Achieving quality in complex systems

Mike Richardson speaks to National Instruments' application segment manager for embedded software validation, Chris Washington to discover how the company's hardware-in-the-loop software tools have helped Embraer perform a full aircraft simulation of its new Legacy 500 mid-sized business jet.
The term, ‘flying by the seat of one's pants' originates from early aviation parlance where aircraft had only the most basic means of pre-flight testing. Instead, much of the qualification of airworthiness was accomplished by means of the pilot's judgment. Fortunately, the use of ‘Iron Birds' - test rigs used to reproduce numerous situations that could conceivably occur during flight - now enable engineers to test flight controls, landing gear and the hydraulics of an aircraft system before it gets anywhere near its maiden flight.

Faced with the challenge of performing electronic systems integration testing by connecting the complete electrical system of its Legacy 500 aircraft to a simulation of the rest of the aircraft, Brazilian aircraft manufacturer Embraer turned to National Instruments' (NI) VeriStand real-time testing application environment to improve the efficiency of its Iron Bird.

The final solution saw the creation of a full aircraft simulator comprising 21 real-time PXI systems networked together using GE Fanuc's reflective memory and Ethernet interfaces. The NI real-time testing platform reduced Embraer's development and testing time by one year, from 42 months to 30 months, when compared to the previous aircraft simulation approach used by Embraer.

Simulate and innovate

NI VeriStand is a software environment for configuring real-time testing applications, helping aerospace engineers to configure a multicore-ready real-time engine to execute tasks such as real-time stimulus generation, data acquisition for high-speed and conditioned measurements, and calculated channels and custom channel scaling. NI VeriStand can also import control algorithms, simulation models, and other tasks from NI LabVIEW software and third-party environments.

“NI is a leader in the test & measurement arena,” begins the company's application segment manager for embedded software validation, Chris Washington. “As software technology used in aircraft expands, the role of testing becomes more complex because of increasing software-related quality challenges in the mechanical world.

“Obviously you cannot simply restart an aircraft if it does have a critical software problem, so therein is the challenge that my group supports as other engineers validate these systems. NI VeriStand is our core product focused on this type of application, whether it is pure simulation or model-in-the-loop (MIL) testing, all the way through component and system hardware-in-the-loop (HIL) testing, to system integration labs, such as the Embraer application and then extending beyond this to test cell and data logging applications.”

Washington reckons NI has created a product that ‘under the hood' is largely built by LabVIEW. NI's developers have used their own environments to build this tool to provide - out of the box - a ready-to-use experience for customers performing HIL or system integration labs.

“Where NI VeriStand differs from others is that firstly, it's not a closed environment, meaning that we very deliberately designed the product so it can be used throughout all testing applications in the development process as well as support customisation by a variety of environments in each application,” he continues. “If a customer performs a pure simulation test and wants to use some models from the SCADE suite application software or LabVIEW models, i.e. mix and match them, then there's the possibility to extend and customise it for this purpose.

“In the latter phases of customer development, simulated components are replaced with real-world components requiring real-time hardware I/O to provide an interface between the simulated and real-world components of the aircraft. It's at this point that NI can offer its breadth of hardware to connect the flight computers and actuation systems to the simulation. Whilst being open and extensible with third party software, NI VeriStand is most commonly used on the PXI platform which is an industry standard, open environment for modular hardware I/O, giving us access to many I/O interfaces.

Testing for all possibilities

Embraer's Legacy 500 business jet is claimed to be the first aircraft in its class to fully implement fly-by-wire technology. It requires more than 50 flight computers to simulate flying the aircraft and before it had even performed its maiden voyage, Embraer had completely tested it on the ground.

“The system integration lab built by Embraer had 21 of our PXI system simulators that allowed them to perform flight simulation across a variety of aircraft configurations – even to the point of being able to do dangerous and ‘un-testable' situations, such as how the aircraft would respond to an engine failure for example - situations that you hope never to see, but which enable engineers to understand that their software-enable sub-systems won't prevent the pilot from being able to recover the situation to the best of their ability,” explains Washington.

“Embraer contacted us about the Legacy project around the time we had just released the first commercially available version of NI VeriStand. Through a close working relationship, we understood what features were still needed to make NI VeriStand ideal for a system integration lab setting. Our desire to make NI VeriStand ideal for these types of applications meant we were eager to take Embraer's feedback and fill in the missing blanks.”

Embraer claims that the use of NI technology allowed them to complete the Legacy 500 Iron Bird 12 months sooner than the previous project. Washington states that Embraer's feedback helped NI improve the out-of-the-box features that NI VeriStand provides for applications of this scale, improve the application programming interfaces (APIs) that enabled Embraer to invest in automation, and improve the multicore processor technology that allowed them to simplify the complexity of the system by getting more processing power out of the box.

“I would say the complexity of this project was at the upper end of what we have experienced to date,” he notes. “Embraer is pushing the envelope in technology and quality simultaneously, so working with them really pushed our limits too. We sent specialists to Embraer regularly to ensure we truly understood their demands and respond to them as quickly as possible. The project was a tremendous success and one that has strengthened the capabilities of our tools.

“Critical to our success was that Embraer had several highly-talented and certified engineers in the use of our tools and their third party tools. We provided more out-of-the-box technology, allowing Embraer to become more efficient and endure less maintenance-related concerns.”

Distributed across 21 PXI systems, the model used to simulate the aircraft required 90,000 individual parameters.

“We've received helpful feedback from Embraer in how to improve the performance of our software and hardware of NI VeriStand and PXI to execute these simulations more efficiently, as well as importing and managing data sets, because they can really affect your productivity when you are dealing with 90,000 parameters for example,” he states. “We feel these kinds of simulations and their complexities will increase as aircraft avionics systems become more complex themselves. NI wants to be at the vanguard of what is the upper end of these needs, so that we never limit the ability of our customers to implement leading edge technology.

“We're focusing on the individual execution performance on a single PXI multicore controller, as well as the distributed performance across multiple PXI systems in terms of how customers can manage large sets of I/O and model parameters. Huge swathes of data are produced by these simulations, so learning from Embraer, as well as other customers across many industries regarding this huge data challenge and how to manage that data and allow customers to get the most out of it is vital.”

Providing a holistic view

Washington closes by stating that from an NI viewpoint, the technique of using system integration labs will continue to grow as the use of distributed embedded software expands in these systems. However, two areas where NI really see the validation of these systems evolving is in providing continuity in the way the system is tested from concept to production and in how efficiently this test data can be used to make decisions.

“We need the ability to look at the system throughout the entire development process in a consistent way,” he concludes. “When developing complex systems such as an aircraft, the design is transitioned from a pure simulation to a physical system – incrementally converting simulated subsystems to real-world components while testing at each stage. Instead of independently developing tests for each stage of development, NI VeriStand enables customers to perform the same test throughout the entire process, even though there are different simulated and real parts at each stage. This provides engineers with a consistent base-line of tests allowing them to compare how system performance changes throughout the development process. This ability also allows engineers to re-use the same flight profiles and stimulus and analysis routines across each development stage, providing efficiency and consistency in the validation process.

“The second area we've invested in is what to do with all the data produced by these applications. We're trying to make testing more efficient and accurate, whilst simultaneously helping customers deal with all of the data produced - whether they need to generate reports for audited compliance, or archive data they can investigate later to improve their processes. Engineers don't execute tests to produce data – they execute tests to get results they can make decisions with, and we are working to help them more efficiently produce this data and make it useful for decision making. We're investing in both how data is managed and how it can be leveraged once it is available to perform analysis.”

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