Measure Twice Measurement Solutions for Aerospace

The old saying goes, measure twice, cut once and nowhere is that more important than in aviation and aerospace. Thankfully technology has advanced, making leaps in development and this old saying obsolete.

Aerospace measurement and testing has developed significantly in recent years, and new solutions have been introduced. The aerospace market has also diversified, and there are new players, start-ups and also government-driven organizations investing in the development of state-of-the-art test and measurement technology. In this feature, we have reached out to industry experts to assess the state of the art of aerospace measurement and testing technology, the drivers of change, and what future solutions will be focused on.

State of the Art

According to Manuel Vögtli, who is the head of business development at Kistler, there is a more competitive environment and more budget and benefit sensitivity. “Customers do not automatically choose the highest performing sensors and measuring chains but more and more look for a trade-off between cost and benefit, sometimes ‘good enough’ is good enough. Technologically, we do not see any revolutionary or disruptive developments,” he said. “Applications such as payload and propulsion testing will always play a major role, but the technological limits do expand, for example in terms of temperature. Thanks to our own-grown PiezoStar crystals, we are able to deliver high temperature sensors for environments with more than 1000°C and cryogenic ones for low temperatures down to -196°C and lower.”

Manuel Vögtli, Kistler

Engine fuel consumption has become crucial — both for airline cost savings and also for CO2 and NOx reduction, thus, engine testing during development requires many and very accurate thermocouple measurements, explains Ingo Pletschen, aerospace business development manager at IPETRONIK. “Even optimizations of 0.05% in fuel consumption are important and therefore one needs extremely precise temperature measurements,” he said. “In general, engine and aircraft original equipment manufacturers (OEM) aim for universal data interfaces to ease integration of new data acquisition and test equipment. Even more important is to reduce test cell time by installing the data acquisition (DAQ) to the engine already in the preparation room — so very rugged DAQ is needed.”

PiezoStar is a registered trademark that refers to all crystal types that Kistler grows in-house. PiezoStar crystals offer higher sensitivity and better high-temperature stability than standard quartz crystals. PiezoStar crystals are typically used in sensors for measuring very small forces, i.e., pressure signals or perform measurements at higher temperatures. A PiezoStar sensor can extend the application range in place of commonly used quartz-based pressure sensors Kistler says. Kistler image.

According to François Lachance, product manager at Creaform, traditional measurement techniques have evolved to incorporate more advanced technologies such as 3D scanning, non-destructive testing (NDT) methods, and digital inspection tools. “These developments have improved accuracy, efficiency and data collection capabilities, enabling better quality control and faster decision-making processes,” he said.

Ingo Pletschen, IPETRONIK

For what concerns new solutions, Vögtli affirms that there is a trend towards miniaturization, because mounting space and weight are crucial parameters in aerospace testing. “We recently launched a 6 mm cube triaxial accelerometer which also features a PiezoStar crystal for remarkable temperature stability,” he said. “In addition, we see that piezoelectric force sensors are more and more applied for applications in aircraft testing such as drop tests and landing gear testing where strain gauges were most common before.”

IPETRONIK say jet engine tests require multi-channel measurement technology that is highly precise and reliable, even at extreme ambient temperatures and offers rugged data acquisition solutions. IPETRONIK image.

One thing that is really new is fiber optics, according to Vögtli. “Principally there are two approaches called fiber brag grating (FBG) and fiber segment interferometry (FSI), the newer but more complex FSI is very promising in terms of sampling frequency and resolution, FSI sensors can be used to measure strain, temperature and deformation (shape) in various applications,” he said. “A typical example from aerospace testing is the complex design of helicopter blades. With an FSI shape sensor, digital reconstruction and structural health monitoring can be realized on nanometer level. In addition, FSI sensors complement research and development (R&D) in the areas of ground and flight testing.”

