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Y-20B Up-Engined = Stretched?

Y-20 The Xi'an Aircraft Industry (Group) Company Ltd under the state-owned Aviation Industry Corporation of China, the maker of the Y-20, released a photo that showed a turbofan engine with a high bypass ratio that had never been seen before, Beijing-based Aerospace Knowledge magazine reported on 21 November 2020. This engine is probably China's domestically developed WS-20, and if this speculation is true, it is the first time the WS-20 has made a public appearance in an official media source, the magazine said.

Unverified photos and videos of a Y-20 with serial number 7810 have been circulating on social media in 2021. The engines of this particular Y-20, dubbed by military observers as the WS-20, are shorter but have a larger diameter than the current ones in service, meaning they have a higher bypass ratio, the eastday.com report said, noting that the AVIC's Weibo post could be the first confirmation on these speculations.

The bypass ratio on turbofan engines refers to the ratio between the air flow of the bypass stream and the air flow entering the core. An engine with a high bypass ratio is shorter but with a larger diameter. Usually, engines with a high bypass ratio are larger but consume less fuel, making it suitable for long-range transport aircrafts while engines with a low bypass ratio are used on fighter jets, the report said, noting that the Y-20s currently in service are equipped with engines with a medium bypass ratio and their power and fuel efficiency are not optimal.

With the new engines, the Y-20 will get a boost in not only range and endurance, but also in cargo capacity. In a program aired by China Central Television in November 2020, Chinese military experts also revealed some new information on the WS-20. Song Xinzhi, one of the experts, mentioned that compared with the Russian D-30 engine currently used on the Y-20, the Chinese engine is much larger in diameter and can provide more powerful thrust, uses less fuel, and enables the plane to take off and land in shorter runways. Although the Xian Y-20 is far less exciting than China's advanced fighter jets, the Xian Y-20 is equally important or even more important when it comes to achieving China's ambitious overseas strategy. The ability to use aircraft that do not rely on the support of foreign entities to transport super-large cargo over transnational distances has given China a high-speed logistical support to support more and more bases and military operations outside of mainland China. In other words, Y-20 is crucial to China's core foreign policy and national defense strategy.

The design of the Y-20 is somewhat similar to that of the American C-17 transport aircraft. Its main limitation is still the engine. Currently, the Russian middle bypass ratio D-30KP-2 turbofan engine is used. China's ultimate goal is to use the domestically produced WS20 turbofan engine with a large bypass ratio on this model, so as to maximize the design potential of the aircraft and eliminate any major external dependence. Flight testing is in progress, but WS-20 will not be put into production until 2024. This is only an estimated timetable.

With the continuous increase of the Chinese military's activity area in the future, the pace of actual combat exercises on the Yun-20 will continue to increase in the future, and the distance to participate in major transportation activities will also become farther and farther. For example, Chinas military base in Djibouti, Africa, is 8,000 kilometers away from Beijing in a straight line and more than 5,000 kilometers away from Xinjiang. In the future, Yun-20 is very likely to participate in the transportation of personnel and supplies to the base. The voyage, especially the voyage in the reloaded state, poses a severe test. In the future, the Chinese army may also carry out various activities in more distant areas, such as direct delivery of personnel and equipment to Chinese overseas peacekeeping forces, and emergency evacuation operations, which may require transport -20 to participate. In this case, the range of Yun-20 may be lacking.

As initially seen, the aircraft appears to be powered by four WS-18 low-by-pass engines [the Chinese version of the Russian Soloviev D-30KU], each with a power of 21,000 pounds of thrust. Ultimately it is expected that the Y-20 would be powered by the WS-20 [the long delayed Chinese copy of the 1960s vintage American GE F101 engine] with a power of 27,600 pounds of thrust each, or more likely the highly fuel efficient CFM LEAP-X high-bypass engine with a power of about 30,000 pounds of thrust each. The narrow dimensions of the engine nacelles, indicative of a low-by-pass engine, are in rather striking contract to the pleasingly plump engine nacelles of the American C-17, which is powered by four Pratt & Whitney F117-PW- 100 turbofan engines, each with a thrust of 40,900 pounds.

