Influence of Variable Inceptor Coupling on Dual Pilot Helicopters using Active Sidesticks

Abstract

Safety reports indicate that the control transfer near the ground can lead to loss of control accidents. This controllability problem is recurrently associated with control interference during takeover control performed by the flight instructor in helicopter training flights. Since the standard flight control system features mechanical coupling between pilot’s and copilot’s flight controls, an inceptor decoupling system was not available. As an alternative to the mechanical linkages across the cabin, the next generation of fly-by-wire helicopters can be equipped with electronically coupled active sidesticks. In order to address the controllability problem, this research aims to investigate how electronically coupled active sidesticks can assist pilots during takeover control in dual pilot helicopters. To this end, this research proposes the introduction of a variable inceptor coupling, which provides the ability to electronically couple and decouple inceptors according to the pilots’ needs, either by manual (pushbutton) or automatic (force threshold) means. To achieve the research aim, the following scientific contributions are considered: validate the electronic inceptor coupling system for helicopter demands; propose an acceptable force threshold range and tactile functions to alleviate control overshoot and attitude oscillations for automatic inceptor decoupling; and demonstrate the ability of the active sidesticks to support the flight instructor to takeover control in low level flight. Nine pilots (seven of them test pilots) participated in the flight test campaign in a dual pilot helicopter simulator. Three set of evaluations were designed to investigate the influence of active sidesticks coupling on the: a) situation awareness; b) helicopter flying qualities; and c) helicopter controllability, pilot acceptance, and pilot workload. The electronically coupled inceptors were found to contribute positively to situational awareness of the flight instructors in helicopter scenarios, especially regarding the ability to project future states of the helicopter. Moreover, findings confirmed the possibility to mitigate control overshoots due to the automatic inceptor decoupling through the implementation of a force fading logic. Consequently, this logic showed to be effective to alleviate helicopter attitude oscillations, even in case of poor handling qualities. A new methodology combined quantitative and qualitative data to define the force threshold range (20 N to 30 N in pitch axis), which was useful to avoid unintentional decoupling and excessive attitude oscillation. Lastly, findings indicated that both manual and automatic inceptor decoupling functions reduced the control activity in case of control interference. Also, pilots considered the decoupling functions useful, predictable and easy, whereby successful takeover control maneuvers were performed in lower levels of perceived workload compared to the configuration without inceptor decoupling.