'Flaws identified in the B-21 configuration': Chinese scientists claim their mysterious PADJ-X stealth design software exposed major weaknesses in the USAF’s B-21 Raider program using digital twins

• PADJ-X modeled B-21 geometry using only publicly available imagery
• Simulation claims suggest a 15% improvement in aerodynamic efficiency
• Leaked files show partial validation of radar cross-section simulation components

A Chinese aerospace simulation tool called PADJ X has reportedly identified aerodynamic and stability limitations in America’s most advanced stealth bomber, the B-21 Raider.

The software operates as an integrated platform that combines five major disciplines: aerodynamics, propulsion, electromagnetics, infrared signature, and sonic boom design.

According to a peer-reviewed paper published in Acta Aeronautica et Astronautica Sinica, the researchers applied 288 parameters to simulate a B-21-type layout, using publicly available imagery rather than classified specifications.

Claimed capabilities exceed existing Western platforms

Their analysis claimed that aerodynamic optimization could increase the aircraft’s lift-to-drag ratio by 15%, while reducing shock wave effects that degrade stealth and efficiency.

The PADJ X system uses adjoint optimization technology to calculate optimal design directions across all parameters simultaneously, reducing computational costs compared with traditional trial-and-error methods.

A Chinese researcher noted that the software “boasts full intellectual property rights” and enables “comprehensive optimization of aircraft aerodynamic configurations.”

Western platforms such as NASA’s FUN3D and Germany’s FLOWer solvers do not integrate as many physics disciplines into a single environment.

These existing systems often require manual adjustments when moving optimization from one discipline to another, making multi-objective tuning slower and more fragmented.

PADJ X’s all-at-once approach suggests a step forward in integrated aircraft design, but its practical impact on real-world stealth bombers remains unproven.

Available data suggests a functional but unverified system

The leaked 20GB of files associated with PADJ X contain earlier versions of the project, including work on the Northrop Grumman X-47B drone and the Chinese CHN-F1 benchmark model.

Individual components of the software pipeline have been verified to operate correctly, including radar cross-section calculations run in third-party tools such as Altair FEKO.

However, running a full multi-parameter geometry optimization from scratch would require more computing power and time than has been publicly demonstrated.

The research papers referenced in the leak — numbers 10.7527/S1000-6893.2025.32221 and 10.7527/S1000-6893.2025.32816 — cannot currently be found anywhere, even in Chinese-language repositories.

Access to these documents appears either to have been tightly restricted from the outset or to have been removed after the leak from the National Supercomputing Center of China.

The absence of verifiable access to the final December 2025 software package leaves room for doubt, as does the convenient narrative of a “mother of all leaks” that cannot be independently confirmed.

What remains unclear is whether Chinese scientists genuinely cracked the B-21’s aerodynamic limits or whether the entire episode serves a different strategic purpose.

The leaks may rely mostly on open-source imagery and publicly known design constraints rather than genuine espionage.

This suggests that the claims could blend real technical capability with a carefully managed narrative aimed at influencing perceptions of U.S. stealth superiority.

Via SCMP

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