Formulation of mathematical models using parameter estimation techniques and flight test data for the Bell 427 helicopter and the F/A-18 aircraft

Cette recherche presente differents modeles mathematiques d'aeronefs developpes a partir de donnees d'essais en vol pour trois modeles: la dynamique au sol pour Fatterrissage de I'helicoptere Bell 427, le comportement des rotors et des moteurs pour le meme helicoptere et la simulation des deflections aeroelastiques de I'avion militaire F/A-18. La structure du modele de dynamique au sol du B-427 est deduite par des lois de la physique, dans lesquelles la force normale de contact avec le sol est modelisee par le ressort vertical et la force de friction est modelisee par les coefficients statiques et dynamiques. Les coefficients du modele sont optimises afin que sa sortie corresponde aux donnees d'atterrissage a I'interieur des marges de tolerance definies par la FAA {Federal .Aviation administration) pour un simulateur de vol de niveau D. Les torques du rotor principal, du rotor de queue et des moteurs ainsi que la \itesse du rotor principal sont estimes par un modele d'espace d'etat. Les entrees non-lineaires du modele sont construites a partir des commandes du pilote et des etats de I'helicoptere. Les parametres du modele sont identifies par la methode subspace et optimises par l'algorithme Levenberg-Marquardt. Le modele donne une excellente estimation des sorties a I'interieur des marges de tolerances de la FAA. Le modele aeroelastique de I'avion F/A-18 est represente sous forme d'espace d'etat, et la recherche concernant ce modele est divisee en deux parties. Premierement, la déflection d'une partie de l'avion suite a une entree d'ailerons differentiels est representee par un modele lineaire MISO {Multiple Inputs Single Outputs). Les entrees du modele sont les posifions des ailerons et les déflections des autres parties de l'avion. Deuxièmement, un seul modele d'espace-etat non-lineaire est utilise pour calculer les déflections aeroelastiques des ailes et des volets de bords de fuite. Les non-linéarités sont introduites en multipliant les entrees entre elles avant de les utiliser dans les matrices d'espace-etat. Dans les deux cas, les modeles sont identifies par la methode subspace. D'excellents resultats ont ete obtenus ou la plupart des coefficients de correspondance et de correlation sont respectivement au dessus de 73 % et 90%

Updating Rotorcraft Simulation Environments by Using “Black-Box” Input Filters

Rotorcraft simulation environments such as training simulators or engineering simulations require high-fidelity models to be suitable for tasks such as pilot training, handling qualities analysis, and flight control system development. Deficits in model fidelity can arise from inaccurate data and unmodeled higher-order dynamic effects. Mitigating these deficits through physics-based modeling usually requires high effort. Therefore, a method is presented that improves a baseline simulation model by a “black-box” (i.e. non-physical) low-order input filter. The baseline can be a linear model or a nonlinear simulation model. Several options for deriving the input filter are elaborated and demonstrated in this paper using data from the CH-47, AH 135, and Bell 412 helicopters. In all cases the simulation fidelity was improved by approximately a factor of two

Simulation model fidelity enhancement using corrective force and moment increments: Review of activity performed in NATO-AVT Panel 296

Copyright © 2021 by the Vertical Flight Society. All rights reserved.The Applied Vehicle Technology (AVT) Panel of the NATO Science and Technology Organization has recently engaged a Research Task Group on the topic of rotorcraft flight simulation model fidelity. This group aimed to explore a comprehensive set of methods for flight mechanics simulation fidelity enhancement, including training simulation applications. Particular effort was also directed to the metrics used for simulation fidelity model assessment as suitable for the final intent of the model. The work presented in this paper was carried out in the framework of this Research Task Group, AVT-296, which examined seven different approaches; our paper focusses on just one of these. The objective was to assess flight-model renovation methods through four different applications. As a common approach, flight data from various helicopters were used to extract a set of flight dynamics information (state and control derivatives) that were used to compute corrective force and moment terms. The approach consists of a comparison between flight-test and flight mechanics model derivatives to compute delta forces and moments. These delta terms are added to the forces and moments through a linear combination and to generate the additional accelerations needed to capture any lacking dynamics. The derivatives that require updating need to be identified and, of course, will depend on the nature of the modelling deficiency. This paper shows how this method is applied to enhancing the lateral-directional oscillatory characteristics of flight models and how they can be upgraded to achieve higher fidelity for design and development applications but with special attention to meeting the fidelity requirements for flight training simulators

