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In Lighting the Path to Innovation Blog
authored by Flexible Partners: Structural Testing of Aircrafts Using Fiber Optics

Most frequent fliers don’t know (or want to know) that aircraft wings are designed and engineered to bend. This flexibility is called deflection. Today’s aircrafts are heavy structures that must be able to carry large engines, fuel tanks and a huge payload capacity. The flexibility in their structure allows wings to bend as competing forces of airflow push up and down on the wing’s surface. This bend allows for the regulated release of airflow force and prevents the wing from breaking. In fact, the entire plane – fuselage, wings, nose to tip, are designed with materials that, imperceptibly to the human eye, bend, arch, contract, and twist.

Measuring these minute changes are of paramount importance to the aviation and aerospace industry’s chief concerns – safety and performance. The ability to monitor, measure, and analyze exactly how a wing deflects in flight allows pilots and engineers to identify small issues that could become large problems over the lifespan of a plane. These measurements inform vehicle health decisions like end-of-service and fleet maintenance planning, and play an important role to support mission success when determining payloads and range. In addition to ensuring aircraft safety, understanding wing deflection and strain fields provides engineers with the data they need to enhance the performance of future aircrafts.

Conventional methods to measuring a plane’s structural changes (e.g. strain/stress) involve a straightforward, but labor-intensive process of gluing gauges or sensors at even intervals connected with a wire along the surface of the substrate. In addition, “strain rosettes” (three gauges installed in a triangle to allow for multi-dimensional recordings) are often necessary for accurate measurements. Once all of the gauges have been placed, lead wires are then routed to a centralized data collection system. These systems are fast becoming limiting as the internal structures of aircrafts continue to evolve with new material technology.

Think of the challenge of gluing a flimsy copper foil along every surface on a plane that would be useful to measure. There are literally thousands of areas of interest for structural testing. Most of the areas involve complex features where stress is likely to concentrate, such as fasteners, or moveable parts like flaps, doors, and landing gears. As a result, when measuring with traditional systems, there can be a lot of ambiguity in determining the best place for the gauges and a lot of work required to carefully and neatly bundle hundreds of gauge wires in a place already lacking in available infrastructure real estate. Further adding to the challenge is that only tens or hundreds of sensors can be used for in-flight testing. Similarly, the cumbersome nature of the cabling and data acquisition systems means that strain gauges are not viable for embedding in end products.

In order to keep up the constant evolution in the aerospace and materials science industries – which are constantly delivering better, lighter, and economical aircraft components – a new way of structural measuring must be established as an industry standard. Eventually, the current means of stress testing and measurement will not be able to keep cycle with ever-increasing and changing safety and performance standards. The challenge is about pairing the right tool with the right job. After all, you wouldn’t measure miles with a ruler. Enter Compact Fiber Optic Sensing (FOS). Fiber optic technology has long proved its potential beyond telecommunications, and its flexibility and scalability make it an ideal tool for the aerospace industry.

When fiber optic cables are manufactured with inscribed fiber bragg gratings (FBGs), the wavelength of reflected light passing through the fiber can be used to measure behaviors such as strain, temperature, 2D deflection and 3D shape. Since FBGs can be easily placed next to each other, a single fiber optic cable can contain thousands of sensors consecutively. The signals can be read simultaneously and are accurate within 2 microstrain. Unlike many non-light based systems, fiber optic sensing has complete immunity to electromagnetic interference. Extremely customizable, the cables can be installed in almost any location with relative ease, use very little space and can run in any orientation. Since fiber is embeddable in composite materials, Sensuron’s FOS systems can provide engineers with a reliable platform not only for testing, but for including as a component in final aircraft designs and manufacturing quality control.

Fiber optic sensing is a simple, elegant and sophisticated solution to structural testing and analysis. The flexibility of the fiber optic cables, ease of installation, real-time monitoring capabilities and ability to measure multiple variables, make the Sensuron FOS platform the right choice for endless monitoring applications in the aerospace industry. Read more on specific aerospace applications, or to learn more about our history and expertise working with NASA.

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