Snecma Silvercrest

Cessna Aircraft Company (groupe Textron) a annoncé ce jour avoir sélectionné le turboréacteur de nouvelle génération Silvercrest de Snecma (groupe Safran) pour motoriser son nouvel avion d’affaires Citation Longitude.

Le Citation Longitude est un jet d’affaires de la catégorie Super Mid-Size capable d’une vitesse de croisière maximum supérieure à 900 km/h (490 nœuds). Son rayon d’action intercontinental de 7 408 km (4 000 miles nautiques) sera le plus long de la gamme Cessna. Il est prévu pour entrer en service en 2017.

« Nous sommes ravis d’avoir choisi le Silvercrest, parce que c’est le meilleur de sa catégorie pour offrir aux clients de Cessna performances, fiabilité et qualité, a déclaré Scott Ernest, président-directeur général de Cessna. Ce moteur apportera au Citation Longitude des performances inégalées et permettra d’offrir à nos clients le rayon d’action, l’efficacité et la réduction de bruit dont ils ont besoin pour réussir dans l’environnement concurrentiel que nous connaissons aujourd’hui ».

Le Silvercrest destiné au Cessna Longitude aura une poussée de 11 000 livres. Intégrant les technologies les plus innovantes issues de la recherche Snecma, il offrira des performances inégalées, avec des objectifs ambitieux en termes de consommation de carburant, de fiabilité et de respect de l’environnement. Conçu pour permettre une grande maintenabilité, il disposera aussi de fonctionnalités avancées de Health Monitoring.

« Nous sommes très heureux d’avoir été sélectionnés par Cessna pour motoriser son nouvel appareil, a déclaré Pierre Fabre, président-directeur général de Snecma. Le Citation Longitude est un programme passionnant et prometteur, auquel nous sommes fiers de contribuer en apportant nos technologies innovantes et notre expertise dans le domaine de la motorisation des avions commerciaux

Ground trials of the first Silvercrest engine are due to begin this summer as Snecma works to begin flight trials of the business aircraft engine in the first half of next year.

Snecma is providing the engine in an 11,000 lb. thrust version for Cessna’s new Longitude super mid-size aircraft, as well as Dassault’s yet-to-be-announced SMS, which is due to fly in 2014. The Silvercrest design covers a thrust range of 9,500 lb to 12,000 lb. with the SMS version expected to be similar to the Longitude.

Engine certification is planned in 2015, says Francois Planaud, Snecma’s general manager for commercial aircraft engines.

The company will build eight development engines, adds Laurence Finet, the Silvercrest general manager. Flight trials will take place on a company Gulfstream G3.

The engine, with a 5.9:1 bypass ratio, will sport a 42.5 inch diameter fan with 20 wide-chord metallic blades, a high pressure compressor with four axial blisk stages and a single centrifugal compressor. Silvercrest also will have a single-stage high-pressure turbine, a compact four-stage booster and four-stage low-pressure turbine.

A high pressure core demonstrator ran in 2007-2008, with full scale development launched in the third quarter of 2010.

Snecma promises 15% better fuel burn versus current engines, 50% margin against CAEP/6 emissions standards, and up to 20 dB noise margin on Stage 4 noise requirements. Moreover, “we are introducing true on-condition maintenance,” notes Planaud

Snecma sees a market for 1,260 super mid-size aircraft and 1,136 large aircraft through 2021 the Silvercrest can target, says Snecma CEO Pierre Fabre.

Silvercrest is not the only new engine on Snecma’s planning horizon. The aircraft maker also is looking at launching a turboprop development for the 80-90 seat market. Exploratory talks are due with ATR, which is looking at launching such a program, although Snecma’s deliberations go beyond that program.

Another manufacturer looking to break into the sector is Snecma, whose focus remains on development of the 9,500-12,000-lb.-thrust Silvercrest engine. The super-midsize and large business jet engine project emerged initially from studies into a 50-seat regional jet engine, and is now aimed at programs such as Dassault's SMS twinjet. Although Rolls-Royce's RB282-3 was originally selected for the SMS in 2007, the engine contest was reopened in 2009 with the Silvercrest tipped as the front-runner. Snecma is widely expected to officially confirm at EBACE its position on the Dassault aircraft, which is targeted at certification in 2016.

