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The use of augmented rotor inflow to predict rotorcraft responses in hover and low-speed manoeuvres
- Dheeraj Agarwal, Linghai Lu, Gareth D. Padfield, Mark D. White, Neil Cameron
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- Journal:
- The Aeronautical Journal / Volume 126 / Issue 1301 / July 2022
- Published online by Cambridge University Press:
- 28 January 2022, pp. 1168-1186
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The rotorcraft is a complex dynamical system that demands specialist modelling skills, and a high level of understanding of the aeromechanics arising from the main rotor wake and aerodynamic couplings. One such example is the difficulty predicting off-axis responses, particularly in hover and low-speed flight, associated with induced velocity variation through the rotor disk resulting from the rotor wake distortions. Various approaches have been developed to deal with this phenomenon but usually demand prerequisites of high levels of expertise and profound aerodynamic knowledge. This paper presents a new and practical approach to capturing this wake distortion through an augmented rotor inflow model. The proposed model is coupled with a nonlinear simulation using the FLIGHTLAB environment, and comparisons are made between the simulation results and flight test data from the National Research Council of Canada’s Advanced System Research Aircraft in hover and low speed. Results show good predictability of the proposed nonlinear model structure, demonstrated by its capability to closely match the time responses to multi-step control inputs from flight test. The results reported are part of ongoing research at Liverpool and Cranfield University into rotorcraft simulation fidelity.
The making of helicopter flying qualities: a requirements perspective
- Gareth D. Padfield
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- Journal:
- The Aeronautical Journal / Volume 102 / Issue 1018 / December 1998
- Published online by Cambridge University Press:
- 04 July 2016, pp. 409-437
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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.
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