Sometimes the revolution begins with a whimper instead of a bang. After investing $10 billion over nearly 30 years in geared turbofan engine technology, the staging of the entry into service of the first pair of Pratt & Whitney PW1100Gs on a newly-delivered Lufthansa A320neo seemed more tentative than triumphant.
With zero fanfare and little notice, Lufthansa on 25 January quietly loaded passengers on an A320neo for a routine flight from Frankfurt to Munich, making for one of the most anticlimactic moments in aviation history.
The silence was made more awkward by coming two years late. Delays to the Mitsubishi Regional Jet and the Bombardier CSeries family pushed the arrival of the geared turbofan engine from late 2013 to early 2016 and allowed Airbus to claim the honour of introducing the first all-new centreline engine to enter the single-aisle market in nearly 30 years.
For some customers, however, the long-awaited PW1100G was still not quite ready for primetime. P&W’s main engine rival – CFM International – will no doubt face similar scrutiny when the first Leap-1A-powered A320neo enters service this year. But the PW1100G’s roughly eight-month lead on the Leap-series engine family meant it was the first to feel the pressure.
P&W plans to begin deliveries of PW1100G engines with upgraded software “soon”, said Rick Deurloo, senior vice-president of sales, marketing and customer support, on 1 March at the ISTAT Americas conference in Phoenix.
Those upgrades should address about 80% of the teething issues that prompted Qatar Airways in December 2015 to withdraw as A320neo launch operator, Deurloo says. Further hardware upgrades are also coming to address the most prominent flaw in the PW1100G engine.
In all turbofan engines, superheated air can become trapped inside the casing after engine shutdown. Restarting the engine with that air inside can cause slight deformations in components, which can lead to more extensive damage. To prevent problems, a cycle of cooling air is run through the engine igniting the fuel. For most engines, this cooling cycle takes less than 1min for each engine. Indeed, CFM says the cooling cycle for the Leap is within a few moments of the 50s cooling cycle for the CFM56.
A damper is now installed on the third and fourth shaft bearings, starting with the geared turbofan engines destined for the 11th A320neo off the production line. The first 10 A320neos off the production line will be retrofitted with the new damper, which should help stiffen the shaft against thermal deformations.
How much the initial teething troubles will cost P&W in the long run is unclear. The competing Leap-1A engine for the A320neo will not enter service until this year, so no comparison is possible. But P&W officials point to other aspects of the PW1100G’s performance, citing a comment by Airbus chief executive Fabrice Bregier that fuel burn is “perfect” and a claim by Lufthansa the fuel efficiency is slightly better than expected.
Although the Leap-1A has yet to enter service, the non-geared alternative to the P&W option remains on the same schedule set by CFM International at programme launch in July 2008. The Leap-1A received airworthiness certification in late November 2015, fulfilling CFM’s pledge, more than seven years earlier, to complete that milestone by 2016.
“The Leap achieved either the exact date which has been set four years ago or we were able to be ahead of schedule,” says Jean-Paul Ebanga, chief executive of CFM.
The certification campaign for the Leap-1B engine that powers the Boeing 737 Max is ongoing. Only one “minor” certification test remains unfinished as of early March, and final approval from the US Federal Aviation Administration is expected within weeks, said Ebanga at the ISTAT Americas conference on 29 February.
In addition to being on time, CFM officials also assert both engines for the A320neo and 737 Max are meeting promised fuel-burn performance.
P&W achieved a 20% reduction in specific fuel consumption, mostly by inserting a gearbox between the low-pressure turbine and the inlet fan, allowing designers to increase the length of the fan blades and thus raise the ratio of air bypassing the engine core from about 6:1, in the International Aero Engines V2500, to about 12:1 in the PW1100G.
CFM relies on a conventional architecture with the low-pressure turbine directly driving the front fan. That limited the expansion of the bypass ratio to grow from 6:1 to 10:1, but CFM compensated by increasing the efficiency of the engine core. CFM added a stage to the high-pressure compressor, raising the overall pressure ratio from the 30:1 class in the CFM56 to the 40:1 class in the Leap-1 series. As pressure loads rose, CFM added a second stage to the high-pressure turbine. The internal cooling was also reduced by inserting heat-resistant ceramic matrix composites in the shrouds of the first stage of the high-pressure turbine.
Despitethe upgrades, questions lingered about the Leap-1 engine’s ability to meet fuel specifications. Airbus and Boeing officials have said repeatedly the engines should meet promised levels by the time the aircraft are ready to enter service.
Within months of the entry-into-service date of the Leap-powered A320neo, CFM officials insist the verity is already in on the fuel specification.
“In terms of engine performance, the Leap engines we are shipping right now, either in Toulouse or Seattle are on spec,” Ebanga says.
In a subsequent interview at CFM headquarters in Cincinnati, CFM executive vice-president Allen Paxson added the same engines delivered to Airbus have demonstrated fuel-burn results on GE Aviation’s flying testbed.
“I am confident that the engines we have delivered to Airbus are right on specification,” he says.
Airbus has not named the launch operator for the Leap-powered A320neo, but CFM expects to deliver engines to six airlines within three months of entry into service, Paxson says.
The Leap-1B engines installed on the first 737 Max 8 had completed 22 test sorties within a month of the type’s first flight, on 3 February, Paxson says.
“We are running the engines now on the ground and they are right on specification – and I’m talking ten-thousandths of a percent,” he adds. “We are right there. We are very, very confident. Is it done? No, because we have not delivered it. But the engines are drinking the amount of fuel to meet our spec level so we are there. We are very confident that the -1A and the -1B will meet the committed level of performance.”
A version of the Leap-1A is also developed for the Comac C919. CFM delivered the first Leap-1Cs to the Chinese narrowbody programme last year, as the C919 was originally scheduled to be the first to enter flight tests. First flight of the C919 is now scheduled in the third quarter.
By comparison, P&W’s development work is still ramping up. The PW1500G is scheduled to enter service this year with Swiss on the Bombardier CS100. Russian manufacturer Irkut expects P&W to certificate the PW1400G engine for the MC-21 in the second quarter, although first flight has slipped to at least the end of this year.
Although the Mitsubishi Regional Jet (MRJ) completed first flight in November, the PW1200G-powered airliner is scheduled to enter service at around the same time as the Embraer 190-E2, which is powered by the PW1900G engine. The PW1700G selected for the E175-E2 is scheduled to enter service two years later. P&W has delivered the first pair of PW1900Gs to the E190-E2, ahead of first flight in the second half of this year.
Additional reporting by Dominic Perry in Cincinnati
Source: Airline Business
