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Chinas Comac Ponders Materials For C919
By Bradley Perrett
Shanghai
Adding to the many decisions to be made in designing a commercial aircraft, the choice of material is becoming more complicated as more choices become available. Yet the issue is as decisive as almost any other, since overly costly construction will burden an aircraft with a competitive disadvantage throughout its life, while an airliner that is cheap but heavy will burn too much fuel for decades ahead—decades in which fuel prices could rise far beyond expectations.
This is a key question that Comac is now working on as it refines the design of its C919 narrowbody airliner.
One theme in the design of the C919 is to aim for moderate advances while preparing conventional alternatives, say executives involved in the Chinese program. And that applies particularly to the structure, which is far from fixed, even though the first flight is now only about three years away.
One structural decision that has been made is the material for the tail and moveable surfaces: they will be of composite, as they routinely are on new commercial aircraft these days. But the material for the center wing box, outer wing boxes and fuselage is still under study.
According to current program thinking, the inner wing box should be composite, as the Airbus A380’s is. But an aluminum design has been prepared just in case. The outer wing boxes could be either aluminum or composite; officials are leaning toward composite as the likely choice, but this cannot be assumed to be final. Again, Comac has prepared designs for both types.
Although the Boeing 787 is almost all composite, the benefits of the costly material are lower for smaller aircraft that spend less of their lives in cruise. Moreover, Comac’s structural suppliers, plants belonging to Avic Aircraft, have not done well in delivering aluminum structural sections for the Comac ARJ21 regional jet on schedule; shifting to large-scale composite construction can only increase their challenges.
The C919 design will use more titanium than is usual for its size, says an executive whose company supplies that metal. Titanium is becoming popular partly because its inertness and thermal properties are well matched with carbon fiber.
Composite is least likely to be used for the fuselage, industry officials say.
While considering aluminum, Comac must also consider the specific kind of aluminum. Essentially, three types are available: the traditional alloy used in the Boeing 737 and A320; so-called advanced aluminums, which are stronger; and the latest aluminum-lithium alloys.
The latter use significant portions of the low-density metal lithium to increase the bulk of the material and therefore its resistance to bending. So less weight is needed to take a given load, but it costs a great deal more.
Material cost is a greater factor in structural design than is often imagined. Mitsubishi Aircraft’s studies led it to choose the heaviest but cheapest material for its MRJ regional jet, traditional 7050-alloy aluminum.
One executive who would like the C919 to be made entirely of the material that his company makes expects that Comac will go for a mix: an all-composite wing and an aluminum-lithium fuselage. One reason for doing so would be that the latest Western narrowbody airliner, the five-abreast Bombardier CSeries, uses that combination.
Moreover, Bombardier has proposed that it and Comac standardize their materials so that they can purchase jointly. The two companies are looking at a long-term cooperation agreement that would increase commonality between their commercial aircraft.
A sample nose section of the C919 was built in 2009 of aluminum. A tail cone sample section built last year is of composite.
Comac’s published figures for the C919 suggest that the aircraft will be disappointingly heavy for one that can employ technology far newer than that used in the 737 and A320 (AW&ST Nov. 22, 2010, p. 20). One executive working on the program believes those figures are deliberately conservative, however.
The C919’s joint definition phase was scheduled to be completed by late 2010, but loose ends are still being tied up. Suppliers are addressing questions that arose in the review at the completion of the phase.
The seating of the C919 has increased by two to 158 since data was last shown, at the Zhuhai air show in November. That is presumably because of a cabin rearrangement, such as squeezing six narrow seats instead of four standard seats into a row in the tapering rear cabin. The galley and lavatories might have been repositioned, too.
The low priority now accorded to the ARJ21 was evident at the Shanghai International Business Aviation Show, held here April 13-15. For many years, Comac has displayed a model of a business jet adaptation of the ARJ21-700, the launch version of the regional aircraft. At the show, whose sole focus was business aviation, only an airliner model was on view, suggesting that Comac is not interested in making even a small engineering effort to widen the appeal of the ARJ21.
The ARJ21 looks increasingly likely to be an unloved orphan until the C919 enters service—in 2016, according to the schedule. The C919 is a project of national priority for the government of President and Communist Party Chairman Hu Jintao. The ARJ21 is not.
