Airbus Helicopters Enhances Hydraulic Design Simulation

makers to settle on better plan decisions and validate systems integration right on time in the outline process

In 1993, NHIndustries, mainly owned by the Eurocopter group (now Airbus Helicopters), started to design the NH90, a medium-sized military helicopter. Thirteen years later, it entered service.

The pace of technological change has increased so rapidly and the competition has become so fierce that helicopter manufacturers usually have no more than four years to develop their most sophisticated models. As a result, manufacturers must make better design choices and validate systems integration early in the design process, using modeling all along the V-cycle.

In addition, rotorcraft manufacturers must provide their customers with reliable pilot training solutions. However, flight simulators must often be delivered before the first helicopter is produced. The level D full flight simulator (FFS), which is the current standard with comprehensive high-fidelity aerodynamic and systems modeling, is increasingly being requested, most recently for the Eurocopter EC175, Airbus Helicopters’ new medium-sized twin-engine helicopter.

Investing in simulation

Airbus Helicopters, part of the Airbus Group, is Europe‘s leading fully-integrated aeronautical company, known for its high-performance, cost-effective, safe and comfortable helicopters.

To maintain its leadership position, the company has invested in virtual testing to meet different needs along the development cycle, such as rapid prototyping, desktop simulation, real-time pilot-in-the-loop simulation, test rig development and training solution production. Airbus Helicopters’ simulation policy stipulates that, if possible, a unique model should be used for each component throughout the V-cycle.

This approach had already been used for avionics equipment, flight control kinematics and aircraft environment modeling, such as wind, atmosphere and ground conditions. However, to apply this simulation approach to physical system modeling, Airbus Helicopters needed a tool that would ensure high predictability and easy model integration into the real-time environment. The company had such a tool in LMS Imagine.Lab Amesim software from Siemens PLM Software.

Reducing cycle time and costs

Airbus Helicopters has used LMS Amesim since 2007 for hydraulic and air-conditioning system simulation. In 2009, the company extended the use of LMS Amesim to thermo-hydraulic component and system modeling.

Prior to adopting LMS Amesim, specialists in the Hydraulic and Flight Controls Department were only able to obtain a quasi-static representation of the hydraulic system. The majority of parameters were determined during the prototype testing phase. Moreover, these hydraulics models were incompatible with a broader co-simulation environment. To take into account the behavior of the hydraulic circuit in real-time simulation, Airbus Helicopters used to build another model using a specification that a hydraulics specialist had prepared for a supplier, but those simulations had not been predictive and required the involvement of the hydraulic engineer.

The use of LMS Amesim enabled hydraulics design engineers to move from a quasi-static to a dynamic world. Now, not only can they model hydraulic systems and subsystems, such as pumps, actuators or tanks, they can also use the same model to gain insight into the systems behavior when interacting with thermal, mechanical or electrical systems.

“By using LMS Amesim for the hydraulic system design, we estimate that we have reduced optimization time by a factor of 3, and prototype costs by a factor of 4,” says Thibaut Marger, analysis and simulation specialist in the Hydraulic and Flight Controls Department at Airbus Helicopters Research and Development. “The first prototype that we manufacture is to fine-tune the LMS Amesim model. The system optimization is performed virtually. That leads to the creation of a new prototype that is very close to optimizing performance.”

Providing top-notch services

Siemens PLM Software has recently helped Airbus Helicopters find a solution to carry out real-time simulation, which supports the development of test rigs and system engineering. The next step will be the design of full flight simulators.

Thanks to its experience in methodology development, LMS Engineering services provided Airbus Helicopters with best-in-class support to convert hydraulic circuit plant models built using LMS Amesim into real-time compatible models. These models were then used on Airbus Helicopters’ unique real-time simulation platform for the development of the Eurocopter EC175.

First, LMS Engineering analyzed the computer processing unit (CPU) time required by existing hydraulics models, and helped Airbus Helicopters optimize its models, taking into account potential dysfunctions, such as a broken hydraulic pump, actuator leakage or inadvertent back-up pump activation. Next, the company used a unique model so it could understand the thermal dynamic behavior of the system for many scenarios. Finally, the model was reduced in order to keep only the phenomena that are compatible with the real-time, fixed step solver frequency.

Using several standard LMS Amesim libraries, capabilities and tools made this project feasible. These included thermal-hydraulic, hydraulic component design, signal and mechanical libraries, super component functionality, and activity index, linear analysis and performance analyzer tools.

The cooperation between Airbus Helicopters and Siemens PLM Software can be considered a pilot project to demonstrate the feasibility and advantages of this approach. Conducting fuel and electric model export in future programs could be a next step toward optimization of the design process throughout the V-cycle. To this end, Siemens PLM Software continues to support the customer by working on a methodological guide for model reduction and automating model conversion to the real-time target.

Adapting to customer needs

This project has resulted in Airbus Helicopters identifying new opportunities to enhance its simulation process. Since the same model is re-used and refined throughout the design cycle, development specialists are now interested not only in the performance of their system, but also in the way it interacts with other systems. It allows them to assess the system performance under different conditions and modes as well as to anticipate undesirable behavior in the system prior to it being integrated into a helicopter.

“Being able to anticipate a problem is a significant source of cost and risk reduction,” says Nicolas Damiani, expert in simulation and operational analysis in the Simulation Department at Airbus Helicopters Research and Development. “This approach allows us to master the development cycle and delivery time. These costs can’t be directly measured, but it enables us to avoid late penalties that can be substantial when the delivery is delayed due to a problem identified once all components are integrated.”

“As a multi-domain platform, LMS Amesim fosters a closer dialogue between departments,” says Marger. “For instance, the same model is now used by the hydraulics and thermal teams, which was hardly feasible before. Moreover, constantly increasing usability in LMS Amesim will allow our non-specialists to easily run simulations.”

This new modeling approach is a logical extension of Airbus Helicopters’ standard practice. By reducing the number of models and making it easier to keep simulation models updated, this standard ensures consistency, easier model management and better traceability.

“We’ve easily been able to adapt LMS Amesim to our standard despite the constraints inherent in the hydraulic systems simulation, such as a generated code, a large number of state variables changing at every system evolution and a big difference of time constants or multiple oscillating modes at high frequencies,” says Damiani. “The same hydraulics LMS Amesim model, which is much more accurate and is available much earlier than our previous real-time model, can now be used throughout the V-cycle.”

Damiani notes,“We opted for LMS Amesim for its capacity to adapt to customer needs and the quality of our exchanges with the Siemens PLM Software team. We are convinced that LMS Engineering enables Siemens PLM Software to stay close to customers while capitalizing on experience gained through multiple projects.”