Progress in the development of a time-to-contact autorotation cueing system

Abstract

Autorotation to landing is a difficult manoeuvre to accomplish successfully in an emergency. During autorotation, it is critical to simultaneously maintain the desired flight path, decelerate the aircraft appropriately, all whilst locating and reaching a safe location to land. This significantly increases the pilot work load in the cockpit. Therefore, there is a clear need to develop a set of pilot cueing and control augmentation technologies that lead to a higher probability of a successful autorotation landing. Tau theory and the associated guides have been shown be of benefit when used to provide guidance cueing in flight, where �tau� is the instantaneous time-to-contact a surface at the current rate of closure. This article presents a detailed analysis of real autorotation flight data in the tau domain. The findings indicate that the taus of pitch angle and range distance can be modelled as being coupled to intrinsic tau motion guides (constant acceleration and deceleration respectively). Additionally, the article presents the development and analysis of a method to generate deceleration trajectories in autorotation using tau as the basis. A point mass model is used to rapidly evaluate trajectory feasibility and enforce reachability constraints in an autorotative flare. This approach of using a low-order model to evaluate reachability shows promise in terms of both accuracy and runtime guarantees. The tau-based control and tau-based trajectory generation schemes can be combined to create a control augmentation system in which reachable areas are depicted visually to the pilot, and inceptor cues are given to reach a selected desired landing point.