Chinas Comac Ponders Materials For C919
By Bradley Perrett
Shanghai
Adding to the many decisions to be made in designing a commercial aircraft, the choice of material is becoming more complicated as more choices become available. Yet the issue is as decisive as almost any other, since overly costly construction will burden an aircraft with a competitive disadvantage throughout its life, while an airliner that is cheap but heavy will burn too much fuel for decades ahead—decades in which fuel prices could rise far beyond expectations.
This is a key question that Comac is now working on as it refines the design of its C919 narrowbody airliner.
One theme in the design of the C919 is to aim for moderate advances while preparing conventional alternatives, say executives involved in the Chinese program. And that applies particularly to the structure, which is far from fixed, even though the first flight is now only about three years away.
One structural decision that has been made is the material for the tail and moveable surfaces: they will be of composite, as they routinely are on new commercial aircraft these days. But the material for the center wing box, outer wing boxes and fuselage is still under study.
According to current program thinking, the inner wing box should be composite, as the Airbus A380’s is. But an aluminum design has been prepared just in case. The outer wing boxes could be either aluminum or composite; officials are leaning toward composite as the likely choice, but this cannot be assumed to be final. Again, Comac has prepared designs for both types.
Although the Boeing 787 is almost all composite, the benefits of the costly material are lower for smaller aircraft that spend less of their lives in cruise. Moreover, Comac’s structural suppliers, plants belonging to Avic Aircraft, have not done well in delivering aluminum structural sections for the Comac ARJ21 regional jet on schedule; shifting to large-scale composite construction can only increase their challenges.
The C919 design will use more titanium than is usual for its size, says an executive whose company supplies that metal. Titanium is becoming popular partly because its inertness and thermal properties are well matched with carbon fiber.
Composite is least likely to be used for the fuselage, industry officials say.
While considering aluminum, Comac must also consider the specific kind of aluminum. Essentially, three types are available: the traditional alloy used in the Boeing 737 and A320; so-called advanced aluminums, which are stronger; and the latest aluminum-lithium alloys.
The latter use significant portions of the low-density metal lithium to increase the bulk of the material and therefore its resistance to bending. So less weight is needed to take a given load, but it costs a great deal more.
Material cost is a greater factor in structural design than is often imagined. Mitsubishi Aircraft’s studies led it to choose the heaviest but cheapest material for its MRJ regional jet, traditional 7050-alloy aluminum.
One executive who would like the C919 to be made entirely of the material that his company makes expects that Comac will go for a mix: an all-composite wing and an aluminum-lithium fuselage. One reason for doing so would be that the latest Western narrowbody airliner, the five-abreast Bombardier CSeries, uses that combination.
Moreover, Bombardier has proposed that it and Comac standardize their materials so that they can purchase jointly. The two companies are looking at a long-term cooperation agreement that would increase commonality between their commercial aircraft.
A sample nose section of the C919 was built in 2009 of aluminum. A tail cone sample section built last year is of composite.
Comac’s published figures for the C919 suggest that the aircraft will be disappointingly heavy for one that can employ technology far newer than that used in the 737 and A320 (AW&ST Nov. 22, 2010, p. 20). One executive working on the program believes those figures are deliberately conservative, however.
The C919’s joint definition phase was scheduled to be completed by late 2010, but loose ends are still being tied up. Suppliers are addressing questions that arose in the review at the completion of the phase.
The seating of the C919 has increased by two to 158 since data was last shown, at the Zhuhai air show in November. That is presumably because of a cabin rearrangement, such as squeezing six narrow seats instead of four standard seats into a row in the tapering rear cabin. The galley and lavatories might have been repositioned, too.
The low priority now accorded to the ARJ21 was evident at the Shanghai International Business Aviation Show, held here April 13-15. For many years, Comac has displayed a model of a business jet adaptation of the ARJ21-700, the launch version of the regional aircraft. At the show, whose sole focus was business aviation, only an airliner model was on view, suggesting that Comac is not interested in making even a small engineering effort to widen the appeal of the ARJ21.
The ARJ21 looks increasingly likely to be an unloved orphan until the C919 enters service—in 2016, according to the schedule. The C919 is a project of national priority for the government of President and Communist Party Chairman Hu Jintao. The ARJ21 is not.
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