As the plane moves toward new, more efficient shapes, the surface of the craft itself could become more aerodynamic. A material comparable to sharkskin--an outer casing made of plastic, shaped with microscopic grooves--could repel dirt and reducing air friction up to 5 percent. (Strange but true: Bug carcasses appreciably add to aerodynamic drag.) Airbus, the European aircraft manufacturer, suggests that by midcentury aircraft skin could alternate between transparent and opaque, somewhat like today's light-sensitive eyeglasses, giving passengers a wide-angle view of the clouds.

The surfaces of planes may achieve further efficiency gains by dynamically adapting to each situation. "You might have a morphing wing," says David Hills, an aerodynamicist at Airbus. "When a bird hovers, it makes microchanges to capture every last degree of performance from the conditions it's experiencing. That's where we need to go." Instead of slats and flaps, wings could be covered with sensors and small moving plates, allowing them to change shape during flight and counteract turbulence. Airbus may embed small, instantly responsive air jets to improve aerodynamics. Doing so would let airlines fly more people while burning less fuel.