New Aviation Anti-Ice Approach

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A promising new technology for airplane ice protection was reported by researchers at the Virginia Tech University – it eliminates the use of both heating elements and chemicals in removal of ice that can accumulate on aircraft’s wings, thus potentially endangering the flight. The technique is therefore more energy efficient and environmentally friendly. It involves the use of stripes made of silicone dioxide materials that are attached to the aircraft’s control surfaces. The researchers tested the concept and found that under subfreezing temperatures, cold water on the stripes’ surfaces changed to ice, attracting water droplets on the areas not covered by the stripes. As a result, the uncovered spaces in between the stripes remained dry. With no track of water at the surfaces uncovered by the stripes, it is expected the ice to be accumulated in the areas that are less sensitive to the flight mechanics, if installed strategically, and so the ice may be controlled in terms of formation and removal [1].

Ice prevention on the aircraft’s control surfaces is a subject that has been of interest since 1950s. The extra load created by the formation of ice on the control surfaces, especially leading edges in the form of clear, rime, frost, large super-cooled droplet, or a combination of them, reduces the aircraft’s effective lift force and increases the stall speed—the cause of the majority of ice-related incidents during the cold season. Most of the incident reports associated with aircraft icing are related to accumulation of ice on the air frame or inside the engine during the takeoff when the anti-icing measures are not fully observed. Piston and turboprop aircraft are among the fleet that are more sensitive to the ice formation since their engine’s bleed air is not hot enough to either prevent ice formation or melt the layer that has already been formed. There are special certification requirements for aircraft’s ice-prevention systems.

There are ice prevention and removal techniques such as installing boots, made of flexible materials at the leading edges of the wings and other sensitive control surfaces. The pressurized air bled from the engine pulses through the interior of the boots, eventually breaking the ice under cyclic stresses. There is also possibility of using electric heating elements in the control surfaces and therefore preventing ice formation. Hybrid approaches employ the combination of these techniques.

The formation of ice creates extra load on the control surfaces being barely balanced by the thrust component generated when employing set recommended flight performance data. Tactile checks either visually or using hands are highly recommended before taking off; however, they may not be as effective as one would hope; especially, when using gloves. Installing ice detectors although possible may not be as reliable since they may be only sensitive to detecting ice when the ice layer is as thick as 0.5 mm.

There are ice tunnels in which the behavior of aircraft contaminated by ice, fully or partially, or when exposed to the super-cooled water droplets (just below 0 degree Celsius), is studied. This phenomenon can also be analyzed using CFD models to improve the design or investigate the effectiveness of ice controlling devices. In addition to the said methods, remote ice detecting sensors are being studied in which the 3D location of the ice both airborne and on the ground can be detected and reported to the crew.

Although it is possible to set the stall speed using an ice-speed button in number of aircraft models so that the stall warning goes off at higher speeds, the best approach is to check the weather reports, pilot operating hand books for allowable ice conditions, and especially ensure the combination of the outside air temperature and humidity level is not amenable to the formation of ice.

UK Civil Aviation Authority (CAA) has launched a de-icing awareness campaign: “Don’t think twice, de-ice” [2].

NASA Glenn Research Center campaign: “We Freeze to Please”.

References:

[1] “Ice Stories: The End of Frost o Airplanes,” ASME Mechanical Engineering, 02(141), February 2019.

[2] https://www.flightglobal.com/news/articles/breaking-the-ice-201743/