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A novel trajectory generation and control architecture for fully autonomous autorotative flare that combines rapid path generation with model-based control is proposed. The trajectory generation component uses optical Tau theory to compute flare trajectories for both longitudinal and vertical speed. These flare trajectories are tracked using a nonlinear dynamic inversion (NDI) control law. One convenient feature of NDI is that it inverts the plant model in its feedback linearization loop, which eliminates the need for gain scheduling. However, the plant model used for feedback linearization still needs to be scheduled with the flight condition. This key aspect is leveraged to derive a control law that is scheduled with linearized models of the rotorcraft flight dynamics obtained in steady-state autorotation, while relying on a single set of gains. Computer simulations are used to demonstrate that the NDI control law is able to successfully execute autorotative flare in the UH-60 aircraft. Autonomous flare trajectories are compared to piloted simulation data to assess similarities and discrepancies between piloted and automatic control approaches. Trade studies examine which combinations of downrange distances and altitudes at flare initiation result in successful autorotative landings. [ABSTRACT FROM AUTHOR]

Physical-law-based models are widely utilized in the aerospace industry. One such use is to provide flight dynamics models for use in flight simulators. For human-in-the-loop use, such simulators must run in real-time. Owing to the complex physics of rotorcraft flight, to meet this real-time requirement, simplifications to the underlying physics sometimes have to be applied to the model, leading to errors in the model's predictions of the real vehicle's response. This study investigated whether a machine-learning technique could be employed to provide rotorcraft dynamic response predictions. Machine learning was facilitated using a Gaussian process (GP) nonlinear autoregressive model, which predicted the on-axis pitch rate, roll rate, yaw rate, and heave responses of a Bo105 rotorcraft. A variational sparse GP model was then developed to reduce the computational cost of implementing the approach on large datasets. It was found that both of the GP models were able to provide accurate on-axis response predictions, particularly when the model input contained all four control inceptors and one lagged on-axis response term. The predictions made showed improvement compared to a corresponding physics-based model. The reduction of training data to one-third (rotational axes) or one-half (heave axis) resulted in only minor degradation of the sparse GP model predictions. [ABSTRACT FROM AUTHOR]

The time-to-contact t theory posits that purposeful actions can be conducted by coupling the actor's motion onto the so-called τ guides generated internally by their central nervous system. Although significant advances have been made in the application of t for flight control purposes, little research has been conducted to investigate how pilots are able to adapt their τ-guidance strategy to different aircraft dynamics, or how a τ-guide-based pilot-aircraft model might be used to represent control behavior. This paper reports on the development of such a model to characterize the adaptation of pilot guidance to variations in aircraft dynamics using data obtained from a clinical pilot-in-the-loop flight simulation experiment. The results indicate that pilots tend to maintain a constant coupling between the dynamic system's motion and the r guide across a range of different configuration parameters. Simultaneously, the pilot modulates the guidance maneuver period to adapt to these different aircraft dynamics that result in changes in workload. Modeling the complete pilot stabilization and guidance function as a regulator plus inverter yields good comparative results between the pilot-aircraft model and simulator trajectory data, and it supports the hypothesis that the following r-based guidance strategies suppress an aircraft's natural dynamics. [ABSTRACT FROM AUTHOR]

With recent increased interest in autonomous vehicles and the associated technology, the prospect of realizing a personal aerial vehicle seems closer than ever. However, there is likely to be a continued requirement for any occupant of an air vehicle to be comfortable with both the automated portions of the flight and their ability to take manual control as and when required. This paper, using the approach to landing as an example maneuver, examines what a comfortable trajectory for personal aerial vehicle occupants might look like. Based upon simulated flight data, a "natural" flight trajectory is designed and then compared to constant deceleration and constant optic flow descent profdes. It is found that personal aerial vehicle occupants with limited flight training and no artificial guidance follow the same longitudinal trajectory as has been found for professionally trained helicopter pilots. Further, the final stages of the approach to hover can be well described using the Tau theory. For automatic flight, personal aerial vehicle occupants prefer a constant deceleration profile. For approaches flown manually, the newly designed natural profile is preferred. [ABSTRACT FROM AUTHOR]

