How fast is fast enough? There is an innate desire to cut travel time so as to enjoy or work harder once one gets where is going. In air flight that dream was the Concorde which was retired from use a few years back due to fuel economics as well as other reasons. For 27 years, the Concorde provided its passengers with a rare luxury: time saved. For a pricey fare, the sleek supersonic jet ferried its ticketholders from New York to Paris in a mere three-and-a-half hours — just enough time for a nap and an aperitif. Over the years, expensive tickets, high fuel costs, limited seating and noise disruption from the jet’s sonic boom slowed interest and ticket sales. On Nov. 26, 2003, the Concorde — and commercial supersonic travel — retired from service. A number of groups have been working on designs for the next generation of supersonic jets. Now an MIT researcher has come up with a concept that may solve many of the problems that grounded the Concorde. Instead of flying with one wing to a side, why not two?