The people who brought you the first supersonic aircraft and the hypersonic X-15 are redesigning the humble wing to make flying greener. Nasa’s X-66A prototype with a transonic truss-braced wing (TTBS) is meant to deliver 10 per cent fuel savings with no loss of speed for single-aisle civilian airliners. It sounds fancy, but is simple: a longer, thinner wing, with trusses that also provide lift, gives more lift with less drag overall. What’s ironic about this supposedly breakthrough design is how much it has in common with old biplanes (the trusses) and how little it changes about the fundamentals of jet aviation. The jets themselves will still need kerosene or a synthetic carbon-neutral equivalent that’s unaffordable for airlines. Flying is destined to return to being an expensive luxury.