NITROS An Innovative Training Program to Enhance Rotorcraft Safety

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Particularities of Rotorcraft in Dealing with Advanced Controllers

Advanced nonlinear controllers are a desirable solution to rotorcraft flight control as they can solve the system high nonlinear dynamic behavior. However, conventional nonlinear controllers such as Nonlinear Dynamic Inversion (NDI) controller heavily rely on the availability of accurate model knowledge and this can be problematic for rotorcraft. Therefore, incremental control theory can solve the modelling errors sensitivity by relying on the information obtained from the sensors instead. The paper applied the Incremental Nonlinear Dynamic Inversion (INDI) controller to rotorcraft case. It will be demonstrated that, for rotorcraft, the incremental nonlinear controllers depend on the delays introduced in the controller by the rotor dynamics. To correct this behaviour, residualization and synchronization methods need to be applied accordingly in order to remove the effects of rotor flapping (disctilt) dynamics from the controller. These particularities of rotorcraft in dealing with advanced controllers shows that incremental nonlinear controllers can have relatively small stability robustness margin and careful controller design is needed in order to account properly for rotorcraft time delays and unmodelled dynamics

Towards an Energetic Modeling of Rotorcraft Using Bond-Graphs

Presented at the AHS 69th Annual Forum, Phoenix, Arizona,May 21 –23, 2013. Copyright © 2013 by the AmericanHelicopter Society International, Inc. All rights reserved.The paper presents an energetic method of helicopters dynamics analysis to study the air resonance (AR)phenomena. First, a brief state of art of AR phenomena is presented and a simple energetic explanation is given.Then part of the state of art is devoted to the Bond Graph (BG) and Multi-Bond Graphs (MBG) modeling methodshowing several advantages of the tool and few examples of MBG researches applications. This work proposes amacroscopic energetic description of a helicopter through the Word Bond Graph representation. The MBG is thenused for Rotor/fuselage structure modeling in order to study the AR phenomena instability. The MBG model resultsare presented and show the potential of the MBG method to predict such a complex phenomenon.International audienceThe paper presents an energetic method of helicopters dynamics analysis to study the air resonance (AR)phenomena. First, a brief state of art of AR phenomena is presented and a simple energetic explanation is given.Then part of the state of art is devoted to the Bond Graph (BG) and Multi-Bond Graphs (MBG) modeling methodshowing several advantages of the tool and few examples of MBG researches applications. This work proposes amacroscopic energetic description of a helicopter through the Word Bond Graph representation. The MBG is thenused for Rotor/fuselage structure modeling in order to study the AR phenomena instability. The MBG model resultsare presented and show the potential of the MBG method to predict such a complex phenomenon

Assessment of the Feasibility of an Extended Range Helicopter Operational Standard for Offshore Flights

The accident rate of rotorcraft has improved signi1cantly over the years but at a slow pace, and in any case the number of accidents per 2ight hours is one or two orders of magnitude higher than that of commercial aircraft, a consideration that could be reasonably related to the inherent higher risk associate with rotorcraft operations. This represent a strong evidence of the necessity to introduce airworthiness operation standards also in the rotorcraft community, as an effective mean to improve safety records, borrowing from the experience done in the commercial air transport community with the introduction of ETOPS. In this paper, a 1rst proposal of development of a safety standard for helicopter offshore operation is discussed together with the possible support to this development that could be given by the EU H2020 project NITROS

Towards an Energetic Modeling of Rotorcraft Using Bond-Graphs

Presented at the AHS 69th Annual Forum, Phoenix, Arizona, May 21 –23, 2013. Copyright © 2013 by the American Helicopter Society International, Inc. All rights reserved.The paper presents an energetic method of helicopters dynamics analysis to study the air resonance (AR) phenomena. First, a brief state of art of AR phenomena is presented and a simple energetic explanation is given. Then part of the state of art is devoted to the Bond Graph (BG) and Multi-Bond Graphs (MBG) modeling method showing several advantages of the tool and few examples of MBG researches applications. This work proposes a macroscopic energetic description of a helicopter through the Word Bond Graph representation. The MBG is then used for Rotor/fuselage structure modeling in order to study the AR phenomena instability. The MBG model results are presented and show the potential of the MBG method to predict such a complex phenomenon.“Complex Mechanical Systems Dynamics” project - EADS Foundation - Arts et Metiers Paritec

