Tech Briefs

Virtual Testing of High Lift Systems

Virtual testing serves as an additional, equivalent means of testing versus existing, established physical means of compliance.

For aircraft system certification, a huge amount of testing is required to guarantee safe, robust, and error-free behavior under all operating and environmental conditions. Typically, these tests on the system level are performed on physical test benches (left, in figure) where all the relevant components including actuators, sensors, and control computer are integrated. Due to the increasing complexity of systems on the one hand, and drastically reduced development times on the other, virtual testing has become one of the solutions to overcome this challenge.

Multibody simulation is the preferred approach for virtual testing in the case of high lift devices. In a system that is modeled by flexible bodies as well as rigid bodies — showing big, rigid body motions — and that is operated statically as well as dynamically, the multibody simulation approach offers a very good compromise between computational speed and accuracy.

This simulation approach is based on the strong coupling of physical and virtual testing to obtain the highest possible confidence in the simulation results. Starting with a model variant that represents the physical test bench in all relevant details (right, in figure), the model is validated using results from the test bench and then extended to an aircraft-like variant.

The main differences between test bench models and aircraft models are the application of airloads (discrete load cylinders vs. distributed pressure loads), the interface conditions (attaching the high lift system to a rigid test bench vs. a flexible wing), and the consideration of loaddependent wing deformation. Results of physical tests combined with results from virtual tests lead to a deeper understanding of the system under test and its behavior earlier in the process, thus reducing the risk of finding problems later, resulting in late design changes.

The use of simulation for aircraft system certification is not just related to building simulation models with sufficient accuracy and quality. Regulations from airworthiness authorities also request a well defined and robust process for the complete data chain involved in the certification. Currently, requirementsbased engineering (RBE) is the formal way of developing new aircraft and their systems.

All required functions and properties of the system in terms of performance, safety, etc. are specified verbally within single requirements managed by a database system. Using a Test Management System (TMS), the formal verification of each of the requirements is assigned to one or more of the existing test tools. Each test tool has a local process and data management environment. After test execution, the TMS collects all the results from the local platforms and automatically generates the required test analysis reports and the certification documentation (coverage report).

Besides the need for traceability of the relationships between all relevant simulation data, it is also mandatory to have simulation process management in place for the efficient use of virtual testing and the related simulation technology. This comprises all the major steps of the simulation process, starting with pre-processing such as creating the simulation models; continuing with solving, as in the execution of the models to generate simulation results; and finishing with post-processing of the results including extracting key values and generating tables and plots.

For successful implementation of virtual testing in the existing test process, a solution was developed based on MSC SimManager. This High Lift System Virtual Test Portal (HLSVT Portal) fulfills the following general requirements:

• Interface with global TMS
• Simulation data management
• Workflow management and process control and automation
• Configuration management and lifecycle management
• Traceability and reproducibility
• Interface with other software
• Diverse model library, supporting multidisciplinary system simulation
• User friendly graphical environment

One of the most important and critical aspects was correctly capturing the virtual test process itself and its interface with the TMS. A detailed specification capturing all objects, process steps, and related attributes was established and refined during setup of the portal.

The execution of a multibody simulation model generally leads to a considerable amount of data. The parameters measured in the model lead to an important number of time series, each consisting of a large number of time steps. It is mandatory to have an efficient post-processing process in place, enabling robust and convenient keyvalue extraction out of the simulation raw results. This process also covers the global virtual test requirement for traceability and reproducibility of data.

This work was done by Tobias Ulmer and Jaymeen Amin of Airbus Operations GmbH. The full technical paper on this technology is available for purchase through SAE International at http://papers.sae.org/2013-01-2280.