As aircraft companies prepare to introduce hypersonic flights that can travel from London to New York in just two hours, manufacturers are developing a new jet coating that is up to the task of handling the increased speed and temperature. Researchers at the Royce Institute and the University of Manchester have partnered with the Central South University of China to develop a coating made of zirconium carbide, a compound used on drill bits. The material is reinforced with a carbon-carbon composite, a substance used in braking systems for Formula One cars. The resulting combination is capable of protecting aircraft flying at speeds up to five times the speed of sound under temperatures up to 3,000 degrees Celsius.
Innovations like this illustrate the scientific research required to develop materials durable enough to handle the stresses planes experience during flight. Here’s a look at three of the amazingly resistant materials that make air travel possible.
Early airplanes made extensive use of wood, but wood splinters easily and requires heavy maintenance, so as early as the Wright Brothers, aircraft designers began using aluminum. Aluminum is one quarter as strong as steel, yet only a third as heavy, as well as significantly more malleable. Unlike steel, it doesn’t rust, making it more resistant to corrosion. Due to these advantages, aluminum makes up approximately 80 percent of the weight of aircraft frames, with widespread use for wings, fuselage and supporting structures.
Current aluminum research and development focuses on the casting process, aiming to lower manufacturing costs while allowing more flexibility for shapes and designs. Three-dimensional printing is helping cut costs and empower developers to experiment with more designs. The future use of aluminum lies with aluminum-lithium alloys. Lithium is even lighter than aluminum and can lower the weight of single-aisle fuselage applications by up to 10 percent compared to other options, improving fuel efficiency by 20 percent, while also cutting costs by 30 percent. Aluminum-lithium alloys are also less susceptible to lightning strikes than alternatives.
While aluminum has many advantages, one of its drawbacks is that it cannot withstand high temperatures, making it unsuitable for skins on planes that travel at twice the speed of sound. This has helped make titanium a popular alternative to aluminum for airplane exterior frameworks. While not as light as aluminum, titanium is as strong as steel, and it resists high temperatures and erosion better than either substance, with a melting point of 1,668 degrees Celsius. It can sustain long periods of exposure to salt water vapor, making it particularly useful for flying in coastal areas. Its ductility makes it easy to shape, while it is nonmagnetic and a poor conductor of electricity and heat, making it less susceptible to damage from these factors. These properties have made titanium a common material for parts of aircraft exposed to high temperatures, including skins, engines, landing gear and other components.
Titanium is relatively expensive, but innovations are helping lower costs. Boeing has found that 3-D printing can lower the cost of titanium parts by as much as $3 million per plane.
While titanium is resistant to the high temperatures generated by airplane engines, it is not suitable for all engine parts. For instance, seals are needed to prevent oil leaking and control air flow, and these are typically made of rubber.
To accommodate rubber to the high temperatures and chemical environment of aircraft engines, aircraft manufacturers have adopted Viton, a material made of synthetic rubber and fluorocarbon polymers. Long used for SCUBA tank o-rings, Viton can handle a wide temperature range from -40 Celsius to 230 Celsius. It also has high resistance to chemical change and swelling in fuel mixtures. All these properties help make it an ideal material for seals in aircraft engines.