Satellite Images Reveal New Chinese Widebody Transonic Test Site

In its most recent commercial market outlook, Boeing forecasts China will need approximately 9,000 new airliners by 2044 to support projected growth, 1,550 of which will be widebody aircraft.

However, while China is on track to have the world’s largest widebody fleet, the big question is: Who will provide them? Although Airbus and Boeing—the only Western manufacturers of twin-aisle aircraft—will necessarily share the spoils for the next decade, Chinese civil aircraft developer Comac has other ideas. It plans to challenge the duopoly starting in the 2030s with new widebodies of its own, the C929 and C939.

• Mianyang complex includes at least five large-scale wind tunnels
• The new Chinese site appears to be similar to the European Transonic Wind Tunnel

To make this giant leap in airliner development capability, China first must fill critical gaps in its test infrastructure—particularly with sophisticated wind tunnels. Although modern aircraft aerodynamic design relies increasingly on advances in simulation tools like computational fluid dynamics (CFD), wind tunnels remain fundamental and have taken on new importance in validating results from simulations.

Satellite images of a vast new wind tunnel complex in Sichuan province in southwest China appear to reveal the existence of a nearly complete cryogenic facility able to test large, transonic transport aircraft at close to flight conditions. Dubbed the China Transonic Wind Tunnel (CTW), the facility is part of the world’s largest wind tunnel complex, built by the China Aerodynamics Research and Development Center (CARDC) in Mianyang to support the country’s commercial aircraft industry.

• Related content: 
  NASA Reshapes Aeronautics Research To Cope With Drastic Budget Cut

Developed in secrecy since 2007, the Mianyang complex was officially acknowledged in 2013. But the addition of the CTW, only noticed by Western observers in recent months, is a clear sign of China’s growing investment in facilities supporting development of indigenously designed widebody airliners as well as other large aircraft, potentially including blended wing body (BWB) transports.

Ironically, the expansion of China’s advanced test facility comes as NASA prepares to mothball several sites because of budget issues. The Trump administration’s 2026 budget calls for five of NASA’s 12 wind tunnels to be put into standby mode, an unprecedented number, says Robert Pearce, associate administrator for the agency’s Aeronautics Research Mission Directorate.

“The reason cryogenic tunnels came into being is because airliners started to get bigger, and so the gap grew between what you could test in a conventional tunnel and what you began to see in flight test,” a NASA expert says. “At that stage, CFD was virtually nonexistent, so you had a lot more surprises when you got to first flight.”

The CTW appears to be similar to the European Transonic Wind Tunnel (ETW) in Cologne, Germany, notes the NASA specialist, who is familiar with U.S. and European transonic test capabilities. Operational since 1994, the ETW is more modern than the world’s first cryogenic wind tunnel, NASA’s National Transonic Facility (NTF) in Langley, Virginia. The NTF was completed in 1982 and has been used to test the development of the Boeing 777 and 787 as well as the space shuttle orbiter, Northrop Grumman B-2 and several other research configurations, including BWB transports and supersonic airliners.

The NTF and ETW both use high-pressure, cold-temperature nitrogen as a test gas to enable evaluation of aircraft models at Reynolds numbers close to those encountered in flight. A scaling factor that measures the ratio between inertial and viscous forces in fluid flow, the flight Reynolds number can approach 50 million or more in cruise for large subsonic aircraft, but most conventional wind tunnels only operate at 10-20 million. The ETW provides test conditions equal to around 50 million for full-span models and 90 million for half-span models.

The use of cryogenic nitrogen gas as the working fluid increases the available Reynolds number by 5-6 times compared with a conventional wind tunnel. Nitrogen also reduces the power required to drive the wind tunnel fan by more than 40%, as its higher density requires less energy to move the same amount of gas.

An Airbus test specialist says the start of development of the CTW in 2007-08 coincides with Comac’s use of the closely aligned German-Dutch DNW wind tunnel organization to conduct tests of the C919 single-aisle aircraft. The Airbus expert adds that the internal layout and configuration of at least one of the DNW sites was later altered to improve security, after the Chinese test team was seen taking photographs of the facility and engineering documents.

A paper published in the Chinese journal Acta Aerodynamica Sinica in December 2023, authored by researchers from CARDC and the AVIC Aerodynamics Research Institute in Shenyang, included the CTW among a list of wind tunnels built since China launched its large civil aircraft program in 2007. Satellite imagery indicates work began in 2010 to clear the greenfield site south of Mianyang. The first major wind tunnel then took shape on the facility’s western boundary in 2013. Additional test areas and infrastructure quickly followed, and clearing of ground for the CTW and two other very large wind tunnels began in 2018.

Specialists note the “giveaways” that help identify the cryogenic tunnel include the presence of a tall vent stack and two large nitrogen storage tanks close to the facility. NASA’s NTF also has two nitrogen tanks, while the ETW has one. Described as a “low-temperature, continuous type” wind tunnel—the same description given to the NTF and ETW in the paper—the CTW is listed as having a 2.6 X 2.2-m (8.5 X 7.2-ft.) working section, Mach 0.2-1.6 speed range and a Reynolds number capability similar to that of the ETW.

“When the large aircraft special project was officially launched in 2007, China’s aerodynamic test equipment foundation, test simulation capabilities and test data correction technology were significantly behind those of developed aviation countries in the U.S. and Europe,” the paper states.

“Compared with the well-equipped transonic test equipment system in developed aviation countries in the U.S. and Europe, [China’s] main gaps are the serious shortage of transonic wind tunnels, the small size of wind tunnel test sections and the lack of high Reynolds number test simulation capabilities,” the authors write.

China’s growing wind tunnel capabilities are now thought also to include a transonic dynamics tunnel (TDT), similar to the long-running facility at NASA’s Langley Research Center. Unlike the CTW, which is focused on aerodynamic testing, the TDT is designed for high-risk aeroelastic and dynamic condition testing. It remains unclear if China’s TDT is also located within the Mianyang complex, which now incorporates at least five large-scale tunnels, including the CTW.

The Mianyang site’s immediate focus is expected to be on supporting the development of the C929 widebody, which is similar in size to the A350 and 787. Comac revealed at June’s Paris Air Show that detailed design of the C929 is underway, type certification is targeted for 2032 and service entry for 2035—significantly behind the initial plans when it was still a joint project with Russia. As with hopes for a stretched C919, Comac still needs government approval to unlock funding.

Designed to carry 282 passengers in a standard layout over a maximum of 6,500 nm (7,480 mi.), the C929 is planned to be followed by the C939, which is to be positioned as a competitor to the 777X. A service entry date and further technical details have not yet been made public.