The B-21 Raider was displayed at the company’s secretive Plant 42 complex about 34 years after a similar ceremony for its predecessor the B-2.
aviationweek.com
The aerodynamics of this thing fascinate me; some comment is given in the article. The hundreds if not thousands of iterative computer designs have converged on several classic historical features that are generally ignored or forgotten by the mainstream.
The tailored airflow over the centre section echoes Reimar Horten's deep concern for the subtleties of the
mitteneffekt (middle effect), which he never entirely resolved. He also wanted to improve the engine installation to a more conformal design.
Those intakes remind me somewhat of the NACA duct used for many small auxiliary intakes in the cold war era and trialled as an engine intake on the North American YF-93. No doubt the B-21 version is far more advanced, but the principle appears to be the same, and is I suspect the secret to decelerating the leading-edge flow at transonic speeds.
The wing outer sections have pronounced washout and, as far as I can tell, leading-edge droop. These features may be traced historically back through the majority of tailless swept wings, including the production Convair deltas, Avro Vulcan and Horten types, to the Dunne machines of the pioneer era and his 1909 patent. The first such design to fly, the D.5 biplane of 1910, received the first ever official certificate of performance for a stable aeroplane. Twenty or so years after that Ludwig Prandtl developed the theory of the bell-shaped lift distribution which offers the lightest structure and lowest drag for any given wing size, and for which these two features are necessary. Lippisch published a simplified calculation, which Horten adopted (though for some reason Lippisch seldom did). NASA only publicly caught up in this millennium, with Jonathan Bowers' PRANDTL-D flying wing project. Clearly, the key benefit for the digitally-controlled B-21 is not the inherent stability but Prandtl's minimal weight and drag. Once you sweep the wing, the stability comes with that package. Also of interest is that, right up to his rediscovery by Bowers, Prandtl was ignored by the mainstream and it was believed that these design features increased drag; this was voiced as a major criticism of the Dunne, and Northrop never incorporated them, not even in the B-2. Now, we see that they actually enhance the B-21's low drag characteristics.
The question I ask myself now is, did Northrop Grumman secretly take forward all these long-known but also long-obscure aerodynamic features, or did their computers arrive at something they knew nothing of beforehand? Either way, the B-21 looks like becoming a major vindication of all those maverick forebears.
time.com
