Windshields and lateral cockpit windows of the future might be smarter than those of today, as manufacturers find new combinations of materials to extend functionality and meet the needs of sometimes contradictory requirements.
Designing a structural part that is essentially made of glass and is attached to a metallic frame presents a major challenge. A windshield or lateral cockpit window must withstand air pressure from the inside. It also has to endure huge thermal variations, from the cold environment at 30,000 feet to a hot apron in a Middle Eastern summer.
The heating system may be for anti-fog for the interior surface or anti-ice for the exterior surface. It must be failsafe. Finally, many flight deck windows require coatings to be applied for electromagnetic interference, electrostatic discharge and infrared protection, explained Meredith Siegfried Madden, CEO of Nordam. All these requirements conflict sometimes, noted Tony Salerno, general manager at GKN Aerospace Transparency Systems.
Several initiatives are under way to address these challenges. Saint-Gobain Sully, for example, is developing a new antistatic surface. It discharges the acrylic glass windshield, thus avoiding phenomena such as arcing blue flash, Thibaut Heitz, deputy CEO, told AIN.
The France-based company has also improved a de-icing system for curved windshields. “It is hard to spread current lines evenly so they have the same de-icing power everywhere,” Heitz said. The technology uses a laser to divide the heating layer into small elements. It is being used on the Airbus A350 XWB. SGS is endeavoring to make finer cuts and establish this technology as the new standard.
Heitz believes future enhancements will be based on a more holistic approach to the development process. For example, for de-icing, the windshield supplier should work with the manufacturer of the control system and the airframer, he suggested. Such cooperation, he said, could help reduce power consumption–now on the order of 10 kilowatts for de-icing the entire windshield.
Some areas are more prone to icing than others, and temperature sensors inside the windshield already record this data, but so far each stakeholder has kept a lid on its data.
At GKN Aerospace, for complex-shaped windshield de-icing, “We grade the coating’s thickness over the surface to have a constant heating,” Salerno explained. This is the case on many airliners and business jets, such as the HondaJet.
To reduce the weight of its system, GKN is replacing some layers of glass with acrylic laminates. “The challenge is that these two different materials have two different thermal expansion coefficients,” Salerno noted. GKN has found a solution with adhesion coating and lamination processes.
Modeling Efforts
Another area of progress should be modeling. Saint-Gobain Sully, in a joint effort with a commercial aircraft manufacturer and an aerostructure specialist, has validated 90 percent of a software program that simulates how the windshield deforms in a bird strike. “This won’t eliminate the need for certification testing, but it allows us to design a better windshield more quickly,” Heitz said. GKN’s Salerno hopes the database will grow over time and thus allow data analysis to replace some tests.
In modeling, Salerno also referred to the optical quality of a windshield. ASTM’s inspection consists of looking at a grid board through the windshield, in a dark room, to check for distortion. “We have proprietary tools to simulate a pilot’s view,” Salerno said.
As engineering analytical and design platforms such as Catia become more sophisticated, transparencies are becoming thinner and thinner to reduce weight, noted Nordam’s Madden.
GKN’s Salerno predicts windows will get larger and more complex over the next five years. New functional coatings and materials will appear, such as for hydrophobic and solar protection. The electrochromic technology used in dimmable cabin windows might find its way into lateral cockpit windows to reduce the heat load. However, it will have to be failsafe, Salerno emphasized.