Design Flaws in B-21 Raider? China Claims Its Software Exposed Issues in U.S. $203B Stealth Bomber – Reality Check

For the US Air Force (USAF), a lot is riding on the USD 203 billion B-21 Raider program. The long-range stealth bomber will eventually replace the aging fleet of B-1 Lancers and B-2 Spirit bombers, providing the US with advanced capabilities to deliver both conventional and nuclear strike missions.

The USAF has committed to buying at least 100 B-21 Raiders, with some recommendations pointing to a need of 145 to 200 aircraft to meet modern strategic needs against threats like China and Russia.

While the overall program cost was pegged at US$203 billion in Fiscal Year 2019 dollars, just the development of the stealth bomber could cost over US$25.1 billion.

As of now, Northrop Grumman has delivered two flight-test aircraft, and testing is underway at Edwards Air Force Base, California.

However, a new research paper published in China claims that their newly developed aerospace simulation tool has uncovered several structural weaknesses in the B-21 Raider’s design, potentially limiting its aerodynamic stability.

The powerful stealth aircraft design software, ‘PADJ-X’, has been described as an “all-in-one” system, highlighting its interdisciplinary approach to aircraft design and simulation testing.

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The software system, based on adjoint optimisation technology that integrates multiple engineering disciplines into a single optimization process, was unveiled last month in a paper published by the peer-reviewed Acta Aeronautica et Astronautica Sinica.

China’s Big Claims on B-21 Raider

The paper claims that PADJ-X might be the first fully integrated, multidisciplinary platform for stealth aircraft design, and uses an algorithmic method that allows thousands of design parameters to be tested and adjusted simultaneously, dramatically reducing computational costs.

This differs from traditional approaches that rely on repeated trial-and-error simulations, which are costly and time-consuming and yield only incremental improvements.

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The research team, led by Huang Jiangtao of the China Aerodynamics Research and Development Centre, applied PADJ-X software to analyse the B-21’s configuration and found that the stealth bomber, currently undergoing flight testing, might fall short in aerodynamic and stability performance, according to the paper.

The researchers claimed they applied 288 parameters to simulate a B-21 layout, though they did not specify the data they used for their analysis.

The paper claims that aerodynamic optimization increased the aircraft’s lift-to-drag ratio by about 15% and significantly reduced shock-wave effects.

The pitching moment also improved from 0.07 to -0.001, the paper said. The closer this value is to zero, the smoother the flight.

When the pitching moment is close to zero, the aircraft can maintain stable level flight without pilot intervention on the control stick, enhancing natural trim capability and fuel efficiency.

The paper claimed that, with increased lift and reduced wave drag, the optimised B-21 design suggested the aircraft had a high potential for extended range, Huang wrote.

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“Future combat environments demand higher integrated performance from aircraft configurations, driving the need to consider deeper interdisciplinary coupling in design.

“PADJ-X, which boasts full intellectual property rights, integrates five major disciplines: aerodynamics, propulsion, electromagnetics, infrared signature, and sonic boom. It enables comprehensive optimisation of aircraft aerodynamic configurations,” the Hong Kong-based South China Morning Post reported, quoting the paper.

Similarly, the team ran simulations on the US Navy’s X-47B stealth drone, which was cancelled in 2015 but remains classified, like the B-21.

B-21 Raider

The paper claimed that the PADJ-X model reduced the drag coefficient by about 10 per cent and decreased the average forward Radar Cross Section (RCS) from 13.55 square metres (44 sq ft) to a mere 1.33 square metres, with a slight improvement in intake performance.

This dramatic improvement in the drone’s stealth characteristics was achieved by the PADJ-X model, which excels at multidisciplinary coordination – identifying the optimal compromise between a sharper shape to reduce drag and rounded curves that minimise radar reflection for stealth, the paper claimed.

The Chinese scientists fed publicly available information about the B-21 Raider and the X-47B stealth drone to the PADJ-X system, and then let the algorithm run simulations to probe for design vulnerabilities.

The team claims that the system represents a technological leap, as it can handle stealth shaping, left, drag, and control characteristics within a single framework, unlike traditional software systems used by the US, France, and Germany, which rely on repeated simulation cycles.

Many research institutions have been actively using adjoint optimisation platforms for decades, including NASA’s FUN3D platform, developed in the 1990s; Germany’s aerospace research centre’s FLOWer and TAU solvers; and France’s ONERA, which has built tools using the elsA solver.

However, according to the paper, these systems do not cover as wide a range as PADJ-X, and their operations often require manual adjustment when extending the optimisation process across disciplines.

Further, the paper claims that the PADJ-X could accelerate aircraft development, reduce the need for wind tunnel testing, lower prototyping costs, and enable future drones and manned aircraft to achieve longer ranges and superior performance.

These are impressive claims, especially the claim that the PADJ-X platform has uncovered vulnerabilities in the B-21 Raider’s design, and that the optimizations suggested by the system can improve the stealth bomber’s lift-to-drag ratio by about 15% while also improving its pitching moment.

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Given that the US has spent years and over US$25 billion on the B-21 Raider development, could a new software system expose vulnerabilities in its structural design?

Image for Representation: B-21

How Accurate Are China’s Claims?

While the research paper deserves attention, its tall claims must be taken with a pinch of salt for various reasons.

Firstly, as the team admitted, the findings were based on theoretical models and publicly inferred shapes rather than on classified design data.

Both the B-21 Raider and the US Navy’s X-47B stealth drone are classified programs, and details about their internal capabilities or external design features are not publicly available.

Therefore, the PADJ-X simulations for the B-21 Raider and X-47B are explicitly based on publicly available configurations and estimates, not classified U.S. data.

The information fed to the PADJ-X platform was likely based on approximations from photos and videos, and on guesses about the materials, coatings, and internal systems.

Any vulnerabilities identified are thus likely speculative rather than based on real-world aircraft performance.

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The paper itself admits that, given that the actual parameters of the B-21 and X-47B are classified, it remains uncertain whether the results produced by PADJ-X could match specific mission needs or tactical goals of the US military.

Simulations without full data can’t possibly accurately predict operational performance.

Furthermore, the US has been using such adjoint optimization software for decades, as the team acknowledges.

The research team claims that PADJ-X differs from traditional systems by integrating various engineering disciplines into a single software application rather than running separate optimization simulations.

However, Western software has been in use for decades and has evolved through AI integration and real-world validation, often without the need for manual adjustments, as alleged.

Additionally, stealth design trade-offs are well-known challenges that U.S. engineers have tackled since the F-117 and B-2 eras. The B-21’s flying-wing design is an evolution of proven tech, and its ongoing test flights suggest stability.

Any shortcomings must already have been identified and corrected during extensive simulation, wind-tunnel, and real-world flight tests.

Also, China has a track record of making tall claims about its systems and tools, which often fall short during real-world performance.

For instance, China has made big claims about its JY-27 “anti-stealth” radars, which were marketed as stealth killers. However, their performance in Venezuela during the recent Operation Absolute Resolve shows otherwise, where they failed to detect and counter USAF operations despite nearly 150 sorties.

Given these limitations, the research paper must be read with caution and cannot be detached from the broader geopolitical and technological rivalry between the US and China.

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• Sumit Ahlawat has over a decade of experience in news media. He has worked with Press Trust of India, Times Now, Zee News, Economic Times, and Microsoft News. He holds a Master’s Degree in International Media and Modern History from the University of Sheffield, UK. 
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