Novel Approach to Rotorcraft Simulation Fidelity Enhancement and Assessment

Lead Research Organisation: Liverpool John Moores University
Department Name: Engineering Tech and Maritime Operations

Abstract

The vision for this research is to develop a novel toolset for flight simulation fidelity enhancement. This represents a step-change in simulator qualification, is well-timed making a significant contribution to the UoL initiated NATO STO AVT-296-RTG activity and will have an immediate impact through engagement with Industry partners.

High fidelity modelling and simulation are prerequisites for ensuring confidence in decision making during aircraft design and development, including performance and handling qualities estimation, control law development, aircraft dynamic loads analysis, and the creation of a realistic piloted simulation environment. The ability to evaluate/optimise concepts with high confidence and stimulate realistic pilot behaviour are the kernels of quality flight simulation, in which pilots can train to operate aircraft proficiently and safely and industry can design with lower risk.
Regulatory standards such as CS-FSTD(H) and FAA AC120-63 describe the certification criteria and procedures for rotorcraft flight training simulators. These documents detail the component fidelity required to achieve "fitness for purpose", with criteria based on "tolerances", defined as acceptable differences between simulation and flight, typically +/- 10% for the flight model. However, these have not been updated for several decades, while on the military side, the related practices in NATO nations are not harmonised and have often been developed for specific applications. Methods to update the models for improved fidelity are mostly ad-hoc and, without a strong scientific foundation, are often not physics-based.

This research will provide a framework for such harmonisation removing the barriers to adopting physics-based flight modelling and will create new, more informed, standards. In this research two aspects of fidelity will be tackled, predictive fidelity (the metrics and tolerances in the standards) and perceptual fidelity (pilot opinion). The predictive fidelity aspect of the research will use System Identification techniques to provide a systematic framework for 'enhancing' a physics-based simulation model. The perceptual fidelity research will develop a rational, novel process for task-specific motion tuning together with a robust methodology for capturing pilots' subjective assessment of the overall fidelity of a simulator. Extensive use will be made of flight simulation and real-world flight tests throughout this project in both the predictive and perceptual fidelity research.
 
Description In previous work at the University of Liverpool (UoL), a frequency domain renovation technique based on SID was developed to improve the fidelity of a FLIGHTLAB Bell 412 (F-B412) simulation model, and the identified model was compared with FLIGHT TEST data over a range of forward flight conditions. The flight test data are from trials conducted on the National Research Council's (NRC) ASRA Bell 412. A group of candidate SID derivatives (having a high impact on the fidelity 'cost-function' metrics) were used to improve the off-axis and cross-coupling response of the model. Although efficient in improving the fidelity of a simulation model, this tuning approach does not necessarily reveal the physics responsible for these modelling discrepancies. This work continues in Liverpool's awarded Rotorcraft test Simulator Fidelity (RSF) project aimed at developing a physics-based toolset for fidelity enhancement. As part of the RSF project, a new approach to SID in the time-domain is being developed and will be presented in this paper. We refer to this method as Additive System-IDentification (ASID), with the model parameters identified sequentially based on their contribution to the local dynamic response of the system, i.e. over a defined time range. One or more candidate parameters in a proposed model structure are identified using the primary response characteristic of the rotorcraft; others are then identified in a sequential manner. wo initial studies have been conducted on both the nonlinear F-B412 response and flight test data for roll dynamics, using an equation-error process, to illustrate the effectiveness of the ASID approach, and to develop guidelines for the process. The results are very encouraging and outperforms that classical Stepwise Regression method.
Exploitation Route they can access the results and approach through the related publications
Sectors Aerospace, Defence and Marine,Transport

