Boeing would have spent much engineering effort on mitigation of the hot gas ingestion in mode 4 problems. It's impossible to know now how difficult or easy tha

Boeing would have spent much engineering effort on mitigation of the hot gas ingestion in mode 4 problems. It's impossible to know now how difficult or easy that issue would have been to resolve. The lesson that I take away from this is: STOVL is not easy. LM, Rolls Royce, and Pratt&Whitney have had their hands full with the LiftFan.