Silvercrest incorporates a centrifugal compressor in combination with four axial stages—a first for Snecma. The compressor configuration enables the number of stages to be reduced to around 10, compared with more than double that for some competing current designs. It was developed in conjunction with Snecma sister company Turbomeca and in early tests demonstrated a better-than-expected stall margin. Silvercrest also features counterrotating core and power shafts and builds on experience gained from the CFM56 program with GE. Although Snecma has become increasingly tight-lipped about the program in recent years, the overall performance targets are still thought to include a decrease in fuel burn by up to 15% and an increase in climb and cruise thrust by around 25%, relative to similarly rated state-of-the-art engines.

Snecma will this summer begin running the first of eight Silvercrest turbofans taking part in the engine certification programme for Cessna's newly announced Longitude twin-engine business jet.

The two-spool 11,000lb (49kN) thrust engine will feature a 5.9:1 bypass ratio using a 1.08m (42.5in) diameter 20-blade Snecma-built fan, a four-stage axial compressor built by Techspace Aero, a single-stage centrifugal compressor built by Turbomeca and a single-stage high-pressure turbine and four-stage low-pressure turbine, both built by Snecma. Snecma will also build the full-authority digital engine controller for the turbofan.

Francois Planaud, Snecma's executive vice-president of commercial engines, says Cessna will provide the nacelle and thrust-reverser for the aircraft, which will enter service in 2017. He says Snecma is not a risk-sharing partner with Cessna on the programme.

Following first-engine-to-test operations this summer, Planaud says Snecma will transition in the first quarter of 2013 to in-flight testing on its Gulfstream III testbed at the company's base in Villaroche, France.

Officials say the engine will have a 15% lower specific fuel consumption than other engines in the 11,000lb-thrust class, with on-condition maintenance that requires no hot section inspection, and real-time flight monitoring, diagnosis and prognosis.

“Silvercrest testing began in the last week of September,” program director Laurence Finet told AIN.
The engine had left the assembly hall in the middle of the month, and
it then had to undergo the installation and instrumentation process.
Some 1,000 measurements are performed during a test. Reaching takeoff
power was a target for mid-October. Asked about a planned number of
hours or cycles, business aviation marketing manager Loïc Nicolas
answered, “Checking the engine’s behavior is more important than a
number of hours.” Eventually, eight engines will be involved in the
development program.

One of the Silvercrests will fly on a Gulfstream GII,
modified as a flying testbed. The first flight is pegged for mid-2013.
This is “a project in the project,” as Finet put it. Modification work
will take a total of one and a half years. Pylon changes and the
addition of telemetry equipment are the bulk of the job. The GII will keep one of its original Rolls-Royce Speys.

What about studying a re-engining of the GII and even the GIII,
as they share the same engines? “The Spey is rated at 12,400 pounds at
takeoff; the Silvercrest could provide as much thrust at takeoff and
even more than the Spey in cruise,” Finet answered. Although some
contacts with GII and GIII
owners have been encouraging, the idea is not deemed mature yet. Snecma
wants to see a solid business case before moving forward.

For the Silvercrest program, full-scale engine development began in
the third quarter of 2010. The core had undergone 80 hours of ground
tests in 2008, after which Snecma toiled to find an application. The
contract with Cessna for the Longitude was signed in May. The
Silvercrest has long been rumored to be the choice for the
still-under-wraps Dassault Falcon SMS, but as of early October, Snecma would not confirm this rumor.

The Silvercrest’s cold section consists of a 42.5-inch fan, a
four-stage booster and a five-stage compressor (including four axial
blisks and one centrifugal stage). The 20 fan blades are metallic. The
low-emission combustor is said to have a high-altitude relight
capability, and it is followed by a single-stage high-pressure (HP) turbine featuring single-crystal blades and a four-stage low-pressure (LP) turbine. The HP and LP spools are contra-rotating for better fuel efficiency. The bypass ratio is close to 6:1.

Snecma is claiming that the Silvercrest will burn 15 percent less fuel, emit 50 percent less NOx than the CAEP/6
standard and halve the noise footprint, “compared to existing engines
in the 10,000- to 12,000-[pound thrust] class.” Finet named the two
reference engines (actually a bit below the aforementioned class), the
9,200-pound GE CF34-3 and the 9,440-pound Rolls-Royce AE3007C2.

In terms of maintenance, Snecma said the Silvercrest is a “true
on-condition engine,” with no fixed interval. No hot-section inspection
will be required. Another feature will be in-flight engine
monitoring capability.