Material gains underpin modern supersonic and hypersonic aircraft

Joseph Flaig

Projects such as the Overture from Boom Supersonic are using new materials to overcome the stresses and strains of supersonic flight (Credit: Boom Supersonic)
Projects such as the Overture from Boom Supersonic are using new materials to overcome the stresses and strains of supersonic flight (Credit: Boom Supersonic)

Boom Supersonic’s name is an explosive statement of intent, neatly illustrating the firm’s aim of transforming business-class commercial aerospace with a new supersonic airliner.

In reality, however, the Colorado start-up hopes that its Overture craft will be quieter than the company name suggests. The firm recently announced a collaboration with Collins Aerospace Systems to work on systems that could help reduce aircraft noise. 

“Through improved acoustics and lightweight materials systems, we can provide the next generation of supersonic propulsion systems with the nacelle technologies that not only enable higher performance and lower fuel burn, but also quieter operation,” said Marc Duvall, president of aerostructures at Collins Aerospace.

The engineering team will explore the development of advanced acoustics and variable inlet and exhaust technologies to minimise noise for passengers and airports, while also aiming to enhance performance. 

Lightweight innovation

Materials innovation is a key part of Boom Supersonic’s mission. Reducing aircraft weight is an important aim, letting it use more carbon-neutral jet fuel from Prometheus Fuels. 

The company’s prototype XB-1 aircraft makes use of materials including titanium, which will form the main landing gear bulkhead. Weighing just 30kg, the 100mm-thick plate offers one of the highest strength-to-weight ratios of any material in the aircraft. 

Elsewhere, 3D-printed brackets and clamp blocks are made from the thermoplastic Ultem 9085. The parts are strong, lightweight and flame retardant, while also enabling quick design iterations. 

The key enabling materials for Boom Supersonic, however, are carbon composites. Unlike aluminium, carbon composites can be moulded, allowing careful control of the aircraft cross-section to reduce drag while maintaining high strength. The materials will be key to withstanding the extreme temperatures of supersonic flight, which could reach more than 125ºC. Those high exterior temperatures saw Concorde’s aluminium alloy airframe expand and contract up to 30cm during flight.  

The Overture’s composites fuselage, on the other hand, has a low coefficient of thermal expansion, meaning it will stretch less while at high speeds. This reduces wear and tear, cutting maintenance costs and enabling higher speeds. 

Advanced materials technology could reduce the effects of high temperatures on other supersonic projects. Researchers at Drexel University in Pennsylvania and North Carolina State University took inspiration from human veins, which help cool us during hot weather, to develop a computational platform for the creation of ‘microvascular composites’. 

Active cooling

The platform produces designs for vascular networks with the ideal configuration of micro-vessels to actively cool material through liquid circulation. These designs can then be built into 3D-printed carbon-fibre composites, giving the usual benefits – low weight, high strength and durability – with improved cooling and more uniform temperature distribution. 

Of course, as speed increases, so does the heat. Shock waves at hypersonic speed – Mach 5 and above – can create such intense thermal loads that extra protection is needed to prevent holes burning through aircraft exteriors. 

Materials to prevent such catastrophic damage are likely to receive increased focus in the coming years, especially after the announcement of a hypersonic Air Force One project from US firm Hermeus. Suitable candidates could include carbon-fibre-reinforced polymer composites or boron-nitride nanotubes.

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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers. 


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