Fidelity is a fundamental concept for crucial decision-making processes during engineering design, test and evaluation of aircraft and rotorcraft. Fidelity, as applied to rotorcraft, proves to be a prerequisite for most human factors research and simulator development programs. This paper reviews the concept of fidelity, its metrics and methods concentrating on rotorcraft applications. The paper stems from the Applied Vehicle Technology (AVT) Panel of the NATO Science and Technology Organization (STO) work of NATO AV-296 concentrating on recent advancements on rotorcraft flight simulation model fidelity prediction and assessment. Starting from the question of what is meant with the term simulation fidelity, the paper will demonstrate that even though the term fidelity can be loosely translated as simulation goodness or faithfulness to reality, when it comes to fidelity assessment, this concept has a multidimensional and multifaceted character depending on the configuration considered. A key message of the paper is that simulation fidelity should be decomposed in different dimensions and attributes with their own metrics. Using multiple fidelity metrics is therefore meaningful for assessing simulation fidelity in general and in particular for the case of rotorcraft.

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This paper presents the validation of a Level-D rotorcraft simulation framework by comparing different quantitative model fidelity metrics. The simulation framework uses a non-linear blade element rotor model to simulate the flight dynamics of rotorcrafts with accurate stability and control characteristics identified from system identification techniques. For this study, frequency-domain system identification is used to generate linear state-space 6-DoF quasi-steady models and an automated process is used to adjust the non-linear simulation framework. Regulatory authorities assess performance models for Level-D simulators by comparing time-domain simulation responses with measured aircraft responses for the same set of control inputs. Over the years, new quantitative fidelity metrics were proposed, like the Maximum Unnoticeable Added Dynamics and the Allowable Error Envelopes. This paper will focus on the blade element rotor model hover modeling process to demonstrate its application using a Bell 412 flight test data package. It will also show how this modeling approach can be used to match both Level-D requirements and the alternative fidelity metrics stated above.

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Helicopters are currently used in important applications providing a valuable contribution to society and economic growth. Thanks to their operational flexibility it is possible to accomplish increasingly complex missions. If the expansion of the usage of rotorcraft is to follow the pace of growth achieved by the fixed-wing public transport in the last years, several issues need to be urgently addressed to increase the use and the public acceptance of rotorcraft. Aspects related to complexity of the operations and safety are of primary importance, since in the last 20 years helicopter accident rates, worldwide, remained unacceptably high, when compared to fixed-wing aircraft. The complexity of the phenomena involved in rotorcraft flight calls for the training of engineers with a genuine multidisciplinary background. This paper presents the doctoral research and training program NITROS, which is set up under the Marie Skłodowska-Curie Action of the European Union to address complex solutions to rotorcraft safety.@en

The effects of a wind turbine wake on General Aviation and the behaviour of helicopters in the tip vortex of large fixed-wing aircraft has been topic of research in the past years, but less is known about the interactions of helicopters operating in a wind turbine wake. A dedicated GARTEUR Action Group, HC-AG23, consisting of European universities and research institutes was formed to investigate helicopter behaviour in a wind turbine wake and to study the consequences for helicopter handling and safety of flight. The activities are structured in work packages addressing wind turbine wake identification, wake experiments and computations, offline and piloted simulations and management and dissemination activities. This paper presents an over-view of the partners’ activities and provides a short overview of the results that have been achieved in the past three years.@en