- PADJ-X modeled B-21 geometry using only publicly available images
- 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 works as an integrated platform combining five main 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 used 288 parameters to simulate a B-21-type layout using publicly available images instead of classified specifications.
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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 shockwave 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 cost compared to traditional trial-and-error methods.
A Chinese researcher noted that the software “boasts full intellectual property rights” and enables “extensive optimization of the aircraft’s aerodynamic configurations.”
Western platforms such as NASA’s FUN3D and Germany’s FLOWer solvers do not integrate so 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-in-one approach suggests a step forward in integrated aircraft design, but its practical impact on real-world stealth bombers remains unproven.
Available data suggest a functional but unconfirmed system
The leaked 20GB 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 function 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, not even in Chinese-language archives.
Access to these documents appears to have been either strictly restricted from the beginning or to have been removed following the leak from China’s National Supercomputing Center.
The absence of verifiable access to the final software package from December 2025 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 really cracked the B-21’s aerodynamic limits, or whether the whole episode serves another strategic purpose.
The leaks mostly rely on open source images and publicly known design limitations rather than actual espionage.
This suggests that the claims could mix real technical capability with a carefully managed narrative aimed at influencing perceptions of US stealth superiority.
Via SCMP
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