Review of ADS-33E Requirements for Helicopter Control Augmentation in Degraded Visual Environments

Abstract

Helicopters are increasingly required to operate independently of environmental conditions. However, in degraded visual environments (DVE), for example, night or bad weather, handling qualities will be corrupted. This issue has been a focus in the development of the US Army helicopter handling qualities specification ADS-33. An overview of the specification structure is given and the process of tailoring this generic specification for a particular helicopter is explained. The usable cue environment as combined metric of visual environment and pilot vision aids and displays is introduced and the evaluation process explained. Following ADS-33, reduced visual cues can be compensated for with increased stability augmentation. The character of the stabilization is described in terms of response types, as rate or attitude command. The criteria and requirements of ADS-33 define the dynamic properties of the different response types. This is why ADS-33 is a true functional requirement for the flight control system and should be used throughout the control law design process. Not addressed in ADS-33 is the issue of guidance in DVE. Still being subject of current research, a possible approach to this problem is outlined.