Imagine a future where a plane lands at an airfield that doubles as a rail yard. The cabin — one of three that cling to the underbelly of the aircraft like a baby possum to its mother — detaches, is seamlessly transferred to a nearby train, and then continues its journey toward the city center. Your multi-seat trip (taxi-to-subway-to-airtrain) from home to hotel suddenly becomes a one-seat, hassle-free ride. That’s the aim of a consortium of Swiss researchers with the conceptual Clip-Air, a bold-looking plane-train hybrid that despite its high-minded possibilities, will probably never get made. In essence, Clip-Air is a modular aircraft in four parts. There are three cabins, or capsules, which can carry passengers, freight, or fuel. Then there's an aircraft, complete with cockpit and engines, which looks like a stealth bomber on stilts. The capsules can decouple from the aircraft to continue the journey by road or rail, depending on the mission. This would allow for quick rotations on the ground and enable operators…