Comment by kojiromike

I'd be pretty interesting in their predictions for the operating cost/cost per hour of flying this machine. My uninformed guess (informed only by knowing how expensive and thirsty normal jet engines are) is that it's two orders of magnitude more per hour than a conventional jet, and that these companies are still hoping they can somehow engineer their way to making it worthwhile. I think first they have to bring a product to market to prove feasibility in some dimensions (physical, marketable), which will ironically prove that it's not economically feasible.