Taking a Cue From NASA's X-15, Chinese Engineers Test Skids for Landing Hypersonic Aircraft - Report

A team of researchers at Nanjing University of Aeronautics and Astronautics (NUAA) is reportedly planning to test out skids as a form of landing gear on the hypersonic plane they are designing, the South China Morning Post (SCMP) reported on Tuesday.

Wei Xiaohui, a professor at the university’s laboratory of fundamental science for national defense, told the Hong Kong-based paper that the design is based on existing technology and the aircraft will be able to land at almost any airport “as long as it has a concrete airstrip.”

Skids are most commonly seen on helicopters, certain types of seaplanes, or specific uses like the tail of the Blackburn Buccaneer, a Cold War-era UK attack aircraft, but not typically used for airplanes because they’re less maneuverable or cushioned than wheeled landing gear. However, there’s one historic instance of skids being used that’s relevant to the Chinese hypersonic plane: NASA’s X-15 rocketplane.

Built in the 1950s as an experimental high-speed, high-altitude aircraft, the X-15 holds the record for the fastest crewed, powered level flight on October 3, 1967, when it achieved Mach 6.7 (4,520 miles per hour) at an altitude of 102,100 feet.

The X-15 was basically a giant manned missile. It launched from underneath the wing of a B-52 Stratofortress and was powered by a massive rocket engine, with little room for anything else. That’s why its designers gave it two skids that popped out of the rear wings.

NASA's X-15 manned hypersonic research plane landing at Edwards Air Force Base, showing the experimental rear skids instead of wheeled landing gear.

The clumsy design meant the X-15 could only land on a dry lakebed and had to jettison part of its tail section just before landing so the skids could reach the ground. The legs were flimsy, too, and in 1962 one broke, sending the aircraft tumbling upon landing. However, according to the Nanjing researchers, they’ve found a way to steer after landing by applying brakes to each of the skids. They have also relied on machine learning algorithms to incorporate other factors, such as weather, to keep the super-fast plane on track as it lands.

However, the landing gear isn’t the only thing the NUAA team working on the hypersonic aircraft is borrowing from rejected American designs. In December, they tested out an engine that could switch from regular turbojet operation to a ramjet for reaching hypersonic flight, which is typically too fast for turbojets to reach. The design was originally proposed by a NASA engineer in the 1990s, rejected, shelved, and then declassified in 2011, the SCMP reported at the time.

Hypersonic aircraft and weapons travel faster than Mach 5, or five times the speed of sound, meaning they can cover enormous distances much more quickly than existing vehicles. For weapons, that means they can easily evade most air defenses, and for aircraft, it means arriving at your destination more than twice as fast as the fastest fighter jets and airliners, and five times faster than typical airliners. Such an aircraft could fly from Tokyo to Los Angeles in as little as two hours.

While several hypersonic weapons have been developed in recent years, vehicles are a little harder to manage because of their larger size and more fragile cargo that cannot handle the extreme stresses of such rapid acceleration.