The involuntary interaction of a pilot with an aircraft can be described as pilot-assisted oscillations. Such phenomena are usually only addressed late in the design process when they manifest themselves during ground/flight testing. Methods to be able to predict such phenomena as early as possible are therefore useful. This work describes a technique to predict the adverse aeroservoelastic rotorcraft-pilot couplings, specifically between a rotorcraft's roll motion and the resultant involuntary pilot lateral cyclic motion. By coupling linear vehicle aeroservoelastic models and experimentally identified pilot biodynamic models, pilot-assisted oscillations and no-pilot-assisted oscillation conditions have been numerically predicted for a soft-in-plane hingeless helicopter with a lightly damped regressive lead-lag mode that strongly interacts with the roll mode at a frequency within the biodynamic band of the pilots. These predictions have then been verified using real-time flight-simulation experiments. The absence of any similar adverse couplings experienced while using only rigid-body models in the flight simulator verified that the observed phenomena were indeed aeroelastic in nature. The excellent agreement between the numerical predictions and the observed experimental results indicates that the techniques developed in this paper can be used to highlight the proneness of new or existing designs to pilot-assisted oscillations. [ABSTRACT FROM AUTHOR]

This paper describes research to develop handling qualities guidelines and criteria for a new category of aircraft: the personal aerial vehicle, which it is envisaged will demand no more skill to fly than that associated with driving a car today. Testing of concept personal aerial vehicle response types has been conducted with inexperienced "pilots" ranging from private pilot's license holders through to those with no prior flight experience. The objective was to identify, for varying levels of flying skill, the personal aerial vehicle response type requirements that will ensure safe and precise flight. Conventional rotorcraft response types such as "rate command", "attitude command/attitude hold" are unsuitable for likely personal aerial vehicle pilots. However, response types such as "translational rate command" and "acceleration command, speed hold" permit "flight-naive" pilots to perform demanding tasks repeatably and with the required precision. [ABSTRACT FROM AUTHOR]

This paper describes the development of a methodology to assess the handling qualities requirements for vertical takeoff and landing-capable personal aerial vehicles. It is anticipated that such a personal aerial vehicle would be flown by a "flight-naïve" pilot who has received much less training than is typically received even by today's general aviation private pilots. The methodology used to determine handling requirements for a personal aerial vehicle cannot therefore be based entirely on existing best practice; the use of highly experienced test pilots in a conventional handling assessment limits the degree to which results apply to the flight-naïve pilot. Using rotary-wing handling qualities methods as a start point, this paper describes both existing and newly developed alternative methods to subjectively and objectively analyze the performance and workload of flight-naïve pilots in typical personal aerial vehicle tasks. A highly reconfigurable generic flight dynamics simulation model that has been used to validate the methodology is also described. Results that highlight the efficacy of the various methods used are presented, and their suitability for use with flight-naïve pilots demonstrated. [ABSTRACT FROM AUTHOR]

The aviation community relies heavily on flight simulators as a fundamental tool for research, pilot training and development of any new aircraft design. The goal of the present paper is to provide a review on how effective ground simulation is as an assessment tool for unmasking adverse Aircraft-and-Rotorcraft Pilot Couplings (APC/RPC). Although it is generally believed that simulators are not reliable in revealing the existence of A/RPC tendencies, the paper demonstrates that a proper selection of high-gain tasks combined with appropriate motion and visual cueing can reveal negative features of a particular aircraft that may lead to A/RPC. The paper discusses new methods for real-time A/RPC detection that can be used as a tool for unmasking adverse A/RPC. Although flight simulators will not achieve the level of reality of in-flight testing, exposing A/RPC tendencies in the simulator may be the only convenient safe place to evaluate the wide range of conditions that could produce hazardous A/RPC events. [ABSTRACT FROM AUTHOR]