NATO AVT-365 Lecture Series: Rotorcraft Flight Simulation Model Fidelity Improvement and Assessment

Slides and Educational Notes for the Lecture Series NATO AVT-365 which presents results from the working group AVT-296 with the same titl

Rotorcraft Flight Simulation Model Fidelity Improvement and Assessment

Rotorcraft flight dynamics simulation models require high levels of fidelity to be suitable as prime items in support of life cycle practices, particularly vehicle and control design and development, and system and trainer certification. On the civil side, both the FAA (US) and EASA (Europe) have documented criteria (metrics and practices) for assessing model and simulator fidelity as compared to flight-test data, although these have not been updated for several decades. On the military side, the related practices in NATO nations are not harmonised and often only developed for specific applications. Methods to update the models for improved fidelity are mostly ad-hoc and lack a rational and methodical approach. Modern rotorcraft system identification (SID) and inverse simulation methods have been developed in recent years that provide new approaches well suited to pilot-in-the-loop fidelity assessment and systematic techniques for updating simulation models to achieve the needed level of fidelity. To coordinate efforts and improve the knowledge in this area, STO Applied Vehicle Technology Panel Research Task Group (STO AVT-296 RTG) was constituted to evaluate update methods used by member nations to find best practices and suitability for different applications including advanced rotorcraft configurations. This report presents the findings of the AVT-296 RTG. An overview of previous rotorcraft simulation fidelity Working Groups is presented, followed by a review of the metrics that have been used in previous studies to quantify the fidelity of a flight model or the overall perceptual fidelity of a simulator. The theoretical foundations of the seven different update methods and a description of the eight flight databases (Bell 412, UH-60, Iris+, EC135, CH-47, AW139, AW109, and X2, provided by the National Research Council of Canada, US Army, Airbus Helicopters, Boeing, Leonardo Helicopter Division, and Sikorsky) used by the RTG is presented. Both time- and frequency-domain fidelity assessment methods are considered, including those in current use by simulator qualification authorities and those used in the research community. Case studies are used to show the application, utility, and limitations of the update and assessment methods to the flight-test data. The work of the RTG has shown that time- and frequency-domain SID based metrics are suitable for use for assessing the model fidelity across a wide range of rotorcraft configurations. Gain and time delay update methods work well for well-developed flight dynamics models and can be used for flight control system design, but do not provide physical insights into the sources of errors in a model. Deriving stability and control derivatives from flight-test data and nonlinear simulation models using SID provides insight into the missing dynamics of the simulation model, which can subsequently be updated using additional forces and moments to significantly improve the fidelity of the model and can be used to update models for flight simulation training application methods. Reduced order model and physics-based correction methods provide large benefits when extrapolating to other flight conditions but does require detailed flight-test data. SID can quickly provide accurate point models, if detailed flight-test data is available, which can be "stitched" together to produce models suitable for real-time piloted simulation and control design applications. However, the dependency on flight-test data means that this method is not suitable for early aircraft development activities. This documentation of rotorcraft simulation fidelity assessment and model update strategies will benefit NATO nations by allowing for common, agreed-upon best practices and recommendations, ensuring each country's flight dynamics and simulation models are of the highest calibre possible. The collaboration between industry, academia, and government laboratories has been key to the success of this RTG; this cooperation model should be adopted in future research activities. As industries strive to achieve greater efficiency and safety in their products, the fidelity of simulation should match commercial aspirations to ensure that the "right first time" ethos is fully embedded into industrial best practices. Militaries will be able to use the methods and metrics presented to set criteria that will underpin the use of modelling and simulation in certification to accelerate development and acquisition and reduce the cost of new aircraft systems, e.g. advanced high-speed rotorcraft and legacy system upgrades. The criteria may also set standards for training devices used to support the expansion of synthetic environments for training to offset the high costs of flight hours. This RTG has identified that current flight training simulator standards could be updated to use the flight model and perceptual fidelity metrics presented in this report to ensure that models are not "over-tuned" and a more rigorous method of subjective simulator assessment is adopted