“Our intent is to put a number of demonstrator engines through a pretty rigorous characterization and test program, prove that we understand the technology and that we’re completely ready to productionize it,” Geer says.
Standing up to Super Speeds
Hypersonic aircraft, used primarily by the defense and weapons industry, are designed to travel high in the earth’s atmosphere at speeds ranging from Mach 5 (about 3,800 mph) to Mach 20 (about 15,000 mph) or more. One of the biggest challenges in designing aircraft for these speeds is developing materials that can handle the effects of atmospheric drag.
A hypersonic vehicle must withstand temperatures ranging from around 1,200 degrees F to more than 4,000 degrees F in certain areas, depending on how fast the aircraft is traveling. “The ability of the materials and structure to react to rapid changes in temperature and to work properly when the vehicle experiences large temperature differences over various parts of the structure is absolutely essential,” says Chris Boshers, senior director and chief engineer of defense engineering at Spirit AeroSystems.
The structures that provide thermal protection for a hypersonic aircraft require high strength and stiffness because they also have to withstand the large dynamic pressures and g-loadings (forces of acceleration) of hypersonic flight. Composite materials can provide these properties, but those unidirectional fibers may suffer from delamination and premature failures.
“The strongest and most efficient temperature materials [for hypersonic aircraft] have fibers oriented in three directions to react to three-dimensional applied loads,” Boshers says.
To produce these hypersonic-ready composite materials, Spirit AeroSystems, which has expertise in material design and fabrication, recently acquired FMI, which has been developing and producing high-temperature composites for more than 50 years. The combined teams hope to improve the value proposition for hypersonic flight by making the required materials, and thus the aircraft, more affordable, more efficient and producible in quantity.
Spirit is working with two different types of composite materials for hypersonic applications – carbon/carbon and ceramic matrix. Carbon/carbon (C/C) composite materials can maintain high strength at temperatures above 4,000 degrees F while also retaining a predictable aerodynamic strength. In hypersonic aircraft, C/C composites are used for nose tips, control surfaces, thermal protection systems (TPS), aeroshell applications, and the nozzles and throats of rocket motor exhaust systems. Other potential applications include TPS for space re-entry vehicles, heat shields and high-temperature engine components, as well as oven walls and high-temperature probes for industrial applications.