Unmasking aircraft pilot couplings (APCs) prior to vehicle entry into service have been a long standing challenge in the aerospace industry. APCs, often only exposed through unpredictable or very specific circumstances, have arisen throughout the history of manned powered flight and have required stopgap "fixes" to ensure system safety once a problem has been identified. This paper describes two newly created novel tools, one objective and one subjective, to detect and analyze APCs. The Phase Aggression Criterion is the objective assessment method and, in the advanced form described in this paper, is capable of APC detection in near real time. The innovative Adverse Pilot Coupling Scale is a subjective assessment method for APCs experienced during completion of closed-loop tasks. Results from the application of both of these tools are presented as well as the very good correlation between them. Furthermore, the application of the tools to simulated flight-test data has shown how existing handling qualities mission task element courses and their associated performance tolerances can be inadequate when used to unmask the proneness of a pilot-vehicle system to APC. [ABSTRACT FROM AUTHOR]

This paper presents the development of a multiloop pilot model for use in boundary-triggered pilot-induced oscillation investigations. In doing so, the point-tracking and boundary-avoidance elements of the pilot control strategy are assumed to act simultaneously for a point-tracking-dominant task during a boundary-avoidance tracking event. The theoretical analysis indicates that the essence of the boundary-avoidance tracking phenomenon consists of an additional requirement for the pilot to provide lead equalization as the boundary is approached as the task transitions from a full-attention point-tracking task to both a point-tracking and boundary-avoidance task. This process leads to a narrower open-loop system bandwidth and a larger tracking error, or the triggering of a pilot-induced oscillation. It is also found that the severity of the boundary-avoidance influence can be reduced by including the effects of vestibular and proprioceptive cues into the model. The boundary-avoidance tracking pilot model exhibits pilot-vehicle responses that are consistent with those observed in a piloted-simulation study and can therefore be considered to be representative of pilot activity. Consideration of the results in the round indicates that the boundary-triggered pilot-induced oscillation can be categorized as Category III pilot-induced oscillation within the existing recognized taxonomy. [ABSTRACT FROM AUTHOR]

Abstract: Fixed and rotary wing pilots alike are familiar with potential instabilities or with annoying limit cycle oscillations that arise from the effort of controlling aircraft with high response actuation systems. Understanding, predicting and suppressing these inadvertent and sustained aircraft oscillations, known as aircraft (rotorcraft)-pilot couplings (A/RPCs) is a challenging problem for the designers. The goal of the present paper is to give an overview on the state-of-the-art in RPC problem, underlining the future challenges in this field. It is shown that, exactly as in the case of fixed wing APCs, RPCs existed from the beginning of rotorcraft development and that the problem of eliminating them is not yet solved: the current rotorcraft modelling for RPC analysis is rather limited to the particular case analysed and there is a lack of quantitative pilot behavioural models to analyse RPCs. The paper underlines the importance of involuntary pilot control actions, generally attributed to biodynamic couplings in predicting RPCs in rotorcraft. It is also shown that recent experiences demonstrate that modern rotorcraft seem to embed tendencies predisposing the flight control system FCS system towards dangerous RPCs. As the level of automation is likely to increase in future designs, extending to smaller aircraft and to different kinds of operation, the consequences of the pilot ‘fighting’ the FCS system and inducing A/RPCs needs to be eradicated. In Europe, the ARISTOTEL project (2010–2013) has been launched with the aim of understanding and predicting modern aircraft's susceptibility to A/RPC. The present paper gives an overview of future challenges to be solved for RPC-free design and some new solutions herein. [Copyright &y& Elsevier]