Instability Mechanism of Roll/Lateral Biodynamic Rotorcraft–Pilot Couplings

The paper investigates the basic mechanism of aeroservoelastic pilot-assisted oscillation about the roll axis due to the interaction with pilot's arm biomechanics. The motivation stems from the observation that a rotor imbalance may occur as a consequence of rotor cyclic lead–lag modes excitation. The work shows that the instability mechanism is analogous to air resonance, in which the pilot's involuntary action plays the role of the automatic flight control system. Using robust stability analysis, the paper shows how the pilot's biodynamics may involuntarily lead to a roll/lateral instability. The mechanism of instability proves that the pilot biodynamics is participating in the destabilization of the system by transferring energy, i.e., by producing forces that do work for the energetically conjugated displacement, directly into the flapping mode. This destabilizes the airframe roll motion, which, in turn, causes lead–lag motion imbalance. It is found that, depending on the value of the time delay involved in the lateral cyclic control, the body couples with rotor motion in a different way. In the presence of small or no time delays, body roll couples with the rotor through the lead–lag degrees of freedom. The increase of the time delay above a certain threshold modifies this coupling: The body no longer couples with the rotor through lead–lag but directly through flap motion

ROTORCRAFT-PILOT COUPLINGS: ANALYSIS AND DETECTION IN A SAFETY ENHANCEMENT FRAMEWORK

Nowadays, the complexity of high speed civil transport and highly-augmented rotorcraft, has led to an increase in the chances of encountering unwanted unstable phenomena, such as the so called Aircraft/Rotorcraft-Pilot Couplings (A/RPCs) or Pilot-Induced Oscillations (PIOs), whose unpredictability has given rise to a serious problem concerning the safety of a mission. When talking about PIOs, McRuer defined them as "inadvertent, sustained aircraft oscillations which are a consequence of an abnormal joint enterprise between the aircraft and the pilot". However, A/RPCs, these undesirable events associated with the interaction between pilot and aircraft, have become diverse and more complex than those encountered in the past. At the moment, there are different methods available to prevent and detect Cat. I/II A/RPC, but particular interest has recently arisen in this topic for 2ight simulation applications as any enhancement of these tools in order to accurately and objectively predict, detect (in real-time) and alleviate RPCs will be greatly welcomed. One of the main questions to be answered through the efforts carried out within this work is related to the better detection in real-time of embedded tendencies to RPCs in modern aircraft. To answer this question, initially an assessment of the eZcacy of the Phase-Aggression Criterion (PAC), which has been designed a few years ago at the University of Liverpool, will be undertaken either: as a means of alerting the pilot to conditions likely to lead to the onset of a PIO; or, given that the time available for the pilot to counteract may be extremely limited, as a means to assist him/her in alleviating (automatically) the PIO condition itself. Preliminary results from 2ight simulation trials to explore how best to achieve this will be reported. Moreover, this work will report on the development of PAC boundaries for more highly augmented response types. Furthermore, as classified by McRuer, Cat. III PIO, which is nonlinear in essence, is the most complex one. However, the researches on Cat. III PIO are rare. This paper will reveal some elementary results of Cat. III PIO. Since there is no existing method used for predicting and detecting Cat. III PIO, this paper utilized the characteristics of PIO, such as the amplitude, the oscillation frequency and ultimate tendency of key aircraft response states to judge Cat. III PIO preliminarily. By using this elementary judgment of PIO, we studied the following factors: time delay of pilot input and helicopter main body, actuator position saturation, actuator rate limit and SCAS control authority in triggering PIO. Results show that PIO induced by actuator position saturation, actuator rate limit and SCAS control authority can be regarded as Cat. III PIO as the variation of these factors can be viewed as a kind of transition of effective controlled vehicle dynamics. These kinds of transition can cause a mismatch between the effective controlled vehicle dynamics and pilot control strategy, which is the main cause of Cat. III PIO

Assessment of the Feasibility of an Extended Range Helicopter Operational Standard for Offshore Flights

The accident rate of rotorcraft has improved signi1cantly over the years but at a slow pace, and in any case the number of accidents per 2ight hours is one or two orders of magnitude higher than that of commercial aircraft, a consideration that could be reasonably related to the inherent higher risk associate with rotorcraft operations. This represent a strong evidence of the necessity to introduce airworthiness operation standards also in the rotorcraft community, as an effective mean to improve safety records, borrowing from the experience done in the commercial air transport community with the introduction of ETOPS. In this paper, a 1rst proposal of development of a safety standard for helicopter offshore operation is discussed together with the possible support to this development that could be given by the EU H2020 project NITROS