Future hybrid aircraft. Illustration of a design for a future hybrid aircraft. This design was produced by Boeing. The concept centres around a blended wing body design like the X-48. Pratt and Whitney geared turbofan engines on the plane's back end are flanked by vertical tails to reduce noise pollution. Long-span wings improve fuel efficiency. This design is one of several designs produced by the aviation industry in 2011 in response to a NASA challenge to design future aircraft that were more fuel efficient, less polluting, and less noisy. The designs were assessed by NASA Aeronautics Research Mission Directorate's Environmentally Responsible Aviation Project.