Two other cost savers for MRJ production are the adoption of a circular body cross section, which has simplified tool design, and the use of conventional aerospace aluminum, that is cheaper than so-called advanced aluminums and aluminum-lithium alloy. Those newer metals offer weight savings that Mitsubishi Aircraft judged unjustified for a regional aircraft. A 2009 decision to build the wing of aluminum, instead of carbon-fiber composite, also saved money, though the main aim was reducing weight for the MRJ70.
Of MHI's plants around Nagoya, the one at Oye is making detail parts and the tail surface assemblies while Tobishima is building the major assemblies, including the outer wings and the fuselage modules, which it is also joining to create the whole fuselage, incorporating a wing center box. This includes fitting onboard equipment. The Komaki South plant, also at Nagoya, will perform final assembly, checking out and flight testing. MHI is building six MRJ airframes, five for flight-test aircraft and one for static ground testing. Pratt & Whitney will supply PW1217G engines.
In September, the fuselage sections of the first prototype were lined up but not connected. The outer wings were still being made, so a manufacturing prototype of the left outer wing was placed alongside them to show the final appearance. MHI also displayed a completed left winglet. The machinery for series production was employed in making the parts for the prototype.
Approaching an aircraft manufacturing program, production engineers first address the processes and parts where they see the greatest risks. For the MRJ, MHI engineers focused particularly on the wing, where the challenge to precision was the length of spars and skins, and the nose and tail fuselage sections, which presented the difficulties of double curvatures. Those end sections also typically use thicker skins, adding to the challenge in achieving required tolerances for length, width, curvature and so on.
The nose, especially, was seen as a risk, because MHI had no experience in making that part of a jet transport, says Tatsuoka. “We had to make it very tight, but for us, it was new,” he says. “We tried many methods to do that, starting with windscreen,” around which the rest of the nose was built. “There were several different ways to do that.” The outer wing boxes, too, required repeated attempts.
Development delays have given the production engineers time to progressively address smaller risks. Tatsuoka gives the example of drilling vertical holes in the upper chord of the center wing box, where that part protrudes for joining with the skin of the outer wing boxes. It is a classic problem area in commercial transport aircraft, because of the constricted space beneath the fuselage. Tatsuoka says the team has now worked out how to drill the holes there properly. It was an issue that would have been worked out much later in the manufacturing development schedule had the aircraft made its first flight in late 2011, as initially planned.
Mitsubishi Aircraft says that, with two big delays caused by its unfamiliarity with airworthiness certification now behind the MRJ, design development should proceed normally. If the production engineers have used the unexpected time well, the manufacturing side of the program may turn out to be smoother than normal.