degraded visual environments are shown, under certain circumstances, to cause a breakdown in the tau relationships observed. Potential uses of these results are presented in terms of application to future pilot vision aids, which is the planned next stage of this work.