Airframe and engine icing remain of significant concern for turbine aircraft operators, with a pair of high-profile airline accidents over the past decade highlighting the potentially deadly consequences of icing encounters. With these issues in mind, the National Research Council of Canada (NRC) has collaborated with the commercial aviation industry to develop two minimally intrusive and cost-effective devices aimed at mitigating the risk of icing encounters.
Developed concurrently over the past four years, the ultrasound ice accretion sensor and particle ice probe are designed to be installed separately, or as part of a comprehensive icing-detection package, to address what the NRC considers to be “an industry-wide gap” in the arsenal against icing.
Both systems came about from the NRC’s Rair (reducing aviation icing risk) research program, which is an offshoot of the Haic (high-altitude ice crystal) project launched by Airbus in 2012. The NRC is one of 34 partners from 15 countries participating in Haic, which is funded by the European Commission.
The particle ice probe detects ice crystals by measuring changes in the electrical characteristics of the surrounding air. The small, lightweight device–about the size of a clenched fist–is designed to be flush-mounted to any aircraft or engine inlet surface, with no measurable effect on fuel consumption or aerodynamics. The device draws about the same amount of aircraft power as a cellphone charger.
“We’ve worked on this basic technology for the better part of a decade for other aerospace applications, most notably debris detection in oil,” Dan Fuleki, NRC icing group project manager, told AIN. “We identified the value of detecting ice particles through our R&D and customer testing, and then developed the necessary sensor algorithms to coincide with a dedicated icing index.”
The probe has been exposed to 750 hours of ice-crystal altitude tunnel testing, and 140 hours of flight time with four research flight campaigns on NRC and Airbus research aircraft. NRC’s testing protocol subjected the device to conditions at the mid-latitudes around Ottawa and at equatorial latitudes, at altitudes above 40,000 feet.
Although intended for use at the higher flight levels, the particle ice probe can detect icing in nearly any operating environment. “Testing indicates that altitude actually doesn’t have much effect,” added NRC research officer Craig Davison. “The sensor measures icing particles passing around it, so what matters is how quickly the sensor is moving.”
A similar goal also drove development of the ultrasound ice accretion sensor, which sends out acoustic signals to measure potential icing conditions inside an aircraft’s engine. The credit card-sized sensor detects the buildup of ice particles from airflow passing through the engine, as well as “classical” icing formed by super-cooled liquid water on engine surfaces.
Use of acoustic waves allows the sensor to be mounted anywhere near the engine, away from the intake and airflow. “The methodology behind both technologies is fundamentally similar, to be unobtrusive and easy to install, with the primary difference involving sensor design,” Fuleki noted. “In both cases, we needed to maximize the signal available while minimizing sensor ‘noise.’”
With development work on both systems largely complete, the NRC’s next step is to find manufacturers to support and implement the technologies. Although development has focused on the airline side, both systems offer readily apparent benefits to general aviation and business aviation users.
That brings up the question of cost. “Our rough idea throughout development is that wide-scale equipage wouldn’t happen at $1 million,” Davison added, “and that was part of our engineering considerations. The industry has vetted these technologies throughout the process, and I think they would have told us a while ago if these systems appeared to be cost-prohibitive.”
“Our hallmark at the NRC is that from the beginning, we involve the industry and regulators so that we may better understand their needs,” Fuleki noted, adding that the NRC is “nearing the threshold for commercialization” for both systems. “We don’t expect implementation of either system to present any more complexity than other sensors on an aircraft.”