Fitted with high-lift devices on the wing's leading and trailing edges, the aircraft would be capable of taking off from relatively short and unpaved runways, giving access to temporary airfields near the battlefield. It is unclear whether the aircraft will have an IFR probe installed or not. The four engines that would power the Y-XX remain a focus of speculation. While the project is planned with Ukrainian development assistance, it is unclear whether China would use home-made engines or get the engine production line from Ukraine. The prototypes and the initial production run may be powered by the WS-18 turbofans (Russian D-30KP-2), while later production aircraft would be powered by a High Bypass Ratio [HBR] turbofan derived from the modified FWS-10 by 603 Institute.

In 2012, China's large bypass ratio turbofan engine exhibited at the Zhuhai Air Show. It is reported that the engine has four major characteristics: high efficiency, low fuel consumption; high reliability, long service life; low emissions, low noise; low maintenance costs, good repairability, will be used in domestic large aircraft.

Bill Sweetman and Bradley Perrett noted in February 2013 that "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.... 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.... 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. ... With abundant thrust and, it is hoped, world-class efficiency, the CJ-1000 would transform the performance of the Y-20."

Y-20In April 2013, a photo of a turbofan engine with a large bypass ratio in the flight test of China's Il-76 aerial test rig was exposed, causing widespread media attention. It is reported that this photo shows a new engine that is different from the Russian-made D-30 engine. It is installed on an Il-76 aerial test bed. The nacelle and structure of the engine are similar to the American CFM56-7 engine and GE90 engine. Some analysts pointed out that this engine is Chinas self-developed turbofan-20 large bypass ratio turbofan engine based on the "Taihang" engine. This engine will be mainly used for the Yun-20 large transport aircraft. The main power of large passenger planes, new twin-engine medium transport aircraft, flying-wing long-range stealth bombers and second-generation long-range anti-submarine patrol aircraft. [In April 2016, photograph emerged of the Il-76LL transport aircraft near the airport of the Russian Flight Laboratory in Perm with the PD-14 engine under the wing. This marked that the engine has entered the flight test stage.]

In January 2014, a photo of a turbofan engine with a large bypass ratio was exposed on an air test in China. This photo showed a new engine completely different from the Russian-made D-30 engine, which was installed on an air test bench. Tests show that the nacelle and structure of the engine are similar to the American CFM56-7 engine and GE90 engine. Some analysts pointed out that this engine is Chinas self-developed turbofan-20 large bypass ratio turbofan engine based on the "Taihang" engine. This engine will be mainly used for the Yun-20 large transport aircraft. The main power of large passenger planes, new twin-engine medium transport aircraft, flying-wing long-range stealth bombers and second-generation long-range anti-submarine patrol aircraft.

Y-20According to foreign media speculation, the turbofan engine with a large bypass ratio had entered the flight test stage and would be put into use in the next 5 to 7 years. So far, China had become the fifth country after the United States, Britain, France, and Russia that can independently develop high-performance turbofan engines with large bypass ratios. This type of engine not only fills an important gap in Chinas aero engine field, but also serves as a major milestone in the development of Chinas aero-engines, it can be said that after this hurdle, Chinas aero-engines will officially enter the "fast lane" of development, just like breaking through the "window paper". According to a news report on March 12, 2017, Tang Changhong, member of the National Committee of the Chinese People's Political Consultative Conference and chief designer of Yun-20, said in an interview with the West China Metropolis Daily that the Yun-20 has a timetable for installing domestic engines. "About two years later, we can see the Yun-20 with domestic engines."

In July 2008 CFM International launched LEAP-X, an entirely new baseline turbofan engine to power future replacements for current narrow-body aircraft. CFM International (CFM) is a 50/50 joint venture between Snecma (SAFRAN Group) and General Electric Company. LEAP-X1C engine will be assembled in China. LEAP-X thrust baseline for the C919 starts at 30,000 lbs - with much more growth potential. The first full demonstrator engine was scheduled to run in 2012, and LEAP-X could be certified by 2016. The LEAP-X1C-powered C919 is the beginning of a new chapter in the collaboration between CFM, the Chinese aviation industry and Chinese airline customers - a relationship that goes back more than 25 years. as of 2010 there were more than 2,300 CFM56 engines in service or on order with Chinese airlines, representing more than 10 percent of CFM's commercial fleet.

