Just three days after imagery surfaced of China’s first known crewed tiltrotor aircraft to take to the air, we have gotten our first sight of a previously unknown compound coaxial helicopter. The aircraft, the designation of which remains unknown, is also now undergoing test flights and is a direct clone of the U.S.-made Sikorsky S-97 Raider. The development confirms that China, too, is looking at harnessing the benefits of this kind of aircraft, which offers much higher speeds than a conventional helicopter, as well as increased maneuverability.
The images showing the new compound coaxial helicopter emerged today, apparently first being posted to China’s Weibo microblogging site. They show the rotorcraft in flight and immediately betray its close connection to the S-97. Most fundamentally, the Chinese design adopts the same propulsion configuration, with four-blade coaxial main rotors — which looks like a rigid design — and a pusher propeller. The Chinese aircraft appears to be of almost identical size and also has the same ‘tadpole’-like fuselage shape and landing gear configuration. Like the S-97, the Chinese helicopter also has a relatively large, plank-like horizontal tail with endplate tailfins. However, the tailfin design is different, with the larger part of the fin projecting above the tailplane, rather than below it.
At this point, it’s worth recalling that this is far from the first Chinese design to share a significant superficial resemblance to a Western aircraft. In the rotary field, the Harbin Z-20 helicopter is widely regarded as a Chinese clone of the H-60/S-70 Black Hawk/Seahawk, while the Chinese FH-97 drone looks like a carbon copy of the XQ-58A Valkyrie. These are just two examples, and while accusations of simply aping existing Western designs are an oversimplification, China has been accused on multiple occasions of hacking detailed design information from U.S. aerospace defense contractors.
Central to the compound coaxial configuration of the S-97/Raider X (and now the analogous Chinese rotorcraft) is the pusher prop in the tail and the rigid, contrarotating rotors that eliminate the need for a tail rotor. The pusher prop allows for bursts of speed and rapid deceleration, increased maneuverability, and a higher sustained cruise speed. Range will also be increased compared to a standard helicopter, although not to such an extent as a tiltrotor. Unlike a conventional helicopter, a compound coaxial like this can fly forward with its nose up or backward with its nose pointed at the ground, while the Raider has routinely demonstrated an ability to ‘pirouette’ nose-down around a single point.
These compound coaxial helicopters can also fly at top speed while maintaining a level attitude, compared to a regular helicopter that has to point its nose down to accelerate forward. In forward flight, the pusher prop can be activated, and the spinning rotors are slowed to act more like wings than rotors, reducing drag and boosting speed and efficiency. Essentially, unlike a standard helicopter where the blades create lift during only part of their rotation, the rotor blades generate lift on both sides of the aircraft as they spin.
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