NASA has long been the leading experimenter in future aircraft design. They believe new designs could save airlines $250 billion in coming decades. Along with reducing fuel and pollution by 70 percent, these prototypes make 50 percent less noise than conventional passenger planes. The aircraft shown here is one of several N + 3 designs—aircraft that can be used three generations into the future. Dubbed the Double Bubble, this MIT model places three engines at the rear of a double-wide fuselage, enabling the wings to be smaller and lighter. Rear engine placement allows for smaller engines and reduced weight. Each optimization on large aircraft has cascading benefits to other components, resulting in groundbreaking efficiency.