Safran Aircraft Engines is assembling a Silvercrest engine containing redesigned axial high-pressure compressor (HPC) stages but retaining the original HPC design’s centrifugal stage and will begin testing the redesigned engine early next year.
The engine manufacturer redesigned the Silvercrest’s HPC after flight tests of the engine on the company’s flying testbed in October 2017 found HPC response problems at high altitudes and low airspeeds. That redesign focused entirely on the HPC’s axial stages, according to a spokesperson for Safran Aircraft Engines.
However, the redesign did not involve adding or removing any of the four axial stages—all of which were one-piece "blisks" with integrated blades and disks—which featured in the original HPC design. “The architecture of the Silvercrest remains the same, including the compressor centrifugal stage, which is ‘on spec’ in terms of performance,” the spokesperson told AIN.
The rig testing Safran Aircraft Engines performed in May and June to validate the performance of the axial HPC redesign confirmed “the significant progress…made over the [previous] 12 months, according to the plan defined in 2018,” and the rig tests were “completed in June, in line with the timetable agreed with our customer” Textron Aviation, the company said on June 17. “The results…exceeded our expectations.” In October, the spokesperson told AIN that, “during this test campaign, we demonstrated a better performance in terms of stall margin and efficiency.”
Nevertheless, despite the Silvercrest HPC demonstrating what Safran Aircraft Engines regarded as a significant performance improvement in the May-June rig tests, on June 17 Textron Aviation announced it was shelving the Cessna Citation Hemisphere development program. Textron CEO Scott Donnelly said during the company’s second-quarter financial-results conference call that the Silvercrest hadn’t yet demonstrated the performance the Hemisphere required.
However, immediately upon losing its last aircraft-application for the Silvercrest engine, Safran Aircraft Engines responded that it would continue developing the Silvercrest as a research and technology (R&T) program. In October, the company confirmed to AIN it is “continuing engine tests as planned in the development schedule.” The new testing “includes additional flight tests, to complete the overall engine performance and durability validation,” the spokesperson said.
“The test plan may include some certification tests,” the spokesperson added. “For instance, we [have] performed some certification tests, such as low-pressure turbine (LPT) stress and endurance tests, to ensure the robustness of this engine. We are currently assembling an engine with the new axial compressor, which will be on test [starting] early 2020. However, an aircraft application will be required to optimize the configuration, utilization and engine/aircraft systems integration, and thus to fully complete the certification.”
To date, Safran Aircraft Engines has logged more than 10,000 hours of ground and flight testing with the Silvcrest and the engine has completed more than 300 flights. “Safran Aircraft Engines continues to work on the Silvercrest,” the spokesperson said, reiterating that the company would update Textron upon completion of Silvercrest development, to give Textron “an opportunity for a reassessment of the situation.”