The investigation of motion guidance and its subsequent application using tau (T) theory relies on the accurate calculation of the coupling term between the T (time to contact) of the motion and the appropriate r guide. However, the traditional approach for this calculation can be numerically unstable, requires experience and skill to execute in a meaningful manner, is sensitive to the data selected, and has limited application when the motion information is incomplete or deviates from the ideal. To deal with these issues, a new approach, based on positive wavelet analysis, is proposed in this paper. The mother wavelet is constructed using the desired r-guide shapes, with its scale considered to be defined by the maneuver period. The scale and time information of interest are found by searching for the best local correlation within the whitened original signal. An inverse dewhitening process is then used to reconstruct an approximation to the original motion signal. The adequacy of the positive wavelet method has been demonstrated using data obtained from piloted simulation test campaigns. The results show that the approach is not only feasible, but it has better numerical stability, reliability, enhanced performance, and wider applicability than those that have been used to date. [ABSTRACT FROM AUTHOR]

Significant effort has been expended to develop criteria to predict the susceptibility of an air vehicle to so-called pilot-induced oscillations. Much of this work has been carried out for fixed-wing aircraft and it is only recently that their applicability to rotorcraft has started to be assessed. Real time pilot-induced oscillation identification methods provide an alternative means to at least warn the pilot that a pilot-induced oscillation is in progress so that preventative action can be taken. Existing methods, however, have some limitations and have rarely been used for rotary-wing purposes. Specifically, the existing methods assessed in this paper do not provide an indication of the severity of the event and mask the underlying data that are being used to generate the warning. This paper proposes and presents a new method to identify pilot-induced oscillations, either in near real time or as a postprocessing aid for recorded flight-test data, that addresses both of these issues. The new method, entitled "phase-aggression criterion," is compared with current methods. It is shown, for a specific set of test cases and a limited test pilot population, that not only can it provide more information about the pilot-induced oscillation but it can also provide an earlier warning of its onset. [ABSTRACT FROM AUTHOR]

Pilot–vehicle interaction represents a critical aspect of aircraft design. Very low-frequency, voluntary although unintentional interaction has been extensively investigated in fixed and rotary wing aeromechanics. Higher frequency, involuntary and thus passive interaction received similar attention in fixed wing aeromechanics, but not as much for rotary wing. The results of an experimental campaign for the characterization of the passive behaviour of rotorcraft pilots' biomechanics are presented. A flight simulator has been used to excite human subjects. The accelerations of their limbs and the motion induced by the vibrations of the limbs in the control inceptors have been recorded. The vertical, longitudinal and lateral directions have been independently excited, while measuring the motion of the arm directly involved in the control inceptor mostly affected by motion in each direction, namely the left and the right arms for the collective and the cyclic sticks, respectively. The frequency domain response has been evaluated; resulting noteworthy behaviour is discussed, addressing its relevance in modelling the passive behaviour of pilots within the bioaeroservoelastic rotorcraft analysis. The measurements of human body impedance, under realistic cockpit motion, are used to identify the direct transfer functions between the motion of the seat and the controls inadvertently fed back into the rotorcraft. [ABSTRACT FROM AUTHOR]

Understanding, predicting and supressing the inadvertent aircraft oscillations caused by Aircraft/Rotorcraft Pilot Couplings (A/RPC) is a challenging problem for designers. These are potential instabilities that arise from the effort of controlling aircraft with high response actuation systems. The present paper reviews, updates and discusses desirable practices to be used during the design process for unmasking A/RPC phenomena. These practices are stemming from the European Commission project ARISTOTEL Aircraft and Rotorcraft Pilot Couplings – Tools and Techniques for Alleviation and Detection (2010–2013) and are mainly related to aerodynamic and structural modelling of the aircraft/rotorcraft, pilot modelling and A/RPC prediction criteria. The paper proposes new methodologies for precluding adverse A/RPCs events taking into account the aeroelasticity of the structure and pilot biodynamic interaction. It is demonstrated that high-frequency accelerations due to structural elasticity cause negative effects on pilot control, since they lead to involuntary body and limb-manipulator system displacements and interfere with pilot's deliberate control activity (biodynamic interaction) and, finally, worsen handling quality ratings. [ABSTRACT FROM AUTHOR]