The time for refinements to the Mitsubishi MRJ has nearly passed, as Mitsubishi Aircraft expects to freeze the regional jet’s design within the next two months. The company has frozen all the interfaces between the various systems and the structural components, both in the 88-seat MRJ90, scheduled for Japanese certification in late 2013, and the 76-seat MRJ70, which would likely gain its certification roughly a year later.

“The next milestone will be critical design review, then we will start manufacturing parts,” said Mitsubishi Aircraft executive vice president Junichi Miyakawa, who explained that the company will undertake a series of critical design reviews (CDRs) between now and the end of September. “As far as the major features of the structures or systems are concerned, they’re not going to be changed,” he told AIN.

Meanwhile, the so-called MRJ100X–a prospective 100-seat version of the airplane–remains in the preliminary design phase. But this airplane has yet to draw a customer and so likely won’t reach the market until 2016 or 2017, depending on when the company decides to launch the program, said Miyakawa. Nevertheless, Mitsubishi possesses a firm grasp of the form it will take.

“As a result of the preliminary design review, we know what needs to be changed between the MRJ70/90 and the 100X,” said Miyakawa. “The wing is going to need to be beefed up, although we’re going to use the same wing box.” Another change will involve strengthening the landing gear, he said, although engineers do not believe they’ll need to change the actual design.

Of course, designers will have to incorporate a more robust air-conditioning system to accommodate the larger cabin, added the Mitsubishi executive. Otherwise, engineers believe adding three more rows to the MRJ90 will prove a fairly straightforward exercise.

Miyakawa said Mitsubishi has calculated the specifications of the 100X based on preliminary design work, but that the company “is not ready” to publish the numbers yet. “We are carefully looking at the customers and the market, and also we are looking at the business plan of an additional airplane,” he said.

JCAB, FAA Coordinating
The more immediate concern centers on preparations for the 2012 first flight and certification of the MRJ90, plans for which Mitsubishi works closely with the Japanese Civil Aviation Bureau (JCAB) at its offices at Nagoya Airfield, coincidentally the regional airport located adjacent to the eventual site of MRJ production–MHI’s Komaki South plant.

The JCAB and the U.S. FAA have begun to coordinate efforts toward issuance of a shadow type certificate, said Miyakawa, ensuring that the airplane gains U.S. approval in early 2014, soon after the JCAB issues its approval.

So far, according to Miyakawa, the JCAB hasn’t encountered any problems or expressed special interest in any particular design element. “You might understand that our airplanes are using conventional structure and conventional systems, except the [Pratt & Whitney PW1000G] engine, and the engine certification is not our business… We really haven’t seen any challenges in our airplane as far as JCAB is concerned,” he said.

In fact, one of the changes to the design that Mitsubishi instituted in the summer of 2009 involved scrapping its original plans for an all-composite wing. Using composites in an airplane as small as the MRJ, the company found, would not yield enough of a weight reduction to warrant their use, particularly given the need for metal reinforcements in the structure. Another reason centered on a desire to “optimize” the wing boxes across the entire family.

The aluminum box–as opposed to composite–allowed for a shorter lead time for structural changes because the company plans to use the same wing box across the entire family, including for the 100X.

Other changes involved the carbon-fiber fuselage, which began life as a 114-inch tube, only to morph into a 116.5-inch-wide oval, then again into a 116.5-inch-diameter cylinder. The result–a two-and-a-half-inch larger barrel–leaves more room for a four abreast passenger configuration than any other regional jet in its class, according to Mitsubishi.

Although moving from the original 114-inch circular fuselage to a wider design did add some weight to the structure, the second change resulted in no further weight penalty due to the uniform stress characteristics inherent in a nearly perfectly round design.

Airline Input
While industrial considerations led to the decision to switch from composites to aluminum for the wings, most of the other changes resulted from consultations with airlines during a series of advisory group meetings.

The seat design, for example, went through a series of iterations, the most recent of which appears on display here at the show. “That is going to be very close to the final design of our seat,” said Miyakawa. “We’ve been hearing from many customers about the evaluation of the seat throughout the development, so we are trying to put all those voices into our product. The latest design is basically the result of those efforts.” 

Mitsubishi chose Hiroshima’s Delta Kogyo, the company perhaps best known for the seats it manufactures for Mazda automobiles, to supply the airplane’s slim-profile seats. Rather than urethane, Delta Kogyo’s 3-D net seats use fibers woven into three-dimensional structures that act as small springs and dampers. The approach results in thinner yet stronger seats, according to Mitsubishi. In fact, although the company assumes a 31-inch pitch in its calculation of both airplanes’ typical capacity, several airlines have expressed interest in a 29-inch pitch due to the extra space the thin seats afford.

Airline consultation also led to the decision to combine the pair of cargo holds–one in the front and one in the rear–to a single 644-sq-ft compartment in the rear. To help compensate for what might have presented a c.g. problem, designers moved the avionics equipment to the forward belly, where an access panel will replace the baggage door.

Another improvement related to baggage capacity took the form of expanded overhead bins, the capacity of which designers managed to increase 12 percent by adding width and changing the contour of the side that faces the fuselage wall. According to Miyakawa, the bins can hold the largest roller bags allowed by any airline.

While Mitsubishi Aircraft carries responsibility for design, procurement, sales and support, parent company Mitsubishi Heavy Industries (MHI) will take care of manufacture and final assembly, as well as flight testing. Production will take place at MHI’s Komaki South plant, located adjacent to Nagoya Airfield, the regional airport north of the city center. Although it stopped building the MU-300 business jet at Komaki South after Raytheon bought that airplane’s marketing rights and renamed it the Beechjet 400 in 1985, MHI (Hall 2 Stand C17) still assembles the
F-2 fighter jet at the plant for the Japanese Self Defense Forces.

To date, only one airline has definitively proved its readiness to commit to the MRJ program as a whole with a firm order. Japan’s All Nippon Airways holds an order for 15 MRJ90s, along with options on another 10. Meanwhile, converting a letter of intent signed by Trans States Holdings of the U.S. that called for an eventual firm order for 50 MRJs and options on another 50 stood as a top priority for Mitsubishi Aircraft.

“We are discussing with [Trans States] the final description of the details of the definitive contract,” said Miyakawa. “We’re expecting that business to be finished very soon.”