Sure, but B-21 (from my understanding) will make do with a pair of modified F-135s. Sure, B-21 doesn't have afterburners, but if the requirement had called for B-21 to be more of a fighter (as with J-36) they could have souped up the engines. Also the J-36's ventral intake will have air flow issues with high angles of attack. If the third engine is about electricty, sensors and so forth...wouldn't sharp changes of AoA disrupt this?If it was 3 engines for a smaller plane the “inefficient engines” line of thinking would have more cache. But this is a very large plane, easily 50% bigger by volume than any flying 5th gen today, which tells you they’re not simply trying to compensate for lower thrust. The actual reason has far more to do with electrical power. This plane is designed to have a massive amount of available electrical power to power its hungry sensor and EW capabilities, and the higher the electrical power demands the more beneficial it is to have an always available power source. A third engine simplifies the power architecture to enable this since you won’t have to constantly optimize power availability between thrust and electrical demands.
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