 
Description The International Helicopter Safety Team (www.IHST.org) set a goal to reduce accidents over the period 2006-16 by 80%. This has not been realised (FAA briefing to IHST, 36% reduction achieved by 2015). Pilot judgements and actions continue to be a major contributory factor to these accidents: in nearly 70% of the 537 accidents in the European area (Analysis of European Helicopter Accidents, 2006-2010; EASA EHEST analysis report, 2015). Improved fidelity of the flight training devices will help pilots to make more-informed judgements. The outputs of the project will effectively improve the fidelity of simulation environment. The exploitation of advanced and improved training facilities can help to reduce the number of training in the real aircraft. Therefore, the awarded project offers an immediate benefit in terms of the overall certification cost, schedule and safety. The outcome of this project will be closely integrated into the recent EU Cleans SKy awarded project - The ROtorcraft Certification by Simulation (RoCS). This project aims to explore the possibilities, limitations, and guidelines for best practices for the application of flight simulation to demonstrate compliance to the airworthiness regulations related to helicopters and tiltrotors. The results of the EPSRC project have a direct impact on the RoCs project. For example, the advanced techniques developed in the EPSRC project for modelling a rotor and tuning its key parameters to improve its fidelity can be immedicably adopted for those aircraft models in the RoCs project (e.g., AW109, AW189, and AW609 etc). Finally, all these results from both projects will be applied on Leonard helicopter simulators and also be used by the European Aviation Safety Agency (EASA) to update a few aircraft certification and compliance guidelines, e.g., CS-FSTD.
Sector Aerospace, Defence and Marine,Transport
Impact Types Policy & public services

 
Description Certification by Simulation for Rotorcraft Flight Aspects
Geographic Reach Europe 
Policy Influence Type Gave evidence to a government review
Impact The ROtorcraft Certification by Simulation (RoCS) project aims to explore the possibilities, limitations, and guidelines for best practices for the application of flight simulation to demonstrate compliance to the airworthiness regulations related to helicopters and tiltrotors. The results of the awarded project will be directly integrated in to the RoCS to improve the fidelity of a simulation aircraft model, and then to improve the fidelity of the overall simulation environment. The research sees the opportunity within RoCS for the European rotorcraft community to take the lead in the development of new standards for certification using simulation. The European Union Aviation Safety Agency (EASA), the aerospace safety policy maker in Europe, is also a project partner and they are of great interest in using these research outcomes for upgrading existing aircraft certification and compliance guidelines, e.g., CS29 to increase the safety.
 
Description Certification by Simulation for Rotorcraft Flight Aspects
Amount € 3,000,000 (EUR)
Funding ID H2020-CS2-CFP08-2018-01 
Organisation European Commission H2020 
Sector Public
Country Belgium
Start 05/2019 
End 04/2022
 
Title Rotorcraft fidelity enhancement using 'additive' system identification 
Description In previous work at the University of Liverpool, a frequency domain renovation technique based on system identification (SID) was developed to improve the fidelity of a FLIGHTLAB Bell 412 (F-B412) simulation model, and the identified model was compared with FT data over a range of forward flight conditions. A group of candidate SID derivatives (having a high impact on the fidelity cost-function metrics) were used to improve the off-axis and cross-coupling response of the model. Although efficient in improving the fidelity of a simulation model, this tuning approach does not necessarily reveal the physics responsible for these modelling discrepancies. This work continues in the recently awarded Rotorcraft Simulator Fidelity (RSF) project10 aimed at developing a physics-based toolset for fidelity enhancement. As part of the RSF project, a new approach to SID in the time-domain is being developed and will be presented in this paper. We refer to this method as Additive System-IDentification (ASID), with the model parameters identified sequentially based on their contribution to the local dynamic response of the system, i.e. over a defined time range. One or more candidate parameters in a proposed model structure are identified using the primary response characteristic of the rotorcraft; others are then identified in a sequential manner. 
Type Of Material Improvements to research infrastructure 
Year Produced 2019 
Provided To Others? No  
Impact An initial study has been conducted for nonlinear roll dynamics, using an equation-error process. The results have shown that the new approach is superior than the classical Stepwise Regression approach for identifying the speed related derivatives. 
 
