Fuel Efficiency Takes Flight

Caitlin Harrington

Decades of NASA research have led to breakthroughs in understand­ing the physical processes of pollution and determining how to secure unprecedented levels of propulsion and aerodynamic efficiency to reduce emissions. Goaded by recurring fuel supply crises, NASA has responded with a series of research plans that have dramatically improved the efficiency of gas turbine propulsion systems, the lift-to – drag ratio of new aircraft designs, and myriad other challenges.

LTHOUGH NASA’S AERONAUTICS BUDGET has fallen dramatically in recent years,[1372] the Agency has nevertheless managed to spear­head some of America’s biggest breakthroughs in fuel-efficient and environmentally friendly aircraft technology. The National Aeronautics and Space Administration (NASA) has engaged in major programs to increase aircraft fuel efficiency that have laid the groundwork for engines, airframes, and new energy sources—such as alternative fuel and fuel cells—that are still in use today. NASA’s research on aircraft emissions in the 1970s also was groundbreaking, leading to a widely accepted view at the national—and later, global—level that pollution can damage the ozone layer and spawning a series of efforts inside and outside NASA to reduce aircraft emissions.[1373]

This case study will explore NASA’s efforts to improve the fuel effi­ciency of aircraft and also reduce emissions, with a heavy emphasis on the 1970s, when the energy crisis and environmental concerns cre­ated a national demand for "lean and green” airplanes.[1374] The launch of

Sputnik in 1957 and the resulting space race with the Soviet Union spurred the National Advisory Committee for Aeronautics (NACA)— subsequently restructured within the new National Aeronautics and Space Administration—to shift its research heavily toward rocketry— at the expense of aeronautics—until the mid-1960s.[1375] But as commer­cial air travel grew in the 1960s, NASA began to embark on a series of ambitious programs that connected aeronautics, energy, and the envi­ronment. This case study will discuss some of NASA’s most important programs in this area.

Key propulsion initiatives to be discussed include the Energy Efficient Engine program—perhaps NASA’s greatest contribution to fuel-efficient flight—as well as later efforts to increase propulsion efficiency, includ­ing the Advanced Subsonic Technology (AST) initiative and the Ultra Efficient Engine Technology (UEET) program. Another propulsion effort that paved the way for the development of fuel-efficient engine technol­ogy was the Advanced Turboprop, which led to current NASA and indus­try attempts to develop fuel-efficient "open rotor” concepts.

In addition to propulsion research, this case study will also explore several NASA programs aimed at improving aircraft structures to pro­mote fuel efficiency, including initiatives to develop supercritical wings and winglets and efforts to employ laminar flow concepts. NASA has also sought to develop alternative fuels to improve performance, maximize efficiency, and minimize emissions; this case study will touch on liquid hydrogen research conducted by NASA’s predecessor—the NACA—as well as subsequent attempts to develop synthetic fuels to replace hydro­carbon-based jet fuel.