With launch and follow-on customers already signed up, the new director of Snecma’s Silvercrest engine programme, Eric Portejoie, has taken over the reins from former Silvercrest director Laurence Finet at a very advantageous moment. Snecma’s business jet engine programme is currently progressing steadily towards the halfway point in its pre-certification testing regime, with ice and hail tests already successfully behind it. Ahead lies endurance testing and, ultimately, flight testing.
Since finding a launch customer is undoubtedly one of the more stressful things about developing a new engine, Snecma was fortunate in having Cessna come on board so rapidly. The whole Silvercrest programme, which targeted creating a brand-new business jet engine in the 11,000lb thrust class, first hit the drawing boards back in 2006 as a concept design. By May 2012 the company had a good enough story to get Cessna signed up as the initial launch customer. This was for the Longitude, Textron’s first business jet in the 7,000 kilometre range class.
With Cessa and the Longitude in the bank, as it were, by May 2013 Snecma and Silvercrest were able to roll up another mainstream business jet manufacturer. Dassault announced that it was adopting Silvercrest for its new Falcon 5x, which it intends to bring to market sometime in 2017, the same year Cessna plans to debut the Longitude. According to Portejoie, discussions are continuing with a number of OEMs. The sweet spot for Silvercrest, he says, is in the 9,000 to 12,000lb thrust range. As for distance, that is the airframe manufacturer’s call, since distance depends on a combination of factors – a lean burning engine is just one of a number of variables. Others include the weight of the aircraft and how much fuel it carries, which is often down to the kinds of compromises the airframe OEM favours in the design process. Where the engine does come into play very significantly is in short field performance. Dassault in particular has favoured leaning towards short field performance in its designs since that opens up far more airports for its customers.
However, the Falcon 5X is quintessentially a long-range aircraft, capable of 9,600 kilometre flights, linking Johannesburg with Geneva, or Los Angeles with London, for example. So what is important here is Silvercrest’s lean burning capabilities, giving it better fuel performance than rival engines in its thrust range. Much the same is true of the Citation Longitude, which is planned to have a slightly shorter range, at 4,000 nautical miles – but again, it is the fuel efficiency of the engine that translates directly into a greater reach when it comes to trip planning.
“What we have set out to do with Silvercrest is to introduce into the mid-range business jet market all the gains that we have made from building engines for mainstream commercial airlines. Our goal is to bring to business aviation the best from the commercial markets, where there has been decades of work on making engines highly reliable and able to fly for two thousand or more hours a year. The average business jet will probably fly somewhere between 300 and 600 hours a year which is much less demanding, but reliability is very much a critical factor. We are aware of the fact that the business jet operator probably has much less engineering capability within their operation than you would find with a commercial airline. So for them reliability, coupled with long intervals between scheduled maintenance periods, is very important,” Portejoie notes.
Snecma intends to make sure that when Silvercrest engines start to be used in earnest, once Dassault and Cessna launch their new models, there will be a substantial global support network for the new engine. “We will have support capacity for repairs and line maintenance on all continents,” Portejoie notes. “We are looking at where the airframe OEM support hubs are around the world, and we will take that into account as we plan our MRO support structures for Silvercrest.”
Pratt & Whitney’s PW800
At NBAA Pratt & Whitney unveiled the PurePower PW800 engine family, which, in Pratt & Whitney Canada’s (P&WC) words, it intends as “a game changer that sets new standards in aircraft performance, dependability and fuel efficiency in the ultra-long range business jet market.” The PW800 is pitched at a significantly higher thrust range than Snecma’s Silvercrest, at 16,000lb of thrust versus 12,000 maximum for Silvercrest. Where the latter targets the mid-range market, P&WC’s PW800 is very definitely aimed at the heavy jet segment and has already achieved two huge wins, having been chosen by Gulfstream to power its new G500 and G600 large-cabin business jets.
For the PW800, P&WC has taken the same engine core technology used in its PurePower family of geared turbofan commercial engines but melded it with a direct drive rather than the geared approach used by P&WC’s commercial airline PurePower engines. The engine also includes a high-pressure compressor developed jointly by P&WC and P&W. P&WC’s Mike Perodeau, VP of corporate aviation and military engines, reckons that P&WC has nine PW800 engines already doing test runs in the development programme. By NBAA this year, the PW800 engine on P&WC’s Boeing 747 test aircraft had already put in some 250 flight hours, amassed in 35 flights since April.
According to Perodeau, among the many unique design elements incorporated in the PW800 are several that are designed to enhance ease of maintenance. For example, there are steps incorporated into the nacelle cowl doors and large access panels in the engine bypass ducts, allowing mechanics to access the engine’s core quickly and efficiently. In addition, the accessory suite has been carefully designed so that most accessories can be replaced in under 30 minutes. The team conducted benchmarking initiatives to optimise the design of the PW800 accessories. Virtual mannequin studies were conducted to ensure access for the mechanic. “From a maintenance perspective, the PW800 engine and nacelle system have set out to be the new industry standard. The engine requires 40% less scheduled maintenance and 20% fewer inspections than other engines in its class,” Perodeau says.
There are a host of technical features that improve the efficiency of the engine, starting with a high, optimised bypass ratio and the latest full authority digital engine control (FADEC) system, which helps to achieve optimised fuel burn. The engine also has highly durable ceramic ball bearings and a high efficiency oil system that requires less cooling and oil than comparable engine systems. On the green front, Perodeau says that the PW800 is inside the anticipated CAEP/8 environmental protection regulations by a double-digit margin and is able to deliver ultra-low levels of unburned hydrocarbons and smoke thanks to its unique TALON X combustor. The design process throughout has sought to minimise the use of materials that cause environmental concern and to maximise the use of sustainable materials.
The engine has been designed to ensure best-in-class availability, and will meet its target of 99.99% dispatch reliability. Perodeau points out that no other engine in the business aviation market offers that level of reliability today.