Unlocking the Next Wave of HIL Capabilities for Aerospace and Defense

When launching rockets into space and flying above Earth, logistical challenges grow exponentially. Hardware-in-the-loop (HIL) technologies enable test teams to effectively conquer logistics, optimize costs, and meet safety requirements in unpredictable circumstances. In aerospace and defense, where some of the most unpredictable circumstances occur, HIL technologies are particularly crucial.

Organizations depend on HIL to make certain aspects of testing possible. Certifications such as DO-178, DO-254, and so on ensure that complete physical product testing is the only way to prove requirements have been met. HIL allows such testing to be done in a non-destructive manner. Getting enough hours and resources are necessary to validate flight test, or in many cases, flight crashes, yet can be hard to justify to your business. However, leveraging simulation with HIL makes cost prohibitive and sometimes logically unrealistic validation possible. It’s not a question of if you should be utilizing HIL in test, but rather how you should be currently standardizing and optimizing your systems.

Let’s explore how HIL truly expands the possibilities of test.

Adapting HIL Systems for the Future

Simply stated, HIL takes the “brains” of a system, meaning the physical controllers, and plugs them into a physical and/or simulated environment. By giving the ability to switch between physical and simulated aspects, HIL ensures that all elements operate per expectations. HIL also enables high-fidelity emulations of functional or scenario-based testing by essentially putting software in a state where it believes that it is performing the intended mission. “HIL is the bridge to bringing your models into the real world,” NI’s Barron Stone explains.

While HIL isn’t exactly new technology, it has come a long way in the last decade. Many systems, past and present, are “homegrown,” with various pieces built in-house by engineers, but today, development timelines are shorter than ever. Teams face increased requirements for computer power, standardization, and automation that leave many homegrown systems struggling. Additionally, the test equipment components on many of those original systems have become obsolete over time, having a detrimental impact on aged HIL systems. In the past 10 years, there has been a shift towards modular solutions that can automate more processes, streamline workflows, and connect data across silos. And with these modern systems, engineers can get the right test coverage sooner in the development timeline.

To keep up with the pace of innovation, teams must look critically at their entire process to identify areas to optimize workflows. Physical space and time are some of the biggest opportunities for improvement. Streamlining even the smallest details with automation such as SW-controlled faulting can make a huge difference when it comes to optimizing test.

Think of something that seems simple: connectors. When working with HIL, you could easily have a huge wall of connectors. Without automation, to test any given situation, a specialized technician would need to physically come out to move the cable plugged into the wall to run the test. That might sound feasible in theory, but it’s frustrating when you’re waiting hours for a single person to just come out and move a plug! With an automated system, this can all be electronically switched with no waiting or figuring out where to take a plug and put it in another place. Something that seems so simple can save hundreds of hours compared to manual switching with nonstandard connectors.

Whether it’s a wall of physical switches or a homegrown HIL system, you don’t want your engineers to spend all their time building, maintaining, and fixing tools. Your hardware and software should be assets bringing value to the organization rather than a constant source of frustration. Being proactive and having a system that is robust enough for your needs, instead of having to react in a frenzy to add new capabilities or accommodate a new controller at the last minute, sets your team up for success. Engaging in forward thinking saves time in the long run, instead of constantly reacting to time-crunched crises. All that time equals dollars spent.

Shifting to Simulation

In an industry of high costs and even higher stakes, the cost-saving benefits of HIL add a huge impact to overall performance. Leveraging HIL and simulation helps avoid test flights, which are incredibly expensive and oftentimes impractical. There are many scenarios where you can’t test a live flight even if you wanted to: Availability of assets, ability to get time on high-demand test ranges, defense security, and even factors completely outside of your control such as the weather impede the possibilities for test. For all these use cases, HIL saves expensive flight hours while still offering real-world results.

Savings and benefits aren’t restricted to practical logistics. With any kind of test, earlier is better. HIL allows testing earlier in the process to catch bugs closer to the design phase when they are easier—and less expensive—to fix. The types of failures that HIL exposes are ones that would typically be found much later in in-flight testing or even in deployed and operational assets. Catching failures sooner with HIL means a safer end product with far less cost associated in test. Utilizing HIL can also help teams get through complete validation quicker, meaning production can start sooner to ultimately improve the overall speed of getting products to market.

To fully unlock the capabilities HIL can offer, engineers need to look to shifting from legacy systems to modular HIL solutions. Modern systems advance test timelines by enabling engineers to keep up with changes to unit under test (UUT) definition and requirements. Today, it’s common to wait until the UUT has fully stabilized, since it’s risky and cost prohibitive, to make changes to it. But optimizing performance is about making the development of the test equipment and TPS happen more in parallel with UUT development, rather than having to wait. The UUT can and will change, but it’s how you accommodate those changes that makes a difference. By employing parallel HIL rigs, you can reuse test equipment. Having a truly modular hardware and software approach enables engineers to swiftly modify test equipment to adjust to UUT design changes and also enables engineers to reuse valuable, expensive assets. When a new UUT comes in, you can take an existing test asset and readily modify it to test the new UUT, which is a shift from how most teams operate today, as the test asset is usually locked to a particular UUT. Modifying the test asset creates inevitable setbacks as even a similar, new UUT typically requires a completely new design and build of a test asset. Upscaling your HIL system increases performance by allowing engineers to be proactive.

In the years to come, simulation will only become more integral to aerospace and defense test. Simulation will be key not only due to costs and practical issues for product test, but also for security and espionage when it comes to defense. HIL is now, and will continue to be, the essential connector for digital models in the real world.

Creating Your Modern HIL System

In the future, test systems will become more automated, allowing tasks to be executed in a predictable, deterministic way. But automation also increases the complexity of a system (and the complexity of testing it). A modern HIL system will be key to building a potentially “infinite” test space to accommodate a bigger number of tests.

With growing prevalence of HIL in aerospace and defense, it’s likely that you’re already using this technology to some degree. So, a better question to ask yourself is, “Is your current system serving your organization to its full potential?” When answering, it’s important to not let the status quo hold you back. Just as new technologies push innovation, your overall test process and approach to HIL validation testing can innovate as well.

Think about how you design, build, and acquire HIL test equipment. Chances are there is a lot of room for optimization by using new, yet proven, approaches that don’t inject unacceptable risk. By identifying bottlenecks and challenges in your process, you can investigate replacing sub-systems one at a time. Itemizing things in this way will make what might feel like a huge leap seem manageable. You’ll be able to test earlier and validate faster by optimizing and adapting existing workflows.

As time goes on, HIL and simulation will only become more essential for aerospace and defense. A software-centric platform will eventually be industry status quo as automation and reusability become more important. We’re in the middle of that shift now. Rather than reacting constantly to fix and regroup, leverage proactive planning and powerful tools to thrive against changing requirements.

To learn more about how to reduce cost and schedule risk using HIL simulation, read our Hardware-in-the-Loop Resource Kit for technical tutorials.