BEIJING—Flight testing of the COMAC C919 has exceeded the designed cruise speed of the narrowbody airliner and reached its intended ceiling, with the fleet of six prototypes now complete.
Elsewhere in the program, COMAC and propulsion partner CFM have modified LEAP 1C engines and nacelles of the six prototypes to cope with previously miscalculated loads, an industry source said.
CFM has further changed the design of transfer gearboxes on the turbofans, the engine company said. According to the source, this modification has been implemented.
The highest speed reached so far has been Mach 0.82, the source said; this compares with the design cruise speed of Mach 0.785. The highest altitude so far has been 39,800 ft. (12,100 m), the source said, the maximum intended for operation. The C919 is designed to carry 158 passengers in a standard two-class configuration.
A second source confirmed that loads on the LEAP 1C engines and nacelles had been unexpected. According to the first source, this resulted in undesirable shuddering. “There was vibration,” that person said. “But the modifications have been made.”
Asked about that issue, a spokesperson for CFM said: “There is no issue with the joint design of the C919 program beyond the normal iteration between the engine manufacturer and the airframer.” Reuters first reported that the issue had arisen. COMAC did not respond to a request for comment on this matter, but the issue does not appear to be unusually serious.
The transfer gearbox has been modified to improve durability, the CFM spokesperson said. The issue was entirely the responsibility of the engine company, said the first source, who added: “All six flight-test aircraft now have the new configuration. So far, there’s been no problem with it.”
CFM said in June 2019 it was redesigning the bearing of the radial drive shaft of the LEAP 1B, the version on the Boeing 737 MAX. This was done after five inflight shutdowns due to particles coming from the shaft, which, with the accessory gearbox and transfer gearboxes, is part of the engine’s accessory drivetrain. The CFM spokesperson declined to say whether the change to the LEAP 1C was related to this or any other product, however. The LEAP 1C is most similar in design to the LEAP 1A of the Airbus A320neo family.
The C919 program is five or six years behind schedule. COMAC said in August 2019 it was aiming at achieving certification in 2021.
The sixth C919 prototype, aircraft 106, flew on Dec. 27, 2019. It will be used mainly for verifying characteristics of the cabin, lighting and exterior noise, COMAC said.
The static strength-test airframe, meanwhile, has undergone all tests necessary for the program’s certification effort. Additionally, the static fatigue-test airframe has been built. The type’s normal flight control law has been verified. COMAC said it, not a supplier, developed this system. Wing de-icing has been tested in a wind tunnel.
Final assembly time for C919s is progressively shortening, COMAC said. The flight-test aircraft are numbered 101-106. Of the static test airframes, the one used for verifying strength is 01, and the one for demonstrating fatigue life is 02. Testing on 01 was completed on Nov. 30, 2019, COMAC said.
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