Research about hypersonic vehicles has been ongoing for quite a while and the very idea sends chills down the spines of engineering. Imagine being able to travel in an aircraft moving at over 6000km/h (>Mach 5) – it would only take a couple of hours to move from Beijing to New York! As fun as this sounds, though, it’s not as easy. Moving at such a high velocity requires an aerodynamic configuration that will provide high lift coefficient, high lift to drag ratio (L/D) and high volumetric efficiency, all of which are now provided by the new Hypersonic I-shaped Aerodynamic Configuration (HIAC).

Principle test model (left) and artistic concept for future applications (right) of HIACs (Source: Science China Press)

A high L/D is always a priority for designers, since there’s a linear relationship between the flight range and L/D (Breguet’s equation). However, generic configurations have a hard time attaining a high L/D due to the massive viscosity and shock wave drag present in the hypersonic regime.

The waverider which was considered the most promising design, managed to achieve a high L/D but was volumetrically inefficient (with a figure of 0.12) and was too thin to accommodate enough fuel and payloads. The obvious solution to this was to transform the upper surface into an upwarp to increase the volume, but this increases aerodynamic drag and results in a lower overall L/D.

HIAC solves these problems by introducing a high-pressure capturing wing (HCW) to the top of the upwarp frame. According to the shockwave compression theory, the HCW takes the hit from the high-pressure airflow compressed by the vehicle’s upper surface. This consequently results in a significant increase in L/D, while still allowing for an improved volumetric efficiency. This, of course, opens the door to producing hypersonic vehicles of great volumetric capacity.

A HIAC test model with a 0.175 volumetric efficiency was generated and tested and the results showed that it enjoyed a much higher L/D (above 4.5) at Mach 5-7 and an increased lift coefficient, which was 60% better than generic configurations. With this novel configuration, hypersonic airplanes may be poised to replace their subsonic counterparts in the near future.

This research was carried out for over seven years by Prof. Kai Cui, Dr. Ying-Zhou Xu, Dr. Guang-Li Li and Dr. Yao Xiao of the Institute of Mechanics at the Chinese Academy of Sciences. Their finding was published in the cover page of the 2018 edition of Science China Physics, Mechanics & Astronomy. The full text is available here.