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Franco-Russian engine tests slated to start late this month

 - June 12, 2007, 7:18 AM

The Franco-Russian Powerjet SaM146 turbofan engine, which is to power the Sukhoi Superjet 100 regional airliner, is set to fly by the end of this month. The first example of the 14,000- to 17,500-pound-thrust family made its first ground run in July 2006 at Rybinsk in Russia.

The Snecma-NPO Saturn joint venture is planning to use an Ilyushin 76 flying testbed. These first flights were initially planned for the first quarter of this year but have been delayed slightly.

“The engine-aircraft interface is complex, so it has taken more time than expected,” Jean-Pierre Cojan, Snecma’s executive vice president for commercial engines, told AIN.

For example, the engine controls on the Ilyushin twinjet are hydromechanical, while the SaM146 is managed by a full-authority digital engine control. Also, the test pylon must be mechanically and aerodynamically representative of the one that will be used on the smaller Superjet 100. It must still ensure compatibility between the existing Ilyushin pylon and SaM146 installation. Russian flight test center LII Gromov will operate the test airplane.

“We have used the first two engines mainly for mechanical and thermal validation,” Cojan explained. In addition, the new turbofan’s surge margin has been checked in ground tests. Performance testing was due to start last month in Rybinsk at an open-air facility.

At the same facility, engine number-three is being tested. It is the first unit to be fitted with the SaM146 nacelle developed by French company Aircelle. “Open-air test results give more accurate data to prepare flight testing,” said Cojan.

So far, more than 200 test hours have been logged on the ground. Engine number two ran for the first time with its production fan blades in February. It has since reached greater than 18,000 pounds of thrust, which is well above the required emergency thrust of 17,400 pounds for the 95-seat version of the Superjet 100.
Automatic power restore emergency thrust is applied when one engine fails at takeoff. “Reaching this thrust level means the fan has enough flutter margin,” Cojan said.

In total, eight engines and one high-pressure core engine will be used for development. “From engine number three, we are very close to the certification standard,” Cojan said.

So far, the engine maker’s engineers do not expect any major change in the design. Certification is slated for March 2008.

Cojan said the SaM146’s distinctive features are its family concept [for the various versions of the Superjet], lower maintenance cost and reduced noise levels. “We have total hardware commonality on applications from 70 to 115 seats,” Cojan explained. The only difference will be the thrust ratings. The competing General Electric CF34-8 and -10 engines, used on the Embraer 170 and 190, respectively, are different–although they share the CF34 family name.

The manufacturer claims that maintenance costs will be reduced because of the engine’s relatively small number of parts, which partly derives from the lower number of stages in the turbofan design.

The SaM146 totals 14 stages, while the CF34-10 has 18. Moreover, “the exhaust gas temperature’s generous margin contributes to the reduction of the maintenance cost,” Cojan stated.

The target is to cut hourly maintenance costs by 20 percent, compared to current engines. At the highest thrust rating, the first shop visit should take place after 17,000 flight hours. Thereafter, the time between overhaul is hoped to be 12,000 hours.

The SaM146 is intended to have a 10-dB margin to Chapter 4 noise levels. Both the 4.43 bypass ratio and the long nacelle contribute in this respect. In terms of specific fuel consumption, the SaM146 will be one percent better than the CF34-10, Cojan said.

Powerjet is a 50-50 joint venture created for the SaM146 program. Italian-based Avio has a 20-percent stake in Snecma’s holding [that is, 10 percent of the overall program] and is providing the combustor module and gearbox. Powerjet hopes to sell 5,000 engines over the life of the program–projected to be 30 years.

Cojan said the financial break-even point for the program is below 2,000 engines, which is the expected number of engines to be sold for the Superjet 100 alone. So far, engines have been sold for 61 aircraft.

The SaM146 by the Numbers

Thrust range: 14,000 to 17,500 pounds
Fan diameter: 4 feet
Length: 6.8 feet
Bypass ratio: 4.43
Pressure ratio: 28

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