Boeing’s F-47 Next Generation Air Dominance (NGAD) sixth-generation fighter has been designated “Stealth++” by the U.S. Air Force — a classification one tier above the F-22 Raptor’s “Stealth+” rating, suggesting that the new aircraft will be substantially stealthier than the F-22, which already has a frontal radar cross-section roughly 50 times smaller than the F-35 Lightning II. The stealth advance is being enabled in part by a new ceramic coat…