The WS-20 is a high-bypass turbofan being developed to power the Y-20 strategic airlifter, based on the core of the low-bypass turbofan Shenyang WS-10A. In 2014 a photo of a large bypass turbofan engine flying in China's Il-76 air test bed was exposed. This photo shows a new engine completely different from the Russian-made D-30 engine. Tested, the engine nacelle and structure are similar to the US CFM56-7 engine and GE90 engine. China's heavy strategic transport aircraft Yun-20 has no suitable domestic engine for the time being, so the test flight Yun-20 is the same as the current Il-76, and both are equipped with D-30 engines. In February 2019 a picture came out from the Internet showing that the Yun-20 783 prototype aircraft that had been flying at the Zhuhai Air Show was replaced with a turbofan engine with a large bypass ratio than the D30 on the inside of the left wing. The WS-20, which has been in development for more than 20 years, began testing before formal equipment. This engine is far better than the Russian-made D30KP-2 engine with a small bypass ratio in terms of fuel consumption and thrust, and will allow the Yun-20 to reach the designed load and range.

In February 2020, another image appeared, possiblly showing two D-20 engines on the starboard wing.

Y-20, Possible  WS-20 engine, February 2019 Y-20, Possible  WS-20 engine, February 2020 Y-20, Possible  WS-20 engine, February 2020

In the future, Yun 20 can not only use the turbofan 20 to replace the D-30KP-2 engine, but also replace the turbofan 20 with a newer generation CJ1000A turboduct engine with a higher bypass ratio, or use the former technology to improve the latter. This can both improve the performance of Yun 20, especially the performance of critical load range. On the other hand, it can also verify the practical application of the new generation of domestic turbofan engines with large bypass ratios, laying a foundation for the commercial use of domestic turbofan engines with large bypass ratios and accumulating experience.

The Lockheed (now Lockheed Martin) C- 141 was the first jet aircraft designed to meet military standards as a troop and cargo carrier. The C-141 became operational within the US Air Force in 1965. According to US Air Force studies, C-141 payloads were almost always limited by available floor space or cabin volume [the Space Shuttle encountered the same issue]. Since space limits are generally reached before weight limits, excess lift capacity goes to waste. The primary reason for this is that the density of bulk and oversize cargo is frequently less than the optimal density of cargo in which lift potential equals volume limits (known as the cross-over cargo density) in the C-141. By increasing volume capacity without changing lift potential, the crossover cargo density is lowered, bringing it more in line with actual cargo densities. Ironically, stretching the C-141 would decrease its maximum airlift potential because of the added weight of the two fuselage inserts. Productive airlift would increase, however, because remaining lift could be used more efficiently.

The actual increase in productivity varies by type of cargo. A light unit, like the 101st Airmobile Division, would still fill out the cargo compartment before reaching payload limits. Nonetheless, the proportionate increase in payload with the modification is greater for lighter divisions than for heavier divisions.

To use the C-141 capacity fully, the US Air Force proposed to manufacture and insert an additional 23 feet of fuselage on the fleet of C-l41s. This would increase their potential payload by as much as 30 percent, with only an insignificant increase in annual operating and personnel costs. In 1975, the Lockheed Corporation proposed (1) increasing the length of the C-141 fuselage by over 23 feet to increase its cargo volume by 3 pallet positions and (2) adding an aerial refueling capability. In 1977, the Air Force approved the stretch proposal. The first stretched aircraft was delivered to the Air Force in December 1979 and the final modified aircraft was received in 1982. As of June 1992, there were 265 stretched C-141 aircraft in the AMC fleet. The C-141 stretch program clearly provided increased lift capacity at less cost than procuring new organic planes, ven though the longer airframes were powered by the same engines as the original shorter aircraft.

It would stand to reason that new "Y-20B" aircraft equipped with more powerful high-bypass turbofans would also feature such a stretched fuselage to take full advantage of the more powerful engines.

Y-20 Military Transport

Y-20 Military Transport




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Page last modified: 19-07-2021 18:26:47 ZULU