April 30, 2013
Just a bare three months after declaring it was ready to move ahead with a composite wing box, Comac has abandoned major use of composite structures in the C919 airliner, claim industry executives familiar with the design.
Development of a composite wing box would have delayed the program, Comac’s managers reportedly decided, because it presented many complications, including the challenge of conducting electricity from lightning strikes, say two industry officials familiar with progress in the design. Expansion and contraction with temperature changes would have differed from the rest of the airframe, too. and so the center wing box will now be made from conventional aluminum, like the rest of the wing.
As recently as January, Comac was working towards building the massive structure at the intersection of the wing and fuselage out of composite. It announced Jan. 18 that after a critical design review “the design of C919 composite [central wing] structure was evaluated finally and could proceed to the next phase.”
Despite early ambitions, it now seems that the materials scheme of the C919 airframe will be little more advanced than that of the Airbus A320 and Boeing 737.
The fuselage could include some aluminium-lithium, a stronger but much more costly material. Industry executives familiar with the design believe it’s notable that Comac has still not settled this issue, despite intending to fly the first prototype C919 in June 2014.
Moreover, materials experts working on the project doubt that Comac is in a position to determine the characteristics of new aluminium alloys to the satisfaction of the certification agency, the Civil Aviation Administration of China, which itself probably lacks experience in the field. Suppliers might be able to help to some degree, however.
Composites will be widely used in the tail of the C919 and in its moveable structures, following a practice that has been widespread in Western aircraft since the 1980s.
In another sign of slow progress, nothing has been fitted to the C919 iron bird, the ground rig on which a new aircraft’s equipment is mounted for static testing, a third industry official says. The C919 is supposed to enter service in 2016.