Francois Lachance, Creaform

New solutions in aerospace measurement and testing include high-precision 3D scanners like the ones developed by Creaform, said Lachance. “These scanners can capture detailed geometry and surface information of aircraft components, facilitating reverse engineering, dimensional inspection, and damage evaluation,” he says. “We are always looking for new and innovative solutions to solve industry challenges. The latest addition to our product portfolio is a complete software solution for the assessment of damaged surfaces, VXintegrity. In this platform, we really aim to streamline and improve the way people assess in-service damage, such as dents, with powerful in-house algorithms. By digitizing the approach, the results are easy to communicate between engineers, more repeatable and more traceable.”

Drivers of Change

One of the drivers of changes in aerospace measurement and testing concerns extreme temperature applications, emphasizes Vögtli. “In rocket engine testing, both cryogenic and high temperature accelerometers and pressure sensors are typically required for propulsion testing. And on the other hand, high-temperature sensors are needed as part of the test scope,” he said. “Another driver is the need for piezoresistive pressure sensors which are really small and capable of measuring in high-temperature environments for both static and dynamic pressures.”

According to Lachance, the need for higher accuracy, increased efficiency, and improved collaboration and conformity are driving the changes in aerospace measurement and testing. “The aerospace industry, alike other industries, is seriously affected by the labor shortage and more importantly skilled labor shortage,” he said. “Moreover, the aerospace industry is recovering from COVID-19 and adding pressure to inspection and dimensional demand.”

The HandySCAN 3D is a portable metrology-grade 3D laser offered by Creaform. The company says it is ideal for product development and quality control. Creaform images.

The time it takes for new measurement and testing solutions to be deployed can vary depending on the complexity of the technology and the level of certification required, according to Lachance. “Typically, it can take several years from the initial research and development phase to full-scale deployment. This timeline includes rigorous testing, validation, obtaining necessary certifications if required, alpha and beta tests, and modification of the solution to meet industry requirements,” he said.

Kistler develops base technologies which are then customized to multiple applications for sensor development satisfying specific requirements, explains Vögtli. “Product development can often take several years. However, with our custom product lane (CPL) department, we offer a unique way to deliver customer-specific solutions in a short time,” he said. “The CPL has a team of experts to develop individual products and sensing systems for a given application with end-to-end responsibility from development over production to qualification. This typically includes sensors and systems that do not yet exist. With the help of rapid prototyping and further advanced methodology and processes, we are able to accelerate development processes on demand.”

Future Solutions

For urban air mobility (UAM) and electrical aircraft, new measurement and testing solutions are being researched — especially for electrical power measurements with its high sample rates, but also for capturing new and modern data interfaces, affirms Pletschen.

An important application field is indeed the emerging market for UAVs, drones and eVTOL aircraft, according to Martin Marinák, who is in charge of eVTOL business development at Kistler. “The electrification of aviation comes along with a variety of applications such as propulsion system vibration measurement, battery testing, structural analysis and optimization and electric motor testing, e.g., torque and speed measurement on custom test benches,” he affirmed. “For space testing, propulsion optimization with the trend to liquid fuels is a topic that is currently heavily investigated, just think of ever stronger and reusable rockets, for example.”

There is also much development of new satellites and related testing, like the nanosats, with a weight between 1 and 10 kilograms only that require different components and therefore new test and measurement solutions, affirms Vögtli. “In general, the development and refinement of reaction wheels and cryocoolers is a research area that has continued development year over year,” he said.

Future solutions need to focus on the ongoing trend of big data and digitalization, said Vögtli. “For the digital twin of an aircraft, for example, one needs to conduct several series of real-time measurements with lots of sensors mounted on the unit under test and this of course leads to a vast amount of data to be processed,” he says. “This is why software becomes more and more important: to manage big test data, to process and analyze it reliably and efficiently and to even find hidden patterns and correlations with the help of artificial intelligence (AI) over the long term.”

Indeed, the digitalization of assets will keep being a big trend in the aerospace measurement market, emphasizes Lachance. “When it comes to 3D scanning technologies, our future measurement solutions would likely focus on better integration based on the industry challenges. Future measurement solutions are likely to integrate AI for automated data interpretation, augmented/virtual reality (AR/VR) integration to improve conformity and onboarding experience, and more collaborative tools to ease communication between multiple stakeholders,” he concluded.