Boeing has taken the wraps off of a new ultra-thin wing concept designed to improve the performance of transonic aircraft traveling at speeds of Mach 0.8 (593 mph, 955 km/h). The latest version of the company's Transonic Truss-Braced Wing (TTBW) can fly higher and faster than previous iterations thanks to its optimized support truss and adjusted wing-sweep angle.
We hear a lot these days about the return to commercial supersonic air travel and even the advent of hypersonic flight, but the real cutting edge in aerospace engineering at the moment is in transonic flight. Almost all flying outside of military circles takes place in the subsonic realm. That is, speeds under Mach 0.8 (609 mph, 980 km/h). However, in the highly competitive world of commercial passenger and freight hauling, that's not quite good enough.
You might be asking yourself, if the speed of sound is Mach 1 (767 mph, 1,235 km/h), why is subsonic below Mach 0.8? The reason is that the realm between Mach 0.8 and Mach 1.2 (913 mph, 1,470 km/h) is what is known as transonic. That is, the range of speeds just before breaking the sound barrier, and just after that's marked by an increase in air resistance and other factors that can be rough on an airframe.
Ideally, engineers would like to get as close to transonic as possible without pushing the sound barrier, but it's far from easy. That's because it isn't a matter of the whole aircraft going from subsonic to transonic. As one approaches the transition point, some parts of the plane will be over the limit while others will be below it. An example of this is prop-driven fighter planes at the end of the Second World War that would suddenly start to shake themselves apart because they were flying so fast their faster-spinning propellers were breaking the sound barrier.
According to Boeing, the TTBW was originally designed to operate in a range of Mach 0.70 to 0.75 (519 to 556 mph, 835 to 895 km/h), but the new truss, wing sweep, and integrated design allows for better speed and altitude performance by creating a thin, foldable wing with a span of 170 ft (52 m).
The purpose of this is not only to produce a better wing for transonic flight, but also one that is more eco-friendly. It was developed as part of NASA's Subsonic Ultra Green Aircraft Research (SUGAR) program, which aims at creating sub and transonic aircraft that are 71 decibels quieter than current FAA noise standards, have a 71-percent reduction in nitrogen oxide emissions, and burn 70 percent less fuel.
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