ANALYSIS: How did CSeries perform during first flight?

Washington DC
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Bombardier’s 2.5h-long maiden flight of the CS100 flight-test vehicle on 16 September went smoothly enough for the landing gear to be retracted, a promising sign during any initial sortie.

“It’s a bit of a cliché, but it really did fly like our predictions,” says chief test pilot Chuck Ellis.

The only anomaly occurred when the crew received a “small advisory message from one of the subsystems”, Ellis says, without elaborating. However, the message would not have required a certificated aircraft carrying passengers to call an emergency.

And even in the conservative setting of a first test flight, the message still did not curtail the operation. “It just affected that we were being more careful,” Ellis says.

For Bombardier’s team, completing the flight offered the relief of ending an eight-month delay. The challenge is now bringing the remaining four flight-test aircraft for the 110-seat CS110 variant into the campaign. All four are in various stages of assembly, but Rob Dewar, Bombardier’s vice-president and general manager of the CSeries programme, declined to specify when each would be ready.

“We’re going to assess the data of [the first flight] and decide if there are any changes required, but so far [it’s] very positive and we’ll keep you posted,” Dewar says.

The CSeries represents Bombardier’s boldest foray yet in the commercial sector. In addition to introducing Pratt & Whitney’s geared turbofan engine series, Bombardier designed the CSeries with a composite wing and an aluminium-lithium fuselage – both firsts in the narrowbody segment.

One of the technologies most under scrutiny on CSeries is the fly-by-wire flight-control system, a first for Bombardier. Though the smaller CRJ1000 features a fly-by-wire rudder, the CSeries is the first production aircraft designed by Bombardier with a full three-axis fly-by-wire system.

Fly-by-wire replaces mechanical linkages with a computer that interprets control-column inputs by the pilot and commands the flight-control surfaces to accomplish the pilot’s intent. The system also adds flight-envelope protections to prevent, for example, aircraft stalls.

Moreover, the CSeries uses a bespoke version of the generic fly-by-wire system supplied by Parker Aerospace. Only four years ago, the CRJ1000’s flight-test programme was shut down for nine months when Bombardier detected an anomaly with the fly-by-wire rudder in an early test sortie.

Bombardier learned from that episode and, with the CSeries, made a huge upfront investment in testing and simulation to ensure that the flight controls were mature before entering flight testing. Inside a new facility called the complete integrated aircraft systems test area (CIASTA), Bombardier’s engineers have run thousands of hours of tests using an “iron bird” simulator called the integrated systems test certification rig – all in preparation for first flight.

So far, the validation of all that work still lies ahead in the 2,500h CSeries flight-test programme. Bombardier’s maiden flight profile was designed cautiously, given the clean-sheet design of the aircraft and the airframer’s inexperience with full fly-by-wire technology.

For instance, Ellis explained that the entire flight was operated in the direct flight-control law of the fly-by-wire system, which deactivates all the flight-envelope protections available in normal law.

“We made it so that you can’t flip the switch [to normal law]. We blocked it out,” Ellis says. “We wanted to be able to see the airplane and not the computers and fly-by-wire system interacting.”

Under normal control law, the CSeries fly-by-wire system is designed with a set of soft stops in pitch, roll and yaw, Ellis says, which provide the basic envelope protections. The system, however, allows the pilot to push through a soft stop to a hard limit, Ellis says.