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Mitsubishi is planning a fleet of small regional aircraft – but has abandoned plans to make the wings from composites. Lou Reade finds out why.
A recent study by Lucintel says that the need for fuel efficient, durable, low maintenance aircraft will boost the industry’s demand for composites – swelling sales to nearly $36 billion by 2018. The report states that ‘although aluminium is the predominant material in the aerospace industry, companies are showing increased interest in composite materials because of a desire for more fuel efficient, corrosion resistant aircraft’.
This makes a recent decision by Mitsubishi all the more surprising: in September 2009 - late into the design of its Mitsubishi Regional Jet (MRJ) - the company backed away from using carbon fibre composites, deciding instead to make the plane’s wings and wing box from aluminium.
The move to aluminium was doubly surprising because the company had talked proudly about how the aeroplane would be ‘the first regional jet to adopt composite materials for its wings and vertical fins on a significant scale’, helping to differentiate it from its main rivals – regional jets from Bombardier and Embraer.
“We realised that the projected weight savings were not there for such a small aeroplane,” explains Yosuke Takigawa, senior vice president of sales and marketing at Mitsubishi Regional Jet in Nagoya, Japan. “We challenged ourselves to use composite wings for this size of aircraft. That’s why we marketed it that way. Before switching to aluminium, we worked very hard to develop composite wings – but they were not beneficial from a weight point of view.”
The aluminium industry, of course was delighted. Steve Larkin, president of the Aluminum Association – the US-based group that promotes use of the metal – says: “We welcome Mitsubishi’s decision. Aluminium is the material of choice for aerospace customers and continues to grow. Its light weight and strength is an advantage in primary and secondary weight savings, structural performance, fuel savings and design flexibility.”
Despite its decision, Mitsubishi is not planning to abandon composites – and does not expect its decision to slow adoption of composites in other aircraft: it builds composite wings for the Boeing 787 and plans to use composites elsewhere on the MRJ.
“Our composite issues were a size-weight trade-off, and have no bearing on larger aircraft,” Takigawa confirms. “The MRJ will feature composites in its empennage. However, the technology being used for the empennage is different to what was tried for the wings, because the needs are quite different. Empennage sections are under less stress than the wings.”
The company cites two other main reasons for switching to aluminium: manufacturing flexibility; and manufacturing speed. Since announcing the launch of the new aircraft in March 2008, Mitsubishi has so far confirmed two aircraft in the fleet: the MRJ-70, seating 78 people; and the MRJ-90, for 92 passengers. Following customer feedback, it has also drawn up plans for a ‘stretch’ version – the MRJ-100 – but it has yet to confirm that it will build this aircraft.
According to Takigawa, aluminium will allow the company to design a different wing for each model in its fleet. With composites, it would have needed to use the same wing in each case. “Aluminium allows us to build the optimum wing for each model,” he adds. “It is easier to scale up and down, and can be done so more quickly. With composites, we would have to use the same wing structure for the MRJ-70 and the MRJ-90.”
The composite wing design would have been optimised for the MRJ-90, which would have meant weight penalties for the MRJ-70, he says. It is likely that composite wings would have needed reinforcement – adding further weight. “With an aluminium wing, one way to further reduce weight is to scrape the surface,” he says. “You can’t do that with a composite wing.”
In addition, using aluminium should help Mitsubishi make up for lost time: the MRJ-90 (which is ahead of the MRJ-70 by about a year) was originally scheduled for completion in late 2013. This has fallen back to early 2014 – with a first flight due in mid-2012. These dates would have been delayed even further had the wings been made from composites. “By switching to aluminium, we can eliminate many of the composite tests – such as stress testing – which can delay production,” claims Takigawa.
The wings were not the only change to be made at the September 2009 design review. Following customer feedback, Mitsubishi made some other alterations. Two separate cargo compartments will be combined into a single compartment, but taking up the same overall volume (644ft³). At the same time, the plane’s dimensions have been increased slightly: a 2.5in increase in fuselage height creates an extra 1.5in of headroom. The volume of overhead bins has been increased by 12%, which will allow more carry-on baggage. A critical design review will take place this summer.
And the company has already signed up two customers. Japan All Nippon Airlines (ANA) was first to pitch in, with an order for 25 planes (15 firm, 10 options). This coincided with the official launch of the aeroplane back in March 2008. More recently, in October 2009, US regional carrier Trans States Holdings (TSH) ordered 50 planes – with an option on 50 more.
TSH president Richard Leach said: “The MRJ is a game changing regional jet that takes into account the environment, as well as passenger and airline needs. It will reduce fuel consumption, noise and NOx emissions – this means savings on operating costs. By combining the largest cabin in the regional jet market with innovative seat design and a very quiet cabin, we can offer the best comfort of any regional jet.”
Neither TSH nor ANA has specified what proportion of MRJ-90 and MRJ-70 models they will take. At the same time, neither is likely to have any interest in the MRJ-100 – should it be built. According to Takigawa, that plane is aimed squarely at Europe.
“In the US, small regional airlines can’t operate larger aircraft. That’s not the case in Europe. Announcing a launch date for the MRJ-100 will depend on the reactions of customers in Europe – that’s the only market looking for 100-seat aircraft.”