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Rotorcraft Certification by Simulation

Periodic Reporting for period 1 - RoCS (Rotorcraft Certification by Simulation)

Reporting period: 2019-05-01 to 2020-10-31

Before a newly developed aircraft may enter into operation in civil airspace, it must obtain a type certificate from the aviation regulatory authority. This certificate testifies that it meets the safety requirements set by the authority. After defining the certification basis, the aircraft manufacturer and the authority must agree on the certification program and on the means to demonstrate compliance. This expensive and time-consuming aspect of certification involves high safety risk within control system and engine failures. To answer this challenge, advanced analysis methods as flight simulation offer immediate benefits as cost/time saving and risk reduction, with huge potential impact on the whole process.
RoCS aims to explore possibilities, limitations, and guidelines for best practices for the application of flight simulation to demonstrate compliance to the airworthiness regulations of helicopters and tiltrotors. It will be possible to reduce the number of flight tests with respect to current certification standards, within the Operational Flight Envelope (OFE) and further tests, including those which are high risk, outside of the OFE, and may lead to catastrophic failure (e.g. emergency conditions), to be tested in simulation.
RoCS ambitious objectives can be declined in a three-way approach:
• Developing guidelines for rotorcraft certification for flight aspects by simulation, consolidating past experiences and dedicated research into a set of guidelines supported by both industry and certification authority, ensuring model and cueing system fidelity. RoCS will ultimately develop a set of standard tools to to evaluate these metrics in a fast, efficient and reliable way.
• Developing a low-cost, effective, flight simulation environment suitable for certification compliance demonstration for helicopters and tiltrotors, overcoming the concept of flight simulation just for training and reaching the fidelity level for certification. This will lead to the development of a new product, competitive in terms of acquisition and maintenance costs in comparison to flight tests, and affordable by small companies, to be a driver for the development of new certified aircraft.
• Verifying if certification by simulation could reduce the scope of testing required for the next generation of tiltrotors. This final ambitious goal, reached through the issue of final guidelines for CSRFA verified on tiltrotors, will represent a formidable tool to compensate for the lack of experience of manufacturers and certification authorities, limiting significantly the amount of hazardous flight-testing to be performed.
During the first 18 months, 8 RoCS deliverables have been completed and 5 milestones achieved. In particular, in addiction to project management outcomes, we achieved important scientific results:
• WP2: a process was developed to evaluate candidate requirements against significant criteria for demonstrating simulation compliance and allowing a selection. Potential candidates were evaluated and five scenarios selected. The evaluation and selection process and the results of the application of this process are detailed in D2.1
• WP3: past research, industry practice, and proposed certification application of flight simulation model predictive fidelity metrics and tools for the assessment of simulation credibility in the absence of validation test data were detailed. The model fidelity enhancement plan was defined, highlighting areas for improving the baseline model, currently under discussion with LH. A secure version-control server for collaborative simulation model development and performed preparatory work on in-house rotorcraft model for state-space rotor inflow model identification from high-fidelity VPM solution was set up.
• WP4: the literature review on simulator cueing fidelity metrics and proposal of metrics to be used within the simulation campaigns was carried out. The definition of possible scenarios for simulation cueing tests started, alongside the integration of new AR technology into NLR simulator. A first version of a FoV-limitation in AVES simulator was integrated, to prepare piloted simulator campaigns to investigate degraded visual environment. Preparation work was performed to assess tuned motion parameters.
• WP6: the collection of detailed drawings, technical documents and on site reliefs of AWARE simulator was performed, and the preliminary design and layout of the new tiltrotor simulator issued. Initial assembly of parts of the screen is ongoing.
• WP7: RoCS dissemination strategy was defined, together with several updates of the website. RoCS brochure was issued, target groups and stakeholders identified, implementation of social media communication implemented and internal procedures defined.
RoCS is an ambitious project, proposing breakthrough innovation with significant impacts on the target industry. The new methodologies and fidelity metrics will allow a more frequent, standardised, and cost/time-effective application of flight simulation in rotorcraft certification, going beyond the current practice for fixed-wing aircraft. Significant progress is foreseen also in the following areas:
• Rotor wakes, interference modelling and aerodynamic environment (including two-way rotorbody interference effects and the interference of rotor wakes with obstacles),
• Structural aeroelastic modelling (by adding aeroelastic models of rotor/wing/pylon systems to improve loads and vibrations generated in flight and transmitted to the airframe),
• Control system modelling (including FCS),
• Model fidelity evaluation metrics (producing a methodology for defining task specific predictive and perceptual fidelity metrics),
• Credibility of simulation models (providing methodologies to verify and validate the credibility of models outside of the tested envelope),
• Physics-based model update (providing provide a systematic physical tuning process using flight test data for fidelity enhancement and simulator acceptance and certification)
• Flight simulators for certification (setting up an ultimately effective but low-cost COTS simulation system),
• Flight simulator visual system (including a system of mirrors designed to limit the number of projectors to obtain the required wide field of view, possibly complemented by AR devices),
• Motion and vibration cueing systems in flight simulators (proposing a low-cost simple and effective motion platform for motion and vibration cues).
RoCS outcome will have important impacts on safety, economy, duration and effectiveness of tests. The risks associated to rotorcraft certification compliance demonstration will decrease significantly. The safety of certification flight testing can be improved, thus allowing for the most hazardous test to be performed in a safe environment reducing to 0 the risk in case of failure. The number of tests can be increased, improving data collection for gaining greater insights of the rotorcraft characteristics. Costs of certification will be reduced again by the possibility of test repetition and the prevention of accidents. Cost reduction is estimated up to 88%. RoCS will allow for a time reduction to complete rotorcraft certification, and so the time-to-market of new products. In the end, the ambitious outcomes of RoCS are expected to form the first steps in the classification of simulation devices for CSFRA topics, to define a new family of flight simulators.