Two new contenders vie to power future RJs

 - October 16, 2007, 10:43 AM

Pratt & Whitney Canada and the French-Russian Snecma-NPO Saturn joint venture are knocking at the door of the market for regional-jet turbofan engines. The geared-fan PW800 and the more conventional SM146 are not yet fully launched programs, but development is well under way. As both are looking for their first application, P&WC and Snecma are hoping the engine selection for the Russian Regional Jet (RRJ), which is being studied by Ilyushin, Sukhoi and Boeing, will be announced soon. Both had been short-listed for the RRJ last summer during the Farnborough Air Show.

A third major engine development in the regional segment is the General Electric CF34-10, which looks like a new engine rather than a derivative of the CF34-8. The CF34-10 is being designed for the Embraer 190/195 and the ARJ21 family under study by China’s  AVIC I. Today, General Electric CF34 engines power all in-production and in-development regional jets with more than 50 seats, including the Bombardier CRJ700/900 and the Embraer 170/190.

GE shares the 50-seat RJ market with Rolls-Royce–their CF34 and AE3007, respectively, power the CRJ100/200 and the ERJ-145. The smaller ERJ-135 and -140 also use Rolls-Royce AE3007s. Since BAE Systems canceled its Avro RJX program more than one year ago, Honeywell, which used to be another player in the field, has no regional application for its turbofans. P&WC has a hand in RJ powerplants with its PW306, which powers the Fairchild Dornier 328JET, an aircraft program that may soon wind up in the hands of U.S.-based Avcraft if the proposed deal secures its needed government approvals.

The PW800 geared-fan engine could be certified 36 months after full-scale development launch, P&WC officials say. Two demonstration engines have been tested for more than two years. Since last summer, the advanced technology fan integrator (ATFI) demonstrator has been in phase two, with design of a dedicated core engine under way. The high-pressure spool is scheduled to run next year. So far the thrust range has been defined as “10,000 to 20,000 pounds.”

The ATFI ran for the first time in March 2001 to validate the low-pressure spool technologies, including the advanced-technology fan with twisted, swept blades; the reduction gearbox; the low-pressure compressor; and the low-pressure turbine.

German firm MTU is responsible for the high-pressure compressor and the low-pressure turbine. The former has been derived from MTU’s HDV12 research compressor, which is also the basis for the new high-pressure compressor on the PW6000, now slated for introduction on the Airbus A318 in 2005. The combustor will draw from some existing Pratt & Whitney-patented technologies, such as the low-NOx Talon and floating-wall designs.

“Our current baseline consists of a seven-stage high-pressure compressor together with a single-stage high-pressure turbine and a two-stage turbine driving the fan; the specific architecture will depend on the launch application and the engine thrust class,” Steve Stamm, P&WC general manager of marketing operations for regional airline engines, told AIN.

Pratt & Whitney Canada and MTU recently signed a memorandum of understanding with Russian engine design company Aviadvigatel “in support of the development of the PW800.” FiatAvio is another partner on the PW800.

Geared for the Future
Should full-scale development get a green light, it would be the first time a gear would be used at this level of power on a commercial engine. For the 15,000-pound-thrust engine, the output from the reduction gearbox is about 14,500 hp at takeoff power. This is much higher than any in-service geared turbofan or turboprop. The PW150A turboprop, which powers the Bombardier Q400, is in the 7,500-shp range. The Honeywell TFE731 used on several business jets is the most powerful in-service geared turbofan, with a power output of some 4,400 hp at the gearbox.

Operators often view the gear as a critical component on engines. “Our experience with similar configurations of gearboxes on turboprop applications is that reduction gearboxes are highly reliable and durable,” P&WC officials said. The PW800 fan gearbox is a single-stage, star-configuration gearbox with five spur-type planet gears. The gear ratio is 2.2:1.

Gearing is a creative solution to ease a difficult compromise in engine design. Engineers like to increase the fan diameter because it makes the bypass ratio higher, which brings benefits in terms of increased thrust and efficiency and lowers noise. But the fan’s tip speed has to be limited to keep noise levels acceptable. On a conventional engine, this means that as fan diameter increases, rotational speed has to be lowered.

However, the low-pressure compressor and turbine blades do less work as rotational speed decreases. This is why designers often have to build large, complex compressors and turbines. Moreover, as the rotational speed slows down, the torque increases, demanding a stronger, thicker low-pressure shaft, which makes a poor match with a small, compact core.

With a gear between the fan and the low-pressure system, every component can spin at its optimum speed. The low tip speed reduces noise, thanks to both the gear and new fan blades. In fact, P&WC anticipates a 24-dB margin under current Stage 3 regulations, which still translates into a substantial margin under proposed Stage 4 rules. Additionally, the high bypass ratio boosts propulsive efficiency and reduces fuel burn. The low-pressure compressor and turbine can be downsized and still do much work, thanks to a higher rotational speed.

