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Avic Y-20 Airlifter Awaits Better Engines

avic Y20 600x400

This article first appeared in Aviation Week & Space Technology.

If ever there were an aircraft that should grow in capability, China's newly flown Y-20 airlifter would be it. The prototype that took to the air on Jan. 26 mates what looks like a modern airframe with obsolete 1960s-technology engines. Together, they probably represent no more than a serviceable design standard, offering only modest advances in capability over the Ilyushin Il-76 that China already operates.

But a better engine is under development for the Y-20. If and when China's technologically challenged aero-engine industry can get that high-bypass turbofan ready, then the airlifter should surge in performance. More distantly, a truly modern engine under development for the Comac C919 airliner could also be available.

Successful development of the Y-20 airframe is in itself an important accomplishment for the Chinese industry, which in more than six decades of Communist history has been only slowly and haltingly weaning itself from copying foreign types, mostly Soviet-era Russian designs. Underscoring this point, the Y-20 is the largest indigenous Chinese aircraft built so far, exceeding the unsuccessful Y-10 airliner tested in the early 1980s.

The Y-20 will not enter service before 2017, according to two Chinese military academics, Zhang He and Li Wei, writing in China Youth Daily, a major national newspaper. They also say that the Y-20 airframe incorporates composite materials (although most of it appears to be aluminum) and a “supercritical” wing. It is not clear whether the objective is to have a new engine ready by service entry.

The Y-20 is an entirely new design, even though it is close in size and shape to the Il-76, which uses the same Saturn D-30KP medium-bypass engine as the Chinese airlifter's prototype. Compared with the Il-76, the Y-20 has a shorter wingspan and a shorter, but slightly wider, fuselage. The Y-20 is larger than the Airbus A400M and has about the same fuselage diameter, but is much smaller than the Boeing C-17.

Specifications estimated by Aviation Week (see table) and including dimensions determined photometrically, vary from figures quoted by Zhang and Li. The academics say the Y-20's span is 45 meters (148 ft.), length 47 meters, height 15 meters, gross weight “over 200 tons” and payload 66 tons. They give no source, but their figures could be preliminary numbers estimated in 2006, when the project was launched after about 15 years of study. Comparison with the Il-76 suggests that the published weight and payload figures are too high for a version fitted with the D-30KP.

In late 2009, Hu Xiaofeng, the general manager of Avic Aircraft -- the large-airplane specialist subsidiary of aeronautics group Avic -- said the Y-20 was in the “200-ton class” and would be unveiled at the end of that year. But it was not unveiled then, suggesting that the airframe or engine program had hit trouble. The Xian Aircraft plant is building the Y-20, which was rolled out in December 2012.

The Y-20 follows the configuration set by the Lockheed C-141, with a high-mounted wing, moderately swept to combine good low-speed performance with reasonable cruising speed, fuselage-mounted landing gear and a T-tail. (Since the C-141, all successful jet airlifters have used that configuration, except the An-124, which has a low tail.) The Y-20's wing has full-span slats and triple-slotted trailing-edge flaps, the latter comprising two articulated segments with a fixed vane on the forward surface. The engines are hung low as on the Il-76 -- in its current form at least, the Y-20 does not use externally blown flaps in the same way as the C-17.

The ailerons can also droop to increase lift at low speeds, and large spoilers are fitted for roll control and lift dumping. Like the C-17, the Y-20 has a four-piece rudder, with upper and lower double-hinged segments. This provides both redundancy and the ability to use higher deflection on the lower half than on the upper rudder panels, reducing loads on the vertical tail.

In comparison with the Il-76, a smaller cockpit for just three crew members should have helped designers to increase cargo volume. Chinese media stress that the aircraft is fatter than the Il-76, the skinniest of the strategic airlifters now in service, though the difference may not be great. Extra diameter should help in stowing outsize items such as helicopters and engineering vehicles, but the Y-20's cargo bay is shorter than the Il-76's.

The landing gear looks similar in layout to the A400M's, with three separate twin-wheel units on each side. Operating jet airlifters from truly unimproved surfaces is more spectacular than practicable, but the Y-20 should be as good as any of its contemporaries in this regard. Zhang and Li say it can operate from “relatively simple” fields. The nose wheel can pivot 90 deg., they add, giving a detail that suggests they have been well-briefed. (Zhang is on the faculty of the Command College of the Second Artillery and Li is of the National Defense University.)

The Y-20's overall size and weight are such that it could be an effective aircraft with D-30KP engines, which China already imports for its H-6K cruise-missile carrier. At least 20% more thrust will probably be available from the Chinese turbofan that Avic Engine is developing at Shenyang, possibly under the name WS-20. It is believed to be a derivative of the WS-10 Taihang fighter engine.

In contrast to the medium-bypass D-30KP, it will have a high bypass ratio, making it comparable with the CFM56, to which it may be related. The Y-20 must have entered flight testing with the D-30KP because the Chinese engine was not ready -- perhaps not fully developed or maybe just not trusted for early flights.

A more distant prospect is the CJ-1000, which Avic Commercial Aircraft Engines is developing for the Comac C919 airliner as an alternative to the CFM Leap-1 and with the aim of matching the performance of that Franco-U.S. engine. CJ-1000 development faces great technical challenges but is probably being well funded. With abundant thrust and, it is hoped, world-class efficiency, the CJ-1000 would transform the performance of the Y-20.

The prospective use of the Y-20 raises a contradiction that has become familiar as the Chinese navy has developed its amphibious assault capability and commissioned an aircraft carrier. China's government consistently downplays its interest in power projection. And, like all authoritarian states, it strongly promotes the principle of non-intervention in the internal affairs of other countries. No wonder, then, that state media stress the humanitarian and disaster-relief role of the Y-20. Those will undoubtedly be prominent roles of the Y-20, internationally as well as domestically, helping China's image abroad.

As a tool of power projection, the Y-20 will probably not worry China's neighbors too much, says Andrew Davies, an analyst with the Australian Strategic Policy Institute in Canberra. Naval forces, which can transport much more than aircraft can, are likely to be of greater concern. “The Y-20 is part of the bigger picture of Chinese power projection, but it is a less significant element,” he says. Also, China is such a big country that the aircraft has obvious internal uses.

The country does, however, place strong emphasis on airborne forces, as Russia does. China has built a rapid reaction force around the 15th Airborne Corps, which is able to respond to crises within China and around its borders. It has continued to develop specialized combat vehicles designed to be air-dropped. The most recent type is the Norinco ZBD03, derived from the Russian BMD-3 and armed with a 30-mm 2A72 cannon. The 15th Airborne also operates with its own helicopter force, so the Y-20's relatively high and wide cabin will be useful in ferrying helicopters with minimal dismantling and reassembly. China's airborne force has been restricted in its mobility by the small available force of Chinese Il-76s.

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Aircraft Design People's Republic of China
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