Online Safe Flight Envelope Protection for Icing Aircraft Based on Reachability Analysis
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ORIGINAL PAPER
Online Safe Flight Envelope Protection for Icing Aircraft Based on Reachability Analysis Zhilong Yu1 · Yinghui Li1 · Zhe Zhang2 · Wenfeng Xu1 · Zehong Dong1 Received: 5 November 2019 / Revised: 14 February 2020 / Accepted: 3 March 2020 © The Korean Society for Aeronautical & Space Sciences 2020
Abstract Icing encountered by an aircraft in flight can pose a great threat to flight safety, which is the foremost concern in aviation. Ice accretion has nonlinear and coupling properties, and therefore, a conventional envelope protection system cannot successfully deal with the condition. A safe flight envelope based on reachability analysis is proposed in this paper as a basis for designing an online envelope protection system for aircraft under icing conditions. This system uses a neural network method to identify changes in the aerodynamic coefficients and to classify the degrees of icing and uses a database-driven approach to solve the onboard safe flight envelope computation problem. The database of icing safe flight envelopes is created offline and can be retrieved in real time. The Research Civil Aircraft Model (RCAM) encountering icing conditions in the climbing phase was taken as an example to verify the feasibility of the online safe flight envelope protection system. The simulation results showed that the system can classify the degrees of icing efficiently, prevent the aircraft from deviating from the safe flight envelope, guide it back to the envelope along the fastest path, and reduce the risk of loss of control under icing conditions. Keywords Reachability analysis · Safe flight envelope · Online envelope protection · Loss of control
1 Introduction Icing is an important environmental factor threatening flight safety because it can change aircraft aerodynamic performance, affecting the airflow field and resulting in an increase in aircraft drag and a decrease in lift. Severe ice accretions can even cause flight accidents [1, 2]. During 1990–2000, there were in total 3230 aircraft flight accidents caused by adverse weather condition according to the statistical data given by the American Safety Advisor, of which icing accidents accounted for about 12% [3]. In 1994, the Roselawn ATR-72 accident reinforced the importance of icing aero-
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Yinghui Li [email protected] Zhe Zhang [email protected] Wenfeng Xu [email protected] Zehong Dong [email protected]
1
Aeronautics Engineering College, Air Force Engineering University, Xi’an, China
2
Chinese Flight Test Establishment, Xi’an, China
dynamics research and the focus on envelope protection [4]. In this accident, the iced aircraft experienced loss of control (LOC) when the roll angle was only 5°, which is much smaller than the conventional envelope limit (18.1°), meaning that conventional envelope protection is no longer applicable when considering coupled multiple factors under upset conditions, such as external hazards (icing, wind gusts, turbulence, and others), and aircraft failure. To prevent LOC in an icing environment, it is very
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