Avicopter Pursues High-Speed Compound Demo

By Bradley Perrett
Source: Aviation Week & Space Technology
September 16, 2013

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.

Sikorsky 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.


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