If one accepts the premise that the B-21 will be powered by twin unaugmented F135 engines, one can then assume that the new bomber will be larger than a Boeing F-15E Strike Eagle or General Dynamics F-111 but smaller than the B-1 or B-2. Given the types of threats from low frequency radars that are projected to be out there in the future and the limitations of current low observables materials, B-21s subsonic flying wing design will be large enough to counter low frequency radars.\r
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A tical fighter-sized stealth aircraft must be optimized to defeat higher-frequency bands such the C, X and Ku bands as a simple matter of physics, but a strategic bomber like the B-2 or LRS-B can be larger to counter lower frequency radars. There is a “step change” in a stealth aircrafts signature once the frequency wavelength exceeds a certain threshold and causes a resonant effect. Typically, that resonance occurs when a feature on an aircraft—such as a tail-fin—is less than eight times the size of a particular frequency wavelength. That means a bomber like the B-21 has to have allowances for two feet or more of radar absorbent material coatings on every surface or the designers are forced to make trades as to which frequency bands they optimize the aircraft to operate in. As such, to defeat low frequency radars operating in the L, UHF and potentially the VHF bands (this is easier said than done—and could in f be impossible), a flying wing design is in effect, mandatory.
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A tical fighter-sized stealth aircraft must be optimized to defeat higher-frequency bands such the C, X and Ku bands as a simple matter of physics, but a strategic bomber like the B-2 or LRS-B can be larger to counter lower frequency radars. There is a “step change” in a stealth aircrafts signature once the frequency wavelength exceeds a certain threshold and causes a resonant effect. Typically, that resonance occurs when a feature on an aircraft—such as a tail-fin—is less than eight times the size of a particular frequency wavelength. That means a bomber like the B-21 has to have allowances for two feet or more of radar absorbent material coatings on every surface or the designers are forced to make trades as to which frequency bands they optimize the aircraft to operate in. As such, to defeat low frequency radars operating in the L, UHF and potentially the VHF bands (this is easier said than done—and could in f be impossible), a flying wing design is in effect, mandatory.
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