The making of helicopter flying qualities: a requirements perspective

Abstract In this review paper, a recurring theme is the interplay between flying qualities as a technical discipline and flying qualities as an operational attribute. This interplay provides the setting for a presentation on the status of helicopter flying quahties, using maritime helicopter operations as the focus, particularly the recovery phase and the helicopter-ship dynamic interface. Poor weather, inducing high sea states and ship motion, along with complex, invisible and disturbing airflow and degraded visibility, make the dynamic interface a particularly demanding environment for both pilot and helicopter. Flying qualities are a product of four elements — the aircraft, the pilot, the task and the environment — and the maritime application serves to give this viewpoint its full perspective. Mission-oriented flying quahties engineering is described within the systems framework of Aeronautical Design Standard 33 (ADS-33), utilising concepts like the mission task element, usable cue environment, response type and dynamic response criteria. The innovative constructs introduced by ADS-33 for flying qualities in degraded visual conditions are given special attention. The paper argues that the requirements for what constitutes safe and easy, or Level 1, flying qualities now exist and are well substantiated. New aircraft can now be designed to achieve these performance and safety standards while existing aircraft can be upgraded with integrated flight management systems featuring advanced control/flying qualities technologies. In this context, the paper also promotes the concept of concurrent requirements capture and preliminary design, to maximise the likelihood that user requirements are achieved and that designs are robust and work first time. The multidisciplinary nature of flying qualities is emphasised, embracing aeromechanics and flight dynamics, controls and displays and human factors. Similarly, the importance of high-fidelity design tools and comprehensive evaluation methods in the concurrent process is stressed. Handling deficiencies can increase the risk of helicopter accidents, particularly in degraded visual conditions or in emergencies where excursions beyond the operational flight envelope can lead to piloting difficulties. These situations are the new challenges for flying qualities engineers, and two areas are discussed here in some detail. First, flight in severely degraded visual conditions, highlighting the importance of understanding the fundamentals of human visual perception in the development of integrated control and display augmentation. Second, handling qualities following tail rotor failures are discussed and results from current research to develop new advice for aircrew are presented. The author takes the view that much more can and needs to be done to assist the pilot in the management of the tension between performance and safety in helicopter operations, through the provision of improved flying qualities.