“The PW800 has two low-pressure turbine stages and two low-pressure compressor stages less than competing engines,” P&WC officials pointed out. Last, but not least, the low-pressure shaft shrinks back to a normal size, making the core more compact and efficient.


Lower-cost Engines

Competing Snecma-NPO Saturn has a more conservative approach. Snecma officials believe the SM146 will be the right answer for the market in terms of cost reduction. “Regional jets are still too expensive to operate if you think of the relatively low yield airlines get in feeder operations,” they said.

Partnering with Russian-based NPO Saturn should help keep production costs lower than the competition, Snecma hopes. It is confident that its Eastern partner can meet Western quality standards, especially since some CFM parts are already manufactured in Russia. Moreover, “Embraer has proved that new entrants can be successful in the regional jet market when they bring cost cuts,” it added. Operating costs should be addressed by reducing the number of stages and parts in the engine, which simplifies maintenance.

An SM146 core engine (under the name “DEM21” demonstrator) made its first run last May and completed the first phase of ground tests in mid-August. During this first test campaign, the core engine met or exceeded its targets, Snecma said.
The SM146 is a 50/50 joint project, with Snecma and NPO Saturn being responsible for the high-pressure system and the low-pressure system, respectively. October 2005 is the certification target date, depending on actual program launch.

The DEM21 core includes a six-stage high-pressure compressor with “a high pressure ratio” and “sail-shaped” vanes. The low-emissions combustor is inspired by that of Snecma’s M88 military engine. The single-stage pressure turbine features an active clearance control system and single-crystal materials. Thrust range for the SM146 will span 13,500 to 17,500 pounds.

NPO Saturn will “draw from Snecma’s experience on the CFM56 but will fully design the SM146’s low-pressure system,” French officials said. Their Russian counterparts added that 700 of its engineers have been working for 10 months on this program, both in Rybinsk and Moscow. There are joint Snecma-NPO Saturn teams in both cities. Two-hundred Snecma technicians and engineers have been working on the French side of the program.

Before the RRJ short-list was issued, other contenders were Rolls-Royce with its BR710 and General Electric with its CF34.

General Electric’s CF34-10 program is “on schedule,” according to Tim Schweikert, director of marketing and sales for GE’s small commercial engine operations. In the spring a test engine will be fitted to GE’s Boeing 747 testbed for a series of in-flight trials. The program schedule calls for engine certification by year end.

“The Embraer 195 should make its maiden flight shortly after, and airplane certification should be granted late in 2004,” he added. The engine test program involves one core engine and seven engines. Of these seven, one will be dedicated to flight-testing.

The core of the CF34-10 is scaled down from that of the CFM56, Schweikert explained. (The CFM56 turbofan powers the Boeing 737, Airbus A320 family and A340-200/300.) The high-pressure turbine is single-staged to cut weight and maintenance costs, as is that of the CFM56. And both engines have nine-stage compressors. Even the low-pressure spools have similar architectures on the CF34-10 and the 737’s CFM56-7: three stages on the booster and four on the low-pressure turbine.

CFM56 Clone?
“The CF34-10 is a clone of the CFM56,” a competitor claimed. However, according to Schweikert, “no hardware is transferable between a CF34-10 and a CFM56.” And the low-pressure turbine and the thrust reversers are derived from those of the CF34-8, he said. Further, the wide-chord fan draws from “the CF6 and GE90 as well as CFM56 experience,” he added.

The high-pressure turbine features a “low solidity” design, which means 14 percent fewer airfoils and thus reduced maintenance costs, Schweikert told AIN.

In addition, the low-pressure turbine uses a low-solidity design. The combustor is a single-annular design, said to be simpler and cheaper than double-annular models. Still, “research on aerodynamic patterns and profiles” and “a quick-quench technology” help reduce NOx emissions. GE claims these emissions are 12 percent less than those of current-technology single-annular combustors.

The three variants of the CF34-10 are similar: “Differences are limited to some installation hardware, but the turbomachinery does not change,” Schweikert said. The -10E on the Embraer 190/195 series is located under the wing. The -10A on the ARJ21 will be fuselage-mounted. The -10D, for the 70-seat 728JET of now-bankrupt Fairchild Dornier, was to be underwing. The first two engines equipped the first and only 728JET, which was rolled out in March last year. However, those engines are now back in the U.S., Schweikert said.

