China's rotary-wing specialist reveals work on advanced concepts
Avicopter has joined the trend for developing high-speed helicopters. The Chinese manufacturer is building a technology demonstrator with a compound configuration that combines coaxial rigid rotors and nose-mounted, counter-rotating propellers.
A smaller test aircraft less than two meters long has been flown for at least a year under manual control to lay groundwork for the technology demonstrator, an unmanned aircraft designed to fly at 450 kph (280 mph). That 800-kg (1,760-lb.), turbine-powered aircraft, named Jueying, is to fly within a few years, industry officials say. Avicopter, the rotary-wing division of Chinese aeronautics state group Avic, would eventually like to build a manned aircraft with the technology, but that possibility is far in the future.
Since Avicopter has revealed the project publicly—at the China Helicopter Exhibition on Sept. 5—and officials speak only of hopes of signing a customer, it is evidently not sponsored by the Chinese army. At the show, Avicopter displayed a 1:1 model of the small test aircraft, which itself appears to be a faithfully scaled version of the forthcoming demonstrator.
The manufacturer has chosen counter-rotating, coaxial rigid rotors to overcome the intrinsic problem of driving a conventional helicopter at high speeds: With a single rotor, parts of retreating blades stall and therefore lose lift, while advancing blades have so high an airspeed, because of their necessary length, that they suffer badly from shock waves. With two rotors, the blades can be shorter, and with counter-rotation the loss of lift on each side is balanced; a fixed wing is unneeded.
tested this idea as the Advancing Blade Concept with its XH-59 in the 1970s, though that aircraft used jets for propulsion. The recent Sikorsky X2, tested from 2008-11, has a configuration closer to that of the Jueying, but with a single aft propellor. It demonstrated 460 kph.
Avicopter believes 500 kph is achievable with a compound, coaxial configuration. The Jueying's counter-rotating propellers improve stability, the manufacturer adds, but their location would hardly suit an attack helicopter, which must be able to mount sensors and weapons forward. Also, its drive shaft passes through the usual location of a cockpit and the main rotors are spaced farther apart than on the highly rigid arrangement of the X2.
The Jueying's tailwheel landing gear arrangement also suits high speed, Avicopter says, without elaborating. The overall configuration of the aircraft makes it stealthier than conventional helicopters, adds the manufacturer. Military tasks would include battlefield reconnaissance and attack, but the concept would also have civil roles.
The Jueying demonstrator will have a rotor diameter of 4 meters (13.1 ft.) and propeller diameter of 1.3 meters, says Avicopter. The fuselage will be 5.12 meters long and 0.76 meters wide. Height will be 2 meters, and the structure mainly composite. The complex mechanical arrangement is notable, since one of Avicopter's weaknesses is in the technology of dynamic components.
At the show Avicopter also exhibited its Feihong vertical-takeoff-and-landing airplane, a technology demonstrator that is in flight testing. A lift fan is embedded in the middle of the airframe of the aircraft, driven by a piston engine.
Flight testing revealed only straightforward problems at first, say officials, but the program is now working with advanced issues, such as trying to find the optimum method of achieving maximum altitude: with wing lift only, or with the aid of the fan. The Feihong is also a project of Avicopter's Changhe Aircraft at Jingdezhen. The aircraft, not a model, was displayed at Tianjin.
A bold but presumably distant concept displayed in model form at the show was the Blue Whale, a four-engine tiltrotor with a designed payload of 20 metric tons (44,000 lb.). Similar to the Jueying, it is far more likely to be an idea hatched within Avicopter than a project of the Chinese military, though an army or navy order would surely be needed to launch development.
The Blue Whale features two mainplanes, with tilting engines on the tips, a tail fin on the portly body, but no tail planes. The span of the forewing is less than that of the aft wing, reducing interference between the two sets of rotors, though they overlap by more than half their diameter. Loading is apparently through a rear door, as usual for a military airlifter.
With unusual precision, range is estimated at 3,106 km (1,930 mi.), maximum speed 538 kph, ceiling 8,615 meters (28,264 ft.) and “combat radius” 815 km.
The Blue Whale could satisfy future army and navy requirements, says Avicopter, adding that the aircraft would be able to maintain safe flight with only two engines operating. “It uses distributed integrated avionics to improve mission capability and to cope with air turbulence,” the manufacturer says in a brochure. Flight controls would be signaled with fiber optics and the structure would include some composite material.
—With Graham Warwick in Washington.