The PurePower P1000G engine, often referred to as the GTF or Geared TurboFan, from Pratt & Whitney (a division of United Technologies) will have significant economic benefits over existing aircraft engines as well as its new technology competition from CFM International and Rolls-Royce.
The P1000G, which will enter service on the Bombardier CSeries in 2013, the Mitsubishi MRJ in 2014 and the Irkut MS-21 in 2016, has been described as a “game changing technology” due to a dramatic improvement in operating economics. These improvements are technologically possible through a breakthrough in gearbox design that enables different sections of the engine to turn at different speeds to optimize their performance.
Unlike conventional engines that operate at one speed, the gearbox enables the front fan section of the engine to turn slowly, optimizing airflow, while at the same time enabling the low pressure section of the engine to rotate at higher speeds, optimizing performance. The result is a dramatic improvement in bypass ratio and fuel economy.
Today’s narrow-body engines have bypass ratios in the range between 5.5:1 to nearly 6:1 (, Boeing 737-700, Airbus A319) The latest technologies for emerging wide-body aircraft have ratios between 9.5:1 (Boeing 787) and 11:1 (Airbus A350XWB). The PW1000G will have an ultra high bypass ratio of 12:1 in its first application, with the potential for even higher growth. Bypass ratio is a surrogate measure for fuel efficiency — a higher bypass ratio indicating better fuel efficiency.
Pratt & Whitney believes that the P1000G engine will continue to become more efficient as the engine is refined after entry into service, and believes that this engine will become as efficient as open-rotor or unducted fan engines when mature, with fuel burn 30% lower than today’s narrow body engines. PW expects to achieve that level with continuous improvements yielding, on average 1-1.5% improvements annually as the program matures.
Achieving a 30% improvement is significant, as that level will provide performance equivalent to that of an open-rotor design, but without the difficulties of size, noise, and lower speeds that an open-rotor design would require.
The P1000G also has a significant advantage in maintenance costs over today’s engines, primarily because the engine can be efficient with fewer low pressure turbine stages. Fewer stages equal fewer blades, and fewer blades equals fewer life limited parts to replace. With fewer parts to replace, maintenance costs for the P1000G will be 20% lower than today’s engines, a significant reduction. With engines typically accounting for about half the maintenance cost for an aircraft, that reduction is meaningful for airlines.
The elimination of blades and airfoils in an engine makes a significant difference not only in maintenance cost, but also in downtime for operators. Keeping an engine on wing is a key to lowering maintenance costs, and PW believes it will provide industry leading performance with the P1000G.
Of course, the great unknown for maintenance and reliability is the gearbox itself, which is the source of the economic advantages. The key element in the GTF design, this lightweight gearbox, containing only seven moving parts and advanced lubrication systems, has been designed for reliability. Routine service is the equivalent of an “oil change” that will enable the gearbox to stay on wing for long periods of time.
The concept of a geared turbofan is not new, as the Honeywell TFE-731 and Avco Lycoming ALF 502 and 507 were geared turbofans without gearbox-associated maintenance problems and had successful service lives on business jets and the BAe146/Avco RJ, respectively. The PW breakthrough is the design of a lightweight system that is robust enough to handle higher thrust levels and is scalable from narrow-body to wide-body size engines.
While maintenance is always a concern for new technology products, PW and its UTC affiliates have experience with 54,000 engines with gearboxes (all turboprop and helicopter engines have them) operating more than 640 million flight hours. This provides a level of comfort with respect to gearbox know how.
The major competitor to the PW GTF is the Leap-X from CFM International, a joint venture between General Electric and Safran, through its Snecma business unit. The Leap-X, expected to enter service with an initial variant in 2016 for the COMAC C919, is also promised to provide a 15% improvement in fuel economy, and maintenance costs comparable to the current CFM-56.
However, most observers believe that the GTF has significant potential for fuel economy improvements as it matures, while the Leap-X, which uses more conventional technologies, will peak at around a 20% improvement without moving to an open rotor design. This will result in a significant long-term performance advantage for Pratt & Whitney, which expects to achieve 30% improvements as the engine matures over the next decade. With a three year lead on entry into service and a significant maintenance cost advantage, we would expect the GTF to continue to improve its competitive advantage by the time the Leap-X reaches the market with an initial offering for COMAC in 2016.
Both GE and Rolls Royce are looking at open rotor concepts to compete with the GTF. Open rotor engines, however, have large propellers that preclude under wing installation due to size, problems in noise mitigation from the open design, and must operate at lower speeds. These concerns will require entirely new aircraft designs tailored to open rotor technology, which remains unproven. The GTF will provide similar benefits, without the need for radical designs, reducing speed, or compromising on noise.
Better fuel economy and lower maintenance costs will provide the PW 1000G Pure Power engine with a significant competitive advantage over the CFM Leap-X and Rolls Royce RB285, which utilize conventional technology that forces a compromise in performance. This advantage should make it the engine of choice for narrow-body programs for the next two decades.