Lightweight heat shield protects superfast aircraft

Carbon nanotubes form the basis of “buckypaper” material to protect hypersonic aircraft in flight

While passengers endure 19 hour non-stop flights from London to Sydney, aerospace researchers are working on ways to speed up flight. Materials scientists from Florida State University (FSU) reports in the journal Carbon that they have developed a thin, lightweight material that they believe could help shield aircraft from the intense heat that they would experience flying at  around five times the speed of sound.

hypersonic
Professor Zhiyong (Richard) Liang and research faculty member Ayou Hao holding pieces of carbon fibre reinforced polymer composites with a protective heat shield made of a carbon nanotube sheet that was heated to a temperature of 1,900 degrees Celsius. Image: © 2019 FAMU-FSU College of Engineering

Hypersonic flight has always been dogged with problems of high temperatures, caused by friction from air resistance. In experimental ramjet-powered flights in the 1960s, high temperatures caused by shock waves that melted parts of the aircraft. But as with all materials problems in aerospace, light weight is crucial. Increasingly, builders of fast jets, rockets and satellite launchers are turning to lightweight carbon composites, but these tend to behave poorly at high temperatures so attention is turning to heat shield materials. But these too have to be light, and current materials tend to form heat shields that are thicker than the material they are protecting.

“Right now, our flight systems are becoming more and more high-speed, even going into hypersonic systems, which are five times the speed of sound,” said Professor Richard Liang, director of the High Performance Materials Institute at FSU, who led the research. “When you have speeds that high, there’s more heat on a surface. Therefore, we need a much better thermal protection system.”

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Further reading

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The material described in the Carbon paper is formed from sheets of carbon nanotubes – which the team refers to as “buckypaper “ – soaked in a phenol-based resin. This yields a lightweight, flexible material that can form a heatproof skin that protects the aircraft structure while also providing mechanical reinforcement.

Testing the material with a blowtorch showed that the material retains much of its strength and flexibility after heating, in contrast to ceramic-based heat shield materials which are prone to cracking after heating.

The buckypaper material retained 39 per cent  of its flexural strength and 70 per cent of its modulus of elasticity after heating, in comparison to 11 per cent  and 21 per cent  for a standard carbon fibre reinforced plastic control material.