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Modular Platform for Aircraft Flight and Ground Operation

Periodic Reporting for period 2 - OPeRATOR (Modular Platform for Aircraft Flight and Ground Operation)

Reporting period: 2020-04-01 to 2021-05-31

The aeronautical sector is a critical player in contributing to one of the key Societal Challenges, namely "smart, green and integrated transport" as defined in Horizon 2020, as well as facing new challenges regarding its competitiveness, performance and environmental sustainability. A major goal is the reduction of atmospheric CO2 emitted from aircraft and fleets by developing more efficient systems and components, novel propulsion concepts and operational procedures.

In the Clean Sky 2 programme, new technologies towards these challenges are developed, where the SYSTEMS ITD, and more specifically, the MISSION workpackage deals with aircraft optimization with respect to green objectives. These are expected to yield a reduction in fuel burn, pollutant emissions and noise disturbance on the ground and to help in developing new engine and aircraft system designs with better efficiency regarding these metrics.

Embedded in this workpackage, the project OPeRATOR was launched to develop a modeling and simulation software library to perform virtual aircraft mission simulation in realistically modelled environments, including aerial and on-ground movement phases. These are part of the design and evaluation process of various aircraft components, for example actuators, propulsion and avionics like the flight control systems. Furthermore, the library needed to be designed in a modular way and with comprehensive interfaces to implement and use models from different sources.
The first phase of OPeRATOR covered the evaluation of the state of the art with respect to mission simulation software, as well as the definition of requirements and model interfaces. The library is written in the high-level programming and modeling language Modelica, which allows physics-based modeling (acausal statement of equations), modularity through object-oriented concept as well as interoperability through various interfaces to other tools and languages (like the industry standard FMI).

Following this, several use cases provided by MISSION, were implemented in the library. These are designed to serve as verification and validation tests for the library and to work as base setups for studies with the partner’s proprietary models. The use cases comprise actuator force-fight in flight, actuator failure cases, rejected take-off scenario, a city-pair mission and landing cases.

Based on this, the final library version was finished, including a fully functional aircraft model based on components from the library and model data for an A320-sized aircraft. The aerodynamics are based on a gridded Vortex Lattice Method (VLM) in combination with manual tuning to meet stall speeds yielding a full aerodynamic model that covers all aircraft flight configurations. Also a weight and balance, landing gear, engine and actuator systems models were implemented. A redundant actuator model allowing actuator failures and force fights in various modes was developed, while a sensor suite modeling common sensor types (inertial, aerodata, GPS, ILS and others) provides realistic feedback variables to the flight control and management systems.

In order to let the aircraft model virtually fly prescribed missions, a fully functional autoflight system and pilot models have been integrated. The control algorithms allow for the simulation of full flights, including taxi, take-off, climb, cruise, descent, approach, landing and flare /cross wind alignment and braking.

All components are replaceable. In this way, MISSION components can be implemented and tested in a "virtual aircraft", which was performed for a proprietary engine model by the MISSION partner Collins Aerospace.

A video-based tutorial was recorded using the library in the SimulationX IDE, to serve as a reference for current and future users of the library. In conclusion of the project, a final demonstration meeting was held online with the stakeholders showing the structure and capabilities of the library.

Aside from the usage of the OPeRATOR library with MISSION partners, exploitation has started within the DLR project HAP (High Altitude Platform), in which a solar powered, autonomous pseudo satellite is being developed. The HAP aircraft needs to be an extremal design with minimum weight and should support operation timespans of days up to weeks, which is why mission simulation and optimization play a key role in evaluating its performance. The industry trend towards More Electric Aircraft with higher integration of different subsystems into a common energy network also requires new methods for the energy management. These research directions are pursued within the DLR in several projects (for example EU project ENERGIZE), and profit from the mission simulation framework developed in OPeRATOR, to conduct realistic performance evaluations of new propulsion and energy system concepts. OPeRATOR also leads to a number of publications, starting with an overview paper at the Modelica Conference 2021 with subsequent journal publication. Future dissemination activities are planned with respect to the delayed CEAS 2021 conference and the European Open Research Platform.
In summary, the OPeRATOR project marks a next step towards highly integrated and physically detailed modeling and simulation of aircraft operation. Previous model based simulation environments used for the pre-design, typically focused on individual- or smaller assemblies of components in specific application scenarios which do not, for example, model a complete mission with on-ground and aerial phases. OPeRATOR in turn combines a modular approach allowing to model aircraft and their systems with increased depth, and the ability to apply these detailed models to realistic mission scenarios in the air and on ground.

This has several impacts: On the side of aircraft manufacturers and suppliers, more efficient and detailed modeling tools help to reduce development time and to perform extended virtual prototyping and testing. This reduces or avoids errors during the design phase, provides means for simulation based qualification and certification and allows optimizing products towards better performance and environmental sustainability. In this way, airlines and eventually passengers will profit from improved safety and lower prices, due to the reduced operating costs and emission charges. Research departments, institutions like the DLR and universities can employ the developed library to better assess and develop future concepts (for example in the field of electric propulsion), test new control algorithms, as well as AI-based methods and to perform large-scale optimizations (e.g. studying the climate effect of air traffic, predictive maintenance of aircraft and systems, etc.). Most importantly, in light of global climate change, lower pollutant emissions have a worldwide effect on the population. More efficient systems will consume less fuel and hence produce less CO2 emissions, which slows down atmospheric warming. By reducing the output of other harmful emissions like NOx, either through propulsion design or optimized flight operation, production of ozone and the local air quality around airports will be improved. Finally, the simulation and optimization of noise-abatement routes and operations helps to mitigate possible disturbance of the population living close to airports and increases the overall acceptance of air traffic.
Fig.: Redundant actuator assembly for force-fight simulation.
Fig.: The structure of the OPeRATOR library.
Fig.: Screenshot of the mission simulation tutorial (SimulationX version 4.1.3).
Fig.: Results of force fights for three deviation cases (see project report for details).