Pratt and Whitney spent more than 20 years and $1 billion developing its new geared turbofan engines, which use larger fans (up to 81 inches in diameter on the A320neo) and a gearbox to make the fans rotate more slowly than the internal turbine that drives them, making them more efficient than traditional engines. Adding the gearbox, however, makes the engines heavier and increases aerodynamic drag. The PurePower PW1000G engine's fan-drive gear system is just one component of this next-generation engine. The PurePower PW1000G engine also incorporates advances in aerodynamics, lightweight materials and other major technology improvements in the high-pressure spool, low-pressure turbine, combustor, controls, engine health monitoring and more.
The CFM International Leap engine uses lightweight composite materials, such as carbon fiber fan blades, to achieve energy efficiency gains that the company says are comparable to those of the Pratt and Whitney engine. The Leap represents “the ultimate refinement of the traditional turbofan engine,” says aviation analyst Richard Aboulafia, vice president for analysis at the Teal Group.
NASA is supporting R and D on a number of experimental aircraft, including the D8, a novel jumbo-jet design being developed by a partnership that includes Pratt and Whitney, MIT, and Aurora Flight Sciences.
The D8 configuration has the potential of achieving a 71% reduction in fuel burn, a 60 EPNdB reduction in noise, and an 87% reduction in LTO NOx – all relative to a best-in-class Boeing 737-800 narrow-body aircraft.
The efficiency gains of the D8 are the result of a tightly integrated design approach, considering the air vehicle as a single, integrated system rather than an assembly of individual parts. For example, increased lift generated by the wide “double-bubble” fuselage means smaller wings are needed to carry the vehicle’s weight, resulting in less fuel to fly a given mission. When the engines are integrated into the back of the fuselage, thrust requirements are further reduced due to efficiencies from Boundary Layer Ingestion (BLI). This means that smaller engines can be used, which reduces weight, and hence fuel even further. This cycle of repeated optimization is what gives the D8 such groundbreaking efficiency, but it requires that all facets of the aircraft be designed together.