According to GE-Snecma agreements for their CFM 50/50 joint venture, neither partner can develop a civil engine between 18,500 and 50,000 pounds of thrust on its own. As the CF34-10 is targeted at 18,500 pounds of thrust for certification, Schweikert noted, “We have some thrust margin; we do not plan any application beyond 18,500 pounds.” For instance, the CF34-10A will provide 17,000 pounds of thrust on the long-range, 99-seat version of the ARJ21. The smaller, shorter-range version will use a 15,000-pound-of-thrust variant of the CF34-10A. AVIC I announced GE’s selection in November, and the ARJ21 is scheduled to enter in 2007.

It has been two years since the CF34-8C1 entered service at Air France’s regional subsidiary, Brit Air, aboard a CRJ700. “We have had neither an inflight shutdown nor an engine-caused aborted takeoff to report,” Schweikert said. Dispatch reliability is said to be 99.94 percent.

CF34-8 engines have logged 200,000 flight hours and 175,000 cycles on 70 aircraft flown by eight operators. The 13,800-pound-of-thrust CF34-8C1 was the first GE regional jet turbofan with a FADEC. GE is now “formulating a plan” to solve a teething problem–airfoil distress has been found in the high-pressure turbine on some high-time engines, Schweikert told AIN.

To cut the noise on the 14,500-pound-thrust CF34-8 “growth versions,” namely the Embraer 170’s CF34-8E and the CRJ900’s CF34-8C5, GE engineers have designed a so-called “chevron” nozzle. It is a saw-tooth-shaped nozzle that mixes the hot gases that come out of the engine and the colder bypass flow from the fan. The chevron nozzle is said to be lighter and cheaper than conventional, long-duct mixers, and it provides “most of the acoustics benefits” of the latter since noise is reduced by about 2.5 dB.

The CF34-8C5 was to enter commercial service last month on the 84-seat Bombardier CRJ900 delivered to Mesa Air Group. “The engine performed flawlessly during the flight-test program,” Schweikert added.

The CF34-8E for the Embraer 170 has a slightly higher than expected specific fuel consumption (SFC), however. The solution will be a combination of “many small things.” Emissions and noise are said to meet ICAO standards.

On the 9,000-pound-thrust GE CF34-3, which entered service in 1992, dispatch reliability is said to be 99.99 percent. This year, GE is offering a new performance upgrade kit, which should improve both SFC and climb performance. The kit focuses on increasing the durability of some turbine components. Early CF34-3 teething problems, such as flameouts caused by fuel control units, a limited life of the high-pressure turbine disk and, more recently, an accessory gearbox issue, have been solved, Schweikert said.

It is still unknown whether Honeywell will one day re-enter the regional jet turbofan market. In late 2001 BAE Systems canceled the Avro RJX, which was powered by Honeywell’s only in-development engine at the time. The upgraded version of the four-engine regional jet was to be fitted with AS977 turbofans. Since then, no in-development or in-production engine has been reported by the Phoenix-based company. However, “We are continuously working on LF502/507 improvements,” Laurena Ketzel-Kerber, Honeywell’s director of regional aircraft propulsion, told AIN. The LF502/507 powers in-service BAe 146s and Avro RJs. Ketzel-Kerber believes the regional jet market is a “good” one. Thus, aside from supporting LF502/507 customers, Honeywell is in discussion with OEMs for possible new RJ applications. Development of new RJ engines could be launched, “depending on market demand.”

Within the Rolls-Royce group, Rolls-Royce Deutschland is responsible for civil twin-shaft engines in the thrust range of 13,000 to 23,000 pounds. At the company’s headquarters near Berlin no new variant in the BR700 family is under development, and no new engine program has been recently launched. However, Rolls-Royce Deutschland engineers are involved in a research and technology program with German Aerospace Center DLR. Technologies under study focus on low-emissions combustors and may eventually find applications in regional-jet turbofans.

While the BR715 was not selected for either the ARJ21 or RRJ, Rolls-Royce still hopes to power the export version of the Tupolev Tu-334 with the BR715.

The BR715 entered service in 1999 on the Boeing 717. According to Rolls-Royce Deutschland, the 12-month engine basic dispatch reliability of the 717 stands at 99.96 percent. The increase of the BR715’s average turbine gas temperature after 10,000 cycles is predicted to be less than 40 degrees, with a corresponding SFC deterioration of “just around 4 percent.” This should translate into increased time on wing and lower maintenance costs, the company said.

The other Rolls-Royce subsidiary involved in regional jet applications is in Indianapolis. The former Allison engine company reports no new AE3007 variant or engine in development. The latest version of the AE3007 turbofan is the -A1E that powers the ERJ-145XR. It was certified in August last year. On the AE3007A1E, a hot-section upgrade allows for 7 percent more thrust and a software upgrade increases EGT margin, the company said. According to a spokeswoman, dispatch reliability stands at “99.94 to 99.96 percent for the entire family.” However, she would not comment on a Fadec issue that occurred in 2000.