Title FLIGHTLAB Bell412 model 
Description A fully nonlinear and complex mathematical model has been developed for Bell412 aircraft in the FLIGHTLAB environment. The model has been validated against the real flight test data at Hover and 95 knots. All results show that the developed model has reached high fidelity. The model is also suitable for real time flight simulation. 
Type Of Material Computer model/algorithm 
Year Produced 2019 
Provided To Others? No  
Impact 1.) The high fidelity of the developed model guarantees the continuous research. 2.) Good results from this model lead to higher impact on the on-going NATO STO AVT-296 RTG3 and increase the position of UK as a key player in the rotorcraft field. 3.) Good research conducted on this qualified model makes it possible contributing more to RoCs project. The related results are more appropriate for being used the source and reference information for EASA to update the current aircraft Certification and Compliance design guidelines. 
 
Title FT1 
Description We conducted the first sortie flight test on May and September 2019 and gathered an amount of data at hover and 90knots. 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
Impact This database can help to understand better the Dull-roll oscillation, that is one of key handling qualities index. In addition, the database can be used to build a high fidelity rotorcraft simulation model that can improve safety. 
 
Description Collaboration with National Research Council of Canada 
Organisation National Research Council of Canada
Department Aerodynamics Laboratory
Country Canada 
Sector Public 
PI Contribution not suitable
Collaborator Contribution National Research Council of Canada's provides their Bell 412 Advanced Systems Research Aircraft for conducting flight test for the awarded research. These flight test data are one of factors guaranteeing the successful delivery of this project.
Impact So far we conducted the 1st flight test in October 2018 on the Bell 412 helicopter and the 2nd flight test has been scheduled and will occur June 2019.
Start Year 2018
 
Description leonardo helicopters 
Organisation Leonardo S.p.A.
Country Italy 
Sector Private 
PI Contribution We will use the methodology developed in the EPSRC funded RSF project to improve the AW109 FLIGHTLAB model provided by Leonardo S.p.A.
Collaborator Contribution Leonardo S.p.A. will provide AW109 FLIGHTLAB model and full sets of flight data for usage.
Impact not yet
Start Year 2019
 
Title ASID 
Description High fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complex nonlinearities arising from aerodynamic couplings and interferences. a new Additive System IDentification (ASID) approach in the time-domain is developed to explore rotorcraft flight dynamics in the low-speed regime where such nonlinearities abound and to aid investigations of these complexities. The ASID approach identifies flight model parameters sequentially based on their contribution to the local dynamic response of the system, in contrast with the averaged values of conventional System IDentification (SID) approaches over a whole manoeuvre. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2019 
Impact The approach can be used to study nonlinearities attributed to Maneuver Wake Distortion (MWD) that is notoriously known for the difficulty of modelling. 
 
Description NATO STO AVT-296 RTG activity 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact The research is directly contributing to a NATO STO AVT-296 RTG3 entitled "Rotorcraft Flight Simulation Model Fidelity Improvement and Assessment" led by the US Army Aviation Development Directorate. This AVT consists of the key players of rotorcraft research in the world, e.g., US Army, Sikorsky Aircraft Corporation, DLR etc. The work of this awarded project has attracted significant interest of the partners.
Year(s) Of Engagement Activity 2018,2020
 
Description Verification & Validation: Metrics for the Qualification of Simulation Quality 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact an Exploratory Group under the GARTEUR Group of Responsables Helicopter (GoR-HC) with the aim to define metrics for the qualification of the quality of rotorcraft simulations, as a contribution to the Verification and Validation (V&V) process of numerical codes.
The Exploratory Group will therefore consider the following activities to be performed within the timescale appropriate to an Action Group programme:
1. to review the current status of methods and metrics that may already exist to qualify a simulation quality;
2. to make a list of relevant information (physical quantities) that would be well suited for the qualification of simulation quality in the field of rotorcraft (belonging to different disciplines);
3. to consider how a Garteur activity could be linked to CleanSky proposal (under evaluation) on Certification by Simulation of Rotorcraft;
4. to apply the methodologies to the physical quantities and comparisons for which data already exist;
5. to propose metrics that could define the quality of such comparisons;
6. to cost a proposal for the work, showing partner workshare and financial (manpower and other costs) contributions.
Year(s) Of Engagement Activity 2019